User talk:PAR/archive 4

MacAdam ellipses diagram: permission request

Dear PAR: MIT OpenCourseWare would like to use this image http://en.wikipedia.org/wiki/File:CIExy1931_MacAdam.png in some imaging course material published under Creative Commons by-nc-sa (attribution-noncommercial-sharealike) license. As our license is legally a bit different from the GFDL you've placed on the Wikipedia image page, may we have your permission? Best regards, Curt Newton - Publication Manager, MIT OpenCourseWare - cjnewton@mit.edu Cjnewton mit (talk) 20:02, 18 March 2009 (UTC)

Analemma

"The width of the analemma is a result of the ellipticity of the earths orbit. Please explain how this relates to vibration in universal joints."

The "figure-8" related East-West motion in the analemma has absolutely nothing to do with the eccentricity of the Earth's orbit. Eccentricity causes a 12 month period East-West motion, not a 6 month period! It distorts the "figure-8". The "figure-8" East-West motion is due to the tilt of the Earth's axis. Assuming a circular orbit for simplicity, the 24 hour strobed position of the sun follows a great circle across the earth with constant velocity and one year period. During the equinoxes this sun circle crosses the equator at an angle, so it's eastward movement is slower that the 24-hour strobed rotation of the Earth. During the solstices the sun is moving parallel to the equator, and since by defintion of the solar day they must have the same yearly average, it is moving faster that the Earth's eastward rotation. —Preceding unsigned comment added by Cloudswrest (talk • contribs) 18:25, 10 September 2008 (UTC)

Gibbs Paradox

I noticed that you edited the article on Gibbs Paradox, and seem to have some comfort level with the material. I have reason to be suspicious of the information theory treatment, but am not technically competent to review it. If you are, would you please take the time to review that section carefully?Kww (talk) 21:46, 21 November 2007 (UTC)

Yes, I plan to do that. This information was added by Shu-Kun Lin, who has apparently published articles on this subject in various respectable journals, so it cannot be rejected without serious consideration. PAR (talk) 22:02, 21 November 2007 (UTC)

RE: Multiple wikify requests

Hi,

Thanks for the message..

Right now... I am prepareing for an exam on "Material Science"..

While going through these articles, I encountered situations where I couldn't proceed to next page due to lack of Wiki links (internal links).. I corrected some of them.. but right now I do not have enough time to correct all of them so just put wikify requests.. :)

Will either put links, or explanation in talk page after my exams.. :)

The articles I put wikify requests inclue (as u mentioned in your message) :

Slip (materials science)‎ Non-Newtonian fluid‎ Strain (materials science)‎ Creep (deformation) Tensile stress‎ Frank-Read Source‎ Annihilation‎ Burgers vector Interstitial defect‎

Thenks.. DhananSekhar 18:45, 30 November 2007 (UTC)

re: Pulley

Good morning, PAR. I just had to revert your latest edit to the Pulley article. I understand your point but when you made the change, you brought the vandalism back. If you're going to fix the article, please fix it completely. It is more important that we keep the vandalism out than that we make a technical correction about "unit weight". Thanks. Rossami (talk) 16:22, 10 December 2007 (UTC)

Well, to be factual, we are both screwing this up, and I apologize for my part in it, by not checking for vandalism before making my edit. The use of "unit weight" though, is simply wrong, and you didn't correct that when you tried to edit back in what I had done. Can we proceed slowly from here? I know its a pain to go through a bunch of good edits, looking for the vandalism, but I will try. I reverted to my version, but fixed the "flute and tackle" and "flute and picolo" vandalism. Now, rather than revert because it might still contain vandalism, can you just search for any further vandalism and correct it? Again, sorry about my contribution to this problem. PAR (talk) 16:54, 10 December 2007 (UTC)

In a perfect world, that's the way it should go. In this case, the vandalism went undetected for enough time and your edits hit so many parts of the article simultaneously that it was very difficult to find and fix them all. Again, I will argue that it is far more important that we fix vandalism than to correct technical issues of wording. Even with the mistake, the basic concepts of the page were understandable. Vandalism, on the other hand, discredits the project. I usually can merge the good edits but in this specific case, it really seemed safer for our readers to over-revert and ask you to recreate your edits.
Anyway, the vandals still messed with the figure numbering. I'll go fix that. And something about your edits is adding non-breaking spaces that have to be cleaned up. If you could look into why those are showing up, that would be helpful. Thanks. Rossami (talk)

It looks good. The non-breaking spaces are there on purpose, they prevent italicized letters from running into the next letters. This W does not have a non-breaking space, this W  does. PAR (talk) 19:53, 10 December 2007 (UTC)

The first example looks right. The second forces an odd double-space after the W and looks like a misprint. In neither case did not italicized letters run into the subsequent letters. Rossami (talk) 03:07, 11 December 2007 (UTC)

Images of two-dimensional coordinate systems?

