Gamma Correction Problem with Bitmaps

[marcdevon]

Dear Group,

I am using LWF for my renderings. I have read numerous tutorials in this forum about the process. In particular, I have read through the tutorial for LWF on the following site:

http://www.gijsdezwart.nl/tutorials.php

Since I use Viz 2005, I use the the Viz gamma correction function in Preferences -> Gamma for gamma correcting my bitmaps and ColorCorrect for gamma correcting colors. When gamma correcting bitmaps, I set the input and output gamma to 2.2 (I use HSV Exponential Color Mapping).

I have noticed something very peculiar. For starters, some of my renders have looked washed out. But more than this, I have noticed that the diffuse maps in my renders also look washed out. For example, observe the following (Please excuse the poor quality; these were only crude tests):

In this rendering, I noticed that the floor map and stone map for the hearth looked washed out:



The following is a clip of the two maps in question:



As you can see, the maps as they are rendered in the scene are washed out. What I decided to do is use ColorCorrect for the diffuse maps. In ColorCorrect, I set the Source to the respective bitmaps and I set the gamma at 2.2. I rendered the scene and here is the result:



As you can see, the stone hearth and the wood floor have far more fidelity to the tone of their respective bitmaps. This leads me to believe that there may be a bug in VRay for gamma correcting bitmaps. Or it could be that I do not know what I am doing Has anyone else experienced the same issue?

[vlado]

V-Ray itself does not do anything to bitmaps; the gamma settings are supposed to be handled internally by 3dsmax/VIZ, so I'm not sure what may be wrong there...

Best regards,
Vlado

[dlparisi]

Just a guess, but could it be the HSV Exponential Color Mapping you're using? Try using linear color mapping with no multipliers.

[marcdevon]

Just a guess, but could it be the HSV Exponential Color Mapping you're using? Try using linear color mapping with no multipliers.

Typically I use HSV Exponential but the above renders were rendered using Linear Mapping.

[bluescreen2]

what gamma options did you pick, when impoting ypur bitmaps to your material?

[dlparisi]

Any bright or dark multipliers other than '1'? Can you post a scene?

BTW: I've used Viz 2005 w/ LWF for a couple of years with no problems.

[marcdevon]

V-Ray itself does not do anything to bitmaps; the gamma settings are supposed to be handled internally by 3dsmax/VIZ, so I'm not sure what may be wrong there...

Best regards,
Vlado

Vlado,

There is something definitely wrong. I have manually set the gamma setting for the bitmap to 2.2. I did not experience this problem when I tried a scanline render of the scene (see below):

[vlado]

The scanline renders with Linear color mapping at 1/1 multipliers always, so you need to use that in V-Ray too, for any comparisons between them. If you wish, you can send me just the floor of your scene along with its bitmap so that I can take a look at it.

Best regards,
Vlado