francescotorregrossa/hold-and-modify

Simulate HAM6 constraints for RGB images

Developed with Giuseppe Marino

Hold and modify

The HAM6 method allows to store images with 2^12 colors by using only 6 bits per pixel (instead of 12) and a palette with 16 colors, 12 bits each.

When displaying a pixel, the first 2 bits are used to determine what to do with the remaining 4 bits:

• 00 means that the other 4 bits should be used to access the palette
• 01 means that the green and blue channel are the same as the previous pixel, while the red channel is interpreted as true color from the remaining four bits
• 10 and 01 act just like the last one, changing the green and the blue channel respectively

The method only describes how to display the image, it doesn't take care of its creation.

Usage

This implementation simulates this behaviour by limiting the colors that can be used, but doesn't output a 6 bpp image. For each pixel, each of the four methods is executed (00, 01, 10 and 11). Whichever gives the smaller error is chosen, in a greedy way.

h = ham6(img);
figure; imshow(h);

RGB	HAM6