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Why so splotchy?

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    Why so splotchy?

    Why do interior renderings always seem to have these splotches? It would be greatly appreciated if anyone has any tips or tricks to help me.

    Thanks, Joe
    Attached Files

    Hi joeyd,

    I’ve never seen an explanation for why the splotchies exist, it just seems to be a ‘feature’ of the mental ray rendering engine. I’ve tried different material settings, without much success. But there is a render setting that controls the level of splotchiness. The setting is called ‘Indirect illumination Smoothness’ and it is found under the Indirect Illumination Options in the Advanced Render Settings. You can reach the advanced render settings by choosing ‘Edit…’ in the Quality Setting dropdown in the Rendering dialog. I’ve found that you need to bump this setting up to 9 or 10 to reduce the splotchy shadows (the default for Best setting is 8). Of course there is always a trade off and in this case it is increased render time. One thing you might try to reduce render time is starting with the ‘High’ quality setting and just bumping up the Indirect Illumination Smoothness to 9 or 10. I did a few tests and attached the results.

    Test 1: Default Best quality; render time = 6:27
    Test 2: Best w/ custom Indirect Illumination Smoothness 9; render time = 16:46
    Test 3: High w/ custom Indirect Illumination Smoothness 8; render time = 2:21
    Test 4: High w/ custom Indirect Illumination Smoothness 9; render time = 6:20
    Test 5: High w/ custom Indirect Illumination Smoothness 10; render time = 13:40

    Notice in my example there is not much difference in quality between Test 4 & 5, but Test 5 with the Indirect illumination Smoothness at 10 took significantly longer to render. However a different scene may benefit from the higher setting. Also, in order to find the best setting I will use the render region option so I don’t have to render the entire scene to see the results, thus saving quite a bit of time. Finally, I’ve read that enabling Daylight Portals (also found in the advanced render settings) helps reduce splotchies, but I haven’t found that to be the case in my experience so I don’t recommend it since it increases render time.
    Attached Files


      Something I tend to do is set the Indirect Illumination Smoothness very high (like eight or nine) but set the Indirect Illumination Accuracy very low (like a two or three).

      This gives you smooth, non-splochy 'light mold' views but doesn't take forever.

      Unless you're rendering something with lots of reveals, tiny gaps, or other inside corners, having the Indirect Illumination Accuracy be low isn't even noticeable.

      Another thing I commonly do is raise the Bounce number by one. So that's two or three. Which does add more time, every additional Bounce takes a lot more time.

      Finally, if I just can't get what I need via the 'real' lights of the scene, I'll turn off most of the interior lights, and then just have the sun and few large square 'soft box' studio lights instead. Makes for impressive if inaccurate renders!

      As far as I know, the splotches have to do with the Final Gather and Photon settings in Mental Ray, something we can't directly access in Revit. In Max, there are many fixes for this problem, because you've got finer control over the settings. But it's also harder to use, for those settings get to be rather complex quickly...
      Last edited by JeffreyMcGrew; December 11, 2010, 06:05 PM. Reason: fixing link
      Jeffrey McGrew
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        According to what I have read, the splotchiness is caused by a low number of 'rays' during the final gather process. But since we don't have access to that number, the smoothness field is the only way to eliminate the splotches.


          After reading (a bit) more, it seems that photons are shot at the scene, which create white spots. The more accurate the photons, the smaller the spots, and more photons = more spots. Less accurate photons make for less noise, but sacrifice detail, making it blurry. The final gather process uses rays to (insert part of the process I do not understand here) resulting in the photon 'noise' reduction and a final rendering that is more evenly lit.


            Thank you everyone here for your input. I do appreciate it. I have not had time yet to try out the different scenarios, but will let you know how it works when I do.

            In the past I have never really messed around with the custom settings much, as I was confused on what effected what and found that the rendering time was being increased drastically. Your ideas sounds very promising though.

            Thanks again, Joe


              Originally posted by muttlieb View Post
              I did a few tests and attached the results.
              This kind of thing is immensely helpful and will save me many hours of time. Thank you, muttlieb!


                After running the rendering again, the difference is huge. The splotches are minimal. I Set the rendering to High, with the IIS to 9. The rendering time was about 31 minutes. I think my previous rendering was set to Best.

                This has helped me greatly! Now that I know what to change in the settings I feel confident I will be producing much better interior renderings. Thank you muttlieb. :thumbsup:
                Attached Files


                  That's a nice improvement Joe! I'm glad the suggestions helped. And I'm glad you posted your results so others can see that it is possible to get good interior renderings out of Revit. :thumbsup:


                    I wanted to update my comments regarding Daylight Portals. I mentioned that activating Daylight Portals never made any difference in my renderings. I never bothered to explore why until now. The windows I use are made up of nested components that are assigned to the generic category. Since the sash with the glazing is assigned to the generic category, it is not recognized as a window and therefore not recognized as a daylight portal. After running some tests with the OOTB windows, enabling daylight portals did in fact greatly improve the quality of light. But keep in mind it can also significantly increase render time, so I would only use them if you have a really tough scene that is not improved using the other tips already mentioned in this thread.
                    Attached Files
                    Last edited by muttlieb; December 16, 2010, 12:34 AM.


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