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Is Lab color (L*a*b*) still relevant?

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  #41  
Old 04-24-2015, 11:35 AM
klev klev is offline
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Re: Is Lab color (L*a*b*) still relevant?

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Originally Posted by Doug Nelson View Post
So it's still relevant because it's still relevant? I see your logic, but could use some more details.

Yes, it is the connection space, but that's like thinking about cooking in terms of carbon and heat. You can do it, but is it anything more than an intellectual exercise with all the tools we have available today?

There are things that can only be done in every color space, but do we care in 2015?
Not the connection space. A connection space. There are cmms other than photoshop's default one. The ICC v2 and v4 specifications do not require this to be defined in terms of LAB. That is left as an implementation detail. Slightly off topic but LAB is also defined for more than one illuminant, so it really isn't as absolute as you may think. It was intended to roughly correlate with cone response, and it's definitely not based on purely radiometric data.

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Originally Posted by Alfred View Post
Dough, your question if Lab is still relevant is rather odd, I thought you would know better!
Lab is a absolute color space and is the underlying space for all other ones, without Lab there would be no other space, so now tell me if Lab is still relevant.
Beside being the connection space for all other color spaces, there are things which can only be done in Lab.
Well it's a reference space that is often used as a profile connection space. You could use something like xyz to describe values, although that has its own issues such as clamping due to signed or unsigned overflow in some cases where the color may have a real representation in the destination gamut.
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  #42  
Old 04-24-2015, 11:58 AM
Dennis Dunbar Dennis Dunbar is offline
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Re: Is Lab color (L*a*b*) still relevant?

Fascinating discussion.

As a retoucher with more than a couple of decades of experience I can see the points being by both "sides" in this thread.

Yes, Lab does have a lot of advantages. If you have to mask out sky from a bunch of trees the b channel usually gives you a much better starting place than most of the other channels will.

And it can be easy to manipulate color and luminance independently in Lab. Lots of folks love that aspect as well.

Years ago I read through a good part of Dan's terrific book on Lab. But since most of my work at the time was on movie posters where we had to wind up with a layered RGB file I did not have the luxury of working in Lab much of the time so I had to find ways of adapting some of Dan's techniques to RGB or CMYK workflows.

For instance I found I could take easily adjust color and luminosity separately in RGB or CMYK by making 2 adjustment layers, one set to Color blending and the other set to Luminosity blending.

So for me the answer to this question all comes down to just what challenges you're facing and what tools/techniques you have for solving them. One of the things I love about Photoshop is that there are so many ways to tackle any challenge. We get to choose the ways that feel easiest to each of us.

There are times when Lab gives me an easier solution than some other color space. And there are times I can mimic those solutions without having to switch over to Lab. The more fluent I get with these mimicking tricks the less I need to use Lab, but I'd still not want to give it up.
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  #43  
Old 04-24-2015, 01:17 PM
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andrewrodney andrewrodney is offline
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Re: Is Lab color (L*a*b*) still relevant?

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Originally Posted by Alfred View Post
Dough, your question if Lab is still relevant is rather odd, I thought you would know better!
I believe the question was somewhat rhetorical and presented to gather people together for a discussion which it did.
Quote:
Lab is a absolute color space and is the underlying space for all other ones, without Lab there would be no other space, so now tell me if Lab is still relevant.
First, Lab is a color model, 2nd, I'm not sure what makes you say that based on CIEXYZ and Lab, a mathematical model that was supposed to fix issues with the original work done by the CIE. CIELAB was 'recommended' by the CIE in 1976, long before Photoshop and digital retouching to address a specific problem, namely, while identical XYZ values could tell you when two stimuli would be experienced as the same 'color' by most observers, it did not tell you how 'close' two colors were if they were not exactly the same XYZ value. Lab was just an attempt to create a perceptually uniform color space where equal steps correlated to equal color closeness based on the perception of a viewer. The CIE didn't claim it was prefect (cause its not)

