Calculate mean of gray Value

Hello, In this picture I want to calculate mean of the circle. but when I use mean( ) it calculates all the pixels including the black ones, so the mean value decreases. Is there a way to calculate only the gray value?

Thank you in advance.

Answer 1

[DGM]

Something like this:

% mean of non-black regions
mean(mypicture(mypicture>0))

This assumes that the image background is actually zero; otherwise, you can test that it's above some threshold value

Answer 2

[Chad Greene]

Try this. Below I'm creating an example matrix M, and calculate the mean of only the values that exceed zero:

M = peaks(100); % example matrix
M(M<=0) = 0; 

figure
imagesc(M)
colormap(gray) 
colorbar

mask = M>0; % logical mask corresponding to all values greater than zero

figure
imagesc(mask)

mean(M(mask),'all') % mean of all values of M that exceed zero.

ans = 1.1528