Jim Worthey, Lighting and Color Research
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Jim Worthey • Lighting & Color Research • jim@jimworthey.com • 301-977-3551 • 11 Rye Court, Gaithersburg, MD 20878-1901, USA
Research
Vectorial Color
Static thumbnail for Locus of Unit MonochromatsWhy are the dots on a TV screen red, green, and blue? You could say "Well, the eye has red, green and blue receptors, so there you are." That idea is correct as far as it goes, but it skims over details, like the fact that red cones are most sensitive in the yellow. Confronting the details leads to a practical new formulation for the facts of color mixing. Traditional textbook color deals with a color vector [X Y Z], but the XYZ system impedes the use of vector concepts. One benefit of the new formulation is that it makes the notion of color vectors more intuitive and practical, so the new work can be called "Vectorial Color." It merges ideas from William A. Thornton, Jozef B. Cohen, Michael H. Brill, Sherman Lee Guth, Tom N. Cornsweet, James A. Worthey and others into a set of 3 color-matching functions and related methods. The materials linked below explain vectorial color, and include supplementary material for formal publications appearing elsewhere.
Supplementary Materials for Vectorial Color
1. Orthonormal functions graph and VRML (virtual reality) presentation of the Locus of Unit Monochromats.

2. The results of a color-matching experiment depend on the choice of primary wavelengths. Nonetheless, the results---the color matching functions---tend to peak at certain fixed wavelengths. To make this discovery for yourself, watch the animated color matching functions.

3. Animated version of Figures 6 and 7 in "Vectorial Color." 

4. An early concept of "Strength of Action in Mixtures," published by MacAdam and Thornton, but now presented in animated form.

5. Tabulation of orthonormal color matching functions: Work with them yourself!

Complete Papers about Vectorial Color
1. New draft article "Vectorial Color" and the Figures to go with it. The whole story (24 pages + 16 figures), but needs a reference list.

2. Self-contained paper
Color Matching with Amplitude not Left Out, as presented at  Color Imaging Conference 12, in Scottsdale, Arizona, USA, in 2004 November.

3. The graphical material for the oral presentation in Scottsdale and the speech as it was read. The graphical presentation is a long web page with animated and 3-dimensional materials. It should be stimulating even if it's not totally self-explanatory.

4. Summary of a talk given at Lighting and Color Conference, Orlando, Florida, 2006 Feb. 8: "How White Light Works."


Lighting Quality and Light Source Size.
Capitol reflected thumbnailHow do we see the shape of a shiny object? What causes the dappled sunlight in the shade of a tree? Suppose it is a sunny afternoon and you stand outside a store or school with fluorescent lighting. Looking in the window, you see that the fluorescent-lit interior looks washed out. Why is that?  No mystery! It looks washed out because it is washed out. It is obvious that some light sources are small and bright, while others are large and comparatively dim. This variation has effects which are seldom discussed in clear language. A 1990 article addresses these topics, and now in 2005 January, the article is available as a web page: "Lighting quality and light source size," Journal of the IES 19(2):142-148 (Summer 1990).

Effect of Veiling Reflections on Vision of Colored Objects.
Available chips, Glossy vs MatteIf a large-area light source causes veiling reflections, what colors are lost? Why are many objects, photos and printed pictures shiny? A 1989 article addresses these topics, and now in 2005 January, the article is available as a web page: "Effect of veiling reflections on vision of colored objects," Journal of the IES 18(2):10-15 (Summer 1989).


What primaries work best? A fresh presentation of an idea from Bill Thornton.
What primary colors work best in a color matching experiment? A new computer animation helps to answer this question. The animation grows out of basic textbook methods, so it can be understood "out of context," with little reference to other ideas. Fans who have viewed the visuals of the 2004 "Amplitude for Color Matching" talk know that the animated graph led Michael Brill to discover a new theorem. Brill and Worthey have now written a short article about that theorem, and about Prime Colors in general. Read the preprint, now accepted for publication: "Color Matching Functions When One Primary Wavelength is Changed". This is a preprint of an article to be published in Color Research and Application © 2006 Wiley Periodicals, Inc.

Color Rendering
Two color rendering articles have been published in Color Research and Application, in the last issue of 2003 and the first issue of 2004. The pdf files below (for Adobe Acrobat Reader ) contain the final versions as submitted.

Introductory Article
If a source emits light within a single narrow band of wavelengths, color vision is lost. An example is low-pressure sodium vapor lights, which are occasionally used to light streets or parking lots. Now suppose that a light would emit in two narrow bands. There is no example of a familiar light with two extremely narrow bands, but many lights tend in the direction of two bands. They are rich in yellow and blue, but fall short in the red and the green. The curious fact is that a light can be deficient in red and green and yet have a white appearance—any shade of white that you like. To give good color contrasts to objects, a light must contain red and green and blue. This should not be a surprise, because a TV screen has red, green and blue phosphors, the primary colors of the TV palette. Dr. William Thornton calls the key wavelengths the Prime Colors, and pins them down at 450 nm, 540 nm, and 610 nm.

