reduceColors

function reduceColors(input, reductionValue){
  input.loadPixels();
  for (let x=0;x<input.width;x++){
    for (let y=0;y<input.height;y++){
      let pIndex = 4*(x+y*input.width);
      //create variables for r,g,b values
      let r = input.pixels[pIndex+0];
      let g = input.pixels[pIndex+1];
      let b = input.pixels[pIndex+2];

      r = round(map(r,0,255,0,reductionValue));
      g = round(map(g,0,255,0,reductionValue));
      b = round(map(b,0,255,0,reductionValue));

      //set those values
      input.pixels[pIndex+0]=map(r,0,reductionValue,0,255);
      input.pixels[pIndex+1]=map(g,0,reductionValue,0,255);
      input.pixels[pIndex+2]=map(b,0,reductionValue,0,255);
    }
  } 
  input.updatePixels();
  return input;
}