ImageScanner+CropImage.swift

extension ImageScanner {
    private func cropImage(_ inputImage: CIImage, with detectedRectangle: VNRectangleObservation) -> Result<UIImage, Error> {
        let imageSize = inputImage.extent.size
        let transform = CGAffineTransform.identity.scaledBy(x: imageSize.width, y: imageSize.height)
        let boundingBox = detectedRectangle.boundingBox.applying(transform)
        guard inputImage.extent.contains(boundingBox) else {
            return .failure(ImageProviderError.internalError)
        }

        let topLeft = detectedRectangle.topLeft.applying(transform)
        let topRight = detectedRectangle.topRight.applying(transform)
        let bottomLeft = detectedRectangle.bottomLeft.applying(transform)
        let bottomRight = detectedRectangle.bottomRight.applying(transform)
        let correctedImage = inputImage.cropped(to: boundingBox)
            .applyingFilter("CIPerspectiveCorrection", parameters: [
                "inputTopLeft": CIVector(cgPoint: topLeft),
                "inputTopRight": CIVector(cgPoint: topRight),
                "inputBottomLeft": CIVector(cgPoint: bottomLeft),
                "inputBottomRight": CIVector(cgPoint: bottomRight)
            ])
            .transformed(by: CGAffineTransform.identity.rotated(by: 90 / 180.0 * CGFloat.pi))

        let imageRef = CIContext().createCGImage(correctedImage, from: correctedImage.extent)!
        return .success(UIImage(cgImage: imageRef))
    }
}