Crop image captured with camera session - ios

Question

I am trying to crop image captured with camera session with specific rect of interest. For find proportional crop rect I am using previewLayer.metadataOutputRectConverted method. But after cropping i got wrong ratio.
Debug example:
(lldb) po rectOfInterest.width / rectOfInterest.height
0.7941176470588235
(lldb) po image.size.width / image.size.height
0.75
(lldb) po outputRect.width / outputRect.height
0.9444444444444444
(lldb) po Double(cropped.width) / Double(cropped.height)
0.7080152671755725
As you can see, I am expecting that cropped image ratio will be ~0.79 as rectOfInterest which I am using for cropping.
Method:
private func makeImageCroppedToRectOfInterest(from image: UIImage) -> UIImage {
let previewLayer = cameraController.previewLayer
let rectOfInterest = layoutLayer.layoutRect
let outputRect = previewLayer.metadataOutputRectConverted(fromLayerRect: rectOfInterest)
guard let cgImage = image.cgImage else {
return image
}
let width = CGFloat(cgImage.width)
let height = CGFloat(cgImage.height)
let cropRect = CGRect(x: outputRect.origin.x * width,
y: outputRect.origin.y * height ,
width: outputRect.size.width * width,
height: outputRect.size.height * height)
guard let cropped = cgImage.cropping(to: cropRect) else {
return image
}
return UIImage(cgImage: cropped, scale: image.scale, orientation: image.imageOrientation)
}
Target rect:

Answer 1

I'm not an expert, but I think you misinterpreted the metadataOutputRectConverted method usage.
There is no way your code could return a cropped image with the same aspect ratio since you are multiplying (what I think are) virtually unrelated numbers one to each other.
You can try this method
previewLayer.layerRectConverted(fromMetadataOutputRect: CGRect(x: 0, y: 0, width: 1, height: 1))
To get an idea on what the actual calculations made from the metadataOututRectConverted are.
I think you could explain better what you want to achieve, and maybe provide a sample project (or at the very least some more context on what are the actual images/rects you are using) to help us debug, if you want to have more help on this.

Answer 2

Thanks to #Enricoza I understand how to fix my problem. Here is code:
private func makeImageCroppedToRectOfInterest(from image: UIImage) -> UIImage {
let previewLayer = cameraController.previewLayer
let rectOfInterest = layoutLayer.layoutRect
let metadataOutputRect = CGRect(x: 0, y: 0, width: 1, height: 1)
let outputRect = previewLayer.layerRectConverted(fromMetadataOutputRect: metadataOutputRect)
guard let cgImage = image.cgImage else {
return image
}
let width = image.size.width
let height = image.size.height
let factorX = width / outputRect.width
let factorY = height / outputRect.height
let factor = max(factorX, factorY)
let cropRect = CGRect(x: (rectOfInterest.origin.x - outputRect.origin.x) * factor,
y: (rectOfInterest.origin.y - outputRect.origin.y) * factor,
width: rectOfInterest.size.width * factor,
height: rectOfInterest.size.height * factor)
guard let cropped = cgImage.cropping(to: cropRect) else {
return image
}
return UIImage(cgImage: cropped, scale: image.scale, orientation: image.imageOrientation)
}