Prayag - assuming that the user actually chooses a file via
image=uigetfile([folder '\' ext]) ;
then image (this is poorly named as it conflicts with a built-in MATLAB function of the same name) will just be the name of the file and not the image itself (and so is an invalid input for imshow). Instead consider the following
[filename, path] = uigetfile(fullfile(folder,ext)) ;
imageData = imread(fullfile(path, filename));
imshow(imageData);
