Page 157 - DCAP104_EXPOSURE_TO_COMPUTER_DISCPLINES

Exposure to Computer Disciplines

Notes 7.3.14 Page Description Language (PDL) Formats
Page description languages (PDLs) are actual computer languages used for describing the layout,
font information, and graphics of printed and displayed pages. PDLs are used as the interpreted
languages used to communicate information to printing devices, such as hardcopy printers, or
to display devices, such as graphical user interface (GUI) displays. The greatest difference is
that PDL code is very device-dependent. A typical PostScript file contains detailed information
on the output device, font metrics, color palettes, and so on. A PostScript file containing code
for a 4-color, A4-sized document can only be printed or displayed on a device that can handle
these metrics.
Markup languages, on the other hand, contain no information specific to the output device. Instead,
they rely on the fact that the device that is rendering the markup language code can adapt to the
formatting instructions that are sent to it. The rendering program chooses the fonts, colors, and
method of displaying the graphical data. The markup language provides only the information
and how it is structured.
Although PDL files can contain graphical information, we do not consider PDLs to be graphics file
formats any more than we would consider a module of C code that contains an array of graphical
information to be a graphics file format. PDLs are complete programming languages, requiring
the use of sophisticated interpreters to read their data; they are quite different from the much
simpler parsers used to read graphics file formats.
If your image size is say 3000x2000 pixels, then this is 3000x2000 = 6 million
pixels (6 megapixels). If this 6 megapixel image data is RGB color (if 24 bits,
or 3 bytes per pixel of RGB color information), then the size of this image data
is 6 million x 3 bytes RGB = 18 million bytes. That is simply how large your
image data is then file compression like JPG or LZW can make the file smaller,
but when you open the image in computer memory for use, the JPG may not
still have the same image quality, but it is always still 3000x2000 pixels and 18
million bytes. This is simply how large your RGB image data is (megapixels
x 3 bytes per pixel).

7.4 Graphics Software

Graphics software or Image editing software encompasses the processes of altering images,
whether they be digital photographs, traditional analog photographs, or illustrations. Traditional
analog image editing is known as photo retouching, using tools such as an airbrush to modify
photographs, or editing illustrations with any traditional art medium. Graphic software programs,
which can be broadly grouped into vector graphics editors, raster graphics editors, and 3d
modelers, are the primary tools with which a user may manipulate, enhance, and transform
images. Many image editing programs are also used to render or create computer art from scratch.

In computer graphics, graphics software or image editing software is a program or collection of
programs that enable a person to manipulate visual images on a computer.

Computer graphics can be classified into two distinct categories: raster graphics and vector
graphics. Before learning about computer software that manipulates or displays these graphics
types, you should be familiar with both.
Many graphics programs focus exclusively on either vector or raster graphics, but there are a few
that combine them in interesting and sometimes unexpected ways. It is simple to convert from
vector graphics to raster graphics, but going the other way is harder. Some software attempts
to do this.

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