How to fix reflection spikes in mental ray Maya 2010 – Tip

This problem appear when using a combination of mia_material , HDRI and floating point framebuffer.
One would get very high spike in the reflected area of the Shader.

A first look will appear as it’s a bad filter, but it’s actually the camera that could not handle the reflection high value .
since we already have advanced lense shader in mental ray, the fix will be utilizing one of them.
In this case, we will use the  mia_exposure_simple which will solve the problem by clamping or damping color values of the exposure control .

Note that the mia_exposure_simple default gamma value  is 2.2, so we need to drop to 1.00 to match the original render.

Now we have a nice render with no spikes/artifacts.

The good news is : Maya 2011 and 2012 renders it with no render artifacts.:)

Note: I like to thank Renzo Gavino for allowing me to use his model for this post.

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4 Responses to “How to fix reflection spikes in mental ray Maya 2010 – Tip”

  1. clumsyrabbit:) Says:

    Thank you for this, sir. I already subscribed to your podcast and I always visit this blog. :) I’m a fan :)

  2. EdW Says:

    FYI – You are solving a problem that isn’t a problem!
    What you are doing with the exposure node is applying a tonemap onto HDR data, which is only useful if you have no plans to composite the image later.

    The “camera” can handle the HDR data just fine, it’s the *viewer* that is having problems — it cannot display color values greater than 1, and so it clips to those ugly-looking artifacts. This is in fact correct. Bring this image into Nuke, and you can do all kinds of fun stuff with all that extra data.

    The best way to deal with this “problem” is to render linearly (the artifacting image above) and tonemap the values later in your compositing package or Photoshop when converting back to LDR file formats.

    By the way, if you DO work this way, make sure to only render as an 8-bit image, because you’re wasting space by encoding any more pixel depth than that.


  3. abo nabam Says:

    hey. This is the same issue i come across while rendering in maya 2013. There are some real high hot spots on my materials i.e xpasses. It does have alot of reflections and refraction but still i dont understand why it is doing that. Like, in Arnold we can just say to clamp the value that goes real high, but in maya what u did here u say works for maya 2010, but how to fix that in 2013. Please help.Thanks and i love your blog

  4. Ashraf Says:

    can you send me a sample file to look at ?

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