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Questions about LAB mode

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  #1  
Old 08-24-2016, 04:05 PM
Chacaboy Chacaboy is offline
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Questions about LAB mode

Hi,

I am a new member as of yesterday. I teach Photoshop and Lightroom, college level, and I would like some practical suggestions about how to demo useful or creative methods using LAB mode. I understand how it is structured, and that the lightness or luminosity is isolated from the color, that it is a pure model that doesn't speak to devices, etc. But I don't have any interesting uses for it that make sense to my students. Any suggestions would be appreciated. Thanks!
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Old 08-24-2016, 04:38 PM
Tulack Tulack is offline
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Re: Questions about LAB mode

Quote:
Originally Posted by Chacaboy View Post
Hi,

I am a new member as of yesterday. I teach Photoshop and Lightroom, college level, and I would like some practical suggestions about how to demo useful or creative methods using LAB mode. I understand how it is structured, and that the lightness or luminosity is isolated from the color, that it is a pure model that doesn't speak to devices, etc. But I don't have any interesting uses for it that make sense to my students. Any suggestions would be appreciated. Thanks!
Something like that.

https://scontent-dft4-1.xx.fbcdn.net...06984440_o.jpg

https://scontent-dft4-1.xx.fbcdn.net...65160266_o.jpg

https://scontent-dft4-1.xx.fbcdn.net...25667962_o.jpg

LAB is also ideal for creating color masks. Removing color cast for example.

https://scontent-dft4-1.xx.fbcdn.net...92085873_o.jpg

Last edited by Tulack; 08-24-2016 at 04:46 PM.
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  #3  
Old 08-24-2016, 06:50 PM
Chacaboy Chacaboy is offline
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Re: Questions about LAB mode

Thanks Tulack for the links. The fourth one with the tall grass and the color cast on her skin looks interesting. That's what I need - to remove a color cast without changing all the colors. But in this last example, the curve is set in RGB and the channels show RGB. Is this LAB or RGB?
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Old 08-24-2016, 06:56 PM
Tulack Tulack is offline
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Re: Questions about LAB mode

There is two luts to go LAB without leaving RGB
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Old 08-24-2016, 08:22 PM
Shoku Shoku is offline
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Re: Questions about LAB mode

Pick up a copy of this book - old or new edition.

Old -https://www.amazon.com/Photoshop-LAB-Color-Adventures-Colorspace/dp/0321356780/ref=sr_1_2?ie=UTF8&qid=1472091449&sr=8-2&keywords=photoshop+lab+color

New -https://www.amazon.com/gp/offer-listing/0134176103/ref=dp_olp_all_mbc?ie=UTF8&condition=all
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File Type: jpg Old_Edition.jpg (7.1 KB, 12 views)
File Type: jpg New_Edition.jpg (9.6 KB, 23 views)
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  #6  
Old 08-25-2016, 01:17 PM
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andrewrodney andrewrodney is offline
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Re: Questions about LAB mode

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Originally Posted by Chacaboy View Post
But I don't have any interesting uses for it that make sense to my students.
Begging the question, are they really uses that make season in a world where many images come from raw data? Is there a compelling reason to switch color models and undergo (in 24-bit color if you're stuck with that encoding) significant data loss?

For example, in the old days, we were told by the Lab proponents that for applying say USM, you had to do this in Lab on the Luminosity channel ignoring Fade>Luminosity blend mode that solves the same issue, with more control (opacity) and without ever having to convert to Lab.

Before you decide you have to teach your students some such techniques using Lab, is there a reason to do so with modern workflows?

