Various
popular standards for compressing
multimedia data.
JPEG
JPEG stands for Joint Photographic
Experts Group. However, what
people usually mean when they
use the term "JPEG"
is the image compression standard
they developed. JPEG was developed
to compress still images, such
as photographs, a single video
frame, something scanned into
the computer, and so forth.
You can run JPEG at any speed
that the application requires.
For a still picture database,
the algorithm doesn't have to
be very fast. If you run JPEG
fast enough, you can compress
motion video -- which means
that JPEG would have to run
at 50 or 60 fields per second.
This is called motion JPEG or
M-JPEG. You might want to do
this if you were designing a
video editing system. Now, M-JPEG
running at 60 fields per second
is not as efficient as MPEG
2 running at 60 fields per second
because MPEG was designed to
take advantage of certain aspects
of motion video.
Motion JPEG
JPEG compression
or decompression that is applied
real-time to video. Each field
or frame of video is individually
processed.
MPEG
MPEG stands
for Moving Picture Experts Group.
This is an ISO/IEC (International
Standards Organization) body
that is developing various compression
algorithms. MPEG differs from
JPEG in that MPEG takes advantage
of the redundancy on a frame-to-frame
basis of a motion video sequence,
whereas JPEG does not.
MPEG 1
MPEG 1 was the first MPEG
standard defining the compression
format for real-time audio and
video. The video resolution
is typically 352 x 240 or 352
x 288, although higher resolutions
are supported. The maximum bitrate
is about 1.5 Mbps. MPEG 1 is
used for the Video CD
format.
MPEG 2
MPEG 2 extends the MPEG 1 standard
to cover a wider range of applications.
Higher video resolutions are
supported to allow for HDTV
applications, both progressive
and interlaced
video are supported. MPEG 2
is used for the DVD
- Video and SVCD
formats, and also forms the
basis for digital SDTV
and HDTV.
MPEG 3
MPEG 3 was originally targeted
for HDTV applications. This
was incorporated into MPEG 2,
so there is no MPEG 3 standard.
MPEG 4
MPEG 4 uses an object-based
approach, where scenes are modeled
as compositions of objects,
both natural and synthetic,
with which the user may interact.
Visual objects in a scene are
described mathematically and
given a position in a two- or
three-dimensional space. Similarly,
audio objects are placed in
a sound space. Thus, the video
or audio object need only be
defined once; the viewer can
change his viewing position,
and the calculations to update
the audio and video are done
locally. Classical "rectangular"
video, as from a camera, is
one of the visual objects defined
in the standard. In addition,
there is the ability to map
images onto computer-generated
shapes, and a text-to-speech
interface.
MPEG 7
MPEG 7 standardizes the description
of multimedia material (referred
to as metadata), such as still
pictures, audio, and video,
regardless if locally stored,
in a remote database, or broadcast.
Examples are finding a scene
in a movie, finding a song in
a database, or selecting a broadcast
channel. The searcher for an
image can use a sketch or a
general description. Music can
be found using a "query
by humming" format.
