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What is the HV Video Format?
The
format 720p60 is 1280 × 720 pixels, progressive
encoding with 60 frames per second (60 Hz). The format
1080i50 is 1920 × 1080 pixels, interlaced encoding with 50 fields (25
frames) per second. Often the frame or
field rate
is left out, indicating only the resolution and type of the frames or fields,
and leading to confusion
[3].
Sometimes the rate is to be inferred from the context, in which case it can
usually be assumed to be either 50 or 60, except for 1080p which is often
used to denote either 1080p24, 1080p25 or 1080p30 at present but will also
denote 1080p50 and 1080p60 in the future.
A frame or field rate
can also be specified without a resolution. For example 24p means 24
progressive scan frames per second and 50i means 25 interlaced frames per
second, consisting of 50 interlaced fields per second. Most HDTV systems
support some standard resolutions and frame or field rates. The most common are
noted below. Changes in notation
The
terminology described above was invented for digital systems in the 1990s.
Before that, analog TV had no true "pixels" to measure horizontal
resolution, and vertical scan-line count included off-screen scan lines with no
picture information while the CRT beam returned to the top of the screen to
begin another field. Thus NTSC was considered to have "525 lines"
even though only 486 of them had a picture (625/576 for PAL). Similarly the
Japanese MUSE system was called
"1125 line", but is only 1035i by today's measuring standards. This
change was made because digital systems have no need of blank retrace lines unless
the signal was converted to analog to drive a CRT. Standard
resolutions
When
resolution is considered, both the resolution of the transmitted signal and the
(native) displayed resolution of a TV set are taken into
account. Digital NTSC- and PAL/SECAM-like signals (480i60 and 576i50
respectively) are transmitted at a horizontal resolution of 720 or 704
"pixels". However these transmitted DTV "pixels" are not
square, and have to be stretched for correct viewing. PAL TV sets with an
aspect ratio of 4:3 use a fixed pixel grid of 768 × 576 or
720 × 540; with an aspect ratio of 16:9 they use
1440 x 768, 1024 × 576 or 960 × 540;
NTSC ones use
640 × 480
and
852 × 480
or, seldom, 720 × 540. |
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