matrix, window finding median....

Hi,

I need to make a progrqam for the following logic:

1. Consider a matrix of size 120x120. Now consider a section of 3x3 and find the median of the 3x3 section, replacing the values of the matrix to make a new matrix (of a smaller size). The new 3x3 section will be taking the next element as the central element.

2. Please see that there is a command in MATLAB, called medfilt, medfilt2, which does the same, but I need to develop a program which does this manually i.e. it first sorts our the elements in ascending or descending order and then selects the middle value as the median thereby forming a new matrix with the median values.

The program that I am building is more complex than the section which I need help on. Any help in deleveloping this program will be highly appreciated.

 Thanks and Regards

 Manpreet Kaur

[Paulo Silva]

What have you done so far?

[Walter Roberson]

Please do not start a new question that is the same as one you already have active. http://www.mathworks.com/matlabcentral/answers/5656-program-to-find-the-median-of-the-matrix-need-to-use-for-loop

[Manpreet Kapoor]

I wouldn't have if I got the answer, Sorry for inconvenience.

[Walter Roberson]

duplicates http://www.mathworks.com/matlabcentral/answers/5656-program-to-find-the-median-of-the-matrix-need-to-use-for-loop

Answer 1

[Sean de Wolski]

doc blkproc
doc blockproc

[Manpreet Kapoor]

hi,

Actually I am new to MATLAB and I have already gone through this command. But I am unable to develop a program to achieve the sorting and finding median of the window elements.

I need step by step guidance to develop the above logic.

Please help.

Thanks and Regards

Manpreet Kaur

Answer 2

[Sean de Wolski]

Well what are the steps? First you have to sort:

doc sort

then you have to extract the middle value

xmiddle = x(floor(numel(x)/2))

If you can't figure it out from here; ask your professor because they're either failing to teach you properly, or you're sleeping during class.

[Manpreet Kapoor]

Well, its none of the case dear... I am planning for a doctrate degree in Image Processing and have recently thought of working in MATLAB. I need help in learning the language coz I am planning to code a paper to get it published. I need help in coding the simple program rest I can manage.

Thanks and Regards

Manpreet Kaur

[Manpreet Kapoor]

BY the way, I need to ask one more thing, The command u gave does not select 2 values if the sequence is of even numbers. I actually need the program to find the median of the elements in the window.

Thanks and Regards

Manpreet Kaur

[Sean de Wolski]

How are you going to replace one value with two median values in the even that it's even? Also, how can you have an even number of elements in a square window (i.e. a window with even sides centered on one pixel) It will always be odd (one per side=> 3*3=9; two per side => 5*5 = 25 etc.)

PS. A kind word of advice for learning MATLAB is to learn to use the built-in/stock functions and to read/understand the documentation related to them. This will get you much further and save time as there is no reason to reinvent the wheel.

Answer 3

[Andrei Bobrov]

variant (as in medfilt2)

x = randi(125,3);% input array

x = sort(x(:));
I = numel(x)/2;
if rem(I,1), y = x(ceil(I));
else y = sum(x(floor(I)+ [0 1]))/2; end