Bounding box width and Y coordinate in image processing

Hi there can someone help with something...

I need to dete

ct the width of an object surrounded by a bounding box. I have the centroid for it and i need to calculate at first the distance between the centroid and the left side of the box(and put this in a variable); and then the width between the centroid and the right hand side of the box(a new variable). after that i can calculate the width of the whole object buy doing a sum between both variables. i need to do it this way - don't ask why cuz I don't know either. I have attached a photo maybe you will understand better

this is what i have so far in terms of coding

prop = regionprops(imgFill); 

hold on
for n=1:length(prop)
        rectangle('Position',prop(n).BoundingBox,'EdgeColor','b','LineWidth',2);
        x = prop(n).Centroid(1);
        y = prop(n).Centroid(2);
        plot(x,y);
end
hold off

Answer 1

[Image Analyst]

Try this:

props = regionprops(imgFill, 'Centroid', 'BoundingBox');
hold on
for k=1:length(props)
  thisCentroid = props(k).Centroid;
  thisBoundingBox = props(k).BoundingBox;
  rectangle('Position',props(k).BoundingBox,'EdgeColor','b','LineWidth',2);
  x = prop(k).Centroid(1);
  y = prop(k).Centroid(2);
  plot(x, y, 'r+', 'MarkerSize', 13, 'LineWidth', 2);
  % Find the left edge and right edge of the bounding box.
  leftColumn = thisBoundingBox(1) + 0.5;
  rightColumn = thisBoundingBox(1) - 0.5;
  % Find the distance of them to the centroid.
  leftDistance(k) = x - leftColumn
  rightDistance(k) = rightColumn - x
  % Plot a line between them
  line([leftColumn, rightColumn], [y, y], 'Color', 'g');
end
hold off

[Soul Keeper]

yes. that's perfect! thank you!

dare I ask if you know how can i find the distance between the top(or center) of the image and the centroid - more like the Y value

[Image Analyst]

The top is thisBoundingBox(2).

topRow = thisBoundingBox(2) + 0.5;
bottomRow = thisBoundingBox(2) - 0.5;

etc.

[Soul Keeper]

the output of the variable is actually the distance between the top and the top part of the bounding box. I've seen that Y variable returns the right coordinate. is it "safe" to use that one?

[Image Analyst]

How did you finish the code? How did you calculate topDistance(k) and bottomDistance(k)? I assumed you would follow the first chunk of code I gave you. It's perfectly analogous.

% Find the distance of them to the centroid.
topDistance(k) = y - topRow
bottomDistance(k) = bottomRow - y

Did you not realize that "etc." meant that and so you didn't do it? (I thought you would.) Or did you do something different?

[Soul Keeper]

sorry my bad this is what i did

          topDistance(k) = y - topRow;
          botDistance(k) = -(bottomRow - y);

          [max_num_top, max_idx_top]=max(topDistance(:)); 
          [max_num_bot, max_idx_bot]=max(botDistance(:)); 

          max_num_top
          max_num_bot

it gives me the right value. i've got confused with something - don't know what either :-/

[Soul Keeper]

anyway.. i wanted to say .. sir.. you are a star! thank you so much!