Gamma Correction and VRay

[erickdt]

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/essential_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?

[Tommy L]

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.

[erickdt]

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?

[Tommy L]

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.

[erickdt]

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 :-)

[erickdt]

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?

[Nic H]

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

[erickdt]

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?

[Nic H]

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)

[WAcky]

you just need to learn to work with a blown out mat editor.

 

I don't use a blown out mat editor...

[Nic H]

oh how do you get around it?

[Tommy L]

The materials in the materials look like they should. Think about it, how would it look if you were looking straight at a lightbox? Hmmm, pretty blown out maybe?

There is an option in the max gamma settings that asks whether you would like the swatches in the mat editor to be affected by the gamma settings. I work in 2.2, affecting mat ed. I think the most consistent results Ive had come from Exponential exposure (1-1-2.2) but after you get the hang of things you can use the exposure settings to get creative.

I would advise you choose a LWF exposure setting that someone recommends, leave it at that and do a project start to finish. Leave that as a constant in your workflow to begin with, you'll better understand the defaults in other areas. Exposure is the single biggest (non-render-time-affecting) setting imho. Make sure you have 2.2 as the exposure in Max, otherwise you are out of sorts..

Do not, I repeat do NOT try and take a completed project and reverse engineer it to be LWF. It will bu MUCH easier to start from fresh. Bring in a mesh, sure, but strip it and start from scratch with render settings, materials and lights.

[erickdt]

Thanks all for your advice. As Tommy suggests, I'll start a project from scratch and see what it's like from start to finish.

[Devin Johnston]

A few months ago Jeff posted this sRGB to Linear color converter, it "de-gamma's" the colors that you take from Photoshop and converts them to linear color so Max can display it properly. Unfortuantley it's only set up to work with solid colors but it might be able to assist in your problem.

[jinsley]

...

 

check out the sunny 16 rule as a starting point.

 

...

 

thx for this... learned something new today! Something I can use in the office and out taking photos.

 

Cheers

[WAcky]

The LWF checkbox in vray is to be used in scenes that weren't originally set up for LWF. I wouldn't recommend using this.

 

My setup is as follows:

 

MAX settings:

Enable Gamma/LUT correction = checked.

Gamma set to 2.2

Both materials and colours check boxes checked.

Input gamma = 2.2

output gamma = 2.2

 

Vray Settings:

Colourmapping mode = Linear Multiply

Gamma = 2.2

Don't affect colours = Checked.

 

Check the sRGB button in the VFB.

 

This works for me. Whether its correct or not I have no idea but this is a setup that Vlado suggested.

[erickdt]

Thanks James,

 

After doing several tests I've decided that the setup you describe will be my standard setup. As it turns out having both the input and output gamma set to 2.2 was the key to making it so material editor colors weren't blown out so thanks for that :-)

 

One thing about your settings though: having sRGB space ticked in the VFB only makes the gamma correction affect the image in the VFB. When you save the image and open it in PS you'll notice the image is no longer gamma corrected. I've fixed this by unchecking "don't affect colors" in color mapping and unchecking sRGB space in the VFB.

 

My plan is to try these settings with a series of renderings of an existing project that need to be re-rendered today for their "final renderings". I've been having exposure issues with this file that I had been correcting in PS. We'll see what affect this new setup has. I'll keep you posted.

 

E

[Tommy L]

Erick,

Make sure to post progress. I'd really like to see the work come along and the settings you use.

[bmcgonigle]

I agree, this has been a hugely informative thread and I'd also like to see your results. Thanks for taking the time to explore this everyone!

[Sawyer]

I created a tutorial on this stuff a while back. I updated it recently let me know if this is helpful.

[erickdt]

I'll be sure to do that. This "test" project in particular (which is not the one that originally started this thread) is for the Print 2009 show which is currently setting up in Chicago. The show goes from September 11th-16th. I won't be able to post too much here until the show opens as this particular exhibit will be premiering some new whiz-bang technology that is under wraps for the time being.

 

Here are some of the images of the booth were rendered in the beginning of August that have already been released by Kodak: http://growyourbiz.kodak.com/default.asp?item=2416909

 

I've actually just finished prepping my file for re-rendering (revisions, etc.) and started my batch render with the gamma correction settings which I think produced very nice results especially in my problem areas (a series of white conference room interiors) that I talked about earlier. Although I appreciate those results I do not think the client will. The whole rendering is much brighter and less contrasty/dramatic. Because of this I have decided to revert back to my original settings for the sake of consistency with the last series of renderings I did for this job.

 

When this is all over I will post apples to apples comparative examples from this job of the gamma corrected and non-gamma corrected images.

[WAcky]

One thing about your settings though: having sRGB space ticked in the VFB only makes the gamma correction affect the image in the VFB. When you save the image and open it in PS you'll notice the image is no longer gamma corrected. I've fixed this by unchecking "don't affect colors" in color mapping and unchecking sRGB space in the VFB.

 

I see. I always render to floating point so it's not really an issue but it can't hurt to have it coming out of the renderer right from the start.

 

I believe that having this setting checked will reduce noise in shadows significantly. I'm not totally sure but I'll check my book and confirm this on monday if I can remember to.

 

Cheers!

Edited September 5, 2009 by WAcky

[fadi3d]

hi Guys,

it's a bit late i guess but i had to say that maybe you should save as Oexr

and gamma will be right when you open in PS.myself i save as jpeg with gamma 2.2 only if i don't want to edit.

ps my post here are all done in Gamma 2.2 if you had the chance to check them out and tell me what you think of them i'll be gratefull.

thank you.

fadi.