How to calculate the pixels occured by white color in binary image

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ABDUL WAHID MOHAMMED 2017-3-22

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https://ww2.mathworks.cn/matlabcentral/answers/331173-how-to-calculate-the-pixels-occured-by-white-color-in-binary-image

评论： Image Analyst 2020-9-19

After converting the image to binary image and my primary aim is count the area covered by the white color and the black color in the binary image. For Example, we have performed edge detection on the image and we got an output image in binary image. I want to calculate the area of the edge in the image which are in white.

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Image Analyst 2017-3-22

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/331173-how-to-calculate-the-pixels-occured-by-white-color-in-binary-image#answer_259769

在 MATLAB Online 中打开

To find the white and black pixels:

numWhitePixels = sum(binaryImage(:));
numBlackPixels = sum(~binaryImage(:));

To get the number of perimeter pixels of the white regions

perimImage = bwperim(binaryImage);
numPerimeterPixels = sum(perimImage(:));

An alternate way to get the area of the white is to use bwarea():

% A weighted sum of white pixels that depends on shape of perimeter.
area = bwarea(binaryImage);

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Asmalina Mohamed Saat 2020-9-19

okay..thanks

and if I want to calculate the area of white region can I use this coding area = bwarea(numwhitepixel);?? andwhat is the unit of that area?

Image Analyst 2020-9-19

在 MATLAB Online 中打开

spatial_calibration_demo.m

You use bwarea() on a binary image, not a scalar number that is the count of how many pixels there are.

% Method 1
area = nnz(binaryImage);
% Method 2
area = bwarea(binaryImage);

The units are pixels. It uses a different algorithm for computing area. See it's documentation. It's not simply a pixel count but weights the edge pixels according to the shape of the boundary locally.

If you want to report the area in real world units like square centimeters, you'll have to get a spatial calibration factor to convert linear pixels to cm, and areas to cm^2. See my attached spatial calibration demo.

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