Displacement and Gamma issues with V-Ray

This might intrest thos who work in Linear color mapping with a gamma curve (like the so called Linear Workflow LWF with 2.2 gamma correction). I recently bumped into an annoying side effect of putting an input gamma for bitmap files other than 1.0 in Max : Diplacement maps gets corrected aswell…

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But here’s how to fix it !

This example shows the issue with a diplacement map inspired by the facade of the de Young Museum. Note that as the map is diplaced inside and outside, a negative shift value of half the displacement amount has to be applied to avoid the mid grey to push the plane outwards. Since the map is gamma corrected, this negative shift gets messed up aswell.

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Copy of render1.RGB_color.0000

It’s pretty easy to correct this, either with the color correct plugin, either with the new Color Correction that comes with Max 2010. To do this just put a gamma correction on the map of 2.2, in advanced lightness menu, to counter the input gamma initially applied on it)

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Then it goes well ! And the negative shift keeps the plane aligned with the rest of the model…

render1.RGB_color.0000

I’ve noticed that the double gamma correction is not as precise as a simple gamma 1.0 import of the bitmap, but it wil solve the issue in most cases. Maybe an option in V-Ray dipsplacement mod could also do the trick, preventing to apply the gamma in the first place.

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