Question

下面的问题：How Can I Make This Python Script Work With Python 3?

我想使此脚本在python 3中工作。我已经设法解决了一些细节，但仍然无法正常工作。.现在似乎在解压缩块数据时抛出错误。

这是我当前遇到的错误：解压缩数据时出现错误-5：流不完整或被截断

我正在使用Python 3.6.2

这是已将内容迁移到Python 3的脚本。该脚本基本上将自定义iphone格式的PNG标准化。

import pdb
from struct import *
from zlib import *
import stat
import sys
import os
import zlib

def getNormalizedPNG(filename):
    pngheader = b"\x89PNG\r\n\x1a\n"

    pdb.set_trace()

    file = open(filename, "rb")
    oldPNG = file.read()
    file.close()

    if oldPNG[:8] != pngheader:
        return None

    newPNG = oldPNG[:8]

    chunkPos = len(newPNG)

    # For each chunk in the PNG file
    while chunkPos < len(oldPNG):

        # Reading chunk
        chunkLength = oldPNG[chunkPos:chunkPos+4]
        chunkLength = unpack(">L", chunkLength)[0]
        chunkType = oldPNG[chunkPos+4 : chunkPos+8]
        chunkData = oldPNG[chunkPos+8:chunkPos+8+chunkLength]
        chunkCRC = oldPNG[chunkPos+chunkLength+8:chunkPos+chunkLength+12]
        chunkCRC = unpack(">L", chunkCRC)[0]
        chunkPos += chunkLength + 12

        # Parsing the header chunk
        if chunkType == b"IHDR":
            width = unpack(">L", chunkData[0:4])[0]
            height = unpack(">L", chunkData[4:8])[0]

        # Parsing the image chunk
        if chunkType == b"IDAT":
            try:
                pdb.set_trace()
                # Uncompressing the image chunk
                bufSize = width * height * 4 + height

                chunkData = decompress(chunkData, -8, bufSize)

            except Exception as e:
                print("Already normalized")
                print(e)
                # The PNG image is normalized
                return None

            # Swapping red & blue bytes for each pixel
            newdata = b""
            for y in range(height):
                i = len(newdata)
                newdata += chunkData[i]
                for x in range(width):
                    i = len(newdata)
                    newdata += chunkData[i+2]
                    newdata += chunkData[i+1]
                    newdata += chunkData[i+0]
                    newdata += chunkData[i+3]

            # Compressing the image chunk
            chunkData = newdata
            chunkData = compress( chunkData )
            chunkLength = len( chunkData )
            chunkCRC = crc32(chunkType)
            chunkCRC = crc32(chunkData, chunkCRC)
            chunkCRC = (chunkCRC + 0x100000000) % 0x100000000

        # Removing CgBI chunk
        if chunkType != b"CgBI":
            newPNG += pack(">L", chunkLength)
            newPNG += chunkType
            if chunkLength > 0:
                newPNG += chunkData
            newPNG += pack(">L", chunkCRC)

        # Stopping the PNG file parsing
        if chunkType == b"IEND":
            break

    return newPNG


def updatePNG(filename):
    data = getNormalizedPNG(filename)

    if data != None:
        file = open(filename, "wb")
        file.write(data)
        file.close()
        return True
    return data

任何线索将不胜感激。谢谢！：）

Answer 1

原始代码不会立即处理多个IDAT块；它执行正确的操作™，并且仅在将其整体解压缩之前将它们连接为一个大对象。 IDAT块没有单独压缩，但是您的代码假定它们可以压缩-因此，如果有多个块，则失败。

可能有多个IDAT块；如果是这样，它们应连续出现，没有其他中间块。然后，压缩的数据流就是所有IDAT块的数据字段内容的串联。
11.2.4 IDAT Image data

重新连接循环以首先收集所有IDAT可以解决问题。仅当找到IEND块时，此数据才被解压缩，字节被交换，并创建新的IDAT块。最后一步，附加IEND，将关闭文件。

from struct import *
from zlib import *
import stat
import sys
import os
import zlib

def getNormalizedPNG(filename):
    pngheader = b"\x89PNG\r\n\x1a\n"

    file = open(filename, "rb")
    oldPNG = file.read()
    file.close()

    if oldPNG[:8] != pngheader:
        return None

    newPNG = oldPNG[:8]

    chunkPos = len(newPNG)
    chunkD = bytearray()

    foundCGBi = False

    # For each chunk in the PNG file
    while chunkPos < len(oldPNG):

        # Reading chunk
        chunkLength = oldPNG[chunkPos:chunkPos+4]
        chunkLength = unpack(">L", chunkLength)[0]
        chunkType = oldPNG[chunkPos+4 : chunkPos+8]
        chunkData = oldPNG[chunkPos+8:chunkPos+8+chunkLength]
        chunkCRC = oldPNG[chunkPos+chunkLength+8:chunkPos+chunkLength+12]
        chunkCRC = unpack(">L", chunkCRC)[0]
        chunkPos += chunkLength + 12

        # Parsing the header chunk
        if chunkType == b"IHDR":
            width = unpack(">L", chunkData[0:4])[0]
            height = unpack(">L", chunkData[4:8])[0]

        # Parsing the image chunk
        if chunkType == b"IDAT":
            # Concatename all image data chunks
            chunkD += chunkData
            continue

        # Stopping the PNG file parsing
        if chunkType == b"IEND":
            if not foundCGBi:
                print ('Already normalized')
                return None

            bufSize = width * height * 4 + height
            chunkData = decompress(chunkD, -8, bufSize)

            # Swapping red & blue bytes for each pixel
            chunkData = bytearray(chunkData)
            offset = 1
            for y in range(height):
                for x in range(width):
                    chunkData[offset+4*x],chunkData[offset+4*x+2] = chunkData[offset+4*x+2],chunkData[offset+4*x]
                offset += 1+4*width

            # Compressing the image chunk
            #chunkData = newdata
            chunkData = compress( chunkData )
            chunkLength = len( chunkData )
            chunkCRC = crc32(b'IDAT')
            chunkCRC = crc32(chunkData, chunkCRC)
            chunkCRC = (chunkCRC + 0x100000000) % 0x100000000

            newPNG += pack(">L", chunkLength)
            newPNG += b'IDAT'
            newPNG += chunkData
            newPNG += pack(">L", chunkCRC)

            chunkCRC = crc32(chunkType)
            newPNG += pack(">L", 0)
            newPNG += b'IEND'
            newPNG += pack(">L", chunkCRC)
            break

        # Removing CgBI chunk
        if chunkType == b"CgBI":
            foundCGBi = True
        else:
            newPNG += pack(">L", chunkLength)
            newPNG += chunkType
            if chunkLength > 0:
                newPNG += chunkData
            newPNG += pack(">L", chunkCRC)

    return newPNG


def updatePNG(filename):
    data = getNormalizedPNG(filename)

    if data != None:
        file = open(filename+'_fixed.png', "wb")
        file.write(data)
        file.close()
        return True
    return data

updatePNG("broken_image.png")

这将生成有效的固定文件。

此代码不不会恢复断开的CgBI alpha通道！如果需要适当的Alpha透明度，则需要应用行滤镜以获取向上的RGB值，反转Alpha，然后应用行滤镜的逆值，然后再次进行压缩。

您可以使用Python wrapper for PNGDefry，它是确实执行这些遗漏步骤的C程序。

^{免责声明：我是PNGdefry的作者。}

将python 2中的脚本迁移到python 3.x

1 个答案: