shrinkArgb
fun shrinkArgb(width: Int, height: Int, shrinkX: Int, shrinkY: Int, readRows: (pixels: IntArray, y: Int, rows: Int) -> Unit): ByteArray
A bitmap of width by height straight (not premultiplied) ARGB pixels, averaged down like shrinkRgba into straight RGBA bytes. readRows fills its array with the rows rows that start at row y, shrinkY rows at a time, so a large decoded bitmap is never copied whole.