Talk:Color difference

message: In the CIE 1994 formula for delta_H_star_ab, shouldn't the last term read delta_C_star_ab rather than delta_C_star?
Gggustafson (talk) 16:20, 16 August 2011 (UTC)
thread_title:  delta h in CIE 1994 

message: In color difference 94, isn't the "h1 - h2" term adjusted so it is not greater than pi?  h is an angle, if this is really using LCh coordinates.  But I've seen other formulas that seem to calculate a dH term from a, b and C.  I'm unsure about the accuracy of this section of the article now.  DonPMitchell (talk) 16:17, 9 July 2009 (UTC)
thread_title:  delta h 

message: In the CIEDE2000 section, it looks like a1, a2, b1, and b2 are missing stars, but I'm not familiar enough with this stuff to say for sure. If they're not missing stars then it should be clarified what a1, a2, b1, and b2 are supposed to be. Hixie (talk) 06:28, 11 April 2011 (UTC)
replies: text: You are right, the asterisks were missing (see ref #12), now added. Note that Bruce Lindbloom (ref #13) does not use the asterisks but naked 'a' and 'b'.--SiriusB (talk) 16:56, 20 January 2013 (UTC)
thread_title:  missing stars? 

message: In the initial square root of the sum of the squares formula, it references ∆H', but the following equations only reference ∆H'bar and ∆h'. I think it is referring to ∆h', but am not certain. These equations should be case sensitive, so could someone with more precise knowledge verify and correct the formula?
PJV (talk) 17:30, 11 May 2011 (UTC)
replies: text: \Delta H' = 2 \sqrt{C'_1C'_2}sin(\Delta h'/2)
(this is from http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CIE2000.html, a reference of the article section)
PJV (talk) 19:18, 11 May 2011 (UTC)

text: Yup, you’re right, \Delta \bar{H}^\prime should be just \Delta H^\prime. Looks like just a typo. –jacobolus (t) 03:06, 16 November 2011 (UTC)
thread_title:  ∆H' in the CIEDE2000 equation 

message: I am having problems understanding from the article whether \bar{H}' is in degrees or radians (For CIEDE2000)
This part seems to imply it is degrees,
R_T = -2 \sqrt{\frac{\bar{C}'^7}{\bar{C}'^7+25^7}} \sin \left[ \frac{\pi}{6} \exp \left( -\left[ \frac{\bar{H}'-275^\circ}{25} \right]^2 \right) \right]
But at the same time this part seems to (as far as I can tell) imply it is radians.
  T = 1 - 0.17 \cos ( \bar{H}^\prime - \pi/6 )
        + 0.24 \cos (2\bar{H}^\prime)
        + 0.32 \cos (3\bar{H}^\prime + \pi/30 )
        - 0.20 \cos (4\bar{H}^\prime - 21 \pi/60)
Would it be possible for someone with more knowledge about this to clarify ? 109.189.51.196 (talk) 13:38, 29 December 2011 (UTC)
replies: text: How important is it that it is degrees? Would converting everything to radians (taking care to make them in the range [0, 2pi] where appropriate, as is suggested for degrees currently) give an equivalent result? Most intrinsic functions seem to use radians rather than degrees, and it seems weird to go through degrees for the sake of it. NeruYume (talk) 01:31, 2 November 2012 (UTC)
replies: text:  Sadly, colorists use degrees rather than radians; its easy to add or subtract 360; 2π not so much. The color difference definition and secondary sources use degrees, so this article should use degrees. WP is not a how-to guide. An earlier version of this article used radians (see above), but then stopped with the expression for RT (presumably due to the argument for the exponential; the specification used 25 instead of 25° in the denominator; I made the degrees explicit). One may certainly rewrite the equations to use radians, but any software implementation should be tested against published values to make sure the implementation is correct. Many test cases are designed to trip up naive implementations. I don't see the radian-degree conversions as a big deal - a few extra multiplications that can be hidden using macros/functions such as sind(angle) instead of sin((M_PI/180)*angle). Instead of using atan2() directly, stick it in a function that not only does the degree conversion, but also checks for the degenerate case and returns 0 to 360°; turns out that function is needed for some colorspace conversions anyway. The problem with not doing the conversions is the risk of messing up somewhere; if somebody sees a variable h, then they may assume it is in degrees. Glrx (talk) 02:13, 4 November 2012 (UTC)
thread_title:  Degrees or radians? 

