How to find the dark pixels in an image?
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Hello. I have a lot of images like this one:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/170275/image.bmp)
From the whole shrimp, I would like to determine the area of dark pixels as a percentage of the visible surface. Does anybody have an idea how to do that? My idea is to first define/find the desired color and then filter the image for that defined color.
Thanks Falamanki
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Bshara Murr
2017-11-28
I = imread('shrimp.bmp');
N = I(:,:,3)>100;
I(:,:,2) = I(:,:,2)>100;
Where the second line treats each color channel separately, 3 represents the blue color, you can use 1 and 2 for red and green the 100 is the threshold that you can change as you with, you can use < as well, this gives you a bw image of the desired channel. the third line returns an rgb image but with a certain color channel thresholded but it will alter your white background as well.
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Walter Roberson
2017-11-28
You could try rgb2gray, then imbinarize using some brightness level you consider to be "dark", and count the number of 0 in the result.
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