[BUG] Pixel 7a detected face boundaries not correct

[nonam4]

[BUG] Pixel 7a detected face boundaries not correct

[nonam4]

@imelos this will be difficult to fix without access to the device, logs, and other relevant information.

However, I suspect the problem might be related to scale values.

Perhaps these values are higher than they should be? 🤔

[mrousavy]

@nonam4 I also btw just experienced a similar issue on iOS, not sure if it's the same cause, but basically scaleX and scaleY shouldn't be done.

react-native-vision-camera-face-detector/ios/VisionCameraFaceDetector.swift

Lines 245 to 246 in 22c87fe

	let scaleX = screenBounds.size.width / CGFloat(frame.width)
	let scaleY = screenBounds.size.height / CGFloat(frame.height)

You are making assumptions about a preview view here, whereas the coordinate system of a Frame Processor should always be the same of the Frame (.width/.height).

The user is responsible for converting that to preview coordinates. Maybe I can expose a function that does that.
But in reality it's just not as simple to scale it, because sometimes there's a pixel-shift involved, sometimes the width/height are flipped on Android, etc.

And in my case that was wrong (I explicitly patched this lib and set scaleX and scaleY to 1) because I am drawing in a Skia Frame Processor - and those use the same coordinate system as the Frame. It will be auto-scaled by the Preview later. mrousavy/react-native-vision-camera#2743

So I recommend you remove the scaling from your code, and let the user manually convert that to preview coordinates if needed. In Skia Frame Processors the user doesn't need to do that, it is just always the Frame coordinates.