2. Table of contents
• What is data compression?
• The need of data compression.
• What factors lead to data compression?
• Methods of data compression.
3. What is data compression?
• Data compression is the process of encoding
data more efficiently to achieve a reduction
in file size.
• Data compression is a reduction in the
number of bits needed to represent data.
• Data compression is also called compaction.
• Data may be Text, Image, Audio and Video
4. The need of data compression
• Storage Space
– Less storage space as size of file get reduced.
• Transmission time
– Less time taken as smaller size file transferred
from source to destination.
• Transmission speed.
– Uploading and downloading of file take less
time due to smaller size.
5. What factors lead to data
compression?
Redundancy refers to the amount of wasted space consumed by
storage media to record picture information in a digital image.
Image compression is achieved by exploiting redundancies in
the image. These redundancies could be spatial, spectral, or
temporal redundancy.
Spatial redundancy: elements that are duplicated within a
structure, such as neighboring pixels in a still image.
Exploiting spatial redundancy is how compression is
performed.
Spectral redundancy is due to correlation between different color
planes.
6. What factors lead to data
compression?(Cont..)
• Temporal redundancy: pixels in two video
frames that have the same values in the
same location.
• Exploiting temporal redundancy is one of
the primary techniques in video
compression.
7. Methods of data compression.
• There are two kinds of compression: Lossless and
Lossy.
• Lossless:
– No Loss of Information
• When we encode/decode, we get back original data.
– Most widely used in text compression.
– Compression ratio is very less.(3:1)
• Compression ratio=uncompressed size(in bytes)/
compressed size(in bytes)
– E.g. Run-length coding, Huffman coding, Arithmetic
coding, Lempel-Zev-Welch(LZW)
8. Methods of data compression.
• Lossy
– Always loss of information.
• When we encode/decode, we get back an
approximation of the original data.
– Most widely used in Image, Audio and Video
compression.
– Compression ratio is very high.(10:1)
– E.g. JPEG(Joint photographic expert group):
compressed image
– MP3: compressed audio
– MPEG(Motion picture expert group): compressed
video
