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Home Concept Builders Light Waves and Colors Color Pigments Help Help 15

Color Pigments - Questions 15 Help

There are three primary pigments. Each pigment is designed to absorb a single primary color of light. Cyan pigments absorb red light and reflect blue and green light. Magenta pigments absorb green light and reflect red and blue light. And yellow pigments absorb blue light and reflect red and green light.

There are three similar versions of this question. Here is one of those versions:
 

Version 1:

You have just sent a Gum Drop picture to your color printer. What color ink(s) must the printer use to color each individual part of the picture as intended?

 
Gum Drop 1: C M Y
Gum Drop 2: C M Y
Gum Drop 3: C M Y
Gum Drop 4: C M Y
Gum Drop 5: C M Y

Vocabulary Terms
Let's begin with some vocabulary terms that you should become acquainted with:

Incident: incident means to approach. Incident light is light that is approaching the printed image of the gum drops. In all cases, white light will be approaching the gum drops. This white light can be thought of as being equivalent to red, green and blue primary colors of light.

Pigments: a chemical or ink that is present on a sheet of paper in order to give the paper the ability to absorb specific colors of light.

Absorb: pigments sprayed on a printed image make the image capable of absorbing certain colors of light. A cyan pigment absorbs red light. A magenta pigment absorbs green light. And a yellow pigment absorbs blue light.

Reflect: reflect means to bounce off. The light color(s) that does not get absorbed by the printed image will be reflected to an observer's eye.


Using the Incident-Absorbed-Refleted Model
A useful model for analyzing color questions is what we call the incident-absorbed-reflected model. The model suggests that a successful analysis includes three steps ... with each step involving the answering of a question. Those steps or questions are ...

  1. What primary color(s) of light are incident upon the gum drop (printed on paper)?
  2. Of the primary light colors that are incident, which color(s) is/are absorbed by the gum drop image?
  3. Of the primary light colors that are incident, which color(s) is/are reflected by the gum drop image?


The absorbed light color(s) is/are subtracted from the red, green, and blue incident light. Once the subtraction process is complete, the result is the reflected light color. It is the reflected light color that reaches the observer's eye and determines the color appearance of the gum drop.

Applying the Model
There are five colored gum drops in this image - red, green, blue, yellow and black. Each color is created by applying one or more of cyan, magneta, and yellow inks to the whitte paper in order to subtract one or more of the primary light colors (red, green, and blue).

For the black gum drop, you will want to absorb all three light colors so that no light is reflected. To do this, all three pigments will have to be used since each pigment absorbs one of the primary light colors. A useful representation used by the incident-absorbed-reflected model is a color subtraction equation. The color subtraction equation for the black gum drop can be written as RGB - R- G- B = 0

The red appearance is obtained by subtracting both green and blue light from the incident light colors. That is, RGB - G - B = R. This can be accomplished by using magenta ink to subtract the green light and yellow ink to subtract the blue light.

The green appearance is obtained by subtracting both red and blue light from the incident light colors. That is, RGB - R - B = G. This can be accomplished by using cyan ink to subtract the red light and yellow ink to subtract the blue light.

The blue appearance is obtained by subtracting both red and green light from the incident light colors. That is, RGB - R - G = B. This can be accomplished by using cyan ink to subtract the red light and magenta ink to subtract the green light.

The yellow appearance shouldn't be too difficult to figure out. If you want a gum drop to appear yellow, just apply the yellow ink. The yellow pigment or ink will subtract the blue light and reflect the red and green light. That could be described as RGB - B = RG = yellow.

Try this link to The Physics Classroom Tutorial for more help with the understanding how filters interact with the incident light:

Color Subtraction

Concept Builder Teacher Notes Directions