Happenings Feb 27

Okay, it’s Saturday morning.

I’ve put in my hour of stream of consciousness, mostly about mathematics. My kid has had a shot at whatever he wanted to do. Late today I plan to work on the next color post; it should be a detailed look at the fundamentals and the residuals of four spectra. Before I work on the post, and after I finish this, I will do some mathematics.

Even I find it a little hard to believe, but I’m not actually sure what mathematics I am going to work on this afternoon.

My kid isn’t the only one who does mathematics for fun. The bottom line is that my grown-up does too. The difference is that my kid gets to have a little fun every day. That is, on the days I don’t do real work — although he’s been known to get in some at the end of a real work day.
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Yet More Books on Color

The following books have been added to the bibliographies page.

“Real World Color Management” by Fraser, Murphy, and Bunting..
“The Reproduction of Colour” by Hunt.
Giorgianni and Madden’s “Digital Color Management: Encoding Solutions”.
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Color: 12 metameric grays from Wyszecki & Stiles


I want to work a major exercise from Wyszecki & Stiles. Actually, it will be one calculation repeated for 12 gray spectra. Given each spectrum, I will calculate the tristimulus values XYZ. (We first did this, here.)

The key is that these 12 spectra are supposed to be metameric. This exercise is interesting for three reasons:

  1. 10 of the 12 spectra have virtually identical XYZ values;
  2. I am encouraged that those virtually identical answers come from using linear algebra — without numerical integration;
  3. I believe that the other two spectra have typos in them — and I think I found (most of) them!

My starting point is Wyszecki & Stiles, page 784. The table heading says that the 12 spectra on that page are metameric with respect to standard illuminant D65 and the CIE 1931 standard observer.

I will show you that they are indeed metameric under D65. I will also show you that they cease to be metameric under D50.
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Happenings — Feb 20

I have made a few changes: search on “edit”.

It has been a very long time since I put out a diary post. I got a kick out of looking at the last one: written when the very popular Fourier Series & Fourier Transform post was just an idea, and when I had just picked up Cohen’s Color Theory.

Let me try writing a short one. (Hmm. Here’s what it turned out to be….

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Color: Color-primary transformation XYZ to RGB

this was titled “Glassner’s transformation XYZ to RGB”


There is a marvelous calculation in Glassner (vol 1, p 103; see my bibliography). Oh, I do not mean to imply that he originated this calculation, merely that I have only ever seen it in his book. And for all I know, he might actually be the originator.

edit: As I said in “Yet More Books on Color“, I found this calculation, done much the way Glassner did but not quite, in Giorgianni & Madden. I decided that I should use a title that did not pretty much credit it to Glassner, despite my disclaimer. end edit.

As he puts it: “Our goal is to find a matrix M which will take a three-element vector representing an XYZ color and transform it to an equivalent RGB vector for some particular monitor.”

The only information given to us will be the chromaticity coordinates x,y for each of the three phosphors, and for the white point.
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