fwind1() - Image Processing

fwind1 designs two-dimensional FIR filters
using the window method. fwind1 uses a one-dimensional
window specification to design a two-dimensional FIR filter based
on the desired frequency response Hd. fwind1 works
with one-dimensional windows only; use fwind2 to
work with two-dimensional windows. h = fwind1(Hd, win) designs
a two-dimensional FIR filter h with frequency response Hd.
(fwind1 returns h as a computational
molecule, which is the appropriate form to use with filter2.) fwind1 uses
the one-dimensional window win to form an approximately
circularly symmetric two-dimensional window using Huang's method.
You can specify win using windows from the Signal
Processing Toolbox software, such as boxcar, hamming, hanning, bartlett, blackman, kaiser,
or chebwin. If length(win) is n,
then h is n-by-n.Hd is a matrix containing the desired frequency
response sampled at equally spaced points between -1.0 and 1.0 (in
normalized frequency, where 1.0 corresponds to half the sampling frequency,
or π radians) along the x and y frequency
axes. For accurate results, use frequency points returned by freqspace to
create Hd. (See the entry for freqspace for
more information.)h = fwind1(Hd, win1, win2) uses
the two one-dimensional windows win1 and win2 to
create a separable two-dimensional window. If length(win1) is n and length(win2) is m,
then h is m-by-n.h = fwind1(f1, f2, Hd,...) lets
you specify the desired frequency response Hd at
arbitrary frequencies (f1 and f2)
along the x- and y-axes.
The frequency vectors f1 and f2 should
be in the range -1.0 to 1.0, where 1.0 corresponds to half the sampling
frequency, or π radians. The length of the windows controls
the size of the resulting filter, as above.

Syntax

h = fwind1(Hd, win)h = fwind1(Hd, win1, win2)h = fwind1(f1, f2, Hd,...)

Example

[f1,f2] = freqspace(21,'meshgrid');
Hd = ones(21); 
r = sqrt(f1.^2 + f2.^2);
Hd((r<0.1)|(r>0.5)) = 0;
colormap(jet(64))
mesh(f1,f2,Hd)

Output / Return Value

Limitations

Alternatives / See Also

Reference