Hi PAR,

Have we met before? I'm thinking that we have, but, unfortunately, I can't remember where — maybe at the equipartition theorem? :)

I noticed your wonderful red-and-cyan pictures at the articles for prolate and oblate spheroidal coordinates! I really like the way you labeled the individual isosurfaces, too. Would you be willing to do something similar for the other two- and three-dimensional orthogonal coordinate systems, or at least tell me how to do it? I've long been thinking of fixing them up and would really appreciate your help. :) Willow (talk) 23:45, 17 January 2008 (UTC)

Hi - yes, your name sounds familiar. Those pictures were intended to be temporary, they are not really high quality. I used gdl (gnu data language) to generate them, and I can give you the program, if you like. They really should be .SVG files rather than bitmap, but I haven't figured out how to generate a .SVG file from gdl yet. Im pretty sure it can be done. Let me know if you need the program. Im working on writing up different harmonics right now (cylindrical, oblate, prolate, etc.) but eventually, I will do one for the parabolic coordinates (and the parabolic cylinder coordinates as well). PAR (talk) 23:58, 17 January 2008 (UTC)

Hey PAR,

Thanks for your really nice letter! You can send any articles you like to the same e-mail address. I'd like to see the pictures you mention!

I'm ploughing ahead with making images for the other orthogonal coordinate systems. I'll try to do conical coordinates tomorrow, since they seem one of the very coolest. I like the little taco shape where the sphere and the elliptical cone intersect; it's somehow elegant, no? I just realized today that I hadn't understood even some of the basic stuff about the coordinates, e.g., that you need to eliminate the degeneracy in the bipolar coordinates. :( I should've realized that if the coordinate surfaces meet in two places, you need to take special precautions against degeneracy. For the bipolar coordinates, it turns out that σ can range from -π to π, not merely half that range as I'd originally thought; I think I was scared off by the infinity! ;) Ta-ta for today, Willow (talk) 21:39, 6 February 2008 (UTC)

MacAdam ellipse

The MacAdam ellipse delineates—not defines—the contour for the minimum perceptible distance. The concept of distance is defined by the distance metric (cf. color difference). The distance may be zero, just noticeable (JND), or anything at all. How would you draw the ellipses without the formal definition provided by color difference? That sentence is wrong. --Adoniscik (talk) 17:15, 19 January 2008 (UTC)

No, you've got it backwards. The distance metric and the Lab spaced is derived from the MacAdam ellipses. You ask how the ellipses would be drawn without the formal definition of the metric. The answer is "the same way MacAdam did". MacAdam drew the ellipses before the Lab space or the distance metric was ever defined. He chose a color specified by its CIE xy coordinates, then determined experimentally the set of colors, different from the original color, which could not be distinguished by his test subjects. These regions turned out to be ellipses, and they became known as MacAdam ellipses. The distance between any two colors in xy space was then defined to be the smallest number of MacAdam ellipses, that were just touching each other, that could be fit between the two points. To be more accurate, a metric was defined in xy space (which varied with x and y, and direction and was therefore a tensor) in which the unit of distance was the distance across a MacAdam ellipse.

The next step was to invent a new color space, a distortion of the CIE xy space, in which all of these ellipses became circles with radii equal to unity. If such a space could be invented, and "a,b" were the coordinates in this new space, then the metric tensor would be unvarying over the entire space, and the distance between two points would be just like the Euclidean distance in physical space. Such a space was in fact invented, and the new space was called "Lab" space. Its not a perfect fit to the MacAdam ellipses: The MacAdam ellipses in Lab space are not perfect circles, but its close enough. The distance in Lab space is not a definition, it is a result derived ultimately from the work of MacAdam. Actually there have been a number of attempts to invent such a space and each improvement replaces the previous approximation. Perhaps a newly concocted space will replace the present Lab space in the future, and the concept of distance will be expressed somewhat differently in that space, but before the concept of distance is redefined, a new experimental determination of the MacAdam ellipses will have to be made.

