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Monday, October 10, 2011

Fixing washed out textures and image when using Physical Sun and Sky (Maya)

File textures may get washed out, because of incorrect gamma. The mia_exposure_control applies gamma correction on the final image. Mental Ray expects file textures to be 'gamma neutral', which they are (probably) not. Chances are you've created them for a gamma of 2.2 or so, which is the default for computer screens. If the mia_exposure control corrects the final rendered image to the gamma you specified, the textures would get gamma-corrected again, which causes them to look washed out:
MR gamma correction off.jpg
MR gamma correction on.jpg
The left side shows a render without proper gamma correction, the right side shows the render as it is supposed to be, after proper gamma correction of the file textures.
There are two main methods to solve this problem: Change the Mental Ray internal framebuffer gamma and the Exposure control gamma, or gamma-correct each filetexture.
The first method is the easiest to implement:
  • Open you Render settings, Mental Ray tab. Find the Framebuffer section and open the Primary Framebuffer subsection. Set the gamma to 1/desired gamma, so 1/2.2 = 0.4545 for a end-result gamma of 2.2
  • Set the Gamma of your mia_exposure_simple to 1.00.
Alternatively you could use the MR Gamma correction MEL script to correct the gamma. This will add gamma correction nodes to all file textures, counter-correcting them for the specified gamma, so the end result should look good.

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