Source code for png

# !/usr/bin/env python

# $URL: $
# $Rev: 201 $

# - PNG encoder/decoder in pure Python
# Copyright (C) 2006 Johann C. Rocholl <>
# Portions Copyright (C) 2009 David Jones <>
# And probably portions Copyright (C) 2006 Nicko van Someren <>
# Original concept by Johann C. Rocholl.
# LICENSE (The MIT License)
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation files
# (the "Software"), to deal in the Software without restriction,
# including without limitation the rights to use, copy, modify, merge,
# publish, distribute, sublicense, and/or sell copies of the Software,
# and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
# Changelog (recent first):
# 2009-03-11 David: interlaced bit depth < 8 (writing).
# 2009-03-10 David: interlaced bit depth < 8 (reading).
# 2009-03-04 David: Flat and Boxed pixel formats.
# 2009-02-26 David: Palette support (writing).
# 2009-02-23 David: Bit-depths < 8; better PNM support.
# 2006-06-17 Nicko: Reworked into a class, faster interlacing.
# 2006-06-17 Johann: Very simple prototype PNG decoder.
# 2006-06-17 Nicko: Test suite with various image generators.
# 2006-06-17 Nicko: Alpha-channel, grey-scale, 16-bit/plane support.
# 2006-06-15 Johann: Scanline iterator interface for large input files.
# 2006-06-09 Johann: Very simple prototype PNG encoder.

# Incorporated into Bangai-O Development Tools by drj on 2009-02-11 from

# Incorporated into pypng by drj on 2009-03-12 from
# //depot/prj/bangaio/master/code/

Pure Python PNG Reader/Writer

This Python module implements support for PNG images (see PNG
specification at ). It reads
and writes PNG files with all allowable bit depths (1/2/4/8/16/24/32/48/64
bits per pixel) and colour combinations: greyscale (1/2/4/8/16 bit); RGB,
RGBA, LA (greyscale with alpha) with 8/16 bits per channel; colour mapped
images (1/2/4/8 bit).  Adam7 interlacing is supported for reading and
writing.  A number of optional chunks can be specified (when writing)
and understood (when reading): ``tRNS``, ``bKGD``, ``gAMA``.

For help, type ``import png; help(png)`` in your python interpreter.

A good place to start is the :class:`Reader` and :class:`Writer` classes.

Requires Python 2.3.  Limited support is available for Python 2.2, but
not everything works.  Best with Python 2.4 and higher.  Installation is
trivial, but see the ``README.txt`` file (with the source distribution)
for details.

This file can also be used as a command-line utility to convert
`Netpbm <>`_ PNM files to PNG, and the reverse conversion from PNG to
PNM. The interface is similar to that of the ``pnmtopng`` program from
Netpbm.  Type ``python --help`` at the shell prompt
for usage and a list of options.

A note on spelling and terminology

Generally British English spelling is used in the documentation.  So
that's "greyscale" and "colour".  This not only matches the author's
native language, it's also used by the PNG specification.

The major colour models supported by PNG (and hence by PyPNG) are:
greyscale, RGB, greyscale--alpha, RGB--alpha.  These are sometimes
referred to using the abbreviations: L, RGB, LA, RGBA.  In this case
each letter abbreviates a single channel: *L* is for Luminance or Luma or
Lightness which is the channel used in greyscale images; *R*, *G*, *B* stand
for Red, Green, Blue, the components of a colour image; *A* stands for
Alpha, the opacity channel (used for transparency effects, but higher
values are more opaque, so it makes sense to call it opacity).

A note on formats

When getting pixel data out of this module (reading) and presenting
data to this module (writing) there are a number of ways the data could
be represented as a Python value.  Generally this module uses one of
three formats called "flat row flat pixel", "boxed row flat pixel", and
"boxed row boxed pixel".  Basically the concern is whether each pixel
and each row comes in its own little tuple (box), or not.

Consider an image that is 3 pixels wide by 2 pixels high, and each pixel
has RGB components:

Boxed row flat pixel::

    list([R,G,B, R,G,B, R,G,B],
        [R,G,B, R,G,B, R,G,B])

Each row appears as its own list, but the pixels are flattened so that
three values for one pixel simply follow the three values for the previous
pixel.  This is the most common format used, because it provides a good
compromise between space and convenience.  PyPNG regards itself as
at liberty to replace any sequence type with any sufficiently compatible
other sequence type; in practice each row is an array (from the array
module), and the outer list is sometimes an iterator rather than an
explicit list (so that streaming is possible).

Flat row flat pixel::

    [R,G,B, R,G,B, R,G,B,
    R,G,B, R,G,B, R,G,B]

The entire image is one single giant sequence of colour values.
Generally an array will be used (to save space), not a list.

Boxed row boxed pixel::

    list([ (R,G,B), (R,G,B), (R,G,B) ],
        [ (R,G,B), (R,G,B), (R,G,B) ])

Each row appears in its own list, but each pixel also appears in its own
tuple.  A serious memory burn in Python.

In all cases the top row comes first, and for each row the pixels are
ordered from left-to-right.  Within a pixel the values appear in the
order, R-G-B-A (or L-A for greyscale--alpha).

There is a fourth format, mentioned because it is used internally,
is close to what lies inside a PNG file itself, and has some support
from the public API.  This format is called packed.  When packed,
each row is a sequence of bytes (integers from 0 to 255), just as
it is before PNG scanline filtering is applied.  When the bit depth
is 8 this is essentially the same as boxed row flat pixel; when the
bit depth is less than 8, several pixels are packed into each byte;
when the bit depth is 16 (the only value more than 8 that is supported
by the PNG image format) each pixel value is decomposed into 2 bytes
(and `packed` is a misnomer).  This format is used by the
:meth:`Writer.write_packed` method.  It isn't usually a convenient
format, but may be just right if the source data for the PNG image
comes from something that uses a similar format (for example, 1-bit
BMPs, or another PNG file).

And now, my famous members

from __future__ import generators

__version__ = "$URL: $ $Rev: 201 $"

from array import array

try:  # See :pyver:old
    import itertools
import math
import operator
import struct
import sys
import zlib
import warnings

__all__ = ['Reader', 'Writer', 'write_chunks']

# The PNG signature.
_signature = struct.pack('8B', 137, 80, 78, 71, 13, 10, 26, 10)

_adam7 = ((0, 0, 8, 8),
          (4, 0, 8, 8),
          (0, 4, 4, 8),
          (2, 0, 4, 4),
          (0, 2, 2, 4),
          (1, 0, 2, 2),
          (0, 1, 1, 2))

def group(s, n):
    # See
    return zip(*[iter(s)] * n)

def isarray(x):
    """Same as ``isinstance(x, array)`` except on Python 2.2, where it
    always returns ``False``.  This helps PyPNG work on Python 2.2.

        return isinstance(x, array)
        return False

try:  # see :pyver:old
    def tostring(row):
        l = len(row)
        return struct.pack('%dB' % l, *row)
    def tostring(row):
        """Convert row of bytes to string.  Expects `row` to be an
        return row.tostring()

def interleave_planes(ipixels, apixels, ipsize, apsize):
    Interleave (colour) planes, e.g. RGB + A = RGBA.

    Return an array of pixels consisting of the `ipsize` elements of data
    from each pixel in `ipixels` followed by the `apsize` elements of data
    from each pixel in `apixels`.  Conventionally `ipixels` and
    `apixels` are byte arrays so the sizes are bytes, but it actually
    works with any arrays of the same type.  The returned array is the
    same type as the input arrays which should be the same type as each other.

    itotal = len(ipixels)
    atotal = len(apixels)
    newtotal = itotal + atotal
    newpsize = ipsize + apsize
    # Set up the output buffer
    # See
    out = array(ipixels.typecode)
    # It's annoying that there is no cheap way to set the array size :-(
    # Interleave in the pixel data
    for i in range(ipsize):
        out[i:newtotal:newpsize] = ipixels[i:itotal:ipsize]
    for i in range(apsize):
        out[i + ipsize:newtotal:newpsize] = apixels[i:atotal:apsize]
    return out

def check_palette(palette):
    """Check a palette argument (to the :class:`Writer` class) for validity.
    Returns the palette as a list if okay; raises an exception otherwise.

    # None is the default and is allowed.
    if palette is None:
        return None

    p = list(palette)
    if not (0 < len(p) <= 256):
        raise ValueError("a palette must have between 1 and 256 entries")
    seen_triple = False
    for i, t in enumerate(p):
        if len(t) not in (3, 4):
            raise ValueError(
                "palette entry %d: entries must be 3- or 4-tuples." % i)
        if len(t) == 3:
            seen_triple = True
        if seen_triple and len(t) == 4:
            raise ValueError(
                "palette entry %d: all 4-tuples must precede all 3-tuples" % i)
        for x in t:
            if int(x) != x or not (0 <= x <= 255):
                raise ValueError(
                    "palette entry %d: values must be integer: 0 <= x <= 255" % i)
    return p

class Error(Exception):
    prefix = 'Error'

    def __str__(self):
        return self.prefix + ': ' + ' '.join(self.args)

class FormatError(Error):
    """Problem with input file format.  In other words, PNG file does
    not conform to the specification in some way and is invalid.

    prefix = 'FormatError'

class ChunkError(FormatError):
    prefix = 'ChunkError'

