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Re: Color Measurement
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Re: Color Measurement


  • Subject: Re: Color Measurement
  • From: Rolf Gierling <email@hidden>
  • Date: Mon, 20 Jul 2009 13:10:32 +0200

Hello Robin and Graeme,

it is important to note that it's not the Just Noticable Difference JND that is in question here,
but the non-uniformity of the color spaces used that lead to other results.


If CIECAM02 is a nearly visual uniform space, one could say that one unit represents one JND.
CIELab definitively isn't, so a JND might be represented by other unit values (bigger or
lesser than one, depending on the color).


some quotes of Jan Morovic, Color Gamut Mapping, Wiley 2008

page 27:
2.6.2 Color difference and uniform color spaces
While being able to tell whether two stimuli will match is a useful first step, it is even more important
to predict how different stimuli are when they do not match. This is precisely what color difference
equations, typically denoted by dE, set out to do with two key aims:
1. that a color difference equal to one (i.e. dE = 1) should represent a just noticeable difference (JND),
i.e. the smallest stimulus difference that results in a different response by a viewer, for all color pairs;
2. that color difference predictions should relate uniformly to judgments made by observers
(i.e. a color pair with dE 10 should be seen as 10 times as different as another pair with dE = 1).


page 58:
For simple originals, the perceptibility threshold (for 50% of the population of observers) is one dE,
since dE metrics are set up so that their unit is a JND (Section 2.6) when applied to spatially uniform stimuli.
Note, however, that this is the intention for all dE metrics and that it is, therefore, important to use as accurate
a dE metric as is available, which currently is CIEDE2000 (CIE, 2001).


Rolf Gierling


Am 20.07.2009 um 03:33 schrieb Robin Myers:

I do not have a reference for the rule of thumb that dE2000 is about half of dE1976. It was a verbal conversation at the Color Imaging Conference a few years ago. Like all rules of thumb, large tolerances are often involved.

However, the dE1976 of 1 unit being a JND has never really worked. In the near grays, it has often been my experience that 1/2 to 1/4 unit is a JND depending on the difference direction vector and position in the color space.

What all of this boils down to for me is that there is a large body of work left to be done on color difference metrics.

Robin Myers


On Jul 18, 2009, at 12:21 AM, Graeme Gill wrote:

Robin Myers wrote:
Just as the scale changes in going from dE 1976 to dE 2000, the tolerance range also changes. Where 1 dE 1976 was "roughly" assumed to be a Just Noticeable Difference (JND), now that number should be about 0.5 dE for a JND in dE 2000. As the scale changes, so does the interpretation.

Do you have a reference for this ?

Looking thought the "The Development of the CIE 2000 Colour Difference Formula: CIEDE2000"
and "The CIEDE2000 Color-Difference Formula: Implementation Notes, Supplementary Test
Data, and Mathematical Observations" it isn't obvious that there is any intention
that the JND threshold be different.


This plot also seems to contradict this idea:

<http://www.digitalcolour.org/Difference.htm>

ie. differences of about 1 CIE 1976 DE are also close to 1 CIE DE2000 in
near the neutral axis.


Graeme Gill.
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References: 
 >Re: Color Measurement (From: "Mike Eddington" <email@hidden>)
 >Re: Color Measurement (From: Robin Myers <email@hidden>)
 >Re: Color Measurement (From: Graeme Gill <email@hidden>)
 >Re: Color Measurement (From: Robin Myers <email@hidden>)

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