while True: chunk_type, data, crc = read_chunk(fin) if chunk_type == CHUNK_TYPE_MPNG: idx = struct.unpack('>I', data[:4])[0] if replace_map and idx in replace_map: new_compressed = replace_map[idx] else: # Find matching stream and reflate for stored_idx, comp in streams: if stored_idx == idx: new_compressed = reflate_stream(comp, recompress_level) break else: new_compressed = data[4:] # unchanged new_data = struct.pack('>I', idx) + new_compressed write_chunk(fout, CHUNK_TYPE_MPNG, new_data) else: # Copy other chunks unchanged fout.write(struct.pack('>I', len(data))) fout.write(chunk_type) fout.write(data) fout.write(struct.pack('>I', crc))
def extract_mpng_streams(png_path): """Extract all zlib-compressed streams from MPNG chunks""" streams = [] with open(png_path, 'rb') as f: # Verify PNG signature if f.read(8) != PNG_SIGNATURE: raise ValueError("Not a valid PNG file") xtool -mpng+reflate
def rebuild_png_with_mpng(input_path, output_path, streams, recompress_level=6, replace_map=None): """Rebuild PNG with modified MPNG streams""" with open(input_path, 'rb') as fin, open(output_path, 'wb') as fout: fout.write(fin.read(8)) # PNG signature while True: chunk_type, data, crc = read_chunk(fin) if