pkfilter - program to filter raster images

Description

pkfilter  implements  spatial  and spectral filtering for raster data.  In the spatial domain (X, Y), the
       filter typically involves a rectangular convolution kernel (moving window).  To avoid image shifting, the
       size of the window should be odd (3, 5, 7, ...).  You can set the window sizes in X and Y directions sep‐
       arately with the options -dx and -dy.  A circular kernel (disc) is applied if option -circ  is  set.   An
       overview of the supported filters (option -f|--filter) is given below.  You can create customized filters
       by defining your own filter taps (multiplicative elements of the filter kernel) via an ascii file (option
       -tap).   In  the spectral/temporal domain (Z) you can filter multi-band raster inputs.  The kernel filter
       size can be set with the option -dz (use odd values only).

   FILTERSINSPATIAL(DX,DY)ANDSPECTRAL/TEMPORAL(DZ)DOMAIN
       The number of output bands equals number of input bands
       Filter                Description
       dilate                morphological dilation
       erode                 morphological erosion
       close                 morpholigical closing (dilate+erode)
       open                  morpholigical opening (erode+dilate)
       smoothnodata values   smooth nodata  values  (set  --nodata
                             option!)

       Example: "Smooth" (interpolate) nodata in spectral/temporal domain (-dz1), using a linear interpolation

       pkfilter-iinput.tif-osmoothed.tif-dz1-fsmoothnodata-interplinear

       Example: Filter input.tif in spatial domain with morphological dilation filter with kernel size 3x3.

       pkfilter-iinput.tif-odilated.tif-dx3-dy3-fdilate

       In  case  of  moving  window, the number of output bands equals number of input bands.  In case dz=1, the
       single output band is calculated as the result of the statistical function applied to all bands.
       Filter       Description
       nvalid       report number of valid  (not  nodata)
                    values in window
       median       perform  a  median  filter in spatial
                    (dx, dy)  or  spectral/temporal  (dz)
                    domain
       var          calculate variance in window
       min          calculate minimum in window
       max          calculate maximum in window
       sum          calculate sum in window
       mean         calculate mean in window
       stdev        calculate  standard deviation in win‐
                    dow
       savgolay     Savitzky-Golay filter (check examples
                    page!)
       percentile   calculate percentile value in window
       proportion   calculate proportion in window

       Example: Median filter in spatial domain

       pkfilter-iinput.tif-omedian.tif-dx3-dy3-fmedian

       Example: Calculate statistical variance in spectral/temporal domain (single output band)

       pkfilter-iinput.tif-ovar.tif-dz1-fvarWAVELETFILTERS
       The number of output bands equals number of input bands
       Filter    Description
       dwt       discrete wavelet transform
       dwti      discrete inverse wavelet transform
       dwt_cut   discrete wavelet + inverse transform,
                 using threshold option  to  cut  per‐
                 centile of coefficients

       Example: Calculate discrete wavelet in spatial domain

       pkfilter-ilena.tif-olena_dwt.tif-fdwt

       Example: Calculate discrete wavelet in spectral/temporal domain

       pkfilter-itimeseries.tif-odwt.tif-fdwt-dz1

       The number of output bands equals number of input bands
       Filter         Description
       dwt_cut_from   discrete wavelet + inverse transform,
                      setting  all  high  frequence coeffi‐
                      cients to zero (scale >= threshold)

       Example: Calculate low frequency time series based on discrete  wavelet  +  inverse  transform  in  spec‐
       tral/temporal domain, retaining only coefficients until scale 3.

       pkfilter-itimeseries.tif-olowfrequency.tif-fdwt_cut_from-dz1-t4FILTERSINSPATIALDOMAINONLY(DX,DY>1ANDODD).
       The number of output bands equals number of input bands.
       Filter                   Description
       mrf                      Markov random field
       ismin                    pixel is minimum?
       ismax                    pixel is maximum?
       shift                    perform a pixel shift in spatial win‐
                                dow
       scramble                 scramble pixels in a spatial window
       mode (majority voting)   perform   a   majority   voring  (set
                                --class option)
       sobelx                   horizontal edge detection
       sobely                   vertical edge detection
       sobelxy                  diagonal edge detection (NE-SW)
       sobelyx                  diagonal edge detection (NW-SE)
       countid                  count digital numbers in window
       order                    rank pixels in order
       density                  calculated the density
       homog                    central pixel must  be  identical  to
                                all other pixels within window
       heterog                  central  pixel must be different than
                                all other pixels within window
       sauvola                  Sauvola's thresholding method

       Example: Sobel edge detection in horizontal direction

       pkfilter-ilena.tif-osobelx.tif-fsolbelx-dx5-dy5

Example

Filteringinspatialdomain

Filter input.tif with morphological dilation filter. Use a circular kernel (instead of rectangular) of
size 3x3.

pkfilter-iinput.tif-ofilter.tif-dx3-dy3-fdilate-circ

Similar to previous example, but consider only values of 255 for filtering operation. Typical usage: di‐
late cloud values in input image that are flagged as 255

pkfilter-iinput.tif-ofilter.tif-dx3-dy3-class255-fdilate-circFilteringinspectral/temporaldomain

Calculate the median value for each pixel, calculated on a moving window of width 3 (-dz3) over all in‐
put bands. The output raster dataset will contain as many bands as the input raster dataset.

