Gamma correction - do you care?

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View Poll Results: Do you have a linear workflow and gamma corrected output?
I have a fully linear workflow and everything under tight control. 282 32.49%
I understand gamma correction/linear rendering but it's too much hassle. 146 16.82%
My clients/boss/coworkers/tools don't care so why should I? 48 5.53%
I read about it but never quite understood that topic. 289 33.29%
What are you talking about anyway? 103 11.87%
Voters: 868. You may not vote on this poll

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  03 March 2008
Originally Posted by blazelet: I have been looking around in Photoshop, I can't seem to find an inverse gamme correction plugin anywhere. Could it go by another name? I found some gamma tutorials on-line which mess with the levels, is that where I should be looking?

Don't all monitors have different levels of darkness that need to be corrected? I noticed at work and home one of my 3D renderings look really good, but when I take them in to school to show the prof they appear super dark. So do I eyeball what gamma correction looks good, or is there a rule of thumb?


Rule of thumb is 2.2 for pcs, 1.7 for macs, iirc.

There's no 'inverse gamma' thing. You just use the gamma control in photoshop to apply a gamma of 0.454545... if you're on a pc and 0.588234... if you're on a mac (assuming that the numbers I mentioned above are correct).

Alternatively, most renderers nowadays have options to do this automatically for you at rendertime.

Of course, even if you do all this, there's no accounting for how different random monitors everywhere else in the world will be calibrated...
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  03 March 2008
Well, I know roughly about linear workflow, but don't understand it's benefits clearly.

What do I get after going through gamma correction jazz and fixing issues with textures/normalmaps/selecting colors e.t.c. ?
 
  03 March 2008
Originally Posted by Sandr0: Well, I know roughly about linear workflow, but don't understand it's benefits clearly.

What do I get after going through gamma correction jazz and fixing issues with textures/normalmaps/selecting colors e.t.c. ?


From what I understand it gives you richer, clearer details in the high and low end of your colors - the shadows and highlights.

Sort of like in Photography when you overexpose and underdevelop ... overexpose the shadows and underdevelop the highlights, get detail everywhere.

Is this correct?
 
  03 March 2008
Correct me if I'm wrong:
monitors can't show linear space with full midtones. If no gamma-correction is applied to an image, it will look too saturated and dark.This may be the reason why so many renders look too saturated and contrasty, because people are unaware of gamma-correction and how to use it.
But why we don't see pictures in photoshop etc with wrong output then? Because software like photoshop uses color profiles and applies gamma-correction (?). Or do the digital cameras apply gamma-correction when creating the images?

Your monitor, when you are rendering something, shows you by default wrong output, because it cannot for some reason (maybe we just have bad monitors) show linear space with full midtones. So this is not "I use it because I like it", or "I don't like it, so I'm not gonna use it". You should use it (be aware of it) always. Amazing that this very important subject is not explained in many beginner's books.
What you are doing by applying gamma correction is you force your monitor to show you correct linear result, and that's it. No magic here.

When you save your renders as 32-bit floating-point image, you save it without gamma correction, because you will apply it in post-processing that algorithms would work with linear space (I may be wrong about whether it works better with linear space).
Why this it not by default in rendering software? Maybe because it's more clever to save renders are 32-bit floating images, so this is not needed in this case. But we still need to view while rendering the gamma-corrected result to view it correctly. It could be a switch button there damnit.
So one good way to see if your gamma is wrong, just save your rendered image as HDRI and open it in photoshop, and you will see whether it differs from what you see in your rendering viewer.
So what you should do:
save your rendered image as hdri and open in photoshop and see if it differs from what you see in your rendering viewer. If the HDRI looks washed-out in photoshop, then your gamma is wrong
find out where in your software gamma-correction is
use 2.2 gamma when you are rendering in 8-bit per channel image, it should look just as your HDRI verion in photoshop
use no gamma-correction (1.0) when you are rendering in 32-bit floating image, hdri or exr etc
there also an issue with bitmaps, maybe someone could explain it: what adjustments must be done to bitmap files? As fas as I know, some renderers do it automatically. I just use 2.2 for input and output for bitmaps, and it shows me what I see in photoshop. Would like to hear a better explanation.

