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Thread: Gamma Correction and VRay

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    Veteran Member erickdt's Avatar
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    Default Gamma Correction and VRay

    Hello All,

    So I was browsing the thread about setting up a night scene with VRay in which someone posted a link to CG Digest tutorials. I read through the gamma correction tutorial located here: http://www.aversis.be/tutorials/vray...l_gamma_01.htm

    Generally speaking I found this tutorial to be very interesting and easy to follow. I think that the gamma corrected workflow is definately something that yields better results than an uncorrected workflow and therefore worth pursuing. I do however have one huge problem: I design tradeshow exhibits. Almost all of these exhibits are attached to advertising/branding campaigns that require that specific colors are used. Simly adjusting a "washed out" color to some other random color is not really an option. So, I am wondering if there's anyway around this issue. In the tutorial the author says that you can asign individual gamma correction to texture maps (bitmaps) but what about straight colors?

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    Veteran Member Tommy L's Avatar
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    Default Re: Gamma Correction and VRay

    Erick,
    In a gamma corrected (linear) workflow, the colors you assign will be alot closer to 'correctness' in the final rendering. The whole point of LWF versus non-lwf is that non-LWF doesnt compensate for the gamma space that windows/display uses. There-fore, you are always compensating with extra lights, bitmap brightness adjustments etc to make up for the fact that the mid-range values are too dark.
    The longer you work in LWF, the more you realise that although its not the only way to work, its a far more predictable and reliable way of attaining accurate values (input matches output). You will also find that alot more of the default values make sense. Max/Vray etc seems to me like it was written to be used in LWF.
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    Veteran Member erickdt's Avatar
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    Default Re: Gamma Correction and VRay

    Quote Originally Posted by Tommy L View Post
    In a gamma corrected (linear) workflow, the colors you assign will be alot closer to 'correctness' in the final rendering.
    I am not finding this to be the case at all. I am comparing the color (which is a deep purple) I dialed into the material editor via. RGB values which were based on the Pantone color to the physical Pantone swatch. Before gamma correction they were almost dead on (discrepancy caused by the difference between how a monitor generates color and how a printer does). When I use the gamma corrected workspace it is waaaay off (more like a desaturated violet) both in the material editor as well as the rendered view.

    I do agree that the light distribution, especially as it pertains to bounced light, is much more realistic with the gamma correction, but I have got to figure out this color issue otherwise it's a non-starter for what I do. No ammount of explaining will convince a client that there is a good reason for "their colors" being off in a rendering. I could probably fix it in post but that doesn't really save me much time.

    Any other suggestions?

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    Veteran Member Tommy L's Avatar
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    Default Re: Gamma Correction and VRay

    What exposure setttings are you using? Post your settings.
    You do kind of have to rethink afew steps in LWF. You need to forget a few compensation habits that are pushing your colours too far because of your old way of working.
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    Veteran Member erickdt's Avatar
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    Default Re: Gamma Correction and VRay

    I typically use the VRay physical camera with the following settings:

    F 1.8

    Shutter Speed 125

    I realize that F 1.8 is a large aperture. I'll do some experimentation with smaller F numbers. Any suggested setups would be appreciated :-)

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    Veteran Member erickdt's Avatar
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    Default Re: Gamma Correction and VRay

    Okay, So I found that tweaking my exposure settings within my VRay physical camera didn't make much of a difference. I have found what I believe will be a good solution from playing around with the various color mapping types. I am getting good results from Reinhard mapping with gamma set to 2.2 and linear workflow checked (it had not been checked before per the tutorial I sighted). Actually pretty much all of the modes with the gamma corrected to 2.2 with linear workflow checked seem to yield nice results.

    Is there anything about this setup that seems fishy? Do people normally set their gamma at 2.2? Or is 2.5 better since most monitors are supposedly calibrated for 2.5?

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    Veteran Member nicnic's Avatar
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    Default Re: Gamma Correction and VRay

    hmm your camera settings are pretty weird, esp if you end up needing to do DOF / Moblur in camera.

    check out the sunny 16 rule as a starting point.

    LWF should make it easy to get 'correct' colours (that sounds like such a nightmare tbh, cant you multimatte and colour in post?)

    the way i use LWF (only occasionally on indoor shots really)

    colour mapping to linear
    bright and dark at 1
    gamma at 2.2 -tick dont affect colours adaptation only
    tick linear workflow button
    vrayframebuffer and srgb button

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    Veteran Member erickdt's Avatar
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    Default Re: Gamma Correction and VRay

    I looked up the "sunny 16". Thanks for the tip!

    I like the results these settings produce (after the lighting has been adjusted) but it still presents two issues: 1.) In order to get VRay light materials, which I use extensively for lightboxes, to display bright enough I have to turn them up to multipliers of 60 which blows them out in the material editor. 2.) My background enviroment, which is usually almost white, is now almost black. This could be fixed in PS though.

    Are there any ways of dealing with these two issues within MAX?

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    Veteran Member nicnic's Avatar
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    Default Re: Gamma Correction and VRay

    you just need to learn to work with a blown out mat editor, do a few tests and you will be set. i use light materials between 30 - 50 generally and region render to get it set up.

    is your sun / sky set at 1 intensity yes?

    when you say background envrionment do you mean the sky? i normally do that in post and render on black for flexibility.

    sopmething like F12 200 ISO, 200 shutter speed is a good starting point

    (note having iso and shutter on same value locks them meaning you can expose using only f number)

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    Veteran Member WAcky's Avatar
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    Default Re: Gamma Correction and VRay

    Quote Originally Posted by nicnic View Post
    you just need to learn to work with a blown out mat editor.
    I don't use a blown out mat editor...

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