Why LOG filter is returning the black background image?

Question

I had taken co-relation of image with LOG filter via imfilter command.

z=imfilter(I,fspecial('log',11,1.5)); 
figure
imshow(z);

Image:

Answer 1

Converting the image to double (double precision) will resolve the issue because imread command took the image in default unit8 (unsigned int) format.

Answer 2

The problem you have is that you are not showing the result properly.

Your result is in range 0-31, but you need to convert it to 0-255 to plot it!

do

imshow(mat2gray(z))