tag:blogger.com,1999:blog-1840985738235902482.comments2017-08-16T10:14:41.460-05:00John the Math GuyJohn Seymourhttps://plus.google.com/107565394741171719003noreply@blogger.comBlogger411125tag:blogger.com,1999:blog-1840985738235902482.post-69448113817481482772017-08-15T16:55:14.240-05:002017-08-15T16:55:14.240-05:00John, LOL! But I always thought you looked like Br...John, LOL! But I always thought you looked like Brad Pitt anyway. You don't?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-69285293339627537772017-08-15T15:22:24.582-05:002017-08-15T15:22:24.582-05:00Very informative, thank you!Very informative, thank you!Maryhttps://www.blogger.com/profile/06869390489143180811noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-6803849313973516032017-08-13T03:54:58.358-05:002017-08-13T03:54:58.358-05:00Helmholtz KorlharausxhHelmholtz Korlharausxhmichaelejahnhttps://www.blogger.com/profile/01612159241045672522noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-80858929157934502792017-08-03T00:49:00.498-05:002017-08-03T00:49:00.498-05:00I cant get past "the ace of hearts is white&q...I cant get past "the ace of hearts is white"¿Hanshttp://www.colourisintheeyeoftheoneviewingit.comnoreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-56378200977857413292017-08-02T20:06:48.064-05:002017-08-02T20:06:48.064-05:00Ah, excellent! Thanks!Ah, excellent! Thanks!Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-36268065810928394172017-08-02T16:32:35.862-05:002017-08-02T16:32:35.862-05:00Was it the TAGA paper from Tony Johnson, perhaps? ...Was it the TAGA paper from Tony Johnson, perhaps? I don't have a reference handy, either.<br /><br />I agree with you, as usual, Steve. CIELAB is icky all by itself, because 1) it is based on nonlinear functions applied to the XYZ functions which do not exist in nature, and 2) it applies a piecewise function, which again, does not exist in nature.John Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-86309720139953181542017-08-02T16:20:36.281-05:002017-08-02T16:20:36.281-05:00The 2000 formula is only the second ugliest?
Ther...The 2000 formula is only the second ugliest?<br /><br />There is at least one study (sorry, I do not have the citation handy) that shows that the 2000 formula did not perform better than the 1994 color difference formula. An oblique application of Occam's razor would favor the 1994 formula, a relatively straightforward extension of the 1976 a*, b* formula.<br /><br />Personally, I believe if one must go to lengths as Herculean as those employed in the 2000 formula, there is a fundamental flaw in the foundation, and your time might be more productively spent elsewhere.<br /><br />IPT and related spaces are only slightly more complicated than CIELAB, and are far more uniform. They avoid the oversimplification made in CIELAB that the x-bar, y-bar, and z-bar color matching functions are cone fundamentals, and use a more realistic set of cone fundamentals. IPT-like spaces should be investigated further as a replacement for CIELAB.<br /><br />Apostasy, heresy, iconoclasm, or just plain practicality? I would like to think the latter, but many disagree with me.Steve Viggianohttp://acolyte-color.comnoreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-79643067434030952162017-08-02T11:20:49.559-05:002017-08-02T11:20:49.559-05:00Three years ago, I predicted that you would ask th...Three years ago, I predicted that you would ask that question, so I blogged on it:<br />http://johnthemathguy.blogspot.com/2014/11/measuring-fluorescent-inks.html<br /><br />I agree, the practical answer is that if you have a well defined light source (which is defined down into the UV) that you can have a meaningful definition of the color of something that fluoresces. Such a standard light source was defined for the print industry in ISO 13655.<br />http://johnthemathguy.blogspot.com/search?q=m3<br /><br />For more information on fluorescence:<br />http://johnthemathguy.blogspot.com/2017/04/on-nature-of-emitted-light-part-3.html<br />John Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-5878080703913277742017-08-02T10:38:12.911-05:002017-08-02T10:38:12.911-05:00Does this discussion also apply to fluorescent col...Does this discussion also apply to fluorescent colors (e.g. DayGlo)?<br /><br />My initial guess is yes: You can illuminate a fluorescent color with a defined light source (e.g. D50) and measure the resulting reflectance spectrum, which can then be converted to L*a*b*. Unlike a non-fluorescent color, there will be more energy in certain parts of the spectrum than was present in the light source, but I don't think that should affect the calculations. The color will probably just have a brightness and/or saturation beyond what would be expected given the white point. (Maybe L* could end up greater than 100?)Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-11301458534234699482017-08-01T17:27:58.365-05:002017-08-01T17:27:58.365-05:00Two photons enter in bar. They wave at each other....Two photons enter in bar. They wave at each other. The end.<br />Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-80563234376287517452017-07-30T09:22:16.449-05:002017-07-30T09:22:16.449-05:00I got an email from the venerable Danny Rich. It s...I got an email from the venerable Danny Rich. It seems that Google blogger doesn't like him, since it doesn't let him post a comment. If anyone else is having problems posting comments please post a comment here so that I can look into it.