Talk:Lab color space

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This article needs reorganization (suggested split)[edit]

This article covers material which is broader than the title, currently "Lab color space", implies. Putting the Lab/L*a*b* (Hunter Lab vs CIELAB) issue aside, color spaces which do not even include "a" and "b" as part of the nomenclature are being mentioned and discussed, such as CIELUV. I could imagine someone adding the OSA color space, whose coordinates are L, j, and g, and possibly the CIECAM Brightness/Colorfulness rectangular appearance space with coordinates Q, a_m, and b_m. Is an article entitled "Lab Color Space" the right place for these, as well?

What I suggest is:

  • Create an article for Opponent Color and Appearance Spaces. Mention that Photoshop and similar applications use (a possibly encoded version of) CIELAB, with a link (see next item). Topics common to all these spaces (rectangular to/from cylindrical, opponent mechanisms, Hering et alli, etc). Beside the Photoshop etc issue, which is what people seeing this mentioned in these programs will want to know first and foremost, it should be written from a colorspace-neutral perspective.
  • Create individual articles for each opponent space: CIELAB, CIELUV, Hunter Lab, OSA, and CIECAM spaces. Maybe some historical ones, like U*V*W* and Hunter Lαβ, which would kind of clutter the existing works like the Hunter Lab thing seemed to have done.
  • Remove the redirection from "CIELAB" to "Lab Color Space" as CIELAB will need a dedicated article of its own, and "Lab" ≠ "CIELAB," as somebody has pointed out. Likewise for "CIELUV".
  • Redirect "Lab Color Space" to the new Opponent Color Space article mentioned above. Folks wondering what's under Photoshop's hood will need that discussion.

I can get some of these started, but I certainly don't want to mess around with the redirection business unless/until we're both ready and are in some kind of agreement. I believe one can edit a page which has a redirect at the top, and view it with an appropriate query string.

What say you, fellow editors and users? Shall this article be re-organized along these lines? Anybody have other (hopefully constructive) ideas? Lovibond 03:14, 5 April 2007 (UTC)

  • I say go for it, in the spirit of WP:BOLD. --jacobolus (t) 11:00, 16 April 2007 (UTC)
  • More specifically, I've been doing a bit of editing on the Munsell color system article, which is still woefully inadequate. It would be nice to somewhere in the wiki have a good historical explanation of color order systems, which can then link out to the Munsell article, this proposed article about opponent color spaces, RGB/CYMK color spaces, etc. I think all of your suggestions here are quite reasonable, so please don't hesitate to dive in. --jacobolus (t) 11:07, 16 April 2007 (UTC)
  • I suggest you subsume the opponent process article in your new article about opponent color and appearance spaces. --jacobolus (t) 11:17, 16 April 2007 (UTC)
  • [1] seems like a pretty reasonable description of Luv, Lab, and other modern color spaces. --jacobolus (t) 21:07, 16 April 2007 (UTC)

Thanks for adding "split" to the section header so I could it. I only half agree with the proposal. I agree that the Luv stuff doesn't belong here at all. And an article opponent color is a good idea. But I think we should leave Hunter Lab and CIELAB both in this article, since they are so closely related and need to be understood jointly to avoid confusions between them. Dicklyon 22:14, 5 May 2007 (UTC)

