#!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
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