Digital Media

Lecture 7: Color part 2

Georgia Gwinnett CollegeSchool of Science and Technology

Dr. Jim Rowan

Refer to Supplemental text:

You have a blue ball and walk into a room lit with a red light. What color is the ball while in the room?

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Color Models other than RGB

CMYK– cyan– magenta– yellow– key (black)

HSV, HSB, HSL– Hue– Saturation – value. brightness, lightness

Colored light shining on a white surface

One red light, one blue light and one green light…

Arranged to overlap… Creating Cyan, Magenta and Yellow and… White

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Cyan = Green + BlueCyan = White - Red

Yellow = Red + GreenYellow = White - Blue

Magenta = Red + BlueMagenta = White - Green

This color model can be used as an Additive model appropriate for use with light

This color model can also be used as a Subtractive model appropriate for use with ink and paint... things that absorb light

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White = Red + Green + Blue

white paper

white paper cyan ink

magenta ink

white light

removes green

removes redwhite light

white light

removes green

removes red

leavingblue light

magentaleavinglight

magentaleavinglight

cyanleavinglight

CMYK model Cyan Magenta Yellow Key (black)

– While you should be able to make black by mixing Cyan, Magenta and Yellow…

– Paint (and ink) is not perfect Subtractive model Used by the printing industry

HSV model

Another way of looking at color Hue

– The color described as degrees from red Saturation

– How pale the color is– Think of it as adding white to the color

Brightness– How intense the color is– Thinks of it as adding black to the color

Adjusting the Hue

Adjusting the Hue

Adjusting the Hue

Adjusting the Hue

Adjusting the Saturation

Adjusting the Value

Full-On Red in RGB model

Full-On Green in RGB model

Full-On Blue in RGB model

The transition from B&W to Color TV

B&W just needs intensity changes to make white-gray-black– intensity varies as the electron beam is drawn across the screen

Color is RGB+Intensity for each– could transmit each color with its intensity and it would work for

color tv but– can’t use the same signal model for color because the B&W tv’s

wouldn’t work– Solution: Transmit the necessary color information during the

retrace.– Color is transmitted as luminance and two colors– B&W tv’s simply ignore it because the beam is off

RGB RGB RGB

RGB RGB RGB

RGB RGB RGB

B B B

B B B

B B B

G G G

G G G

G G G

R R R

R R R

R R R• Allows the use of the

brightness and contrast of each individual color to be manipulated using levels and curves

• Allows a very fine level of control

• Very time consuming• Color balance, hue and

saturation adjustments on the whole image is a shortcut

RGB

Channels

http://en.wikipedia.org/wiki/Channel_(digital_image)

Channels

Red Green

Blue