compare intensity values of a dicom image with png

Hi, I am trying to compare intensity values of a dicom image with png image.I am seing intensity values with help of data cursor .I downloded this dicom image from http://www.mathworks.com/matlabcentral/fileexchange/2762-dicom-example-files/all_files('brain_007.dcm'). It shows fraction values for png for ex .233 but integer values for dicom pixels for ex 340.Why is it so? I want to convert dicom image pixel intensities to fraction.How can I do that? Richa