Gamma Correction... the correct way?

IsaacNewton

I'm looking in to Gamma Correction (GC) and I'm a bit confused; perhaps some knowledgable person could advise me?

I was reading an interesting post by Parris which can be found here: https://www.daz3d.com/forums/discussion/54913/approaching-realism-in-daz-studio-and-gamma-correction-demystified/p1
In the first page of this thread, the forth post, Parris explains how to use GC. He (or she) states that GC should be applied (at a value of 2.2) in the Render Settings and also on the diffuse input image (texture) via the DS Image Editor. Parris explains that applying GC at 2.2 on the input image tells the Renderer to apply an anti-GC to the input image so that the input image can mix correctly with light and shadow and won't be brightened twice. (see the attached image)
To me this seems ilogical (if anti-GC is required on the input image to compensate for the GC on the output, then why put GC on the output in the first place, and why would a GC value of +2.2 on the input image result in a negative or anti GC?), however, I accept that this is probably because I don't understand how the GC is being applied and how it all works.

Assuming Parris is correct (and I do), the next question is why is the default value on all input images (eg diffuse texture) set to 0.0? Surely, if the input image GC value needs to be set to 2.2 then that would be the default value. Further is there any way of setting the default GC value on all input images (for the diffuse texture) to 2.2? Please don't tell me that each diffuse texture in a scene has to have it's GC set to 2.2 individually manually.

Richard Haseltine

They are two separate operations. Telling the renderer that the colour (as opposed to cotnrol) maps were created at gamma 2.2 (which is probably correct) allows it to linerarise them, for best results when rendering.

After rendering you can aply a gamma correction (usually 2,2) to the final output so it looks good - otherwise it's likely to seem unduly dark. Applying the post-render gamma correction in DS is a good idea as it is still working with an extended colour depth, but if you save as a regular image (rather than using a canvas to produce an .exr) then apply gamma correction (or use other tonal adjustments) in an image editor the result will be some level of posterisation.

IsaacNewton

Hi Richard, are you saying that the input diffusion texture only needs a GC of 2.2 applying if it was not created with one? How would I know whether the original diffuse texture has/had a GC applyed?

If the diffuse textures do not have a GC and I must/should apply the GC myself in the Image Editor, how can I do that automatically so that I don't need to change every single texture separately and manually?

Richard Haseltine

Most images that are created to look right in an image editor or viewer, or to render correctly with the default or no colour management settings, will have an effective gamma of 2.2. In the unlikely event that you do get an image that wants a gamma of 1 but is in colour on a colour proeprty you will ahve to edit its gamma value - but such things are likely to be very rare.

IsaacNewton

OK, so best option is to leave gamma correction alone unless the rendered textures look too dark, in which case the gamma correction on the input diffuse texture may need to be changed one by one. I'm not sure if it is easy or worth the effort to implement but in the latter case a master slider in the Surfaces tab to change GC for diffuse textures would be useful.

Padone

Just to add that also it is important to calibrate your monitor for srgb space that's gamma 2.2, otherwise you will not get the right perception of colors and contrast. Many modern monitors, especially with va and ips panels, may have a srgb preset that's calibrated from factory.