Again, the MacAdam ellipse defines the concept of distance in any color space. PAR (talk) 18:06, 19 January 2008 (UTC)

I think it would be more accurate to say "MacAdam experimentally verified that measuring difference between two colors by using the Euclidean distance (between two color vectors) in an appropriate color space agrees with intuition". He then went on to define an "appropriate" color space. Obviously, an ellipse by itself is not a distance, it's an ellipse.--Adoniscik (talk) 18:36, 19 January 2008 (UTC)

Thats really not the case. MacAdam was an experimentalist, I don't think he or anyone else was worried about metric tensors and appropriate spaces. He certainly didn't invent the Lab space, that came years later. Also, the outer boundary of a MacAdam ellipse is, by definition, at a distance of one from its center. Its just that in xy space, the space is "stretched" in some places more than others and in some directions more than others. Thats why the metric is a full tensor in xy space, and that tensor changes with position in xy space. If we had a perfect Lab space, it would perfectly "unstretch" the xy space, the distance from a point would be the same in any direction, the ellipses would become circles which were all of unit radius, the metric tensor would become the unit tensor, and the distance would be Euclidean, s^2=a^2+b^2. If you can get hold of a copy of Wyszecki and Stiles "Color Science", it is the best book on color science I have seen, and it goes through all of this in detail. PAR (talk) 19:00, 19 January 2008 (UTC)

CIE

What I did is explicitly allowed, per the page you cited: "Deleting material not relevant to improving the article". None of that stuff is relevant, so please remove or archive it. p.s. your talk page is a bit long. --Adoniscik (talk) 02:04, 19 February 2008 (UTC)

Ok,ok, I archived it :)

Regarding the guidelines, I see the line you are referring to, but I also see the first few lines IN ITALICS "Do not strike out the comments of other editors without their permission." and "Editing others' comments is sometimes allowed, but you should exercise caution in doing so". A few points:

• I have been editing on Wikipedia for more than three years and I have never seen anyone delete whole sections of a talk page, saying they were "irrelevant". I have gotten the distinct impression that it is bad form to edit the talk page in any way except by adding material, or editing your own comments before anyone has responded to them.
• There is no need to delete the material, it does not interfere with the article, nor does it interfere with any editors ability to edit.
• By deleting this stuff, you make extra useless work for other editors who must scan over the entire deleted section and verify that it is in fact irrelevant.
• Finally, in my opinion, the deleted material is not, in fact, irrelevant. Most of it is addressing article quality. It's not very useful, I agree, but it's not irrelevant. PAR (talk) 07:38, 19 February 2008 (UTC)

It's only a talk page so I'm not bothered, but the junk currently on it only confuses new editors. When I looked at the talk page I wondered why the discussion was so off-topic. If you look at the dates of the comments, you'll see they are referring to a former state of article that barely addresses the actual subject. ColorRendering and chromaticity coordinates?? —Preceding unsigned comment added by Adoniscik (talk • contribs) 09:20, 19 February 2008 (UTC)

Gas-related Articles

Hey PAR! I was wondering if you wanted to help me re-write the gas-related articles. I just finished Gas and would like you to take a look at it since I've seen you contribute a lot to these types of articles. I know you're a fan of thermo, as am I... so I figured it would be great if we could work together to make these articles actually make sense. Ideal gas is falling apart and it needs to be redone. Honestly, I feel that the thermo eqns are great but also excessive in this article. Honestly, they dont really talk about ideal gases at all... its just kind of a stand-alone "heres some thermo!" kind of thing. I think they would be better fit in a different article and just taken out of the ideal gas article.

I think the Ideal gas page should be more of a model assumption clarification more than a thermo class. so basically... when we analyze a gas, we establish a set of assumptions that we're gonna go with for the model and then do it. an "ideal gas" is just one of these assumption bases. I think this article just needs to define what these assumptions are. A separate article, Real gas, can be expanded on to include all the different types of models and lack of assumptions and all the statistical thermo and compressibility and all the magical deviations from the "ideal" model.

Please take a look at these articles and get back to me. let me know if you want to help me out! Thanks! Katanada (talk) 07:12, 26 February 2008 (UTC)

Fair use rationale for Image:Masuda2.png

Thanks for uploading or contributing to Image:Masuda2.png. I notice the image page specifies that the image is being used under fair use but there is no explanation or rationale as to why its use in Wikipedia articles constitutes fair use. In addition to the boilerplate fair use template, you must also write out on the image description page a specific explanation or rationale for why using this image in each article is consistent with fair use. Suggestions on how to do so can be found here.

