UIImageTransformer.swift

extension UIImage {
    /// CGAffineTransform to apply orientation of the image
    var orientationTransformer: CGAffineTransform {
        var transform = CGAffineTransform(translationX: size.width / 2, y: size.height / 2)
        switch imageOrientation {
        case .up, .upMirrored:
            break
        case .down, .downMirrored:
            transform = transform.rotated(by: CGFloat.pi)
        case .left, .leftMirrored:
            transform = transform.rotated(by: -CGFloat.pi / 2)
        case .right, .rightMirrored:
            transform = transform.rotated(by: CGFloat.pi / 2)
        }
        switch imageOrientation {
        case .upMirrored, .downMirrored, .rightMirrored, .leftMirrored:
            transform = transform.scaledBy(x: -1, y: 1)
        default:
            break
        }
        switch imageOrientation {
        case .left, .leftMirrored, .right, .rightMirrored:
            return transform.translatedBy(x: -size.height / 2, y: -size.width / 2)
        case .up, .upMirrored, .down, .downMirrored:
            return transform.translatedBy(x: -size.width / 2, y: -size.height / 2)
        }
    }

    /// CGAffineTransform to revert orientation of the image
    var inverseOrientationTransformer: CGAffineTransform {
        var transform = CGAffineTransform.identity

        switch imageOrientation {
        case .left, .leftMirrored, .right, .rightMirrored:
            transform = transform.translatedBy(x: size.height / 2, y: size.width / 2)
        case .up, .upMirrored, .down, .downMirrored:
            transform = transform.translatedBy(x: size.width / 2, y: size.height / 2)
        }

        switch imageOrientation {
        case .upMirrored, .downMirrored, .rightMirrored, .leftMirrored:
            transform = transform.scaledBy(x: -1, y: 1)
        default:
            break
        }

        switch imageOrientation {
        case .up, .upMirrored:
            break
        case .down, .downMirrored:
            transform = transform.rotated(by: CGFloat.pi)
        case .left, .leftMirrored:
            transform = transform.rotated(by: CGFloat.pi / 2)
        case .right, .rightMirrored:
            transform = transform.rotated(by: -CGFloat.pi / 2)
        }
        return transform.translatedBy(x: -size.width / 2, y: -size.height / 2)
    }

    /// CGAffineTransform which converts coordinate of CGImage to coordinate of UIImage
    var transformer: CGAffineTransform {
        return orientationTransformer.scaledBy(x: 1 / scale, y: 1 / scale)
    }

    /// CGAffineTransform which converts coordinate of UIImage to coordinate of CGImage
    var inverseTransformer: CGAffineTransform {
        return CGAffineTransform(scaleX: scale, y: scale).concatenating(inverseOrientationTransformer)
    }
}