Pixelation towards RGB/CMYK halftone image processing

Hi

I am attempting to convert a pixelated image I have generated from the image sampler into a split RGB/CMYK image. While this is rather easy in photoshop, I haven't seen anyone try it in GH. (See the mona lisa image below)...

I suppose the logic would be to sample an image at a certain resolution and then replace the proper pixels with their RGB or CMYK (depending on preference) colours. I am not certain what the logic is to replace the color is. I am guessing that you could subdivide the image and then sample the average color. Once this average color is sampled, if it fits in the the domain of R, G, or B, then change the color ?

Unfortunately, I have tried this to no avail. (this can be seen in my definition). The pixelation part with the original colours is not a problem..