This document discusses image compression techniques. It explains that the goal of compression is to reduce the amount of data needed to represent a digital image by eliminating redundant information like coding, interpixel, and psychovisual redundancies. Compression can be lossy or lossless. Lossy methods allow for data loss but provide higher compression, while lossless preserves all image data. Common lossy techniques include JPEG, which uses discrete cosine transform and quantization, and lossless methods include run length and Huffman encoding.

1.  Refers to reducing the amount of data required to
represent a digital image.
Principle of compression:
reduce the redundant information, e.g.,
 coding redundancy
•
Coding redundancy is present when less than optimal code
words are used.
 interpixel redundancy
•
Interpixel redundancy results from correlations between
the pixels of an image.
 psychovisual redundancy
Psychovisual redundancy is due to data that is
ignored by the human visual system
(i.e. visually non essential information).

2. Principal objective: To minimize
the number of bits required to
represent an image.
*Intended to yield a compact
representation of an image.
*Reducing the image storage.
*Transmission requirements.

3. Image data compression methods
fall into two common categories:
*Lossy compression
*Lossless compression

4. * A lossy compression method is one where
compressing data and then decompressing it
retrieves data that may well be different from
the original, but is close enough to be useful
in some way.
* Used to compress multimedia data (audio,
video, still images), especially in applications
such as streaming media and internet
telephony.
 Provide higher levels of data reduction
 Result in a less than perfect reproduction
original image
of the

5. * Also called Information preserving
compression.
* Compress and decompress images without
losing information.

7. *Run length encoding
* Huffman encoding
* LZW coding
* Area coding

8. The RL code for a gray scale image is :{ Vi ,Ri}
Vi is the intensity of pixel and
Ri refers to the number of consecutive pixels
with the intensity Vi .

9. Examples
*Transformation coding
* Vector quantization
* Fractal coding
* Block Truncation Coding
* Subband coding

10. *In this coding scheme, transforms such as DFT
and
DCT are used to change the pixels in the original
image into frequency domain coefficients (called
transform coefficients).
*These coefficients have the energy compaction
property i.e. energy of the original data being
concentrated in only a few of the significant
transform coefficients. Only those few significant
coefficients are selected and the remaining are
discarded.

11. * Joint Photographic Experts Group created the
standard.
* Lossy Compression Technique based on use of
Discrete Cosine Transform (DCT)

12. Steps in JPEG Compression
*Divide Each plane into 8x8 size blocks.
*Compute DCT of each block
*Treat separately DC components of each
block.
*Apply Quantization to discard values
*Separately encode DC components
transmit data.
and

14. Results

15. *Broadcast TV via satellite.
* military communications via aircraft,
teleconferencing.
* computer communications etc.