2 dimensional image processing (filter)

ImageProcessing.kt

object ImageProcessing {

    fun smoothing(stride: Int, buffer: ByteArray): ByteArray =
        buffer.toIntList()
            .convolution(stride)
            .map { (it / 9).toByte() }
            .toByteArray()

    fun sharpen(stride: Int, buffer: ByteArray): ByteArray =
        buffer.toIntList()
            .let { it.amplify(10).zip(it.convolution(stride)) { x, y -> x - y } }
            .map { it.toByte() }
            .toByteArray()

    private fun List<Int>.convolution(stride: Int): List<Int> =
        chunked(stride)
            .map {
                it.zip(it.take(1) + it) { x, y -> x + y }
                    .zip(it.drop(1) + it.takeLast(1)) { x, y -> x + y }
            }
            .let {
                it.zip(it.take(1) + it) { a, b -> a.zip(b) { x, y -> x + y } }
                    .zip(it.drop(1) + it.takeLast(1)) { a, b -> a.zip(b) { x, y -> x + y } }
            }
            .flatten()

    private fun List<Int>.amplify(c: Int) = map { it * c }

    private fun ByteArray.toIntList() = toList().map { (256 + it) and 255 }

}