<br /><br />Danny has provided us with a bit more detail about JND:<br /><br />"I find a couple of premises in this blog that are not supported in the literature and lead to a questionable conclusion. The first is that visual color space (not some mathematical approximation to it) is visually uniform across all hues, lightness and chromas (using your Munsell notations). Thus trying to equate any form of DeltaE to a visual jnd is a bit like trying to catch the wind. The second is that someone, somehow invented MacAdam ellipses and then he just adopted them for his research. Reading his papers and his presentations to the OSA one observes, that despite the complicate schematic, his experiment was relatively simple. There was a reference color field and a test color field. They began as being equal and the test field was varied along a single direction in chromaticity (no differences in the brightness). When his observe (Mr. Nutting) could detect a visual difference the experiment stopped, the setting of the test color recorded and the experiment was repeated, moving in a different direction in chromaticity. This process was repeated a number of times and the distance to jnd determined from the standard deviations of the trials. So the final experimental data was the 20 or so color centers with a lot of little "sticks" pointing outward. Today we might cast a convex hull around those points but in the 1940s such arithmetic was not easy to do. Since the lengths of the sticks were not equal in all directions, a circle would not be a good fit and the next simple geometric figure was an ellipse. So ellipses were cast around his data points. A later paper by Brown, Jackson (also of Kodak) and Howe (an intern at Kodak from NC State) demonstrated that the ellipse was simply the 2D standard deviations of the bivariate Normal statistical distribution. Brown went on to derive the same mathematical analysis for combined lightness and chromaticity differences as the 3D ellipsoid, again simply represented by the trivariate Normal distribution. The reason that the shape should be elliptical or ellipsoidal lies in the relationship between the coordinates. (x,y) or (Y,x,y) are not independent but are correlated so that the covariance is not zero. A good discussion of this can be found in the section on Color Metrics in the textbook Color Science by Wyszecki and Stiles. The arguments apply to the work on differences in CIELAB space. L*, a*, b* all contain the Y tristimulus value and as a result are correlated. Since L*,a*,b* are not independent they will not form a Euclidean space and the standard deviations of visual judgments will always form an ellipsoid. So if we have to assign a cause for MacAdam's jnd's being elliptical perhaps it should be R. A. Fisher "John Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-40883347014864112302017-07-26T10:37:10.767-05:002017-07-26T10:37:10.767-05:00One topic you haven't covered with DeltaE (wit...One topic you haven't covered with DeltaE (with reference to the picture of chips on a grocery store shelf) is that it is defined in terms of a specific observer and illuminant. If the illuminant (or possibly observer) is not the same as used for measuring DeltaE and making decisions about acceptability then the DeltaE doesn't correspond to perceived color difference.Max Derhakhttps://www.blogger.com/profile/13411859960497744293noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-16705920918651171502017-07-26T10:35:59.276-05:002017-07-26T10:35:59.276-05:00This comment has been removed by the author.Max Derhakhttps://www.blogger.com/profile/13411859960497744293noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-37885861426308227552017-07-23T19:40:23.617-05:002017-07-23T19:40:23.617-05:00Hi John,
My studies show that your "Level 4 &...Hi John,<br />My studies show that your "Level 4 "pleasing color" difference, DE00 of 6" is called a different color between standard and sample by most people and not an acceptable color difference throughout most of the gamut of color space. Further, isn't close tolerance color difference considered less than 5.0 units? Jack Ladsonnoreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-1784498953617995892017-07-20T20:59:27.960-05:002017-07-20T20:59:27.960-05:00I've seen several references in my quest for c...I've seen several references in my quest for color smarts that state we see hue differences first, chroma differences second and lightness differences last. So, I think you're good to go on that one.funcolorshttps://www.blogger.com/profile/05807098581903734655noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-24073899251661810712017-07-19T08:07:47.062-05:002017-07-19T08:07:47.062-05:00Hi John. This is in line with the conventional wis...Hi John. This is in line with the conventional wisdom of "application specific" color difference tolerance. A while back I did a job regarding retail packaging in which the product and the competition were never viewed side-by-side. (They are both retail products, but shared exactly zero retailers in common.) The time course of color matching for this specific color - kind of a dark teal - was dE00 of ~ 4. This was was effectively a tolerance around the product color that defined, after 15 minutes or more, the region that was indistinguishable from the product color.<br /><br />There is ample literature on the perception of color over time. It took a while to come up with a plausible and defensible strategy (these were attorneys, of course) but in the end I think I achieved both.Dave Wyblehttps://www.blogger.com/profile/09623357167770566661noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-69072911751531826122017-07-18T14:00:55.808-05:002017-07-18T14:00:55.808-05:00Thank you, Roger!
