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Contrast on linear floating point images

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Johan Boekhoven

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Contrast on linear floating point images

PostMon Aug 06, 2018 10:37 am

Hi,

Is it me or is grading and particularly tweaking contrast very hard in Fusion atm?
If I take linear 16 or 32 bit float exr's and pull on contrast the thing goes haywire fast, I can only use very low numbers like 0.0025 and so on to do anything with it. At the moment I even try to stay away from contrast at all and use gamma or curves to tweak stuff.

Is the color logic for linear floating point images wrong? If I add a color space (sRGB) node it behaves better, but then I don't have linear space color math (like layering lightpasses).

Is Fusion just not capable or am I doing it, or understanding it wrong?

Thanks!
-Johan
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Bryan Ray

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Re: Contrast on linear floating point images

PostMon Aug 06, 2018 5:39 pm

Yeah, the Color Correct, Luma Key, Ranges, and possibly a couple of other tools were built before linear color processing was common, so they work best on sRGB or 709 images. You can bracket your linear image between two Gamuts: convert to sRGB, Color Correct, then back to linear.
Bryan Ray
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MikeRochefort

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Re: Contrast on linear floating point images

PostTue Aug 07, 2018 1:26 am

If that’s not rectified in Fusion 10 or FuVinci, I think I’m going to have to book a plane ticket to Australia... ;)

Cheers,
Mike
https://michaelrochefort.com/
3D Lookdev, Compositing, and Sysadmin
Fusion Studio 9.0.2
DaVinci Resolve Studio 15.1.0.25
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Bryan Ray

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Re: Contrast on linear floating point images

PostTue Aug 07, 2018 3:27 am

Well, it's been 15 years since Stu Maschwitz started blowing the linear horn, and it hasn't changed in the 5.5 versions since then… I wouldn't hold my breath. Make a macro. Takes 15 seconds and you never have to deal with it again.
Bryan Ray
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Chad Capeland

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Re: Contrast on linear floating point images

PostTue Aug 07, 2018 5:31 am

Contrast works as expected on linear images for me. Are you using a LUT to view your result?
Chad Capeland
Indicated, LLC
www.floweffects.com
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Bryan Ray

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Re: Contrast on linear floating point images

PostTue Aug 07, 2018 10:19 pm

Mathematically, the Contrast control works correctly on linear images. That is, it performs its work around 0.5. Visually, that tends to not look right, though, because 0.5 in lin is in the brighter parts of the image, not where we perceive "middle gray" to be. By converting first to sRGB, the center point of the Contrast will be around 0.2, which is much closer to the 18% we're used to calling middle gray.
Bryan Ray
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Johan Boekhoven

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Re: Contrast on linear floating point images

PostWed Aug 08, 2018 1:40 pm

(I didn't get notifications, sorry for not replying yet)

@Chad: I am using a view lut (sRGB) while I do my work. I'm under the impression it's the best way to work when in Linear Workflow mode. I understand I could convert in and out of sRGB while doing corrections, but that adds an huge amount of nodes, because I have 3d render layers, like lightpasses reflections etc. I add them all up in linear node to get the correct results and then I grade some lightpasses for example. Adding them together while all footage is converted to sRGB probably doesn't give the correct results. I want to be as accurate to the source footage as possible.

The question is then, what is "as expected", I guess.

So the fix could probably be a contrast bias slider or colorspace selector on the color tools. Because even if we can work around it with extra nodes, that is just that, a workaround and not at all (!!) a user friendly way of working and managing comps.

Thanks for your input, at least I know it isn't me :)

-Johan
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michael vorberg

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Re: Contrast on linear floating point images

PostWed Aug 08, 2018 3:57 pm

Your not alone, along time ago there was build a tool to help with contrast adjustment on linear images:
http://www.comp-fu.com/2010/11/contrast/

Download is now here:
https://www.steakunderwater.com/VFXPedi ... arty_Fuses


If you don't want to use the standard node or the custom one, there is always the option to use a color curve and make the adjustments where you want them
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Bryan Ray

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Re: Contrast on linear floating point images

PostWed Aug 08, 2018 4:29 pm

Johan Boekhoven wrote: I understand I could convert in and out of sRGB while doing corrections, but that adds an huge amount of nodes,


Seriously, make a macro! Okay, 15 seconds was a massive underestimation of how many controls are in a CC, but here:
Attachments
CC_in_sRGB.zip
(3.36 KiB) Downloaded 3 times
Bryan Ray
http://www.bryanray.name
http://www.musevfx.com
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Chad Capeland

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Re: Contrast on linear floating point images

PostWed Aug 08, 2018 7:26 pm

BC isn't meant for that type of work. Ideally, there would be a port of Resolve's color panel to Fusion, or a tool built more in the vein of doing grading work. The math on BC isn't meant to be based on anything remotely related to the HVS.
Chad Capeland
Indicated, LLC
www.floweffects.com
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Bryan Ray

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Re: Contrast on linear floating point images

PostThu Aug 09, 2018 2:40 am

But Color Correct is, and the Contrast control there works exactly like the one in BC. I'd love to see a "do this in gamma-corrected space" switch on some tools.
Bryan Ray
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Chad Capeland

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Re: Contrast on linear floating point images

PostThu Aug 09, 2018 1:20 pm

Bryan Ray wrote:But Color Correct is, and the Contrast control there works exactly like the one in BC. I'd love to see a "do this in gamma-corrected space" switch on some tools.


Agreed. The metadata tells the tool all it needs to know about the colorspace.
Chad Capeland
Indicated, LLC
www.floweffects.com

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