Calculating the area of the black objects in mm2

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Mathew
Mathew 2024-5-17
回答： Image Analyst 2024-5-17
hi, i am struggling to find the area of whole black objects in the image down blown and i dont know how to convert this area from pixels to mm2

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回答（2 个）

Ayush Modi
Ayush Modi 2024-5-17
Hi Mathew,
You can calculate the area of all black objects using the function regionprops. Here is the sample code for your reference:
grayImage = rgb2gray(image); % Convert to grayscale if necessary
binaryImage = imbinarize(grayImage, 'adaptive'); % Convert to binary image
binaryImage = ~binaryImage; % Invert if necessary so objects of interest are white
cc = bwconncomp(binaryImage);
stats = regionprops(cc, 'Area');
allAreas = [stats.Area];
totalAreaInPixels = sum(allAreas);
Refer to the below Mathworks documentation for more information on regionprops function:
https://www.mathworks.com/help/images/ref/regionprops.html
To convert the area into mm2, you would need to know scale of the image (pixels/mm). See the below thread for more information:
https://www.mathworks.com/matlabcentral/answers/421059-find-area-of-the-object-in-mm-2-from-binary-image
Image Analyst
Image Analyst 2024-5-17
You need to know the length of your field of view or of some known thing in the image. See my attached spatial calibration demo.
To get a list of all the areas of the black blobs in your binary image, you can do
props = regionprops(~binaryImage, 'Area'); % Measure areas.
allAreas = [props.Area];
histogram(allAreas); % If you want to see a particle size distribution.

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