#!F-adobe-helvetica-medium-r-normal--18*
#!N
#!N #!Rfilter Filter #!N #!N Category #!N
#!N #!Lcattrn,dxall763 h Transformation #!EL #!N #!N Function #!N #!N Filters a field. #!N
#!N Syntax #!CForestGreen #!N #!N #!F-adobe-courier-bold-r-normal--18* #!N #!F-adobe-times-bold-r-normal--18* output #!EF =
Filter( #!F-adobe-times-bold-r-normal--18* input, filter, component, mask #!EF ); #!EF #!N #!N
#!EC #!N #!N Inputs #!N #!N #!T,1,91,276,461,646 #!F-adobe-times-medium-r-normal--14* #!F-adobe-times-bold-r-normal--18* #!N TAB
Name TAB Type TAB Default TAB Description #!EF #!N TAB input
TAB field TAB none TAB data to be filtered #!N TAB
filter TAB value or string TAB "gaussian" TAB filter to be
used #!N TAB component TAB string TAB "data" TAB component to
be operated on #!N TAB mask TAB value or string TAB
"box" TAB rank-value filter mask #!N TAB - TAB - TAB
- TAB #!EF #!N #!N Outputs #!N #!N #!T,1,161,321,646 #!F-adobe-times-medium-r-normal--14* #!F-adobe-times-bold-r-normal--18*
#!N TAB Name TAB Type TAB Description #!EF #!N TAB output
TAB field TAB filtered data #!N TAB - TAB - TAB
#!EF #!N #!N Functional Details #!N #!N The specified filter can
be convolution or rank-value type. #!N #!N Convolution filters, as the
name implies, perform a convolution of the filter coefficients with the
input data (i.e., the output value at a given point is
the sum of the product of the filter coefficients and the
corresponding values neighboring the point in question). #!N #!N Rank-value filters
sort all of the elements under a mask surrounding the point
in question and either select or interpolate the value specified by
the given rank. For "min," "max," and "median" (special cases of
rank-value filters), the rank values are respectively #!F-adobe-times-medium-i-normal--18* 1 #!EF ,
#!F-adobe-times-medium-i-normal--18* n #!EF , and ( #!F-adobe-times-medium-i-normal--18* n #!EF + #!F-adobe-times-medium-i-normal--18*
1 #!EF )/2, where #!F-adobe-times-medium-i-normal--18* n #!EF is the number of
nonzero elements in the mask. #!N #!N Convolution filters are useful
for neighborhood smoothing, edge detection, and other gradient-based operations. Rank-value filters
are useful for random-noise removal and morphological operations. #!N #!I0 #!N
#!N #!I0 #!N #!F-adobe-times-bold-r-normal--18* #!F-adobe-times-bold-r-normal--18* input #!EF #!EF #!I50 #!N is
the object to be filtered. Each field containing the component to
be filtered must also contain both a "positions" and a "connections"
component. The "connections" component must be regular. #!N #!I0 #!N #!F-adobe-times-bold-r-normal--18*
#!F-adobe-times-bold-r-normal--18* filter #!EF #!EF #!I50 #!N specifies, by name, the filter
to be used on #!F-adobe-times-bold-r-normal--18* input #!EF . See #!Lfilttab15,dxall849 t Table 15 #!EL for
valid names. #!N #!I0 #!N #!F-adobe-times-bold-r-normal--18* #!F-adobe-times-bold-r-normal--18* component #!EF #!EF #!I50
#!N specifies the field component to be filtered. By default, Filter
operates on "data." To filter an image, this parameter should specify
"colors." #!N #!N If the component to be filtered contains several
channels (e.g., red, green, and blue in an image), each channel
is filtered independently. #!I0 #!N #!N #!N #!N #!Lfilttab15,dxall849 t Table 15 #!EL defines the
filters and masks that can be specified by name. While most
of these are 2-dimensional, some are also available in 1- and
3-dimensional versions (as indicated by "1d" or "3d" after their names).
