Calculating the area of the black objects in mm2

Question

Mathew 2024-5-17

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https://ww2.mathworks.cn/matlabcentral/answers/2120006-calculating-the-area-of-the-black-objects-in-mm2

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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Answer 1

Ayush Modi 2024-5-17

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https://ww2.mathworks.cn/matlabcentral/answers/2120006-calculating-the-area-of-the-black-objects-in-mm2#answer_1459641

在 MATLAB Online 中打开

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

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Answer 2

Image Analyst 2024-5-17

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2120006-calculating-the-area-of-the-black-objects-in-mm2#answer_1459651

在 MATLAB Online 中打开

spatial_calibration_demo.m

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.