Highlight Compression & Tonemapping

[leehenshall]

Hello just a few questions regarding tonemapping in Octane.

Are you able to provide more information about what Octane is using for highlight compression?

Is highlight compression using Global Reinhard similar to many post process tonemappers?

Does the highlight compression attempt to de-saturate the highlights like some post processing tonemappers.

It would be nice if Octane could output a LUT from the imager node that could be reapplied in comp. Is this possible?

[sigurdhoeyen]

I was just about to aske the same questions, would be nice to get some more info on this since I find it really hard to get accurate colors when using highlight compression.

[milanm]

It is definitely not Reinhard. It looks like an Exponential tone mapping operator.

I was able to get very very close using this in all three channels in the Fusion custom tool: 1-(e^(-(c1/0.99))) + Linear to sRGB transform after that. The difference is very subtle. Octane Imager is clipping the highlights a little bit and both are equally horrible at handling saturated colors in highlights (notice the floor turning yellow).

This is the general formula:
https://www.desmos.com/calculator/lr5ive07lv

I used HDR texture from Maxime Roz as Environment map with power set to 1 and rendered untonemapped and tonemapped version using Exposure 1, Gamma 1 and sRGB tone response settings and a ridiculously high max sample value.

Camera Imager with Highlight Compression set to 1:

Exponential TMO:

I hope this helps.

Cheers
Milan