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Image:Baboon24.png

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Speedy deletion of Template:CallTest

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Thanks. --MZMcBride (talk) 21:04, 23 March 2008 (UTC)

Non-free use disputed for Image:Mae_West_Signature.png

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Fair use rationale for Image:TeriCopley.png

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Replaceable fair use Image:EmmylouHarris80.jpg

Replaceable fair use

Thanks for uploading Image:EmmylouHarris80.jpg. I noticed the description page specifies that the media is being used under a claim of fair use, but its use in Wikipedia articles fails our first non-free content criterion in that it illustrates a subject for which a freely licensed media could reasonably be found or created that provides substantially the same information. If you believe this media is not replaceable, please:

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Ok, I have done that.PAR (talk) 18:22, 22 May 2008 (UTC)

optics images

I like your image on the "real image" article. I would like to add one that I think would help the article. Can you tell me how I can upload the svg file I made? Thanks. 209.253.120.198 (talk) 01:12, 6 June 2008 (UTC)

Sure, go to the commons upload page (here) and follow the directions. Be sure to pick permissions of Public Domain-Own work. PAR (talk) 15:35, 6 June 2008 (UTC)

Speedy deletion of Image:BuffaloNYFlag.jpg

A tag has been placed on Image:BuffaloNYFlag.jpg requesting that it be speedily deleted from Wikipedia. This has been done under section I8 of the criteria for speedy deletion, because it is available as a bit-for-bit identical copy on the Wikimedia Commons under the same name, or all references to the image on Wikipedia have been updated to point to the title used at Commons.

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values for CIE1931 XYZCMF.png

You seem to be the person who uploaded Image:CIE1931 XYZCMF.png, and so I'd like to ask you where you got the values for the chart. Specifically, I'm trying to find the area under the curves, and data tables for them would be quite helpful.

(In theory, I think you're supposed to explain how you came up with the chart, but I'm not going to get all Wikilawyer on you) superluser_tc 2008 August 29, 07:58 (UTC)

Hello - I got the data from Wyszecki and Stiles, page 725. I added this line to the image:

Data from Wyszecki, Günter and Stiles, Walter Stanley (2000). Color Science: Concepts and Methods, Quantitative Data and Formulae (2E ed.). Wiley-Interscience. p. 725. ISBN 0-471-39918-3.{{cite book}}: CS1 maint: multiple names: authors list (link)

PAR (talk) 09:48, 29 August 2008 (UTC)

See, that is *extremely* useful information. Now, let's see if I can find that on Amazon. Thanks. superluser_tc 2008 August 29, 11:51 (UTC)

Disputed non-free use rationale for Image:Lenna.png

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Please investigate the history and use of this image. PAR (talk) 13:13, 17 October 2008 (UTC)

Broken images

Hi,

images broken, please check:

• Image:GroupDiagramMiniC3.png
• Image:GroupDiagramMiniD6.png
• Image:GroupDiagramMiniC12.png

Maksim-e (talk) 22:26, 14 November 2008 (UTC)

Ok, I fixed it, thanks for pointing that out. PAR (talk) 00:55, 15 November 2008 (UTC)

File:Lenna.png

You undid my removal of your Lenna image from her biogaphical page. The use of her image does not qualify as fair use on her biographical page, as any image of her could do here. There fore on the Lena Soderberg page it fails WP:NFCC 1. No free equivalent. The use of the image on the other pages is justified as the image is not replacable on the Lenna page, for example. However just because fair use is allowed on other pages doesn't mean fair use is allowed on any page. That is why no biographical pages of living persons have a fair use image. Rambo's Revenge (talk) 14:41, 12 December 2008 (UTC)

P.S. My original edit summary for removing it: "remove rationale for biographical person (as a free image can be made), just because they aren't cracking down on the use of this image does not make it public domain" was wrong. I didn't mean public domain, i meant fair use. 14:44, 12 December 2008 (UTC)

I restored the image and the fair use rationale, for reasons indicated on each page. Basically, the image was not presented on the biographical page as simply a picture but "as pictured in the Lenna image". As such, its use there and anywhere else is irreplaceable. Also, just because they aren't cracking down on the use of this image does not make it NOT fair use. PAR (talk) 19:42, 12 December 2008 (UTC)

Can we move this conversation to File talk:Lenna.png? —Chowbok ☠ 19:53, 12 December 2008 (UTC)

good idea, I will copy this to the Lenna.png talk page PAR (talk) 20:01, 12 December 2008 (UTC)

Entropy expression on erlang distribution page

Hi PAR. Yours was the first entry for entropy on the erlang distribution page. The expression is in error and I corrected it (see Tom Cover's latest edition of his info theory book, page 661)

Cheers,

Chris (talk) 08:05, 6 February 2009 (UTC)

Drying out a log...

