I am compressing a normal map texture using PVRTC 4bpp. To improve image quality, the B component has been set to 0 and only RG remain. Gives ok results. I set 255 for B as an exercise to test a bit further and to my surprise, did not get the same image quality.
My question is: is there an optimal B value that could be computed to get the best PVRTC 4bpp quality given a specific image?
I am using this technique of “droppping” the B component on normal map to have a trade off between file size and image quality. Using uncompressed data is not possible for my application due to excessive file size.
Other PVRTC formats are problematic since image quality is too low in 2bpp mode or simply unsupported. PVRTC 4bpp is then a recquirement.