pixelBuffer缩放

let ciImage = CIImage(cvPixelBuffer: pixelBuffer)
let sx = 416 / CGFloat(CVPixelBufferGetWidth(pixelBuffer))
let sy = 416 / CGFloat(CVPixelBufferGetHeight(pixelBuffer))
let scaleTransform = CGAffineTransform(scaleX: sx, y: sy)
let scaledImage = ciImage.transformed(by: scaleTransform)
ciContext.render(scaledImage, to: resizedPixelBuffer)

Since the camera image is taller than it is wide, this will squash the image a little. That’s not a big deal for this app, but you could use Core Image to first crop out the center square before resizing.

func resizePixelBuffer(_ srcPixelBuffer: CVPixelBuffer,
                       cropX: Int,
                       cropY: Int,
                       cropWidth: Int,
                       cropHeight: Int,
                       scaleWidth: Int,
                       scaleHeight: Int) -> CVPixelBuffer? {

  CVPixelBufferLockBaseAddress(srcPixelBuffer, CVPixelBufferLockFlags(rawValue: 0))
  guard let srcData = CVPixelBufferGetBaseAddress(srcPixelBuffer) else {
    print("Error: could not get pixel buffer base address")
    return nil
  }
  let srcBytesPerRow = CVPixelBufferGetBytesPerRow(srcPixelBuffer)
  let offset = cropY*srcBytesPerRow + cropX*4
  var srcBuffer = vImage_Buffer(data: srcData.advanced(by: offset),
                                height: vImagePixelCount(cropHeight),
                                width: vImagePixelCount(cropWidth),
                                rowBytes: srcBytesPerRow)

  let destBytesPerRow = scaleWidth*4
  guard let destData = malloc(scaleHeight*destBytesPerRow) else {
    print("Error: out of memory")
    return nil
  }
  var destBuffer = vImage_Buffer(data: destData,
                                 height: vImagePixelCount(scaleHeight),
                                 width: vImagePixelCount(scaleWidth),
                                 rowBytes: destBytesPerRow)

  let error = vImageScale_ARGB8888(&srcBuffer, &destBuffer, nil, vImage_Flags(0))
  CVPixelBufferUnlockBaseAddress(srcPixelBuffer, CVPixelBufferLockFlags(rawValue: 0))
  if error != kvImageNoError {
    print("Error:", error)
    free(destData)
    return nil
  }

  let releaseCallback: CVPixelBufferReleaseBytesCallback = { _, ptr in
    if let ptr = ptr {
      free(UnsafeMutableRawPointer(mutating: ptr))
    }
  }

  let pixelFormat = CVPixelBufferGetPixelFormatType(srcPixelBuffer)
  var dstPixelBuffer: CVPixelBuffer?
  let status = CVPixelBufferCreateWithBytes(nil, scaleWidth, scaleHeight,
                                            pixelFormat, destData,
                                            destBytesPerRow, releaseCallback,
                                            nil, nil, &dstPixelBuffer)
  if status != kCVReturnSuccess {
    print("Error: could not create new pixel buffer")
    free(destData)
    return nil
  }
  return dstPixelBuffer
}