kCVPixelFormatType_420YpCbCr8BiPlanarFullRange 帧到 UIImage 转换

我有一个应用程序可以捕获 kCVPixelFormatType_420YpCbCr8BiPlanarFullRange 格式的实时视频来处理 Y 通道。根据苹果的文档：

kCVPixelFormatType_420YpCbCr8BiPlanarFullRange 双平面分量 Y'CbCr 8 位 4:2:0，全范围（亮度=[0,255] 色度=[1,255]）。 baseAddr 指向大端 CVPlanarPixelBufferInfo_YCbCrBiPlanar 结构。

我想在 UIViewController 中呈现其中一些帧，是否有任何 API 可以转换为 kCVPixelFormatType_32BGRA 格式？你能给出一些提示来调整苹果提供的这个方法吗？

// Create a UIImage from sample buffer data
- (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer  {
    // Get a CMSampleBuffer's Core Video image buffer for the media data
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    // Lock the base address of the pixel buffer
    CVPixelBufferLockBaseAddress(imageBuffer, 0);

    // Get the number of bytes per row for the pixel buffer
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);

    // Get the number of bytes per row for the pixel buffer
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
    // Get the pixel buffer width and height
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);

    // Create a device-dependent RGB color space
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    // Create a bitmap graphics context with the sample buffer data
    CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8,
                                                 bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    // Create a Quartz image from the pixel data in the bitmap graphics context
    CGImageRef quartzImage = CGBitmapContextCreateImage(context);
    // Unlock the pixel buffer
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);

    // Free up the context and color space
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);

    // Create an image object from the Quartz image
    UIImage *image = [UIImage imageWithCGImage:quartzImage];

    // Release the Quartz image
    CGImageRelease(quartzImage);

    return (image);
}

谢谢你！

如果您进行更改，我发现的大多数实现（包括此处之前的答案）都将无法工作videoOrientation in the AVCaptureConnection（由于某种原因我不完全理解，CVPlanarPixelBufferInfo_YCbCrBiPlanar在这种情况下结构将为空），所以我写了一个这样做的结构（大部分代码基于这个答案 https://stackoverflow.com/a/30497777/16）。我的实现还向 RGB 缓冲区添加了一个空的 alpha 通道并创建了CGBitmapContext使用kCGImageAlphaNoneSkipLastflag（没有 alpha 数据，但 iOS 似乎需要每个像素 4 个字节）。这里是：

#define clamp(a) (a>255?255:(a<0?0:a))

- (UIImage *)imageFromSampleBuffer:(CMSampleBufferRef)sampleBuffer {
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    CVPixelBufferLockBaseAddress(imageBuffer,0);

    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);
    uint8_t *yBuffer = CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0);
    size_t yPitch = CVPixelBufferGetBytesPerRowOfPlane(imageBuffer, 0);
    uint8_t *cbCrBuffer = CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 1);
    size_t cbCrPitch = CVPixelBufferGetBytesPerRowOfPlane(imageBuffer, 1);

    int bytesPerPixel = 4;
    uint8_t *rgbBuffer = malloc(width * height * bytesPerPixel);

    for(int y = 0; y < height; y++) {
        uint8_t *rgbBufferLine = &rgbBuffer[y * width * bytesPerPixel];
        uint8_t *yBufferLine = &yBuffer[y * yPitch];
        uint8_t *cbCrBufferLine = &cbCrBuffer[(y >> 1) * cbCrPitch];

        for(int x = 0; x < width; x++) {
            int16_t y = yBufferLine[x];
            int16_t cb = cbCrBufferLine[x & ~1] - 128;
            int16_t cr = cbCrBufferLine[x | 1] - 128;

            uint8_t *rgbOutput = &rgbBufferLine[x*bytesPerPixel];

            int16_t r = (int16_t)roundf( y + cr *  1.4 );
            int16_t g = (int16_t)roundf( y + cb * -0.343 + cr * -0.711 );
            int16_t b = (int16_t)roundf( y + cb *  1.765);

            rgbOutput[0] = 0xff;
            rgbOutput[1] = clamp(b);
            rgbOutput[2] = clamp(g);
            rgbOutput[3] = clamp(r);
        }
    }

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(rgbBuffer, width, height, 8, width * bytesPerPixel, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipLast);
    CGImageRef quartzImage = CGBitmapContextCreateImage(context);
    UIImage *image = [UIImage imageWithCGImage:quartzImage];

    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    CGImageRelease(quartzImage);
    free(rgbBuffer);

    CVPixelBufferUnlockBaseAddress(imageBuffer, 0);

    return image;
}