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About the eye and colors
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The human eye only perceives the color that is reflected indirectly from object surfaces or from a lightsource as direct light. Indirect Light exists only in combination with three components: a viewer, an object, and light.
Even if white light is perceived as colorless, it actually contains all colors in the visible spectrum. The spectrum depends on the type of light. The light source. Candle light or Neonlight has diferent sprectra then sunlight. You have to keep that in mind then taking photos from different lightsources and especially when you mix them.
When white light hits an object, it selectively blocks some colors and reflects others; only the reflected colors contribute to the viewer's perception of color as demonstrated in the image. objects, depending on material reflect only an amount of the light back. That is the light we perceive as the color of the object.A white surface would reflect the whole spectrum whereas a black surface will absorb the whole spectrum. |
How a human eye perceives color
The human eye perceives this spectrum using a combination of rod and cone cells for vision. Rod cells are better for low-light vision, but can only sense the intensity of light, whereas while cone cells can also discern color, they function best in bright light. Three types of cone cells exist in the human eye. The different cone cells respond to different wavelength areas as shown in the figure below. The set of signals possible at all three cone cells describes the range of colors the human eye can perceive.
Each sensitivity is not a discrete value or range, it rather is a smooth gaussian range with a varying degree of sensitivity across a broad range of wavelengths.
Construction of colors
All colors perceivable by the human eye can be produced by utilizing some combination of the three primary colors, either by additive or subtractive processes. Additive processes create color by adding light to a dark background, whereas subtractive processes use pigments or dyes to selectively block white light. A proper understanding of each of these processes creates the basis for understanding color reproduction as it is used in print media or in screens.
The color in the three outer circles are termed primary colors, and are different in each of the above figures. Devices which use these primary colors can produce the maximum range of color. Monitors release light to produce additive colors, whereas printers use pigments or dyes to absorb light and create subtractive colors. This is why nearly all monitors use a combination of red, green and blue (RGB) pixels, whereas most color printers use at least cyan, magenta and yellow (CMY) inks. Many printers also include black ink in addition to cyan, magenta and yellow (CMYK) because CMY alone cannot produce deep enough shadows and more often result in a brownish shade.
Subtractive processes are more susceptible to changes in ambient light because they rely on this light to produce their colors. Printed colors often require a specific type of lighting in order to accurately reproduce the color shown on a display.
About hue and saturation
Colored light is different from achromatic light. It distinguished between hue and saturation. Visually describing a color based on each of these terms can be highly subjective, however each can be more objectively illustrated by inspecting the light's color spectrum.
Naturally occurring colors are not just light at one wavelength, but actually contain a whole range of wavelengths. A color's "hue" describes which wavelength appears to be most dominant.
Although this spectrum's maximum happens to occur in the same region as the object's hue, it is not a requirement. If this object instead had separate and pronounced peaks in just the the red and green regions, then its hue would instead be yellow (see the additive color mixing table).
A color's saturation is a measure of its purity. A highly saturated color will contain a very narrow set of wavelengths and appear much more pronounced than a similar, but less saturated color.
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