how image sharpening is perform in matlab?

please suggest.

% Filter 1
kernel3 = [-1 -1 -1; -1 8 -1; -1 -1 -1]/3;
% Filter the image.  Need to cast to single so it can be floating point
% which allows the image to have negative values.
filteredImage = imfilter(single(im), kernel3);
filteredImage =im2double(filteredImage);
filteredImage =1.5 .*filteredImage;
figure(),imshow(filteredImage);
out1=imadd(im,filteredImage);
figure(), imshow(out1);
Z = imabsdiff(im,out1);
% figure(), 
imtool(Z);