05-02-2013, 02:44 PM
DATA COMPRESSION
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Abstract
Data compression is the technique of converting an input data stream or the original data into another data stream which is shorter in length.
There are many known methods for data compression. They are based on different ideas and are suitable for different types of data. But they all have the same principle that they compress data by removing the redundancy in the original data.
Data compression can be looked up on as a change in representation from inefficient to efficient form.
INTRODUCTION
The main aim of the field of data compression is of course to develop methods for better and better compression.
Data compression has become so important that some researches have proposed the "simplicity and power theory".
PRINCIPLES OF D.C
There are many methods of data compression.They are all based on the same basic principle that they compress data by removing the redundancy from the original data in the source file.
“Assign short codes to common events and long codes to rare events".
LOSSY COMPRESSION
In lossy compression some information is lost during the processing, where the image data is stored into important and unimportant data. The system then discards the unimportant data
LOSSLESS COMPRESSION
In this type of compression no information is lost during the compression and the decompression process.
Here the reconstructed image is mathematically and visually identical to the original one. It achieves only about a 2:1 compression ratio.
This type of compression technique looks for patterns in strings of bits and then expresses them more concisely.
BASIC TECHNIQUES
These are the techniques, which have been used only in the past. The important basic techniques are run length encoding and move to front encoding.
STATISTICAL TECHNIQUES
They are based on the statistical model of the data. Under this statistical techniques there comes three important technique.
Shannon Fano coding
Huffman coding
Arithmetic coding
JPEG
JPEG method is an important method of data compression. It is a sophisticated lossy/lossless compression method for colour or gray scale still images
JPEG is a compression method, not a complete standard for image representation. This is why it does not specify image features such as pixel aspect ratio, color space, or interleaving of bitmap rows.
APPLICATIONS IN IMAGE COMPRESSION
Photographic digital images generate a lot of data taking up large amounts of storage space To rectify this problem image compression is used depending on the type of data, text, graphics, photographic or video. Image compression reduces image data by identifying patterns in the bit strings, describing pixel values then replacing them with a short code.
CONCLUSION
Data compression is still a developing field. It has become so popular that researches are going on in this field to improve the compression rate and speed. Modifying an algorithm by 1% will improve the right time by 10%.