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Fix icoconvert was not complying with the 1-bit AND mask layer.

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voussoir 2026-08-30 14:19:56 -07:00
parent 3f4476113f
commit 3084c572fb
1 changed files with 63 additions and 41 deletions
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104
icoconvert.py
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@ -12,6 +12,7 @@
# |_______________________|
# ICO header:
# https://en.wikipedia.org/wiki/ICO_%28file_format%29#ICONDIR_structure
# _______________________________________________________________________________
# | Offset | Size (bytes) | Purpose |
# |--------|--------------|-------------------------------------------------------|
@ -24,6 +25,7 @@
# |________|______________|_______________________________________________________|
# Icon directory structure:
# https://en.wikipedia.org/wiki/ICO_%28file_format%29#ICONDIRENTRY_structure
# _______________________________________________________________________________
# | Offset | Size (bytes) | Purpose |
# |--------|--------------|-------------------------------------------------------|
@ -56,7 +58,8 @@
# |________|______________|_______________________________________________________|
# Image data structure
# BMP, starting from the BITMAPINFOHEADER, ignoring normal file header:
# BMP, starting from the BITMAPINFOHEADER, ignoring normal 14-byte file header:
# https://en.wikipedia.org/wiki/BMP_file_format
# _______________________________________________________________________________
# | Offset | Size (bytes) | Purpose |
# |--------|--------------|-------------------------------------------------------|
@ -65,6 +68,8 @@
# | 4 | 4 | Image width in pixels, signed. |
# |--------|--------------|-------------------------------------------------------|
# | 8 | 4 | Image height in pixels, signed. |
# | | | The value will actually be doubled because the 1-bit |
# | | | AND mask is treated as a second stacked layer. |
# |--------|--------------|-------------------------------------------------------|
# | 12 | 2 | Number of color planes. Always 1. |
# |--------|--------------|-------------------------------------------------------|
@ -82,7 +87,7 @@
# |--------|--------------|-------------------------------------------------------|
# | 36 | 4 | Number of important colors. 0 for all. |
# |--------|--------------|-------------------------------------------------------|
# | 40 | n | Pixel bytes, r, g, b, a. |
# | 40 | n | Pixel bytes, R, G, B, A. Then 1-bit AND-mask layer. |
# |________|______________|_______________________________________________________|
import argparse
@ -139,7 +144,7 @@ def load_image(file):
image = imagetools.pad_to_square(image)
return image
def build_ico_header_blob(image_count):
def build_ico_header_blob(image_count) -> bytes:
datablob = b''.join([
# reserved
little(0, 2),
@ -149,7 +154,7 @@ def build_ico_header_blob(image_count):
])
return datablob
def build_icon_directory_blob(image, offset_from_start):
def build_icon_directory_blob(image, offset_from_start) -> bytes:
(width, height) = image.size
datablob = b''.join([
little(width if width < 256 else 0, 1),
@ -162,19 +167,50 @@ def build_icon_directory_blob(image, offset_from_start):
little(1, 2),
# bit depth
little(32, 2),
# image bytes length
little((width * height * 4) + BMP_HEADER_LENGTH, 4),
# image bytes length, plus 1-bit AND mask length
little((width * height * 4) + ((width * height)//8) + BMP_HEADER_LENGTH, 4),
little(offset_from_start, 4),
])
return datablob
def build_image_data_blob(image):
def build_image_data_blob(image) -> bytes:
# The AND mask is one bit per pixel regardless of the image's colour depth:
# a 0 bit draws the corresponding image pixel, while a 1 bit leaves the
# screen unchanged, making the pixel transparent.
# https://en.wikipedia.org/wiki/ICO_%28file_format%29#DIB_format
andmask = []
pixeldata = []
# Image.getdata() is a list of (r, g, b, a) channels
# But the BMP are written (b, g, r, a).
# Also they are written from bottom to top.
pixels = list(image.getdata())
pixels = reversed(chunk_sequence(pixels, image.size[0]))
pixels = [line for chunk in pixels for line in chunk]
for pixel in pixels:
(r, g, b, a) = pixel
if a == 0:
andmask.append(1)
else:
andmask.append(0)
pixeldata.extend((b, g, r, a))
pixeldata = bytes(pixeldata)
andmask = [str(bit) for bit in andmask]
andmask = chunk_sequence(andmask, 8)
andmask = (''.join(chunk) for chunk in andmask)
andmask = (int(chunk, 2) for chunk in andmask)
andmask = bytes(andmask)
datablob = b''.join([
# header size
little(40, 4),
little(BMP_HEADER_LENGTH, 4),
little(image.size[0], 4),
# "Even if the AND mask is not supplied, if the image is in Windows BMP
# format, the BMP header must still specify a doubled height." - wikipedia
# The height declared in the BITMAPINFOHEADER is twice the height
# declared in the image directory, because the DIB holds two stacked
# parts of equal dimensions: the colour image (the XOR mask) above the
# 1-bit AND mask.[9][8] Rows in both parts are padded to a multiple of
# four bytes.
# https://en.wikipedia.org/wiki/ICO_%28file_format%29#DIB_format
little(image.size[1] * 2, 4),
# color planes
little(1, 2),
@ -192,51 +228,37 @@ def build_image_data_blob(image):
little(0, 4),
# important palette
little(0, 4),
pixeldata,
andmask,
])
pixeldata = []
# Image.getdata() is a list of (r, g, b, a) channels
# But the BMP are written (b, g, r, a)
# Also they are written from bottom to top.
pixels = list(image.getdata())
pixels = reversed(chunk_sequence(pixels, image.size[0]))
pixels = [line for chunk in pixels for line in chunk]
for pixel in pixels:
(r, g, b, a) = pixel
pixeldata.extend((b, g, r, a))
datablob += bytes(pixeldata)
return datablob
def images_to_ico(images):
# For some reason Windows reads the icons in reverse order.
# Windows reads the icons in reverse order.
images.sort(key=lambda i: i.size[0] * i.size[1], reverse=True)
# The directory entries need to know their image's address, so therefore
# we must know the lengths of all the image binaries before we can write
# any directory entries.
# We will calculate the image blobs first, store them separately,
# and then put them after the directory blobs.
datablobs = []
imageblobs = []
directory_blobs = []
image_blobs = []
ico_header_blob = build_ico_header_blob(image_count=len(images))
datablobs.append(ico_header_blob)
for (index, image) in enumerate(images):
imageblob = build_image_data_blob(image)
imageblobs.append(imageblob)
# Since the ICO header and directory entries are of fixed length, we know
# the location of the first image.
# After that, the offset just gains the size of the previous image.
offset_from_start = ICO_HEADER_LENGTH + (len(images) * ICON_DIRECTORY_ENTRY_LENGTH)
for (index, (image, imageblob)) in enumerate(zip(images, imageblobs)):
directoryblob = build_icon_directory_blob(image, offset_from_start=offset_from_start)
datablobs.append(directoryblob)
offset_from_start += len(imageblob)
for (index, image) in enumerate(images):
directory_blob = build_icon_directory_blob(image, offset_from_start=offset_from_start)
directory_blobs.append(directory_blob)
image_blob = build_image_data_blob(image)
image_blobs.append(image_blob)
offset_from_start += len(image_blob)
datablobs.extend(imageblobs)
final_data = b''.join(datablobs)
final_data = [
ico_header_blob,
*directory_blobs,
*image_blobs,
]
final_data = b''.join(final_data)
return final_data
def icoconvert_argparse(args):