pngjs/lib/paeth-predictor.js

PNG encoder/decoder in pure JS, supporting any bit size & interlace, async & sync with full test suite.

"use strict";

module.exports = function paethPredictor(left, above, upLeft) {
  let paeth = left + above - upLeft;
  let pLeft = Math.abs(paeth - left);
  let pAbove = Math.abs(paeth - above);
  let pUpLeft = Math.abs(paeth - upLeft);

  if (pLeft <= pAbove && pLeft <= pUpLeft) {
    return left;
  }
  if (pAbove <= pUpLeft) {
    return above;
  }
  return upLeft;
};