A simple way to good results with physical sky.

[ghostlake114]

Sorry but doesnt your method bring gamma correct in lense shader = 1 and let the gamma of texture alone.

If you do that because of just want to preserve the color swatch, I see you are doing sth nonsense by let the mia_simple at a value affect nothing to scene. So why not you remove it :shrug:, It play no role in scene as I see.

The gain, or like mia_photo shader is some kind of physical camera. If in physical sky shader, we must have just kind of tonemap/filter light before it go to light because the sun and sky is very bright. And with a very bright light source, it make sense if we make fstop and shutter change, it affect much to the final output.

The advantage of linear space (Gamma 2.2) has been discuss too much. It really make your final mood of your render smoother. And you do nothing but return to the normal way with gamma = 1, and use a lower value of physical sun to make it less bright.So, sorry, I see your network is much complex,more tweak but solve nothing

[davegreenwood]

Absolutely, this is not the best way to go about it, but it is one way to tie all the values together, and achieve predictable results. You gain visual continuity with file textures, procedural textures and colour swatches with a quick set up. I left the mia_exposure in the network so tonemapping is still available (ie. compression >0) you can also mix in surface shaders with your scene, and if you need to do that you cant use tone mapping anyway (not if you want in value to equal out value). It is a quick cheap trick... but in the end its better to de-gamma all your shaders so all the render values are derived in linear space. This would also be true of every maya scene, not just those with physical sky.
Dave

[davegreenwood]

Here are some comparison renders:

as in my first post:
link (http://picasaweb.google.com/dgrnwd/Cgtalk/photo#5203629691420804466)

then remove the gamma node on the physical_sky, with the file textures gamma corrected, with mia_exposure gamma 2.2:
linear1 (http://picasaweb.google.com/dgrnwd/Cgtalk/photo#5203629691420804482)

then with some further gamma correction on the reflection atributes:
linear2 (http://picasaweb.google.com/dgrnwd/Cgtalk/photo#5203629695715771794)

and finally the gain correction is swapped back into the mia_exposure, and the physical_sky has its multiplier set to 1.0:
gain (http://picasaweb.google.com/dgrnwd/Cgtalk/photo#5203629695715771810)
its interesting to note that this makes no difference to the physical_sky.

to compare the results of the first image, with the linear workflow images, there is clearly a difference in highlight rendition. I don't know but I put this down to the 2+2 =10 factor in the first image. It could also be the rounding off difference when de-gamma-ing various nodes. When trying to linearise the shading network, it's necessary to compensate every contributing attribute of every shader... quite a task. In this example the reflections don't end up the same, and it's not clear why. All said though, what differences there are between the first and last example are quite small, and either one could be made to look like the other with a little tweak. I've left compression at zero all through these examples, but it's equally useful in both set-ups.
Anyway hope it helps someone.
Dave.

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