52
When shown on a computer screen, digitized analog video may show interlacing effects such as
tearing and shapes may be off slightly since the pixels generated may not conform to the square
pixels on the computer screen. Interlacing effects can be reduced using deinterlacing techniques
(
see Chapter 5
), while aspect ratio correction can be applied to video before it is displayed to
ensure, for instance, that a circle in an analog video remains a circle when shown on a com-
puter screen.
Figure 6.1a At left, different NTSC image resolutions. At right, different PAL image resolutions.
6.2
VGA resolutions
With 100% digital systems based on network cameras, resolutions that are derived from the
computer industry and that are standardized worldwide can be provided, allowing for better
flexibility. The limitations of NTSC and PAL become irrelevant.
VGA (Video Graphics Array) is a graphics display system for PCs originally developed by IBM. The
resolution is defined as 640x480 pixels, which is a common format used by non-megapixel
network cameras. The VGA resolution is normally better suited for network cameras since VGA-
based video produces square pixels that match with those on computer screens. Computer
monitors can handle resolutions in VGA or multiples of VGA.
Table 6.2 VGA resolutions.
4CIF 704 x 480
2CIF 704 x 240
CIF 352 x 240
QCIF 176 x 120
D1 720 x 480
4CIF 704 x 576
2CIF 704 x 288
CIF 352 x 288
QCIF 176 x 144
D1 720 x 576
Display format
Pixels
QVGA (SIF)
320x240
VGA
640x480
SVGA
800x600
XVGA
1024x768
4x VGA
1280x960
CHAPTER 6 - RESOLUTIONS
