How your eyes see color

Photo receptors

There are two different kinds of photo receptor cells in your retina: rods and cones. The rods are not capable of perceiving color. They are only sensitive to variations in the intensity of light. Rod cells function only in dim light. Some animals have almost no color vision because their eyes are full of almost entirely rod receptors.

The cone receptors in our eyes are responsible for our ability to perceive color, but there are much fewer of these types of receptors in our eyes. As a matter of fact rods outnumber cones by a factor of about 20 to 1, except i n the retina's center (called the fovea). They are highly concentrated in this part of the eye. The cones require bright light in order to be activated and able to function.

There are three different kinds of cone receptor cells in our eyes. The cones contain three different photosensitive pigments. One type of color receptor is sensitive to red light, another to green light and another to blue light. Color blindness occurs in humans when one or more of these photosensitive cone receptor types are missing from a person's eye.

Visible light

White light, the regular kind of sunlight we deal with everyday, contains the wavelengths of all visible (and some invisible colors). These colors can be separated with a prism and can be seen in a rainbow when droplets of water achieve a similar effect.

Objects appear to be a certain color because they absorb certain wavelenghts of the light specture and reflect some wavelengths more than others. White occurs when an object reflects all of the wavelengths towards your eyes, black occurs when an object absorbs all the wavelengths and reflects none.

Color systems

There are two different ways of producing color that reaches your eye. You can produce the color by shining light directly into your eyes like you do when you look at a monitor or by using the reflective quality of objects to bounce colors not absorbed by objects into your eyes. You can use software like Illustrator or photoshop to emulate a color in one of these two models.

Additive Color System

Your computer monitors uses three phosphors to emit beams of light in three different wavelengths that can combine to produce all the colors it can create. Each of these differently colored beams of light affects a specific conal receptor in your eye and therefore lets you see the color. Notice when you combine red and green beams of light, you see yellow, when you combine green and blue beams of light, you see cyan, when you combine blue and red beams of light, you see magenta. If you send each of the three beams of light with equal intensity, you'll see white. If you don't combine any of the beams of light you'll see black or an absence of light on your monitor. Red, Green and Blue are called the Additive Primaries.

Substractive Color System

You can also create color by allowing the reflective quality of objects to substract colors from the white light available in nature before it reaches your eyes. You don't see the colors that get absorbed, you only see the colors that are reflected. This is how color paints and pigments work. Printing uses this substractive system by using four colors Cyan, Magenta, Yellow and Black to create all of the colors you see in most magazines and printed materials. In printing these colors are know as the process colors. Black is added because artificial pigments are not capable of absorbing all colors except one, they are impure. If you were to combine the cyan, magenta and yellow pigments in full intensity they would produce a dark brown instead of a pure black as in the example above.

Color models affect printing

This is why it's important to choose the right color model when working with printing materials. If you place a photograph that has been developed in the RGB model and send it to a printer, the photo will look dark brown where it should be black because the RGB colors will translate into CMY colors with no blacks in them.

Color Gamuts

Notice that the two color models produce slightly different versions of the color. The blue in the substractive color system is much darker than the blue in the additive system. That's because they come from different sources or different originals. The source of the colors and the medium through which they are transmitted affects how many colors can be produced by the system. So different devices can produce a different range or gamut of colors. This is why when you see a Shuttle launch on the Television, it looks a lot different than a real life launch. The colors in nature have a different range than the colors on a TV screen.

Proximity in Color

We do not see color by itself. Color is related to light, texture and other colors.

The type of light under which a color is seen has a direct effect on its perception. When the source of light changes, the color also changes. Natural daylight is the best light in which to view color. Artificial incandescent light projects yellow and red onto color. Fluorescent lights tend to cast blue to green tones on color.

Rough textures tend to absorb light, making colors appear deep and dull, while shiny surfaces tend to make colors appear clear and bright.

Colors are also influenced by other colors. When two colors are placed side by side, differences appear greater. Those differences will vary directly according to how much the colors differ in hue, value and intensity.

Complementary colors (e.g., red and cyan) placed next to each other improve each other's brilliance/intensity by giving off each other as accidental color. Thus, the red appears redder, and the cyan appears more cyan. Grey receives the complementary hue of any color in its presence; e.g., grey placed next to yellow appears bluish-grey.

A color patch will appear brighter or less gray if the background color is relatively dark or black. The same patch will look dimmer or more gray if the background color is relatively light or white.

blog comments powered by Disqus