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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.