Rolf Kuehni’s books on color systems are some of the best that have been written on the topic in the past 50 years (I own them all and refer to them frequently). Kuehni’s authorship of Scholarpedia’s article on color mixture will identify that article as entirely reliable.
The article gives a solid, accurate, and engaging description of color mixture. The article is certainly acceptable for publication on the Scholarpedia website, and will be a great benefit for people interested in the topic.
Since the intended audience for the article will be predominantly people new to the field, I assigned the article to students entering my laboratory (a first-year Ph. D. and two senior undergraduates), and I asked them to provide with comments. Below, I summarize my discussions with the students:
1. All three students found the article useful and well written.
2. Two students had questions about the brief description of the use of the CIE diagram: "The diagram is quantitative in nature and its additive basis allows relatively simple calculation of stimuli required to match a given target stimulus. The diagram does not consider the brightness of light which requires the third dimension." Given the students’ comments, it seems that readers who are not already familiar with the use of the CIE diagram may not be able to understand the description. It would perhaps be useful to expand on the description, or create another Scholarpedia article on the CIE diagram and its uses, with a link to that article in this article.
Response: I think that this article is not the place to make a fuller presentation of the CIE chromaticity diagram. It should be done as a separate article (Editor, please note).
3. Two students had difficulty understanding the stimuli in the section “Additive mixture due to rapid succession of stimuli.” After we discussed this section, we agreed that a more detailed example of the stimulus would have been helpful.
Response: I can add figures of the addition of reflected spectral powers in disk mixture and of the corresponding visual result. This enlarges the article and adds two figures. The editor should decide if this should be done.
4. One student felt that “The optical effect of subtractive mixture” could be improved if a more direct example and comparison were added.
I expect that this Scholarpedia article will be widely read. I would like to thank Rolf Kuehni for writing this article for Scholarpedia. I apologize for the delay in response.
User 1 (Editor User:) : Editor's comments
I'm sorry my "Reviewer's comments" didn't come along with my identity. I received an e-mail from the server telling me that the second reviewed had accepted the article and that I should go and have one last look at it. I did, had a few comments, and the rest is history. I wasn't seeing my comments as another review, just some questions that occurred to me and that might occur to other readers.
To get the comments into (I hope) the discussions section of the article, here they are:
You said: "Color mixture is a colloquial". I said: ""Colloquial"? Why would Scholarpedia have an article for a colloquial term? Wouldn't it normally have an article for the technical term to which the colloquial term redirects? More importantly, what is the technical term?"
You said: "All forms of color mixture rely ultimately on subjective" I said: "All forms of color rely ultimately on subjectivity. As Newton said, colour is not in the light (or words to that effect). My point is that up to here, and for quite a few paragraphs after here, a naive reader would assume that color is a property of the light, not of the mind. But most of the description requires the reader to have the sophisticated understanding that color *is* in the mind, and that the article is talking about the *appearance* of lights, not about the physics of lights. This is an important distinction that might need to be drawn here"
You said: "The most surprising case is that an appropriate mixture of lights appearing slightly yellowish green" I said "Is that true? I've been telling my students for years that this light can appear unambiguously green (and that the other light can appear unambiguously red), but I certainly could be wrong. I guess my point for my students is that the lights can be spectrally very narrow-band, with no energy at wavelengths that would be seen as yellow, yet the mixture is metameric with another narrow-band light that contains only energy from wavelengths from the part of the spectrum that appears yellow. Your description implies that there really are some "yellow wavelengths" and that the "red and green wavelengths" cancel each other, in the same way that occurs for color subtraction."
You said: "where x is any positive factor increasing or decreasing the radiant power" I said "brightness in Helmholtz's case? More critically, there is a sudden jump here from describing colors (which are in the realm of the "psycho" part of psychophysics) to describing the physics. The reader is not prepared for this jump."
You said: "Colorants achieve their perceived color: I said: "Perceived color is tautologial and implies that there is real color (see earlier comments)."
Robert P. O'Shea, Editor of Vision category of Scholarpedia, Professor and Head of the Discipline of Psychology, Deputy Director of the Cognitive Neuroscience Research Cluster, School of Health and Human Sciences, Southern Cross University, Hogbin Drive, Coffs Harbour, 2450, Australia phone: +61 2 6659 3313; fax: +61 2 6659 3202 e-mail: firstname.lastname@example.org www: http://www.researcherid.com/rid/C-5723-2008
User 2 (Assistant Editor User:) : Another comment
Looking at the article and Dr. O'Shea's comments I think the primary issue is just one of emphasis. Dr. O'Shea thinks that "the subjectivity of color" is an important point that should have more space in this article. While I certainly agree with the underlying philosophy motivating these remarks, I am unsure whether it is essential to have such a discussion in this article. Much of this article is concerned with the history of the field and viewing color as a perceptual (rather than physical) phenomenon seems to be a relatively modern perspective. As far as I know, the "psycho" part of "psychophysics" was not clearly explained until Fechner or around that time. It seems unlikely to me that Newton and others discussed in this article would have thought of color as being a perceptual property...
Perhaps the solution is to reference a separate (new) article about "psychophysics" or "philosophy of psychophysics" that could explain these issues in greater depth.
- Joel Z Leibo
ResponseAs I have expressed in a separate note to the editor, I do not think that this article is the place to have an exchange about philosophical hypotheses on the ontology of color. I have pursued a relatively neutral path in the article. This is my response to points 1, 2, 4 and 5 of the the editor's comments. I have made a small change in the area of his point 3. Rolf Kuehni