Resize a CVPixelBuffer - ios

Question

I'm trying to resize a CVPixelBuffer to a size of 128x128. I'm working with one that is 750x750. I'm currently using the CVPixelBuffer to create a new CGImage, which I resize then convert back into a CVPixelBuffer. Here is my code:
func getImageFromSampleBuffer (buffer:CMSampleBuffer) -> UIImage? {
if let pixelBuffer = CMSampleBufferGetImageBuffer(buffer) {
let ciImage = CIImage(cvPixelBuffer: pixelBuffer)
let context = CIContext()
let imageRect = CGRect(x: 0, y: 0, width: 128, height: 128)
if let image = context.createCGImage(ciImage, from: imageRect) {
let t = CIImage(cgImage: image)
let new = t.applying(transformation)
context.render(new, to: pixelBuffer)
return UIImage(cgImage: image, scale: UIScreen.main.scale, orientation: .right)
}
}
return nil
}
I've also tried scaling the CIImage then converting it:
let t = CIImage(cgImage: image)
let transformation = CGAffineTransform(scaleX: 1, y: 2)
let new = t.applying(transformation)
context.render(new, to: pixelBuffer)
But that didn't work either.
Any help is appreciated. Thanks!

Answer 1

There's no need for pixel buffer rendering and alike. Just transform the original CIImage and crop to size. Cropping is necessary if you source and destination dimensions aren't proportional.
func getImageFromSampleBuffer (buffer:CMSampleBuffer) -> UIImage? {
if let pixelBuffer = CMSampleBufferGetImageBuffer(buffer) {
let ciImage = CIImage(cvPixelBuffer: pixelBuffer)
let srcWidth = CGFloat(ciImage.extent.width)
let srcHeight = CGFloat(ciImage.extent.height)
let dstWidth: CGFloat = 128
let dstHeight: CGFloat = 128
let scaleX = dstWidth / srcWidth
let scaleY = dstHeight / srcHeight
let scale = min(scaleX, scaleY)
let transform = CGAffineTransform.init(scaleX: scale, y: scale)
let output = ciImage.transformed(by: transform).cropped(to: CGRect(x: 0, y: 0, width: dstWidth, height: dstHeight))
return UIImage(ciImage: output)
}
return nil
}

Answer 2

Try this
func getImageFromSampleBuffer (buffer:CMSampleBuffer) -> UIImage? {
if let pixelBuffer = CMSampleBufferGetImageBuffer(buffer) {
let ciImage = CIImage(cvPixelBuffer: pixelBuffer)
let resizedCIImage = ciImage.applying(CGAffineTransform(scaleX: 128.0 / 750.0, y: 128.0 / 750.0))
let context = CIContext()
if let image = context.createCGImage(resizedCIImage, from: resizedCIImage.extent) {
return UIImage(cgImage: image)
}
}
return nil
}
Here I assume that pixel buffer is square and size is equal to 750x750, you can change it to work with all aspect ratios and sizes