How to count the black pixels in a segmented section of image?

I am using this code to show a segmented image using active contour method.

iteration=50;
img=im2bw(imageArray,threshlod_value);  %making it black&white
mask=roipoly(img);
bw=activecontour(img,mask,iteration,'Chan-Vese');
imshow(imageArray) 
hold on
visboundaries(bw,'Color','r');
hold off

And the output is this:

I want to calculate the black pixels within the segmented boundary after it is turned black and white. How do I do that?

Answer 1

[Rik]

activecontour returns a logical array. That means you can count the black pixels by inverting and using sum (or nnz).

[Tawsif Mostafiz]

@Rik can you pleae elaborate? How do I write it in code?

[Rik]

If you don't share the source image along with your code, why do you expect a turn-key solution?

Inverting a logical array is as simple as using the not operator on your variable. In Matlab you can either use the ~ or you can use the not function.

Counting the number of white pixels is a question of either counting the number of non-zero values (nnz), or using the implicit conversion of true to 1 and using sum.

sum(~bw,'all')

That's it.

If you want more explicit help, remember to share the source data.