With cycles, how do I render only highlights and only shadows and nothing else?

I want to render a scene that only the shading and highlights including reflections is rendered in gray scale without rendering diffusion.

Would I be able to do such a thing?

Image example: The lower part shows where it is darker it's black and white where light hits it and gray where it's in the middle.

I just found the effect I'm looking to create here: https://developer.valvesoftware.com/wiki/Screen_Space_Ambient_Occlusion_(SSAO)

• What do you mean by the "highlights": specular? glossy? Would you have an example screenshot available? – Bruno Mar 24 '18 at 21:32
• @Bruno I updated with an image example. – Eric Huelin Mar 24 '18 at 22:55
• I guess I am missing something but what would be wrong with just turning the image to black and white (grayscale)? – Bruno Mar 24 '18 at 23:34
• @Bruno if it was just black and white you would not see the same thing textures would darken the whites. There are labels on the bottles but you only see where light that affects its brightness, the canister on the right is silver but it's completely black minus where it reflects light. – Eric Huelin Mar 25 '18 at 2:27
• If you need this kind of render for "diagnostic" purposes, for instance to identify "burnt" area of too high or too low light, you can use the "False Color" option under Properties > Scene > Color Management > Render > View – Nicola Sap Mar 25 '18 at 11:47

I'm not exactly sure about what features you need to highlight, and you might not like my solution because it will just tell "global" highlights from "global" shadows, instead of underlining "local" sharp changes in lighting (however, I think this is exactly what your example image is doing).

With that in mind, I think you can start with a very simple Compositing Nodes setup:

Take your RenderLayer input, and between it and the output, add a "RGB to BW" and a "ColorRamp" node.

Move the sliders around on the ColorRamp node to find your highlight/shadow range.

The only simple thing that comes to mind is to turn on Clay-style rendering. Two ways to do this:

1. under Properties/Render/Render. Enable Clay Render and just select the color needed, ex: 50% grey:
2. if you need more control over the clay look and want to perform some compositing over your standard rendering, you have to create your own custom clay material then enable multiple render layers with one of them set to render with a single material:

Caveats:

• any mesh with emissive shader will be rendered with the clay material thus loosing all lighting for those objects. Ex:
• Bump mapping, bump displacement as well as adpative true displacement will also be removed with the clay rendering
• Please explain why I don't have clay render in my panel and you do. – Eric Huelin Mar 27 '18 at 3:57
• I am using 2.79a, you? – Bruno Mar 27 '18 at 12:28
• I have 2.79a, the only time I seen clay mode is with 2.8 betas. – Eric Huelin Mar 27 '18 at 21:15
• I thought it was avail by default but may be it's one of the addons (I can't check at the moment) – Bruno Mar 27 '18 at 21:44