Talk:Impossible color/Archive 1

message: Please comment on the proposed merger at the target article's talk page, Talk:Color vision, in the section "Proposed merger of Imaginary color". To have this article be in any way comprehensible, you need to repeat so much of Color vision that I think it makes more sense to add this as a section to that article. There just does not seem to be enough content here to require a separate article. Edison 19:47, 21 May 2007 (UTC)
replies: text: No, that's wrong.  The article can be perfectly intelligible with a link to color vision, and adding the information that belongs on this article to color vision would just add bloat, and confuse that article.  In any case, you should stop adding discussion on this page if you want the discussion to be there. --jacobolus (t) 00:19, 23 May 2007 (UTC)
thread_title: Merger

message: Because of this little revert war, which I'm not escalating since I follow 1RR, I started rewriting the Utility section, but I gave up. As it is, the section has so many inconsistencies that it's hard to fix without a major revamp:
# Use of term "real color" without definition. (Understanding that term is a precondition for understanding imaginary colors.)
# Use of term "chromaticity" interchangably with "color" without explanation.   
# Statement that "additive mixture of two real colors is also a real color" only parenthetical, although most of the section refers to it. Conversely, term "convex" is introduced with prime mention but never used.
# There is no logical flow from the introduction of polygon to the place where it is used. In fact, the text first goes (without motivation) back to three primary colors, mentions in passing something about more primary colors, goes back to three, and only after a paragraph break really uses the polygon property, without explicitly referring to it. 
I canceled editing because before I invest any more of my time I want to ensure that my edits won't be stubbornly reverted. I belive that editors should take the time to understand good faith changes, and take it from there to further improve Wikipedia. — Sebastian 01:39, 10 June 2007 (UTC)
replies: text: Hey, thanks for taking my hastily written starter text to pieces. Note that I didn't revert you, and I have no problem with you changing it as radically as you want. I'd love to see your version. —Keenan Pepper 04:17, 10 June 2007 (UTC)
replies: text:  Thank you for your nice reply! I'm sorry that I was a bit grumpy yesterday. I finished the rewrite; please feel free to take it from there. — Sebastian 18:24, 10 June 2007 (UTC)
replies: text: Looks great as it is now (after Jacobolus tinkered with it). Now we're doing things the wiki way! If anyone wants to replace the image of the ProPhoto gamut with one more appropriate for this article, be my guest. I just used it because you can clearly see that the gamut contains imaginary colors. —Keenan Pepper 20:51, 10 June 2007 (UTC)
thread_title:  Utility section 

message: The old version mentioned "some clipping or compression must take place". I tried to preserve it, but it has been removed since. That seems like a pertinent topic for an article about imaginary colors. Can anyone elaborate this topic? — Sebastian 21:22, 11 June 2007 (UTC)
replies: text: As written, it didn't make any sense, so I took it out.  What does it mean to be "ruled out"?  Any color which is out-of-gamut for the target device will be clipped or compressed, whether it is an "imaginary color" or not.  So the statement just confuses the reader without informing him.   --jacobolus (t) 22:45, 12 June 2007 (UTC)
replies: text:  I agree that it wasn't very helpful. My intent was not to say that the deleted phrase was instructive, but to point out that the question how models deal with imaginary colors is pertinent to the article, and to ask if someone who knows more about it could add that information. — Sebastian 18:55, 13 June 2007 (UTC)
replies: text:  The article makes that pretty clear already I think.  Feel free to improve it though.  --jacobolus (t) 09:35, 14 June 2007 (UTC)

text:  Later edit: oh wait, you said "how models deal with" them.  The answer to that is that "models" (like L*a*b* or RGB) don't make decisions.  It is users of those models who must decide what to do, when converting to the color space used by an output device.  So what to do with these colors is defined by the color management software, and the answer is (pretty universally AFAIK) that they are treated identically to any other color outside the gamut of the output space, which is that depending on the rendering intent selected, all of the colors in the image are either compressed or clipped, often by pulling them in towards middle gray in L*a*b* space, or some similar space.  --jacobolus (t) 10:24, 14 June 2007 (UTC)
thread_title: Clipping and compression

