Explain the various file format such as PDF, TIFF, JPEG , MP3,
MPEG and its compression methodology and its
In This Chapter, you’ll learn on:
Describe image compression such as:
o Grayscale compression
o GIF compression
o JPEG compression
Describe audio compression such as:
o Lossless compression
o Lossy compression
Describe video compression such as:
Raw Multimedia Data Representation
What exactly is Raw Multimedia Data
Representation? In simple terms with reference to
Digital Imaging it literally means "raw" as in
"unprocessed". A RAW file contains the original
image information as it comes off the sensor before
in-camera processing so you can do that processing
afterwards on your PC with special software. RAW
files are huge in file size and contain redundant data
A single color, monochrome usually refers to a black-
and-white image, also referred to as line art or
bitmap mode. Grayscale refers to an image output
in shades of gray.
An image representation in which each pixel is
represented by a single sample value, representing
overall luminance on a scale from black to white.
A conversion from color to grayscale will reduce the
file size as the file has only one channel. An RGB
color image will have a separate channel for Red,
Green & Blue.
GIF, which stands for Graphics Interchange Format, is a
lossless method of compression. All that means is that
when the program that creates a GIF squashes the
original image down it takes care not to lose any data. It
uses a simple substitution method of compression.
If the algorithm comes across several parts of the image
that are the same, say a sequence of digits like this;
1 2 3 4 5, 1 2 3 4 5, 1 2 3 4 5
It makes the number 1 stand for the sequence 1 2 3 4 5
so that you could render the same sequence as 1 1 1.
Obviously this saves a lot of space and it stores the
key to this (1 = 1 2 3 4 5) in a hash table, which is
attached to the image so that the decoding
program can unscramble it.
The maximum compression available with a GIF
therefore depends on the amount of repetition there
is in an image. A flat colour will compress well -
sometimes even down to one tenth of the original
file size - while a complex, non-repetitive image will
fare worse, perhaps only saving 20% or so.
This file compression method can obtain a very high
compression ratio if it is used with detailed
photographic images, which was its intended use.
Part of JPEG’s success in high compression is due to
the fact it is a "lossy" compression method, meaning
the compression results in the loss of some data that
is determined to be unimportant or unnecessary.
JPEG is highly flexible in that it allows you to make a
"quality" setting, which determines the amount of loss
that will occur and affects the size of the resulting
compressed file. The JPEG algorithm takes into
account the fact that the human eye is more
sensitive to changes in brightness than to number of
Rather than saving the color data from each pixel in
an image, it saves information on the rate of change
of color, or "frequency information."
An audio file format is a file format for storing audio
data on a computer system. There are many file
formats for storing audio files.
There are two categories of audio file formats:
lossless formats e.g.WAV, PCM
lossy format e.g. MP3, Windows Media Audio (WMA)
Lossy audio formats are based on human audio
system, which leave out sounds that human cannot
or can hardly hear e.g. MP3.
In lossless audio formats no data or quality is lost in
the compression - when uncompressed; the data will
be identical to the original. It will be best used to
keep the music's original quality.
Lossless compression of sound is not as widely used
as lossy compression can provide a much greater
data compression ratio, with nearly the same
MOV, AVI and WMV
Apple QuickTime (MOV)
QuickTime is the multi-platform industry-standard multimedia
architecture used by software tool vendors and content
creators to create and deliver synchronized graphics, sound,
video, text and music. Developed by Apple, it has become
one of the most widely used formats on the World Wide Web.
QuickTime movies can be compressed using software
packages such as Adobe Premiere of Media Cleaner Pro to
sizes that are feasible for use over the Internet. Most CD-ROMs
use QuickTime movies and there are several sites on the
Internet that make use of the format. The images are of higher
quality, but file sizes can be significantly larger than other video
MOV, AVI and WMV
Microsoft AVI Video (AVI)
AVI is a format for video files that offers minimal compression
ability and is available on the Windows platform only. It is widely
used on the World Wide Web.
Because AVI is not compressed with one specific codec,
rather it is a file that can be compressed by any one of
hundreds of codecs like DivX, MPEG-4v2, Indeo 3.2, Cinepak
to name a few, it makes the file hard to play.
In Windows it is rather easy to play an AVI file IF you have the
correct codec installed. There are a whole lot of Windows
applications available that can play AVI files like Windows
Media Player. Unfortunately if you do not have the codec
needed to play the file Windows Media Player will not be able
to play it.
MOV, AVI and WMV
Windows Media Video (WMV)
Windows Media Video (WMV) is a video
compression format developed by Microsoft. The first
version of the codec, WMV 7, was introduced in
1999. Originally, it was designed for Internet
streaming applications, as a competitor to
RealVideo. To date, its main competitors are MPEG-4
AVC, AVS, RealVideo, and MPEG-4 ASP. Software
that can play WMV files includes Windows Media
Player, RealPlayer, MPlayer, The KMPlayer, Media
Player Classic and VLC Media Player.