ABCs of DEW Software chapter 1:

Introduction to Three-Color Light

Many of us were taught at a young age that the primary colors are red, yellow, and blue.

  Adding Color Pigments

Our early experiences with color mixing were blending together paints where yellow and blue make green and the three colors stirred together make colors ranging from brown, gray, or black. From this we have two errors in our understanding of color. First, primary colors can be mixed together to create all other colors. Second, red, yellow, and blue are the primary colors.

When we talk about primary colors, we generally think about three colors which can be mixed together to create all of the colors of the rainbow. Have you ever tried to make black out of your red, yellow, and blue? Even more difficult—try to make fluorescent pink, silver, or gold. Primary colors cannot make all other colors, but they can make the most colors from the fewest starting resources.

Difference Between Pigments and Light
  Adding Color Light

There are two sets of primary colors: one for pigment (dyes and paints) and another for light. Look at the printing process for the color pages of your local newspaper or a color printer, and you will see that the rainbow of colors is created from four colors of ink: cyan, magenta, yellow, and black. Modern printing has found that combinations of cyan, magenta, and yellow (which are very specific shades of blue, red, and yellow) can create the maximum number of colors. When mixed together in equal parts, the three create black (or gray). In printing, the black ink has been added as a fourth color to use less ink. To see how this works, take a microscope or magnifying glass to a color picture in the morning paper or a magazine.

What you see up close is a series of overlapping dots of various sizes and transparency in those four colors. You may even see a newspaper once in a while where the color layers were not properly lined up so the images appear to be double and the picture colors are not right.

In light, the primary colors are red, green, and blue. Despite what you learned in paint, when you mix yellow and blue light the result is white. Likewise, magenta + green makes white; and cyan + red makes white. Color television and computer monitors use the three primary colors of light to display thousands or millions of different colors. If you take a magnifying glass to your computer monitor or television, you will see a regular pattern of red, green, and blue lines or dots. Each of these glows at varying intensities, just as a color printer drops varying amounts of ink. In both cases, what you perceive is the mixing of the primary colors and up to 16.8 million different colors on the screen.

 Investigation

Investigation 1-1. Newsprint and Video Displays

With a microscope or magnifying glass examine a color picture in the morning paper or a magazine. Look for the overlapping dots of various sizes and transparency in four colors of ink: cyan, magenta, yellow, and black.

With a magnifying glass, examine your computer monitor or television. Look for the regular pattern of red, green, and blue lines or dots.

1.1 How does the paper print dots compare with what you see on the computer monitor or TV?


The difference between mixed pigments and mixed light rests on how light gets reflected and absorbed. Pigment and paint are substances that absorb specific wavelengths of light, subtracting them from the light energy reflected by the surface. A blue painted surface will absorb all colors of light except the blue, which it reflects back. The reflected light reaches your eyes and you perceive the color blue. A colored light bulb or a computer monitor is a light source which shines or adds light energy of specific wavelengths. A red light bulb shines red light directly to your eyes and you perceive the color red.

Computer Monitors

A number of different technologies are used at present for computer displays or monitors. The two most common are the cathode ray tube (CRT) and the liquid crystal display (LCD; common in laptop computers). Here is a brief introduction to the CRT, although this is only the tip of the iceberg.

A CRT consists of a negatively charged heated metal filament, called a cathode, inside a glass vacuum tube. Coming out from the cathode is a ray of electrons. A positively charged metal piece, called the anode, attracts the electron beam and focuses it onto the screen at the front of the glass vacuum tube, which is the front of the monitor. When excited by the beam, a coating of phosphors on the screen glows. A color CRT has three electron beams and the screen is coated with phosphors that glow in three different colors: red, green, and blue (RGB). Each electron beam will excite only the dots or lines on the screen that have been coated for its color (i.e. the beam for red excites the dots coated in a red phosphor).



Naming Colors

People have given many names to the colors they see. When Isaac Newton wrote down the colors he saw in the rainbow, he chose to break them out into seven names. We still use that list of names today, although you may find it difficult to pick out the color indigo or the color violet somewhere in the room.

There are a number of basic color names that people refer to: red, orange, yellow, green, blue, purple, brown, white, and black. But individual people may not agree on what to call a specific block of color. Is it red, orange-red, salmon, burnt-sienna, or watermelon? Naming or distinguishing between colors is a very subjective process. As you study light and color throughout this course, you may find that what you think is pure red has more blue in it than the computer’s pure red. Don’t let that confuse you; when it comes to studying color it is not the name of the color that matters most.

 Investigation

Guess colors produced by the combination of red, green, and blue intensity values. Explore how colors are made using the ColorBasics software program (using the Make Colors tab).



Color In Computer Images

Computer use intensities of the colors red, green, and blue to create a myriad of different colors on our monitors. Throughout this activity, you have used percentages to create over a million colors-primary color intensities ranged on a scale of 0 to 100 percent. Most digital images use a binary scale with 2^8 levels. Instead of 101 possible intensity values, there are 2^b or 256 possible intensity values for each color. These images can display over 16.8 million different colors.

 A digital picture is made of three fields of color intensity measurements, and a pixel is the mixture of the red, green, and blue intensities at a location in the picture


 For new material relating to this chapter, please see the GSS website “Staying Up To Date” page:
http://www.globalsystemsscience.org/uptodate/dew/ch1