Page 190 - DCAP303_MULTIMEDIA_SYSTEMS

Multimedia Systems

notes the ratio will be a value near 10. It reduces non-sensitive information to the human eyes and the
compressed media will not be the media that was available before compression.
Advantage: Can reduce the file size more than in the lossless compression.

Disadvantage: The original file cannot be taken after the decompression.
Mathematical and Wavelet transformation
In this process, images are converted to the mathematical functions. Discreet Cosine Transformation
uses series of cosine functions to approximate image. This technique is used with JPEG, MPEG1
and MPEG 2 formats. A wavelet function is used to approximate the image. This can be used
with the JPEG 2000 and MPEG 4 formats.
JpeG encoding
In this encoding, an image is represented by a two dimensional array of pixels. A Grayscale
picture of 307*200 pixels is represented by 2,457,600 bits and a colour picture is represented
by 7,372,800 bits. Due to the number of calculations to be had in a JPEG format of a grayscale
picture, it is divided into blocks of 8*8 pixels. The number of the units’ id equal to the number
of mathematical equations of each picture. The whole idea of JPEG is to change the picture into
a linear set of numbers that reveals the redundancies. In addition to those techniques, MPEG is
also a Lossy Compression technique. It is a way to encode the moving images and audio included
in it. It supports many video formats from mobile phone to HD TV.
H.261, H.263, H.264
The H.261 is designed for video telephony and video conferencing applications. It was developed
in 1988–1990. Data rate is a multiplication of a 64 kb/s. The H.263 is a video coding technique for
low bit rate communication. In addition, a 30% of bit saving can be done by this technique when
it is compared to the MPEG-1. The H.264 is a joint project of ITU-Ts Video Experts Group and
the ISO/IEC MPEG group. All those three methods use different methods of reducing redundant
data. There for the output differs from bit rate, quality and latency.

Compress an image using lossy compression technique.

self assessment
Choose the correct answer:

1. ………… is also a lossy compression technique.
( a) MPEG (b) JPEG

( c) H.264 (d) None of these
2. The H.261 is designed for video telephony and video conferencing applications which was
developed in…………….

( a) 1986–1988 (b) 1888–1890
( c) 1988–1990 (d) None of these
3. Various amounts of data may be used to represent the same amount of information.

( a) True (b) False
4. The DST stands for ……………
( a) Direct Stream Transfer (b) Direct Stress Transfer

( c) Digital Stream Transfer (d) None of these

184 LoveLy professionaL University