将 UIImage 转换为 CVImageBufferRef

Question

这段代码大部分都可以工作，但结果数据似乎失去了一个颜色通道（我在想什么），因为结果图像数据在显示时被染成蓝色！

代码如下：

UIImage* myImage=[UIImage imageNamed:@"sample1.png"];
CGImageRef imageRef=[myImage CGImage];
CVImageBufferRef pixelBuffer = [self pixelBufferFromCGImage:imageRef];

该方法 pixelBufferFromCGIImage 是从 stackoverflow 上的另一篇文章中获取的：How do I export UIImage array as a movie?（尽管此应用程序与我正在尝试做的事情无关）它是

+ (CVPixelBufferRef)pixelBufferFromCGImage:(CGImageRef)image
{
    CGSize frameSize = CGSizeMake(CGImageGetWidth(image), CGImageGetHeight(image));
    NSDictionary *options = @{
                              (__bridge NSString *)kCVPixelBufferCGImageCompatibilityKey: @(NO),
                              (__bridge NSString *)kCVPixelBufferCGBitmapContextCompatibilityKey: @(NO)
                              };
    CVPixelBufferRef pixelBuffer;
    CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, frameSize.width,
                                          frameSize.height,  kCVPixelFormatType_32ARGB, (__bridge CFDictionaryRef) options,
                                          &pixelBuffer);
    if (status != kCVReturnSuccess) {
        return NULL;
    }

    CVPixelBufferLockBaseAddress(pixelBuffer, 0);
    void *data = CVPixelBufferGetBaseAddress(pixelBuffer);
    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(data, frameSize.width, frameSize.height,
                                                 8, CVPixelBufferGetBytesPerRow(pixelBuffer), rgbColorSpace,
                                                 (CGBitmapInfo) kCGImageAlphaNoneSkipLast);
    CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image),
                                           CGImageGetHeight(image)), image);
    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);
    CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);

    return pixelBuffer;
}

我认为这与 kCVPixelFormatType_32ARGB 和 kCGImageAlphaNoneSkipLast 之间的关系有关，尽管我尝试了每种组合并得到相同的结果或应用程序崩溃。再一次，这会将 UIImage 数据放入 CVImageBufferRef 中，但是当我在屏幕上显示图像时，它似乎失去了颜色通道并显示为蓝色。图片是 png。

Answer 1

听起来可能就是这种关系。可能是 jpg 和 RGB，而不是带有 png 的索引颜色？

Answer 2

解决方案是此代码按预期完美运行。 :) 问题在于使用数据创建 OpenGL 纹理。与此代码完全无关。任何搜索如何将 UIImage 转换为 CVImageBufferRef 的人，您的答案都在上面的代码中！

Answer 3

只是为了澄清上面的答案：我遇到了同样的问题，因为我的着色器代码期望图像缓冲区中有两个分层样本，而我使用的是单层缓冲区

这一行从一个样本中获取 rgb 值并将它们传递给（我不知道是什么），但最终结果是全彩色图像。

 gl_FragColor = vec4(texture2D(SamplerY, texCoordVarying).rgb, 1);

Answer 4

如果有人还在寻找这个问题的解决方案，我通过切换 pixelBuffer 选项中的 BOOL 来解决它：

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                     [NSNumber numberWithBool:NO], kCVPixelBufferCGImageCompatibilityKey,
                     [NSNumber numberWithBool:NO], kCVPixelBufferCGBitmapContextCompatibilityKey,
                     nil];

从否到是：

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                     [NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
                     [NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
                     nil];

Answer 5

我遇到同样的问题并找到一些示例：http://www.cakesolutions.net/teamblogs/2014/03/08/cmsamplebufferref-from-cgimageref
尝试改变

CGBitmapInfo  bitmapInfo = (CGBitmapInfo)kCGBitmapByteOrder32Little |
                  kCGImageAlphaPremultipliedFirst)

Answer 6

以下是真正有效的方法：

+ (CVPixelBufferRef)pixelBufferFromImage:(CGImageRef)image {
    CGSize frameSize = CGSizeMake(CGImageGetWidth(image), CGImageGetHeight(image)); // Not sure why this is even necessary, using CGImageGetWidth/Height in status/context seems to work fine too

    CVPixelBufferRef pixelBuffer = NULL;
    CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, frameSize.width, frameSize.height, kCVPixelFormatType_32BGRA, nil, &pixelBuffer);
    if (status != kCVReturnSuccess) {
        return NULL;
    }

    CVPixelBufferLockBaseAddress(pixelBuffer, 0);
    void *data = CVPixelBufferGetBaseAddress(pixelBuffer);
    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(data, frameSize.width, frameSize.height, 8, CVPixelBufferGetBytesPerRow(pixelBuffer), rgbColorSpace, (CGBitmapInfo) kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image), CGImageGetHeight(image)), image);

    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);
    CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);

    return pixelBuffer;
}

您可以将像素缓冲区更改回 UIImage（然后显示或保存）以确认它可以使用此方法：

+ (UIImage *)imageFromPixelBuffer:(CVPixelBufferRef)pixelBuffer {
    CIImage *ciImage = [CIImage imageWithCVPixelBuffer:pixelBuffer];
    CIContext *context = [CIContext contextWithOptions:nil];
    CGImageRef myImage = [context createCGImage:ciImage fromRect:CGRectMake(0, 0, CVPixelBufferGetWidth(pixelBuffer), CVPixelBufferGetHeight(pixelBuffer))];
    UIImage *image = [UIImage imageWithCGImage:myImage];

    // Uncomment the following lines to say the image to your application's document directory
    //NSString *imageSavePath = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"myImageFromPixelBuffer.png"]];
    //[UIImagePNGRepresentation(image) writeToFile:imageSavePath atomically:YES];
    return image;
}