ACES way to control how much the highlights gets compressed?

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Re: ACES way to control how much the highlights gets compressed?

Postby SSmolak » Thu Aug 11, 2022 5:28 am

SSmolak Thu Aug 11, 2022 5:28 am
At last I found final solution to use ACES in all lighting conditions in Octane. It produce perfect equalized gamma and vivid colors as should be. Without dark, shadow clipping areas. And all of that saved using native ACEScg file.

The problem : ACES was developed for real cameras which works in real lighting conditions where outside light intensity produced by direct sunlight or scattered light in atmosphere is hard to achieve without exposure system which works only for point of view or averaging whole view.

This is why images or film stored be real cameras works fine with ACES. In computer generated images where we works with artificial light conditions especially architectural visualizations ACES produce very dark and even clipped ( RGB 0,0,0 ) areas.

I think that CGI generated skies like Hosek&Wilkie or HDRI maps are not compatible with ACES system.

Solution :

To compensate darkness there is need to crank up sky power to values near 8 but it produce problems with materials.

I found that for ACES default Hosek&Wilkie values are wrong. Strenght of Sunlight should be much lower than power of Sky. This will produce much less dark shadows and overall brightness would be better. But this is not final solution.

The best is to crank up camera exposure by 600-800% and lower overall Sun and Sky values by 70-80%. This will produce perfect equalized gamma with great highlight compensation without any badly darkness but still with the most darknened areas at RGB 0,0,0 where they should be.

For example. When I use for my most strong sunlight exteriors Sky power at 4 and Sun power at 1.25 I must crank up camera exposure to 6-8 and lower Sky power to 1 and Sun power to 0.5-75 to make ACES looks perfect. Without changing any material parameters.
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Re: ACES way to control how much the highlights gets compressed?

Postby sethRichardson » Fri Aug 19, 2022 7:02 pm

sethRichardson Fri Aug 19, 2022 7:02 pm
SSmolak wrote:At last I found final solution to use ACES in all lighting conditions in Octane. It produce perfect equalized gamma and vivid colors as should be. Without dark, shadow clipping areas. And all of that saved using native ACEScg file.

The problem : ACES was developed for real cameras which works in real lighting conditions where outside light intensity produced by direct sunlight or scattered light in atmosphere is hard to achieve without exposure system which works only for point of view or averaging whole view.

This is why images or film stored be real cameras works fine with ACES. In computer generated images where we works with artificial light conditions especially architectural visualizations ACES produce very dark and even clipped ( RGB 0,0,0 ) areas.

I think that CGI generated skies like Hosek&Wilkie or HDRI maps are not compatible with ACES system.

Solution :

To compensate darkness there is need to crank up sky power to values near 8 but it produce problems with materials.

I found that for ACES default Hosek&Wilkie values are wrong. Strenght of Sunlight should be much lower than power of Sky. This will produce much less dark shadows and overall brightness would be better. But this is not final solution.

The best is to crank up camera exposure by 600-800% and lower overall Sun and Sky values by 70-80%. This will produce perfect equalized gamma with great highlight compensation without any badly darkness but still with the most darknened areas at RGB 0,0,0 where they should be.

For example. When I use for my most strong sunlight exteriors Sky power at 4 and Sun power at 1.25 I must crank up camera exposure to 6-8 and lower Sky power to 1 and Sun power to 0.5-75 to make ACES looks perfect. Without changing any material parameters.



Ya but at that point, you have moved so far away from those models and what makes them realistic that getting good repeatable results as you would with a photographic approach is out the window.

Aces is overrated and for most artists just a plain bad idea. And you illustrated a very good reason as to why it's bad. It's not just those sky models either. It's blackbody lights, gaussian spectrum lights.... those all are incorrect in aces. You get a far better more real result out of a filmic ocio plain and simple.
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Re: ACES way to control how much the highlights gets compressed?

Postby SSmolak » Fri Aug 19, 2022 7:11 pm

SSmolak Fri Aug 19, 2022 7:11 pm
sethRichardson wrote:Ya but at that point, you have moved so far away from those models and what makes them realistic that getting good repeatable results as you would with a photographic approach is out the window.

Aces is overrated and for most artists just a plain bad idea. And you illustrated a very good reason as to why it's bad. It's not just those sky models either. It's blackbody lights, gaussian spectrum lights.... those all are incorrect in aces. You get a far better more real result out of a filmic ocio plain and simple.


Yes... I lost days, weeks to found some solutions without the need of intense post processing. ACES can be easy for some scenes but for my work it introduce many issues. I went out to make some photos using real cameras and recreating them in Octane using ACES. I compared colors by color picker, tried many things without success. The worst in ACES is how it treat low and low-end colors gamma. I have good calibrated monitor I can see low-end spectrum without problems. But Aces introduce that mid brightness is way too far from low ones also with color shift especially on blues. I have bad colors in shadows on contrasty scenes.

At the moment I'm very impressed with Sobotka's AGX Punchy version. But it needs more power from lighting - it is very good for creating natural bright scenes with great contrast.
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Re: ACES way to control how much the highlights gets compressed?

Postby sethRichardson » Fri Aug 19, 2022 7:50 pm

sethRichardson Fri Aug 19, 2022 7:50 pm
SSmolak wrote:
sethRichardson wrote:Ya but at that point, you have moved so far away from those models and what makes them realistic that getting good repeatable results as you would with a photographic approach is out the window.

Aces is overrated and for most artists just a plain bad idea. And you illustrated a very good reason as to why it's bad. It's not just those sky models either. It's blackbody lights, gaussian spectrum lights.... those all are incorrect in aces. You get a far better more real result out of a filmic ocio plain and simple.


Yes... I lost days, weeks to found some solutions without the need of intense post processing. ACES can be easy for some scenes but for my work it introduce many issues. I went out to make some photos using real cameras and recreating them in Octane using ACES. I compared colors by color picker, tried many things without success. The worst in ACES is how it treat low and low-end colors gamma. I have good calibrated monitor I can see low-end spectrum without problems. But Aces introduce that mid brightness is way too far from low ones also with color shift especially on blues. I have bad colors in shadows on contrasty scenes.

At the moment I'm very impressed with Sobotka's AGX Punchy version. But it needs more power from lighting - it is very good for creating natural bright scenes with great contrast.


That and if you ever work in the product design industry where you are creating product renders along with photographic assets with specific industry standard colors such as Pantone's, ral etc etc. You will NEVER match those colors in aces without having to run everything through a tedious post-production color pipeline where in a filmic pipeline those colors aren't getting destroyed.

The only place I see where aces makes sense is in large studio productions where they have teams of color artists doing post-work on 3d rendered footage and matching live sequence footage. Outside of that I encourage people to just not bother with it. Since Filmic gives what artists are after anyways.
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Re: ACES way to control how much the highlights gets compressed?

Postby SSmolak » Fri Aug 19, 2022 8:26 pm

SSmolak Fri Aug 19, 2022 8:26 pm
I had the same issue in archviz render where client had problem to recognize wall brightness and color from RAL system because on strong sunlight and contrasty scene it was too bright on the front exposed directly to sunlight and very dark on shadow area. Reducing sunlight introduce underlighting under balconies and increasing sky power increase overall scene brightness not only on shadow area. Also it needs to rebuild vegetation materials that are sensitive for lighting. Also crazy colors in window reflections.

No way :)
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