How do I sharpen/refocus an image using only the fspecial and conv2 commands?

We are studying simple convolution in my class. So far we have convolved 2 signals and reduced noise from sine waves. Now we've an assignment to refocus an image.

This is my code so far:

x=imread('Sgrayblur.png');

h=

y=conv2(x,h);

subplot(1,2,1),imshow(x);

subplot(1,2,2),imshow(y);

What must I put after 'h='? Is it possible to use fspecial to sharpen without using imfilter or the like?

Answer 1

[Image Analyst]

You can use a Laplacian to get a high pass filter, then add it to the original image to sharpen the edges. Of course because convolution is a linear filter, you can simply add the kernels together and do a convolution once. So a 3 by 3 filter for a high boost filter would be:

kernel = [-1, -1, -1; -1, 17, -1; -1, -1, -1]/ 9;
sharpenedImage = conv2(double(grayImage), kernel, 'same');

You can use imfilter() instead of conv2() if you want.