Yes. Assuming you have a binary image mask with two regions in there, and a gray scale image "grayImage", do this:
props = regionprops(mask, grayImage, 'MeanIntensity');
allIntensities = [props.MeanIntensity]
To see the intensity as you mouse around over the image, right after you show it with imshow(), call impixelinfo.
imshow(grayImage);
hp = impixelinfo();
% To set location of the status bar
hp.Position = [0.2, 0.4, 0.03, 0.4]; % xLeft, yBottom, width, height, all normalized 0-1.
