Why not use uiputfile and imwrite()?
% Get the name of the file that the user wants to save.
startingFolder = userpath
defaultFileName = fullfile(startingFolder, '*.*');
[baseFileName, folder] = uiputfile(defaultFileName, 'Specify a file');
if baseFileName == 0
% User clicked the Cancel button.
return;
end
fullFileName = fullfile(folder, baseFileName)
imwrite(yourImageMatrix, fullFileName );