Why does tonemapped EXRs get clamped?

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Zom-B
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Why does tonemapped EXRs get clamped?

Post by Zom-B » Mon Jul 28, 2014 11:59 pm

I just noticed something that I wasn't aware of:

Tonemapped EXRs get clamped! Its like 8bit information only written in a 32bit file!
Isn't it possible to apply tonemapping without clamping all the extra informations?!

Indigos (camera) tonemapping is very well suited to achive a good look and a great start for doing final corrections etc.
But by dismissing all the extra image information we are forced to go for the untonemapped version...

Here are two example images (rendered using linear tonemapping @ 1), I just loaded both EXRs back into Indigo GUI:
untonemapped.jpg
tonemapped.jpg
Last edited by Zom-B on Tue Jul 29, 2014 2:53 am, edited 1 time in total.
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kklors
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Re: Why does tonemapped EXRs get clamped?

Post by kklors » Tue Jul 29, 2014 1:39 am

Noticed that too but never bothered enough and exposed them right out of Indigo. Not a biggie for stills, but wouldn't say no for full range on anims.

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Re: Why does tonemapped EXRs get clamped?

Post by galinette » Tue Jul 29, 2014 2:17 am

The camera tonemapping is based on measured, tabulated values about film response. And this tabulated data goes not beyond the clamping luminance threshold! So the tonemapper has no way of knowing how to handle values above this threshold...
If you want unclamped values, you should use the linear tonemapper

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Zom-B
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Re: Why does tonemapped EXRs get clamped?

Post by Zom-B » Tue Jul 29, 2014 2:42 am

galinette wrote:The camera tonemapping is based on measured, tabulated values about film response. And this tabulated data goes not beyond the clamping luminance threshold! So the tonemapper has no way of knowing how to handle values above this threshold...
The example images are rendered using linear tonemapping, and it gets clamped too :/

Is this limitation true for camera tonemapper or tonemapping in general.
Some non destructive adjustments regarding color, light etc. to the render output would be nice...
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Re: Why does tonemapped EXRs get clamped?

Post by galinette » Tue Jul 29, 2014 2:49 am

OK, in that case the linear tonemapper should not clamp EXRs, this would make sense.
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