Re: Colorsync-users Digest, Vol 6, Issue 205
Re: Colorsync-users Digest, Vol 6, Issue 205
- Subject: Re: Colorsync-users Digest, Vol 6, Issue 205
- From: Lee Badham <email@hidden>
- Date: Fri, 28 Aug 2009 09:03:54 +0100
Which is interesting when testing a proofer for ISO 12647-7 - the
black solid ∆H. The target for FOGRA39 (and ISO 12647-2 PT1/2) is 16
0 0, which always produces a ∆H of 0 even though you could be looking
at a brown patch instead of a black one...
What I've done in the past is return the a and b error (sqrt(a1-a2)^2+
(b1-b2)^2) when the chroma is 0.
Lee
On 28 Aug 2009, at 05:26, Bill Whitfield wrote:
Greetings,
On ThursdayAug 27, at 12:03 PM, Steve Upton wrote:
It's fair to say that when a=0 and b=0 that hue is "undefined".
I would suggest you alter your Excel formulae to make hue=0 when
a=b=0
regards,
Steve
That was the ticket. However, since as I have noted my trig skills
are 0, and formula writing in Excel is is something I just started
to explore, I am a little challenged to write the formula correctly.
So, as I challenge myself to write the correct formula, I just
placed 0 in the ∆H*ab column for black and the tolerance result is
correct.
Adding a conditional statement indicating to this ∆H*ab formula:
=((a#2*b#1)-(a#1*b#2))/((0.5*((c#2*c#1)+(a#2*a#1)+(b#2*b#1)))^0.5)
that if a* and b* is greater than 0 return value of formula, if not
return 0, is what I now need to learn and think will fix the "0"
problem.
Thanks to all that replied and especially for continuing my education.
-Bill-
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Lee Badham
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Bodoni Systems Ltd
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