Gamma of material preview doesn't match final render

[Micha]

Hi,

a long time problem - the material preview doesn't show the texture gamma like the final render output. So, it's difficult to adjust materials.

Ciao,
Micha

[fpedrogo]

Can you show me some images of what you mean?

[Micha]

Example:

(a) gamma 1 means no additional correction (global LDR/color correction is enabled for gamma 2.2)


(b) gamma 0.45 means gamma correction for 2.2 gamma


In both cases the final render output is the same, it are the two ways for Gamma 2.2 correction. That's fine, but the material preview of 0.45 looks much to dark.

[fpedrogo]

Umm, the final result should be different too. If the final result is the same, then it is a bug. I will test this here.
Thank you!

[fpedrogo]

Hi Micha
I tested it and it is an issue if you are using the old gamma corrected method. Why you don't use Linearworkflow? Linearworkflow is easier and more precise than correct LDR texture and correct RGB color. I would like to understand better why you still using the old method, but I'll report this, so we could fix it.

[Micha]

Hi Fer,

I don't used a gamma 1 output, since I use the frame buffer for fine adjustment of contrast/brightness/dynamic and so the 8bit output is quite good. The linear workflow is good for HDR output and HDR postwork, right?

[fooprobe]

Yeah I have a hard time understanding how linear workflow is easier if you are not doing HDR output. But I'm very open to changing my mind, so please advise.

also, the tooltip for linear workflow advises that it is the old way of doing things, so I'm confused. Please enlighten.

[mikel.jagan]

The "Linear workflow" box in the Color Mapping roll-out should be considered more of a correction utility for scenes that were created not using a linear workflow method -- it's not that it's out of date, just an option for older scenes not created with Linear color mapping.

Proper linear workflow can affect the secondary ray sampling/illumination and final color output.

Type: Reinhard
Multiplier: 1.0
Burn value: 1.0
Gamma: 2.2
Input gamma: 2.2

Affect background: Checked
Don't affect colors (adaptation only): Checked
Linear workflow: Checked

Note: Enable "sRGB" in the frame buffer if using "Don't affect colors (adaptation only)".

If "Don't affect colors (adaptation only)" is checked, you will need to enable "sRGB" on the frame buffer to see the correct 2.2 gamma exposure in the frame buffer, otherwise it will appear under-gamma. This is recommended because when you open your .exr file in Nuke or Photoshop, what you saw in the Frame Buffer will be what you will see in Nuke/Photoshop.

If you would prefer to do the gamma correction yourself in Nuke/Photoshop, keep the workflow above, but uncheck "Don't affect colors (adaptation only)" -- you will need to disable the "sRGB" button if that is un-checked to display the correct gamma in the frame buffer. Now when you save your .exr your image will come into Nuke/Photoshop over-gamma, but you will now have the ability to add your own gamma 1.0/2.2 (0.4546) gamma correction node/layer.

Edit: Of course if you save a .png or .jpeg the proper gamma will be baked in regardless of whether "sRGB" and "Don't affect colors (adaptation only)" is checked or unchecked. This is because these files are not 32-bit files and it will not matter.

[Micha]

Hi Mikel, thank you for insight in some options I never understand and used before. I will play with it in the next time.

[mikel.jagan]

No problem.

[fooprobe]

The "Linear workflow" box in the Color Mapping roll-out should be considered more of a correction utility for scenes that were created not using a linear workflow method -- it's not that it's out of date, just an option for older scenes not created with Linear color mapping.

Proper linear workflow can affect the secondary ray sampling/illumination and final color output.

ok, I'm following you so far, but if that's the case then why

Linear workflow: Checked

?????

if the "linear workflow" box is a correction for "scenes not created using a linear workflow method", why do you turn it on for scenes using "proper linear workflow"??

what exactly does this checkbox do?

[fooprobe]

Also, if I follow the checklist in your post, some LDR colors don't look right in the frame buffer (and of course not in an 8/16 bit format either). So if I'm not going to save as 32 bit, what settings would you recommend?

[fooprobe]

so for instance, here is a render with linear workflow checked on the right (settings shown), and with it NOT checked (and LDR/RBG checked) on the left:

as you can see, the saturation with linear workflow is completely wrong. it's not the 0.8 burn value btw, i checked

what am i doing wrong?

here's a link to the packed scene:
https://www.dropbox.com/s/ro2swg5te6...t%201.zip?dl=0

thanks

[mikel.jagan]

fooprobe,

In addition to correcting older scenes, the "Linear" workflow" check-box also inverts (0.4546) the gamma 2.2 curve to bring it in line with the linear gamma 1.0 curve. It gamma corrects both the colors and textures in the scene.

The alternative method to this would be un-checking this box and inverting the color on your textures and color one at a time, using the two check-boxes beneath that; Correct LDR textures -- which only inverts the curve for textures using the "Input gamma" value -- and the "Correct RGB colors", which inverts the gamma for your diffuse colors only. Having "Correct LDR textures" and "Correct RGB colors" enabled gives pretty similar results to just having the "Linear workflow" box checked, once again, "Linear workflow" will do both texture and color corrections at once.

And for good measure, to clear up any confusion about these three boxes:
- If "Linear workflow" is ticked, "Correct LDR textures" and "Correct RGB colors" should not be ticked.
- If using "Correct LDR textures" and "Correct RGB colors" boxes, "Linear workflow" should not be ticked.

The difference in using these is one method uses the sRGB curve and the other uses the gamma curve. You may see some differences in some scenes.

[mikel.jagan]

Hi again,

We took a look at your scene with the settings you have set. You're not doing anything incorrectly. You'll notice if you do an A:B comparison between your two renders that the diffuse colors are the same. What seems to be happening is the difference between the gamma curve with LDR/RGB boxes ticked and the sRGB curve using Linear workflow on your background, are massive! In this situation, it is better to use the LDR/RGB boxes. This seems to occur more often in interiors, something worth noting. For things like product design/jewelry etc. there may rarely ever be such a drastic difference in colors like this scene shows.