Trying to count the number of pixels in an image over a specific RBG value

I am trying to count the number of pixels in an image over a specific RBG value by going pixel by pixel and sorting the desired pixels in a varaibale (z). My goal is to then print the number of pixels in the image.

My main issue, however, seems to be that sorting all 1.92 million pixels in a JPG image is too much for my computer to handle.

I am wondering if there is a better way to do / think about his problem / something I'm missing that would make this code work.

function results = darkArea(im)
    im = rgb2gray(im);
    imstd = stdfilt(im,ones(27)); 
    z = zeros(1,numel(imstd));
    for i = 1:numel(imstd)
       if im(i) <= 90
           z(i) = [];
       end
       area = numel(z);
       
      results.area = area; 
    end

Answer 1

[Matt J]

results.area=nnz(imstd>90);

[Nicholas Arnold]

Thanks!

[Matt J]

You're welcome, but please Accept-click the answer to indicate that it did what you need.