我的CGBitmapContext出了什么问题？

我无法在python中创建有效的CGBitmapContext。它只是返回null值，然后导致其他所有内容抱怨缺少定义和python崩溃。我尝试将内存分配设置为None，这意味着它应该自行排除，但这也不起作用。我不认为objC缓冲区也被分配。任何帮助将不胜感激。我的CGBitmapContext出了什么问题？

#!/usr/bin/python 

import os, sys, objc 
from Quartz import * 

os.environ["CG_CONTEXT_SHOW_BACKTRACE"] = '1' 
resolution = 300 #dpi 
scale = resolution/72 

cs = CGColorSpaceCreateWithName(kCGColorSpaceSRGB) 
# Options might be: kCGImageAlphaNoneSkipLast, kCGImageAlphaPremultipliedLast \ or FIRST 
transparency = kCGImageAlphaNoneSkipLast 

#Save image to file 
def writeImage (image, url, type, options): 
    destination = CGImageDestinationCreateWithURL(url, type, 1, None) 
    CGImageDestinationAddImage(destination, image, options) 
    CGImageDestinationFinalize(destination) 
    CFRelease(destination) 
    return 

if __name__ == '__main__': 

    for filename in sys.argv[1:]: 
     pdf = CGPDFDocumentCreateWithProvider(CGDataProviderCreateWithFilename(filename)) 
     numPages = CGPDFDocumentGetNumberOfPages(pdf) 
     shortName = os.path.splitext(filename)[0] 

     # For each page, create a file 
     for i in range (1, numPages+1): 
      page = CGPDFDocumentGetPage(pdf, i) 
      if page: 
     #Get mediabox 
       mediaBox = CGPDFPageGetBoxRect(page, kCGPDFMediaBox) 
       x = CGRectGetWidth(mediaBox) 
       y = CGRectGetHeight(mediaBox) 
       x *= scale 
       y *= scale 
     # Allocate Memory, in this day and age. 
       try: 
        rasterData = objc.allocateBuffer(int(4 * x * y)) 
       except MemoryError: break 
     # Create a Bitmap Context 
       ctx = CGBitmapContextCreate(rasterData, x, y, 8, x, cs, transparency) 
       CGContextSaveGState (ctx) 
       CGContextScaleCTM(ctx, scale,scale) 
       CGContextDrawPDFPage(ctx, page) 
       CGContextRestoreGState(ctx) 
     # Convert to an "Image" 
       image = CGBitmapContextCreateImage(ctx) 
     # Create unique filename per page 
       outFile = shortName + str(i) + ".tiff" 
       url = CFURLCreateFromFileSystemRepresentation(kCFAllocatorDefault, outFile, len(outFile), False) 
     # kUTTypeJPEG, kUTTypeTIFF, kUTTypePNG 
       type = 'kUTTypeTIFF' 
       options = { 
        kCGImagePropertyTIFFXResolution : 300, 
        kCGImagePropertyTIFFYResolution : 300 
        } 
       writeImage (image, url, type, options) 
       CGContextRelease(ctx) 
       del page

来源

2016-08-18 benwiggy

“CGBitmapContextCreate”的'bytesPerRow'参数看起来不对。如果您的位图的像素宽度为x像素，并且它是每个组件8位的RGBA上下文，则每个像素需要4个字节，因此bytesPerRow应该是“x * 4”。（请注意，当你分配内存时，你的数学运算是正确的。） –

是的，我只是让0让Mac为自己工作，而脚本似乎在其他地方失败了。所以，进展。 – benwiggy

输出建议我打开一些额外的日志记录：

os.environ["CG_CONTEXT_SHOW_BACKTRACE"] = '1' 
os.environ["CGBITMAP_CONTEXT_LOG_ERRORS"] = '1'

这就给了我下面的信息，这些信息看似来自苹果自己的文档缺乏：

CGBitmapContextCreate: unsupported parameter combination: 
    16 integer bits/component; 
    48 bits/pixel; 
    RGB color space model; kCGImageAlphaNone; 
    14336 bytes/row. 
Valid parameters for RGB color space model are: 
    16 bits per pixel,  5 bits per component,  kCGImageAlphaNoneSkipFirst 
    32 bits per pixel,  8 bits per component,  kCGImageAlphaNoneSkipFirst 
    32 bits per pixel,  8 bits per component,  kCGImageAlphaNoneSkipLast 
    32 bits per pixel,  8 bits per component,  kCGImageAlphaPremultipliedFirst 
    32 bits per pixel,  8 bits per component,  kCGImageAlphaPremultipliedLast 
    64 bits per pixel,  16 bits per component,  kCGImageAlphaPremultipliedLast 
    64 bits per pixel,  16 bits per component,  kCGImageAlphaNoneSkipLast 
    64 bits per pixel,  16 bits per component,  kCGImageAlphaPremultipliedLast|kCGBitmapFloatComponents 
    64 bits per pixel,  16 bits per component,  kCGImageAlphaNoneSkipLast|kCGBitmapFloatComponents 
    128 bits per pixel,  32 bits per component,  kCGImageAlphaPremultipliedLast|kCGBitmapFloatComponents 
    128 bits per pixel,  32 bits per component,  kCGImageAlphaNoneSkipLast|kCGBitmapFloatComponents

所以只是将透明度常量更改为kCGImageAlphaPremultipliedLast已停止崩溃并修复了上下文。但是，整个脚本仍然不起作用，我只是得到Trace/BPT trap: 5作为回应。

来源

2016-08-19 07:58:39 benwiggy

我的CGBitmapContext出了什么问题？

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