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Texture Compression:

1 bit per pixel = 2 colors

2 bits per pixel = 22 = 4 colors

3 bits per pixel = 23 = 8 colors

8 bits per pixel = 28 = 256 colors

16 bits per pixel = 216 = 65,536 colors

24 bits per pixel = 224 = 16,777,216 colors





1024 x 1024 x 24 = 1048576 bits = 3mb

RGB 24bit gives highest quality but the largest images size

RGB 16bit lower quality for lower size





But let's think about it for moment. How much loss in image quality will happen if I changed from 24bit to 16bit ?

It comes down to the idea of what 24bit and 16bit is. 16bit means it will have less number/collection of colors than the actual true colors. Which means: for an image with gradient or smooth transition between a color and another one, it won't be that smooth. In 16bit the gradient will look sharp as some colors don't exist in this width (i.e. color can't be formed by only 16 bits) and are replaced with nearest available color. For example check the image below:







