The Way to Present the Classics
DVD STORAGE CAPACITY
DVD5 – Single sided / single layered, 4.7gigabytes = approx 135 minutes
DVD9 – Single sided / dual layered, 8.5 gigabytes = approx 244 minutes
DVD10 – Double sided / single layered, 9.4 gigabytes = approx 270 minutes
DVD18 – Double sided / dual layered, 17 gigabytes =
approx 488 minutes
MPEG2 ( Motion Picture Experts Group): has a variable
video transfer rate of up to 10 megabits per second, and is also the
format used for digital TV broadcasting.
Essentially the core process behind DVD and the way
in which the amount of data that needs to be stored on the disk is
reduced, hence DVD’s dramatically increased capacity over previous
digital disk formats. Put simply, the compression process has its
foundation in the fact that film and video footage generally doesn’t
alter much from frame to frame. What the compression process does is
analyse the differences from one frame to the next and it is only those
changes between the frames that are encoded rather than the repeated
information. The first frame of
a shot is referred to as an “I-Frame” and is basically a complete
picture that is the updated with the relevant changes in detail. To avoid
the moving image from deteriorating too much, new I-Frames are generally
inserted every 15 frames or so (or whenever there is a shot change) –
remember that PAL video runs at 25 frames per second and NTSC at 30fps.
When Television started affecting Cinema attendances in 1950’s America, the big movie studios decided to try and lure audiences back by launching a variety of colour, sound and wide screen processes and presentations designed to make cinema-going as spectacular and literally big an experience as possible. Names such as Vistavision, Cinemascope and Panavision will be familiar to most. Although the technology behind each wide screen process differs the aim was the same – a bigger, wider image. Cinema were refitted with larger, wider screen to accommodate this new technology.
Regardless of the size of the image projected onto a screen (or displayed on a TV) the aspect-ratio (i.e. the proportionality of the rectangular image) remains the same.
The aspect-ratio of a feature film depends on how it was originally photographed.
Up till around 1954, feature films with sound were Academy Frame with and aspect-ratio of 1.37:1 i.e. the projected image was 1.37 times wider than it was tall. This is pretty close to the proportions of a normal TV set, which has an aspect-ratio of 1.33:1 (in fact the American National Television Standards Committee adopted the basic Academy Frame ratio for television when it was introduced and simply rounded off the proportions to whole numbers i.e. 4:3).
Vistavision had a ratio of 1.66:1 with both Cinemascope and Panavision being 2.35:1. The widest popular movie was “Ben Hur” (1959) with an aspect-ratio of 2.76:1. Most movies today are around 1.85:1 with some wider at 2.35:1 and very few narrower than 1.66:1.
Note that the only film standard that is anywhere
near the television shape is the Academy format; meaning that, before the
advent of letterboxed VHS’s in the mid 80’s, practically every film
after 1954 had to be “panned and scanned” to fit a standard television
Anamorphic lenses were first used back in the 50’s as part of certain wide screen techniques. Cameras were fitted with anamorphic lenses that squeezed a wide image onto a standard film frame. If projected normally, elements in this image would appear tall and skinny; but with the theatre’s projector fitted with the same kind of anamorphic lens then the filmed image is stretched or unsqueezed back to it’s true proportions as it’s projected. Films shot anamorphically include, for example, all of the “Star Wars” movies.
As far as DVD is concerned anamorphic means something
different but the notions of squeezing and stretching are good ones to
keep in mind. When a letterboxed film is stored on DVD some capacity is
wasted on storing the black bars above and below the image, capacity that
could be better used contributing to picture detail. Anamorphic DVD’s
can enable just that.
Combined with a 16:9 wide screen TV anamorphic disks
can effect a 33% improvement in picture quality. A 1.78:1 wide screen
image is stored anamorphically by stretching it vertically by 33% thus
using the entire vertical resolution of the TV screen. When viewed on a
standard ratio 4:3 TV set the image appears tall and skinny, but when
viewed in the correct mode on a 16:9 wide screen TV the hardware stretches
the picture by 33% horizontally thus effecting a properly proportioned
image and filling the screen. If the image in question is originally a
1.78:1 aspect-ration i.e. matches a wide screen 16:9 TV’s aspect-ratio
then the image fits the whole screen perfectly.
N.B. DVD players are designed to squeeze anamorphic
images back down by 33% on standard 4:3 TV sets (they remove approx. every
third horizontal line and add the black bars top and bottom).
When wide screen images have a different aspect-ratio
from that of the 16:9 TV then we encounter a problem due to the fact that
the hardware can ONLY stretch anamorphic images by 33% horizontally.
Therefore any wide screen images that are wider in proportion than a 16:9
screen will need to have some form of letterboxing at the top and bottom
of the image. This then unavoidably wastes some storage capacity on the
disk and fails to utilise all of the screen’s vertical resolution. Some
wider images have been known to be side cropped to get closer to 16:9
Dolby Digital 5.1
Previously known as AC-3 this is Dolby’s digitally compressed multi-channel audio system. At peak performance the process can offer, through a Dolby Digital decoder, a 6 channel soundtrack consisting of 5 channels of surround sound – left, right, centre, right-rear and left-rear PLUS a dedicated low frequency effects channel routed to a subwoofer for bass ranges.
Blu-ray Disc (also known as BD or Blu-Ray) is an optical disc storage medium designed to supercede the standard DVD format.
Click on the image below for an overview of this format (opens in new window).
All text & Pictures © Laureate Company. Design © Karen Edwards 2002/2010