I’ve been perennially fascinated by the color-matching experiments conducted by Wright and Guild that led to the establishment of the CIE 1931 two-degree observer reference. The experiment was essentially to present a spectral color produced by a monochromator to a subject, and have them dial the intensities of red, green and blue lights to match the color. Wright collected data from ten subjects, Guild from seven. That data now informs the digital imaging we currently practice, allowing us to produce images that fairly closely represent colors at the scene.
Those seventeen subjects had to produce relatively consistent outcomes, I’d surmised, but I hadn’t gone to actually look at the data until recently. From the original papers, here are the plots of their raw observer data. First, Wright:
That is the exact topic I’m currently researching. Yesterday I pasted Wright’s graph for a forthcoming web page. As Wright says, in his diagram the wavelength scale is not uniform, which makes comparison awkward.
I couldn’t find Guild’s data or paper online. Can you point me to it?
Turns out I found it 7 days ago, and downloaded it, but then forgot I had found it.
My head is currently spinning with how they figured out recalculating coefficients of the primaries, to normalise to each other’s data and later to the new CIE RGB standard before they invented XYZ.
As Guild says, “… the values here given can easily be converted to such new basis”. But he doesn’t say where the numbers in the equations on p163 come from. I think I’ve figured it out, but need to test this.
There is a computational neuroscience researcher in our Institute that’s been working for a long time in perceptual color spaces and how humans reconstruct and recognize color from an information and physical point of view (she’s a physicist by training). At some point she was even interested in reproducing these original measurements with modern tools (we were partially involved in that, lack of funds and students derailed the effort). Currently she’s focused in color discrimination, making pretty neat experiments with somewhat low-tech equipment (a normal computer monitor color calibrated by hand with a silicon power-meter).
A useful resource is the “Colour & Vision Research laboratory database” at http://www.cvrl.org . This contains many CSV files of current and historical colour matching functions etc.
A software issue has caused problems the CSV files to begin with <br />, and to be truncated. Thanks to the helpful people at CVRL, today the problem seems to have been fixed.
I must add that their latest results are not published yet, I saw a talk from one of her students a month ago with new experiments trying to quantify the metric of the color discrimination (the size and orientation of the ellipse of “similar colors” around a point)