[docs]class Writer: """ PNG encoder in pure Python. """ def __init__(self, width=None, height=None, size=None, greyscale=False, alpha=False, bitdepth=8, palette=None, transparent=None, background=None, gamma=None, compression=None, interlace=False, bytes_per_sample=None, # deprecated planes=None, colormap=None, maxval=None, chunk_limit=2 ** 20): """ Create a PNG encoder object. Arguments: width, height Image size in pixels, as two separate arguments. size Image size (w,h) in pixels, as single argument. greyscale Input data is greyscale, not RGB. alpha Input data has alpha channel (RGBA or LA). bitdepth Bit depth: from 1 to 16. palette Create a palette for a colour mapped image (colour type 3). transparent Specify a transparent colour (create a ``tRNS`` chunk). background Specify a default background colour (create a ``bKGD`` chunk). gamma Specify a gamma value (create a ``gAMA`` chunk). compression zlib compression level (1-9). interlace Create an interlaced image. chunk_limit Write multiple ``IDAT`` chunks to save memory. The image size (in pixels) can be specified either by using the `width` and `height` arguments, or with the single `size` argument. If `size` is used it should be a pair (*width*, *height*). `greyscale` and `alpha` are booleans that specify whether an image is greyscale (or colour), and whether it has an alpha channel (or not). `bitdepth` specifies the bit depth of the source pixel values. Each source pixel values must be an integer between 0 and ``2**bitdepth-1``. For example, 8-bit images have values between 0 and 255. PNG only stores images with bit depths of 1,2,4,8, or 16. When `bitdepth` is not one of these values, the next highest valid bit depth is selected, and an ``sBIT`` (significant bits) chunk is generated that specifies the original precision of the source image. In this case the supplied pixel values will be rescaled to fit the range of the selected bit depth. The details of which bit depth / colour model combinations the PNG file format supports directly, are allowed are somewhat arcane (refer to the PNG specification for full details). Briefly: "small" bit depths (1,2,4) are only allowed with greyscale and colour mapped images; colour mapped images cannot have bit depth 16. For colour mapped images (in other words, when the `palette` argument is specified) the `bitdepth` argument must match one of the valid PNG bit depths: 1, 2, 4, or 8. (It is valid to have a PNG image with a palette and an ``sBIT`` chunk, but the meaning is slightly different; it would be awkward to press the `bitdepth` argument into service for this.) The `palette` option, when specified, causes a colour mapped image to be created: the PNG colour type is set to 3; greyscale must not be set; alpha must not be set; transparent must not be set; the bit depth must be 1,2,4, or 8. When a colour mapped image is created, the pixel values are palette indexes and the `bitdepth` argument specifies the size of these indexes (not the size of the colour values in the palette). The palette argument value should be a sequence of 3- or 4-tuples. 3-tuples specify RGB palette entries; 4-tuples specify RGBA palette entries. If both 4-tuples and 3-tuples appear in the sequence then all the 4-tuples must come before all the 3-tuples. A ``PLTE`` chunk is created; if there are 4-tuples then a ``tRNS`` chunk is created as well. The ``PLTE`` chunk will contain all the RGB triples in the same sequence; the ``tRNS`` chunk will contain the alpha channel for all the 4-tuples, in the same sequence. Palette entries are always 8-bit. If specified, the `transparent` and `background` parameters must be a tuple with three integer values for red, green, blue, or a simple integer (or singleton tuple) for a greyscale image. If specified, the `gamma` parameter must be a positive number (generally, a float). A ``gAMA`` chunk will be created. Note that this will not change the values of the pixels as they appear in the PNG file, they are assumed to have already been converted appropriately for the gamma specified. The `compression` argument specifies the compression level to be used by the ``zlib`` module. Higher values are likely to compress better, but will be slower to compress. The default for this argument is ``None``; this does not mean no compression, rather it means that the default from the ``zlib`` module is used (which is generally acceptable). If `interlace` is true then an interlaced image is created (using PNG's so far only interace method, *Adam7*). This does not affect how the pixels should be presented to the encoder, rather it changes how they are arranged into the PNG file. On slow connexions interlaced images can be partially decoded by the browser to give a rough view of the image that is successively refined as more image data appears. .. note :: Enabling the `interlace` option requires the entire image to be processed in working memory. `chunk_limit` is used to limit the amount of memory used whilst compressing the image. In order to avoid using large amounts of memory, multiple ``IDAT`` chunks may be created. """ # At the moment the `planes` argument is ignored; # its purpose is to act as a dummy so that # ``Writer(x, y, **info)`` works, where `info` is a dictionary # returned by and friends. # Ditto for `colormap`. # A couple of helper functions come first. Best skipped if you # are reading through. def isinteger(x): try: return int(x) == x except: return False def check_color(c, which): """Checks that a colour argument for transparent or background options is the right form. Also "corrects" bare integers to 1-tuples. """ if c is None: return c if greyscale: try: l = len(c) except TypeError: c = (c,) if len(c) != 1: raise ValueError("%s for greyscale must be 1-tuple" % which) if not isinteger(c[0]): raise ValueError( "%s colour for greyscale must be integer" % which) else: if not (len(c) == 3 and isinteger(c[0]) and isinteger(c[1]) and isinteger(c[2])): raise ValueError( "%s colour must be a triple of integers" % which) return c if size: if len(size) != 2: raise ValueError( "size argument should be a pair (width, height)") if width is not None and width != size[0]: raise ValueError( "size[0] (%r) and width (%r) should match when both are used." % (size[0], width)) if height is not None and height != size[1]: raise ValueError( "size[1] (%r) and height (%r) should match when both are used." % (size[1], height)) width, height = size del size if width <= 0 or height <= 0: raise ValueError("width and height must be greater than zero") if not isinteger(width) or not isinteger(height): raise ValueError("width and height must be integers") # if width > 2 ** 32 - 1 or height > 2 ** 32 - 1: raise ValueError("width and height cannot exceed 2**32-1") if alpha and transparent is not None: raise ValueError( "transparent colour not allowed with alpha channel") if bytes_per_sample is not None: warnings.warn('please use bitdepth instead of bytes_per_sample', DeprecationWarning) if bytes_per_sample not in (0.125, 0.25, 0.5, 1, 2): raise ValueError( "bytes per sample must be .125, .25, .5, 1, or 2") bitdepth = int(8 * bytes_per_sample) del bytes_per_sample if not isinteger(bitdepth) or bitdepth < 1 or 16 < bitdepth: raise ValueError("bitdepth (%r) must be a postive integer <= 16" % bitdepth) self.rescale = None if palette: if bitdepth not in (1, 2, 4, 8): raise ValueError("with palette, bitdepth must be 1, 2, 4, or 8") if transparent is not None: raise ValueError("transparent and palette not compatible") if alpha: raise ValueError("alpha and palette not compatible") if greyscale: raise ValueError("greyscale and palette not compatible") else: # No palette, check for sBIT chunk generation. if alpha or not greyscale: if bitdepth not in (8, 16): targetbitdepth = (8, 16)[bitdepth > 8] self.rescale = (bitdepth, targetbitdepth) bitdepth = targetbitdepth del targetbitdepth else: assert greyscale assert not alpha if bitdepth not in (1, 2, 4, 8, 16): if bitdepth > 8: targetbitdepth = 16 elif bitdepth == 3: targetbitdepth = 4 else: assert bitdepth in (5, 6, 7) targetbitdepth = 8 self.rescale = (bitdepth, targetbitdepth) bitdepth = targetbitdepth del targetbitdepth if bitdepth < 8 and (alpha or not greyscale and not palette): raise ValueError( "bitdepth < 8 only permitted with greyscale or palette") if bitdepth > 8 and palette: raise ValueError( "bit depth must be 8 or less for images with palette") transparent = check_color(transparent, 'transparent') background = check_color(background, 'background') # It's important that the true boolean values (greyscale, alpha, # colormap, interlace) are converted to bool because Iverson's # convention is relied upon later on. self.width = width self.height = height self.transparent = transparent self.background = background self.gamma = gamma self.greyscale = bool(greyscale) self.alpha = bool(alpha) self.colormap = bool(palette) self.bitdepth = int(bitdepth) self.compression = compression self.chunk_limit = chunk_limit self.interlace = bool(interlace) self.palette = check_palette(palette) self.color_type = 4 * self.alpha + 2 * (not greyscale) + 1 * self.colormap assert self.color_type in (0, 2, 3, 4, 6) self.color_planes = (3, 1)[self.greyscale or self.colormap] self.planes = self.color_planes + self.alpha # :todo: fix for bitdepth < 8 self.psize = (self.bitdepth / 8) * self.planes
[docs] def make_palette(self): """Create the byte sequences for a ``PLTE`` and if necessary a ``tRNS`` chunk. Returned as a pair (*p*, *t*). *t* will be ``None`` if no ``tRNS`` chunk is necessary. """ p = array('B') t = array('B') for x in self.palette: p.extend(x[0:3]) if len(x) > 3: t.append(x[3]) p = tostring(p) t = tostring(t) if t: return p, t return p, None
[docs] def write(self, outfile, rows): """Write a PNG image to the output file. `rows` should be an iterable that yields each row in boxed row flat pixel format. The rows should be the rows of the original image, so there should be ``self.height`` rows of ``self.width * self.planes`` values. If `interlace` is specified (when creating the instance), then an interlaced PNG file will be written. Supply the rows in the normal image order; the interlacing is carried out internally. .. note :: Interlacing will require the entire image to be in working memory. """ if self.interlace: fmt = 'BH'[self.bitdepth > 8] a = array(fmt, itertools.chain(*rows)) return self.write_array(outfile, a) else: nrows = self.write_passes(outfile, rows) if nrows != self.height: raise ValueError( "rows supplied (%d) does not match height (%d)" % (nrows, self.height))
