Finding intensity of region inside a circle from image

Hi all, I have this image below of a circular bead (also attached):

I would like to calculate the average intensity of all pixels inside this circular bead, I have read things about regionprops but it unfortunately does not apply in my case as my bead isn't super bright at the centre. Any help would be greatly appreciated!

Answer 1

[DGM]

Something like this:

A = rgb2gray(imread('Bead_pic.png'));
mask = A<100;
mask = imfill(mask,'holes') & ~mask;

% show the thing for sake of clarity
imshow(uint8(double(A).*mask))

avggrayval = mean(A(mask))

avggrayval = 141.7906

[Manny Kins]

Many thanks for your help, this was very useful!