IF you've got rendered images that are ugly and need significant work, like the truly awful photography that needs to be fixed in the books above, OK, that may be a reason to go there. If your students have control over either the photography or the rendering of the raw data, teach them how not to produce turds that need polishing via Lab. Render the data globally as well as possible and move on. GIGO:Garbage In Garbage Out.
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Old 08-30-2016, 08:35 PM
Chacaboy Chacaboy is offline
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Re: Questions about LAB mode

I'm sorry it has taken so long to respond to your response but this is definitely food for thought. I, personally, have never had a use for LAB. I have a student who outputted a file with the wrong white balance, then retouched it in detail. She used LAB to fix it without going back and reprocessing and doing all the retouching over. But yes, she never should have made the turd in the first place. But, as we get skill in this we forget what it's like in the beginning. It's hard to imagine how anyone could not check their white balance before outputting and retouching a file, but they do. I'm still wondering if there are creative uses for LAB that might be worth teaching, but haven't seen one yet.
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Old 08-30-2016, 10:07 PM
Shoku Shoku is offline
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Re: Questions about LAB mode

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Originally Posted by Chacaboy View Post
I'm still wondering if there are creative uses for LAB that might be worth teaching, but haven't seen one yet.
I recommend you review the books I referred to in my earlier post. There are many things LAB can do better than RGB or CMYK. I understand Andrew's point, but when you find a LAB solution to a complicated problem that is quicker, with superior results, I chose LAB. In the real world time is precious and LAB saves time.

All good retouchers should understand the 10 channel possibilities for any image, especially when all you have to work with are jpegs or tiffs (not everyone passes along their RAW files, and when they do, they often forget the XMP file that holds the corrections they applied).

Converting from one color space to another space and back again has never ruined any of the jobs I've completed - and that's thousands of clients over the past twenty years.
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Old 08-30-2016, 11:24 PM
klev klev is offline
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Re: Questions about LAB mode

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Originally Posted by Chacaboy View Post
I understand how it is structured, and that the lightness or luminosity is isolated from the color, that it is a pure model that doesn't speak to devices, etc.
You mention that you teach students about Lightroom. I would really caution you against describing it this way. It's not the most intuitive space, and most of what you said is at least somewhat inaccurate. Depicting it that way is would be a disservice to your students.

I have seen interesting uses of LAB, but it doesn't always work better. Applying curves to L doesn't necessarily give the visual impression of a darker shade of the same color. Shoku's reference is good. It's also a reasonable option for the subset image processing applications where the correlation between RGB channels would be problematic. I have a reference for this one, but it's somewhat theoretical in nature.

Downsides are that it can be unintuitive and may not always produce the best results. Sometimes it produces very bad results. An older problem was an undesirable shift between blue and purple when making color adjustments. The frequent suggestion to make certain adjustments to the L channel is also ridiculous. No one who has ever tried it can tell me that it matches the desired appearance, specifically a slightly lighter or darker shade that is otherwise visually similar to the original color.

Lightroom + raw image files offers quite a bit of latitude as gamma correction and clipping are applied at a later stage than they would be if adjusted in photoshop. Given that you're focusing on those tools, the practical uses of LAB should be minimal. Here's an example (warning large pdf) of the kind of thing that doesn't work well in RGB.

You can mostly ignore the weird notation. µ means average and σ means standard deviation. The important things are the image examples and the histogram showing success rate with respect to color space. Regardless of the choice of RGB space, RGB channels are not independent and are highly correlated with cone response (by virtue of being organized with respect to wavelength).

Last edited by klev; 08-30-2016 at 11:38 PM.
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  #10  
Old 08-31-2016, 08:24 AM
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andrewrodney andrewrodney is offline
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Re: Questions about LAB mode

Nothing in Lightroom has anything to do with Lab expect for where Lab is kind of useful there; as an info palette to define colors unambiguously and based (somewhat) on how we see color. The LR engine is 100% RGB start to finish. Same with Adobe Camera Raw.

IF you have an ugly RGB rendered image and can't get the raw to do the job properly, then maybe Lab would serve your students. Better, teach them to render the best possible RGB data from raw in a good raw converter like LR/ACR, they will be way ahead of the game. Now if you wish to tech techniques like fixing butt ugly photography like you see in the books mentioned and the student is being paid by the hour, disregard everything I've written.
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