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Thread: Occlusion in conflict with Diffusion Image Map

  1. #1
    icon kid
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    Occlusion in conflict with Diffusion Image Map

    When I try to use occlusion on a surface that also has a diffuse image map applied, these two elements affect each other adversely. Perhaps they were not meant to work together but I won't know until I ask about it. The attached diagram illustrates the problem. (A) I have a red surface that is 100% diffuse. I apply a diffuse map to it which makes it 80% and 50%. (B) I disconnect the diffuse map and apply occlusion (just a simulation of my results, not actual output). Occlusion produces the expected results -- a very slight darkening of the surface (largely an optical illusion because the eye tends to blend the darker grains into an overall perceived brightness). (C) This is what I expected to get when re-connecting the diffuse image while occlusion was active (a simple combination of the two effects). The connection for Diffuse on the Surface node accepts only a single node plug-in at a time. I tried plugging them into each other before sending a singular output to the Surface node, and I tried running both though a mixer and then singularly to the surface. (D) This is what I got when I tried it -- a surface change that was either extremely light or extremely dark or fully black. If you can solve this problem I'd appreciate a screen shot of the proper node setup.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  2. #2
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    For blending occlusion and diffuse map,
    you can just use a Math Scalar Multiply node,
    or a Multiply Blend mode in the Mixer node.


    Denis.

  3. #3
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    the nodes; all nodes, could do with an AO slot

  4. #4
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    Quote Originally Posted by dpont View Post
    ...you can just use a Math Scalar Multiply node...
    Or simpler, use AmbOcclusion node from DPKit and plug your diffuse map
    in the Scalar input, does the same thing than above.

    Denis.

  5. #5
    icon kid
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    Thank you dpont and gar26lw. I always follow-up when I get help. Here's the setup that gave me something that is the closest to what I wanted -- showing the actual rendering of a test object. The upper rendering is of only the diffuse map applied. The lower one is with the diffuse map plus occlusion. You can see the grainy texture on the lighter areas of the sphere as well as in the darker areas which are a bit more difficult to perceive but it's there if you look closely enough. The only failing of this "occlusion/map combo" is that it yields a considerably brighter surface than the diffuse map alone. That's funny because I'd think it would do the opposite, if anything, making a slightly darker surface. I can work around that by simply lowering the brightness value of the diffuse map, unless there is some other type of numerical "strength" node I can add to the mix that affects the overall brightness of a rendered surface without having to edit image maps. An object may have several maps where some of the values must match exactly. Changing one may necessitate changing all, so it's easier to change one to all rather than all to one.
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  6. #6
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    A preview doesn't give a great idea of occlusion, I would say even nothing at all,
    you need to see the result of a render and if it is a sphere, place the mesh among other meshes
    or on floor to see the occlusion, the output is ranged from 0 to 1,
    from not occluded open space to occluded cavities (including its own relief).

    Occlusion should be placed (multiplied) at the final step of your setup,
    exactly like a radiosity in a render, and setup all you need with your Diffuse map before.

    Then you can have also several options in an Occlusion node to get a strongest effect,
    panel options in AmbOcclusion or Math Pow node after the native Occlusion,
    Limit the distance may help also.

    Denis.

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