Thanks Graeme,
I'll try to work your method...
Meanwhile, I was forgetting I have a set of laser pointers that includes a
"Violet" color!
So, I fired up the pointer at a GreatagMacbeth White Balance Card and got the
following result:
https://1drv.ms/b/s!AkD78CVR1NBqkKp8u_7w7NtgLXjobA
I think it is interesting as it is the closest I found, so far, to the 430 nm
chromaticities.
430nm = x 0.1689 y 0.0069
Laser (405nm?) = x 0.1743 y 0.0016
The CIE x primary is a little bit "redder" than 430nm but the y is closer to
the required blue y at 0.0016.
Here is my "graphical analysis" result of my "Violet" laser pointer Dominant
Wavelength:
https://1drv.ms/b/s!AkD78CVR1NBqkKp9KOlFkABHF0E2iA
I did a quick research for a numerical recipe on the web for calculating
Dominant Wavelength but could not find much? CIE 15-2:1986 only has the
definition of the concept.
My Minolta CS-200 has a "Color Space" option where it can report "Dominant
Wavelength" for a given measurement, and in this case it gives me 569.5 nm?
CIE 15-2:1986, age 33, notes the following:
For stimuli whose chromaticities lie between those of the specified achromatic
stimulus and the two ends of the spectrum, complementary wavelength is used
instead of the dominant wavelength. So 569.5nm is the "Complimentary
Wavelength" after all? But I don't have a numerical way to figure, other than
graphically, what the "real" dominant wavelength is... -- sigh!
This laser chromaticities are well outside the sRGB gamut, at any rate.
Yet, the RGB simulation on my monitor (out of transforming the CS-200
measurements using Robin Myers Color Converter utility, isn't half bad, when I
visually compare the RGB circle between my monitor and the reflection of the
laser of the pointer off the GM White Balance Card...
/ Roger
P.S. The little sticker on the pointer specifies the laser wavelength as 535 nm
-- stupid?
-----Original Message-----
From: argyllcms-bounce@xxxxxxxxxxxxx <argyllcms-bounce@xxxxxxxxxxxxx> On Behalf
Of Graeme Gill
Sent: Sunday, April 14, 2019 8:42 PM
To: argyllcms@xxxxxxxxxxxxx
Subject: [argyllcms] Re: Convert CIE xy chromaticities to some RGB
graxx@xxxxxxxxxxxx wrote:> My starting point is the spectral color
corresponding to 430 nanometers, some violet. The problem is that I don't
understand how to obtain RGB values from the CIE 15.2 1931 chromaticities.
Simplest way I can think of of converting a spectral locus to RGB values is to
treat it as a chromaticity problem. So working in either x,y or u'v'
chromaticity space:
Identify your RGB primaries and white point in chromaticity space.
For each wavelength you want to convert, identify its chromaticity coordinate.
Find the intersection of the line between the wavelength coord. and white
with the RGB triangle.
Compute the ratio of the two out of the RGB primaries that results in that
intersection coord.
Cheers,
Graeme Gill.
