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Working with custom tonemapping
🕑 Added 2023-04-25 08:09:11 +0000 UTCWith the latest CSP preview we now have custom tonemapping support in Assetto Corsa. So finally we can overcome the limitations of built in Yebis functions, but more importantly, it is now possible to dynamically adjust the tone mapping function itself. Since getting my hands on previews recent enough to allow this functionality, i've been playing around with it. Initially i had the most success with the CSP built in Lottes function, which is similar to sensitometric in that it allows for rich contrast, but highlight saturation can be adjusted.
An example shot with the Lottes function that showcases very rich lows.
Initial results were promising so i dug into a custom implementation that would make dynamic control more straightforward.
I came up with this:
A short walkthrough:
p - controls brightness boost
h - controlls "HDR" - lowers contrast to boost dynamic range
s - fine tunes contrast
b - black level compensation
c - main contrast control
l - controls leveling out at high luma
d - enables smooth falloff
m - base multiplier
I suck at math. So don't take my word for all of this, these are my interpretations of how the parameters effect the curve. Which looks like this:
Essentially an S curve with a smoother falloff. But it can be made harsh, which was something i was playing with.
I was looking for something that would allow me to near crush blacks, but in a controlled manner. And I got fairly close.
ACT 2
Unfortunately after a fair bit of faffing about, I realised that the gains of this tonemapping are marginal, and the tradeoff is much messier code. So instead i opted to start over.
Since the first teasers about this custom tonemapping stuff came to my attention, there were hints about GT style tone mapping - especially since the GT function is apparently quite well documented, this seemed like a reasonable thing to do. But while there's no explicit GT function in the newest CSP, there are ways to add it. Beyond simply the technical and intellectual curiosity, what drove me towards a GT style tone mapping was something emotional. The very first non Sol filter that truly spoke to me, was Gran Turismo Sport by vatsky. It's likely this filter to which I owe my entire journey deeper into the modding aspects of AC.
So what's all this about this GT function then? Well:
Yeah i can't convert that into C++. But luckily, I don't have to. yaoling1998 wrote a unity shader that just so happens to fit the requirements of the new AC approach perfectly. You can find their work on GitHub.
So armed with this approach, and someone else's hard work, we continue our journey into custom tonemapping. Thus far the results are promising. Saturation seems easier to control, low end contrast is marginally lighter, giving light a softer feel, and night time light/dark relationships are ever so slightly more pronounced, giving a more dynamic feel.
Sensitometric:
GT:
Comparison
As you can see from the comparison, saturation is more tightly controlled, and the contrast is a pinch softer. I also need to figure out how glare works, as it seems much less pronounced overall.
I will be releasing a test version of this, but first the discord roles and such needs some work. I am grateful to all of you who have pledged any amount to support my work. I hope this is the beginning of a new chapter for C13 Automotive and i hope you'll join me in building whatever it is it becomes.
Cheers.
