If you already have your image in a variable in your MATLAB script or function, then you don't need imread(). That is only for reading an image in from a disk file into an array in your program. Once you have that image variable, you can display it in a variety of ways, like image(), imshow(), imagesc() or the numbers via sprint() into a string that you display in a label, or you can put an array into a table uicontrol. Or you can use im2html(): http://www.mathworks.com/matlabcentral/fileexchange/32273-im2html-m if you want to display the RGB values in little squares of the same color.
