How to find the area of a segmented image in matlab?
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Ramanathan Anandarama Krishnan
le 17 Juil 2019
Commenté : Rik
le 11 Nov 2020
I need to find the total area of the segmented image(attached below) in Matlab. However i am not able to get that if i use regionprops('Area') command. It gives me total pixel size which is 2048*2048 but i need to find the area of only the segmented region(Black)? Please tell me how to do it.
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Rik
le 17 Juil 2019
Modifié(e) : Rik
le 17 Juil 2019
You can make use of the fact that true is stored as a 1. Make sure your object is the only one marked with true and then use this:
A=sum(IM, 'all');
If you're using on older release, use this instead:
A=sum(IM(:));
6 commentaires
Rik
le 18 Juil 2019
Just as a point of clarification: this code counts the number of nonzero pixels. If you input an RGB image, it will count each pixel 3 times. You need to convert it to black and white image where the white is the area you want to count. rgb2gray followed by a threshold should work best.
If you want to count the black pixels, you will have to invert the image, as Image Analyst suggested. (when you posted the question I either missed that you wanted the black area, or I misread, or you edited the question)
As for the conversion to real external units, you should try to get the dicom header. They will contain the needed information.
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Image Analyst
le 17 Juil 2019
You need to invert your image so that your black region of interest is white. Then call sum() to get the number of pixels:
numberOfBlackPixels = sum(~binaryImage(:));
Or you can get a different area from a different method using bwarea(), which takes into account the shape of the boundary to get like half pixels or whatever:
numberOfBlackPixels = bwarea(~binaryImage);
Or you can use regionprops():
props = regionprops(~binaryImage, 'area');
numberOfBlackPixels = props.Area;
3 commentaires
Image Analyst
le 18 Juil 2019
My answer is correct (Rik mistake was forgetting to invert the image, or else you said you wanted the black instead of the white after he answered) and the answer is in pixels. If you want to have the answer in cm or square cm you'll have to multiply by a factor, like
areaInCm = areaInPixels * cmPerPixel ^2;
See attached demo for a full example. If I helped you please Vote for or Accept the answer.
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