How to find the intersection of the diagonals of a bounding box?

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I need to find the intersection of the diagonals of the of the bounding box, i also need to find the co-ordinates of the same. This is the code I'm using. I need it find out the centre of the ROI, that being hand in my case.
clear all;
close all;
clc;
%intitial setup to acquire image
vid = videoinput('winvideo', 1, 'YUY2_640x480');
%set the FPT to infinity
set(vid, 'FramesPerTrigger', Inf);
%set colour space to RGB
set(vid, 'ReturnedColorspace', 'rgb');
%set frame grab interval as 5
vid.FrameGrabInterval = 5;
%start the acquisation
start(vid);
while(vid.FramesAcquired<=100);
%get the snapshot of the frame
data= getsnapshot(vid);
%subtract gray from individual component
diff_im = imsubtract(data(:,:,1), rgb2gray(data));
%median filtering, each pixel contains median value in the 3 by 3 nhbd
%around the corresponding pixel in the input
diff_im = medfilt2(diff_im, [3,3]);
%adjust image intensity values of colourmap
diff_im = imadjust(diff_im);
%compute global threshold level used to convert bin image
level = graythresh(diff_im);
%convert to binary image
bw = im2bw(diff_im,level);
%fill holes
bw5 = imfill (bw, 'holes');
%contains labels for the connected objects in BW
bw6 = bwlabel(bw5, 8);
%compute area centroid and boundingbox
stats = regionprops(bw6, ['basic']);
s = regionprops(bw6, 'centroid');
[N,M] = size(stats);
if (bw==0)
break;
else
tmp = stats(1);
for i = 2 : N
if stats(i).Area > tmp.Area
tmp = stats(i);
end
end
bb = tmp.BoundingBox;
bc = tmp.Centroid;
imshow(data)
hold on
rectangle('Position', bb, 'EdgeColor', 'r', 'LineWidth', 2)
for z= 1:numel(s)
plot(s(z).Centroid(1), s(z).Centroid(2), 'ro');
end
hold off
end
end
stop(vid);
flushdata(vid);

Answers (1)

Image Analyst
Image Analyst on 14 Jul 2014
Bounding boxes always always align with the image edges, so the center and where the diagonals intersect will always simply be the average of the x and y coordinates.
  3 Comments
Image Analyst
Image Analyst on 14 Jul 2014
xMiddle = (xLeft + xRight) / 2;
yMiddle = (yTop + yBottom) / 2;
xLeft, etc. are the bounding box coordinates, which may change at each frame but you're getting them from the .Boundingbox property of your regionprops() output.
DGM
DGM on 24 May 2023
If you're dealing with a boundingbox from regionprops or something:
S = regionprops(inpict,'boundingbox');
bbox = S.BoundingBox;
boxcenter = bbox(1:2) + bbox(3:4)/2 % [x y]

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