Read the wiki article on wood drying, specifically issues and cracking on the outer parts when moisture evaporates more quickly than in the interior... I noticed that you are a recent contributor to this page. I wonder if the inner section of a log was hollowed out would that reduce risk of cracking? (ie relatively uniform and totally intact outer rim of tree, not bark) Also, if doing this, in the drying process, would the shape warp? Do you know? Can you tell I am looking to make a drum?  :> Please let me know if you have any idea. A post here or email: aruenfire@gmail.com . Thanks. Woodwater (talk) 03:29, 17 February 2009 (UTC)WW

Hollowing out the log will reduce the risk of cracking, the more hollow, the less risk. The wood shrinks more tangentially than it does radially. As it dries, a solid log wants to reduce its circumference faster than its radius, and so it forms radial cracks in order to do that. A ring inside a solid log can't contract because of the wood inside the ring, so it cracks. A thin ring made by hollowing the log will have room to contract, and its inner radius and outer radius wont be at odds with each other as much, and so it will crack less. The best way to prevent cracking is to cut your own radial crack to begin with, but thats not going to make a good drum. Dry it slowly, and if you can, choose a wood that doesn't crack much. Seal the top and bottom with something like paraffin so it dries from the sides, not the top and bottom. It will dry more slowly that way, and it wont set up as much stress. The drum should shrink, but not warp, if you have good straight wood to begin with, and try to follow the growth rings when hollowing. PAR (talk) 10:39, 17 February 2009 (UTC)

Hello! Are you physicist? —Preceding unsigned comment added by 132.199.119.184 (talk) 12:59, 27 March 2009 (UTC)

Hello! Yes. PAR (talk) 14:05, 27 March 2009 (UTC)

Lenna

Hi
I've left you a message at Talk:Lenna#"... changed the course of history"?
Cheers, Amalthea 16:49, 26 July 2009 (UTC)

Chromaticity Diagrams

FYI, 98.216.110.149 (talk · contribs) brought up a question about the diagrams you made, specially the position of the white point. See Wikipedia talk:WikiProject Color#Several incorrect chromaticity diagrams and Talk:Chromaticity#Chromaticity diagram colors are wrong. PaleAqua (talk) 06:28, 4 September 2009 (UTC)

White House/Fox News

FYI. You may want to express your opinion on a recently deleted article: Wikipedia:Deletion_review/Log/2009_October_28 —Preceding unsigned comment added by Jwesley78 (talk • contribs) 21:50, 30 October 2009 (UTC)

Thanks, but I never did read that article before it was deleted, so I can't really form an opinion. Also, I am more or less in agreement with your Anita Dunn edits. The quote really has to be in the article, I would prefer in the body, but if this creates consensus, then good. PAR (talk) 23:36, 30 October 2009 (UTC)

The only way to see the article is through Google's cache. Anyways, I'm glad things settled down on the Anita Dunn article. I hope the article has reached a relatively stable point. Jwesley78 (talk) 06:08, 31 October 2009 (UTC)

User:JohnHistory

FYI. It appears that our comrade User:JohnHistory completely flipped out! I hope he's OK. Jwesley78 (talk) 02:22, 1 November 2009 (UTC)

Jeez, the guy is way too serious. Didn't he say he was going to Europe for a month? I hope he finds a french girl who shows him how to chill. PAR (talk) 03:14, 1 November 2009 (UTC)

Primitive communism

Hi there. I noticed you added a reference, "Scott, John; Marshall, Gordon (2007). A Dictionary of Sociology. USA: Oxford University Press. ISBN 978-0198609872." to primitive communism; I was wondering if you could perhaps dig it up and check to see if it supports the edit made by this user here. If it doesn't, their edit is either incorrect and unsupported, or correct and we need a new reference. I don't know anything about the reference to be able to rollback again in good conscience, so if you could please check it out it would be most appreciated. Cheers. SMC (talk) 00:40, 6 November 2009 (UTC)