[docs] def write_passes(self, outfile, rows, packed=False): """ Write a PNG image to the output file. Most users are expected to find the :meth:`write` or :meth:`write_array` method more convenient. The rows should be given to this method in the order that they appear in the output file. For straightlaced images, this is the usual top to bottom ordering, but for interlaced images the rows should have already been interlaced before passing them to this function. `rows` should be an iterable that yields each row. When `packed` is ``False`` the rows should be in boxed row flat pixel format; when `packed` is ``True`` each row should be a packed sequence of bytes. """ # outfile.write(_signature) # write_chunk(outfile, 'IHDR', struct.pack("!2I5B", self.width, self.height, self.bitdepth, self.color_type, 0, 0, self.interlace)) # See :chunk:order # if self.gamma is not None: write_chunk(outfile, 'gAMA', struct.pack("!L", int(round(self.gamma * 1e5)))) # See :chunk:order # if self.rescale: write_chunk(outfile, 'sBIT', struct.pack('%dB' % self.planes, *[self.rescale[0]] * self.planes)) # :chunk:order: Without a palette (PLTE chunk), ordering is # relatively relaxed. With one, gAMA chunk must precede PLTE # chunk which must precede tRNS and bKGD. # See if self.palette: p, t = self.make_palette() write_chunk(outfile, 'PLTE', p) if t: # tRNS chunk is optional. Only needed if palette entries # have alpha. write_chunk(outfile, 'tRNS', t) # if self.transparent is not None: if self.greyscale: write_chunk(outfile, 'tRNS', struct.pack("!1H", *self.transparent)) else: write_chunk(outfile, 'tRNS', struct.pack("!3H", *self.transparent)) # if self.background is not None: if self.greyscale: write_chunk(outfile, 'bKGD', struct.pack("!1H", *self.background)) else: write_chunk(outfile, 'bKGD', struct.pack("!3H", *self.background)) # if self.compression is not None: compressor = zlib.compressobj(self.compression) else: compressor = zlib.compressobj() # Choose an extend function based on the bitdepth. The extend # function packs/decomposes the pixel values into bytes and # stuffs them onto the data array. data = array('B') if self.bitdepth == 8 or packed: extend = data.extend elif self.bitdepth == 16: # Decompose into bytes def extend(sl): fmt = '!%dH' % len(sl) data.extend(array('B', struct.pack(fmt, *sl))) else: # Pack into bytes assert self.bitdepth < 8 # samples per byte spb = int(8 / self.bitdepth) def extend(sl): a = array('B', sl) # Adding padding bytes so we can group into a whole # number of spb-tuples. l = float(len(a)) extra = math.ceil(l / float(spb)) * spb - l a.extend([0] * int(extra)) # Pack into bytes l = group(a, spb) l = map(lambda e: reduce(lambda x, y: (x << self.bitdepth) + y, e), l) data.extend(l) if self.rescale: oldextend = extend factor = \ float(2 ** self.rescale[1] - 1) / float(2 ** self.rescale[0] - 1) def extend(sl): oldextend(map(lambda x: int(round(factor * x)), sl)) # Build the first row, testing mostly to see if we need to # changed the extend function to cope with NumPy integer types # (they cause our ordinary definition of extend to fail, so we # wrap it). See # enumrows = enumerate(rows) del rows # First row's filter type. data.append(0) # :todo: Certain exceptions in the call to ``.next()`` or the # following try would indicate no row data supplied. # Should catch. i, row = try: # If this fails... extend(row) except: # ... try a version that converts the values to int first. # Not only does this work for the (slightly broken) NumPy # types, there are probably lots of other, unknown, "nearly" # int types it works for. def wrapmapint(f): return lambda sl: f(map(int, sl)) extend = wrapmapint(extend) del wrapmapint extend(row) for i, row in enumrows: # Add "None" filter type. Currently, it's essential that # this filter type be used for every scanline as we do not # mark the first row of a reduced pass image; that means we # could accidentally compute the wrong filtered scanline if # we used "up", "average", or "paeth" on such a line. data.append(0) extend(row) if len(data) > self.chunk_limit: compressed = compressor.compress(tostring(data)) if len(compressed): # print >> sys.stderr, len(data), len(compressed) write_chunk(outfile, 'IDAT', compressed) # Because of our very witty definition of ``extend``, # above, we must re-use the same ``data`` object. Hence # we use ``del`` to empty this one, rather than create a # fresh one (which would be my natural FP instinct). del data[:] if len(data): compressed = compressor.compress(tostring(data)) else: compressed = '' flushed = compressor.flush() if len(compressed) or len(flushed): # print >> sys.stderr, len(data), len(compressed), len(flushed) write_chunk(outfile, 'IDAT', compressed + flushed) # write_chunk(outfile, 'IEND') return i + 1
[docs] def write_array(self, outfile, pixels): """ Write an array in flat row flat pixel format as a PNG file on the output file. See also :meth:`write` method. """ if self.interlace: self.write_passes(outfile, self.array_scanlines_interlace(pixels)) else: self.write_passes(outfile, self.array_scanlines(pixels))
[docs] def write_packed(self, outfile, rows): """ Write PNG file to `outfile`. The pixel data comes from `rows` which should be in boxed row packed format. Each row should be a sequence of packed bytes. Technically, this method does work for interlaced images but it is best avoided. For interlaced images, the rows should be presented in the order that they appear in the file. This method should not be used when the source image bit depth is not one naturally supported by PNG; the bit depth should be 1, 2, 4, 8, or 16. """ if self.rescale: raise Error("write_packed method not suitable for bit depth %d" % self.rescale[0]) return self.write_passes(outfile, rows, packed=True)
[docs] def convert_pnm(self, infile, outfile): """ Convert a PNM file containing raw pixel data into a PNG file with the parameters set in the writer object. Works for (binary) PGM, PPM, and PAM formats. """ if self.interlace: pixels = array('B') pixels.fromfile(infile, (self.bitdepth / 8) * self.color_planes * self.width * self.height) self.write_passes(outfile, self.array_scanlines_interlace(pixels)) else: self.write_passes(outfile, self.file_scanlines(infile))
[docs] def convert_ppm_and_pgm(self, ppmfile, pgmfile, outfile): """ Convert a PPM and PGM file containing raw pixel data into a PNG outfile with the parameters set in the writer object. """ pixels = array('B') pixels.fromfile(ppmfile, (self.bitdepth / 8) * self.color_planes * self.width * self.height) apixels = array('B') apixels.fromfile(pgmfile, (self.bitdepth / 8) * self.width * self.height) pixels = interleave_planes(pixels, apixels, (self.bitdepth / 8) * self.color_planes, (self.bitdepth / 8)) if self.interlace: self.write_passes(outfile, self.array_scanlines_interlace(pixels)) else: self.write_passes(outfile, self.array_scanlines(pixels))
[docs] def file_scanlines(self, infile): """ Generates boxed rows in flat pixel format, from the input file `infile`. It assumes that the input file is in a "Netpbm-like" binary format, and is positioned at the beginning of the first pixel. The number of pixels to read is taken from the image dimensions (`width`, `height`, `planes`) and the number of bytes per value is implied by the image `bitdepth`. """ # Values per row vpr = self.width * self.planes row_bytes = vpr if self.bitdepth > 8: assert self.bitdepth == 16 row_bytes *= 2 fmt = '>%dH' % vpr def line(): return array('H', struct.unpack(fmt, else: def line(): scanline = array('B', return scanline for y in range(self.height): yield line()
[docs] def array_scanlines(self, pixels): """ Generates boxed rows (flat pixels) from flat rows (flat pixels) in an array. """ # Values per row vpr = self.width * self.planes stop = 0 for y in range(self.height): start = stop stop = start + vpr yield pixels[start:stop]
[docs] def array_scanlines_interlace(self, pixels): """ Generator for interlaced scanlines from an array. `pixels` is the full source image in flat row flat pixel format. The generator yields each scanline of the reduced passes in turn, in boxed row flat pixel format. """ # # Array type. fmt = 'BH'[self.bitdepth > 8] # Value per row vpr = self.width * self.planes for xstart, ystart, xstep, ystep in _adam7: if xstart >= self.width: continue # Pixels per row (of reduced image) ppr = int(math.ceil((self.width - xstart) / float(xstep))) # number of values in reduced image row. row_len = ppr * self.planes for y in range(ystart, self.height, ystep): if xstep == 1: offset = y * vpr yield pixels[offset:offset + vpr] else: row = array(fmt) # There's no easier way to set the length of an array row.extend(pixels[0:row_len]) offset = y * vpr + xstart * self.planes end_offset = (y + 1) * vpr skip = self.planes * xstep for i in range(self.planes): row[i::self.planes] = \ pixels[offset + i:end_offset:skip] yield row
def write_chunk(outfile, tag, data=''): """ Write a PNG chunk to the output file, including length and checksum. """ # outfile.write(struct.pack("!I", len(data))) outfile.write(tag) outfile.write(data) checksum = zlib.crc32(tag) checksum = zlib.crc32(data, checksum) outfile.write(struct.pack("!i", checksum))
[docs]def write_chunks(out, chunks): """Create a PNG file by writing out the chunks.""" out.write(_signature) for chunk in chunks: write_chunk(out, *chunk)
def filter_scanline(type, line, fo, prev=None): """Apply a scanline filter to a scanline. `type` specifies the filter type (0 to 4); `line` specifies the current (unfiltered) scanline as a sequence of bytes; `prev` specifies the previous (unfiltered) scanline as a sequence of bytes. `fo` specifies the filter offset; normally this is size of a pixel in bytes (the number of bytes per sample times the number of channels), but when this is < 1 (for bit depths < 8) then the filter offset is 1. """ assert 0 <= type < 5 # The output array. Which, pathetically, we extend one-byte at a # time (fortunately this is linear). out = array('B', [type]) def sub(): ai = -fo for x in line: if ai >= 0: x = (x - line[ai]) & 0xff out.append(x) ai += 1 def up(): for i, x in enumerate(line): x = (x - prev[i]) & 0xff out.append(x) def average(): ai = -fo for i, x in enumerate(line): if ai >= 0: x = (x - ((line[ai] + prev[i]) >> 1)) & 0xff else: x = (x - (prev[i] >> 1)) & 0xff out.append(x) ai += 1 def paeth(): # ai = -fo # also used for ci for i, x in enumerate(line): a = 0 b = prev[i] c = 0 if ai >= 0: a = line[ai] c = prev[ai] p = a + b - c pa = abs(p - a) pb = abs(p - b) pc = abs(p - c) if pa <= pb and pa <= pc: Pr = a elif pb <= pc: Pr = b else: Pr = c x = (x - Pr) & 0xff out.append(x) ai += 1 if not prev: # We're on the first line. Some of the filters can be reduced # to simpler cases which makes handling the line "off the top" # of the image simpler. "up" becomes "none"; "paeth" becomes # "left" (non-trivial, but true). "average" needs to be handled # specially. if type == 2: # "up" return line # type = 0 elif type == 3: prev = [0] * len(line) elif type == 4: # "paeth" type = 1 if type == 0: out.extend(line) elif type == 1: sub() elif type == 2: up() elif type == 3: average() else: # type == 4 paeth() return out class _readable: """ A simple file-like interface for strings and arrays. """ def __init__(self, buf): self.buf = buf self.offset = 0 def read(self, n): r = self.buf[self.offset:self.offset + n] if isarray(r): r = r.tostring() self.offset += n return r
[docs]class Reader: """ PNG decoder in pure Python. """ def __init__(self, _guess=None, **kw): """ Create a PNG decoder object. The constructor expects exactly one keyword argument. If you supply a positional argument instead, it will guess the input type. You can choose among the following keyword arguments: filename Name of input file (a PNG file). file A file-like object (object with a read() method). bytes ``array`` or ``string`` with PNG data. """ if ((_guess is not None and len(kw) != 0) or (_guess is None and len(kw) != 1)): raise TypeError("Reader() takes exactly 1 argument") # Will be the first 8 bytes, later on. See validate_signature. self.signature = None self.transparent = None # A pair of (len,type) if a chunk has been read but its data and # checksum have not (in other words the file position is just # past the 4 bytes that specify the chunk type). See preamble # method for how this is used. self.atchunk = None if _guess is not None: if isarray(_guess): kw["bytes"] = _guess elif isinstance(_guess, (str, unicode)): kw["filename"] = _guess elif hasattr(_guess, "read"): kw["file"] = _guess if "filename" in kw: self.file = file(kw["filename"], "rb") elif "file" in kw: self.file = kw["file"] elif "bytes" in kw: self.file = _readable(kw["bytes"]) else: raise TypeError("expecting filename, file or bytes array")