If possible, the module selects a filter that matches the dimensionality
of #!F-adobe-times-bold-r-normal--18* input #!EF . However, if a filter of lower
dimensionality is available, it can (and must) be specified by appending
"1d" or "2d" to the name. That is, to specify a
filter of lower dimensionality, the specification must be explicit. #!Rfilttab15 #!T,1,216,646
#!F-adobe-times-bold-r-normal--18* #!N TAB Table 15. Filter Names. The names listed here
are all valid specifications for the filter parameter. The specification is
#!N TAB not case sensitive. #!N TAB Filter Name TAB Description
#!EF #!N TAB 4-connected TAB #!N TAB 8-connected TAB #!N TAB
6-connected TAB 3-D analog of 4-connected #!N TAB 26-connected TAB 3-D
analog of 8-connected #!N TAB box TAB Box filter #!N TAB
box:1d TAB #!N TAB box:2d TAB #!N TAB box:3d TAB #!N
TAB compass:e TAB #!N TAB compass:n TAB #!N TAB compass:ne TAB
#!N TAB compass:nw TAB #!N TAB compass:s TAB #!N TAB compass:se
TAB #!N TAB compass:sw TAB #!N TAB compass:w TAB #!N TAB
gaussian TAB Same as gaussian:3x3 #!N TAB gaussian:2d TAB Same as
gaussian:3x3; can be used to force a 2-D gaussian to be
applied to 3-D #!N TAB - TAB data. #!N TAB gaussian:3x3
TAB 3 * 3 Gaussian, ^ = 1.0 #!N TAB gaussian:5x5
TAB 5 * 5 Gaussian, ^ = 1.0 #!N TAB gaussian:7x7
TAB 7 * 7 Gaussian, ^ = 1.0 #!N TAB isotropic
TAB #!N TAB kirsch TAB #!N TAB laplacian TAB Same as
laplacian:2d #!N TAB laplacian:1d TAB #!N TAB laplacian:2d TAB #!N TAB
laplacian:3d TAB #!N TAB line:e-w TAB #!N TAB line:n-s TAB #!N
TAB line:ne-sw TAB #!N TAB line:nw-se TAB #!N TAB prewitt TAB
#!N TAB roberts TAB #!N TAB smoothed TAB Same as prewitt
#!N TAB sobel TAB #!N #!N #!I0 #!N Notes: #!N #!I30
#!N 1. When a lower-dimensional filter is applied to higher-dimensional input,
the input is separated into lower-dimensional units that are filtered and
then reassembled into a higher-dimensional structure. For example, a 2-dimensional filter
applied to a 3-dimensional field will result in individual slices of
the input being filtered and then restacked. #!N #!I30 #!N 2.
Arbitrary filter kernels and masks may also be specified as matrices.
#!N #!I30 #!N 3. If the value specified by #!F-adobe-times-bold-r-normal--18* filter
#!EF is a matrix, the module performs convolution filtering and uses
the values given as the filter coefficients. Filters must have odd
dimensions (e.g., 5 * 5), since the active point is defined
as the central point in the filter. #!N #!I30 #!N 4.
If the value specified in #!F-adobe-times-bold-r-normal--18* filter #!EF is a scalar
or one of the strings "min," "median," or "max," the module
performs rank-value filtering and uses the value of #!F-adobe-times-bold-r-normal--18* mask #!EF
for sorting the elements. #!N #!N Masks, like filters, must have
odd dimensions (e.g., 5 * 5). When specifying a mask, remember
that nonzero elements in the mask matrix signify inclusion; zeros signify
exclusion. In this way, the built-in matrices (e.g., "box") can be
used interchangeably as filters or masks. #!N #!I30 #!N 5. Data
along the boundary are replicated to fill the overlap region for
the filter. #!I0 #!N #!N #!N #!N Components #!N #!N Modifies
the component specified by #!F-adobe-times-bold-r-normal--18* component #!EF . All other input
components are propagated to the output. #!N #!N Example Visual Program
#!CForestGreen #!N #!N #!F-adobe-courier-bold-r-normal--18* #!N UsingFilter.net #!EF #!N #!N #!EC #!N
#!N See Also #!N #!N #!Lcompute,dxall795 h Compute #!EL , #!Lmorph,dxall896 h Morph #!EL #!N #!N #!N
#!F-adobe-times-medium-i-normal--18* Next Topic #!EF #!N #!N #!Lofirst,dxall850 h First #!EL #!N #!F-adobe-times-medium-i-normal--18* #!N