I agree with this somewhat. I think this article needs a much better discussion of the history and motivation of these spaces, and some diagrams, so that readers can get some intuitive understanding of what is being explained. And I think three of the main sections could be labeled “opponent color space,” “Hunter Lab color space,” and “CIELAB,” or similar, and detailed information about those can be split into separate articles (for instance the big blocks of formulae, which aren't of such interest to a general audience, I don't think), and then linked from those sections in the “Main article:«foo»” style. --jacobolus (t) 23:44, 5 May 2007 (UTC)
Okay, I just split the L*u*v* information into a new stub of an article, “CIE L*u*v* color space,” where it won't be cluttering up this page. So that goes some of the way. I'm actually not convinced that all the information about the Hunter Lab space belongs on this page. Does anyone still use that space anymore? Even recommends using L*a*b*. It seems to me that Hunter Lab can be split into its own article, a note about the possible confusion between L*a*b* and Hunter Lab can be added in the introduction to this article (saying something like "the term Lab color space is ambiguous, and can also refer to the historical Hunter Lab space"), and then Hunter's work can be discussed in a history section on this page, as it led to the creation of L*a*b*. But the conversion formulae to and from Hunter Lab seem like mostly a distraction in the context of this page.
So my recommendation: make this article about L*a*b* exclusively, with Hunter Lab discussed in the intro/history sections, and then given its own article, where formulae, etc. can sit. I'd maybe change my mind if there's still any significant use or reason to use Hunter Lab today.
I would then maybe even suggest moving this page to CIE L*a*b* color space, which would make the title prettier and more correct. A large majority of people searching for Lab color are going to hit some sort of redirect anyway, so making the title accurate and pretty wouldn't have any downsides, I don't think.
--jacobolus (t) 23:33, 17 May 2007 (UTC)
Agreed. Lovibond 15:35, 29 May 2007 (UTC)
Okay, Lovibond, will you move the stuff you started putting at CIELAB into the history section of this article, and then maybe we can add a proposal to split out Hunter Lab, or Lαβ or whatever into other articles, linked out of sub-sections of the history section of this article, and a separate proposal to move this article to CIELAB color space, which would mirror the locations of CIELUV color space, RGB color spaces, etc. Dicklyon or others, do you have problems with changing this article to focus on CIELAB? I don't know of any current uses/users of Hunter Lab (I couldn't find any in web searches), so I'm not sure it's of more than historical interest, which makes the extensive emphasis given to it in this article a distraction.
I think the trickiest part of getting this article "right" is figuring out how to present some general information to newcomers, explaining why anyone would want such a color space, etc. without putting too much technical information that would scare them away, and providing lots of pictures. But also putting detail of the history, and technical aspects. I think expanding the "why use Lab" section and leaving it nearish to the top is not a bad idea, and then going on to history, and putting technical details at the bottom, then splitting out all the detailed Hunter Lab info into its own article.
Thoughts? --jacobolus (t) 23:57, 29 May 2007 (UTC)
I think focusing on CIELAB is great. The Hunter Lab stuff can be a separate article, or a minor subsection, but it shouldn't get in the way of the main topic. As far as explaining why anyone would want such a space, I'd say it's not so tricky; just find a source and summarize what they say. That's better than making up reasons for people's opinions or preferences. Dicklyon 00:17, 30 May 2007 (UTC)
Well, what is the main topic? The main topic of this article, based on its name, is "Lab color space", which is different from CIELAB. CIELAB is important enough that it deserves its own article, which is currently being written. Lovibond 15:48, 1 June 2007 (UTC)
In my opinion the main topic should be CIELAB, with other Lab-like spaces mentioned in the history section. --jacobolus (t) 22:56, 1 June 2007 (UTC)
So, Lovibond, are you willing to have this article be changed to focus on CIELAB, with Hunter Lab and other variants appearing in a history section but mostly discussed on other pages? I don't really think we need a "Lab color space" article at all, as CIELAB seems to be the only such space still in widespread use (even Hunter Lab recommends that CIELAB be used for most purposes). It seems like Dicklyon is in agreement with such a policy. I think your idea to “Create individual articles for each opponent space: CIELAB, CIELUV, Hunter Lab, OSA, and CIECAM spaces. Maybe some historical ones, like U*V*W* and Hunter Lαβ” is an excellent one. But I think “Lab color space” should redirect to wherever we put the “CIELAB” article, and a section near the beginning can link out to “opponent process,” and have a paragraph summary of the basic theory, that you suggest in your original comment under this header is necessary to understanding Photoshop's “Lab” color space. If you’re in (even general) agreement, then I think we’re good to go, and should get started. :) --jacobolus (t) 21:51, 10 August 2007 (UTC)
  • From the above conversation, and lack of any more comment since 2007 I assume the split has been done, or is no longer required. I have removed the split tag as part of cleaning up the split backlog. If someone feels there is still a need for a split, please place a new split tag on the article with the current date, and start a new section on this talkpage with the current rationale. SilkTork *YES! 10:54, 8 November 2010 (UTC)

