Substance Painter allows to assign Color Profiles to the viewports by loading LUT textures.
A color profile can be used to calibrate the final color of the screen to match a target, such as a specific camera. Often a profile will manipulate colors by changing the brightness, the gamma, the contrast or even the color balance.
LUT stands for "Look Up Table". It is an optimized way of performing color grading as a post effect. A LUT is used to make up the difference between a source and a result.
Substance Painter use 3D LUTs stored as 2D texture (Floating) of any possible resolution (default are 2048x128 pixels). This means the cube storing the color operations is separated in slices which are displayed side by side. For more technical details, see the GPU Gem article : http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter24.html
Using a Color Profile
A Color Profile can be loaded via the Display Settings window.
Check the "Activate Color Profile" checkbox to affect the viewport and enable a Color Profile.
- When "Activate Color Profile" is disabled the rendering of the viewport is done in sRGB for the Material view (and Linear for some specific channels)
- When "Activate Color Profile" is enabled the rendering of the viewport is done in Linear/Raw for every view (including solo channels)
If a LUT texture is loaded in the ressource slot, then it will be used to manipulate the rendering of the viewport when in Material mode.
Otherwise the rendering will be displayed as Linear/Raw (for example with solo channels views).
The white point setting can be used to change the tone mapping of the input image (before the LUT take effect).
If you are looking at the sun for example, the value should be higher than 1 (default). For a perfect exposure, the white point must be set to the high value of the image.
The white point formula is as follow :
It is possible to apply a specific tone-mapping before using a the Color Profile. See the functions available in the Post-Processing system.
Substance Painter doesn't process the input color other than via the white point setting. There are no Shaper LUT applied for example.
Creating Color Profiles
Substance Painter will shift the viewport to Linear rendering when the "Activate Color Profile" is enabled. This means that when a LUT is applied, it needs to translate color from a Linear profile to the desired target.
Method 1 : Modifying the Identity LUT
Editing the identity LUT can be done in a software supporting 32bits floating textures, such as Substance Designer.
Download the attached identity LUT as a start point to make a new profile : linear_to_linear.exr
Method 2 : Using OpenColor IO to generate a LUT Texture
Install the OpenColor IO tools. Then download the Sample OCIO Configuration, available here : http://opencolorio.org/downloads.html
From there, run the ociolutimage program with the following arguments :
Note : It is also possible to modify the Identity LUT with OpenColor IO by using the ocioconvert program to apply color conversion to this lut.
Importing a new Color Profile in the Shelf/Project
Simply open the import window (or drag and drop the LUT into the shelf). When importing the LUT texture in Substance Painter, be sure to assign the "colorlut" usage to the new ressource. Otherwise the ressource won't be visible properly in the shelf.
For more information, see the documentation about the import of new ressources : Adding content via the import window