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LeeGriggs
11-15-2009, 01:49 PM
Hi,

I have setup my scene with a photographic exposure node. However when I batch render the scene the render passes have no gamma correction.

Is there an easy way to make sure my passes have the same gamma 'look' as my render view (photographic exposure).

Is it simply a matter of using the same gamma in the Framebuffer as my photographic exposure node?

Has anyone got any other 'simple' :) workflows for making them match?



cheers,
lee

Cheesestraws
11-15-2009, 01:57 PM
You can't. Gamma correction has to be done after compositing passes, you get much more control in post anyway.

crispy4004
11-15-2009, 08:08 PM
You can either gamma correct custom color frame buffers in Maya, or do that step in compositing. That is if you are using custom frame buffers with the Mia material (if not, you really should be).

longrayjohnson
11-16-2009, 06:55 AM
hello crispy 4004,

how can you gamma correct custom color frame buffers ? i agree that it makes more sense to do that in comp, but just out of curiosity.

LeeGriggs
11-16-2009, 11:46 AM
crispy4004 You can either gamma correct custom color frame buffers in Maya, or do that step in compositing. That is if you are using custom frame buffers with the Mia material (if not, you really should be). Yesterday 01:57 PM Cheesestraws You can't. Gamma correction has to be done after compositing passes, you get much more control in post anyway.

so are you saying the only way round is to render to 16 or 32 bit?

crispy4004
11-16-2009, 06:23 PM
What I'm saying is if your render passes are set up using custom frame buffers, you can add an extra gamma correct node inbetween them and the shader in the hypershade. Then gamma correct them to Wide Gamut RGB space (http://en.wikipedia.org/wiki/Adobe_Wide_Gamut_RGB_color_space), (gamma of .455). Not sure off the top of my head if you need 32bits to represent the wider color range in the output file. My guess would be yes.

Or, you can just gamma correct all your passes to .455 in compositing. The benefit of doing it this way is the gamma is mathematically computed in the compositor instead of mental ray, meaning you are not relying on the output pass file to hold the extra color information. All of this of course is followed by a gamma correct node with a 2.2 value at the end of the chain.

The benefits of using a compositor and render passes to aid with linear workflow is huge. First, you can color correct every pass within the wide gamut color space. If you were to instead do touch up in photoshop to a Mental Ray render using the photographic exposure, any color correction would result in some color clipping. Second you can have real time control over the exposure.


One last thing, you always want specular and reflectivity passes to be 32-bit because those are the output pass files that can easily have clipping. Using Mia material highlights can help with this, but I still wouldn't trust it completely. Gamma correction can't fix a highlight that has clipping already saved in the render pass file. Sometimes you need the the Indirect pass to be 32-bit as well.

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