Internet Graphics
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Representing Images
Raster Image: Images consist of
“dots” of color, not lines
 Pixel: Picture element-tiny rectangle
 Resolution: Number of pixels

SVGA: 1280 x 1024 = 1,310,720
 VGA: 640 x 480
 Your monitor can be modified
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2
Representing Images
RGB: monitor, each pixel
 Intensity: 0 (dark) – 255 (bright)
 Representing Color: # - # - #

255-255-255 = white
 100-0-0 = scarlet
 16,777,216 = 16 million colors

3
Representing Images
Light media: RGB
 Opaque media: paint



Red, blue, yellow
Printers
Cyan, yellow, magenta
 Must have conversion software for
translating monitor to printer

4
Storage of Images
1 byte = 8 bits = 255 values
 Images are memory hogs
 Causes problems with transmission
 e.g. Image: 5 million pixels = 14 Mb
 Solutions

Less “accuracy”
 Compression

5
Reducing Color Depth
 Reduce
the number of colors
 Depth: measured by bits/pixel
 True color = 3 bytes = 24 bits
6
8-bit Color
1 byte = 8 bits = 256 colors
 Color Palette – 256 colors


Multiple palettes are available
8-bit number represents the
particular color in the palette – not
the mix of RGB
 Uses 1/3 storage space + 768 bytes
to define the palette

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Other Color Depths
1-bit - Black & White
 4-bit = 16 colors
 Simple drawings, icons
 Windows, but can change palette
 Start; Settings; Control Panel;
Display; Appearance; Scheme

8
Color Depth Tradeoff
Color depth vs. Resolution
 Due to storage requirements, must
reduce one
 1280 x 1024  256 colors
 16 M colors  640 x 480
 Photos: need more than 256 colors

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