code: function distManhattan(rgb0, rgb1) {
  		var rd = Math.abs(rgb1[0]-rgb0[0]),
  			gd = Math.abs(rgb1[1]-rgb0[1]),
  			bd = Math.abs(rgb1[2]-rgb0[2]);
  
  		return (Pr*rd + Pg*gd + Pb*bd) / manhMax;
  	}
docs: perceptual Manhattan color distance