message: These sections omit mention of CIELUV and the associated formulae, creating the false impression that CIELAB was the first and only CIE-sanctioned color space for calculating color differences in terms of Euclidean distance, circa 1976.
It also overlooks the many CIELUV/CIELAB predecessors and subsequent alternatives (e.g., Wandell's S-CIELAB). It should at least be mentioned that there are other color-difference measures and the entry restricts attention to the CIE-sanctioned ones.
Therealdp (talk) 14:04, 4 September 2013 (UTC)
replies: text: Worse, I feel is that it omits any discussion of computability and the various approximations. If somebody came to the site and wanted to know about color differences they would be asked to implement a bunch of very cryptic formulae rather than noting the actual fairly good approximations or device dependent descriptions. Tat (talk) 15:22, 22 January 2017 (UTC)
thread_title:  Delta E and CIE76 sections omit CIELUV & others 

message: What is the variable a* in the CIEDE2000 formula?  The a* in LAB?  Thus, the formula needs both LAB and LCH (not that that is a problem since you get one from the other)?  — Preceding unsigned comment added by 173.228.4.22 (talk) 20:18, 19 November 2015 (UTC)
thread_title:  a* in CIEDE2000 

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thread_title:  External links modified 

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thread_title:  External links modified 

message: Using notation not sanctioned by the CIE for a CIE Total Color Difference is not encyclopedic. With respect to the Mahy study, a proper reference is needed, and exactly what color difference he used must be specified. Otherwise, that section of text may be deleted as not properly referenced. Lovibond (talk) 21:58, 29 September 2017 (UTC)
replies: text: You changed the meaning of the text. Glrx (talk) 19:36, 5 October 2017 (UTC)
replies: text:  The paragraph does not have a proper reference; a name (last name only, but the author is known to me) and a year do not constitute an acceptable citation. I cannot check whether the text is supported by a reliable reference. Please provide a proper citation, and explain what color difference is being referred to by Mahy. Until such time, the paragraph is deleted for lack of a reliable reference. Lovibond (talk) 15:25, 6 October 2017 (UTC)
replies: text:  Your edit did not remove the Mahy reference, so that is clearly not the issue. You edit did modify Mahy's JND finding, something that you still fail to recognize. Glrx (talk) 17:10, 12 October 2017 (UTC)
thread_title:  Non-sanctioned nomenclature is not encyclopedic 

message: RGB weights are for use with linear values. Since linear light isn't perceived linear then simple weights - as explained - is naive. If weighting that factors gamma was intended then the explanation for why it doesn't work is misleading or at least incomplete. If not, then the whole discussion of RGB component weighting needs to be rethought.  — Preceding unsigned comment added by David Billen (talk • contribs) 23:01, 31 October 2017 (UTC)
thread_title:  RGB Color weighting 

message: The best color difference function is Manhattan distance of R, G and B, weighted by 0.299, 0.587 and 0.114 respectively.
\text { rederror} \times 0.299 +\text { greenerror} \times 0.587 +\text { blueerror} \times 0.114
155.230.90.52 (talk) 09:34, 21 April 2018 (UTC)
replies: text: Actually no, what you gotta do is convert sRGB to linear RGB, then use this formula
\text { lineardifference} = \text { rederror} \times 0.212671 +\text { greenerror} \times 0.715160 +\text { blueerror} \times 0.072169
then
\text { linearbrightness1} = \text { red1} \times 0.212671 +\text { green1} \times 0.715160 +\text { blue1} \times 0.072169
\text { linearbrightness2} = \text { red2} \times 0.212671 +\text { green2} \times 0.715160 +\text { blue2} \times 0.072169
then convert linearbrightness1 and linearbrightness2 to produce 2 new variables sRGBbrightness1 and sRGBbrightness2 then the final difference is:
\text { difference} = \text { lineardifference} \times (( \text { sRGBbrightness2} - \text { sRGBbrightness1} )\div( \text { linearbrightness2} - \text { linearbrightness1} )) 
or, if linearbrightness1 and linearbrightness2 are the same, use the derivative of sRGB instead:
\text { difference} = \text { lineardifference} \times ( \text { derivativeof} ( \text { sRGBbrightness1} ) ) 
2A01:119F:21D:7900:503A:C616:B438:9F40 (talk) 08:59, 1 August 2019 (UTC)

text: Can you provide any academic or research source material that suggests this is the best color difference function? ∆E2000 is mostly considered the best, with some people advocating for newer difference formulas based on CAM16 UCS. TDcolor (talk) 19:39, 21 June 2022 (UTC)
thread_title:  Best color difference function 

