Re: ISO 12647-7
Re: ISO 12647-7
- Subject: Re: ISO 12647-7
- From: <email@hidden>
- Date: Mon, 21 May 2007 13:33:46 -0400
Hello Lee,
There are two ways to look at Delta-h*:
Delta-h* and Delta-H* !
Delta-h* is the difference in hue angle, where you can
subtract 180 for differences larger than 180 degrees, as
suggested.
Delta-H* is the contribution of the hue difference to the
total error. It is obtained by removing the contributions
of Delta-C* and Delta-L* from Delta-E*:
Delta-H* = sqrt( square(Delta-E*)- square(Delta-L*) -
square(Delta-C*))
As you noted, the angular difference will vary
significantly for neutral tones, but Delta-H* will/should
not.
I do not have ISO 12647-2 i front of me but they are most
likely talking of Delta-H*, not Delta-h*.
Danny Pascale
email@hidden
www.BabelColor.com
On Mon, 21 May 2007 16:02:58 +0100
Lee Badham <email@hidden> wrote:
Hi list
I'm hoping someone one this list can clarify something
from the new ISO 12647-2 proofing standard.
There are now hue tests for the grey balance on a proof.
This is a good thing in my opinion.
The standard lists the tolerances as average ?H <=1.5,
but doesn't list how ?H is calculated. I'm assuming it
is done using only the a and b co-ordinates of the lab
value of the cmy, and black patches. It's just that
using ?H is confusing to me as H represents the hue
angle of a colour. As we are dealing with grey colours,
the hue angle itself can vary wildly, for a very small
?Eab.
Thanks
Lee Badham
Bodoni Systems Ltd
www.bodoni.co.uk
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