ACESCG and SRGB Questions - Texture Asset Creation

[ChrisBrejon (Christophe Brejon)]

Hello @jomallord,

here are a few tips :

@jomallord

Is it correct to say that OCIO-ACESCG color space will make my “color grading, highlight and shadow recovery” more “easy and doable” because I have a bigger gamut range with acescg versus srgb.

It is not correct to say that. Working in ACEScg will give you access to wider primaries in your working space, allowing for a better GI overall and more saturated colors.
The highlight and shadow behavior mostly comes from the Output Transform, not from ACEScg.
You have two possibilities when it comes to choosing your working space for your textures :

1. Keep in Linear - sRGB if your DCC application / render engine can convert on the fly like Maya/Arnold for example.

2. Convert your color maps to ACEScg prior the rendering phase if your rendering engine has not implemented the IDT, like Redshift for example.

Here is a thread on this topic :

How can I convert 200+srgb image or 1000+HDRI to ACEScg in same time?

The reason I don’t want to convert automatically in software, because if I want to set textures to the right colorspace, I have to handle manually in Houdini. Right? If all my local asset library files are already converted to ACEScg colorspace, then I don’t have to manually divide which ones belong to Utility-sRGB-Texture, which ones belong to Utility-Linear-sRGB, which ones belong to Utility-Raw every time.

@jomallord

Now it makes me wonder, most of the people were saying that using OCIO-ACESCG colorspace will make the color map darker and “less” saturate

Converting a sRGB texture to ACEScg will make it darker and less saturated since ACEScg has wide primaries and a linear transfer function (versus SRGB primaries with a sRGB transfer function). But you would also have to display it properly (using an ACES ODT). This is why we should be careful with the above statement and should not display ACEScg textures with a simple sRGB nuke viewer.

@jomallord

Maybe what they meant to say is the “viewer transform”? My viewer is indeed much darker and less saturate when using OCIO-ACESCG colorspace versus the normal srgb of nuke.

If I have understood correctly, you are comparing the sRGB (ACES) ODT versus the sRGB viewer of Nuke. It is completely normal that sRGB (ACES) looks darker since it includes some tonemapping. If I may, I would avoid to use the sRGB viewer of Nuke on CG renders since it does not include any intensity mapping. I think this is well explained in the posts you sent and on my website as well.

The settings you sent in Nuke are both correct. You have now to make a choice between which workflow you want to use.

@jomallord

For the conversions, do I need to use the “OCIO ColorSpace node” to convert my input sRGB color maps (from reality capture) into ACESCG before I can start to process and color grade it? Because if I use the OCIO ColorSpace node, my Color map will be super super dark and unworkable in the Viewer.

This is a common mistake. You do not need to use the OCIOColorSpace node to convert to ACEScg. The IDT already does that. So you would have a double transform. Hence a very dark texture. The IDT, if set correctly on Utility - sRGB - Texture will convert to your working space, aka ACEScg.

@jomallord

I cannot find any thread that directly answers the question - Do I need to use “OCIO ColorSpace node” to process (grade, exposure adjustments etc…) my color map inside Nuke?

No you don’t need it. We have seen a Youtube video a year ago or so that was claiming it. This is pretty much incorrect as you would be having a double transform.

@jomallord

Is that the proper workflow in ACESCG? At first, I thought that nuke is doing the conversion automatically after changing to OCIO-ACESCG colorspace and using Utility-SRGB on the “Read Node” of the color map.
So using a separate OCIO ColorSpace node will “double” the conversion that results to a very dark image? Or maybe my color map is just too dark and is out of the proper albedo range for a PBR workflow (well, I also need to look for these correct albedo range values as I always read it on other threads but no one is posting the “actual” range for people to see.

I have posted a couple of charts for ACEScg albedos if I remember correctly. And your intuition was correct : no need for OCIOColorspace node. If I may, I would avoid using the term OCIO-ACESCG colorspace. They are two different things. OCIO is the “how”, ACES is the “what”. You can just name the colorspace ACEScg or AP1.

@jomallord

It’s 4 different images… I can see that using “Output-SRGB” colorspace on the write node will give a much darker image BUT based on the threads that I have read, people are saying that I should be using Output-SRGB to render my maps as this is the part on the ACES workflow

No no no ! Never render you maps/textures using Output - sRGB. This is for final renders only. What you should do is display you textures with sRGB (ACES) ODT to assess properly their range. But never ever write your textures with the ODT in it.

@jomallord

where the maps are getting converted back to SRGB colorspace to be displayed on the “output device” like monitors.

The ACEScg renders do need to go through the sRGB (ACES) Output Transform to be displayed properly on a sRGB monitor. You can also display your textures with sRGB (ACES) ODT to check them. But never write textures using Output - sRGB, you would burn the tonemapping inside the texture.

@jomallord

What do you think of my color map though?

Honestly it looks fine. I can see that @MrLixm already gave you some pretty good answers. I hope I am not confusing more with mine.

@jomallord

I wanted to use JPG format with my color maps (because of small file size). Looking at this awesome thread. I presume he is referring to a JPG color maps for texture that uses Utility - sRGB inside Maya.

You are presuming right. But I am using flat primary colors here, for a simple cornell box test. Many studios have switched to linear exr textures for all their maps. From the tests we have been doing, it was actually more efficient in terms of memory than tiff or png.

@jomallord

Sorry if I’m misunderstanding, but are you saying that I should not use JPG format as my exported image if I’m gonna use ACESCG as working space in nuke?

You can write a jpg texture file using Utility- sRGB -Texture to then load it in maya as Utility - sRGB - Texture. Or write an ACEScg exr file to load it in Maya as ACES - ACEScg. Never use Output - sRGB to write a texture.

Regards,

Chris