2 degree, 10 degree and observer cmf differences
2 degree, 10 degree and observer cmf differences
- Subject: 2 degree, 10 degree and observer cmf differences
- From: Thomas Lianza <email@hidden>
- Date: Tue, 23 Aug 2011 06:31:59 -0400
- Thread-topic: 2 degree, 10 degree and observer cmf differences
Hi
I've changed the name of the thread to get it more on target. In my discussions with some engineering folk in Japan they mentioned that they felt that displays should be assumed to be a "greater than 10 degree event" The point is that when two displays are put side by side our impression of the white point and natural adaptation is based on the wide field presented by the scene. You will find some displays leave the factory using 10 degree assumptions of D65 or D50. There is some real merit to this thinking, in my opinion. Viewing emissive scenes is quite different than viewing a reflective scene because all colors are combined from the three primaries, plus a relatively constant level of flare which is dependent upon the ambient illumination. This is why small amounts of white point deviation have such large effects upon the absolute color. This is why you can have really sloppy light booths that "appear" to be neutral and yet a small shift in white point on a display is very obvious to a trained observer. With respect to the concept of "chromatic adaptation" emissive displays are completely different than a reflective environment.
In wide gamut situations, the primaries are necessarily narrow (if there are only three). This will tend to increase differences between observers. I am working on some papers in this area ; mostly review documents and retrospectives to demonstrate how we got to where we are today and some discussions of the relevance of sRGB in the brave new world of display technology. The benefit of wide gamut displays can be masked by the artifacts that narrow band viewing carry. For instance, it is more difficult to the display white point with narrow band radiators. In high ambient situations, it is nearly impossible to not have a visible cast in a narrow band display using standard instrumentation to set white point.
Regards to all,
Tom
-----Original Message-----
From: colorsync-users-bounces+tlianza=email@hidden on behalf of Bob Frost
Sent: Tue 8/23/2011 6:00 AM
To: email@hidden; email@hidden
Subject: Re: Colorimeters and third-party developer support
> Yes, they are being very loose and sloppy, to make their case seem
> more impressive - typical marketing stuff.
>
> The actual case of course is that our color vision varies with
> the location on our retina. The central part has all the color
> detectors, and the periphery has the low light, monochrome detectors
> that have a different spectral response to the other three. Hence
> the change in CMF's with different areas of interest (2 degree vs. 10
> degree).
Hi Graeme,
You seem to be a "bit loose and sloppy" yourself with your statement on the
distribution of the color detectors (cones) and monochrome detectors (rods).
;-
Both types of photoreceptor are found throughout the retina, except for a
very small area at the centre of the fovea - the foveal pit - which is only
about 200 microns in diameter. That does just contain cones. Outside that
small area the rest of the macula (6 mm diameter) and the 'periphery' (which
is actually the bulk of the retina up to 22mm diameter) contains a mixture
of rods and cones in varying numbers. The macula/foveal area contains mainly
cones, while the rod distribution peaks at about 4.5mm (18 degrees) off
centre - around the edge of the macula/foveal area. Cones may make up about
5% of the receptors in the outer areas of the retina.
Strangely, the distribution of the three types of cones (L, M, and S) varies
considerably. S-cones for example, seem to make up only 3-5% of the foveal
pit cones, reach 15% in the rest of the fovea, and 8% throughout the
'periphery' of the retina.
So, although a '2 degree calculation' does coincide with the central foveal
pit, that area is mainly M- and L-cones, with more S-cones outside this
2-degree area. I wonder what effect this has on our color vision?
Bob Frost
--------------------------------------------------
From: "Graeme Gill" <email@hidden>
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