Provided by: libvolpack1-dev_1.0b3-10_amd64 
NAME
vpSetFilter - define a resampling filter
SYNOPSIS
#include <volpack.h>
vpResult
vpSetFilter(vpc, num_taps, num_phases, weights)
vpContext *vpc;
int num_taps, num_phases;
float *weights;
ARGUMENTS
vpc VolPack context from vpCreateContext.
num_taps
Number of filter taps.
num_phases
Number of filter phases.
weights
Array containing filter weights.
DESCRIPTION
vpSetFilter is used to specify a table of filter weights before resampling an array with vpResample. The
table can be used to specify an arbitrary separable space-invariant filter.
The vpc argument is a VolPack context for storing a description of the resampling filter. The volume
data and rendering parameters currently stored in the context are not affected by calls to vpSetFilter or
vpResample.
The num_taps argument specifies the number of filter taps. When an array is resampled, the number of
filter taps is equal to the number of input array elements that contribute to one element of the output
array. A filter weight is associated with each tap and determines the contribution of the corresponding
input array element to the output array element. Note that when upsampling the number of taps depends
only on the support of the filter kernel. When downsampling, the number of taps should also depend on
the scale factor (since the filter kernel must also be scaled).
The num_phases argument specifies the number of filter phases, which is equal to the number of times the
filter kernel is sampled. The more filter phases, the more accurate the filtering operation. However,
there is a point of diminishing returns where increasing the number of phases results in very little
increase in accuracy, and has the disadvantages of increased storage requirements and potentially poor
cache performance. To allow for an efficient implementation, num_phases must be a power of two.
The weights array contains the filter weights themselves. The array should have dimensions: float
weights[num_phases][num_taps]; Each element should normally be a number between 0.0 and 1.0 (negative
values are also possible but can lead to ringing), and for any particular phase the entries for all of
the taps should sum to 1.0 (or else ripple is introduced into constant regions of the filtered array).
The easiest way to initialize the weight table is to call one of the predefined routines described in the
vpBoxFilter(3) man page.
ERRORS
The normal return value is VP_OK. The following error return values are possible:
VPERROR_BAD_VALUE
Either num_taps is non-positive or num_phases is not a positive power of two.
SEE ALSO
VolPack(3), vpBoxFilter(3), vpResample(3)