regionprops calculation

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Tulips
Tulips 2012-5-15
hi sir,this is my result of measuring bounding box,area and perimeter Bounding Box are: 30.50 30.50 422.00 412.00 Centroid are: 240.47 236.34 Area: 133907.00 Perimeter: 1567.80
As far as Im concerned, 422 is width,412 is height of bounding.then if I times for example 422*412 to find the area. It shud be 173864. then why the area above just only 133907? same to perimeter. actually to find perimeter, 2*width+2*height=1668. then why it's 1567 only!!!

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回答（2 个）

Walter Roberson
Walter Roberson 2012-5-15
Bounding Box gives the rectangle that includes all pixels. Area does not give the area of the rectangle, it gives the area of the item within the rectangle.
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Tulips
Tulips 2012-5-15
it means that my answer was correct!!thanks sir!
Walter Roberson
Walter Roberson 2012-5-15
I am not sure which part was your answer. Your point starting "As far as Im concerned" about what the area "should be", disagrees with the definition of "Area" used in MATLAB.

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Image Analyst
Image Analyst 2012-5-15
40 thousand pixels - that's a big difference. Sounds like your area doesn't take up the full area of the box, like a circle wouldn't take up the full area of its bounding box.
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Tulips
Tulips 2012-5-15
so my result is correct.becoz it's clearly said that area just cover the number of pixel in region not the bounding box area. thanks guys!
Image Analyst
Image Analyst 2012-5-15
Your result for the bounding box was correct. Your and regionprops()'s answers for the area are also correct because the blob you are getting the area of is smaller than the bounding box of the blob. Like I said, the area of a circle is smaller than the area of its bounding box. So everything agrees, as long as you understand what's going on.

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