Try using the interactive tool 'improfile'
% Import image
I = imread("rods1.png");
% Show image and use improfile to draw a line
figure
imshow(I)
[x,y,val] = improfile;
% Plot intensity values along line
figure
plot(val)
xlabel('Distance along line')
ylabel('Intensity')
Alternativley simply plot the value along a particular row
I = imread("rods1.png");
figure
plot(I(256,:)) % the image is 512 rows so this is halfway down the image
