What is Color?

What is Color?

Before we attempt to control it, let’s explore a bit about what color is and how we sense and specify it.

Light

Light is actually “electromagnetic energy,” of the same general category as X-Rays, AM/FM Radio Waves, and Microwaves. Visible band light occurs between the wavelenghts of approximately 400 billionths of a meter and 700 billionths of a meter. Blue/Violet light has the shortest wavelength, Green an intermediate length, and Red the longest wave. Visible band light just happens to be the range of electromagnetic energy we collect and sense with our eyes and brain.

Just beyond the visible band’s Blue area is Ultraviolet. Infrared exceeds the visible band as wavelength increases. The wavelengths of light are very important when dealing with optical systems because light of various wavelenghts acts differently entering particular mediums (such as lens glass, lens coatings, and even the air between lens elements).

One of the most important fundamental issues about color-one that will appear in this series of basic tutorials regularly-is that while light is remarkably reliable our ability to sense it is not. Vision may vary drastically from individual to individual-reasons may include pathologies (such as diabetes and color blindness), environmental conditions such as how dark it is or the color of ambient light, and even psychological states (the viewer’s mood)!

One of the most common methods of portraying color is called the Color Wheel. Think about a compass: The top will be 0 degrees (or 360 degrees if you wish), with Green at 120 degrees (1/3/ of the 360 degree wheel) and Blue at 240 degrees.

Color WheelThis is consistent with Adobe’s Color Picker layout:

Color Picker

You’ll notice that Blue’s Hue value in the Color Picker’s “HSB” section is showing 240 degrees, corresponding to our Color Wheel above. Hue is the technical name for what you may think of as fundamental color, while Saturation (S) is the purity and Brightness (B) is the luminance value of color-they’re expressed in percent. More on what a Gamut is and how it is measured later…

You can identify color by a number of different methods. The HSB system above is not as common as the RGB system (RGB obviously represents “Red, Green, Blue”) in which Red, Green, and Blue are used as the underlying mixing system. There are other color schemas such as CMYK, L*a*b*, and even schemas for individual devices (such as your monitor and printer). Don’t be intimidated-the strange language we use to talk about them gives a false impression of their actual complexity.

Note this Color Picker showing the HSB and RGB values for a particular color:

Color Picker HSB and RGB values

All four color systems (HSB, RGB, Lab, and CMYK) are actually reading values for the very same color. The value at the bottom of the Color Picker, which is preceded by the pound sign (“#”), is a hexadecimal notation for the specified color used in applications such as .xml and .html.

On your own study: A human vision primer

– Leo