Normalize (-1,1) in Designer ?

Eric Chadwick

Looking for a way to process a 24bit texture such that the red and green channels will be normalized within a -1 to 1 range, and not include the blue channel. 

What does the Normal Normalize node do? I guess it’s only normalizing 0-1 ?

This is intended for an anisotropy texture. But I guess the same process would be needed for flow maps too.

The blue channel is not used for the vectors, it’s a mask for strength of the effect, so I wouldn’t want that factored into the normalization.

Eric Chadwick

What does the Normal Normalize node do? I guess it’s only normalizing 0-1 ?

Answering my own question here. Ctrl E on the node:


So, first it normalizes to -1,1 then it converts that into 0,1. I guess I just need to make my own custom pixel processor, and simply omit that last part?

poopipe

Yep, exactly

Make sure your pixel processor is set to absolute color depth of 16f or 32f or it will clamp all the values In the function between 0 and 1.

Eric Chadwick

Hmm, I’ll need to check that when I get back to my PC. 

I posted my results here for feedback from the rest of the glTF developers https://github.com/KhronosGroup/glTF/issues/2290

Eric Chadwick

I’m trying to visualize what a -1,1 normalized image should look like in RGB. 

Ignoring the blue channel, since this anisotropy texture is XY vectors only. We can’t represent negative red values in 8bit RGB. So what would the result look like? 

poopipe

its just re-ranged to 0:1 and will be expanded back out when it's sampled by the shader - exactly the same as a normal map
just divide the resultant [-1:1] vector by 2 and add 0.5 

Eric Chadwick

So I guess I can't store the png bitmap normalized to -1,1 since the negative range gets clipped. Unless I use a 16 bits per channel PNG? The engineers are asking for a -1,1 normalized texture, instead of a 0,1 texture which I'm more familiar with. I guess they're really just asking for the latter, and will convert it to the former in the shader?

poopipe

Looking through the spec suggests png can theoretically support signed values but I don't think I've ever seen it done and I'd be surprised if most exporters support it. you'd probably want to use tiff or exr (possibly .HDR)  as a source format to store the numbers. it'd need compressing to a gpu friendly format that supports negative values as well
bc6h can support signed values - its not small though (i think 4x the size of dxt1 but possibly 8x)

TLDR : just don't

this should really be treated the same way as a normal map,  store the values in 0:1 range, expand it in the shader.

Eric Chadwick

OK that's what I was hoping. Thanks for the gut check!