IEI Technology iSignager 500A, Руководство пользователя

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iSignager 500A
Page 33
and therefore its introduction sometimes coincides with the introduction of digital television
(DTV). High-definition signals require a high-definition television or computer monitor in
order to be viewed. High-definition video generally has an aspect ratio of 16:9 (1.78:1).
The aspect ratio of regular widescreen film shot today is typically 1.85:1 or 2.40:1.
Standard-definition television (SDTV) has a 4:3 (1.33:1) aspect ratio.
High-definition television (HDTV) resolution is 1080 or 720 lines. In contrast, regular digital
television is 480 lines (NTSC-like) or 576 lines (PAL/SECAM-like).
A.5.1 Notation
In the context of HDTV, the formats of the broadcasts are referred to using a notation
describing:
720 p 60
720: The number of lines in the display resolution.
P: Progressive frames (p) or interlaced fields (i).
60: Number of frames or fields per second.
For example, the format 720p60 is 1280x720 pixels, progressive encoding with 60 frames
per second (60 hertz known as Hz). The format 1080i50 is 1920x1080 pixels, interlaced
encoding with 50 fields (25 frames) per second. Often the frame or field rate is left out.
It can then usually be assumed to be either 50 or 60, except for 1080p which is only
supported as 1080p24, 1080p25 or 1080p30 by consumer HDTV displays.
A frame or field rate can also be specified without a resolution. For example 24p means
24 progressive frames per second and 50i means 50 interlaced frames per second.
A.5.2 Progressive Scan vs. Interlaced Scan
Interlaced scan is the way a television decodes an image–a frame is broken into two fields,
odd (1, 3, 5, 7…) and even (2, 4, 6, 8…). A television scans 60 fields per second with 30
odd and 30 even fields created. By combining the two fields every 1/30 of a second, a
frame is created thus creating 30 frames per second.