Last edited by mister3d : 03 March 2008 at 07:44 PM.
 
  03 March 2008
The simple way:

If you render on a "standard" computer monitor (i.e. an sRGB monitor which has a practical gamma of 2.2 on average) with no regard to gamma anywhere in your workflow (i.e. pretending the monitor has gamma=1, like unfortunately most software defaults to), then when you think you are making something twice as bright, you are actually making it almost 5 times as bright.

This makes even the most trivial math turn out completely wrong. Basically, your renders come out as if 2 + 2 = 10

This is why highlights blow out unrealistically, why reflections look wrong, why you can't seem to be able to use physically correct lights with a quadratic falloff, and why you have to save everything in comp with a bunch of horrendous dirty tricks like "screening" your speculars back on (Yuk!).

wiki


/Z
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Last edited by MasterZap : 03 March 2008 at 07:02 PM.
 
  03 March 2008
Originally Posted by MasterZap: The simple way:

wiki

/Z


That wiki article is fantastic. I am printing it out as I type and will take the highlighter to it this evening.

Thanks Z!
 
  03 March 2008
Talking

Originally Posted by blazelet: That wiki article is fantastic.


Thanks, I actually wrote most of that [is there a blushing smiley ]

As a matter of fact the two links off that page about "linear color" and "what happens without gamma" is raw ramblings of mine someone copied off CGtalk and pasted into the wiki

/Z
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  03 March 2008
That's funny because I printed off the links too

Cheers for sharing your knowledge with us!

I do have another question. I saw something in here about using gamma nodes attached to your shaders (Maya, in this case) to allow you to tweak the gamma in MR.

Do gamma nodes only need to be applied to shaders, or do they also need to be applied to lights? And if I attach gamma nodes to my shaders, does that mean I don't need to mess with my gamma in Photoshop?

I had no idea the RGB scale wasn't linear. That's fascinating.

Last edited by blazelet : 03 March 2008 at 07:34 PM.
 
  03 March 2008
Originally Posted by Sandr0: What do I get after going through gamma correction jazz and fixing issues with textures/normalmaps/selecting colors e.t.c. ?

Correct images.
Your renderer is investing tons of time in calculating GI bounces, energy distributions, shadow nuances etc in the assumption that twice the RGB value equals twice as bright. Unfortunately, your monitor, your scanner and your digital camera disagree and unless you compensate for that, your results will be wrong.
 
  03 March 2008
Talking

Originally Posted by stew: Correct images.
Your renderer is investing tons of time in calculating GI bounces, energy distributions, shadow nuances etc in the assumption that twice the RGB value equals twice as bright. Unfortunately, your monitor, your scanner and your digital camera disagree and unless you compensate for that, your results will be wrong.


Such a short sweet and eloquent way to put it!

/Z
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  03 March 2008
Originally Posted by MasterZap: Thanks, I actually wrote most of that [is there a blushing smiley ]

As a matter of fact the two links off that page about "linear color" and "what happens without gamma" is raw ramblings of mine someone copied off CGtalk and pasted into the wiki

/Z


Any chance of pasting it into the CGWiki?
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  03 March 2008
Originally Posted by stew: Correct images.
Your renderer is investing tons of time in calculating GI bounces, energy distributions, shadow nuances etc in the assumption that twice the RGB value equals twice as bright. Unfortunately, your monitor, your scanner and your digital camera disagree and unless you compensate for that, your results will be wrong.


If most renderers assume linear colour inputs do they produce linear output as well or make an internal gamma adjustment back to the non-linear colour model?
 
  03 March 2008
Sorry for offtopic, but maybe someone also could mention what is a color temperature for a monitor should be? 6500k?
 
  03 March 2008
Alright I just re-rendered a project I am working on and added gamma correction. Yikes!

I'm sold on it. Forever and ever. Now I can say I am a linear-renderer. Is there a merit badge for that?

Thanks guys!
 
  03 March 2008
This topic is for me a typical "you only see what you know". Once you have realized/seen the difference it is obvious and a must, at least for me now. Thanks to MasterZap for shading some light into my gamma-uncorrected darkness !
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