Do you see what I see?June 2012
Lesson 3: Is seeing believing?
Your eyes are good at physics
When you look at this painting Haystacks by Monet, your visual nerves process the colors in terms of the following attributes: the amount of blueoryellow; the amount of light and brightness; and the amount of greenorred. These attributes are opposites of one another; just like hot and cold. As you have learned in the previous reading, color vision is based on the opposition of these colors. Your cone cells sense green or red, but never both; or yellow or blue, and never both. This is why you don’t see reddish greens or bluish yellows.
The color wheel, developed by Ewald Herring in 1920, represents the four primary colors (red, green, blue and yellow) positioned diametrically opposite to each other and the intermediate colors such as orange, purple, etc. formed by additive mixing from these primary colors. You have also learned in the previous reading that mixing lights of colors is an additive process, while mixing dye is subtractive.
The CIE (Commission Internationale d’Eclairage- International Commission of Illumination) mathematically defined color spaces by creating the CIE 1931 XYZ color space in 1931. This chart represents the pure spectral colors (red, green and blue) on the curved edge, and all visible colors represented in the areas in between. This chart is currently used to measure and quantify colors produced on computer screens. The computer or TV screens display images made up of pixels, each of which produced by mixing various portions of red, blue and green dots, and a combination of all of these primary colors at maximum brightness represents white. Mixing red and green light produces yellow, red and blue produces magenta; and blue and green produces cyan. The whole range of color is created by the varying portions and brightness of these three colors.
Visible Spectrum (in the order of short to long wavelength)
So far, we have learned that color is a form of visible light. The limited spectrum of visible light belongs to the big family of electromagnetic radiation spectrum. Electromagnetic waves are waves that are capable of traveling through a vacuum and just like other every kind of electromagnetic radiation; visible colors also have waves, frequencies and electromagnetic energy. Our eyes can see a very small region of the electromagnetic spectrum (between 400 -700 nanometers of wavelength- corresponding to color range violet through red) and we are unable to see radiation with wavelengths outside this area.
Complementary Color pairs:
We usually do not see colors in isolation. When two colors are side by side, they interact with each other and affect our perception. This is called simultaneous contrast. It is most obvious and intense when the two colors are complementary colors, which are pairs of colors that are diametrically opposite on a color wheel (refer to Herring’s color wheel in the previous page): red and green, and blue and yellow are complementary color pairs. Also, in terms of complementary colors of light; red and cyan; green and magenta; and blue and yellow are complementary pairs. Artists, especially Impressionists, have used the juxtaposing effect of complementary colors for a long time (see Van Gogh’s Starry Night painting on the right). Do you think they were aware of the neurophysiological terms of complementary colors?
Absorption, Transmission, Reflection, Emission: How our eyes perceive colors!
Now look at your red t-shirt and under white (full-spectrum) lighting, the sun pretty much emits (generates)light at nearly all wavelengths (full-spectrum) in the visible spectrum. Some of the lights emitted by the sun will hit the t-shirt and it will absorb a part of this light. Absorption is a process by which the energy from light is captured by a form of matter. Which wavelengths of light do you think will be best absorbed by the red t-shirt? Since red and cyan light are complementary pairs; your red t-shirt will best absorb cyan light. What happens to the other part of the emitted light if only some of it is absorbed? The red t-shirt will reflect another part of the emitted light. Reflection refers to the process by which the light contacts and is redirected by some form of matter. Red wavelengths of the emitted light will be best reflected by the red t-shirt. From the t-shirt to our eyes, the reflected light is transmitted through the air. Transmission refers to the transit of light through a non-opaque medium. The reflected red light is then transmitted through the air and activates the “red” cone cells in your retina and creates the perception that the t-shirt is red.
References:
Livingstone, M. (2002). Vision and Art: The Biology of Seeing. New York, NY: Abrams.
Gregory, R.L. (1997) Eye and Brain: the psychology of seeing (5th ed.). Princeton, NJ: Princeton University Press.
Purves, D., Lotto, R. B. (2003). Why We See What We Do? : An empirical theory of vision. Sunderland, MA: Sinauer
Images 1-3 were taken from: Web Exhibits: An interactive museum. Retrieved from on 03.02.2011.
Images 4 and 5 were taken from: Kellowin Blog. Retrieved from
on 03.02.2011.
Image 6 was taken from Van Gogh Gallery. Retrieved from
on 03.02.2011
Image 7 was retrieved from:
on 03.02.2011
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