Raster Graphics

CSCI N351

Andy Harris

Indiana University / Purdue University - Indianapolis

Raster Graphics

• Use numbers to store images
• An image is a matrix of numbers

The most basic Image

Storing the image as binary numbers

Looking at colors

• Cones in the human eye

Examing basic RGB colors

• color Switch

A simple RGB face

• 
• Each pixel has three dots
• Red, Green Blue
• Each can be on or off

Data for the RGB face

Examining 24-bit Colors

• Color Tester
• Use 8 bits each for red, green, and blue

Other Color Schemes

• RGB Scheme
• HSV
• CIE
• Subtractive
• Color Space Conversion An external applet used in the video

RGB

• Often 3, 4, or 24 bits / pixel
• Relate to how computer stores colors
• Does not clearly indicate relationships between colors
• How do you make a color lighter or darker?

HSV Scheme

• Hue, Saturation, Value
• Closer to color wheel
• Better representation of color relationships
• Often measured in percentages (0-100)

Understanding Hue

• Base color
• 'pure' colors (FF0000, 00FF00, FFFF00, etc) easily created
• All bright colors
• Basic color wheel
• Nothing dark, Nothing pastel
• Hue of 0 = Red, 100 = Red

Saturation

• Relationship between 'pure' hue and grayscale
• High Saturation = pure colors
• Low Saturation = grayscale

Value

• Convert to black and white
• Relative grayscale - brightness
• High Values = lighter colors
• Low Values = darker colors

Subtractive Color Schemes

• Used in printing
• CMY - Cyan, Yellow, Magenta
• CMYK - Cyan, Yellow, Magenta, Black