rotate and crop image but get error (Subscript indices must either be real positive integers or logicals)

I'm crop the picture using this code

 v=~im2bw(img,0.7);
 [rows, columns] = find(v);
 row1 = min(rows);
 row2 = max(rows);
 col1 = min(columns);
 col2 = max(columns);
 cropped = img(row1:row2, col1:col2);
 figure, imshow(cropped);title('crop Image');
 [p3, p4] = size(cropped);
 pp=p4/4;   % finde quarter of image width 
 q1 = p4-pp; % size of the crop box
 i3_start = floor((p3-q1)/2); % or round instead of floor; using neither gives warning
 i3_stop = i3_start + q1;
 i4_start = floor((p4-q1)/2);
 i4_stop = i4_start + q1;
 I1 = cropped(i3_start:i3_stop, i4_start:i4_stop, :);
 figure ,imshow(I1);

and then I rotated the image and tried to crop it with the same code but I got this error

 Subscript indices must either be real positive integers or logicals.

 Error in Try (line 47)
 I1 = croppedImage(i3_start:i3_stop, i4_start:i4_stop, :);

Answer 1

[Geoff Hayes]

wisam - it could be that because you are using floor, then one of i3_start or i4_start are zero, since floor rounds toward negative infinity. As zero is not a positive integer, then the above error message makes sense. You may want to add a check to ensure that all four of your indices satisfy the real positive integers or logicals requirement before trying to use them.

[wisam kh]

Thank you, the problem was solved by a small change in the code.

[p3, p4] = size(croppedImage);

pp=p3/4; % finde quarter of image width

q1 = p3-pp; % size of the crop box

i3_start = floor((p3-q1)/2); % or round instead of floor; using neither gives warning

i3_stop = i3_start + q1;

i4_start = floor((p3-q1)/2);

i4_stop = i4_start + q1;

I1 = croppedImage(i3_start:i3_stop, i4_start:i4_stop, :);

figure ,imshow(I1);