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Lab of COMP 319

Lab tutor : Yao Zhang, Shenghua ZHONGEmail: zsh696@gmail.com

csshzhong@comp.polyu.edu.hk

Lab 4: Nov 30, 2011

Final Project: Image Compression with MATLAB

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Outline of Lab 4

Some important reminders of final project

Some important steps and information of final project

How to debug the user defined function

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Important reminders of final project

1. Deadline: Mon Dec. 15 at 23:59pm .

Penalty for late submission

Tue. Dec. 16       00:00 - 23:59          25% deductionWed. Dec. 17     00:00 - 23:59           50% deductionThu. Dec. 18       00:00 - 23:59          75% deductionAfter Dec. 18 23:59                       Zero point

• Please try your best to finish the project and submit it on time !

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Important reminders of final project

2. There are only two functions should be and can be modified and submitted: Compress.m and Decompress.m.

• There is no need to submit a final project report.

• your personal compress.m and decompress.m functions will be scored by using the uniform main.m function, so submission of other functions or files is useless and unallowed.

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Important reminders of final project

3. You can observe the MSE value and the compression ratio to check the performance of your functions.

• The MSE value and compression ratio will be given above your recovered image, you can check them according to the grading sample listed on the course’s webpage.

• The compression ratio should larger than 1, otherwise the score of your final project will be zero!

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Important reminders of final project

4. The components in the matrixes orig_image, comp_image and reco_image should be the integers.

• The size of the reco_image should be same with the size of orig_image.

• Don't make any modification of the provided functions expect  Compress.m  and  Decompress.m.

• Don't read the image file when you modify Compress.m  and  Decompress.m, otherwise, you will get zero point in the final project.

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How to Debug User-Defined Function

• User-defined functions are stored as M-files. Each must start with a function definition line that contains the word “function”, one or several variables that defines the function output, a function name, and one or several variables used for the input argument. Save the function as M-file using the same name in your function

• Some examples: • function output = my_function(x) • function [output1, output2] = my_function(x1,x2,x3)

• Hints: The function name and the names of the input and output variables are arbitrary and selected by the programmer, but the word “function” can not be changed.

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Review of Lab 2 about User-Defined Function

function output = poly(x)% This function calculates the value of a third-order % polynomialoutput = 3*x.^3+5*x.^2-2*x+1

Save above commands into an M-file and then type the below commands in command window to observe the results: >> a=4; >> poly(a) >> b=1:5; >> poly(b)

comments

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How to Debug User-Defined Function

• Compress.m, Decompress.m, and xxx.m except main.m are both user-defined function.

• They like a black box (user only know the input and output parameters)

• Debug is important to check whether the programms are correct.

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The First Step to Debug User-Defined Function

Set breakpoint at the line of the Entry to the user-defined function in the main.m

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The Second Step to Debug User-Defined Function

Run main.m to the Entry

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The Third Step to Debug User-Defined Function

Click Step in button and go into the user-defined function