Issues with presetting an array from a previous matrix, possibly an issue with impixel.

I would like to write a program that would detect a square image in a video and would measure the RGB values in the square. This works if I read the values in the D matrix and set them for x and y (like example 1 below). But what I would like to do is make the code select them from the D matrix. However, when I try to do this (in example 2 below) I get a different result, even though the values are the same. Does anyone understand why using name values in an array has this effect? Could it be something to do with impixel?

 clear all

 A = mmreader('video2.avi');

 for t = 1:2;
     B = read(A, t);
     C = rgb2gray(B);       
     C = edge(C,'sobel');
     C = bwareaopen(C,1000); 
     C = imfill(C,'holes');                                                 
     C = bwlabel(C);                         
     C = regionprops(C,'BoundingBox');                                             
     C = struct2cell(C);
     C = cell2mat(C);
     C = uint16(C);

     if C > 0;
        D(:,t) = C;
        else    
        end

     for x = 137:584;                                            
         for y = 94:416;                                         

             E(:,x-136,y-93) = impixel(B,x,y);
        end
    end
end

What I would like to do is:

 clear all

 A = mmreader('video2.avi');

 for t = 1:2;
     B = read(A, t);
     C = rgb2gray(B);       
     C = edge(C,'sobel');
     C = bwareaopen(C,1000); 
     C = imfill(C,'holes');                                                 
     C = bwlabel(C);                         
     C = regionprops(C,'BoundingBox');                                             
     C = struct2cell(C);
     C = cell2mat(C);
     C = uint16(C);

     if C > 0;
        D(:,t) = C;
        else    
        end

     XMIN = C(1,t);            
     YMIN = C(2,t);
     XMAX = C(3,t)+XMIN;
     YMAX = C(4,t)+YMIN;

     for x = XMIN:XMAX;                                            
         for y = YMIN:YMAX;                                         

             E(:,x-136,y-93) = impixel(B,x,y);
        end
    end
end

I don't understand when XMIN, XMAX, YMIN and YMAX are the same as 137, 584, 94, 416 respectfully I get a different answer for the E matrix. Thanks

The output is as follows with the numbers:

 E ( : , 137:147 , 94 ) =

 45 .. .. .. 
 30 .. .. ..
 18 .. .. ..

and so on, compared with the NAMED variables:

 36 .. .. .. 
 26 .. .. ..
 14 .. .. ..

I don't get it, I've checked and rechecked everything and it should work.

Answer 1

[Walter Roberson]

Your line

E(:,x-136,y-93) = impixel(B,x,y);

needs to be adjusted as well, to

   E(:,x-XMIN+1,y-YMIN+1) = impixel(B,x,y);

[David]

Yes I was going to do this, but I'm already having an issue with the impixel output. So didn't change it just left it as 136 and 93 for now.