[docs] def chunk(self, seek=None): """ Read the next PNG chunk from the input file; returns type (as a 4 character string) and data. If the optional `seek` argument is specified then it will keep reading chunks until it either runs out of file or finds the type specified by the argument. Note that in general the order of chunks in PNGs is unspecified, so using `seek` can cause you to miss chunks. """ self.validate_signature() while True: # if not self.atchunk: self.atchunk = self.chunklentype() length, type = self.atchunk self.atchunk = None data = if len(data) != length: raise ChunkError('Chunk %s too short for required %i octets.' % (type, length)) checksum = if len(checksum) != 4: raise ValueError('Chunk %s too short for checksum.', type) if seek and type != seek: continue verify = zlib.crc32(type) verify = zlib.crc32(data, verify) # Whether the output from zlib.crc32 is signed or not varies # according to hideous implementation details, see # . # We coerce it to be positive here (in a way which works on # Python 2.3 and older). verify &= 2 ** 32 - 1 verify = struct.pack('!I', verify) if checksum != verify: # print repr(checksum) (a,) = struct.unpack('!I', checksum) (b,) = struct.unpack('!I', verify) raise ChunkError( "Checksum error in %s chunk: 0x%08X != 0x%08X." % (type, a, b)) return type, data
[docs] def chunks(self): """Return an iterator that will yield each chunk as a (*chunktype*, *content*) pair. """ while True: t, v = self.chunk() yield t, v if t == 'IEND': break
[docs] def undo_filter(self, filter_type, scanline, previous): """Undo the filter for a scanline. `scanline` is a sequence of bytes that does not include the initial filter type byte. `previous` is decoded previous scanline (for straightlaced images this is the previous pixel row, but for interlaced images, it is the previous scanline in the reduced image, which in general is not the previous pixel row in the final image). When there is no previous scanline (the first row of a straightlaced image, or the first row in one of the passes in an interlaced image), then this argument should be ``None``. The scanline will have the effects of filtering removed, and the result will be returned as a fresh sequence of bytes. """ # :todo: Would it be better to update scanline in place? # Create the result byte array. It seems that the best way to # create the array to be the right size is to copy from an # existing sequence. *sigh* # If we fill the result with scanline, then this allows a # micro-optimisation in the "null" and "sub" cases. result = array('B', scanline) if filter_type == 0: # And here, we _rely_ on filling the result with scanline, # above. return result if filter_type not in (1, 2, 3, 4): raise FormatError('Invalid PNG Filter Type.' ' See .') # Filter unit. The stride from one pixel to the corresponding # byte from the previous previous. Normally this is the pixel # size in bytes, but when this is smaller than 1, the previous # byte is used instead. fu = max(1, self.psize) # For the first line of a pass, synthesize a dummy previous # line. An alternative approach would be to observe that on the # first line 'up' is the same as 'null', 'paeth' is the same # as 'sub', with only 'average' requiring any special case. if not previous: previous = array('B', [0] * len(scanline)) def sub(): """Undo sub filter.""" ai = 0 # Loops starts at index fu. Observe that the initial part # of the result is already filled in correctly with # scanline. for i in range(fu, len(result)): x = scanline[i] a = result[ai] result[i] = (x + a) & 0xff ai += 1 def up(): """Undo up filter.""" for i in range(len(result)): x = scanline[i] b = previous[i] result[i] = (x + b) & 0xff def average(): """Undo average filter.""" ai = -fu for i in range(len(result)): x = scanline[i] if ai < 0: a = 0 else: a = result[ai] b = previous[i] result[i] = (x + ((a + b) >> 1)) & 0xff ai += 1 def paeth(): """Undo Paeth filter.""" # Also used for ci. ai = -fu for i in range(len(result)): x = scanline[i] if ai < 0: a = c = 0 else: a = result[ai] c = previous[ai] b = previous[i] p = a + b - c pa = abs(p - a) pb = abs(p - b) pc = abs(p - c) if pa <= pb and pa <= pc: pr = a elif pb <= pc: pr = b else: pr = c result[i] = (x + pr) & 0xff ai += 1 # Call appropriate filter algorithm. Note that 0 has already # been dealt with. (None, sub, up, average, paeth)[filter_type]() return result
[docs] def deinterlace(self, raw): """ Read raw pixel data, undo filters, deinterlace, and flatten. Return in flat row flat pixel format. """ # print >> sys.stderr, ("Reading interlaced, w=%s, r=%s, planes=%s," + # " bpp=%s") % (self.width, self.height, self.planes, self.bps) # Values per row (of the target image) vpr = self.width * self.planes # Make a result array, and make it big enough. Interleaving # writes to the output array randomly (well, not quite), so the # entire output array must be in memory. fmt = 'BH'[self.bitdepth > 8] a = array(fmt, [0] * vpr * self.height) source_offset = 0 for xstart, ystart, xstep, ystep in _adam7: # print >> sys.stderr, "Adam7: start=%s,%s step=%s,%s" % ( # xstart, ystart, xstep, ystep) if xstart >= self.width: continue # The previous (reconstructed) scanline. None at the # beginning of a pass to indicate that there is no previous # line. recon = None # Pixels per row (reduced pass image) ppr = int(math.ceil((self.width - xstart) / float(xstep))) # Row size in bytes for this pass. row_size = int(math.ceil(self.psize * ppr)) for y in range(ystart, self.height, ystep): filter_type = raw[source_offset] source_offset += 1 scanline = raw[source_offset:source_offset + row_size] source_offset += row_size recon = self.undo_filter(filter_type, scanline, recon) # Convert so that there is one element per pixel value flat = self.serialtoflat(recon, ppr) if xstep == 1: assert xstart == 0 offset = y * vpr a[offset:offset + vpr] = flat else: offset = y * vpr + xstart * self.planes end_offset = (y + 1) * vpr skip = self.planes * xstep for i in range(self.planes): a[offset + i:end_offset:skip] = \ flat[i::self.planes] return a
[docs] def iterboxed(self, rows): """Iterator that yields each scanline in boxed row flat pixel format. `rows` should be an iterator that yields the bytes of each row in turn. """ def asvalues(raw): """Convert a row of raw bytes into a flat row. Result may or may not share with argument""" if self.bitdepth == 8: return raw if self.bitdepth == 16: raw = tostring(raw) return array('H', struct.unpack('!%dH' % (len(raw) // 2), raw)) assert self.bitdepth < 8 width = self.width # Samples per byte spb = 8 // self.bitdepth out = array('B') mask = 2 ** self.bitdepth - 1 shifts = map(self.bitdepth.__mul__, reversed(range(spb))) for o in raw: out.extend(map(lambda i: mask & (o >> i), shifts)) return out[:width] return itertools.imap(asvalues, rows)
[docs] def serialtoflat(self, bytes, width=None): """Convert serial format (byte stream) pixel data to flat row flat pixel. """ if self.bitdepth == 8: return bytes if self.bitdepth == 16: bytes = tostring(bytes) return array('H', struct.unpack('!%dH' % (len(bytes) // 2), bytes)) assert self.bitdepth < 8 if width is None: width = self.width # Samples per byte spb = 8 // self.bitdepth out = array('B') mask = 2 ** self.bitdepth - 1 shifts = map(self.bitdepth.__mul__, reversed(range(spb))) l = width for o in bytes: out.extend(map(lambda i: mask & (o >> i), shifts)[:l]) l -= spb if l <= 0: l = width return out
[docs] def iterstraight(self, raw): """Iterator that undoes the effect of filtering, and yields each row in serialised format (as a sequence of bytes). Assumes input is straightlaced. `raw` should be an iterable that yields the raw bytes in chunks of arbitrary size.""" # length of row, in bytes rb = self.row_bytes a = array('B') # The previous (reconstructed) scanline. None indicates first # line of image. recon = None for some in raw: a.extend(some) while len(a) >= rb + 1: filter_type = a[0] scanline = a[1:rb + 1] del a[:rb + 1] recon = self.undo_filter(filter_type, scanline, recon) yield recon if len(a) != 0: # :file:format We get here with a file format error: when the # available bytes (after decompressing) do not pack into exact # rows. raise FormatError( 'Wrong size for decompressed IDAT chunk.') assert len(a) == 0
[docs] def validate_signature(self): """If signature (header) has not been read then read and validate it; otherwise do nothing. """ if self.signature: return self.signature = if self.signature != _signature: raise FormatError("PNG file has invalid signature.")
[docs] def preamble(self): """ Extract the image metadata by reading the initial part of the PNG file up to the start of the ``IDAT`` chunk. All the chunks that precede the ``IDAT`` chunk are read and either processed for metadata or discarded. """ self.validate_signature() while True: if not self.atchunk: self.atchunk = self.chunklentype() if self.atchunk is None: raise FormatError( 'This PNG file has no IDAT chunks.') if self.atchunk[1] == 'IDAT': return self.process_chunk()
[docs] def chunklentype(self): """Reads just enough of the input to determine the next chunk's length and type, returned as a (*length*, *type*) pair where *type* is a string. If there are no more chunks, ``None`` is returned. """ x = if not x: return None if len(x) != 8: raise FormatError( 'End of file whilst reading chunk length and type.') length, type = struct.unpack('!I4s', x) if length > 2 ** 31 - 1: raise FormatError('Chunk %s is too large: %d.' % (type, length)) return length, type
[docs] def process_chunk(self): """Process the next chunk and its data. This only processes the following chunk types, all others are ignored: ``IHDR``, ``PLTE``, ``bKGD``, ``tRNS``, ``gAMA``, ``sBIT``. """ type, data = self.chunk() if type == 'IHDR': # if len(data) != 13: raise FormatError('IHDR chunk has incorrect length.') (self.width, self.height, self.bitdepth, self.color_type, self.compression, self.filter, self.interlace) = struct.unpack("!2I5B", data) # Check that the header specifies only valid combinations. if self.bitdepth not in (1, 2, 4, 8, 16): raise Error("invalid bit depth %d" % self.bitdepth) if self.color_type not in (0, 2, 3, 4, 6): raise Error("invalid colour type %d" % self.color_type) # Check indexed (palettized) images have 8 or fewer bits # per pixel; check only indexed or greyscale images have # fewer than 8 bits per pixel. if ((self.color_type & 1 and self.bitdepth > 8) or (self.bitdepth < 8 and self.color_type not in (0, 3))): raise FormatError("Illegal combination of bit depth (%d)" " and colour type (%d)." " See ." % (self.bitdepth, self.color_type)) if self.compression != 0: raise Error("unknown compression method %d" % self.compression) if self.filter != 0: raise FormatError("Unknown filter method %d," " see ." % self.filter) if self.interlace not in (0, 1): raise FormatError("Unknown interlace method %d," " see ." % self.interlace) # Derived values # colormap = bool(self.color_type & 1) greyscale = not (self.color_type & 2) alpha = bool(self.color_type & 4) color_planes = (3, 1)[greyscale or colormap] planes = color_planes + alpha self.colormap = colormap self.greyscale = greyscale self.alpha = alpha self.color_planes = color_planes self.planes = planes self.psize = float(self.bitdepth) / float(8) * planes if int(self.psize) == self.psize: self.psize = int(self.psize) self.row_bytes = int(math.ceil(self.width * self.psize)) # Stores PLTE chunk if present, and is used to check # chunk ordering constraints. self.plte = None # Stores tRNS chunk if present, and is used to check chunk # ordering constraints. self.trns = None # Stores sbit chunk if present. self.sbit = None elif type == 'PLTE': # if self.plte: warnings.warn("Multiple PLTE chunks present.") self.plte = data if len(data) % 3 != 0: raise FormatError( "PLTE chunk's length should be a multiple of 3.") if len(data) > (2 ** self.bitdepth) * 3: raise FormatError("PLTE chunk is too long.") if len(data) == 0: raise FormatError("Empty PLTE is not allowed.") elif type == 'bKGD': try: if self.colormap: if not self.plte: warnings.warn( "PLTE chunk is required before bKGD chunk.") self.background = struct.unpack('B', data) else: self.background = struct.unpack("!%dH" % self.color_planes, data) except struct.error: raise FormatError("bKGD chunk has incorrect length.") elif type == 'tRNS': # self.trns = data if self.colormap: if not self.plte: warnings.warn("PLTE chunk is required before tRNS chunk.") else: if len(data) > len(self.plte) / 3: # Was warning, but promoted to Error as it # would otherwise cause pain later on. raise FormatError("tRNS chunk is too long.") else: if self.alpha: raise FormatError( "tRNS chunk is not valid with colour type %d." % self.color_type) try: self.transparent = \ struct.unpack("!%dH" % self.color_planes, data) except struct.error: raise FormatError("tRNS chunk has incorrect length.") elif type == 'gAMA': try: self.gamma = struct.unpack("!L", data)[0] / 100000.0 except struct.error: raise FormatError("gAMA chunk has incorrect length.") elif type == 'sBIT': self.sbit = data if (self.colormap and len(data) != 3 or not self.colormap and len(data) != self.planes): raise FormatError("sBIT chunk has incorrect length.")
