# Homework 8, ECE438, Fall 2011, Prof. Boutin

Due Wednesday November 30, 2011 (in class)

## Question

Consider the following FIR filter:

$h[m,n]: \begin{array}{cccc} & m=-1 & m=0 & m=1 \\ n=1&-\frac{1}{8} & \frac{1}{2} & -\frac{1}{8} \\ n=0&-\frac{1}{4} & 1 & -\frac{1}{4} \\ n=-1&-\frac{1}{8} & \frac{1}{2} & -\frac{1}{8} \end{array}$

a) Write a difference equation that can be used to implement this filter.

c) Compute the CSFT H(u,v) of this filter. Sketch the plot of H(u,0). Sketch the plot of H(0,v).

d) What is the output image when this filter is applied to the following image (using symmetric boundary conditions)?

$g[m,n]: \begin{array}{ccccccccccc} 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0\\ 0 & 0 & 0 & 0 & 0 & 1 & 0 & 0 & 0 & 0 & 0\\ 0 & 0 & 0 & 0 & 1 & 1 & 1 & 0 & 0 & 0 & 0\\ 0 & 0 & 0 & 1 & 1 & 1 & 1 & 1 & 0 & 0 & 0\\ 0 & 0 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 0 & 0\\ 0 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 0\\ 0 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 0\\ 0 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 0\\ 0 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 0\\ 0 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 0\\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0\\ \end{array}$

## Discussion

I wrote a Matlab program that can check your answers. You can take it as reference but don't copy the answer directly. -Bo

I am not sure if you noticed but your function returns a 13x12 matrix for fmn rather than an 11x11 matrix like the original image. Although if you remove the top and bottom rows and also the first column I agree with your answer for the final image.

You can just use the filter2 command for g[m,n] and h[m,n] to get the result. It uses symmetric boundaries.

-jesse

ECE462 Survivor

Seraj Dosenbach