Lighting in post process material

I would like to have just the lighting/shading without any colors in my post process material.
Now there is no SceneTexture: Lighting or any the like but theoretically I should be able to get it by extracting BaseColor from SceneColor. But everything I tried didn’t give me just the lightning, there was always some greyscale from color left in it.

Any ideas or am I wasting my time here because it is not possible?

This is only possible if scene does not contain any specular. In theory on pure diffuse light scene you could just divide scene color with base color(albedo) to get lightning.

That worked! Without specular and with using half of that. I guess making it work with specular is then the impossible part.
I’m using it for mapping it to a ramp texture by Hue and Luminance(Lighting) which now works when there is no specular. To make it work with specular I would then somehow extract specular and make it additive on what I get out of the ramp.

Luminance is not just the lighting part. Just calculate it from scene color.

Yea, I know, I just use Hue and Lighting for my ramp texture, while lighting is just grayscale. So Hue controls color while Lighting controls how that color looks in the shadows and in the light. I calculate Luminance from Base Color and use that to lerp between 3 different ramp textures, dark colors, medium colors and bright colors.
Me mentioning Luminance there didn’t make much sense.