Re: 2 degree vs. 10 degree
Re: 2 degree vs. 10 degree
- Subject: Re: 2 degree vs. 10 degree
- From: Robin Myers <email@hidden>
- Date: Sun, 09 Feb 2003 09:51:06 -0800
- Organization: Robin Myers Imaging
Chris Murphy wrote:
>
>
The LAB debate has caused me to think of yet another possibly "more
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interesting than useful" topic. Everything in ICC-based color
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management is 2-degree, D50 LAB (for output profiles) and I've always
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wondered why we use 2-degree and not the newer 10-degree Standard
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Observer data. Annex A of the ICC spec says the PCS is to be based on
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the 2-degree Standard Observer.
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>
What little I've been able to find on 2-degree vs 10-degree generally
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says that 10-degree is considered to be better (better for what is
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somewhat unclear), and some sources say it's more common. But not in
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ICC-based color management.
Chris,
The 2-degree CIE Standard Observer was based on 2-degree field of view
experiments. These experiments use the foveal region of the eye which
has less of a blue-violet response than the surrounding retinal region
primarily due to the macula, a yellow filter in front of the fovea which
protects it from shortwave UV.
When observing colors that occupy a larger field of view than about 4
degrees, there is increased sensitivity to the blue-violet region of the
spectrum. So, the CIE adopted the 10-degree Standard Observer in 1964
to be used for larger field of view color comparisons.
I believe the reason for the ICC adopting the 2-degree observer is
fairly valid. In most image processing, large fields of view are seldom
encountered. A 2-degree field of view is approximately the size of a
dime at 18 inches from the eye and a 10-degree field of view is 3.2
inches at the same 18 inch viewing distance.
An excellent reference for much of the history of our current color
industry can be found in "The Measurement of Appearance, Second Edition"
by Richard S. Hunter and Richard W. Harold, editors. It has recently
been reprinted and should be available. I like this book because it
explains why various decisions were made and the historical progression
of the color science field. It is also the only book I've seen that has
spectral measurement methods for materials such as fabrics, powders,
food, thread, et cetera.
Another good book that describes the eye and its responses is "Color
Appearance Models" by Mark D. Fairchild.
Robin Myers
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