MATLAB: I have a binary image, how can I count the balck pixels as a group?

digital image processingfilterImage Processing Toolboximage segmentation

I process a rgb image to gray to binary and use filters to remove noise and get some specific black areas. Now I want to count the areas. How many are there? How can I do that? can anyone help me?

Best Answer

Add a white border around the entire image. Now use regionprops() and ask for EulerNumber

"Returns a scalar that specifies the number of objects in the region minus the number of holes in those objects. "

The number of objects in the region would be 1 (all of the white part together as you have no isolated white areas), so the number you get out would be negative; take 1 minus the number to get the number of black regions.

Or you could invert the binary matrix. After that there would be a number of different approaches, including, for example, asking regionprops for any simple statistic such as Area, and then just counting the number of outputs you get

NumberOfBlackAreas = length( regionprops( ~YourBinaryMatrix, 'Area' ) );

Related Solutions

MATLAB: Total area of a region of binary image

Huh? Of course you can use regionprops. No need to use bwboundaries() at all, unless you just want to show the outlines of the segmented areas in the overlay above your original gray scale or color image.

If you want the area of all the white pixels in your binary image you can do it two ways, with slightly different results because they use different calculation methods

pixelSum1 = bwarea(binaryImage);
pixelSum2 = sum(binaryImage(:));

If you want the area of each blob in the image individually, you can do it like this:

labeledImage = bwlabel(binaryImage);
measurements = regionprops(labeledImage, 'Area');
allAreas = [measurements.Area];  % List of all the blob areas.
totalAreaOfAllBlobs = sum(allAreas); % Will be the same as pixelSum2

MATLAB: How to get the edge of a pile of white dots

regionprops( double(BW), 'Area')

The purpose of the double() there is to prevent BW from being a logical matrix, because if BW is a logical matrix then regionprops() will automatically do an object labeling, whereas you just want the total (I guess?) Or if you want clusters to be analyzed then

regionprops( logical(BW), 'Area')

and that will return a structure array that you can later total the areas of.

Best Answer

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MATLAB: Total area of a region of binary image

MATLAB: How to get the edge of a pile of white dots

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