Where Lab is invaluable and why it was designed is for predicting the degree to which two sets of tristimulus values will match under defined conditions thus it is not anywhere close to being an adequate model of human color perception. It works well as a reference space for colorimetrically defining device spaces, but as a space for image editing, it has many problems. So the fact it's used as a connection space doesn't mean it's also useful for other editing tasks per se. There are a slew of other perceptual effects that Lab ignores. Lab is no better, and in many cases can be worse than a colorimetrically defined color space based on real or imaginary primaries. There are no devices that capture or output Lab. That isn't the case for RGB.
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  #44  
Old 04-24-2015, 01:32 PM
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andrewrodney andrewrodney is offline
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Re: Is Lab color (L*a*b*) still relevant?

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Originally Posted by Doug Nelson View Post
Alex: Thank you for your thoughtful post, but many of your points sound more like Photoshop vs ACR rather than Lab vs RGB. Your points 1, 2, and 4 are workflows that shouldn't involve ACR regardless.
I agree. By the time 1,2 and 4 are necessary, ACR is long outside the picture, the raw has been rendered.
Can ACR do everything or much of what Photoshop can do in any color model? Absolutely not. Can ACR render images that bypass 90% of what Dan illustrates in his book in terms of fixing ugly images? Yes. The problem I have with Dan's book and dismissal of ACR or for that matter raw processing workflow boils down to the old saying: If all you have or know is a hammer, everything looks like a nail.
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  #45  
Old 04-25-2015, 06:12 AM
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PixelPurfect PixelPurfect is offline
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Re: Is Lab color (L*a*b*) still relevant?

This is a retoucher's forum right? L A B is a retoucher's dream come true. Try affecting yellow without affecting red in the RGB space.

David
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  #46  
Old 04-25-2015, 06:20 AM
skoobey skoobey is offline
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Re: Is Lab color (L*a*b*) still relevant?

Hue/sat, selective color can affect yellows
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  #47  
Old 04-25-2015, 09:49 AM
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PixelPurfect PixelPurfect is offline
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Re: Is Lab color (L*a*b*) still relevant?

Maybe I should have been more precise with my comment. Try to affect yellow without affecting magenta. Yes skoobey, hue/sat has similar controls, but you have to adjust the color bar slider edge points. Time is money.

David
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  #48  
Old 04-25-2015, 10:25 AM
skoobey skoobey is offline
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Re: Is Lab color (L*a*b*) still relevant?

OK, now let's talk about the disadvantages of LAB?
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  #49  
Old 04-25-2015, 10:47 AM
Doug.S Doug.S is offline
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Re: Is Lab color (L*a*b*) still relevant?

I know of no disadvantages of working in Lab; but of course need to convert to RGB or CMYK for most outputs...and conversions in/out of Lab multiple times yields negligent/insignificant (if any) problems.
I use Lab daily for almost every image I work on...to solve image issues more easily/better than other methods.
Like any tool, it is used selectively, and is not a magic cure all, in my workflow.
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  #50  
Old 04-25-2015, 11:12 AM
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andrewrodney andrewrodney is offline
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Re: Is Lab color (L*a*b*) still relevant?

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Originally Posted by Doug.S View Post
I know of no disadvantages of working in Lab...
Other than the issues of Lab's shortcomings (already mentioned), every time a conversion to LAB is produced, the rounding errors and severe gamut mismatch between the two spaces can account for data loss, known as quantization errors. The amount of data loss depends on the original gamut size and gamma of the working space. For example, if the working space is Adobe RGB, which has 256 values available, converting to 8-bit LAB reduces the data down to 234 levels for neutrals. The net result is a loss of 22 levels. Doing the same conversions from ProPhoto RGB reduces the data to only 225 values, producing a loss of 31 levels. Bruce Lindbloom, a well-respected color geek and scientist, has a very useful Levels Calculator,which allows you to enter values to determine the actual number of levels lost to quantization (see the “Calc page”at http://www.brucelindbloom.com).

So yes, there are possible disadvantages certainly if the data isn't high bit to begin with.
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