[docs] def read(self): """ Read the PNG file and decode it. Returns (`width`, `height`, `pixels`, `metadata`). May use excessive memory. `pixels` are returned in boxed row flat pixel format. """ def iteridat(): """Iterator that yields all the ``IDAT`` chunks as strings.""" while True: try: type, data = self.chunk() except ValueError, e: raise ChunkError(e.args[0]) if type == 'IEND': # break if type != 'IDAT': continue # type == 'IDAT' # if self.colormap and not self.plte: warnings.warn("PLTE chunk is required before IDAT chunk") yield data def iterdecomp(idat): """Iterator that yields decompressed strings. `idat` should be an iterator that yields the ``IDAT`` chunk data. """ # Currently, with no max_length paramter to decompress, this # routine will do one yield per IDAT chunk. So not very # incremental. d = zlib.decompressobj() # The decompression loop: # Decompress an IDAT chunk, then decompress any remaining # unused data until the unused data does not get any # smaller. Add the unused data to the front of the input # and loop to process the next IDAT chunk. cdata = '' for data in idat: # :todo: add a max_length argument here to limit output # size. yield array('B', d.decompress(cdata + data)) yield array('B', d.flush()) self.preamble() raw = iterdecomp(iteridat()) if self.interlace: raw = array('B', itertools.chain(*raw)) arraycode = 'BH'[self.bitdepth > 8] # Like :meth:`group` but producing an array.array object for # each row. pixels = itertools.imap(lambda *row: array(arraycode, row), *[iter(self.deinterlace(raw))] * self.width * self.planes) else: pixels = self.iterboxed(self.iterstraight(raw)) meta = dict() for attr in 'greyscale alpha planes bitdepth interlace'.split(): meta[attr] = getattr(self, attr) meta['size'] = (self.width, self.height) for attr in 'gamma transparent background'.split(): a = getattr(self, attr, None) if a is not None: meta[attr] = a return self.width, self.height, pixels, meta
[docs] def read_flat(self): """ Read a PNG file and decode it into flat row flat pixel format. Returns (*width*, *height*, *pixels*, *metadata*). May use excessive memory. `pixels` are returned in flat row flat pixel format. See also the :meth:`read` method which returns pixels in the more stream-friendly boxed row flat pixel format. """ x, y, pixel, meta = arraycode = 'BH'[meta['bitdepth'] > 8] pixel = array(arraycode, itertools.chain(*pixel)) return x, y, pixel, meta
[docs] def palette(self, alpha='natural'): """Returns a palette that is a sequence of 3-tuples or 4-tuples, synthesizing it from the ``PLTE`` and ``tRNS`` chunks. These chunks should have already been processed (for example, by calling the :meth:`preamble` method). All the tuples are the same size, 3-tuples if there is no ``tRNS`` chunk, 4-tuples when there is a ``tRNS`` chunk. Assumes that the image is colour type 3 and therefore a ``PLTE`` chunk is required. If the `alpha` argument is ``'force'`` then an alpha channel is always added, forcing the result to be a sequence of 4-tuples. """ if not self.plte: raise FormatError( "Required PLTE chunk is missing in colour type 3 image.") plte = group(array('B', self.plte), 3) if self.trns or alpha == 'force': trns = array('B', self.trns or '') trns.extend([255] * (len(plte) - len(trns))) plte = map(operator.add, plte, group(trns, 1)) return plte
[docs] def asDirect(self): """Returns the image data as a direct representation of an ``x * y * planes`` array. This method is intended to remove the need for callers to deal with palettes and transparency themselves. Images with a palette (colour type 3) are converted to RGB or RGBA; images with transparency (a ``tRNS`` chunk) are converted to LA or RGBA as appropriate. When returned in this format the pixel values represent the colour value directly without needing to refer to palettes or transparency information. Like the :meth:`read` method this method returns a 4-tuple: (*width*, *height*, *pixels*, *meta*) This method normally returns pixel values with the bit depth they have in the source image, but when the source PNG has an ``sBIT`` chunk it is inspected and can reduce the bit depth of the result pixels; pixel values will be reduced according to the bit depth specified in the ``sBIT`` chunk (PNG nerds should note a single result bit depth is used for all channels; the maximum of the ones specified in the ``sBIT`` chunk. An RGB565 image will be rescaled to 6-bit RGB666). The *meta* dictionary that is returned reflects the `direct` format and not the original source image. For example, an RGB source image with a ``tRNS`` chunk to represent a transparent colour, will have ``planes=3`` and ``alpha=False`` for the source image, but the *meta* dictionary returned by this method will have ``planes=4`` and ``alpha=True`` because an alpha channel is synthesized and added. *pixels* is the pixel data in boxed row flat pixel format (just like the :meth:`read` method). All the other aspects of the image data are not changed. """ self.preamble() # Simple case, no conversion necessary. if not self.colormap and not self.trns and not self.sbit: return x, y, pixels, meta = if self.colormap: meta['colormap'] = False meta['alpha'] = bool(self.trns) meta['bitdepth'] = 8 meta['planes'] = 3 + bool(self.trns) plte = self.palette() def iterpal(pixels): for row in pixels: row = map(plte.__getitem__, row) yield array('B', itertools.chain(*row)) pixels = iterpal(pixels) elif self.trns: # It would be nice if there was some reasonable way of doing # this without generating a whole load of intermediate tuples. # But tuples does seem like the easiest way, with no other way # clearly much simpler or much faster. (Actually, the L to LA # conversion could perhaps go faster (all those 1-tuples!), but # I still wonder whether the code proliferation is worth it) it = self.transparent maxval = 2 ** meta['bitdepth'] - 1 planes = meta['planes'] meta['alpha'] = True meta['planes'] += 1 typecode = 'BH'[meta['bitdepth'] > 8] def itertrns(pixels): for row in pixels: # For each row we group it into pixels, then form a # characterisation vector that says whether each pixel # is opaque or not. Then we convert True/False to # 0/maxval (by multiplication), and add it as the extra # channel. row = group(row, planes) opa = map(it.__ne__, row) opa = map(maxval.__mul__, opa) opa = zip(opa) # convert to 1-tuples yield array(typecode, itertools.chain(*map(operator.add, row, opa))) pixels = itertrns(pixels) targetbitdepth = None if self.sbit: sbit = struct.unpack('%dB' % len(self.sbit), self.sbit) targetbitdepth = max(sbit) if targetbitdepth > meta['bitdepth']: raise Error('sBIT chunk %r exceeds bitdepth %d' % (sbit, self.bitdepth)) if min(sbit) <= 0: raise Error('sBIT chunk %r has a 0-entry' % sbit) if targetbitdepth == meta['bitdepth']: targetbitdepth = None if targetbitdepth: shift = meta['bitdepth'] - targetbitdepth meta['bitdepth'] = targetbitdepth def itershift(pixels): for row in pixels: yield map(shift.__rrshift__, row) pixels = itershift(pixels) return x, y, pixels, meta
[docs] def asFloat(self, maxval=1.0): """Return image pixels as per :meth:`asDirect` method, but scale all pixel values to be floating point values between 0.0 and *maxval*. """ x, y, pixels, info = self.asDirect() sourcemaxval = 2 ** info['bitdepth'] - 1 del info['bitdepth'] info['maxval'] = float(maxval) factor = float(maxval) / float(sourcemaxval) def iterfloat(): for row in pixels: yield map(factor.__mul__, row) return x, y, iterfloat(), info
@staticmethod def _as_rescale(get, targetbitdepth): """Helper used by :meth:`asRGB8` and :meth:`asRGBA8`.""" width, height, pixels, meta = get() maxval = 2 ** meta['bitdepth'] - 1 targetmaxval = 2 ** targetbitdepth - 1 factor = float(targetmaxval) / float(maxval) meta['bitdepth'] = targetbitdepth def iterscale(): for row in pixels: yield map(lambda x: int(round(x * factor)), row) return width, height, iterscale(), meta
[docs] def asRGB8(self): """Return the image data as an RGB pixels with 8-bits per sample. This is like the :meth:`asRGB` method except that this method additionally rescales the values so that they are all between 0 and 255 (8-bit). In the case where the source image has a bit depth < 8 the transformation preserves all the information; where the source image has bit depth > 8, then rescaling to 8-bit values loses precision. No dithering is performed. Like :meth:`asRGB`, an alpha channel in the source image will raise an exception. This function returns a 4-tuple: (*width*, *height*, *pixels*, *metadata*). *width*, *height*, *metadata* are as per the :meth:`read` method. *pixels* is the pixel data in boxed row flat pixel format. """ return self._as_rescale(self.asRGB, 8)
[docs] def asRGBA8(self): """Return the image data as RGBA pixels with 8-bits per sample. This method is similar to :meth:`asRGB8` and :meth:`asRGBA`: The result pixels have an alpha channel, _and_ values are rescale to the range 0 to 255. The alpha channel is synthesized if necessary. """ return self._as_rescale(self.asRGBA, 8)
[docs] def asRGB(self): """Return image as RGB pixels. Greyscales are expanded into RGB triplets. An alpha channel in the source image will raise an exception. The return values are as for the :meth:`read` method except that the *metadata* reflect the returned pixels, not the source image. In particular, for this method ``metadata['greyscale']`` will be ``False``. """ width, height, pixels, meta = self.asDirect() if meta['alpha']: raise Error("will not convert image with alpha channel to RGB") if not meta['greyscale']: return width, height, pixels, meta meta['greyscale'] = False typecode = 'BH'[meta['bitdepth'] > 8] def iterrgb(): for row in pixels: a = array(typecode, [0]) * 3 * width for i in range(3): a[i::3] = row yield a return width, height, iterrgb(), meta
