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

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  #51  
Old 04-26-2015, 10:50 AM
John Wheeler's Avatar
John Wheeler John Wheeler is offline
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Re: Is Lab color (L*a*b*) still relevant?

Good discussion (and Doug's use of the word "relevant" is always a good way to rev up the discussions

While I do retouching, it is no as a business. I used Lab on occasion before yet even less so now. I spend more time in Lightroom/ACR than I do in PS on average so that explains less use of Lab as well. Also, between PS RGB and PS Lab, I have found more ways to get the job done in PS RGB without the jump to Lab. If I do jump to Lab, I do it through Smart Objects.

As a side note, if I do use Lab
- I stay in 16 mode to avoid the data loss and occasional banding on return to RGB
- If on rare occasion I am using 8 bit mode I make sure the "Use Dither" mode is turned off in Edit > Color settings as round trip to Lab introduces dither noise otherwise (add noise manually if desired)
- I use soft proofing in Lab mode as I found it much easier to blow outside the RGB gamut I am using as well as my monitor gamut (and if one does not bother with soft proofing then one is just allowing the color management system to bring it back in gamut instead of more directly under ones own control)

Like any other tool, if you learn its capabilities and its limits then it can continue to be useful/relevant even if on average it is used less often.
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  #52  
Old 04-26-2015, 11:21 AM
Doug.S Doug.S is offline
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Re: Is Lab color (L*a*b*) still relevant?

Another way to "work" in Lab or RGB or HSB etc., without actually converting image color profile, is to use CurveMeister plugin. It has many very useful tools...including ability to use full screen second monitor to fine tune a curve (I use second monitor in portrait mode).
An excellent toolset for any retouching/correction work...including a "skin" tone mask and ability to "pin" colors.
Another new toolset is Lumenzia.....for making and working with masks.
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  #53  
Old 04-26-2015, 01:03 PM
skoobey skoobey is offline
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Re: Is Lab color (L*a*b*) still relevant?

Quote:
Originally Posted by Doug.S View Post
Another way to "work" in Lab or RGB or HSB etc., without actually converting image color profile, is to use CurveMeister plugin. It has many very useful tools...including ability to use full screen second monitor to fine tune a curve (I use second monitor in portrait mode).
An excellent toolset for any retouching/correction work...including a "skin" tone mask and ability to "pin" colors.
Another new toolset is Lumenzia.....for making and working with masks.
That seems like a great tool.
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  #54  
Old 04-30-2015, 09:50 PM
pixaeiro pixaeiro is offline
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Re: Is Lab color (L*a*b*) still relevant?

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Originally Posted by andrewrodney
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.
Andrew, are these quantization errors still a problem in applications that work in 32 bits per channel mode?
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  #55  
Old 04-30-2015, 10:01 PM
klev klev is offline
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Re: Is Lab color (L*a*b*) still relevant?

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Originally Posted by pixaeiro View Post
Andrew, are these quantization errors still a problem in applications that work in 32 bits per channel mode?
(not Andrew but anyway.....) Quantization errors always exist in some way when dealing with numerical computations, assuming you permit any operations beyond addition and subtraction. It's also important to note that 32 bit per channel mode uses floating point math, which is rounded by its nature to the nearest machine number after each computation. I won't bore you with more of that. An upside to 32 bits is that it creates far less haloing on gaussian blur and sharpening operations. Apart from that just remember that there is always rounding.
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  #56  
Old 05-01-2015, 06:50 AM
skoobey skoobey is offline
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Re: Is Lab color (L*a*b*) still relevant?

Hm.. I still don't find it useful to work in LAB over RGB. I like the 3 channels(6 colors). And I just set adjustment layers to "color" if I want to avoid shifting perceived lightness.
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  #57  
Old 05-01-2015, 02:18 PM
pixaeiro pixaeiro is offline
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Re: Is Lab color (L*a*b*) still relevant?

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Originally Posted by klev
Quantization errors always exist in some way when dealing with numerical computations
Thanks klev... I haven't done the math yet, but I think that if you take a 32 bits per channel float RGB, and convert it to 32 bpcf Lab image, and then back to 32 bpcf RGB image, you won't loose as much as 10% to 12% of the color information because the rounding error of float math is much lower than the rounding error of 8 bit integer math (1/8388608 vs 1/256)... but yes, you are correct... there will always be a penalty to pay for going from one color mode to another.

Quote:
Originally Posted by skoobey
Hm.. I still don't find it useful to work in LAB over RGB. I like the 3 channels(6 colors). And I just set adjustment layers to "color" if I want to avoid shifting perceived lightness.
Working in Lab just gives you more tools to work with... operations like curves, gaussian blur or unsharp mask have a completely different result in Lab mode. I always find more intuitive to adjust the Lightness curve in Lab mode than in RGB mode, because the colors never change to unnatural values...
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  #58  
Old 05-01-2015, 02:20 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 pixaeiro View Post
Andrew, are these quantization errors still a problem in applications that work in 32 bits per channel mode?
What Klev said
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  #59  
Old 05-01-2015, 02:21 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 pixaeiro View Post
I always find more intuitive to adjust the Lightness curve in Lab mode than in RGB mode, because the colors never change to unnatural values...
The Luminosity blend mode or fade is your friend in that respect.
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  #60  
Old 05-01-2015, 08:51 PM
klev klev is offline
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Re: Is Lab color (L*a*b*) still relevant?

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Originally Posted by pixaeiro View Post
Thanks klev... I haven't done the math yet, but I think that if you take a 32 bits per channel float RGB, and convert it to 32 bpcf Lab image, and then back to 32 bpcf RGB image, you won't loose as much as 10% to 12% of the color information because the rounding error of float math is much lower than the rounding error of 8 bit integer math (1/8388608 vs 1/256)... but yes, you are correct... there will always be a penalty to pay for going from one color mode to another.
Well that's true, but it's pretty much what I said. There's always a penalty. I didn't say it was huge, and I've been testing it recently in octave. I don't know that a hit in perceived accuracy is that problematic. A bigger irritation is when visually smooth regions turn into piecewise smooth ones. I'm pleased that someone used the correct number there (mantissa only rather than 2^32).
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