the gameboy mode...

used some spare minutes last evenings and managed to implement the gameboy (camera) version. first approach without dithering was nice but not close to the original gameboy camera's dithering. it appears that it used some sort of ordered dithering. thanks to wikipedia:
http://en.wikipedia.org/wiki/Ordered_dithering
and the matrix
CGFloat bayer4x4[4][4] =
{{0.01,0.09,0.03,0.11},
{0.13,0.05,0.15,0.07},
{0.04,0.12,0.02,0.10},
{0.16,0.08,0.14,0.06}};
it is coming closer now.
here the first approach without dithering:


and now with ordered (bayer) dithering:


gameboy rocks! :-)