[docs] def asRGBA(self): """Return image as RGBA pixels. Greyscales are expanded into RGB triplets; an alpha channel is synthesized if necessary. The return values are as for the :meth:`read` method except that the *metadata* reflect the returned pixels, not the source image. In particular, for this method ``metadata['greyscale']`` will be ``False``, and ``metadata['alpha']`` will be ``True``. """ width, height, pixels, meta = self.asDirect() if meta['alpha'] and not meta['greyscale']: return width, height, pixels, meta typecode = 'BH'[meta['bitdepth'] > 8] maxval = 2 ** meta['bitdepth'] - 1 def newarray(): return array(typecode, [0]) * 4 * width if meta['alpha'] and meta['greyscale']: # LA to RGBA def convert(): for row in pixels: # Create a fresh target row, then copy L channel # into first three target channels, and A channel # into fourth channel. a = newarray() for i in range(3): a[i::4] = row[0::2] a[3::4] = row[1::2] yield a elif meta['greyscale']: # L to RGBA def convert(): for row in pixels: a = newarray() for i in range(3): a[i::4] = row a[3::4] = array(typecode, maxval) * width yield a else: assert not meta['alpha'] and not meta['greyscale'] # RGB to RGBA def convert(): for row in pixels: a = newarray() for i in range(3): a[i::4] = row[i::3] a[3::4] = array(typecode, [maxval]) * width yield a meta['alpha'] = True meta['greyscale'] = False return width, height, convert(), meta # === Legacy Version Support === # :pyver:old: PyPNG works on Python versions 2.3 and 2.2, but not # without some awkward problems. Really PyPNG works on Python 2.4 (and # above); it works on Pythons 2.3 and 2.2 by virtue of fixing up # problems here. It's a bit ugly (which is why it's hidden down here). # # Generally the strategy is one of pretending that we're running on # Python 2.4 (or above), and patching up the library support on earlier # versions so that it looks enough like Python 2.4. When it comes to # Python 2.2 there is one thing we cannot patch: extended slices # # Instead we simply declare that features that are implemented using # extended slices will not work on Python 2.2. # # In order to work on Python 2.3 we fix up a recurring annoyance involving # the array type. In Python 2.3 an array cannot be initialised with an # array, and it cannot be extended with a list (or other sequence). # Both of those are repeated issues in the code. Whilst I would not # normally tolerate this sort of behaviour, here we "shim" a replacement # for array into place (and hope no-ones notices). You never read this. # # In an amusing case of warty hacks on top of warty hacks... the array # shimming we try and do only works on Python 2.3 and above (you can't # subclass array.array in Python 2.2). So to get it working on Python # 2.2 we go for something much simpler and (probably) way slower.
try: array('B').extend([]) array('B', array('B')) except: # Expect to get here on Python 2.3 try: class _array_shim(array): true_array = array def __new__(cls, typecode, init=None): super_new = super(_array_shim, cls).__new__ it = super_new(cls, typecode) if init is None: return it it.extend(init) return it def extend(self, extension): super_extend = super(_array_shim, self).extend if isinstance(extension, self.true_array): return super_extend(extension) if not isinstance(extension, (list, str)): # Convert to list. Allows iterators to work. extension = list(extension) return super_extend(self.true_array(self.typecode, extension)) array = _array_shim except: # Expect to get here on Python 2.2 def array(typecode, init=()): if type(init) == str: return map(ord, init) return list(init) # Further hacks to get it limping along on Python 2.2 try: enumerate except: def enumerate(seq): i = 0 for x in seq: yield i, x i += 1 try: reversed except: def reversed(l): l = list(l) l.reverse() for x in l: yield x try: itertools except: class _dummy_itertools: pass itertools = _dummy_itertools() def _itertools_imap(f, seq): for x in seq: yield f(x) itertools.imap = _itertools_imap def _itertools_chain(*iterables): for it in iterables: for element in it: yield element itertools.chain = _itertools_chain # === Internal Test Support === # This section comprises the tests that are internally validated (as # opposed to tests which produce output files that are externally # validated). Primarily they are unittests. # Note that it is difficult to internally validate the results of # writing a PNG file. The only thing we can do is read it back in # again, which merely checks consistency, not that the PNG file we # produce is valid. # Run the tests from the command line: # python -c 'import png;png.test()' from cStringIO import StringIO import tempfile # import unittest def test(): unittest.main(__name__) def topngbytes(name, rows, x, y, **k): """Convenience function for creating a PNG file "in memory" as a string. Creates a :class:`Writer` instance using the keyword arguments, then passes `rows` to its :meth:`Writer.write` method. The resulting PNG file is returned as a string. `name` is used to identify the file for debugging. """ import os print name f = StringIO() w = Writer(x, y, **k) w.write(f, rows) if os.environ.get('PYPNG_TEST_TMP'): w = open(name, 'wb') w.write(f.getvalue()) w.close() return f.getvalue() def testWithIO(inp, out, f): """Calls the function `f` with ``sys.stdin`` changed to `inp` and ``sys.stdout`` changed to `out`. They are restored when `f` returns. This function returns whatever `f` returns. """ try: oldin, sys.stdin = sys.stdin, inp oldout, sys.stdout = sys.stdout, out x = f() finally: sys.stdin = oldin sys.stdout = oldout return x class Test(unittest.TestCase): # This member is used by the superclass. If we don't define a new # class here then when we use self.assertRaises() and the PyPNG code # raises an assertion then we get no proper traceback. I can't work # out why, but defining a new class here means we get a proper # traceback. class failureException(Exception): pass def helperLN(self, n): mask = (1 << n) - 1 # Use small chunk_limit so that multiple chunk writing is # tested. Making it a test for Issue 20. w = Writer(15, 17, greyscale=True, bitdepth=n, chunk_limit=99) f = StringIO() w.write_array(f, array('B', map(mask.__and__, range(1, 256)))) r = Reader(bytes=f.getvalue()) x, y, pixels, meta = self.assertEqual(x, 15) self.assertEqual(y, 17) self.assertEqual(list(itertools.chain(*pixels)), map(mask.__and__, range(1, 256))) def testL8(self): return self.helperLN(8) def testL4(self): return self.helperLN(4) def testL2(self): "Also tests asRGB8." w = Writer(1, 4, greyscale=True, bitdepth=2) f = StringIO() w.write_array(f, array('B', range(4))) r = Reader(bytes=f.getvalue()) x, y, pixels, meta = r.asRGB8() self.assertEqual(x, 1) self.assertEqual(y, 4) for i, row in enumerate(pixels): self.assertEqual(len(row), 3) self.assertEqual(list(row), [0x55 * i] * 3) def testP2(self): "2-bit palette." a = (255, 255, 255) b = (200, 120, 120) c = (50, 99, 50) w = Writer(1, 4, bitdepth=2, palette=[a, b, c]) f = StringIO() w.write_array(f, array('B', (0, 1, 1, 2))) r = Reader(bytes=f.getvalue()) x, y, pixels, meta = r.asRGB8() self.assertEqual(x, 1) self.assertEqual(y, 4) self.assertEqual(list(pixels), map(list, [a, b, b, c])) def testPtrns(self): "Test colour type 3 and tRNS chunk (and 4-bit palette)." a = (50, 99, 50, 50) b = (200, 120, 120, 80) c = (255, 255, 255) d = (200, 120, 120) e = (50, 99, 50) w = Writer(3, 3, bitdepth=4, palette=[a, b, c, d, e]) f = StringIO() w.write_array(f, array('B', (4, 3, 2, 3, 2, 0, 2, 0, 1))) r = Reader(bytes=f.getvalue()) x, y, pixels, meta = r.asRGBA8() self.assertEquals(x, 3) self.assertEquals(y, 3) c = c + (255,) d = d + (255,) e = e + (255,) boxed = [(e, d, c), (d, c, a), (c, a, b)] flat = map(lambda row: itertools.chain(*row), boxed) self.assertEqual(map(list, pixels), map(list, flat)) def testRGBtoRGBA(self): "asRGBA8() on colour type 2 source.""" # Test for Issue 26 r = Reader(bytes=_pngsuite['basn2c08']) x, y, pixels, meta = r.asRGBA8() # Test the pixels at row 9 columns 0 and 1. row9 = list(pixels)[9] self.assertEqual(row9[0:8], [0xff, 0xdf, 0xff, 0xff, 0xff, 0xde, 0xff, 0xff]) def testCtrns(self): "Test colour type 2 and tRNS chunk." # Test for Issue 25 r = Reader(bytes=_pngsuite['tbrn2c08']) x, y, pixels, meta = r.asRGBA8() # I just happen to know that the first pixel is transparent. # In particular it should be #7f7f7f00 row0 = list(pixels)[0] self.assertEqual(tuple(row0[0:4]), (0x7f, 0x7f, 0x7f, 0x00)) def testAdam7read(self): """Adam7 interlace reading. Specifically, test that for images in the PngSuite that have both an interlaced and straightlaced pair that both images from the pair produce the same array of pixels.""" for candidate in _pngsuite: if not candidate.startswith('basn'): continue candi = candidate.replace('n', 'i') if candi not in _pngsuite: continue print 'adam7 read', candidate straight = Reader(bytes=_pngsuite[candidate]) adam7 = Reader(bytes=_pngsuite[candi]) # Just compare the pixels. Ignore x,y (because they're # likely to be correct?); metadata is ignored because the # "interlace" member differs. Lame. straight =[2] adam7 =[2] self.assertEqual(map(list, straight), map(list, adam7)) def testAdam7write(self): """Adam7 interlace writing. For each test image in the PngSuite, write an interlaced and a straightlaced version. Decode both, and compare results. """ # Not such a great test, because the only way we can check what # we have written is to read it back again. for name, bytes in _pngsuite.items(): # Only certain colour types supported for this test. if name[3:5] not in ['n0', 'n2', 'n4', 'n6']: continue it = Reader(bytes=bytes) x, y, pixels, meta = pngi = topngbytes('adam7wn' + name + '.png', pixels, x=x, y=y, bitdepth=it.bitdepth, greyscale=it.greyscale, alpha=it.alpha, transparent=it.transparent, interlace=False) x, y, ps, meta = Reader(bytes=pngi).read() it = Reader(bytes=bytes) x, y, pixels, meta = pngs = topngbytes('adam7wi' + name + '.png', pixels, x=x, y=y, bitdepth=it.bitdepth, greyscale=it.greyscale, alpha=it.alpha, transparent=it.transparent, interlace=True) x, y, pi, meta = Reader(bytes=pngs).read() self.assertEqual(map(list, ps), map(list, pi)) def testPGMin(self): """Test that the command line tool can read PGM files.""" def do(): return _main(['testPGMin']) s = StringIO() s.write('P5 2 2 3\n') s.write('\x00\x01\x02\x03') s.flush() o = StringIO() testWithIO(s, o, do) r = Reader(bytes=o.getvalue()) self.assert_(r.greyscale) self.assertEqual(r.bitdepth, 2) def testPAMin(self): """Test that the command line tool can read PAM file.""" def do(): return _main(['testPAMin']) s = StringIO() s.write('P7\nWIDTH 3\nHEIGHT 1\nDEPTH 4\nMAXVAL 255\n' 'TUPLTYPE RGB_ALPHA\nENDHDR\n') # The pixels in flat row flat pixel format flat = [255, 0, 0, 255, 0, 255, 0, 120, 0, 0, 255, 30] s.write(''.join(map(chr, flat))) s.flush() o = StringIO() testWithIO(s, o, do) r = Reader(bytes=o.getvalue()) x, y, pixels, meta = self.assert_(r.alpha) self.assert_(not r.greyscale) self.assertEqual(list(itertools.chain(*pixels)), flat) def testLA4(self): """Create an LA image with bitdepth 4.""" bytes = topngbytes('la4.png', [[5, 12]], 1, 1, greyscale=True, alpha=True, bitdepth=4) sbit = Reader(bytes=bytes).chunk('sBIT')[1] self.assertEqual(sbit, '\x04\x04') def testPNMsbit(self): """Test that PNM files can generates sBIT chunk.""" def do(): return _main(['testPNMsbit']) s = StringIO() s.write('P6 8 1 1\n') for pixel in range(8): s.write(struct.pack('<I', (0x4081 * pixel) & 0x10101)[:3]) s.flush() o = StringIO() testWithIO(s, o, do) r = Reader(bytes=o.getvalue()) sbit = r.chunk('sBIT')[1] self.assertEqual(sbit, '\x01\x01\x01') def testLtrns0(self): """Create greyscale image with tRNS chunk.""" return self.helperLtrns(0) def testLtrns1(self): """Using 1-tuple for transparent arg.""" return self.helperLtrns((0,)) def helperLtrns(self, transparent): """Helper used by :meth:`testLtrns*`.""" pixels = zip(map(ord, '00384c545c403800'.decode('hex'))) o = StringIO() w = Writer(8, 8, greyscale=True, bitdepth=1, transparent=transparent) w.write_packed(o, pixels) r = Reader(bytes=o.getvalue()) x, y, pixels, meta = r.asDirect() self.assert_(meta['alpha']) self.assert_(meta['greyscale']) self.assertEqual(meta['bitdepth'], 1) def testWinfo(self): """Test the dictionary returned by a `read` method can be used as args for :meth:`Writer`. """ r = Reader(bytes=_pngsuite['basn2c16']) info =[3] def testPackedIter(self): """Test iterator for row when using