Ranges of a* and b*[edit]

Under the subsection Range of L*a*b* coordinates it states, "As mentioned previously, the L* coordinate ranges from 0 to 100. The possible range of a* and b* coordinates is independent of the color space that one is converting from, since the conversion below uses X and Y which come from RGB." That tells me nothing about the ranges of the a* and b* channels. What I'm really interested in is quantisation errors, specifically whether conversion from 16-bit RGB to Lab and back causes errors due to the (possibly small) number of discrete values of a* and b*. Perhaps I am missing something, perhaps either channel ranges from 0 to 1000000, but the article says very little about this. Ignoring colour, even an 8-bit per channel greyscale RGB image would seem to have more than double the number of tones than Lab (256 values versus 101). Surely this can't be the case? Please tell me I am wrong! nagualdesign (talk) 07:05, 24 November 2011 (UTC)

If 16bit RGB to Lab color is lossless conversion!?[edit]

In the article mentioned that: "... converting an RGB image to Lab and back was a lossy operation. With 16 bit/channel support now common, this is no longer such a problem." What does it mean? If it mean 16 bit RGB to Lab color is LOSSLESS? Further explanation is required in this sentence, in my opinion. — Preceding unsigned comment added by (talk) 05:48, 29 April 2012 (UTC)

No, it just means that the loss due to quantization is negligible; "no longer such a problem"; not quite lossless though. Dicklyon (talk) 06:05, 29 April 2012 (UTC)
It seems your complaint is directed at the word "lossy". This word, however, is in the dictionary and a good understanding of it might (?) clear up any problems with the sentence.

Meaningless sentence[edit]

The following sentence does not make sense and needs to be corrected as appropriate:

These color appearance models, of which CIELAB, although not designed as [2] can be seen as a simple example,[3] culminated with CIECAM02. (talk) 16:54, 23 August 2012 (UTC)

Good catch. Looks like it was added by this anonymous edit in May 2009. –jacobolus (t) 20:39, 23 August 2012 (UTC)

Distance function[edit]

I have been led to believe that the Lab color space has been formulated in such a way that if one wants to determine whether color A is closer to color B or color C, then the ordinary Euclidean distance function is the best guide. In any case, a discussion of some kind of metric seems to be at the heart of any color space. — Preceding unsigned comment added by (talk) 23:25, 7 September 2012 (UTC)

That was one of the most important goals of the CIELAB color space, yes. (Well, more precisely, the goal was to allow specification of color tolerances, for industrial purposes, such that colors matching some spec (of desired color and maximum color difference tolerance) would need to be within some reasonable standard of similarity, based on human vision.) Note, CIELAB was fairly successful, but the color difference metric it defines is far from perfect. [Also, a metric is not necessarily at the heart of every color space; the Munsell color system for example is not based around any Euclidean metric, though a few derived color difference functions have been proposed for it.] –jacobolus (t) 08:32, 2 April 2014 (UTC)

Which form of the Lab color space is used by Photoshop?[edit]

I can select several color modes in Photoshop, RGB, CMYK, Lab, etc. Is the Lab color mode in Photoshop actually Lab (Hunter Lab), or is it really L*a*b* (CIE Lab)?

Benhut1 (talk) 02:54, 25 April 2014 (UTC)

Photoshop has a CIELAB mode. No one has used Hunter Lab for anything in decades. –jacobolus (t) 02:47, 2 May 2014 (UTC)