PNGメタデータを簡単に表示するもの

pnginfo.py

#coding:utf-8
#Print some infomation of a PNG file

import struct
import datetime
import binascii


def crcChecker(data, crc):
    computedCRC = binascii.crc32(data)
    crc = struct.unpack('> I', crc)[0]
    return crc == computedCRC

filename = input('Filename: ')
data = open(filename, 'rb').read()

if data[:8] != bytes((0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A)):
    print('This is not a PNG file')
    exit()

flag_len = 4
seek = 8
IDATCount = 0
CRCError = 0

while seek <= len(data):
    body_len = struct.unpack('> I', data[seek:seek+flag_len])[0]
    chunk_len = body_len + 8
    chunkName, chunkData, CRC = struct.unpack('> 4s {}s 4s'.format(body_len),
                     data[seek+flag_len:seek+flag_len+chunk_len])
    
    if not crcChecker(chunkName+chunkData, CRC):
        CRCError += 1
        print('Broken chunk')
    
    enc = 'ASCII'
    chunkName = str(chunkName, enc)
    
    #chunk specific process
    if chunkName == 'IDAT':
        IDATCount += 1
    else:
        print('---{}'.format(chunkName))
    
    if chunkName == 'IHDR':
        width, height, depth, colourType, compress, filterType, adam7 = \
            struct.unpack('> I I B B B B ?', chunkData)
        print('size: {}x{}'.format(width, height))
        print('depth: {}'.format(depth))
        if colourType == 0:
            colour = 'Gray'
        elif colourType == 2:
            colour = 'RGB'
        elif colourType == 3:
            colour = 'Palette'
        elif colourType == 4:
            colour = 'Gray + Alpha'
        elif colourType == 6:
            colour = 'RGB + Alpha'
        print('colour: {}'.format(colour))
        print('Adam7: {}'.format(adam7))
        
    if chunkName == 'bKGD':
        print('background colour')
        if colourType in {0, 4}:
            backGnd = struct.unpack('> H', chunkData)
            print('Gray {}'.format(backGnd))
        elif colourType in {2, 6}:
            backGnd = struct.unpack('> H H H', chunkData)
            print('R: {},G: {},B:{}'.format(*backGnd))
        elif colourType == 3:
            backGnd = struct.unpack('> B', chunkData)
            print('PaletIndex: {}'.format(backGnd))
    
    if chunkName == 'tIME':
        timestamp = struct.unpack('> H B B B B B', chunkData)
        print(datetime.datetime(*timestamp).isoformat())
        
    if chunkName == 'pHYs':
        ppuX, ppuY, spec = struct.unpack('> I I ?', chunkData)
        if spec:
            dpi = [round(i/100*2.54, 3) for i in (ppuX,ppuY)]
            print('DPI: {}'.format(dpi))
            
    if chunkName == 'gAMA':
        gamma = struct.unpack('> I', chunkData)[0]/100000
        print('gamma(file): {}, gamma(machine): {}'.format(
            gamma, round(1/gamma, 4))
        )
    
    seek += flag_len + chunk_len
    
    if chunkName == 'IEND':
        print('---IDAT chunk: {}'.format(IDATCount))
        print('---CRC Error: {}'.format(CRCError))
        break