User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax)
Steve Kale wrote:
Thanks. I actually found this before I got this digest. Turns out I had
misunderstood Bruce's annotation for the inverse tangents (whatever they
are) and had the coordinates around the wrong way.
Basic Trigonometry, something you would have come across early
in high school maths - <http://en.wikipedia.org/wiki/Tangent>.
atan is often uses in converting polar co-ordinates to rectangular
co-ordinates.
> The spreadsheet you
referenced below helped me find the error. I have not been through their
paper in detail but noticed the mention of "minor discontinuities". What's
the sense out there as to 2000 vs 1974 dE? My assumption is that while
still not perfect, 2000 is still an improvement on 1974.
DE2000 is regarded as being superior, but there are mathematical
issues that can affect some uses. The computation of a mean
hue angle is a discontinuous operation, as two colors that have
opposite hues, have a mean that could be one of two directions,
also opposite. This is nicely illustrated in Figure 1 & 2 of the paper.
Two colors of almost the same hue that lie either side
of zero angle, also illustrate a problem with hue difference
as well. The sign of the hue difference changes depending
on the way the modulo difference is handled, and for DE2000,
the sign of the hue angle difference affects the result.
The sort of things where these discontinuities pose a problem,
are where it's uses for numerical optimization, or the
first derivative is needed for some calculation.
Graeme Gill.
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Colorsync-users mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
http://lists.apple.com/mailman/options/colorsync-users/email@hidden
