struct__examples__parse_binary_files/read_PNG_header/main.py - master - ilya.petrash/SimplePyScripts

struct__examples__parse_binary_files/read_PNG_header/main.py

73 строки2 KB

gil9red

Refactoring. Using black code style

27 июн 2023, 14:00

27 июн 2023, 14:0063804b4

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

__author__ = "ipetrash"


# SOURCE: http://www.libpng.org/pub/png/spec/1.2/PNG-Structure.html
# SOURCE: https://en.wikipedia.org/wiki/Portable_Network_Graphics#File_format


import glob
import struct
import zlib


def crc32_from_bytes(data: bytes) -> int:
    return zlib.crc32(data) & 0xFFFFFFFF


def print_info(file_name: str):
    print(file_name)

    def read_chunk(f) -> (int, bytes, bytes, int):
        (chunk_length,) = struct.unpack(">I", f.read(4))
        chunk_type = f.read(4)
        chunk_data = f.read(chunk_length)
        (chunk_CRC,) = struct.unpack(">I", f.read(4))

        return chunk_length, chunk_type, chunk_data, chunk_CRC

    with open(file_name, "rb") as f:
        # HEADER
        data = f.read(8)

        if data != b"\x89PNG\r\n\x1a\n":
            print("Not valid PNG!")
            return

        # After the header comes a series of chunks, each of which conveys certain information about the image.

        # A chunk consists of four parts: length (4 bytes, big-endian), chunk type/name (4 bytes),
        # chunk data (length bytes) and CRC (cyclic redundancy code/checksum; 4 bytes). The CRC is
        # a network-byte-order CRC-32 computed over the chunk type and chunk data, but not the length.
        #   | Length  | Chunk type | Chunk data    | CRC     |
        #   | 4 bytes | 4 bytes    | Length bytes  | 4 bytes |

        # Need IHDR chunk:
        # IHDR must be the first chunk; it contains (in this order) the image's width (4 bytes),
        # height (4 bytes), bit depth (1 byte), color type (1 byte), compression method (1 byte),
        # filter method (1 byte), and interlace method (1 byte) (13 data bytes total).

        chunk_length, chunk_type, chunk_data, chunk_CRC = read_chunk(f)
        # print(chunk_length, chunk_type, chunk_data, chunk_CRC)

        # Check CRC
        assert crc32_from_bytes(chunk_type + chunk_data) == chunk_CRC

        (
            width,
            height,
            bit_depth,
            color_type,
            compression_method,
            filter_method,
            interlace_method,
        ) = struct.unpack(">IIbbbbb", chunk_data)
        print(f"    Size: {width}x{height}")


if __name__ == "__main__":
    for file_name in glob.glob("*.png"):
        print_info(file_name)
        print()