d65 2 degrees vs d65 10 degrees

9766 Views 8 Replies 4 Participants Last post by <^..^>Smokey Joe, Oct 9, 2007

GbrNole

Discussion Starter · Oct 8, 2007

ok this caught my eye at the other place because someone was still touting behr silver screen and every time i look at that paint it looks both slightly lilac and slightly baby blue to me.

it was stated over at the other venue that behr measured silver screen to be a neutral gray at 205 206 205 but the one thing that jumped out at me was that these measurements were taken at d65 10 degrees.

everything i have seen thus far in the way of referencing neutral gray resulted in RGB measurements being taken at d65 2 degrees so what bearing does this variation have because the silver screen stated measurements posted here sure seem to provide an indication of what i'm seeing (weak green, stronger red, much stronger blue)

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mechman

· #2 · Oct 9, 2007

I wiki'd it! :bigsmile:

The CIE 1964 Standard Observer color matching functions are defined for a 10 degree field of view. They were derived from the work of Stiles and Burch (1959), and Speranskaya (1959). The 1931 standard observer field of view was 2 degrees which covers only the fovea. For the 10 degree experiments, the observers were instructed to ignore the central 2-degree spot. The 1964 supplementary standard observer is recommended for more than about a 4 degree field of view.

What's a fovea?

The fovea, also known as the fovea centralis, is a part of the eye, located in the center of the macula region of the retina. [1] [2] The fovea is responsible for sharp central vision, which is necessary in humans for reading, watching television or movies, driving, and any activity where visual detail is of primary importance.

Watching TV and movies... 2 degrees must be good enough, eh? :bigsmile:

From a chart here on white points, you can see that the difference between 2 degree and 10 degree is about .001- .002 or so.

Bill will pipe in shortly and probably more in depth! :hide:

mech

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wbassett

· #3 · Oct 9, 2007

Not much to add... it covers a 10degree area while the other only a 2 degree area. More is sampled so you get a bigger section. PocketSpec uses 45 degrees, but they are selling colorimeters and not full spectrophotometers.

gbrnole said:
one question i have is that the behr readings were all done at d65 10 degrees while every other neutral reading of gray that i have seen was taken at d65 2 degrees -what is the difference between the two readings especially given that i have seen alternate values for silver screen that seem to more closely represent what i'm looking at (207 202 215)?

The 207 202 215 value was converted using C. If you took the graph and could 'cut' the C reference point and where 207 202 215 falls in respect to it, and could overlay it ontop of the D65 neutral reference point, you'd see the two values match up or be so close nobody would argue any difference.

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<^..^>Smokey Joe

· #4 · Oct 9, 2007

Calibration is typically based upon the 2 degree CIE1931 xy coord system.

It may seem old, but our eyes haven't changed and short of new discoveries in the way we see or perceive this reference probably wont change much.
In the CIE chart D65 is a point x.313,y.329 and it can be black all the to white as this point actually has a 3rd dimension to it. They all (should) equal x0.313,y0.329

D6500 as an iluminate is like an overcast sky, or viewing from under a shady tree.
Measuring a reflective colour is hard without an accurate D6500 illuminance that creates the full spectrum of light as we see it.

Our eyes are better at seeing illuminance as we have billions of rods, where the colour function we have only millions of cones, and these are arranged to see straight ahead, hence the central narrow angle of illuminance and colour accuracy. As the angle widens our colour interpretation changes as does our sensitivity to such artifacts as flicker which is a function of our 22 cycles per second eye/brain resolution.

:reading:

Ive just finished reading 'Intangle Minds' and now Im not sure about reality anymore in that none of this could be real. Quantum mechanics...if it doesn't scare you, you don't get it.

back to work now....bad boy...

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wbassett

· #5 · Oct 9, 2007

Gbr here is also something that hopefully will help with all of the neutral discussions.

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wbassett

· #6 · Oct 9, 2007

<^..^>Smokey Joe said:
Measuring a reflective colour is hard without an accurate D6500 iluminance that creates the full spectrum of light as we see it...

Thanks for answering up Smokey

Also this is why spectrophotometers are such an expensive and precise piece of equipment. They also require routine calibration testing and recertification from an authorized and certified facility. They may remain accurate well after the calibration date expires same as a car will certainly still run after the inspection expires, but unlike the car that only needs to get us from point A to point B and it doesn't matter how fast (but should as far as how safely), a spectrophotometer can't be guanteed to be within specifications once the calibration is expired. A person could use it for their own personal color space as long as they don't try to reference to other values taken from calibrated units. It could be accurate and the same, or it could be off. To emilinate questions, units are calibrated and recertified on a regular basis.

Now, one thing to mention is there are and will be slight variances between two units but those variances should be very small- so small in fact nobody would contest it as a totally different color. Other variables could be the source being tested.

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mechman

· #7 · Oct 9, 2007

wbassett said:
Also this is why spectrophotometers are such an expensive and precise piece of equipment. They also require routine calibration testing and recertification from an authorized and certified facility. They may remain accurate well after the calibration date expires same as a car will certainly still run after the inspection expires, but unlike the car that only needs to get us from point A to point B and it doesn't matter how fast (but should as far as how safely), a spectrophotometer can't be guanteed to be within specifications once the calibration is expired. A person could use it for their own personal color space as long as they don't try to reference to other values taken from calibrated units. It could be accurate and the same, or it could be off. To emilinate questions, units are calibrated and recertified on a regular basis.

X-Rite recommends yearly factory calibrations. :bigsmile:

mech

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mechman

· #8 · Oct 9, 2007

<^..^>Smokey Joe said:
:reading:

Ive just finished reading 'Intangle Minds' and now Im not sure about reality anymore in that none of this could be real. Quantum mechanics...if it doesn't scare you, you don't get it.

back to work now....bad boy...

I'm gonna have to look for that as my current books are all read and stacked... :nerd:

Good read smoke?

mech

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<^..^>Smokey Joe

· #9 · Oct 9, 2007 (Edited)

Oops mis spulled that.

'Intangled Minds'

Interesting read for sure. The chap who wrote this book was part of the PSI experiments like remote viewing and so on. If one is interested in the idea of quantum mechanics and things like effects of 'influence' on the fuzzy world we are part of you will find it interesting. For some the concepts are hard to except.

btw, if you read this book, my sig sentences will make sense. Yes it is true, light does differ in how and when it is received......Einstien' Spooky stuff at a distance'

back to subject matter, our current reality.....

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