message: The opening statement:
"Non-physical, unrealizable, or imaginary colors are combinations of cone cell responses that cannot be produced by any physical light source.[1] " is not supported by the reference. In fact, the phrase "imaginary colors" does not occur at all in the reference.
Re: the statement, "Thus, no object can have an imaginary color, and imaginary colors cannot be seen under normal circumstances."  There is the implication that "imaginary" colors can be seen under non-normal circumstances. Please provide a reference verifying this.
Re: the statement, "Therefore, there is no spectral power distribution that excites only green cones without exciting blue or red cones at all, and that situation corresponds to an imaginary color greener than any physical green."  Please provide a reference showing that there exist "imaginary colors greener than any physical green."  Also, what is a "physical green?"  All color is a perception...
Re: "Real colors are colors that can be produced by a physical light source."  Sorry, but without an observer, there is no color... and what humans can perceive is defined by XYZ or CIELAB.  But I guess the implication is that "imaginary colors are produced by an imaginary light source."  Don't think so.
Re: "Therefore, one selects colors outside of the region of real colors as primary colors; in other words, imaginary primary colors. Mathematically, the gamut created in this way contains so-called “imaginary colors”."
No, the primaries are encodings that do not represent real colors, and the gamut contains real colors as well as lots of encodings that do not represent real colors.  There are no "imaginary colors" - only encodings that do not correspond to real colors.
Color is a perceptual property. So if you can't see it it's not a color. It is a cognitive perception that is the end result of the excitation of photoreceptors followed by retinal processing and ending in the visual cortex. Colors are defined based on perceptual experiments.
A coordinate in a "colorspace" outside the spectrum locus is not a color. These have occasionally been referred to as "imaginary colors" but this is by and large also erroneous. You can't map an imaginary color from one colorspace to another as the math (and experimental data) for each colorspace breaks down outside the spectrum locus.
There is not one reference cited within this topic that justifies the existence of the topic itself.
There is no mention of "imaginary colors" in such standard references as Hunt's The Reproduction of Color, Lee's Introduction to Color Imaging Science, Fairchild's Color Appearance Models, and Berns' Principles of Color Technology.  Even the classic Wyszecki and Stiles Color Science: Concepts and Methods, Quantitative Data and Formulae, 2nd Edition has only a page or so (out of 950) on "imaginary color stimuli."
Colorgeek (talk) 07:21, 8 February 2008 (UTC)
replies: text: It may well be true that you did not find the topic of this article discussed in four books you looked at. But see the discussion at the top of the page. "Human Information Processing" by Peter Lindsay and Donald Norman, Academic Press, 1972, pp 196-216. P 206 says that if a color stimulus is stared at for a while, the receptors are fatigued. It says that if you view a saturated green for a while, then view a saturated red,  you perceive an unnaturally supersaturated red. This is thought to be because the green receptors, being fatigued, no longer send a neural signal to desaturate the red perception from the red receptors. It says "thus the resulting red is more brilliant than can be produced simply by monochromatic light." (p 207) Lindsay and Norman suggest projecting on a screen alternately color negative and positive images of a scene with vivid colors, which would be a good programming challenge for someone to add to the article. 20 seconds of a red circle/blue surround, then 20 seconds of blue circle/red surround, using complementary hues. It is more closely related to receptor fatigue and afterimages than to color reproduction technology. Edison (talk) 14:16, 8 February 2008 (UTC)

text: A solid reference by highly notable scientists, published by a highly respected publisher, does not have to be in your meighborhood library branch to be "available". You can get it through interlibrary loan, at a good college library or for a few dollars from online second hand booksellers. Please read WP:RS and WP:V which discuss referencing of articles in Wikipedia. The phenomenon was regularly demonstrated in college perception lab classes. Unfortunately I do not at the present time have the access to online journals to find recent research on the topic for you. You are welcome to do your own library research and add references showing that the claimed phenomenon does not occur. I have provided a reference stating that it does occur. Edison (talk) 20:29, 9 February 2008 (UTC)

text: If there is a guideline that says references 35 years old are not considered reliable, I have not seen it. If you find reliable sources stating that it is not possible to perceive a color more saturated than a spectral color, after fatigueing a subset of the receptors, then please add it. Many articles have references far older than 35 years, and these have not been removed or deprecated on account of their being old. The fact that some topic is not addressed in your reference book collection does not by itself disprove a statement of fact in an older book. Do your books deal explicitly with the subjective perception of color saturation in an observer with receptors of one color fatigued? Most books on color reprodduion will be dealing with normal observation conditions. Edison (talk) 19:55, 11 February 2008 (UTC)
thread_title:  How about some real (!) references... 

message: For anyone who's interested, here's some Java source code to approximate the effect in the section "Perception of imaginary colors". Maximize the window, position your mouse over the button, and, after 20-30 seconds of staring at the screen, click the button. It looks kind of like magenta to me. « Aaron Rotenberg « Talk « 01:58, 15 March 2008 (UTC)
replies: text: Or you could just view two images, one red, one green, in an image slideshow viewer. --Jaded-view (talk) 04:51, 18 May 2008 (UTC)
replies: text:  For example, http://upload.wikimedia.org/wikipedia/commons/thumb/2/29/Solid_green.svg/2000px-Solid_green.svg.png and http://upload.wikimedia.org/wikipedia/commons/thumb/6/62/Solid_red.svg/2000px-Solid_red.svg.png . We loaded each of these into a Firefox tab, hit F11 to maximize the view, stared at the red until it seemed to be just a washed-out orange, and then hit Ctrl-Pgdn to switch to the green tab. Result: HOLY MOLY THAT IS SO GREEN. What this lacks in scientific rigor it more than makes up for with party awesomeness. We also tried green-then-red as specified in the article. This resulted in a hot pink that wasn't nearly as mind-blowing. I cannot recommend this experiment enough. Yes, it's another exciting Friday night at Chez Matuszek (talk) 05:42, 15 January 2011 (UTC)
thread_title:  Source code for demonstrating "imaginary red" 

message: * I once read that by viewing a laser with a frequency twice that of green light, the green cones can be stimulated without stimulating the red or blue cones, thus giving the viewer the experience of an incredibly pure green light. I may have misread! David (talk) 18:02, 29 March 2010 (UTC)
thread_title:  Another viewable imaginary colour? 

message: To me, it sounds more like that old optical illusion where a checkerboard has a shadow thrown on it, such that the same middle shade of gray looks darker and lighter depending on whether it's surrounded by bright or by dark colours. As in, the grass looks greener because it's more different from pink, than because the pink is fatiguing your red and blue receptors. --122.106.155.219 (talk) 08:34, 30 March 2011 (UTC)
replies: text: I don't think the article actually claims the disney color is “imaginary”, but you’re probably right that the better place for the Epcot factoid is an article about simultaneous contrast. –jacobolus (t) 14:41, 30 March 2011 (UTC)
thread_title:  Is the disney example really demonstration of an imaginary colour?