MTA1 Experiment 1 Question 2a & 2b Solution

MTA1 Experiment 1 Question 2a & 2b Source Code

This few days I received some request.
Most of students couldn't solve the Exp1. 2a and 2b.
So, I will post up the source code for Experiment 1 Question 2a & 2b

Question 2a :
Convert the image ‘peppers.png’ into grayscale, and perform edge detection on the resulting gray image.


Source Code :

I = imread('peppers.png'); %read in an image

A = rgb2gray(I); %convert RGB to Gray format

CN = edge(A, 'canny'); %perform canny edge detection

figure, imshow(I);
figure, imshow(A);
figure, imshow(CN);


Note : This 2a used only canny is because you found that canny is the best edge detection operator for your image by result from Question 1.



Question 2b:
Perform edge detection on each of the three color bands of the image, followed by some fusion rule. Perform edge detection on each of the color bands of the ‘peppers.png’ image and combine the three edge images in order to get the final edge image.

What is the three color bands of the image ?
You are using true color image in this question, so the 3 bands would be RGB.


How to Separate the 3 color bands ?

Example :

R = (I(:,:,1));
G = (I(:,:,2));
B = (I(:,:,3));

Note : I is the read in image.
The 1 2 and 3 indicates the layer of the image.


How to perform edge detection on every layer (band) ?

As you saved each layer into R, G and B variable.
You just need to do edge detection on every R,G and B.

Example :

CN1 = edge(R, 'canny');
CN2 = edge(G, 'canny');
CN3 = edge(B, 'canny');


How to combine the 3 edge detected image into the final image ?

This part, you can use alot of operators.
such as : 'or' , 'and' , 'xor' , 'nand' and etc.


How to use the combination operator ?

Example for 'and' operator :

C = and(CN1,CN2);
D = and(C,CN3);


Example for 'or' operator :

C = or(CN1,CN2);
D = or(C,CN3);

Note : the operator can only have 2 arguments at a time.
So combining the CN1 and CN2 and store into C first, then combine C with CN3 and you will get the final solution and save it into variable D.


-End of Experiment1 2a 2b-

Hope this source code can help you out to continue the experiment
you can always drop me a comment or msg to complain or ask.
I wont be free for chatting through msn and ym because I got an exam on tuesday'night,
if you found any problem executing the code,
you can post in the comment part and i will try to solve for you later.

Copyrighted (c) 2007 , Law Ding Yong

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ECP3086 MTA1 Coding Tutorials

ECP3086 Multimedia Technology Application
MTA1 Lab Report Code Writing Tutorials

Note :
Okay, at first.
I will assume everyone done the Experiment 1 -Q1 & Q2 , Experiment 2 -Q1.
I will give hints on Exp.1 -Q3 and Exp.2 -Q2 & Q3

Experiment 1 Question 3 :

Part a :

How to write a function ?

Example :

function []=FileName(argument1,argument2,argument3...)

Write this at the top of your codes,
The FileName above is the filename.m you saved as your work.
The argument1,argument2,argument3.. in the bracket is the files, values, images and ect. that you wanted to read in when you execute the function. You can have only 1 argument or more, use the comma ',' to separate the argument(s).
The [] above means void. You can define any variable to replace [].


How to use the function ?

Type the filename('imagename.xxx') to execute the function in your Matlab main window.
note : the xxx is the image format. eg. bmp, jpg, tif..


Part b:

How to check the image format ?

Code that can be use :

isrgb --- return true if image is RGB true color format
isgray --- return true if image is Gray format
isind --- return true if image is Indexed format


How to perform all 3 format checking on the image ?

The C language if-else statement can be use in this part.

Example :

if isgray(image)
perform the particular edge detect process;
elseif isrgb(image)
perform the particular edge detect process;
elseif isind(image)
perform the particular edge detect process;
else
fprintf('\n Format Error ! \n')
end

Note : image is the variable that stored the read in image.


Part c :

Same as Q1 and Q2


Part d :

How to display 2 image in the same figure ?


Example :

subplot(1,2,1), imshow(image1);
subplot(1,2,2), imshow(image2);


-End of Experiment 1-


Experiment 2 Question 2 :

Part a :

How to perform the DCT and quantization on all the channels ?

At first, you the rgb2ycbcr function to convert the RGB image into YCbCr image.
Store the YCbCr image in any well defined variable. eg. image2
Define a variable to store the Luminance,Y layer.
Define a variable to store the Crominance,Cb layer.
Define a variable to store the Crominance,Cr layer.

Example :

image2 = rgb2ycbcr(image);

Y = image2(:,:,1);
Cb = image2(:,:,2);
Cr = image2(:,:,3);

After that, perform blkproc on every layer and you will get a new value for every layer.
Store every new layer you get with the same variable. eg. compressed.

Example :

compressed(:,:,1)
compressed(:,:,2)
compressed(:,:,3)

At last, you will need to convert 'compressed' back to RGB format by using ycbcr2rgb.
Note : The system will auto combine all the layer in the same variable.


Part b :

What is 4:2:0 chroma sub-sampling ?

It is mean by compressing the image by using the YCbCr layer.
Keep the resolution of the Luminance, Y layer.
Resize the resolution of the Crominance, Cb & Cr layer into 50% of the original size.
After resize, perform blkproc on every layer and store the new value of every value using the same variable. (same as part a)
Remember to resize the new crominance layers back to the original size before storing into the variable.
After all, convert the YCbCr format back to RGB format.


Example :

Y = A2(:,:,1);
CB = imresize(A2(:,:,2),0.5);
CR = imresize(A2(:,:,3),0.5);

E(:,:,1) = D(:,:,1);
E(:,:,2) = imresize(D,2);
E(:,:,3) = imresize(D,2);



Experiment 2 Question 3 :

The hardest part in this Question is to calculate the SNR.
In this part, I wont repeat how to write function, if-else statement and subplot function.
Please refer the previous examples.


What is SNR ?

In mathematical way, the SNR is defined as

10 Log ( Average value of Square of original signal / Mean Square Error )


What is Average value of Square of original signal ?

Lets say your signal is an image.
The image is stored in variable I.
Average value of Square of original image = mean of the image power of 2.

Example :

ASI = mean(I.^2);


Note :
ASI is the Average value of Square of original image.
I is the variable stored the image.


What is Mean Square Error (MSE) ?

MSE is mean of square of differences between original image and compressed image

Example :

diff = I - I2;
MSE = mean(diff.^2);


Note :
I is the original image.
I2 is the compressed image.
diff is the difference between I and I2.


Last,
You can use Log10 as log of base 10 in Matlab.
You may ask why power of 2 need to be written as '.^2' ?
The dot '.' in front of ^2 is a must.
Because Matlab doesn't recognize '^2'.
The standard function of power of 2 for Matlab is '.^2'


-End of MTA1 coding tutorial-

sorry for any grammar errors

(c) Copyrighted 2007, Law Ding Yong

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