Formation of Clusters in MATLAB

I am working on a switching bilateral filter.. In this, they have formed clusters of pixels to detect the edges in the image. They have used Sorted Quadrant Median Vector.

The code they have used for this purpose is

% Formation of clusters

   if((((m1 < avg) && (m4 < avg))&&((m2 >= avg) && (m3 >= avg))) || (((m2 < avg) && (m3 < avg))&&((m1 >= avg) && (m4 >= avg))))
       p=i+2;
       q=j+2;
       vec=[L(p-2,q) L(p-1,q) L(p+1,q) L(p+2,q)]; % Vertical edge
       dav=double(sum(vec)/4);
       %disp('vertical edge');

   elseif((((m3 < avg) && (m4 < avg))&&((m1 >= avg) && (m2 >= avg))) || (((m1 < avg) && (m2 < avg))&&((m3 >= avg) && (m4 >= avg))))
       p=i+2;
       q=j+2;
       vec=[L(p,q-2) L(p,q-1) L(p,q+1) L(p,q+2)]; % Horizontal edge
       dav=double(sum(vec)/4);
       %disp('horizontal edge');

   elseif((((m1 < avg) && (m3 < avg))&&((m2 >= avg) && (m4 >= avg))) || (((m2 < avg) && (m4 < avg))&&((m1 >= avg) && (m3 >= avg))))
       p=i+2;
       q=j+2;
       vec=[L(p-1,q+1) L(p-1,q-1) L(p+1,q-1) L(p+1,q+1)]; % Diagonal line
       dav=double(sum(vec)/4);
       %disp('diagonal line');

   end

m1,m2,m3 and m4 are the medians.. Please explain me what does these three lines do p=i+2; q=j+2; vec=[L(p-2,q) L(p-1,q) L(p+1,q) L(p+2,q)]; % Vertical edge

Please explain these and suggest me a book/guide related to image processing in MATLAB

Answer 1

[Image Analyst]

It looks like it takes an intensity profile of 4 pixels in length going diagonally.

A book is by Steve Eddins: http://imageprocessingplace.com/DIPUM-2E/dipum2e_main_page.htm

[Premnath]

Please explain in Detail

[Image Analyst]

L is a matrix. Look at this line:

vec=[L(p-1,q+1) L(p-1,q-1) L(p+1,q-1) L(p+1,q+1)]; % Diagonal line

the comment tells a lot. Also the fact that the row and column indexes have + and - 1 means that you're going around the pixel at (p,q). vec is essentially a list of 4 numbers extracted from L. I think you can figure it out if you study it. It's not rocket science.