write_packed. Indicative for Issue 47. """ w = Writer(16, 2, greyscale=True, alpha=False, bitdepth=1) o = StringIO() w.write_packed(o, [itertools.chain([0x0a], [0xaa]), itertools.chain([0x0f], [0xff])]) r = Reader(bytes=o.getvalue()) x, y, pixels, info = r.asDirect() pixels = list(pixels) self.assertEqual(len(pixels), 2) self.assertEqual(len(pixels[0]), 16) def testInterlacedArray(self): """Test that reading an interlaced PNG yields each row as an array.""" r = Reader(bytes=_pngsuite['basi0g08']) list([2])[0].tostring def testTrnsArray(self): """Test that reading a type 2 PNG with tRNS chunk yields each row as an array (using asDirect).""" r = Reader(bytes=_pngsuite['tbrn2c08']) list(r.asDirect()[2])[0].tostring # Invalid file format tests. These construct various badly # formatted PNG files, then feed them into a Reader. When # everything is working properly, we should get FormatError # exceptions raised. def testEmpty(self): """Test empty file.""" r = Reader(bytes='') self.assertRaises(FormatError, r.asDirect) def testSigOnly(self): """Test file containing just signature bytes.""" r = Reader(bytes=_signature) self.assertRaises(FormatError, r.asDirect) def testExtraPixels(self): """Test file that contains too many pixels.""" def eachchunk(chunk): if chunk[0] != 'IDAT': return chunk data = chunk[1].decode('zip') data += '\x00garbage' data = data.encode('zip') chunk = (chunk[0], data) return chunk self.assertRaises(FormatError, self.helperFormat, eachchunk) def testNotEnoughPixels(self): def eachchunk(chunk): if chunk[0] != 'IDAT': return chunk # Remove last byte. data = chunk[1].decode('zip') data = data[:-1] data = data.encode('zip') return chunk[0], data self.assertRaises(FormatError, self.helperFormat, eachchunk) def helperFormat(self, f): r = Reader(bytes=_pngsuite['basn0g01']) o = StringIO() def newchunks(): for chunk in r.chunks(): yield f(chunk) write_chunks(o, newchunks()) r = Reader(bytes=o.getvalue()) return list(r.asDirect()[2]) def testBadFilter(self): def eachchunk(chunk): if chunk[0] != 'IDAT': return chunk data = chunk[1].decode('zip') # Corrupt the first filter byte data = '\x99' + data[1:] data = data.encode('zip') return chunk[0], data self.assertRaises(FormatError, self.helperFormat, eachchunk) def testFlat(self): """Test read_flat.""" import hashlib r = Reader(bytes=_pngsuite['basn0g02']) x, y, pixel, meta = r.read_flat() d = hashlib.md5(''.join(map(chr, pixel))).digest() self.assertEqual(d.encode('hex'), '255cd971ab8cd9e7275ff906e5041aa0') # numpy dependent tests. These are skipped (with a message to # sys.stderr) if numpy cannot be imported. def testNumpyuint16(self): """numpy uint16.""" try: import numpy except ImportError: print >> sys.stderr, "skipping numpy test" return rows = [map(numpy.uint16, range(0, 0x10000, 0x5555))] b = topngbytes('numpyuint16.png', rows, 4, 1, greyscale=True, alpha=False, bitdepth=16) def testNumpyuint8(self): """numpy uint8.""" try: import numpy except ImportError: print >> sys.stderr, "skipping numpy test" return rows = [map(numpy.uint8, range(0, 0x100, 0x55))] b = topngbytes('numpyuint8.png', rows, 4, 1, greyscale=True, alpha=False, bitdepth=8) def testNumpybool(self): """numpy bool.""" try: import numpy except ImportError: print >> sys.stderr, "skipping numpy test" return rows = [map(numpy.bool, [0, 1])] b = topngbytes('numpybool.png', rows, 2, 1, greyscale=True, alpha=False, bitdepth=1) # === Command Line Support === def _dehex(s): """Liberally convert from hex string to binary string.""" import re # Remove all non-hexadecimal digits s = re.sub(r'[^a-fA-F\d]', '', s) return s.decode('hex') # Copies of PngSuite test files taken # from # on 2009-02-19 by drj and converted to hex. # Some of these are not actually in PngSuite (but maybe they should # be?), they use the same naming scheme, but start with a capital # letter. _pngsuite = { 'basi0g01': _dehex(""" 89504e470d0a1a0a0000000d49484452000000200000002001000000012c0677 cf0000000467414d41000186a031e8965f0000009049444154789c2d8d310ec2 300c45dfc682c415187a00a42e197ab81e83b127e00c5639001363a580d8582c 65c910357c4b78b0bfbfdf4f70168c19e7acb970a3f2d1ded9695ce5bf5963df d92aaf4c9fd927ea449e6487df5b9c36e799b91bdf082b4d4bd4014fe4014b01 ab7a17aee694d28d328a2d63837a70451e1648702d9a9ff4a11d2f7a51aa21e5 a18c7ffd0094e3511d661822f20000000049454e44ae426082 """), 'basi0g02': _dehex(""" 89504e470d0a1a0a0000000d49484452000000200000002002000000016ba60d 1f0000000467414d41000186a031e8965f0000005149444154789c635062e860 00e17286bb609c93c370ec189494960631366e4467b3ae675dcf10f521ea0303 90c1ca006444e11643482064114a4852c710baea3f18c31918020c30410403a6 0ac1a09239009c52804d85b6d97d0000000049454e44ae426082 """), 'basi0g04': _dehex(""" 89504e470d0a1a0a0000000d4948445200000020000000200400000001e4e6f8 bf0000000467414d41000186a031e8965f000000ae49444154789c658e5111c2 301044171c141c141c041c843a287510ea20d441c041c141c141c04191102454 03994998cecd7edcecedbb9bdbc3b2c2b6457545fbc4bac1be437347f7c66a77 3c23d60db15e88f5c5627338a5416c2e691a9b475a89cd27eda12895ae8dfdab 43d61e590764f5c83a226b40d669bec307f93247701687723abf31ff83a2284b a5b4ae6b63ac6520ad730ca4ed7b06d20e030369bd6720ed383290360406d24e 13811f2781eba9d34d07160000000049454e44ae426082 """), 'basi0g08': _dehex(""" 89504e470d0a1a0a0000000d4948445200000020000000200800000001211615 be0000000467414d41000186a031e8965f000000b549444154789cb5905d0ac2 3010849dbac81c42c47bf843cf253e8878b0aa17110f214bdca6be240f5d21a5 94ced3e49bcd322c1624115515154998aa424822a82a5624a1aa8a8b24c58f99 999908130989a04a00d76c2c09e76cf21adcb209393a6553577da17140a2c59e 70ecbfa388dff1f03b82fb82bd07f05f7cb13f80bb07ad2fd60c011c3c588eef f1f4e03bbec7ce832dca927aea005e431b625796345307b019c845e6bfc3bb98 769d84f9efb02ea6c00f9bb9ff45e81f9f280000000049454e44ae426082 """), 'basi0g16': _dehex(""" 89504e470d0a1a0a0000000d49484452000000200000002010000000017186c9 fd0000000467414d41000186a031e8965f000000e249444154789cb5913b0ec2 301044c7490aa8f85d81c3e4301c8f53a4ca0da8902c8144b3920b4043111282 23bc4956681a6bf5fc3c5a3ba0448912d91a4de2c38dd8e380231eede4c4f7a1 4677700bec7bd9b1d344689315a3418d1a6efbe5b8305ba01f8ff4808c063e26 c60d5c81edcf6c58c535e252839e93801b15c0a70d810ae0d306b205dc32b187 272b64057e4720ff0502154034831520154034c3df81400510cdf0015c86e5cc 5c79c639fddba9dcb5456b51d7980eb52d8e7d7fa620a75120d6064641a05120 b606771a05626b401a05f1f589827cf0fe44c1f0bae0055698ee8914fffffe00 00000049454e44ae426082 """), 'basi2c08': _dehex(""" 89504e470d0a1a0a0000000d49484452000000200000002008020000018b1fdd 350000000467414d41000186a031e8965f000000f249444154789cd59341aa04 210c44abc07b78133d59d37333bd89d76868b566d10cf4675af8596431a11662 7c5688919280e312257dd6a0a4cf1a01008ee312a5f3c69c37e6fcc3f47e6776 a07f8bdaf5b40feed2d33e025e2ff4fe2d4a63e1a16d91180b736d8bc45854c5 6d951863f4a7e0b66dcf09a900f3ffa2948d4091e53ca86c048a64390f662b50 4a999660ced906182b9a01a8be00a56404a6ede182b1223b4025e32c4de34304 63457680c93aada6c99b73865aab2fc094920d901a203f5ddfe1970d28456783 26cffbafeffcd30654f46d119be4793f827387fc0d189d5bc4d69a3c23d45a7f db803146578337df4d0a3121fc3d330000000049454e44ae426082 """), 'basi2c16': _dehex(""" 89504e470d0a1a0a0000000d4948445200000020000000201002000001db8f01 760000000467414d41000186a031e8965f0000020a49444154789cd5962173e3 3010853fcf1838cc61a1818185a53e56787fa13fa130852e3b5878b4b0b03081 b97f7030070b53e6b057a0a8912bbb9163b9f109ececbc59bd7dcf2b45492409 d66f00eb1dd83cb5497d65456aeb8e1040913b3b2c04504c936dd5a9c7e2c6eb 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'Basn0g03': _dehex(""" 89504e470d0a1a0a0000000d494844520000002000000020040000000093e1c8 2900000001734249540371d88211000000fd49444154789c6d90d18906210c84 c356f22356b2889588604301b112112b11d94a96bb495cf7fe87f32d996f2689 44741cc658e39c0b118f883e1f63cc89dafbc04c0f619d7d898396c54b875517 83f3a2e7ac09a2074430e7f497f00f1138a5444f82839c5206b1f51053cca968 63258821e7f2b5438aac16fbecc052b646e709de45cf18996b29648508728612 952ca606a73566d44612b876845e9a347084ea4868d2907ff06be4436c4b41a3 a3e1774285614c5affb40dbd931a526619d9fa18e4c2be420858de1df0e69893 a0e3e5523461be448561001042b7d4a15309ce2c57aef2ba89d1c13794a109d7 b5880aa27744fc5c4aecb5e7bcef5fe528ec6293a930690000000049454e44ae 426082 """), 'basn0g04': _dehex(""" 89504e470d0a1a0a0000000d494844520000002000000020040000000093e1c8 290000000467414d41000186a031e8965f0000004849444154789c6360601014 545232367671090d4d4b2b2f6720430095dbd1418e002a77e64c720450b9ab56 912380caddbd9b1c0154ee9933e408a072efde25470095fbee1d1902001f14ee 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3b2c6ac52d403c054e019249b087f53d0558995a99ea946c70cc927458b3c1ff 550f30050df988d4284376b4566a8e416654cc921985e037e0df0fc131f00f4b acf0c6211c036f14a239703741740adc7da227edd7e56b833d0ae92549b4d357 25dfb49ed2ff63908e6adf27d6d0dda7638d4154d2778daca17f58e61297c129 41f233b01f5dc3740cac51688c35c6b22580f48224fee9b83502569a66b629f1 09f3713473413e2666e7fe6f6c6efefdfafda1f56f6e06f93496d9d67cb7366a 9964b6f92e64b689196ec6c604646fd3fe4771ff1bf03f65d8ecc3addbb5f300 00000049454e44ae426082 """), } def test_suite(options, args): """ Create a PNG test image and write the file to stdout. """ # Below is a big stack of test image generators. # They're all really tiny, so PEP 8 rules are suspended. def test_gradient_horizontal_lr(x, y): return x def test_gradient_horizontal_rl(x, y): return 1 - x def test_gradient_vertical_tb(x, y): return y def test_gradient_vertical_bt(x, y): return 1 - y def test_radial_tl(x, y): return max(1 - math.sqrt(x * x + y * y), 0.0) def test_radial_center(x, y): return test_radial_tl(x - 0.5, y - 0.5) def test_radial_tr(x, y): return test_radial_tl(1 - x, y) def test_radial_bl(x, y): return test_radial_tl(x, 1 - y) def test_radial_br(x, y): return test_radial_tl(1 - x, 1 - y) def test_stripe(x, n): return float(int(x * n) & 1) def test_stripe_h_2(x, y): return test_stripe(x, 2) def test_stripe_h_4(x, y): return test_stripe(x, 4) def test_stripe_h_10(x, y): return test_stripe(x, 10) def test_stripe_v_2(x, y): return test_stripe(y, 2) def test_stripe_v_4(x, y): return test_stripe(y, 4) def test_stripe_v_10(x, y): return test_stripe(y, 10) def test_stripe_lr_10(x, y): return test_stripe(x + y, 10) def test_stripe_rl_10(x, y): return test_stripe(1 + x - y, 10) def test_checker(x, y, n): return float((int(x * n) & 1) ^ (int(y * n) & 1)) def test_checker_8(x, y): return test_checker(x, y, 8) def test_checker_15(x, y): return test_checker(x, y, 15) def test_zero(x, y): return 0 def test_one(x, y): return 1 test_patterns = { 'GLR': test_gradient_horizontal_lr, 'GRL': test_gradient_horizontal_rl, 'GTB': test_gradient_vertical_tb, 'GBT': test_gradient_vertical_bt, 'RTL': test_radial_tl, 'RTR': test_radial_tr, 'RBL': test_radial_bl, 'RBR': test_radial_br, 'RCTR': test_radial_center, 'HS2': test_stripe_h_2, 'HS4': test_stripe_h_4, 'HS10': test_stripe_h_10, 'VS2': test_stripe_v_2, 'VS4': test_stripe_v_4, 'VS10': test_stripe_v_10, 'LRS': test_stripe_lr_10, 'RLS': test_stripe_rl_10, 'CK8': test_checker_8, 'CK15': test_checker_15, 'ZERO': test_zero, 'ONE': test_one, } def test_pattern(width, height, bitdepth, pattern): """Create a single plane (monochrome) test pattern. Returns a flat row flat pixel array. """ maxval = 2 ** bitdepth - 1 if maxval > 255: a = array('H') else: a = array('B') fw = float(width) fh = float(height) pfun = test_patterns[pattern] for y in range(height): fy = float(y) / fh for x in range(width): a.append(int(round(pfun(float(x) / fw, fy) * maxval))) return a def test_rgba(size=256, bitdepth=8, red="GTB", green="GLR", blue="RTL", alpha=None): """ Create a test image. Each channel is generated from the specified pattern; any channel apart from red can be set to None, which will cause it not to be in the image. It is possible to create all PNG channel types (L, RGB, LA, RGBA), as well as non PNG channel types (RGA, and so on). """ i = test_pattern(size, size, bitdepth, red) psize = 1 for channel in (green, blue, alpha): if channel: c = test_pattern(size, size, bitdepth, channel) i = interleave_planes(i, c, psize, 1) psize += 1 return i def pngsuite_image(name): """ Create a test image by reading an internal copy of the files from the PngSuite. Returned in flat row flat pixel format. """ if name not in _pngsuite: raise NotImplementedError("cannot find PngSuite file %s (use -L for a list)" % name) r = Reader(bytes=_pngsuite[name]) w, h, pixels, meta = r.asDirect() assert w == h # LAn for n < 8 is a special case for which we need to rescale # the data. if meta['greyscale'] and meta['alpha'] and meta['bitdepth'] < 8: factor = 255 // (2 ** meta['bitdepth'] - 1) def rescale(data): for row in data: yield map(factor.