Author Topic: Substance Painter: Filters for ACES rendering and Smart PBR conversion  (Read 501 times)

Two new filters to treat color textures in physical terms. PBR_SmartFit will automatically bring your albedo map into PBR legal range retaining source colorimetry, details and perceptual middle gray, it soft-interpolates the out-of-PBR side so the transform is smooth (no range clamp like "PBR Albedo Safe Color" node). The ACES_ACEScg filter will convert your color maps into the ACEScg color space (AP1 Primaries) which is a space that closely matches and encompasses the Pointer's Gamut, a reference gamut for real surface colors.
These two can be used separately or in conjunction which is the preferred method for physically accurate rendering. By feeding ACEScg maps into the Substance rendering engine the render output is in ACEScg color space so for that matter I made a new ACESFilm lut that converts the render scene-referred linear space to "Output - sRGB" display-referred space. So for all intents and purposes now we are rendering in ACES within Substance Painter. Substance Designer has to wait since currently there is no lut support.
*The ACES_ACEScg filter is based on an implementation of the work of Stephen Hill (@self_shadow).

Some details:

The ACESFilm lut that I shared 2 months ago, even the one updated a week ago, and Brian Leleux ACES lut usually produce dark renders, this comes as no surprise as we are applying the ACES RRT to textures that haven't been passed through an inverse RRT, which most IDTs (Input Device Transform) implement. The ACES_ACEScg filter does the inverse RRT hence we get correct exposure and light interaction.

Take note on your HDRI color space. This is something not usually known but there are hints. If it appears undersaturated most likely the HDRI is not in sRGB but AdobeRGB or RAW. In this case you can convert externally the HDRI from AdobeRGB to ACEScg, this is cumbersome but since the AdobeRGB space is just a bit smaller than the ACEScg if you like what you see you can get away without converting anything, specially when image desaturation is something also frequent when making HDRI in certain applications.

Download with instructions in my Artstation

Own model; 1) Default in SP, 2) with ACESFilm lut (too dark), 3) same but raising gamma (notice the gain in contrast for textures and washed out env), 4) render with ACEScg filter and ACEScg lut (correct exposure, texture and lighting)

Other examples of better light interaction using ACES

PBR_SmartFit: Automatic fit for several Albedo maps

Node tree for the main part of the PBR_SmartFit filter.

ACES test render in Arnold (surface shader) between illegal texture range (HDR), illegal PBR range (0-1), and legal PBR range. IDT and ODT "Output - sRGB"
Last Edit: April 29, 2019, 03:05:54 pm