I think the quote says it very well. This article needs to make clear that it is not an established fact that primitive communism actually did or did not exist in primitive cultures. I'm fairly sure its a contentious question, and both sides need to be presented, along with good references. To say that it "describes a pre-agrarian form of communism" might be taken to mean that it did exist, but to say that it "describes what they interpreted as a pre-agrarian form of communism" might be taken to mean that it did not exist. The quote clearly implies that it is "speculative" which is not to say it is true or false. Somehow we have to have to make the rest of the article inform the reader that it is a contentious issue and give them information from both sides with which to make up their own minds. That will take some thinking and some research. PAR (talk) 04:21, 6 November 2009 (UTC)

Glad I checked with you -- you sure know your stuff! A tricky issue to say the least; unfortunately I don't know anywhere near enough about the topic to contribute something meaningful. I'll put it on my watchlist though, just in case I feel unusually productive sometime. Anyway, thanks for getting back to me. SMC (talk) 13:46, 6 November 2009 (UTC)

Thanks for the barnstar

Hi PAR. Thanks for the barnstar. I've been meaning to ask you for help in the review of the stress (mechanics) article. Right now I am trying to add inline references in the article. If you see any part of the article that needs to be referenced please add the citation-needed tag, or add a reference if you know one. Also, if you see any paragraphs that need improvement for grammar or flow that would help too. Thanks sanpaz (talk) 05:34, 4 March 2010 (UTC)

colors in chromaticity diagrams

Hi PAR, I’ve been trying to draw some chromaticity diagrams, to upload in SVG format, and thought you might have some thoughts about it. I’m somewhat skeptical of coloring the chromaticities outside the sRGB gamut, since it is impossible to properly represent them. Among other things, it seems sorta odd to show colors near the spectral locus at the same luminance as colors near the middle of the gamut – to be at a similar luminance, they’d have to emit quite a bit of light at their specific wavelengths – near the red/blue corners, that would have to be quite a lot indeed, given the low human sensitivity to those wavelengths. Next, I’m not a fan of the bright “star” (your word) artifact near white. It’s not clear to me that showing the maximum available Y for each (x, y) is a good strategy; in trying a few mappings from (x, y) to Y, I think I’ve decided that the one which works best is to take a plane in XYZ space through the XYZ values for the three sRGB primaries. This doesn’t result in a completely uniform luminance, but it is a pretty smooth surface in xyY space, and goes through as-bright-as-possible (1, 0, 0), (0, 1, 0), (0, 0, 1) points in RGB at the three corners. I think I’d just as soon *not* fill in the portion of the “horseshoe” outside the sRGB gamut triangle, instead explaining in captions wherever the image is used that those colors should be “like the ones shown but more colorful” &c. Finally, I think it often it makes sense to use the 1976 (u′, v′) diagram rather than the 1931 (x, y) diagram, for instance in diagrams comparing various RGB gamuts, or diagrams indicating the chromaticity of various white points. I’ll try to upload the diagrams as I’ve been working on them so far and link them here, shortly. –jacobolus (t) 17:02, 10 May 2010 (UTC)

Oh, one other goal I had: make the diagrams as readable/usable as possible at sizes from 200 px wide up to 800 or 1000 px wide; i.e. I used big fonts :). –jacobolus (t) 17:23, 10 May 2010 (UTC)