__mul__, row) pixels = rescale(pixels) meta['bitdepth'] = 8 arraycode = 'BH'[meta['bitdepth'] > 8] return w, array(arraycode, itertools.chain(*pixels)), meta # The body of test_suite() size = 256 if options.test_size: size = options.test_size options.bitdepth = options.test_depth options.greyscale = bool(options.test_black) kwargs = {} if options.test_red: kwargs["red"] = options.test_red if options.test_green: kwargs["green"] = options.test_green if options.test_blue: kwargs["blue"] = options.test_blue if options.test_alpha: kwargs["alpha"] = options.test_alpha if options.greyscale: if options.test_red or options.test_green or options.test_blue: raise ValueError("cannot specify colours (R, G, B) when greyscale image (black channel, K) is specified") kwargs["red"] = options.test_black kwargs["green"] = None kwargs["blue"] = None options.alpha = bool(options.test_alpha) if not args: pixels = test_rgba(size, options.bitdepth, **kwargs) else: size, pixels, meta = pngsuite_image(args[0]) for k in ['bitdepth', 'alpha', 'greyscale']: setattr(options, k, meta[k]) writer = Writer(size, size, bitdepth=options.bitdepth, transparent=options.transparent, background=options.background, gamma=options.gamma, greyscale=options.greyscale, alpha=options.alpha, compression=options.compression, interlace=options.interlace) writer.write_array(sys.stdout, pixels) def read_pam_header(infile): """ Read (the rest of a) PAM header. `infile` should be positioned immediately after the initial 'P7' line (at the beginning of the second line). Returns are as for `read_pnm_header`. """ # Unlike PBM, PGM, and PPM, we can read the header a line at a time. header = dict() while True: l = infile.readline().strip() if l == 'ENDHDR': break if l == '': raise EOFError('PAM ended prematurely') if l[0] == '#': continue l = l.split(None, 1) if l[0] not in header: header[l[0]] = l[1] else: header[l[0]] += ' ' + l[1] if ('WIDTH' not in header or 'HEIGHT' not in header or 'DEPTH' not in header or 'MAXVAL' not in header): raise Error('PAM file must specify WIDTH, HEIGHT, DEPTH, and MAXVAL') width = int(header['WIDTH']) height = int(header['HEIGHT']) depth = int(header['DEPTH']) maxval = int(header['MAXVAL']) if (width <= 0 or height <= 0 or depth <= 0 or maxval <= 0): raise Error( 'WIDTH, HEIGHT, DEPTH, MAXVAL must all be positive integers') return 'P7', width, height, depth, maxval def read_pnm_header(infile, supported=('P5', 'P6')): """ Read a PNM header, returning (format,width,height,depth,maxval). `width` and `height` are in pixels. `depth` is the number of channels in the image; for PBM and PGM it is synthesized as 1, for PPM as 3; for PAM images it is read from the header. `maxval` is synthesized (as 1) for PBM images. """ # Generally, see # and # Technically 'P7' must be followed by a newline, so by using # rstrip() we are being liberal in what we accept. I think this # is acceptable. type = if type not in supported: raise NotImplementedError('file format %s not supported' % type) if type == 'P7': # PAM header parsing is completely different. return read_pam_header(infile) # Expected number of tokens in header (3 for P4, 4 for P6) expected = 4 pbm = ('P1', 'P4') if type in pbm: expected = 3 header = [type] # We have to read the rest of the header byte by byte because the # final whitespace character (immediately following the MAXVAL in # the case of P6) may not be a newline. Of course all PNM files in # the wild use a newline at this point, so it's tempting to use # readline; but it would be wrong. def getc(): c = if c == '': raise Error('premature EOF reading PNM header') return c c = getc() while True: # Skip whitespace that precedes a token. while c.isspace(): c = getc() # Skip comments. while c == '#': while c not in '\n\r': c = getc() if not c.isdigit(): raise Error('unexpected character %s found in header' % c) # According to the specification it is legal to have comments # that appear in the middle of a token. # This is bonkers; I've never seen it; and it's a bit awkward to # code good lexers in Python (no goto). So we break on such # cases. token = '' while c.isdigit(): token += c c = getc() # Slight hack. All "tokens" are decimal integers, so convert # them here. header.append(int(token)) if len(header) == expected: break # Skip comments (again) while c == '#': while c not in '\n\r': c = getc() if not c.isspace(): raise Error('expected header to end with whitespace, not %s' % c) if type in pbm: # synthesize a MAXVAL header.append(1) depth = (1, 3)[type == 'P6'] return header[0], header[1], header[2], depth, header[3] def write_pnm(file, width, height, pixels, meta): """Write a Netpbm PNM/PAM file.""" bitdepth = meta['bitdepth'] maxval = 2 ** bitdepth - 1 # Rudely, the number of image planes can be used to determine # whether we are L (PGM), LA (PAM), RGB (PPM), or RGBA (PAM). planes = meta['planes'] # Can be an assert as long as we assume that pixels and meta came # from a PNG file. assert planes in (1, 2, 3, 4) if planes in (1, 3): if 1 == planes: # PGM # Could generate PBM if maxval is 1, but we don't (for one # thing, we'd have to convert the data, not just blat it # out). fmt = 'P5' else: # PPM fmt = 'P6' file.write('%s %d %d %d\n' % (fmt, width, height, maxval)) if planes in (2, 4): # PAM # See if 2 == planes: tupltype = 'GRAYSCALE_ALPHA' else: tupltype = 'RGB_ALPHA' file.write('P7\nWIDTH %d\nHEIGHT %d\nDEPTH %d\nMAXVAL %d\n' 'TUPLTYPE %s\nENDHDR\n' % (width, height, planes, maxval, tupltype)) # Values per row vpr = planes * width # struct format fmt = '>%d' % vpr if maxval > 0xff: fmt += 'H' else: fmt += 'B' for row in pixels: file.write(struct.pack(fmt, *row)) file.flush() def color_triple(color): """ Convert a command line colour value to a RGB triple of integers. FIXME: Somewhere we need support for greyscale backgrounds etc. """ if color.startswith('#') and len(color) == 4: return (int(color[1], 16), int(color[2], 16), int(color[3], 16)) if color.startswith('#') and len(color) == 7: return (int(color[1:3], 16), int(color[3:5], 16), int(color[5:7], 16)) elif color.startswith('#') and len(color) == 13: return (int(color[1:5], 16), int(color[5:9], 16), int(color[9:13], 16)) def _main(argv): """ Run the PNG encoder with options from the command line. """ # Parse command line arguments from optparse import OptionParser import re version = '%prog ' + re.sub(r'( ?\$|URL: |Rev:)', '', __version__) parser = OptionParser(version=version) parser.set_usage("%prog [options] [imagefile]") parser.add_option('-r', '--read-png', default=False, action='store_true', help='Read PNG, write PNM') parser.add_option("-i", "--interlace", default=False, action="store_true", help="create an interlaced PNG file (Adam7)") parser.add_option("-t", "--transparent", action="store", type="string", metavar="color", help="mark the specified colour (#RRGGBB) as transparent") parser.add_option("-b", "--background", action="store", type="string", metavar="color", help="save the specified background colour") parser.add_option("-a", "--alpha", action="store", type="string", metavar="pgmfile", help="alpha channel transparency (RGBA)") parser.add_option("-g", "--gamma", action="store", type="float", metavar="value", help="save the specified gamma value") parser.add_option("-c", "--compression", action="store", type="int", metavar="level", help="zlib compression level (0-9)") parser.add_option("-T", "--test", default=False, action="store_true", help="create a test image (a named PngSuite image if an argument is supplied)") parser.add_option('-L', '--list', default=False, action='store_true', help="print list of named test images") parser.add_option("-R", "--test-red", action="store", type="string", metavar="pattern", help="test pattern for the red image layer") parser.add_option("-G", "--test-green", action="store", type="string", metavar="pattern", help="test pattern for the green image layer") parser.add_option("-B", "--test-blue", action="store", type="string", metavar="pattern", help="test pattern for the blue image layer") parser.add_option("-A", "--test-alpha", action="store", type="string", metavar="pattern", help="test pattern for the alpha image layer") parser.add_option("-K", "--test-black", action="store", type="string", metavar="pattern", help="test pattern for greyscale image") parser.add_option("-d", "--test-depth", default=8, action="store", type="int", metavar='NBITS', help="create test PNGs that are NBITS bits per channel") parser.add_option("-S", "--test-size", action="store", type="int", metavar="size", help="width and height of the test image") (options, args) = parser.parse_args(args=argv[1:]) # Convert options if options.transparent is not None: options.transparent = color_triple(options.transparent) if options.background is not None: options.background = color_triple(options.background) if options.list: names = list(_pngsuite) names.sort() for name in names: print name return # Run regression tests if options.test: return test_suite(options, args) # Prepare input and output files if len(args) == 0: infilename = '-' infile = sys.stdin elif len(args) == 1: infilename = args[0] infile = open(infilename, 'rb') else: parser.error("more than one input file") outfile = sys.stdout if options.read_png: # Encode PNG to PPM png = Reader(file=infile) width, height, pixels, meta = png.asDirect() write_pnm(outfile, width, height, pixels, meta) else: # Encode PNM to PNG format, width, height, depth, maxval = \ read_pnm_header(infile, ('P5', 'P6', 'P7')) # When it comes to the variety of input formats, we do something # rather rude. Observe that L, LA, RGB, RGBA are the 4 colour # types supported by PNG and that they correspond to 1, 2, 3, 4 # channels respectively. So we use the number of channels in # the source image to determine which one we have. We do not # care about TUPLTYPE. greyscale = depth <= 2 pamalpha = depth in (2, 4) supported = map(lambda x: 2 ** x - 1, range(1, 17)) try: mi = supported.index(maxval) except ValueError: raise NotImplementedError( 'your maxval (%s) not in supported list %s' % (maxval, str(supported))) bitdepth = mi + 1 writer = Writer(width, height, greyscale=greyscale, bitdepth=bitdepth, interlace=options.interlace, transparent=options.transparent, background=options.background, alpha=bool(pamalpha or options.alpha), gamma=options.gamma, compression=options.compression) if options.alpha: pgmfile = open(options.alpha, 'rb') format, awidth, aheight, adepth, amaxval = \ read_pnm_header(pgmfile, 'P5') if amaxval != '255': raise NotImplementedError( 'maxval %s not supported for alpha channel' % amaxval) if (awidth, aheight) != (width, height): raise ValueError("alpha channel image size mismatch" " (%s has %sx%s but %s has %sx%s)" % (infilename, width, height, options.alpha, awidth, aheight)) writer.convert_ppm_and_pgm(infile, pgmfile, outfile) else: writer.convert_pnm(infile, outfile) if __name__ == '__main__': try: _main(sys.argv) except Error, e: print >> sys.stderr, e