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I am using cycles render in Blender for my scene and would like to decompose it into albedo and shading components. The concepts could be referred from these sites:

http://www.cs.toronto.edu/~rgrosse/intrinsic/gallery.html and http://sintel.is.tue.mpg.de/

I have check around Google and most of the forums suggest that the color pass of Diffuse BSDF could be used as albedo. However, it is not really sufficient because (1) cycles has more than 3 component (diffuse + glossy + transmission + more) while the original idea of albedo and shading contains only 3 (albedo * shading + specularity) and (2) the shading concept is usually referred to as a 1-channel grayscale image, while the difuse lighting image (direct + indirect) is shown as 3-channel color image.

I am arguing that the original concept could be too simple to describe a complex scene (as they consider only Lambertian component) however, I couldn't find any support for that (i.e. a scene could be decomposed into more than just Lambertian).

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The basic idea is there in Cycles lighting passes, Cycles just breaks things down further than those images do. Here's the overview of how to reconstruct those albedo+shading+spec images:

Albedo = diffuse color + glossy color (Cycles splits albedo out by type of light interaction. In our case, we don't care, so we just sum them)*

Shading = diffuse indirect + diffuse direct (diffuse shading is split by direct vs indirect, so we need to sum these)

Specularity = glossy indirect + glossy direct (same deal as diffuse shading)

the original idea of albedo and shading contains only 3 (albedo * shading + specularity) and (2) the shading concept is usually referred to as a 1-channel grayscale image, while the difuse lighting image (direct + indirect) is shown as 3-channel color image.

The problem here is it does not account for transmission, colored light sources, coloration of bounced light, or colored specular reflections. Accounting for all those is why Cycles throws out 4 different light passes, and all of them are RGB. It also doesn't account for self-illuminating surfaces, hence why the emit pass also shows up in Cycles.

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  • $\begingroup$ You ARE really the ninja. Been benefitting from your answers one after another. Thanks pal! $\endgroup$ – Sibbs Gambling Aug 25 '18 at 20:56
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I'm not sure if you wrote about compositing or about shaders and materials creating. But the overall idea is the same

You wrote: "original idea of albedo and shading contains only 3" (passes) In my opinion this is not true. Idea of albedo is have only colors without any other light influence. No shadows, no AO, no reflections. For example no shadows, because shadows are create by render engine. As I know, this is valid for all render engines including real time renderers in game engines. How you determine the rest of material (or final render in compositor) depend only on your preferences and what you want to achieve. You usually need more need than 3 maps for material - glossiness, roughness, metallic, normal/bump, AO as well as you need more passes for compositing full image.

Also you wrote "most of the forums suggest that the color pass of Diffuse BSDF could be used as albedo. However, it is not really sufficient because: (2) the shading concept is usually referred to as a 1-channel grayscale image, while the difuse lighting image (direct + indirect) is shown as 3-channel color image."

I can't see any problem here. Of course, the colors are determine by 3 channels images and other maps are only grayscale. You need 3 channels to define color in RGB. On grayscale maps color is not important. Important is value. Of course, value define color, but for render engine color is irrelevant. Render engine use this value as factor for mix two shaders/colors. That's the reason why you can switch from "Colors" to "Non color data" in texture node.

I'm not sure if this is helpful for you, because I don't understand where you see problem:-) I only try explain how it work.

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