Initialize a filter weight table
#include <volpack.h>
\$1 vpBoxFilter(num_taps, num_phases, weights, weights_bytes)
int num_taps, num_phases; float *weights; int weights_bytes;
vpLinearFilter(num_taps, num_phases, weights, weights_bytes) int num_taps, num_phases; float *weights; int weights_bytes;
vpBicubicFilter(b_value, c_value, num_taps, num_phases, weights, weights_bytes) double b_value, c_value; int num_taps, num_phases; float *weights; int weights_bytes;
vpGaussianFilter(sigma, num_taps, num_phases, weights, weights_bytes) double sigma; int num_taps, num_phases; float *weights; int weights_bytes;
Number of filter taps.
Number of filter phases.
Array containing filter weights.
Size (in bytes) of array containing filter weights.
"B" parameter in the formula for a Mitchell bicubic.
"C" parameter in the formula for a Mitchell bicubic.
Standard deviation for a Gaussian.
These routines can be used to initialize filter weight tables for use with vpSetFilter and vpResample. See the vpSetFilter man page for information on the num_taps and num_phases arguments.
vpBoxFilter creates a filter table for a box filter (a zero-order filter). With num_taps equal to 1 the filter is a nearest-neighbor filter, suitable for low-quality upsampling. To create a decimation filter that averages down, the number of taps should equal the decimation factor (as nearly as possible).
vpLinearFilter creates a filter table for a linear filter (a first-order or tent filter). With num_taps equal to 2 the filter performs linear interpolation.
vpBicubicFilter creates a filter table for a Mitchell bicubic filter. The first two arguments can be used to modify the shape of the filter kernel. Some standard parameter values are:
Cubic B-spline.
Catmull-Rom spline.
With four filter taps the cubic B-spline filter is suitable for upsampling. For more details, see the following paper: Mitchell, D.P. and Netravali, A.N., "Reconstruction filters in computer graphics," Proc. SIGGRAPH '88 (Computer Graphics V22 N4), p. 221-8.
vpGaussianFilter creates a filter table for a gaussian filter. The first argument is the standard deviation of the gaussian.
The normal return value is VP_OK. The following error return values are possible:
The filter weight table size is invalid.
The number of phases is not a positive power of two.
VolPack(3), vpResample(3), vpSetFilter(3)