Red, green and blue (RGB): RGB is another way to use 3 numbers to specify a color instead of using an intensity-distribution curve or HSB

• In addition to using Hue, Saturation and Brightness (HSB);

• Many (but not all) colors can be described in terms of the relative intensities of a light mixture of a certain wavelength red, wavelength green and wavelength blue lights

• 650-nm red• 530-nm green• 460-nm blue

• These are called the additive primaries• The mixing of the additive primaries is

called additive mixing• Additive mixing is usually done by mixing

primary color lights with different intensities but there are other ways to be discussed later

• Demonstrate with Physics 2000

cyan magenta

yellow650-nm red530-nm green530-nm green

460-nm blue

http://www.colorado.edu/physics/2000/tv/colortv.html

Complementary additive colors

• Definition of complementary color (for additive mixtures):

• The complement of a color is a second color.

• When the second color is additively mixed to the first, the result is white.

• Blue & yellow are complementary B + Y = W.

• Green & magenta are complementary G + M = W

• Cyan and red are complementary C + R = W

• Magenta is not a wavelength color— it is not in the rainbow

• There is at most one wavelength complementary color for each wavelength color (Fig 9.9)

white

cyan

red

magenta

greengreenyellow

blue

Additive mixing of colored light primaries

Blue added togreen = cyan.

Green added tored = yellow.

Red added toblue = magenta.

Complementary colored lights(additive mixing)

Blue (primary)and yellow.

Green (primary)and magenta.

Red (primary)and cyan.

• Partitive mixing is another kind of additive color mixing but not achieved by superimposing colored lights!

• Instead, it works by putting small patches of colors next to each other. • From a distance these

colors mix just as though they were colored lights superimposed on each other

• Examples:• Seurat pointillism• Color TV and computer

screens (Physics 2000)• Photoshop example

What is partitive mixing?

Partitive mixing

• http://www.learner.org/teacherslab/science/light/index.html

• Read the introduction and click on the “Light in Color” tab. Proceed to work the activity listed below. Made from dots

• Go through and write down at least 5 different color combinations from the program.

A colored filter subtracts colors by absorption.

=

Incident white light Only greengets

through

Cyanfilter subtracts

red

Yellowfilter subtracts

blue

A colored filter subtracts certain colors by absorption and transmits

the rest

=

Incident white light Magentafilter subtracts

green

Cyanfilter subtracts

red

Only bluegets

through

A colored filter subtracts colors by absorption.

=

Incident white light Magentafilter subtracts

green

Only redgets

through

Yellowfilter subtracts

blue

What is the effect of combining (sandwiching) different colored filters together?

• Rules for combining the subtractive primaries, cyan, yellow and magenta:• White light passed through

a cyan filter plus a magenta filter appears blue

• White light passed through a yellow filter plus a magenta filter appears red

• White light passed through a yellow filter plus a cyan filter appears green

• Why?

cyan

magenta

yellow

Colored surfaces subtract certain colors by absorbing them, while

reflecting others

Magenta surfaceabsorbs (subtracts)

green.

Green surfaceabsorbs (subtracts)

red and blue (magenta).

White inMagenta out

White inGreen out

Green light on a magenta surface appears colorless because green is

absorbed

Magenta surfaceabsorbs (subtracts)

green.

Green surfaceabsorbs (subtracts)

red and blue (magenta).

Magenta light on a green surface

appears colorless because magenta is

absorbedGreen in

No color

Magenta in

No colo

r

Halftone

• Left: Halftone dots. • Right: How the human eye

would see this sort of arrangement from a sufficient distance or when they are small.

• Resolution: measured in lines per inch (lpi) or dots per inch (dpi); for example, Laser Printer (600dpi)

Color halftoning

Three examples of color halftoning with CMYK separations. From left to right: The cyan separation, the magenta separation, the yellow separation, the black separation, the combined halftone pattern and finally how the human eye would observe the combined halftone pattern from a sufficient distance.

Paper beneath

Printer's ink