var palette = [ 0xFF, 0xDD, 0xBB, 0x99, 0x77, 0x55, 0x33, 0x11 ]; // palette

var ditheringMatrix = [  0, 48, 12, 60,  3, 51, 15, 63,
                        32, 16, 44, 28, 35, 19, 47, 31,
                         8, 56,  4, 52, 11, 59,  7, 55,
                        40, 24, 36, 20, 43, 27, 39, 23,
                         2, 50, 14, 62,  1, 49, 13, 61,
                        34, 18, 46, 30, 33, 17, 45, 29,
                        10, 58,  6, 54,  9, 57,  5, 53,
                        42, 26, 38, 22, 41, 25, 37, 21  ];

var baseColor  = 0;
var colorIndex = baseColor + (ditheringMatrix[(x % 8) + (y % 8) * 8] / 64);
var finalColor = palette[colorIndex];