Page 13 - DCAP313_LAB_ON_COMPUTER_GRAPHICS

Unit 1: Fundamentals of Computer Graphics

1.2.3 Hard-copy Devices Notes
Pictures are directing to a printer or plotter to produce hard-copy output on 35-mm slides,
overhead transparencies or plain paper. The quality of the pictures depends on dot size and
number of dots per inch (DPI).
Types of printers: line printers, LaserJet, ink-jet, and dot-matrix.
LaserJet: printers use a laser beam to create a charge allotment on a turning drum coated with
a photoelectric material. Toner is applied to the drum and then transferred to the paper. To
produce colour outputs, the 3 colour pigments (cyan, magenta, and yellow) are deposited on
separate passes.
Inkjet: printers produce output by squirting ink in horizontal rows across a roll of paper wrapped
on a drum. To produce colour outputs, the 3 colour pigments are shot simultaneously on a single
pass along each print line on the paper.

Inkjet or Pen Plotters: These are used to generate drafting layouts and other drawings of normally
larger Sizes. A pen plotter has one or more pens of different colours and widths mounted on a
carriage which spans a sheet of paper.
1.2.4 Coordinate Representations in Graphics

General graphics packages are designed to be used with Cartesian coordinate representations
(x, y, and z). Usually several different Cartesian reference frames are used to construct and
display a scene:

Figure 1.6: Coordinate Representation in Graphics

Modelling coordinates: are used to construct individual object shapes.
World coordinates: are computed for specifying the placement of individual objects in appropriate
positions.
Normalized coordinates: are converted from world coordinates, such that x, y values are ranged
from 0 to 1.
Device coordinates: are the final locations on the output devices.

1.2.5 Output Primitives
Shapes and colours of objects can be illustrated internally with pixel arrays or sets of basic
geometric arrangements such as straight line segments and polygon colour areas. The functions

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