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Aspect ratios
Aspect ratio refers to the ratio of the horizontal to vertical measurements of a
television's picture. Mechanically scanned television as first demonstrated by
John Logie Baird in 1926 used a 7:3 vertical aspect ratio, oriented for the head
and shoulders of a single person in close-up.
Most of the early electronic TV systems from the mid-1930s onward shared the
same aspect ratio of 4:3 which was chosen to match the Academy Ratio used in
cinema films at the time. This ratio was also square enough to be conveniently
viewed on round cathode-ray tubes (CRTs), which were all that could be produced
given the manufacturing technology of the time. (Today's CRT technology allows
the manufacture of much wider tubes, and the flat-screen technologies which are
becoming steadily more popular have no technical aspect ratio limitations at
all.) The BBC's television service used a more squarish 5:4 ratio from 1936 to 3
April 1950, when it too switched to a 4:3 ratio. This did not present
significant problems, as most sets at the time used round tubes which were
easily adjusted to the 4:3 ratio when the transmissions changed.
In the early 1950s, movie studios moved towards widescreen aspect ratios such as
CinemaScope in an effort to distance their product from television. Although
this was initially just a gimmick, widescreen is still the format of choice
today and square aspect ratio movies are rare. Some people argue that widescreen
is actually a disadvantage when showing objects that are tall instead of
panoramic, others say that natural vision is more panoramic than tall, and
therefore widescreen is easier on the eye.
Yet the various television systems were not originally designed to be compatible
with film at all. Traditional, narrow-screen movies are projected onto a
television camera either so that the top of the screens line up to show facial
features, or, for films with subtitles, the bottoms. What this means is that
filmed newspapers or long captions filling the screen for explanation are cut
off at each end. Similarly, while the frame rate of sound films is 24 per
second, the screen scanning rate of the NTSC is 29.96 Hz, which requires complex
scanning schedule. That of PAL and SECAM are 50 Hz, which means that films are
shortened (and the sound is offkey) by scanning each frame twice for 25 per
second.
The switch to digital television systems has been used as an opportunity to
change the standard television picture format from the old ratio of 4:3 (1.33:1)
to an aspect ratio of 16:9 (approximately 1.78:1). This enables TV to get closer
to the aspect ratio of modern widescreen movies, which range from 1.66:1 through
1.85:1 to 2.35:1. There are two methods for transporting widescreen content, the
most common of which uses what is called anamorphic widescreen format. This
format is very similar to the technique used to fit a widescreen movie frame
inside a 1.33:1 35mm film frame. The image is compressed horizontally when
recorded, then expanded again when played back. The anamorphic widescreen 16:9
format was first introduced via European PALPlus television broadcasts and then
later on "widescreen" DVDs; the ATSC HDTV system uses straight widescreen
format, no horizontal compression or expansion is used.
Recently "widescreen" has spread from television to computing where both desktop
and laptop computers are commonly equipped with widescreen displays. There are
some complaints about distortions of movie picture ratio due to some DVD
playback software not taking account of aspect ratios; but this may subside as
the DVD playback software matures. Furthermore, computer and laptop widescreen
displays are in the 16:10 aspect ratio both physically in size and in pixel
counts, and not in 16:9 of consumer televisions, leading to further complexity.
This was a result of widescreen computer display engineers' assumption that
people viewing 16:9 content on their computer would prefer that an area of the
screen be reserved for playback controls, subtitles or their Taskbar, as opposed
to viewing content full-screen.
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