Kyocera TASKalfa 4551ci Printing System (11),(12),(13),(14) Color Reference G - Page 72

Raster images and vector graphics, raster images, vector graphics, pixels, resolution, bit depth

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DESKTOP COLOR PRIMER 72 Raster images and vector graphics Two broad categories of artwork can be printed from a personal computer to a color printer: raster images and vector graphics. A raster image, also referred to as a bitmap, is composed of a grid of pixels, each assigned a particular color value (as illustrated in example a in the following figure). The grid, when sufficiently enlarged, resembles a mosaic made from square tiles. Examples of raster images include scans and images created in painting or pixel-editing applications, such as Photoshop and Corel Painter. The amount of data found in a raster image depends on its resolution and bit depth. The resolution of a raster describes the compactness of the pixels and is specified in pixels per inch (ppi). The bit depth is the number of bits of information assigned to each pixel. Black and white raster images require only one bit of information per pixel. Grayscale images require 8 bits per pixel. For photographic quality color, 24 bits of RGB color information are required per pixel, yielding 256 levels of red, green, and blue. For CMYK images, 32 bits per pixel are required. When printing raster artwork, the quality of the output depends on the resolution of the source raster. If the raster resolution is too low, individual pixels become visible in the printed output as small squares. This effect is sometimes called "pixelation." In vector graphics, picture objects are defined mathematically as lines or curves between points-hence the term "vector" (see example b). Picture elements can have solid, gradient, or patterned color fills. Vector artwork is created in illustration and drawing applications, such as Illustrator and CorelDRAW. Page layout applications, such as QuarkXPress, also allow you to create simple vector artwork with their drawing tools. PostScript fonts are vector-based, as well. a b Vector artwork is resolution-independent. You can scale it to any size and resolution without danger of pixels becoming visible in printed output.

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D
ESKTOP
C
OLOR
P
RIMER
72
Raster images and vector graphics
Two broad categories of artwork can be printed from a personal computer to a color printer:
raster images
and
vector graphics
.
A raster image, also referred to as a bitmap, is composed of a grid of
pixels
, each assigned a
particular color value (as illustrated in example a in the following figure). The grid, when
sufficiently enlarged, resembles a mosaic made from square tiles. Examples of raster images
include scans and images created in painting or pixel-editing applications, such as Photoshop
and Corel Painter.
The amount of data found in a raster image depends on its
resolution
and
bit depth
. The
resolution of a raster describes the compactness of the pixels and is specified in pixels per inch
(ppi). The bit depth is the number of bits of information assigned to each pixel. Black and
white raster images require only one bit of information per pixel. Grayscale images require
8 bits per pixel. For photographic quality color, 24 bits of RGB color information are required
per pixel, yielding 256 levels of red, green, and blue. For CMYK images, 32 bits per pixel are
required.
When printing raster artwork, the quality of the output depends on the resolution of the
source raster. If the raster resolution is too low, individual pixels become visible in the printed
output as small squares. This effect is sometimes called “pixelation.”
In
vector graphics
, picture objects are defined mathematically as lines or curves between
points—hence the term “vector” (see example b). Picture elements can have solid,
gradient
, or
patterned color fills. Vector artwork is created in illustration and drawing applications, such as
Illustrator and CorelDRAW. Page layout applications, such as QuarkXPress, also allow you to
create simple vector artwork with their drawing tools. PostScript fonts are vector-based,
as well.
Vector artwork is resolution-independent. You can scale it to any size and resolution without
danger of pixels becoming visible in printed output.
a
b