转换为CMSampleBuffer的vImage帧有错误的颜色

Question

我正在尝试将CMSampleBuffer从相机输出转换为vImage，然后应用一些处理。不幸的是，即使没有任何进一步的编辑，我从缓冲区获得的框架也有错误的颜色：

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实现(不考虑内存管理和错误)：

配置视频输出设备：

    videoDataOutput = AVCaptureVideoDataOutput()
    videoDataOutput.videoSettings = [String(kCVPixelBufferPixelFormatTypeKey): kCVPixelFormatType_32BGRA]
    videoDataOutput.alwaysDiscardsLateVideoFrames = true
    videoDataOutput.setSampleBufferDelegate(self, queue: captureQueue)
    videoConnection = videoDataOutput.connection(withMediaType:  AVMediaTypeVideo)

    captureSession.sessionPreset = AVCaptureSessionPreset1280x720

    let videoDevice = AVCaptureDevice.defaultDevice(withMediaType:  AVMediaTypeVideo)
    guard let videoDeviceInput = try? AVCaptureDeviceInput(device: videoDevice) else {
        return
    }

从摄像机接收到的vImage创建CASampleBuffer：

   // Convert `CASampleBuffer` to `CVImageBuffer`
    guard let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else { return }

    var buffer: vImage_Buffer = vImage_Buffer()
    buffer.data = CVPixelBufferGetBaseAddress(pixelBuffer)
    buffer.rowBytes = CVPixelBufferGetBytesPerRow(pixelBuffer)
    buffer.width = vImagePixelCount(CVPixelBufferGetWidth(pixelBuffer))
    buffer.height = vImagePixelCount(CVPixelBufferGetHeight(pixelBuffer))

    let vformat = vImageCVImageFormat_CreateWithCVPixelBuffer(pixelBuffer)
    let bitmapInfo:CGBitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.last.rawValue | CGBitmapInfo.byteOrder32Little.rawValue)

    var cgFormat = vImage_CGImageFormat(bitsPerComponent: 8,
                                        bitsPerPixel: 32,
                                        colorSpace: nil,
                                        bitmapInfo: bitmapInfo,
                                        version: 0,
                                        decode: nil,
                                        renderingIntent: .defaultIntent)

     // Create vImage
     vImageBuffer_InitWithCVPixelBuffer(&buffer, &cgFormat, pixelBuffer, vformat!.takeRetainedValue(), cgColor, vImage_Flags(kvImageNoFlags))

将缓冲区转换为UIImage：

为了进行测试，CVPixelBuffer被导出到UIImage，但是将它添加到视频缓冲区具有相同的结果。

var dstPixelBuffer: CVPixelBuffer?

    let status = CVPixelBufferCreateWithBytes(nil, Int(buffer.width), Int(buffer.height),
                                              kCVPixelFormatType_32BGRA, buffer.data,
                                              Int(buffer.rowBytes), releaseCallback,
                                              nil, nil, &dstPixelBuffer)

    let destCGImage = vImageCreateCGImageFromBuffer(&buffer, &cgFormat, nil, nil, numericCast(kvImageNoFlags), nil)?.takeRetainedValue()

    // create a UIImage
    let exportedImage = destCGImage.flatMap { UIImage(cgImage: $0, scale: 0.0, orientation: UIImageOrientation.right) }

    DispatchQueue.main.async {
        self.previewView.image = exportedImage
    }

Answer 1

尝试在您的简历图像格式上设置颜色空间：

    let vformat = vImageCVImageFormat_CreateWithCVPixelBuffer(pixelBuffer).takeRetainedValue()

    vImageCVImageFormat_SetColorSpace(vformat,
                                      CGColorSpaceCreateDeviceRGB())

...and更新对vImageBuffer_InitWithCVPixelBuffer的调用以反映vformat现在是托管引用的事实：

    let error = vImageBuffer_InitWithCVPixelBuffer(&buffer, &cgFormat, pixelBuffer, vformat, nil, vImage_Flags(kvImageNoFlags))

最后，您可以删除以下行，vImageBuffer_InitWithCVPixelBuffer正在为您完成此工作：

//        buffer.data = CVPixelBufferGetBaseAddress(pixelBuffer)
//        buffer.rowBytes = CVPixelBufferGetBytesPerRow(pixelBuffer)
//        buffer.width = vImagePixelCount(CVPixelBufferGetWidth(pixelBuffer))
//        buffer.height = vImagePixelCount(CVPixelBufferGetHeight(pixelBuffer))

请注意，您不需要锁定核心视频像素缓冲区，如果您检查headerdoc，它会说“在调用此函数之前没有必要锁定CVPixelBuffer”。

Answer 2

对vImageBuffer_InitWithCVPixelBuffer的调用正在执行修改vImage_Buffer和CVPixelBuffer内容的操作，这有点顽皮，因为在您的(链接)代码中，您承诺不修改像素。

CVPixelBufferLockBaseAddress(pixelBuffer, .readOnly)

初始化CGBitmapInfo for BGRA8888的正确方法是alpha优先，32位小endian，这是不明显的，但在vImage_Utilities.h中的vImage_CGImageFormat头文件中有如下内容：

let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.first.rawValue | CGImageByteOrderInfo.order32Little.rawValue)

我不明白为什么vImageBuffer_InitWithCVPixelBuffer要修改您的缓冲区，因为cgFormat (desiredFormat)应该与vformat匹配，尽管它是用来修改缓冲区的，所以也许您应该先复制数据。