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ab (Lab - L) as a layer in RGB file

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  #1  
Old 04-24-2015, 09:07 PM
Doug Nelson's Avatar
Doug Nelson Doug Nelson is offline
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ab (Lab - L) as a layer in RGB file

Where's Richard Lynch when I need him? He excelled at this sort of thing.

Not for any particular reason, more just to see if it was possible and what would happen, I'm trying to put just the a and b channels of an RGB file converted to Lab together as a single layer in the original RGB file, preserving their visual color data (as if you viewed the Lab version and turned off the L channel).

I know I'm missing something obvious, but I can't seem to get it done.

Any ideas?
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Old 04-25-2015, 02:44 AM
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Tony W Tony W is offline
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Re: ab (Lab - L) as a layer in RGB file

Try Edit /Select All/ then copy on the a and b channels Then in your RGB version add a blank layer then paste the copied a and the same for b.

Depending on your blend mode the a and b channels will act as a mask and mute or accent the underlying colour and contrast
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Old 04-25-2015, 05:10 AM
genf genf is offline
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Re: ab (Lab - L) as a layer in RGB file

Here is a different procedure.
Starting from the LAB version, select the L channel and Edit - Fill 50% Gray. Show all channels, you will see the AB information only.
Then Select All, Edit - Copy and paste into the RGB version.
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Old 04-25-2015, 10:27 AM
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John Wheeler John Wheeler is offline
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Re: ab (Lab - L) as a layer in RGB file

Hi Doug
Here is a third way

- Turn Layer you desire only the A+B channels into a Smart Object
- Open that Smart Object
- Convert to Lab Mode
- In Channels window Select only the L channel
- Fill with 50% Gray
- Save Smart Object (Cmd/Ctrl+S)
- (Optional) - close opened Smart Ojbect
- Done - The Smart Object Layer in your RGB Layer stack should look as you desired.

Hope that helps.
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Old 04-25-2015, 10:48 AM
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Re: ab (Lab - L) as a layer in RGB file

Doug, I am with John on this. What he describes is called a Nested Smart Object. These allow image modules of different color spaces to be nested inside an RGB image. You can have as many as you like. Moreover you can nest smart objects within nested smart objects as deep as you like...until you run out of computer resources. I have stayed out of your other thread on the current relevance of LAB but I can tell you most of the time when I have a significant amount of D&B to do on an image I do it in LAB color on a nested smart object. And when I need to perform an Asymmetric Frequency Separation where the HF layer needs to be have 0% of color in it, I also perform the separation in LAB on a nested smart object. LAB is the only color space in which this can be performed.
Cheers, Murray
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Old 04-25-2015, 11:06 AM
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Re: ab (Lab - L) as a layer in RGB file

Thanks to everyone. Filling the L channel with 50% gray was the step I was missing.

Tons of fun putting an ab layer on top of the RGB original and just changing blend modes. Now on to masks
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Old 05-24-2015, 05:51 PM
unimatrix001 unimatrix001 is offline
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Re: ab (Lab - L) as a layer in RGB file

Try using calculations combining the a channel and the b channel in one and pasting it over the rgb photo. I find that either soft light or overlay seem to be the best for my taste
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