The video beam produces about 262 video lines from top to bottom, of which 200
normally are visible on the screen with an NTSC system. With a PAL system, the beam
produces 312 lines, of which 256 are normally visible. Each complete set of lines
(262/NTSC or 312/PAL) is called a display field. The field time, i.e. the time required for a
complete display field to be produced, is approximately 1/60th of a second for an NTSC
system and approximately 1/50th of a second for PAL. Between display fields, the video
beam traverses the lines that are not visible on the screen and returns to the top of the
screen to produce another display field.
The display area is defined as a grid of pixels. A pixel is a single picture element, the
smallest addressable part of a screen display. The drawings below show what a pixel is
and how pixels form displays.
_______________________
| _ |
| |_| <----------------------- The picture is formed from many
| _ | elements. Each element is called
| _|_|_ | a pixel.
| |_|_|_| |
| |_|_|_| <------------- Pixels are used together to build
|_______________________| larger graphic objects.
___________________________ ____________________________
| | | |
| | | |
| <------ 320 pixels -----> | | <------ 640 pixels ------> |
| | | |
| | | |
| | | |
| | | |
|___________________________| |____________________________|
In normal resolution mode, In high resolution mode,
320 pixels fill a horizontal 640 pixels fill a horizontal
line. line.
Figure 3-2: What Is a Pixel?
The Amiga offers a choice in both horizontal and vertical resolutions. Horizontal resolution
can be adjusted to operate in low resolution or high resolution mode. Vertical resolution
can be adjusted to operate in interlaced or non-interlaced mode.
- Playfield Hardware 35 -
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