# https://en.wikipedia.org/wiki/ICO_(file_format) # All values in ICO/CUR files are represented in little-endian byte order. # Broad file structure: # _______________________ # | ICO header | # |-----------------------| # | Icon directories 1..n | # |-----------------------| # | Image data 1..n | # |_______________________| # ICO header: # _______________________________________________________________________________ # | Offset | Size (bytes) | Purpose | # |--------|--------------|-------------------------------------------------------| # | 0 | 2 | Reserved. Must always be 0. | # |--------|--------------|-------------------------------------------------------| # | 2 | 2 | Specifies image type: 1 for icon (.ICO) image, | # | | | 2 for cursor (.CUR) image. Other values are invalid. | # |--------|--------------|-------------------------------------------------------| # | 4 | 2 | Specifies number of images in the file. | # |________|______________|_______________________________________________________| # Icon directory structure: # _______________________________________________________________________________ # | Offset | Size (bytes) | Purpose | # |--------|--------------|-------------------------------------------------------| # | 0 | 1 | Specifies image width in pixels. Can be any number | # | | | between 0 and 255. Value 0 means image width is 256 | # | | | pixels. | # |--------|--------------|-------------------------------------------------------| # | 1 | 1 | Specifies image height in pixels. Can be any number | # | | | between 0 and 255. Value 0 means image height is 256 | # | | | pixels. | # |--------|--------------|-------------------------------------------------------| # | 2 | 1 | Specifies number of colors in the color palette. | # | | | Should be 0 if the image does not use a color palette | # |--------|--------------|-------------------------------------------------------| # | 3 | 1 | Reserved. Should be 0. | # |--------|--------------|-------------------------------------------------------| # | 4 | 2 | In ICO format: Specifies color planes. | # | | | Should be 0 or 1. | # | | | In CUR format: Specifies the horizontal coordinates | # | | | of the hotspot in number of pixels from the left. | # |--------|--------------|-------------------------------------------------------| # | 6 | 2 | In ICO format: Specifies bits per pixel. | # | | | In CUR format: Specifies the vertical coordinates of | # | | | the hotspot in number of pixels from the top. | # |--------|--------------|-------------------------------------------------------| # | 8 | 4 | Specifies the size of the image's data in bytes | # |--------|--------------|-------------------------------------------------------| # | 12 | 4 | Specifies the offset of BMP or PNG data from the | # | | | beginning of the ICO/CUR file | # |________|______________|_______________________________________________________| # Image data structure # BMP, starting from the BITMAPINFOHEADER, ignoring normal file header: # _______________________________________________________________________________ # | Offset | Size (bytes) | Purpose | # |--------|--------------|-------------------------------------------------------| # | 0 | 4 | The size of this header. Always 40. | # |--------|--------------|-------------------------------------------------------| # | 4 | 4 | Image width in pixels, signed. | # |--------|--------------|-------------------------------------------------------| # | 8 | 4 | Image height in pixels, signed. | # |--------|--------------|-------------------------------------------------------| # | 12 | 2 | Number of color planes. Always 1. | # |--------|--------------|-------------------------------------------------------| # | 14 | 2 | Bits per pixel aka color depth. | # |--------|--------------|-------------------------------------------------------| # | 16 | 4 | Compression method. 0 for None aka BI_RGB. | # |--------|--------------|-------------------------------------------------------| # | 20 | 4 | Image bytes length. 0 for BI_RGB because inferred. | # |--------|--------------|-------------------------------------------------------| # | 24 | 4 | Horizontal print resolution. | # |--------|--------------|-------------------------------------------------------| # | 28 | 4 | Vertical print resolution | # |--------|--------------|-------------------------------------------------------| # | 32 | 4 | Number of colors in palette. 0 for 2^n. | # |--------|--------------|-------------------------------------------------------| # | 36 | 4 | Number of important colors. 0 for all. | # |--------|--------------|-------------------------------------------------------| # | 40 | n | Pixel bytes, r, g, b, a. | # |________|______________|_______________________________________________________| import os import sys from PIL import Image ICO_HEADER_LENGTH = 6 ICON_DIRECTORY_ENTRY_LENGTH = 16 BMP_HEADER_LENGTH = 40 def chunk_sequence(sequence, chunk_length, allow_incomplete=True): ''' Given a sequence, divide it into sequences of length `chunk_length`. allow_incomplete: If True, allow the final chunk to be shorter if the given sequence is not an exact multiple of `chunk_length`. If False, the incomplete chunk will be discarded. ''' (complete, leftover) = divmod(len(sequence), chunk_length) if not allow_incomplete: leftover = 0 chunk_count = complete + min(leftover, 1) chunks = [] for x in range(chunk_count): left = chunk_length * x right = left + chunk_length chunks.append(sequence[left:right]) return chunks def fit_into_bounds(iw, ih, fw, fh): ''' Given the w+h of the image and the w+h of the frame, return new w+h that fits the image into the frame while maintaining the aspect ratio and leaving blank space everywhere else ''' ratio = min(fw/iw, fh/ih) w = int(iw * ratio) h = int(ih * ratio) return (w, h) def little(x, length): return x.to_bytes(length, byteorder='little') def load_image(filename): image = Image.open(filename) if min(image.size) > 256: (w, h) = image.size image = image.resize(fit_into_bounds(w, h, 256, 256), resample=Image.ANTIALIAS) image = image.convert('RGBA') return image def build_ico_header_blob(image_count): datablob = (b'' + little(0, 2) # reserved + little(1, 2) # 1 = ico type + little(image_count, 2) ) return datablob def build_icon_directory_blob(image, offset_from_start): (width, height) = image.size datablob = (b'' + little(width if width < 256 else 0, 1) + little(height if height < 256 else 0, 1) + little(0, 1) # colors in palette + little(0, 1) # reserved + little(1, 2) # color planes + little(32, 2) # bit depth + little((width * height * 4) + BMP_HEADER_LENGTH, 4) # image bytes length + little(offset_from_start, 4) ) return datablob def build_image_data_blob(image): datablob = (b'' + little(40, 4) # header size + 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 + little(image.size[1] * 2, 4) + little(1, 2) # color planes + little(32, 2) # bit depth + little(0, 4) # no compression + little(0, 4) # bytes length, inferred + little(0, 4) # hor print + little(0, 4) # ver print + little(0, 4) # palette + little(0, 4) # important palette ) 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. images.reverse() # 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 = [] 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) datablobs.extend(imageblobs) final_data = b''.join(datablobs) return final_data if __name__ == '__main__': try: inputfiles = sys.argv[1:] except: print('Please provide an image file') raise SystemExit print('Iconifying', inputfiles) images = [load_image(filename) for filename in inputfiles] final_data = images_to_ico(images) name = os.path.splitext(inputfiles[0])[0] + '.ico' output_file = open(name, 'wb') output_file.write(final_data) output_file.close() print('Finished %s.' % name)