Hi Jacobolus - I am strongly in favor of coloring the chromaticities outside the sRGB gamut, because more information is gained than lost. I don't think we should ask someone who has no knowledge at all of the chromaticity diagram to guess what the outer portions will look like. They won't have a clue. As long as we specify that they are not perfectly represented outside the sRGB gamut, I think that is best. I think the absolutely best way to represent a color outside the sRGB gamut is to use the color inside the sRGB gamut that is "closest" to it in the sense of the "distance" between two colors defined by the MacAdam ellipses. In other words, in uv space, if you pick a point outside the sRGB gamut, the color of that point should be the same as the color of the point inside the gamut that is closest in distance to it. That only works in uv space. To do it in xy space, you would have to translate to uv space, find the closest color, and use that color at the point in xy space. I'm also strongly in favor of accurately representing the points inside the gamut, not blurring or smearing them in order to make the picture look "nice". I'm not a fan of the star either, but at the time, I didn't know of a way of getting rid of it while keeping the correct chromaticities. If you have found a way, then excellent, do it. The bottom line is that this is a chromaticity diagram, not a luminance diagram, and we should use any luminance function we want in order to convey chromaticity to the observer, and try to make the luminance as unobtrusive as possible. (No star, no darkness at the edges, etc.). Im not sure why you think it makes more sense to use the uv coordinates rather than the xy coordinates. I think both are important in their own right, xy certainly to understand the history of the concept. Also, another point about xy and uv - if you pick two points on the xy diagram, then every color that can be created by mixing them (additively or subtractively) lies on a straight line in xy space connecting the two points. I am not sure that this is true in uv space. In other words, the sRGB gamut forms a triangle in xy space, but I doubt that it forms a triangle in uv space. This will also have implications when finding the sRGB color closest to any given color on the diagram. Also, the full gamut in xy space is entirely contained in a triangle formed by the x axis, the y axis, and a line which is tangent to the curve at the lower right (red) corner. I wish you luck in your endeavor. I uploaded my original diagrams and have watched them being hacked and smeared no end by the "artists". Every time they redo a diagram, and do not understand something, they simply eliminate it. The third line in the xy gamut triangle never survives an edit, and only remains on the original diagrams e.g. CIE_color_space#Construction of the CIE XYZ color space from the Wright–Guild data. What you wind up with is a very pretty picture that contains little information. PAR (talk) 18:39, 10 May 2010 (UTC)

No blurring here, and “accurate” chomaticities (that is, assuming a monitor is really sRGB): I just took a plane in XYZ space, as mentioned (by solving the system of equations that has aX_R + bY_R + cZ_R + d = 0, aX_G + bY_G + cZ_G + d = 0, etc. for a, b, and c in terms of d as a free variable, and then massaging the equations for xyY-to-XYZ to get XYZ values for each (x, y) pair; I can paste the python code here if you want). –jacobolus (t) 19:45, 10 May 2010 (UTC)

If the full shape is going to be filled in, I think maintaining the hue of points is more important than minimizing ΔE. I think the luminance/lightness function should remain as smooth as possible to avoid giving the impression that it is directly tied to chromaticity. So I think the best approach, assuming filling in the whole “horseshoe” shape is desirable, is: pick some lightness function for the whole shape, ideally one which includes the primaries, or at least somewhat close to them. Then outside the range of actually reproducible colors, take the highest chroma color which matches the hue of a color at the chosen lightness and the chromaticity coordinates. But to be honest, I think showing colors filled in outside the sRGB triangle and including a caption that explains that the others are unrepresentable on the screen less (or at least no more) misleading than faking them and including a similar caption. –jacobolus (t) 20:01, 10 May 2010 (UTC)

In CIELUV (L*, u*, v*) space, additive mixtures won’t fall on a straight line, except for a single luminance level (because of the luminance-based nonlinearities baked into the definitions of L*, u*, v*). But both the 1960 (u, v) chromaticity diagram, and the 1976 (u′, v′) diagram are simple projective transformations of (x, y) (also see keystone effect, homogeneous coordinates). Such transformations map straight lines in the domain to straight lines in the range. Indeed, this is the reason for the transformations chosen for the 1960/1976 diagrams; other functions would make MacAdam ellipses (or similar empirical measurements) more uniform, but it had to be a projective transformation to guarantee that additive gamuts could be drawn as triangles. (Subtractive mixtures are pretty much never going to fall on straight lines, because they depend on the precise nature of the illuminant and reflectances of the pigments/dyes involved, and it gets complicated quickly.) –jacobolus (t) 20:20, 10 May 2010 (UTC)

If it would be useful, I could explicitly draw the z = 0 (i.e. x + y = 1) line; in the diagram shown to the right, it is only implied by the absence of grid lines on the other side of it. And of course the (0, 0), (1, 0), (0, 1) triangle contains the gamut! By definition x + y + z = 1. –jacobolus (t) 20:20, 10 May 2010 (UTC)

One last question: is the data you used to draw the MacAdam ellipses available in an easy-to-process form? I downloaded MacAdam’s 1942 paper, and it includes a big drawing that I suppose I could trace, but it’s not obvious from a 1-minute skim how the ellipses follow from the tables of data; I guess I could always read the paper closely. –jacobolus (t) 20:49, 10 May 2010 (UTC)

