# [argyllcms] Re: How is delta E calculated in colprof?

• From: Claas Bickeböller <lists@xxxxxxxxxxxxxxxxx>
• To: argyllcms@xxxxxxxxxxxxx
• Date: Fri, 20 Jul 2012 17:29:21 +0200

```Hi,

in 2010 Fogra did a research project where several colour difference formulas
were tested for different applications.
Here applications does not mean different coloration-processes but different
aims when choosing a colour difference formula.

If the aim is modelling the judgment of a human observer in terms of how big a
colour difference is perceived, dE2000 performed best for printed samples in
this research.

Some details (also the data set that was used) can be found online:

http://www.fogra.org/en/fogra-research/prepress/completed/colour-difference-metrics/a-colour-difference-metrics.html

Best regards

Claas

Am 20.07.2012 um 16:50 schrieb Jason Campbell:

> Hi there.  Sorry for jumping in but I generally lurk on the list but liked
> this discussion...
>
> dE76 is a generally accepted Delta-E computation for color difference.  As
> Lab is a three dimensional space, dE76 is a simple Euclidean distance between
> the two three dimensional points (your two Lab values).  For the most part,
> it gives a good sense of how far you are off in terms of color difference.
> It is also nice since it is super easy to calculate.
>
> The other varieties of Delta-E all attempt to improve on the simplistic
> approach of dE76 by better modeling human color perception.  The most recent,
> dE2000 is a very convoluted set of equations.  As you have already noted
> Lindbloom's excellent website, you will have no doubt taken a look at this
> monstrosity.  However, it does do a lot to blend many of the nuances of color
> perception into the calculation.
>
> In the end, there is no "right one" or even "best one" as each dE function
> can be considered well-tailored to certain applications.  For example, dE-CMC
> is often used in textiles.  For graphic arts, dE76 is still generally
> considered the 'standard' if you will.  It continues to be the dE used in
> such things as the G7 GRACoL specification.  A colleague of mine participates
> in a number of print industry standards committees and has indicated that
> there has been a lot of talk about moving toward dE2000 as the new
> specification.  But that is talk, still not the de facto.
>
>
>
> On Fri, Jul 20, 2012 at 10:06 AM, Stephen T <stwebvanuatu@xxxxxxxxxxxx> wrote:
> Here are some examples. The input data is a direct cut-and-paste from the
> colprof output. I have calculated delta E with Gaurav Sharma's spreadsheet
> and Bruce Lindblooms web calculator:
>
> http://www.ece.rochester.edu/~gsharma/ciede2000/
> http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CIE2000.html
>
> [5.790875] 0.018533 0.060767 0.188920 -> 16.184140 24.186926 -63.268069
> should be 19.349371 22.206153 -58.841773
>         DE00 Lindbloom = 2.4096
>         DE76 Lindbloom = 5.7909
> [1.906550] 0.863110 0.849700 0.848230 -> 94.689681 -0.383334 0.713823 should
> be 96.521931 -0.897156 0.596434
>         DE00 Lindbloom = 1.3233
>         DE76 Lindbloom = 1.9066
> [3.648782] 0.114370 0.224380 0.096200 -> 54.928708 -42.874429 37.209866
> should be 52.027751 -44.149537 39.018775
>         DE00 Lindbloom = 2.883450
>         DE76 Lindbloom = 3.648781
> [4.530066] 0.286760 0.036334 0.022012 -> 38.996835 61.855796 36.960859 should
> be 36.036227 64.919159 38.501022
>         DE00 Lindbloom = 2.6417
>         DE76 Lindbloom = 3.063
> [5.273161] 0.651050 0.422930 0.106950 -> 79.796759 4.157840 84.383180 should
> be 80.569480 3.851387 89.590407
>         DE00 Lindbloom = 1.2209
>         DE76 Lindbloom = 5.2732
> [3.185483] 0.357800 0.131360 0.220400 -> 48.673987 54.123752 -12.755375
> should be 48.059068 55.331845 -15.638028
>         DE00 Lindbloom = 1.3801
>         DE76 Lindbloom = 3.1855
> [3.829559] 0.071679 0.252420 0.368150 -> 49.812685 -30.674000 -32.260727
> should be 47.791690 -33.193813 -30.203630
>         DE00 Lindbloom = 2.5854
>         DE76 Lindbloom = 3.8296
> [2.015927] 0.023399 0.024048 0.024181 -> 17.588819 -0.942403 -0.176957 should
> be 15.938875 -0.417952 -1.209720
>         DE00 Lindbloom = 1.6780
>         DE76 Lindbloom = 2.0159
> [11.990115] 0.407720 0.321030 0.050649 -> 70.288554 -10.231232 101.435263
> should be 72.415918 -9.806180 89.643040
>         DE00 Lindbloom = 2.7719
>         DE76 Lindbloom = 11.9901
>
> I must have not noticed before that the delta E reported by colprof (flag -y)
> exactly matches DE76. Anyone can easily verify this with their own data and
> calculation of delta E for just one patch will do. Graeme has also confirmed
> that colprof returns DE76 (Euclidean distance).
>
> The next question's are:
>
> Is DE76 used only for reporting errors or is it used in colprof for model
> fitting as well?
>
> Which delta E function is most appropriate for profiling (my application is
> graphic arts)? Note there's a huge difference between DE76 = 11.99 and DE00 =
> 2.77 for the last patch in the above examples.
>
> Stephen.
>
> From: Graeme Gill <graeme@xxxxxxxxxxxxx>
> To: argyllcms@xxxxxxxxxxxxx
> Sent: Thursday, 19 July 2012 11:53 PM
> Subject: [argyllcms] Re: How is delta E calculated in colprof?
>
> Stephen T wrote:
> > Both of the above are consistent but colprof's delta E values are different
> > and do not match
> > DE76 and DE94 either.
>
> Hi,
>     do you have a specific example ?
>
> > Which delta E is colprof reporting? The documentation states only that "a
> > summary of the average
> > and maximum Lab delta E's will be printed out if this flag [-y] is set".
>
> There is no qualification, so this is plain delta E (ie. Euclidean distance).
> It's
> open source, so you can always look at the source code...
>
> > Is colprof applying any weighting to the DE00 calculation: KL, KC, KH not
> > equal to 1.0?
>
> Again, it's open source - it's easy enough to check, and it's noted in the
> source that the equations are taken from:
>
> "The CIEDE2000 Color-Difference Formula: Implementation Notes,
> Supplementary Test Data, and Mathematical Observations", by
> Gaurav Sharma, Wencheng Wu and Edul N. Dalal,
> Color Res. Appl., vol. 30, no. 1, pp. 21-30, Feb. 2005.
>
> Graeme Gill.
>
>
>
>

```