Color Models

Color Models Used to Define High Color Graphics

In the previous topic on Color, I talked about the Additive Color System which uses the Red, Green and Blue components of light to create colors and the Subtractive Color System which uses Cyan, Magenta, Yellow and Black pigments or inks to create colors.  These are the two different ways to produce colors.

These two colors systems are used in many graphics programs to define the colors used in graphical images that have more than 256 colors.  They are called the RGB Color Model and the CMYK Color Model.  Sometimes the term Color Space or Color Gamut is used instead of Color Model.

There are many other color models that are used to define high color images.  Some of them are: HSL, HSV, HSB, sRGB, ROMM RGB, Adobe RGB98, Apple RGB, NTSC. Adobe Wide Gamut RGB and CIE. 

One of the models you are likely to see is the HSB model, which stands for Hue, Saturation and Brightness.

A Color Model defines a range of colors that are possible.

The larger the range of colors that a Color Model defines, it is said that it has a "wide" color Gamut.

The RGB Color Model (Similar to HSL and HSV models)

• The RGB color model defines color using Red (R), Green (G) and Blue (B) light.
• Each color is measured with a value ranging from 0 to 255 where 0 is no light and 255 is maximum intensity.  This is how much information can be stored in 1 Byte of computer memory (256 pieces).
• To define all three colors, you need 3 Bytes (or 24-bits) of information.
• The RGB color model is an Additive Color Model.
• Additive color uses transmitted light to display color.
• Computer Monitors and the human eye use RGB to determine color.
• The combination of amounts of individual red, green, and blue light defines the resulting RGB color.
• When you add red light, blue light, and green light together and each component has a value of 255, then the resulting color is white. When the value of each component is 0, the resulting color is pure black.
• With the RGB additive model, computers can display up to 16.7 million colors.

The CMYK Color Model

• The CMYK model defines color using Cyan (C), Magenta (M), Yellow (Y) and Black (K) inks or pigments.
  This color model is important because it is widely used in the print industry and many times a computer image or photo that uses an RGB color format will have to be converted to the CMYK color format so the printing company can print the image on paper.
• Each color contains an amount of ink that is measured with a percent from 0 to 100.  A value of 100 means that the inks is applied at full saturation.
• The CMYK color model is a Subtractive Color Model.
• Subtractive color uses reflected light to display color.
• Printed materials are produced using the CMYK color model.
• The combination of the amounts of cyan, magenta, yellow, and black ink defines the resulting CMYK color.
• When you combine cyan, magenta, yellow, and black ink together and each component has a value of 100, then the resulting color, in theory, would be black. When the value of each component is 0, the resulting color, in theory, is pure white.
• On a computer monitor, (0,0,0,0) does result in white, but on print material (0,0,0,0) means no ink is added to the paper, so the resulting color will be the color of the underlying paper..
• With the CMYK subtractive model, in theory, you should be able to product millions of colors, but due to the limitations of printing inks and paper (such as dot size, paper saturation limits, and the printing hardware), you generally can't produce over 80,000 colors and In reality, it's probably closer to 40,000 colors.
• Computer monitors don't have these printing and ink limitations so they can display millions of CMYK colors, but all the displayed colors can't be reproduced on a printer.

• The HSB color model defines three fundamental properties of color: Hue, Saturation, and Brightness.
• It is predicated on the principle that every real color originates from a single pure color (Hue), which is then mixed with various amount of white or/and black color to give various shades of that pure color.
• Hue is the name or pure value of the color such as red, green, yellow, etc.  It is measured in degrees from 0 to 360.  (0 is Red, 60 is Yellow, 120 is Green, 180 is Cyan, 240 is Blue and 300 is Magenta.)
• Saturation is the purity of the color and is the amount of pure color mixed with white color.  It varies from white to pure color.  It is measured in percent from 0 to 100.  The higher the percentage, the more pure will be the color.
• Brightness determines the intensity of the color and is the amount of pure color mixed with black color.   It varies from black to pure color.    It is measured in percent from 0 to 100.  The higher the percentage, the brighter the color.

How The Color Models Compare in the Number of Colors that they Define

In the next section on Color Depth, I'll explain how "bits and bytes" are used to represent different Colors and by using more bits, you can represent more colors.