As for why I think it’s often better to use the 1976 diagram instead of the 1931 diagram: obviously the xy diagram is important for explaining itself, and for explaining the development of the CIE 1931 space, and so on, but for purposes like comparing color gamuts of RGB spaces, the CIE recommends using the 1976 diagram (which obsoletes earlier chromaticity diagrams) because the 1931 diagram is severely distorted with respect to visual perception, as MacAdam and later others extensively documented. :-) –jacobolus (t) 21:20, 10 May 2010 (UTC)

Hi - I put the MacAdam data in the MacAdam Ellipse picture at ((File:CIExy1931 MacAdam.png)). Regarding outside the gamut, we have to put ourselves in the position of someone who has never seen the whole thing filled in. We have seen it over and over again, until its obvious how to extrapolate the colors, but for someone who has not seen it, they will be lost, or they will be searching the web for a picture that tells them intuitively how to fill in the colors. If I saw this for the first time, I might make a guess, but I would not trust my guess, I would have to search out something that at least gave me a rough idea of whether my guess was right. Lets save the new reader from all of that. Again, I favor making outside-the-gamut points to have the xy coordinates of the "closest" in-gamut point. That is, closest a some space like CIELUV where distances are closely proportional to the MacAdam distance. If you are satisfied that the sRGB gamut is a triangle, I will take your word for it, I always wondered about that. Regarding the enclosing triangle of the gamut in xy space, yes, by your equation, it follows. What I think is relevant is that the gamut boundary is tangent to that triangle at the lower right corner. It runs through that point, and the slopes match. Regarding which space is most useful, why not ask around to other editors and take a poll? My viewpoint is narrow, the color work I have done treated xy space as the experimental bottom line, and uv space as an adjunct to be used to determine approximate color distances. So naturally I favor that, but it is the reader we have to satisfy, not you or me.

Well ultimately the whole basis of CIE colorimetry is the 1931 standard observer, and XYZ. An (x, y) chromaticity diagram is obviously the most direct representation of that basis. The problem is that drawing a bunch of RGB gamuts in (x, y) space implies that their area is proportional to the gamut, and implies that computer displays (in sRGB, say) are “missing” a huge portion of the possible bright greens but including most blues/reds. Really no two-dimensional diagram can do proper justice to these gamuts, and some 3d representations should be included. But (u′, v′) – which is, notice, different than (u, v) – is much more uniform/less misleading, and has been recommended for 35 years now. –jacobolus (t) 23:36, 10 May 2010 (UTC)

Yes, those three, uv, u'v', ab, all are kind of pick and choose for me depending on what needs to be done. I "think" in terms of xy and then those are like second languages when I want to say something special, and I kind of lump them all together under the label "other" in my mind. I'm not saying that this is a good viewpoint. What is "best" should not depend on anyone's "favorite" way of viewing things, it should depend on what the reader needs, and if you are convinced that the u'v' is the way to go, and other editors don't disagree, well then u'v' it is. I see your point about how the xy gamut is misleading in the way it misrepresents the area of missing colors as being larger than it really is. I will ask DickLyon about his opinion, maybe another color editor or two. PAR (talk) 03:01, 11 May 2010 (UTC)

File:CIExy1931.png

You wrote:

The process of maximizing the value of R, G, or B results in a distinct 3-pointed star in the diagram, centered at the D65 white point. This is because, although the chromaticities are correct, the luminosities (brightness values) are not equal across the diagram. If the luminosities were all made equal, then the entire diagram would be rather dark, since pure blue has a low luminosity. Any attempt to equalize luminosity to remove the star will reduce the overall luminosity of the diagram, and the star will not completely disappear until the diagram is very dark. Alternatively, we could blur the colors to get rid of the star, which would give incorrect chromaticities.

Two things can be done.

1) The luminosity needs not be constant to make the star disappear, just smooth enough.

2) You can add green and red to blue in proper proportions and stay at the same chromaticity while increasing its luminosity. —Preceding unsigned comment added by 82.139.86.131 (talk) 10:06, 11 May 2010 (UTC)

Look up a tiny bit to the discussion right above this. There are obviously various choices of Y for each (x, y), and it is not too hard to choose a smooth function for this. The main question is: what Y(x, y) function best serves the needs of users trying to read these diagrams. I’m not sure what your point (2) is saying, but adding red and green, without changing blue, will definitely change the chromaticity. –jacobolus (t) 06:57, 12 May 2010 (UTC)