How do I extract intensity values from a diffraction grating image in MATLAB?

[MRL]

Homework Statement

Hi. I'm attempting to find the fringe visibility of an interference pattern from a diffraction grating, using MATLAB. I have an image of this pattern, and have used the following code so far in MATLAB:

myimage = imread('IMG_0166.JPG')
image = rgb2gray(myimage);
imshow(image)

I'm struggling to find a way in which i can go about obtaining the intensity values from this image.

Homework Equations

The fringe visibility is given by:
Visibility = (Imax-Imin)/(Imax+Imin)

The Attempt at a Solution

Above.

Any help would be appreciated,

Thanks.

 

[MRL]

Is anyone able to help please?