在Swift中从CVPixelBufferRef获取像素值

Question

如何从CVPixelBufferRef获取RGB（或任何其他格式）像素值？香港专业教育学院尝试了许多方法，但没有成功。

func captureOutput(captureOutput: AVCaptureOutput!,
                   didOutputSampleBuffer sampleBuffer: CMSampleBuffer!,
                   fromConnection connection: AVCaptureConnection!) {
  let pixelBuffer: CVPixelBufferRef = CMSampleBufferGetImageBuffer(sampleBuffer)!
                CVPixelBufferLockBaseAddress(pixelBuffer, 0)
  let baseAddress = CVPixelBufferGetBaseAddress(pixelBuffer)

  //Get individual pixel values here

  CVPixelBufferUnlockBaseAddress(pixelBuffer, 0)
}

Answer 1

baseAddress是不安全的可变指针，或更确切地说是UnsafeMutablePointer<Void>。将指针转换Void为更特定的类型后，即可轻松访问内存：

// Convert the base address to a safe pointer of the appropriate type
let byteBuffer = UnsafeMutablePointer<UInt8>(baseAddress)

// read the data (returns value of type UInt8)
let firstByte = byteBuffer[0]

// write data
byteBuffer[3] = 90

确保使用正确的类型（8、16或32位unsigned int）。这取决于视频格式。最有可能是8位。

缓冲区格式的更新：

您可以在初始化AVCaptureVideoDataOutput实例时指定格式。您基本上可以选择：

• BGRA：一个平面，其中蓝色，绿色，红色和alpha值分别以32位整数存储
• 420YpCbCr8BiPlanarFullRange：两个平面，第一个平面包含每个像素的字节，每个像素的Y（亮度）值，第二个包含像素组的Cb和Cr（色度）值
• 420YpCbCr8BiPlanarVideoRange：与420YpCbCr8BiPlanarFullRange相同，但Y值限制为16 – 235（出于历史原因）

如果您对颜色值和速度（或更确切地说，最大帧速率）不感兴趣，那么请选择更简单的BGRA格式。否则，请选择一种更有效的本机视频格式。

如果有两个平面，则必须获取所需平面的基址（请参见视频格式示例）：

视频格式示例

let pixelBuffer: CVPixelBufferRef = CMSampleBufferGetImageBuffer(sampleBuffer)!
CVPixelBufferLockBaseAddress(pixelBuffer, 0)
let baseAddress = CVPixelBufferGetBaseAddressOfPlane(pixelBuffer, 0)
let bytesPerRow = CVPixelBufferGetBytesPerRowOfPlane(pixelBuffer, 0)
let byteBuffer = UnsafeMutablePointer<UInt8>(baseAddress)

// Get luma value for pixel (43, 17)
let luma = byteBuffer[17 * bytesPerRow + 43]

CVPixelBufferUnlockBaseAddress(pixelBuffer, 0)

BGRA示例

let pixelBuffer: CVPixelBufferRef = CMSampleBufferGetImageBuffer(sampleBuffer)!
CVPixelBufferLockBaseAddress(pixelBuffer, 0)
let baseAddress = CVPixelBufferGetBaseAddress(pixelBuffer)
let int32PerRow = CVPixelBufferGetBytesPerRow(pixelBuffer)
let int32Buffer = UnsafeMutablePointer<UInt32>(baseAddress)

// Get BGRA value for pixel (43, 17)
let luma = int32Buffer[17 * int32PerRow + 43]

CVPixelBufferUnlockBaseAddress(pixelBuffer, 0)