How would you change the intensity of a normal map?

anonymous_user_fbe2d247 · May 9, 2016, 8:43pm

mariomguy;527137:

Eh, not ENTIRELY. The Red and Green channels provide values for shifting the light left and right over the surface. The Z values shift light up and down in the Z direction. Typically the Z channel gets compressed because normal maps don’t require a lot of definition shifting light in the Z direction (again, too much shifting would require the texture to be backlit), so scaling that value instead would not only result in incorrect lighting, but it would also reveal more artifacts as you scale up. Flattening, it would make sense to fade the Z value to 1 so it completely stops the backlighting effect, but for stronger normals you shouldn’t scale or touch it. Emphasizing backlighting is not the effect you want with stronger normals. The effect you want with stronger normals is the light shifting more to the left and right as described in the RG channels. From what I understand, the RG channels are uncompressed too, so you can get more detail out of that. For that, though, you will need to use either my method or RI3DVIZ’s method.

This is not how normal mapping works.

Normal maps in UE4 is stored in BC5 format. This is block based compression format that stores only two channels. Only R and G(x and y) channels are stored. Channels are compressed separately. Each 4x4 block stores just two endpoints and each texel just lerp between those endpoints. In shader Z component is recalculated using knowledge/assumption that all normals are unit normals.(length is exactly 1). So: z = sqrt(1 - xx + yy).
All that happens automatically in engine when you use normal map texture compression and normal map sampler. After this point you can make any math for your tangent space normal. In this case you want to change it’s intensity. After this engine transform your normal map from tangent space to world space. Engine also normalize the result. This is reason you don’t have to normalize it after scale operation that actually leave the normal unnormalized.

Lighting code does not care or even know do you use normal mapping or not. It’s totally unrelated.