从 CGImage 获取 RGB 像素数据

Question

我正在尝试从 CGImage 访问像素数据。我希望能够以整数形式访问 RGB 值。我想我已经用这段代码完成了：

UIImage* theImage = [UIImage imageNamed:@"rgb.png"];
CGImageRef cgImageRef = CGImageRetain(theImage.CGImage);
CFDataRef* imageData = CGDataProviderCopyData(CGImageGetDataProvider(cgImageRef));
NSLog(@"the data = %@", imageData);

然后记录：

data = <010002fe fffdff02 0200fe04 0003fc>

该图像是一个 5x1 png，按顺序包含黑色、白色、红色、绿色和蓝色像素。

我真的不明白我在这里看什么。我怎样才能获得 RGB 值数组或类似的值，以便我可以使用它们。

谢谢， 富有的

Answer 1

下面是一些示例代码，它将打印一堆有关图像的相关信息，以及图像像素数据的转储。它适用于具有 Alpha 通道的图像，以及不具有 Alpha 通道的图像。该代码甚至可以处理不在 RGB 颜色空间中的图像，尽管我怀疑您是否可能在 iOS 上获得这些图像。

将其复制粘贴到您的项目中，并尝试针对一些图像文件运行它，然后也许您可以根据您的需要调整它

-(void)imageDump:(NSString*)file
{
    UIImage* image = [UIImage imageNamed:file];
    CGImageRef cgimage = image.CGImage;

    size_t width  = CGImageGetWidth(cgimage);
    size_t height = CGImageGetHeight(cgimage);

    size_t bpr = CGImageGetBytesPerRow(cgimage);
    size_t bpp = CGImageGetBitsPerPixel(cgimage);
    size_t bpc = CGImageGetBitsPerComponent(cgimage);
    size_t bytes_per_pixel = bpp / bpc;

    CGBitmapInfo info = CGImageGetBitmapInfo(cgimage);

    NSLog(
        @"\n"
        "===== %@ =====\n"
        "CGImageGetHeight: %d\n"
        "CGImageGetWidth:  %d\n"
        "CGImageGetColorSpace: %@\n"
        "CGImageGetBitsPerPixel:     %d\n"
        "CGImageGetBitsPerComponent: %d\n"
        "CGImageGetBytesPerRow:      %d\n"
        "CGImageGetBitmapInfo: 0x%.8X\n"
        "  kCGBitmapAlphaInfoMask     = %s\n"
        "  kCGBitmapFloatComponents   = %s\n"
        "  kCGBitmapByteOrderMask     = 0x%.8X\n"
        "  kCGBitmapByteOrderDefault  = %s\n"
        "  kCGBitmapByteOrder16Little = %s\n"
        "  kCGBitmapByteOrder32Little = %s\n"
        "  kCGBitmapByteOrder16Big    = %s\n"
        "  kCGBitmapByteOrder32Big    = %s\n",
        file,
        (int)width,
        (int)height,
        CGImageGetColorSpace(cgimage),
        (int)bpp,
        (int)bpc,
        (int)bpr,
        (unsigned)info,
        (info & kCGBitmapAlphaInfoMask)     ? "YES" : "NO",
        (info & kCGBitmapFloatComponents)   ? "YES" : "NO",
        (info & kCGBitmapByteOrderMask),
        ((info & kCGBitmapByteOrderMask) == kCGBitmapByteOrderDefault)  ? "YES" : "NO",
        ((info & kCGBitmapByteOrderMask) == kCGBitmapByteOrder16Little) ? "YES" : "NO",
        ((info & kCGBitmapByteOrderMask) == kCGBitmapByteOrder32Little) ? "YES" : "NO",
        ((info & kCGBitmapByteOrderMask) == kCGBitmapByteOrder16Big)    ? "YES" : "NO",
        ((info & kCGBitmapByteOrderMask) == kCGBitmapByteOrder32Big)    ? "YES" : "NO"
    );

    CGDataProviderRef provider = CGImageGetDataProvider(cgimage);
    NSData* data = (id)CGDataProviderCopyData(provider);
    [data autorelease];
    const uint8_t* bytes = [data bytes];

    printf("Pixel Data:\n");
    for(size_t row = 0; row < height; row++)
    {
        for(size_t col = 0; col < width; col++)
        {
            const uint8_t* pixel =
                &bytes[row * bpr + col * bytes_per_pixel];

            printf("(");
            for(size_t x = 0; x < bytes_per_pixel; x++)
            {
                printf("%.2X", pixel[x]);
                if( x < bytes_per_pixel - 1 )
                    printf(",");
            }

            printf(")");
            if( col < width - 1 )
                printf(", ");
        }

        printf("\n");
    }
}

以下是我尝试过的两个图像的一些示例输出。它们都是 5x3 RGB。 “a.png”图像具有 Alpha 通道，而“b.rgb”则没有。

===== a.png =====
CGImageGetHeight: 5
CGImageGetWidth:  3
CGImageGetColorSpace: <CGColorSpace 0x4d08ff0> (kCGColorSpaceDeviceRGB)
CGImageGetBitsPerPixel:     32
CGImageGetBitsPerComponent: 8
CGImageGetBytesPerRow:      20
CGImageGetBitmapInfo: 0x00000003
  kCGBitmapAlphaInfoMask     = YES
  kCGBitmapFloatComponents   = NO
  kCGBitmapByteOrderMask     = NO
  kCGBitmapByteOrderDefault  = NO
  kCGBitmapByteOrder16Little = NO
  kCGBitmapByteOrder32Little = NO
  kCGBitmapByteOrder16Big    = NO
  kCGBitmapByteOrder32Big    = NO
Pixel Data:
(00,00,00,FF), (FF,FF,FF,FF), (FF,00,00,FF), (00,FF,00,FF), (00,00,FF,FF)
(00,00,00,FF), (FF,FF,FF,FF), (FF,00,00,FF), (00,FF,00,FF), (00,00,FF,FF)
(FF,FF,FF,00), (FF,FF,FF,00), (FF,FF,FF,00), (FF,FF,FF,00), (FF,FF,FF,00)


===== b.png =====
CGImageGetHeight: 5
CGImageGetWidth:  3
CGImageGetColorSpace: <CGColorSpace 0x4d08ff0> (kCGColorSpaceDeviceRGB)
CGImageGetBitsPerPixel:     24
CGImageGetBitsPerComponent: 8
CGImageGetBytesPerRow:      15
CGImageGetBitmapInfo: 0x00000000
  kCGBitmapAlphaInfoMask     = NO
  kCGBitmapFloatComponents   = NO
  kCGBitmapByteOrderMask     = NO
  kCGBitmapByteOrderDefault  = NO
  kCGBitmapByteOrder16Little = NO
  kCGBitmapByteOrder32Little = NO
  kCGBitmapByteOrder16Big    = NO
  kCGBitmapByteOrder32Big    = NO
Pixel Data:
(00,00,00), (FF,FF,FF), (FF,00,00), (00,FF,00), (00,00,FF)
(00,00,00), (FF,FF,FF), (FF,00,00), (00,FF,00), (00,00,FF)
(00,00,00), (FF,FF,FF), (FF,00,00), (00,FF,00), (00,00,FF)