This introductory article asks: "How does color rendering arise as a practical problem?" and "How do Prime Colors relate to other ideas, such as Matrix R, and Opponent Colors?" Detailed graphical examples are presented.

Read the preprint of Render Asking: download text - PDF (77 KB) download figures - PDF (210 KB)

New calculation for color rendering
An opponent method is appropriate to the color-rendering discussion because it brings to the surface the notion of chromatic color, meaning actual departure from white or gray. In this article, an opponent method expresses the predictability of object colors, and leads to a matrix formulation that serves two purposes. The effects of replacing a light L1 by another L2 are estimated with a 3x3 “rendering matrix” P. Given an object’s tristimulus vector under L1, the method makes an approximate prediction of the new tristimulus vector under L2. Thanks to the opponent formulation, matrix element P22 quantifies the gain or loss of redness and greenness, while P33 expresses gain or loss of blueness and yellowness. These in fact are major effects, so the method predicts color changes item by item, and also in more general terms.

Read the preprint of Render Calc: download text - PDF (244 KB) download figures - PDF (139 KB)

30 (approximately) New Ideas in the 2 Articles Above
The discussion of lighting is often burdened with preconceived ideas and hidden assumptions. In the two articles above, I use prior research, but throw out the hidden assumptions in favor of more rational ideas. In the 2 articles are about 30 new ideas, which are now listed on a web page of new ideas. Most of these are not entirely new, but are old ideas often overlooked in the discussion of lighting and applied color.

Linear Models and the Mean Vector
It is often desired to represent object colors or lights by a linear model with only a few terms, perhaps 3 or 4 terms. For example, the color rendering article above uses a 3-term model to model all object spectral reflectances. To get such a model from data, it is convenient to use so-called Principal Components Analysis. Such an analysis expresses a population of data as a mean vector plus a set of basis vectors, each times a coefficient. This new research by Michael Brill and me discusses the role of the mean vector and shows that it can sometimes be left out of the model. This article has been accepted for publication in Color Research and Application.

Read the preprint of Linear Models and the Mean Vector: download article - PDF (259 KB)
web site designed by
Nick Worthey
Basic Facts, New Ideas, etc.
<>Seek some basic facts?
Color Rendering Basic Facts

30 New Ideas from the two color rendering articles

Who is Jim Worthey?
Read a short biography

Jim's Past Publications?
See list of articles on color, lighting, etc.

Cargo Cult Science
Read a version of Richard Feynman's talk on cargo cult science

Cargo Cult Science --- Explanation on Wikipedia
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Articles

Render Asking:

Color rendering: asking the question

download text - PDF (77 KB)

download figures - PDF (210 KB)

This is a preprint of an article published in Color Research and Application © 2003 Wiley Periodicals, Inc. James A. Worthey, "Color Rendering: Asking the Question," Color Research and Application 28(6):403-412, December 2003. The article as published is available for a fee at http://www.interscience.wiley.com

Render Calc:
Color rendering, a new calculation that estimates colorimetric shifts

download text - PDF (244 KB)
download figures - PDF (139 KB)


This is a preprint of an article published in Color Research and Application © 2004 Wiley Periodicals, Inc. James A. Worthey, "Color Rendering, a new calculation that estimates colorimetric shifts," Color Research and Application 29(1):43-56, February 2004. The article as published is available for a fee at http://www.interscience.wiley.com
Linear Models and the Mean Vector:
Principal Components Applied to Modeling: Dealing with the Mean Vector

download article - PDF (259 KB)

This is a preprint of an article published in Color Research and Application © 2004 Wiley Periodicals, Inc. James A. Worthey and Michael H. Brill, "Principal components applied to modeling: dealing with the mean vector," Color Research and Application  29(4):261-266, August 2004.
Problems viewing these articles?
Some users have had trouble in displaying and printing the pdf files. I believe that I have resolved these problems as of 2003 April 16. Still I would be happy to hear from you about color rendering or pdf files or anything. Please email jim@jimworthey.com

Items of Interest

How do you feel about logic?
Try a couple brain teasers

Who is Nick Worthey?
My son, Nick J. Worthey, is an illustrator and animator. You may enjoy his web page, http://www.nickworthey.com. I enjoy Nick's black and white cartoons and his new prize-winning animated movie.


Math Software
O-matrix, Data Analysis and Visualization for Engineeering, Science and Technical Computing.

Linear Programming with lp_solve and O-Matrix

Statistical Time Series Analysis for O-Matrix

Using SigmaPlot to Graph O-Matrix Results



Copyright © 2002 - 2005 James A. Worthey, email: jim@jimworthey.com
Page last modified, 2006 January 27, 09:55