blob: 71185f1368611d1ca29a82f4124835a49ca5d3a2 [file] [log] [blame]
#!/usr/bin/env python
# Copyright 2015 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""Windows ICO file crusher.
Optimizes the PNG images within a Windows ICO icon file. This extracts all of
the sub-images within the file, runs any PNG-formatted images through, then packs them back into an ICO file.
NOTE: ICO files can contain both raw uncompressed BMP files and PNG files. This
script does not touch the BMP files, which means if you have a huge uncompressed
image, it will not get smaller. 256x256 icons should be PNG-formatted first.
(Smaller icons should be BMPs for compatibility with Windows XP.)
import argparse
import logging
import math
import os
import StringIO
import struct
import subprocess
import sys
import tempfile
OPTIMIZE_PNG_FILES = 'tools/resources/'
logging.basicConfig(level=logging.INFO, format='%(levelname)s: %(message)s')
class InvalidFile(Exception):
"""Represents an invalid ICO file."""
def IsPng(png_data):
"""Determines whether a sequence of bytes is a PNG."""
return png_data.startswith('\x89PNG\r\n\x1a\n')
def OptimizePngFile(temp_dir, png_filename, optimization_level=None):
"""Optimize a PNG file.
temp_dir: The directory containing the PNG file. Must be the only file in
the directory.
png_filename: The full path to the PNG file to optimize.
The raw bytes of a PNG file, an optimized version of the input.
logging.debug('Crushing PNG image...')
if optimization_level is not None:
args.append('-o%d' % optimization_level)
result =, stdout=sys.stderr)
if result != 0:
logging.warning('Warning: optimize-png-files failed (%d)', result)
logging.debug('optimize-png-files succeeded')
with open(png_filename, 'rb') as png_file:
def OptimizePng(png_data, optimization_level=None):
"""Optimize a PNG.
png_data: The raw bytes of a PNG file.
The raw bytes of a PNG file, an optimized version of the input.
temp_dir = tempfile.mkdtemp()
logging.debug('temp_dir = %s', temp_dir)
png_filename = os.path.join(temp_dir, 'image.png')
with open(png_filename, 'wb') as png_file:
return OptimizePngFile(temp_dir, png_filename,
if os.path.exists(png_filename):
def ComputeANDMaskFromAlpha(image_data, width, height):
"""Compute an AND mask from 32-bit BGRA image data."""
and_bytes = []
for y in range(height):
bit_count = 0
current_byte = 0
for x in range(width):
alpha = image_data[(y * width + x) * 4 + 3]
current_byte <<= 1
if ord(alpha) == 0:
current_byte |= 1
bit_count += 1
if bit_count == 8:
bit_count = 0
current_byte = 0
# At the end of a row, pad the current byte.
if bit_count > 0:
current_byte <<= (8 - bit_count)
# And keep padding until a multiple of 4 bytes.
while len(and_bytes) % 4 != 0:
and_bytes = ''.join(map(chr, and_bytes))
return and_bytes
def RebuildANDMask(iconimage):
"""Rebuild the AND mask in an icon image.
GIMP (<=2.8.14) creates a bad AND mask on 32-bit icon images (pixels with <50%
opacity are marked as transparent, which end up looking black on Windows). So,
if this is a 32-bit image, throw the mask away and recompute it from the alpha
data. (See:
iconimage: Bytes of an icon image (the BMP data for an entry in an ICO
file). Must be in BMP format, not PNG. Does not need to be 32-bit (if it
is not 32-bit, this is a no-op).
An updated |iconimage|, with the AND mask re-computed using
(_, width, height, _, bpp, _, _, _, _, num_colors, _) = struct.unpack(
'<LLLHHLLLLLL', iconimage[:40])
if bpp != 32:
# No alpha channel, so the mask cannot be "wrong" (it is the only source of
# transparency information).
return iconimage
height /= 2
xor_size = int(math.ceil(width * bpp / 32.0)) * 4 * height
# num_colors can be 0, implying 2^bpp colors.
xor_palette_size = (num_colors or (1 << bpp if bpp < 24 else 0)) * 4
xor_data = iconimage[40 + xor_palette_size :
40 + xor_palette_size + xor_size]
and_data = ComputeANDMaskFromAlpha(xor_data, width, height)
# Replace the AND mask in the original icon data.
return iconimage[:40 + xor_palette_size + xor_size] + and_data
def OptimizeIcoFile(infile, outfile, optimization_level=None):
"""Read an ICO file, optimize its PNGs, and write the output to outfile.
infile: The file to read from. Must be a seekable file-like object
containing a Microsoft ICO file.
outfile: The file to write to.
filename = os.path.basename(
icondir =
zero, image_type, num_images = struct.unpack('<HHH', icondir)
if zero != 0:
raise InvalidFile('First word must be 0.')
if image_type not in (1, 2):
raise InvalidFile('Image type must be 1 or 2.')
# Read and unpack each ICONDIRENTRY.
icon_dir_entries = []
for i in range(num_images):
icondirentry =
icon_dir_entries.append(struct.unpack('<BBBBHHLL', icondirentry))
# Read each icon's bitmap data, crush PNGs, and update icon dir entries.
current_offset = infile.tell()
icon_bitmap_data = []
for i in range(num_images):
width, height, num_colors, r1, r2, r3, size, _ = icon_dir_entries[i]
width = width or 256
height = height or 256
offset = current_offset
icon_data =
if len(icon_data) != size:
raise EOFError()
entry_is_png = IsPng(icon_data)'%s entry #%d: %dx%d, %d bytes (%s)', filename, i + 1, width,
height, size, 'PNG' if entry_is_png else 'BMP')
if entry_is_png:
icon_data = OptimizePng(icon_data, optimization_level=optimization_level)
new_icon_data = RebuildANDMask(icon_data)
if new_icon_data != icon_data:' * Rebuilt AND mask for this image from alpha channel.')
icon_data = new_icon_data
if width >= 256 or height >= 256:
# TODO(mgiuca): Automatically convert large BMP images to PNGs.
logging.warning('Entry #%d is a large image in uncompressed BMP '
'format. Please manually convert to PNG format before '
'running this utility.', i + 1)
new_size = len(icon_data)
current_offset += new_size
icon_dir_entries[i] = (width % 256, height % 256, num_colors, r1, r2, r3,
new_size, offset)
# Write the data back to outfile.
for icon_dir_entry in icon_dir_entries:
outfile.write(struct.pack('<BBBBHHLL', *icon_dir_entry))
for icon_bitmap in icon_bitmap_data:
def main(args=None):
if args is None:
args = sys.argv[1:]
parser = argparse.ArgumentParser(description='Crush Windows ICO files.')
parser.add_argument('files', metavar='ICO', type=argparse.FileType('r+b'),
nargs='+', help='.ico files to be crushed')
parser.add_argument('-o', dest='optimization_level', metavar='OPT', type=int,
help='optimization level')
parser.add_argument('-d', '--debug', dest='debug', action='store_true',
help='enable debug logging')
args = parser.parse_args()
if args.debug:
for file in args.files:
buf = StringIO.StringIO(), os.SEEK_END)
old_length = file.tell(), os.SEEK_SET)
OptimizeIcoFile(file, buf, args.optimization_level)
new_length = len(buf.getvalue())
# Always write (even if file size not reduced), because we make other fixes
# such as regenerating the AND mask.
if new_length >= old_length:'%s : Could not reduce file size.',
saving = old_length - new_length
saving_percent = float(saving) / old_length'%s : %d => %d (%d bytes : %d %%)',, old_length,
new_length, saving, int(saving_percent * 100))
if __name__ == '__main__':