Biophysics of Color and the Castle Illusion
Both centre crosses in these objects are the same colour.
In honesty, JPG artifacting probably makes them slightly different, but I can at least say they are FAR similar than they appear in the image.
That illusion is portrayed on
a web site with other color illusions that I shared with Renee Rynn a while back to try and convince her that colors didn't have the properties she believed they had.
All optical illusions make the same point: don't trust your perceptions.
I published an article on color reproduction that was actually used in high school science classes. It seems like we get stuck on semantic aguments -- are we talking about what colors are in the world or how colors appear to observers?
I made the point in my article:
There really is no such physical thing as "color." Color is an illusion our minds create when our eyes pick up various combinations of wavelengths of light in various contexts (the optical illusions demonstrate this).
A good example is the color yellow. An object in nature can look yellow if it actually reflects one wavelength of light that we see as yellow.
However...
...an object in nature can reflect the wavelength of red AND the wavelength of green and NONE of the wavelengths of yellow, and we will still see yellow.
Therefore...
...the color seen as "yellow" is an illusion, since we will see yellow when there is no yellow light at all. Look closely through a magnifier at a yellow area of a video screen, and you will see no yellow at all -- only red and green areas.
The castle illusion also demonstrates this. Here's its biophysics:
Brightly lit scenes are picked up by the "cones" in our retinas. We have three types: red, green, and blue. If we stare unmoving at a scene, the various colors exhaust the particular cones that are picking up the colors and transmitting their signals to the brain. When the image changes, the un-exhausted cones dominate and the exhausted ones fail to register their assigned colors until they recover their sensitivity.
For example...
...in the
castle photo the original blue sky is represented in the chroma isolated negative as yellow -- more specifically the red and green wavelengths from your computer monitor. By staring at the picture without moving the eyes, the red and green cones of your eyes become exhausted but the blue cones become more sensitive from being unstimulated. When the cursor moves over the picture, the B&W representation appears. Keep in mind that the B&W picture on your computer monitor is actually not quite B&W but rather the sum of red, green, and blue light specifically (no yellow light). Now the blue cones in your eyes see the gray sky, but having become extra sensitive from a few seconds of deprivation, send a strong blue signal to the brain. The red and green cones, desensitized, fail to pick up much of their colors. The result is the gray looks blue -- the opposite color of the first image.
So that we don't get lost in a semantic argument, may I suggest that we be specific about the difference between the colors in the physical world (wavelengths of light in combination), and the colors in our perception? It seems that would keep away the goofy Uninteresting Ian interpretations.
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