View topic - Tone mapping awareness-raising thread

Tone mapping awareness-raising thread

General discussion on lighting, backgrounds, Global Illumination, rendering parameters and tonnemapping.

Re: Tone mapping awareness-raising thread

Post Sun Jul 29, 2012 9:20 pm

I am a bit late for the party... :cry:
Anyway I was trying to have a linear workflow with yafaray...

Is there any diference in having
gamma output 1.8 and gamma input 1.8
vs
gamma output 2.2 and gamma input 2.2
I assume that only a gamma correction on textures is made right?

Does anyone has experience in converting textures to gamma 1 and rendering with linear workflow on yafaray?
I presume 8bits for textures may destroy too much info. What's your opinion?

Thanks.
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Re: Tone mapping awareness-raising thread

Post Mon Jul 30, 2012 7:21 pm

I think modern versions of most operating systems use gamma 2.2 internally nowadays, so you should probably use that value in yafaray. You should make sure your monitor is calibrated to that gamma value too.

Textures are converted to linear gamma according to the gamma input value. Yafaray actually expects to use linear textures when rendering, so instead of converting each texture manually you can set the gamma input to 2.2 (or whatever gamma you use) and yafaray will automatically convert from that gamma value to linear.

If you are saving to an 8-bit format like png and you want a gamma-corrected render then you will set gamma output to 2.2 or whatever gamma value you want the render saved with.

But I agree with you that an 8-bit format is not very suitable for tonemapping, so you should use a 32-bit float format like exr instead. In this case, if you render into the blender image editor then you will want to explicitly set gamma output to 1.0 (of course leave gamma input at 2.2). Your render will seem very dark when you render this way but don't worry, it will be fixed in the tonemapping phase.

For the tonemapping itself I recommend the Reinhard05 method in Luminance HDR (was qtpfsgui), or use the tonemapping node in blender (it uses the same Reinhard algorithm). I guess the tonemapping itself is already discussed in this thread.
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Re: Tone mapping awareness-raising thread

Post Mon Jul 30, 2012 9:06 pm

wizofboz wrote:I think modern versions of most operating systems use gamma 2.2 internally nowadays, so you should probably use that value in yafaray. You should make sure your monitor is calibrated to that gamma value too.

Yup. Monitor calibrated :)
But Ubuntu pangolim default value is 1
I can change it using xgamma -gamma 2.2
Interesting issue because the default pregamma and gamma value on blender yafaray exporter for linux is 1.8 and i didn't change it! :(
I was cheating yafaray :oops:
I will try to render them now with pregama and gamma same as default ubuntu value of 1.

wizofboz wrote:Textures are converted to linear gamma according to the gamma input value. Yafaray actually expects to use linear textures when rendering, so instead of converting each texture manually you can set the gamma input to 2.2 (or whatever gamma you use) and yafaray will automatically convert from that gamma value to linear.


Cool feature. People should debate it more often. I was afraid I had to use image magick! :)
Yafaray saves everyone time! :D
So, if I want a linear workflow is easy
xgamma -gamma 1 in command line
pregamma 1 in yafaray exporter
output gamma 1 in yafaray exporter
8)

wizofboz wrote:If you are saving to an 8-bit format like png and you want a gamma-corrected render then you will set gamma output to 2.2 or whatever gamma value you want the render saved with.


Ok, that's a tonemap feature.
I think i prefer luminance for that, but that's a cool feature of yafa.

wizofboz wrote:But I agree with you that an 8-bit format is not very suitable for tonemapping, so you should use a 32-bit float format like exr instead. In this case, if you render into the blender image editor then you will want to explicitly set gamma output to 1.0 (of course leave gamma input at 2.2). Your render will seem very dark when you render this way but don't worry, it will be fixed in the tonemapping phase.

Yes, very dark in windows because of their default 2.2 value ...Not in Ubuntu 8) because in Ubuntu it is by default 1.

wizofboz wrote:For the tonemapping itself I recommend the Reinhard05 method in Luminance HDR (was qtpfsgui), or use the tonemapping node in blender (it uses the same Reinhard algorithm). I guess the tonemapping itself is already discussed in this thread.

Yes, clearly discussed! :)

Thank you very much for your clear explanation!
Linear Workflow is a must!
But in Yafaray I see it is very easy to do it! :D
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Re: Tone mapping awareness-raising thread

Post Tue Jul 31, 2012 1:19 am

Arquitecto wrote:But Ubuntu pangolim default value is 1
I can change it using xgamma -gamma 2.2

- do you have a link, I'm not sure I understand this? Your monitor output will already be 1.8 or 2.2

Arquitecto wrote:Yes, very dark in windows because of their default 2.2 value ...Not in Ubuntu 8) because in Ubuntu it is by default 1.

I believe Photoshop tags .exr files as display gamma 2.2 - for your 'convenience'. It seems Adobe believes its users will become confused if float file formats should be gamma 1.0, so for the sake of 'consistency' they are all given a display gamma of 2.2. (This can make life more complicated if you share files between Windows and linux, and indeed can cause banding. If you use Photoshop to edit .exr you can turn off colour management, though this may not be possible with recent versions. You can leave it on for other file formats.)
However I find on linux .exr files are correctly handled by all applications with support for them.

But your monitor output should already be 2.2 and it would be a mistake to work with it set to 1.0. It makes much more sense to gamma correct the image when saving down from linear to rgb.

I would recommend if you are calibrating your monitor and intend to display work on the web calibrate for 2.2. I would also recommend you assign an rgb profile to images before uploading to the web. You can also colour manage Firefox with the colour management addon - https://addons.mozilla.org/en-US/firefo ... anagement/ It is fairly simple to do it manually, but the addon makes it easier. Just browse to your saved monitor profile. Don't forget to also point Gimp and Luminance etc to your monitor profile.

Colour management is almost as big a can of worms as gamma correction, especially since most rendering applications are not colour managed. I believe this is in development for Blender though. In the Tomato Branch iirc ?
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Re: Tone mapping awareness-raising thread

Post Tue Jul 31, 2012 10:37 am

Thanks Condar, i agree.
:oops: Oops
I discoverded that Ubuntu default gamma value is not 1.
It seems that xgamma outputs 1 but not the actual gamma value of the os.
On ubuntu I have my monitor calibrated and it seems that I have correct results when I give yafaray the pregamma and output gamma value of 2.
On windows 2.2 seems perfect.
Can anyone confirm the default gamma of 2.0 under ubuntu? Where can I confirm this?
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Re: Tone mapping awareness-raising thread

Post Tue Jul 31, 2012 12:00 pm

I don't really want to give advice as I don't feel qualified, but I have found it may depend on the monitor whitepoint settings. I use dispcalgui, and calibrating with whitepoint D55 I get gamma 2.2, though with D65 it is 2.6.

As I said, its not an easy subject. With Dispcalgui in Tools you can create a report on the calibrated and uncalibrated device. I think it is best to base the calibration on gamma 2.2. I know that linux used to use 1.8, but I have heard since that that is no longer the case and an output gamma of 2.2 is the default now.

I was asking around recently as I am only just beginning to use colour management and opened a thread at cgsociety:-
http://forums.cgsociety.org/showthread. ... &t=1061807

The links provided there to opencolorio.org seem overly complex but maybe they are of some use.
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