Why the imfilter give different result with textbook?

As the textbook say,this code ( gd=imfilter(f,w)) will give a result with blurry edge like follow

But actually I will get a result :

w=ones(31);
gd=imfilter(f,w);
imshow(gd)

This is original picture.Maybe I have missed something.

Answer 1

[Image Analyst]

Because you did not divide by 31^2 the image gets clipped to 256 instead of having much, much greater values. If you want to see it blurred, either convert to double (but the blurred image will be in a much brighter intensity range than the original), or divide your kernel by 31^2:

windowWidth = 31;
w = ones(windowWidth) / windowWidth ^ 2;
gd = imfilter(grayImage, w);

[Yode]

Oh god,the book fool me.Thank very very very very much...

[Walter Roberson]

Also notice that they used imshow(gd, []) but you used imshow(gd) without the []