MATLAB Answers

Mariam Sheha

How to calculate Area ??

Asked by Mariam Sheha
on 13 Jun 2013

Hey every body....

I am asking "how can i compute area of the bounding box and convex hull where i had already get it's parameters?"

Thank you


When you say "already get it's parameters", could you be more specific about what information you already have?

FOR EXAMPLE: Bounding Box Parmeters for image: 113.5000 138.5000 407.0000 259.0000

3 Answers

Answer by the cyclist
on 13 Jun 2013
Edited by the cyclist
on 13 Jun 2013
 Accepted answer

If you have the vertices of the convex hull, use the polyarea() command.


thanx alot , but what if i have more than one vertices for that image

(convex hull i calculate: is for segmented image located at bounding box)

polyarea() with a single vertex would tell you that you had area 0. Area is not meaningful until you have at least three vertices. polyarea() is somethng you would apply to the array of vertices.

Answer by Image Analyst
on 13 Jun 2013

For the bounding boxes, you can simply multiply the last two numbers


Or you can ask regionprops to calculate the areas of the convex hulls. You just need to pass your binary image into bwconvhull() and then into regionprops

chulls = bwconvhull(binaryImage);
measurements = regionprops(chulls, 'Area', 'BoundingBox');
% Compute the areas of each convex hull:
allAreas = [measurements.Area];
% Compute the area of each bounding box.
boundingBoxes = [blobMeasurements.BoundingBox];
allBBAreas = boundingBoxes(3:4:end) .* boundingBoxes(4:4:end);


Thanx alot ; Rally your answer is very usefull.... only i wana to ask if you are sure that their is a command named: bwconvhull because it's undefined ?!!

Thank you :)

You must have a really old version - time to upgrade. It's been in there for a few years now.

o0o0ops ok, i thought that i am updated using Matlab 10, i will try to upgrade it... Thanks for the note :)

Answer by Walter Roberson
on 13 Jun 2013

Bounding boxes are usually represented as [x y height width] . In that representation, the area is the height multiplied by the width.

  1 Comment

Thanks alot, i get your point and i tried it manually and it works, so you mean their are no ready function for that..

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