File Compression Techniques

abcde…

abcde… {

n uses

nR bits

compress decompress

Why data compression?

To reduce memory storage requirements.

Faster technique ,so less transmission time and reducing bandwidth also.

It reduces consumption of expensive resources such as hard disk space.

How data compression is possible?

Compression is possible by removing usual redundancies or information that is often repeated.

By using various formats to store data.

By shrinking one or more files into a single file.

IMAGE FORMATS

JPEGJoint Photographic

Expert Group.Lossy compression for

photographic images.24 Bits/pixel.Degradation of quality.

BMP Bitmap File Format

for digital images.Support 24 bits/pixel

to store color information.

Device independent format.

GIFGraphic Interchange

Format.Supports 8 bits/pixel

for color storage.Lossy compression

when colors of image > 256

Lossless when colors < 256.

AUDIO FORMATS MP3Moving Picture Expert Group Format for

audio encoding.Lossy compression.Used on internet for downloading and

uploading.Quality of sound is still clear.Works by reducing certain parts of audio.

WAVWaveform Audio File

Format.Compatible for only

Microsoft and IBM O.S.

Quiet large files.Lossless

compression.

WMAWindows Media Audio

File Format by Microsoft.

Lossless compression.Competitor to MP3.Basically meant for

windows media player.

High compressing than Mp3.

VIDEO FORMATS FLVFlash Video File format.Compatible with media flash players.Better quality of video.File size is small.Users of this format are Hulu, Youtube,

Google video etc.

WMVWindows Media

Video Compression Format.

High definition video content.

Small in size.Used in emails also.

AVCHDAdvanced Video

Coding High definition.

Basically ,playstations and video games have this file formats.

Provides good resolution video.

RUN LENGTH ENCODING

This method reduces the consecutive occurrences of a given symbol.

Real life example is fax machine.

Shows only one copy of symbol along with the count.

DIFFERENTIAL PULSE CODE MODULATIONIn this methodFirst a reference symbol is placed.

Difference is placed between that symbol and reference symbol.

DICTIONARY BASED ENCODING

Lempel- Ziv (LZ) Compression Algorithm.

Dictionary of variable length strings is built.

Contain every string expected to occur in data.

AUDIO COMPRESSION

PREDICTIVE ENCODING- Differences between the samples are encoded.

Normally used for speech.

PERCEPTUAL ENCODING-Used to create cd quality audio.

Based on the science of psychoacoustics.