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Extracting alpha changes alpha...

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Clayton Krause

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Extracting alpha changes alpha...

PostFri Nov 03, 2017 3:21 pm

Having issues with BLM Fusion 9 and extracting alphas with both Channel Bool and bitmap node. I'm loading a 32bit openEXR.

What I'm finding is that the alpha from the loader is changing on me when extracting it. See the photo below. Left is extracted alpha with Channel Bool and the right is the alpha that came in with the loader. Why the change in intensity?

Thank you for any help.

Image

Image

Image
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David_Cox

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Re: Extracting alpha changes alpha...

PostFri Nov 03, 2017 3:36 pm

Do you have a viewing lut enabled on the side of the monitor that is showing the boolean output? Just wondering if the RGB copy of the alpha channel has a gamma curve applied within the viewer?
DC
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Clayton Krause

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Re: Extracting alpha changes alpha...

PostFri Nov 03, 2017 3:39 pm

Yeah, I have an sRGB LUT. Followed these instructions on it-

http://www.comp-fu.com/2012/02/linear-gamma-workflow-in-fusion/

My output is all rendered output out of Vray and sRGB is big part of it.
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David_Cox

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Re: Extracting alpha changes alpha...

PostFri Nov 03, 2017 3:43 pm

If you have the LUT enabled on your viewing monitor (the little LUT icon is lit up under the viewer), then this will effect the view of the RGB channels, but not the alpha. So could it be that you are comparing a direct alpha channel with a copy of the same that has a viewing lut applied? If so, unchecking the LUT should show you that the alphas are the same.
DC
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Website: www.davidcox.tv
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Clayton Krause

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Re: Extracting alpha changes alpha...

PostFri Nov 03, 2017 3:49 pm

Wow. That was way too obvious... Thank you for the help! Since the LUT is just previewing the RGB in sRGB space and not actually backing anything, if I take that RGB of the alpha and reapply it as an alpha further down the node tree, it'll act appropriately, right?

It should as the LUT isn't really changing anything other than the preview. Thanks!
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David_Cox

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Re: Extracting alpha changes alpha...

PostFri Nov 03, 2017 3:56 pm

Yes that's exactly correct - the viewer LUT doesn't touch the data in your pipeline, other than just making a conversion for the purpose of the viewer. It's so we can run a linear image pipeline and still be able to see what we are doing on an sRGB / 709 / etc monitor without having to drop LUTS into the node area itself (which could be dangerous if we accidentally left them there!!)

If you want to render out a version as seen on your viewer, there is an identical colour space transform function under the saver's export tab.

DC
Showreels: vimeo.com/davidcoxtv
Website: www.davidcox.tv
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Clayton Krause

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Re: Extracting alpha changes alpha...

PostFri Nov 03, 2017 4:19 pm

Alright, that's good to know. Now while we are on the topic of LUTs and color space... I've been noticing that when opening up the fusion output in photoshop for further processing before handoff to our design dept, the colors and overall image doesn't look as crisp and juicy as it does in the Fusion image viewer window.

I'm exporting the same as what I'm importing. 32bit exr. Would you have any advice on this? It pains me to see a pretty decent image come out of fusion and get the definition sort of pooped on by photoshop.

I've actually noticed this happening directly out of my Vray Frame Buffer which also is able to work/display 32bit data. The image in photoshop loses it's "pop" even when opened as 32 bit depth in PS.

Great help! Thank you for your time.

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