Re: Hue Angle for Black
Re: Hue Angle for Black
- Subject: Re: Hue Angle for Black
- From: Klaus Karcher <email@hidden>
- Date: Thu, 27 Aug 2009 09:27:52 +0200
At 9:16 AM -0700 8/26/09, email@hidden wrote:
Greetings,
(FYI, I posted a similar question on the Print Planet list - for those that are concerned about cross posting. Thanks, as
always, to Mike E for your reply)
Can black have a hue angle?
Steve Upton wrote:
It's fair to say that when a=0 and b=0 that hue is "undefined".
Yes. And one cold use any angle, it shouldn't make any difference in
color calculations as C=0 when a=0 and b=0. The Chroma Vector has zero
length and therefore no direction.
I would suggest you alter your Excel formulae to make hue=0 when a=b=0
Exactly -- that's the usual way to deal with this situation.
Many atan2 implementation will handle this situation without further
ado, i.e. they return atan2(0,0)=0, but Excel needs some tutoring.
A CIE hue angle function in Excel could look like this:
=IF(
AND(a<>0;b<>0);
IF(ATAN2(a;b)<0;
ATAN2(a;b)*180/PI()+360;
ATAN2(a;b)*180/PI());0)
see also <http://en.wikipedia.org/wiki/Atan2>
Klaus
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Colorsync-users mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden