Jim Worthey, Lighting and Color Research
home page contact about me
Jim Worthey James A. Worthey • Lighting & Color Research • jim@jimworthey.com • 301-977-3551 • 11 Rye Court, Gaithersburg, MD 20878-1901, USA
Recent Short Course: I presented a short course on Vectorial Color, 2008 November 11, 1:30 to 3:30 pm, at Color Imaging Conference 16 , in Portland, Oregon. For details, please see the Vectorial Color Short Course Page. This year, CIC 17 will be held in Albuquerque, on November 9–13, but I am not offering the short course at that conference in 2009. In March of '09, I have submitted 2 journal articles on vectorial color, and this may be a good year for more writing, rather than going to meetings. I would be very interested to give the short course at other meetings, or in an industrial or academic setting. If a few people are interested in lighting or camera design, the 2-hour class could be extended, with more time for questions. Then we could talk in more detail about applications. The country code is 1, the phone number is above. My Skype name is jimworthey .    
Google 10100 Contest Entry
In the fall of 2008, Google ran a contest called the Project 10100. That's Project 10 to the 100 power. I submitted an entry which is a good statement of what needs to be done to improve lighting. As of  2009 July 5, the finalists are not known. Even if my entry is not a finalist, the entry is good reading.

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. Locus of Unit Monochromats: Orthonormal functions graph and VRML (virtual reality) presentation of the Locus of Unit Monochromats.

2. CMFs: 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. Orthonormal Color Functions: Animated version of Figures 6 and 7 in "Vectorial Color." 

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

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

6. Computing: Programming for color using O-Matrix.

7. Q and A: Some questions and detailed answers about Matrix R.

Complete Papers about Vectorial Color
2 new articles have been submitted for possible publication:
1. Preprint of article "Vectorial Color" and the Figures to go with it. The whole story is here (28 pages + 16 figures). Please be sure to download the figures in addition to the text.

2. Also ready to publish: "Applications of Vectorial Color," and the figures for this article. There are 6 applications, including information transmission, camera design, machine vision, and dichromacy.

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

Earlier papers for meetings:
4. More CIC 12: 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.

5. Color Rendering with emphasis on
LEDs, light emitting diodes : In 2006 February, there was a Lighting and Color Conference in Orlando, Florida. Jim Worthey made a presentation called "How White Light Works."  At this link you'll find the graphical material for "How White Light Works" as presented at the conference. The beginning of the page is similar to the talk of 2004 November. However, the Quick Example of color shifts under mercury light is new, and farther along are some detailed examples, mostly involving LED lights.  A first attempt at combining LEDs to make white light falls short on red-green contrast. The vector composition graphs show it, and the light's effect on object colors (64 Munsell chips) confirms it. A second attempt gives too much red-green contrast, and the third try is "just right." The third LED combo does not track the blackbody spectrum perfectly, but succeeds in a more subtle way. All the graphs are in Cohen's space, and represent detailed facts about color stimuli. The pictures with colored borders are links to more detail. You can jump directly to the color rendering examples.

6. CIC 14, Camera Sensors: A 6-page article, Camera Design Using Locus of Unit Monochromats, by Worthey and Brill, prepared for Color Imaging Conference 14, to be held in Scottsdale, Arizona, 2006 November 6-10. A web page has Further Examples of Camera Design Using LUM. The Further Examples page has links to a page about computer programming, or you can jump directly there. The poster itself is almost ready: CIC14 Poster. As an alternative, see the Overview Page, which lists all the "camera design" links .

Cartoon "Ghosts," from Chris Harding's "We The Robots" web site, http://www.wetherobots.com , 2008 September 26:
Cartoon by Chris Harding;
Bob's arm doesn't cast a shadow. In Bob's office, shiny objects lack highlights and their details are hidden by veiling reflections. Read more...
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 primary wavelengths work best? A fresh presentation of an idea from Bill Thornton.
What primary colors work best in a color matching experiment? A 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 published in Color Research and Application, 32(1):22-24 (2007), © 2007 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. The figures are in a separate file from the text!

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. The figures are in a separate file from the text!

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 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

Computer Programming for Vectorial Color:  Programming Page

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

1855 Color Article by James Clerk Maxwell:
Experiments on Colour, As Perceived by the Eye.

Q and A: Some questions and detailed answers about the projection Matrix R.

Browse Working Files: color data, computer routines .
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Articles

Articles about Theory and the role of Obvious Issues:

To study the fundamentals of a topic, it is often necessary to study things that are obvious. Fairly obvious facts are belabored in Physics and in Machine Vision research, for example. So-called lighting experts resist talking about the obvious, which prompted me to write three articles. Click for each pdf:

"The role of theory in lighting research and design," Lighting Design and Application 21(7):15-17 (July, 1991).

"Dealing with obvious issues in lighting," Lighting Design and Application 21(8):15-19 (August 1991).

"Lighting research and theory can create business prospects," Lighting Design and Application 21(9):14-17 (September 1991).

Did I turn any lighting experts into physicists? Not that I am aware of. But please read the articles.

Render Asking:

Color rendering: asking the question download text - PDF (77 KB)
download figures - PDF (210 KB)

Please be sure to get the figures, which are separate from the text. 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)


Please be sure to get the figures, which are separate from the text. 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.

Read about Flumist!

Kaplan-Meier Plot with Many Censored Data. This web page concerns drug testing.

Exteriors of Biotech Greatness, Firstfield Road in Gaithersburg.


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 - 2007 James A. Worthey, email: jim@jimworthey.com
Page last modified, 2009 July 6, 01:58 .
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