Drop me an email, and I will ge...Thank you, Roger!<br /><br />Drop me an email, and I will get you on my mailing list: <br />john@johnthemathguy.comJohn Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-86592526883409579952017-07-18T13:48:19.964-05:002017-07-18T13:48:19.964-05:00I love following this blog. Thank you, Mr Seymour....I love following this blog. Thank you, Mr Seymour.<br />-<br />Roger BretonAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-65488947920931781142017-07-18T12:29:04.295-05:002017-07-18T12:29:04.295-05:00The link worked on my computer, perhaps because th...The link worked on my computer, perhaps because the NPES computer knows I am a special person. Try this link to buy a free copy: http://npes.personifycloud.com/personifyebusiness/Store/ProductDetails.aspx?productId=157515John Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-55681810058734669782017-07-18T12:19:29.637-05:002017-07-18T12:19:29.637-05:00Hello John,
When I try to open the CGATS link, I g...Hello John,<br />When I try to open the CGATS link, I get an error message on a black screen:<br />"Blocked Plug-in"<br />Vots up?ArtShttps://www.blogger.com/profile/18368143617877770700noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-23882995428370591922017-07-17T13:44:57.109-05:002017-07-17T13:44:57.109-05:00I received (via LinkedIn) a correction to this blo...I received (via LinkedIn) a correction to this blog post from Michael Huda:<br /><br />"Hi John, just for clarity, Richard Hunter was the first to develop the De calculation and that was in 1945. It was transferred to CIELab ColorSpace when it was ratified in 1976. Thanks for the interesting article."<br /><br />I made a small correction to Michael's correction:<br /><br />The DE color difference goes back just a bit further than that, Michael.<br /><br />The earliest reference to the DE calculation that I can find is a paper by Deanne Judd of 1939: "Specification of color tolerances at the national bureau of standards". In this paper, he uses the Pythagorean distance formula (same formula as in the 1976 DE calculation) on the UCS color space to derive the "NBS unit of color difference".<br /><br />I have not been able to find a copy of the Judd 1939 paper, but it is described by Richard Hunter in the paper "Photoelectric tristimulus colorimetry with three filters" from the National Bureau of Standards (1942). Hunter provides six different formulas for DE, all of which have some resemblance to the 1976 formula.<br /><br />Judd also provided a description of the NBS formula in "Physiological Optics at the National Bureau of Standards" (1967, Applied Optics). In this paper, he traces the concept of the difference between two colors back to a 1909 paper by Nutting.John Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-92056890663471135312017-07-17T13:42:19.702-05:002017-07-17T13:42:19.702-05:00I received a comment by email from my good buddy, ...I received a comment by email from my good buddy, Robin Myers:<br /><br />I always enjoy your blogs and I was especially interested in reading your latest blog about ∆E and the Munsell system.<br /><br />However, I must correct you on one thing. Although Albert Munsell published “A Color Notation” in 1905, at that time he did not produce a book with actual color chips. The first publication of his “Atlas of The Munsell Color System”, with painted chips, was not published until 1915. This publication had hundreds of color patches, but not thousands. <br /><br />I have measured all 477 surviving patches in my copy (#115). Chart H is missing from my copy, some scurilous miscreant removed it, but from the ghost image of the cover page there were 77 patches on this chart, arranged in 11 columns of 7 patches each. That would bring the total patches originally published to 554.<br /><br />Robin has a data file with measurements of his copy of the Munsell Color System Atlas onine: http://rmimaging.com/spectral_library/library_index.html You will need a copy of SpectraShop to read the file.<br /> John Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-75467975323535548802017-07-14T10:10:46.443-05:002017-07-14T10:10:46.443-05:00Thank you, Roel, for the additional information!Thank you, Roel, for the additional information!John Seymourhttps://www.blogger.com/profile/11350487038873935295noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-89743313733058088032017-07-14T03:09:24.785-05:002017-07-14T03:09:24.785-05:00Hi John, Thanks for mentioning our blog. We also m...Hi John, Thanks for mentioning our blog. We also made an overview of these low cost measuring devices see: http://www.coltechcon.com/publication/overview-low-cost-color-capture-devices/ . It includes price indications and an updated picture.<br />As a comment: these instruments are meant to find colors in a fan deck with an accuracy of say 95%. And most of them come close and each of them have unique properties. My statistics are a bit more optimistic than yours. <br />Roel Gottenboshttps://www.blogger.com/profile/04545381829822042335noreply@blogger.comtag:blogger.com,1999:blog-1840985738235902482.post-6657007194524135952017-07-12T10:17:33.819-05:002017-07-12T10:17:33.819-05:00Very nice story, love it. The evolution of color f...Very nice story, love it. The evolution of color formulas.Roel Gottenboshttps://www.blogger.com/profile/04545381829822042335noreply@blogger.com