Specifications
52
When shown on a computer screen, digitized analog video may show interlacing eects such as
tearing and shapes may be o slightly since the pixels generated may not conform to the square
pixels on the computer screen. Interlacing eects 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, dierent NTSC image resolutions. At right, dierent 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
exibility. 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 dened 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