How to calculate Area ??

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

[Walter Roberson]

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

[Mariam Sheha]

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

Answer 1

[the cyclist]

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

[Mariam Sheha]

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)

[Walter Roberson]

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 2

[Image Analyst]

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

area=BoundingBox(3)*BoundingBox(4);

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);

[Mariam Sheha]

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 :)

[Image Analyst]

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

[Mariam Sheha]

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

Answer 3

[Walter Roberson]

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

[Mariam Sheha]

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