What is the question, exactly? Yes, negative after images go to their opposites — each primary becomes a secondary, and vice versa. When the student says “the red-green opposite we were taught,” does s/he mean taught in your class or just “taught” by her past. Lots of people say that red and green are opposites, but it is important to remember that there is a lot of “slippage” in color-naming. In particular, “magenta” and “cyan” are not words commonly used in colloquial language and so nearby primary names are often substituted.
In addition, when kids are taught colour mixing, it is often with pigments rather than light, and so it is subtractive mixing they are taught rather than additive mixing (which is why “everyone” comes to perception class thinking that mixing “blue” and “yellow” results in “green” — which they do, subtractively). The additive primaries are identical to the subtractive secondaries, and vice versa. BUT, no one ever calls the subtractive primaries “cyan," “magenta," and “yellow." They are always called “blue," “red," and “yellow." There is lots more to this topic, but I don’t want to bore everyone here. Write me off line if you would like to not more about the relation between additive and subtractive mixing. Images like the one above are rarely rendered exactly accurately. True additive primary red is a little more orange than people expect it to be (what North Americans think of a “pure” red actually has a bit of blue in it, a cultural convention that caused Japanese car makers all kinds of consternation when they first tried to sell red cars in the US). Also the additive primary blue appears to North American to be closer to violet (indeed, Helmholtz called it violet in his classic textbook on the topic). I hope this helps. Best, Chris ….. Christopher D Green Department of Psychology York University Toronto, ON M3J 1P3 Canada [email protected] http://www.yorku.ca/christo ………………………………... On Nov 2, 2014, at 1:09 PM, Carla Grayson <[email protected]> wrote: > > > > A student sent me this email and I don't have a response. Can somebody help > me? > > When you did the negative color afterimage demonstration in class on Tuesday, > I looked at the cross in the middle of the four eagles. The blue and yellow > swapped like I thought they would, but red became cyan and green became > magenta. They went to their color opposite instead of the "red green" > opposite we were taught. > > I also did a negative afterimage with this image > http://2.bp.blogspot.com/-bQvF9kxioDc/T-m6569bd6I/AAAAAAAADP4/9yl0NLP1G5Q/s400/red-green-blue-light-make-white.png > > Red, green, and blue turned into cyan, magenta, and yellow respectively (on a > white piece of paper) but the green was much stronger than the red, which was > stronger than blue. Is there a reason why some of these afterimages show up > more strongly? > > Lastly, by focusing on the boundaries of the images I can imagine that there > are only three circles, each with its own filter. When I do this, I can no > longer see the cyan, magenta, yellow, or white parts of the image and this is > easier to do when my eye is unfocused. Do you know the cognitive explanation > for this? > > Thanks, > Carla Grayson > ([email protected]) > University of Michigan > > --- > > You are currently subscribed to tips as: [email protected]. > > To unsubscribe click here: > http://fsulist.frostburg.edu/u?id=430248.781165b5ef80a3cd2b14721caf62bd92&n=T&l=tips&o=39798 > > (It may be necessary to cut and paste the above URL if the line is broken) > > or send a blank email to > leave-39798-430248.781165b5ef80a3cd2b14721caf62b...@fsulist.frostburg.edu > > > --- You are currently subscribed to tips as: [email protected]. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13090.68da6e6e5325aa33287ff385b70df5d5&n=T&l=tips&o=39816 or send a blank email to leave-39816-13090.68da6e6e5325aa33287ff385b70df...@fsulist.frostburg.edu