message: Personal observation told me that in small areas (dozens) of pixels, white and yellow can under some circumstances be difficult to distinguish. I suspect this has to do with gamma values of monitors, and possibly age. Anyone information on that?
alex (talk) 08:08, 27 August 2018 (UTC)
replies: text: white and yellow differ only by the blue channel, and also color differences are easier to distinguish on darker colors than on brighter colors. 2A01:119F:21D:7900:503A:C616:B438:9F40 (talk) 09:01, 1 August 2019 (UTC)
thread_title:  white versus yellow 

message: Let's compare the results of calculations of two formulas.
:\bar r = {{250  + 128 } \over 2} = 189
:\Delta R = 250  - 128 = 122
:\Delta G = 249  - 129 = 120
:\Delta B = 248  - 130 = 118
Formula 1:
:\Delta C = \sqrt {\left( {2 + {{\bar r} \over {256}}} \right) \times \Delta R^2  + 4 \times \Delta G^2  + \left( {2 + {{255 - \bar r} \over {256}}} \right) \times \Delta B^2 } 
= \sqrt {\left( {2 + {{189} \over {256}}} \right) \times 122^2  + 4 \times 120^2  + \left( {2 + {{255 - 189} \over {256}}} \right) \times 118^2 }
= \sqrt {129794.359375}
Formula 2:
:\Delta C = \sqrt {2 \times \Delta R^2  + 4 \times \Delta G^2 + 3 \times \Delta B^2 +  {{\bar  r \times (\Delta R^2 - \Delta B^2) } \over {256}} }
= \sqrt {2 \times 122^2  + 4 \times 120^2 + 3 \times 118^2 +  {{189 \times (122^2 - 118^2) } \over {256}} }
= \sqrt 
As you can see, the formulas give different results. KyberPrizrak (talk) 07:38, 4 March 2019 (UTC)
replies: text: Please note the MathJax/LaTeX implementation used in Wikipedia understand the Western notation with a decimal DOT for separating a fraction part:  but not the Eastern decimal COMMA: . If you want to force a comma, surround it with curly braces to avoid a space after it: . But be aware many readers may get confused with such notation in English-language text. --CiaPan (talk) 08:32, 4 March 2019 (UTC)
replies: text:  The source does not have the second formula, so some editor did the manipulation that dropped a  term. I deleted the second formula. Glrx (talk) 18:10, 4 March 2019 (UTC)
thread_title:  Formulas are not equivalent 

message: Is there any source on this sqrt(2*ΔR^2 + 4*ΔG^2 + 3*ΔB^2) weighted equation? I've been experimenting with my own weighted equations using MacAdam ellipses of just noticeable difference and it seems that these weights are almost backwards. Green has the largest ellipses of just noticeable difference, red the second largest, and blue the smallest, thus green should have the smallest number, red the second smallest, and blue the largest since the ellipse size is inversely proportional to how good human vision is at differentiating between hues in that area.
My own results are more like sqrt(9*ΔR^2 + 5*ΔG^2 + 11*ΔB^2) based on the reciprocal of the major radii of the ellipses in the sRGB primaries areas or sqrt(15*ΔR^2 + 11*ΔG^2 + 17*ΔB^2) based on the reciprocal of the width of ellipses in the sRGB primaries measured perpendicular to lines radiating from D65 white as an approximation of hue.  — Preceding unsigned comment added by TorridGristle (talk • contribs) 13:31, 26 June 2019 (UTC)
replies: text: The thing is, distinguishing values of, say, Green is NOT the same as "differentiating between hues in that area". When green transitions into yellow, it is the RED channel that differs, not the GREEN channel. When green transitions into cyan, it is the BLUE channel that differs, not the GREEN channel. 2A01:119F:21D:7900:503A:C616:B438:9F40 (talk) 08:40, 1 August 2019 (UTC)

text: There is a source. But it's a source written by a programmer that tweaked the numbers based on vibes, so any disagreement is really not a surprise. I would not, however, just use the hue: humans care about how bright it is too, and how saturated it is. Artoria2e5 🌉 14:33, 23 January 2024 (UTC)
thread_title:  Weighted Euclidean RGB Difference is questionable? 

message: We should write about it. CALMAN (I think) is already using it and said it is better. https://www.youtube.com/watch?v=t9ntP01MceQ&t=502 
https://www.itu.int/rec/R-REC-BT.2124/en ZBalling (talk) 03:14, 27 November 2019 (UTC)
thread_title:  BT.2124 : Objective metric for the assessment of the potential visibility of colour differences in television (delta ITP)