Author Topic: Color clamp in EXR 32 bit  (Read 334 times)

Offline Aleksei

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Color clamp in EXR 32 bit
« on: October 27, 2017, 03:44:52 PM »
Hi!
I have a question which I couldn't find answer to for very long time.
When I render anything in 32bit EXR I have colors diferent from viewport render. Usually tone doesn't match. The colors look good in Render view window. And when I save render in 16 bit TIFF. I never succeeded to render anything with a proper colors in 32 bit.

For example, I rendered image to Render view window and then saved it to 2 different formats: 32 bit EXR & 16bit TIFF. The result you can see below very light areas clamp in EXR image.
How to fix this?


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Offline Matt

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Re: Color clamp in EXR 32 bit
« Reply #1 on: October 28, 2017, 12:23:41 AM »
The raw values from the renderer will often go above 1. EXR is a high dynamic range format that stores these raw values, representing the amount of light in the scene. Although it appears to clip in Photoshop, the file has more information in it. EXRs are not really supposed to be displayed directly on the monitor like a photograph; it's better to use them as raw data, and to produce a final output that looks like a photo you would normally have to do some kind of tone mapping like a camera would.

Terragen has some tone mapping options that are enabled by default. The Render View in Terragen shows the image with tone mapping. Terragen's tone mapping options include contrast (an s-curve), gamma and a highlight rolloff that we call "soft clip". When saving an image to a low dynamic range format like TIFF (where values must be in the range 0..1), Terragen saves the tone mapped image exactly as you see it in the Render View. You can turn off all the tone mapping options in the render settings and you'll get something that should look very similar to the EXR, with clipped highlights in the viewer.

If you want to reproduce this with an EXR in Photoshop, I'd suggest importing it with a lower exposure so that highlights don't clip, and then using curves to brighten the image with a curve that doesn't harshly clip the highlights.

Matt
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Offline Aleksei

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Re: Color clamp in EXR 32 bit
« Reply #2 on: October 29, 2017, 09:55:17 AM »
Now I see. Thanks for the clarifying.
In my case the problem was that I tried to edit 32bit image in Photoshop. But it seems to me that Photoshop doesn't have the tools for color correction of 32 bit images. Or they're not intuitive and I can't find them.
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Offline Oshyan

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Re: Color clamp in EXR 32 bit
« Reply #3 on: October 29, 2017, 07:24:31 PM »
Photoshop does have limitations on adjusting 32 bit images vs. 16 or 8 bit, though it's better in newer versions such as CC and 2018.

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Offline Aleksei

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Re: Color clamp in EXR 32 bit
« Reply #4 on: October 29, 2017, 08:09:03 PM »
I though so too, but, unfortunatelly, nothing changed in the latest release.
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Offline D.A. Bentley

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Re: Color clamp in EXR 32 bit
« Reply #5 on: November 08, 2017, 06:28:05 AM »
I though so too, but, unfortunatelly, nothing changed in the latest release.

Have you tried HDR Toning... under Image Adjustments?  If you convert a 32-bit EXR by changing to either 16-bit, or 8-bit channels, HDR Toning will automatically open.  Local Adaptation gives you a lot of control, but there are a few other options like Equalize Histogram etc..


Offline Aleksei

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Re: Color clamp in EXR 32 bit
« Reply #6 on: November 08, 2017, 08:27:54 AM »
Thanks, Bentley. I've tried it and it really has more controls rather than regular tools. But I'm confused with the sircumstances in which I can access the GDR Toning. I prefer to have these color correction tools without converting image to 16 or 8 bit depth.

But I've found 2 workarounds:
1. One of the most crucial adjustments for 32bit the white and black point control can be found in Exposure, here:



Some other controls like Hue/Saturation or Channel Mixer are also available there as well. The most of them are not that intuitive and all they must be applied separately as different effects, which is not comfortable. But this still works, if needed.

2. I've found out that if I want to make only a color correct (without retouching) then using After Effects or Nuke is much more convenient. They have the full range of controls over the 32bit images.
« Last Edit: November 08, 2017, 08:29:32 AM by Aleksei »
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Offline bigben

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Re: Color clamp in EXR 32 bit
« Reply #7 on: November 08, 2017, 09:01:35 PM »
I've used ColorPerfect for dealing with scanned negatives via Camera Raw.. It approaches colour/contrast correction differently, in particular adjusting contrast without altering colour. Demo is fully functional (adds a grid to the image) if you want to try it. I'll have a play later when I get back from camping trip to see if it takes EXR

Offline D.A. Bentley

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Re: Color clamp in EXR 32 bit
« Reply #8 on: November 09, 2017, 01:44:30 AM »
Aleksei,  I forgot to mention that you can use HDR Toning... in Photoshop without converting down to a lower bit depth.  You just go to Image -> Adjustments -> HDR Toning... and use it, and you can re-save your 32-bit image (EXR/TIFF/HDR/PSB).  ;)