Gamma ISP: Reference Manual

bpf

ANSI-C program: bpf.c

NAME

SYNOPSIS
bpf <data_in> <data_out> <width> <fc_x> <bw_x> <fc_y> <bw_y> [roff] [azoff] [nr] [naz] [data_type] [f_mode] [beta] [fir_len]

<data_in>	input data file (fcomplex, scomplex, float)
<data_out>	output data file (fcomplex, scomplex, float)
<width>	number of samples/line
<fc_x>	normalized x-coord. (across) filter center frequency (range: -0.5 --> 0.5)
<bw_x>	normalized x-coord. bandwidth (range: 0 --> 1.0)
<fc_y>	normalized y-coord. (down) filter center frequency (range: -0.5 --> 0.5)
<bw_y>	normalized y-coord. bandwidth (range: 0 --> 1.0)
[roff]	offset to starting range to filter (default: 0)
[azoff]	offset to starting azimuth to filter (default: 0))
[nr]	number of range pixels to filter (default - : width - roff)
[naz]	number of azimuth lines to filter (default - : nlines - azoff)
[data_type]	data type (default 0:fcomplex, 1:scomplex, 2:float)
[f_mode]	fill mode (default 0:force filtered value to 0.0 for input value 0.0, 1:no forcing)
[beta]	Kaiser window beta parameter (default - : 3.384)
[fir_len]	finite impulse reponse filter length (default - : 64)

EXAMPLE
bpf 04657_05158.flt 04657_05158.flt.lp 1000 0.0 0.2 0.0 0.5

bandpass filter 04657_05158.flt, output is in 04657_05158.flt.lp. There are 1000 samples/line. The filter center frequency in range and azimuth is 0.0 with bandwidths of .2 and .5 respectively. The filter is acting as low-pass filter because the center frequencies have been chosen to be 0.0.

DESCRIPTION

bpf is a program that implements a 2-D bandpass filter on an image. The filter is specified in terms of the normalized center frequencies and bandwidths in x (across the image) and y (down). A normalized frequency value of 1.0 is equivalent to the sampling frequency of the data. The filter passband is specified as a fraction of the sampling frequency in the range (0 --> 1.0). Hence a bandwidth of 0.5 reduces the output bandwidth to half of the sampling bandwidth.

Input data can be complex valued (fcomplex, scomplex) or real valued (float). The format of the output data is the same as for the input data. The user can optionally specify if the filtered output shall be forced to 0.0 at location with an input value of 0.0 (= NULL value).

Options for specifying the filter characteristics are the Kaiser window parameter beta and the number of samples in the filter response. The characteristics of bandpass filters designed using the window method are described in most digital signal processing texts, see for example: Digital Signal Processing by A. V. Oppenheim and R. W. Shafer, Prentice-Hall, 1989.

OPTIONS
User-defined filter parameters, region of the image to apply the filter, data type of input and output.

SEE ALSO
display.h,

DIAGNOSTICS
All messages are generally self-explanatory.

NOTES
None.