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“IMAGE COMPRESSION USING DISCRETE WAVELET TRANSFORM IN MATLAB” Aman Kr. Srivastava (0832831004) Rahul Singh (0832831033) Ritika Gupta (0832831037) Sejal Garg (0832831039) [ (EC) – IV year]


Overview What is image compression?? Why image compression?? Principle used. Block diagram. Introduction to MATLAB. Why MATLAB?? Image compression. Why wavelet based compression?? Wavelet Analysis. Brief intro to algorithm used. Functions used. Referances .

What is image compression?: 

What is image compression? Reduction of the amount of data removal of redundant data. Transforming a 2-D pixel array into a statistically uncorrelated data set. << Correlated image Un-correlated image>>

Why image compression?: 

Why image compression? Important in data storage and data transmission Examples: – Progressive transmission of images/videos – Video coding (HDTV, teleconferencing) – Digital libraries and image databases – Remote sensing – Medical imaging

Principle used.: 

Principle used. There are three techniques used in image compression. 1.Pixel Coding 2.Predictive Coding 3. Transform Coding.

Block Diagram.: 

Block Diagram.

Introduction to MATLAB.: 

Introduction to MATLAB. MATLAB® is a high-performance language for technical computing. It integrates computation, visualization, and programming in an easy-to-use environment MATLAB is the tool of choice for high-productivity research, development, and analysis. Toolboxes are available include signal processing, control systems , wavelets simulation , and many others.

The MATLAB System: 

The MATLAB System Development Environment. Mathematical Function Library. The Language. Graphics. Application Program Interface (API).

Images in MATLAB: 

Images in MATLAB

Co-ordinate System in MATLAB: 

Co-ordinate System in MATLAB For image measurement it has two co-ordinate system:- Pixel- the first component r (the row) increases downward, while the second component c (the column) increases to the right. Pixel coordinates are integer values and range between 1 and the length of the row or column. Spacial - Almost same but there is a little difference in orientation & alignment . This is because pixel is discrete & this one is continuous. Co-ordinate system in MATLAB>>

Why MATLAB??: 

Why MATLAB?? So simpler and efficient, in built function to handle text, image and audio text which is core part of our project. Simpler Graphical User Interface is available. Easy to Compile and Debugg . Provides user friendly interface.

Image Compression.: 

Image Compression. A digital image is a two dimensional signal. Images storage requirements are a function of dimensions and color depth. Consider an image of dimensions 512x512, with 8 bit color depth. The size of this image, in bits, would be equivalent to the color depth in bits multiplied by the image size: Size = 512x512x8=2079152 bits = 262144 bytes = 256 kilobytes

Image Compression(contd..): 

Image Compression(contd..) This is the storage requirement for an image of average size and few colors. A true color version of the same image would require 3 times as much space. Images used in photogrammetry routinely occupy more than 100 mega bytes of space. That need for some method of reducing the size of an image.

Different classes of compression techniques: 

Different classes of compression techniques 1)- Lossless vs. Lossy compression: In lossless compression schemes, the reconstructed image, after compression, is numerically identical to the original image. lossy schemes are capable of achieving much higher compression. Under normal viewing conditions, no visible loss is perceived (visually lossless).

Techniques (contd..): 

Techniques (contd..) 2)- Predictive vs. Transform coding: In predictive coding, information already sent or available is used to predict future values, and the difference is coded. Transform coding, on the other hand, first transforms the image from its spatial domain representation to a different type of representation using some well-known transform and then codes the transformed values (coefficients).

Why wavelet based compression??: 

Why wavelet based compression?? Wavelet-based coding is more robust under transmission and decoding errors, facilitates progressive transmission of images. multiresolution nature, especially suitable for applications where scalability and other aspects are important.

Wavelets Analysis.: 

Wavelets Analysis. The first recorded mention of what we now call as "wavelet analysis" seems to be in 1909, in a thesis by Alfred Haar Afterwards many scientists gave many explainations to the word “wavelet analysis”. Wavelet analysis consists of decomposing a signal or an image into a hierarchical set of approximations and details Wavelet analysis allows the use of long time intervals where we want more precise low-frequency information, and shorter regions where we want high-frequency information

What Can Wavelet Analysis Do??: 

What Can Wavelet Analysis Do?? One major advantage afforded by wavelets is the ability to perform local analysis -- that is, to analyze a localized area of a larger signal. Its clear from above fig. Wavelet analysis is capable of revealing aspects of data that other signal analysis techniques miss, aspects like trends, breakdown points, discontinuities in higher derivatives, and self-similarity.

Brief intro to ALGORITHM & Steps: 

Brief intro to ALGORITHM & Steps Given a signal s of length N, the DWT consists of log2N stages at most. The steps used will be. one dimensional DWT one dimensional IDWT two dimensional DWT two dimensional TDWT Several other steps are used.

Functions used.: 

Functions used. dwt - Single-level discrete 1-DWT Syntax [ cA,cD ] = dwt( X,'wname ') idwt - Single-level inverse discrete 1-DWT Syntax X = idwt ( cA,cD,'wname ') wavedec - Multilevel 1-D wavelet decomposition Syntax - [C,L] = wavedec ( X,N,'wname ') waverec - Multilevel 1-D wavelet reconstruction Syntax- X = waverec ( C,L,'wname ')

Functions used (contd..): 

Functions used (contd..) Several other function are : wdencmp De-noising or compression wavread - Read Microsoft WAVE (.wav) imread Read image from graphics file imwrite Write image to graphics file

Referances : 

Referances Our Faculty members. Friends . MATLAB algorithm books. From websites like.