Multi-media Graphics JOUR 205

Color Models & Color Space

5 ways of specifying colors

Multi-media Graphics JOUR 205

Color Models

• RGB - mixing primary light colors

• CMYK - mixing primary pigment colors

• Indexed color - matching colors on screen to a specific color table

• Lab color - international standard, device independent

• HSB - hue, saturation & brightness

Multi-media Graphics JOUR 205

Additive color model (RGB)

• Red, blue & green are primary colors

• Applies when mixing colors of light (on tv & computer screens, theatrical lighting)

• Mixed primaries make white light

Multi-media Graphics JOUR 205

An RGB color image

Redchannel

only

Red +Green

Green + blue

Red + blue + green

Multi-media Graphics JOUR 205

Subtractive color model (CMYK)

• Cyan, magenta & yellow are primary colors

• Applies when pigments are mixed on a surface (printing, painting, etc.)

• Mixed primaries make “black”

Multi-media Graphics JOUR 205

Elements of a CMYK image

Multi-media Graphics JOUR 205

C + M printers

Multi-media Graphics JOUR 205

C + M + Y printers

Multi-media Graphics JOUR 205

C + M + Y + K printers

Multi-media Graphics JOUR 205

The Lab color model• Three axes (L, a & b)

define a “color space.”• All colors can be

precisely defined by their position in this space.

• Lab model is a world-wide standard for all monitors & printers.

Multi-media Graphics JOUR 205

Elements of an Lab image

Luminance (L)

Color axis a (green/magenta)

Color axis b (yellow/blue)

Multi-media Graphics JOUR 205

HSB color model

HSB model is based on human perception of color, represented by the color wheel.

Multi-media Graphics JOUR 205

HSB color model

• Hue is the color reflected from or transmitted through an object. Hue is identified by the name of the color.

• Saturation represents color purity-- the amount of gray in proportion to the hue.

• Brightness is the relative lightness or darkness of the color.

Multi-media Graphics JOUR 205

Photoshop’s HSB controlsNormal image

Image with hue, saturation and

brightness altered.

Multi-media Graphics JOUR 205

Color gamuts

Multi-media Graphics JOUR 205

Out-of-gamut colors

Colors specified in RBG Colors printed in CMYK

Colored inks on paper cannot reproduce the bright, intense colors that are possible when mixing with light on a monitor. If your art is to be printed on paper, specify colors in CMYK mode to avoid “color shock” when your job comes back from the print shop.

Multi-media Graphics JOUR 205

Index color: web-safe palette

Original RGB format Image indexed to web palette

24-bit RGB images may contain 16.7 million colors. Index color images can have no more than 255 colors. The web-safe palette has only 216 colors. Those colors are common to both Macintosh and Windows operating systems.