pkfilter-iinput.tif-ofilter_stdev.tif-dz3-fmedian

No moving window (-dz1). Calculate the standard deviation for each pixel, calculated on all input
bands. The output raster dataset will contain a single band only.

pkfilter-iinput.tif-ofilter_stdev.tif-dz1-fstdev

"Smooth" (interpolate) nodata in spectral/temporal domain (-dz 1), using a linear interpolation. The
following interpolation types are supported: akima (default), linear, polynomial, cspline, cspline_peri‐
odic, akima_periodic (please check gsl ⟨http://www.gnu.org/software/gsl/manual/html_node/
Interpolation-Types.html⟩ page for more information on the interpolation types).

pkfilter-iinput.tif-oinput_smoothed.tif-dz1-fsmoothnodata-interplinear

01 January 2025 pkfilter(1)

Name

       pkfilter - program to filter raster images

Options

-ifilename, --inputfilename
              input image

       -ofilename, --outputfilename
              output classification image

       -ffilter, --filterfilter
              filter function (nvalid, median, var, min, max, sum, mean, dilate, erode, close, open, homog (cen‐
              tral pixel must be identical to all other pixels within window), heterog (central  pixel  must  be
              different than all other pixels within window), sobelx (horizontal edge detection), sobely (verti‐
              cal  edge detection), sobelxy (diagonal edge detection NE-SW),sobelyx (diagonal edge detection NW-
              SE), density, countid, mode (majority voting, only for classes), smoothnodata (smooth nodata  val‐
              ues  only)  values,  ismin,  ismax,  order (rank pixels in order), stdev, mrf, dwt, dwti, dwt_cut,
              dwt_cut_from, scramble, shift, savgolay, percentile, proportion)

       -dxvalue, --dxvalue
              filter kernel size in x, use odd values only

       -dyvalue, --dyvalue
              filter kernel size in y, use odd values only

       -dzvalue, --dzvalue
              filter kernel size in z (band or spectral dimension), must be odd (example: 3).  Set dz>0  if  1-D
              filter must be used in band domain

       -nodatavalue, --nodatavalue
              nodata value(s) (used for smoothnodata filter)

       -vlevel, --verboselevel
              verbose mode if > 0

       Advanced options

       -circ, --circular
              circular disc kernel for dilation and erosion

       -rmethod, --resampling-methodmethod
              Resampling  method for shifting operation (near: nearest neighbour, bilinear: bi-linear interpola‐
              tion).

       -cooption, --cooption
              Creation option for output file.  Multiple options can be specified.

       -wttype, --wavelettype
              wavelet type: daubechies,daubechies_centered, haar, haar_centered, bspline, bspline_centered

       -wffamily, --wffamily
              wavelet family (vanishing moment, see  also  http://www.gnu.org/software/gsl/manual/html_node/DWT-
              Initialization.html)

       -classvalue, --classvalue
              class value(s) to use for density, erosion, dilation, openening and closing, thresholding

       -tthreshold, --thresholdthreshold
              threshold  value(s)  to  use  for  threshold  filter (one for each class), or threshold to cut for
              dwt_cut (use 0 to keep all) or dwt_cut_from, or sigma for shift

       -tapfilename, --tapfilename
              text file containing taps used for spatial filtering (from ul to lr).  Use dimX and dimY to speci‐
              fy tap dimensions in x and y.  Leave empty for not using taps

       -tapzvalue, --tapzvalue
              taps used for spectral filtering

       -padmethod, --padmethod
              Padding method for filtering (how to handle edge effects).  Choose between: symmetric,  replicate,
              circular, constant (pad with 0).

       -fwhmvalue, --fwhmvalue
              list of full width half to apply spectral filtering (-fwhmband1-fwhmband2 ...)

       -srffilename, --srffilename
              list of ASCII files containing spectral response functions (two columns: wavelength response)

       -wincol, --wavelengthIncol
              column number of input ASCII file containing wavelengths

       -woutvalue, --wavelengthOutvalue
              list of wavelengths in output spectrum (-woutband1-woutband2 ...)

       -downvalue, --downvalue
              down sampling factor.  Use value 1 for no downsampling).  Use value n>1 for downsampling (aggrega‐
              tion)

       -betafilename, --betafilename
              ASCII file with beta for each class transition in Markov Random Field

       -epsvalue, --epsvalue
              error marging for linear feature

       -l1, --l1
              obtain longest object length for linear feature

       -a1, --a1
              obtain angle found for longest object length for linear feature

       -a2, --a2
              obtain angle found for shortest object length for linear feature

       -interptype, --interptype
              type   of   interpolation   for   spectral  filtering  (see  http://www.gnu.org/software/gsl/manu‐
              al/html_node/Interpolation-Types.html)

       -ottype, --otypetype
              Data type for output image ({Byte / Int16 / UInt16 / UInt32 / Int32 / Float32 / Float64 / CInt16 /
              CInt32 / CFloat32 / CFloat64}).  Empty string: inherit type from input image

       -ofGDALformat, --oformatGDALformat
              Output image format (see also gdal_translate(1)).

       -ctfilename, --ctfilename
              color table (file with 5 columns: id R G B ALFA (0: transparent, 255: solid)).  Use none  to  omit
              color table

Synopsis

pkfilter-iinput-ooutput [-ffilter | -srffile [-srffile]...  | -fwhmvalue [-fwhmvalue]...  ]
                [options] [advancedoptions]