Update, June 2022: this solution is now broken in the latest G’MIC, due to regrettable changes in the required filter. Should work on G’MIC 3.0.x or lower.
I’ve found a way to just about emulate the Topaz Clean 3 Photoshop plugin, using the free G’MIC filter set in its new Photoshop .8BF form. Since G’Mic also runs on Paint.NET and PhotoLine, it will also work there. I can’t vouch for Krita, as Krita bundles its own variant of G’Mic.
Why is this needed? Because Topaz Clean 3 is no longer sold. Clean was unique and useful for 3D comics people, old manga scanners, and those who wanted to perk up character screenshots from The Sims etc. My specific use case is filtering a ‘colour flats’ base render from Poser, which could be very nicely de-grunged with Clean 3.1 in Photoshop.
This is as close as I can get in 2021 to Clean 3. It uses G’MIC’s standard Artistic | Comic Book filter with the sliders tweaked as you see below. There is also a comparison with the original and the old Clean 3 result. The original render had already been taken some way by using a flat IBL light in Poser, but still had unwanted grunging and speckling.
Pretty close, but there are drawbacks:
1. It takes a long time to run, 60 to 80 seconds on a workstation. Compared to a much more nippy 15 to 20 seconds for Topaz Clean 3.1.
2. You cannot take the Comic Book lines off altogether. Their lowest setting is locked at 0.5. This matters little, however, as you’re going to drop a real-time lineart render on top.
3. There are still some artefacts, that seem like posterization of the colours, here and there. Topaz Clean smoothly cleans them away, but G’MIC doesn’t.
But there you go… if you need free and no longer have Topaz Clean 3 for some reason or can’t (cough) find a copy, then this should help with the degrunging job for 3D comics when using layers (colour flats / details / lineart / shadows, all on their own filter-able and editable layers).
And it can do so in a more satisfactory way than the obvious and cringe-y ‘Posterized in Photoshop’ look, or by applying some swirly-blurry mess-filter that destroys edge details. The aim here being to somewhat emulate the crisp ‘paint-bucket’ flats that a professional comic-book colourist might start the colouring process with.