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Published on Dec 12, 2016



Abstract

An image defined in the "real world" is considered to be a function of two real variables say x,y.Before going to processing an image, it is converted into a digital form. Digitization includes sampling of image and quantization of sampled values. After converting the image into bit information, processing is performed.

Description of Image Processing & Compression

This processing technique may be,

" Image enhancement
" Image reconstruction
" Image compression

Image enhancement refers to accentuation, or sharpening, of image features such as boundaries.
Image restoration is concerned with filtering the observed image to minimize the effect of degradations.
Image compression is concerned with minimizing the no of bits required to represent an image.

Text compression - CCITT GROUP3 & GROUP4
Still image compression - JPEG
Video image compression -MPEG

Modern digital technology has made it possible to manipulate multi-dimensional signals with systems that range from simple digital circuits to advanced parallel computers. The goal of this manipulation can be divided into three categories:

* Image Processing image in -> image out
* Image Analysis image in -> measurements out
* Image Understanding image in -> high-level description out
Image processing is referred to processing of a 2D picture by a computer.

Lossless compression

In this, data is not altered in process of compression or decompression. Decompression generates an exact replica of an original image. “Text compression” is a good example .spreadsheets, processor files usually contain repeated sequence of characters. By reducing repeated characters to count, we can reduce requirement of bits.
Grayscale&images contain repetitive information .this repetitive graphic images and sound allows replacement of bits by codes. In color images , adjacent pixels can have different color values. These images do not have sufficient repetitiveness to be compressed. In these cases, this technique is not applicable.

Motion compensation

It assumes current picture as the translation of some previous pictures. Motion compensation attempts to compensate for movement of objects in compression phase. To make it easier to compare frames, a frame is split into blocks, and blocks are encoded.

For each block in the frame to be encoded, best matching block in the reference frame is searched among the number of candidate blocks. For each block, motion vector is generated. This vector is viewed as an analytical indication of new location. In the frame being encoded from an existing block in the reference frame. This is an attempt to match up new location of a moved object. The process of matching up based on prediction or interpolation.

 

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