Remosaic of RGB image array

Converts a MxNx3 color image array into a 2Mx2N intensity mosaic.

Interleaves the color pages of an MxNx3 color image array into presumably what was the original, 2Mx2N, intensity output of a Bayer image sensor. Useful for capturing a monochromatic image (like actively illuminated IR) with a color sensor (like a cheap color webcam). It does not compensate for effects due to demosaic or any image processing done between the image sensor array and this function.