pkfilter(1)

📦
version 2.6.7.6 · 6 versions
, in ubuntu questing

💖 NAME 💖

Okay bestie, meet pkfilter — it's literally the program to filter raster images. 👑

✨ SYNOPSIS ✨

Here's the vibe check on how you call it:

pkfilter -i input -o output [-f filter | -srf file [-srf file]...  |
         -fwhm value [-fwhm value]...  ] [options] [advanced options]

🌸 DESCRIPTION 🌸

Okay so bestie, 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 separately 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).

✨ FILTERS IN SPATIAL (DX, DY) AND SPECTRAL/TEMPORAL (DZ) DOMAIN ✨

The number of output bands equals number of input bands. slay ✨

  • dilate — morphological dilation
  • erode — morphological erosion
  • close — morpholigical closing (dilate+erode)
  • open — morpholigical opening (erode+dilate)
  • smoothnodata — smooth nodata values (set --nodata option!) 🫶

Example: "Smooth" (interpolate) nodata in spectral/temporal domain (-dz 1), using a linear interpolation

pkfilter -i input.tif -o smoothed.tif -dz 1 -f smoothnodata -interp linear

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

pkfilter -i input.tif -o dilated.tif -dx 3 -dy 3 -f dilate

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.

  • 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 window
  • 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 -i input.tif -o median.tif -dx 3 -dy 3 -f median

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

pkfilter -i input.tif -o var.tif -dz 1 -f var

🦋 WAVELET FILTERS 🦋

The number of output bands equals number of input bands. iconic 💅

  • dwt — discrete wavelet transform
  • dwti — discrete inverse wavelet transform
  • dwt_cut — discrete wavelet + inverse transform, using threshold option to cut percentile of coefficients

Example: Calculate discrete wavelet in spatial domain

pkfilter -i lena.tif -o lena_dwt.tif -f dwt

Example: Calculate discrete wavelet in spectral/temporal domain

pkfilter -i timeseries.tif -o dwt.tif -f dwt -dz 1

The number of output bands equals number of input bands. periodt ✨

  • dwt_cut_from — discrete wavelet + inverse transform, setting all high frequence coefficients to zero (scale >= threshold)

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

pkfilter -i timeseries.tif -o lowfrequency.tif -f dwt_cut_from -dz 1 -t 4

💅 FILTERS IN SPATIAL DOMAIN ONLY (DX, DY > 1 AND ODD). 💅

The number of output bands equals number of input bands. ate 💖

  • mrf — Markov random field
  • ismin — pixel is minimum?
  • ismax — pixel is maximum?
  • shift — perform a pixel shift in spatial window
  • 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 -i lena.tif -o sobelx.tif -f solbelx -dx 5 -dy 5

👑 OPTIONS 👑

  • -i filename, --input filename — input image
  • -o filename, --output filename — output classification image
  • -f filter, --filter filter — filter function (nvalid, median, var, min, max, sum, mean, dilate, erode, close, open, homog (central 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 (vertical 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 values only) values, ismin, ismax, order (rank pixels in order), stdev, mrf, dwt, dwti, dwt_cut, dwt_cut_from, scramble, shift, savgolay, percentile, proportion)
  • -dx value, --dx value — filter kernel size in x, use odd values only
  • -dy value, --dy value — filter kernel size in y, use odd values only
  • -dz value, --dz value — 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
  • -nodata value, --nodata value — nodata value(s) (used for smoothnodata filter)
  • -v level, --verbose level — verbose mode if > 0

🎀 Advanced options 🎀

  • -circ, --circular — circular disc kernel for dilation and erosion
  • -r method, --resampling-method method — Resampling method for shifting operation (near: nearest neighbour, bilinear: bi-linear interpolation).
  • -co option, --co option — Creation option for output file. Multiple options can be specified.
  • -wt type, --wavelet type — wavelet type: daubechies,daubechies_centered, haar, haar_centered, bspline, bspline_centered
  • -wf family, --wf family — wavelet family (vanishing moment, see also http://www.gnu.org/software/gsl/manual/html_node/DWT-Initialization.html)
  • -class value, --class value — class value(s) to use for density, erosion, dilation, openening and closing, thresholding
  • -t threshold, --threshold threshold — 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
  • -tap filename, --tap filename — text file containing taps used for spatial filtering (from ul to lr). Use dimX and dimY to specify tap dimensions in x and y. Leave empty for not using taps
  • -tapz value, --tapz value — taps used for spectral filtering
  • -pad method, --pad method — Padding method for filtering (how to handle edge effects). Choose between: symmetric, replicate, circular, constant (pad with 0).
  • -fwhm value, --fwhm value — list of full width half to apply spectral filtering (-fwhm band1 -fwhm band2 ...)
  • -srf filename, --srf filename — list of ASCII files containing spectral response functions (two columns: wavelength response)
  • -win col, --wavelengthIn col — column number of input ASCII file containing wavelengths
  • -wout value, --wavelengthOut value — list of wavelengths in output spectrum (-wout band1 -wout band2 ...)
  • -down value, --down value — down sampling factor. Use value 1 for no downsampling). Use value n>1 for downsampling (aggregation)
  • -beta filename, --beta filename — ASCII file with beta for each class transition in Markov Random Field
  • -eps value, --eps value — 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
  • -interp type, --interp type — type of interpolation for spectral filtering (see http://www.gnu.org/software/gsl/manual/html_node/Interpolation-Types.html)
  • -ot type, --otype type — Data type for output image ({Byte / Int16 / UInt16 / UInt32 / Int32 / Float32 / Float64 / CInt16 / CInt32 / CFloat32 / CFloat64}). Empty string: inherit type from input image
  • -of GDALformat, --oformat GDALformat — Output image format (see also gdal_translate(1)).
  • -ct filename, --ct filename — color table (file with 5 columns: id R G B ALFA (0: transparent, 255: solid)). Use none to omit color table

✨ EXAMPLE ✨

🌸 Filtering in spatial domain 🌸

Okay bestie, so say you wanna filter input.tif with a morphological dilation filter. But plot twist — you want a circular kernel instead of a rectangular one, and you want it to be size 3x3. Iconic.

pkfilter -i input.tif -o filter.tif -dx 3 -dy 3 -f dilate -circ

Same vibe as before, except this time we're only looking at values of 255 for the filtering operation. Typical usage: dilate cloud values in an input image that are flagged as 255. Very demure, very cloud-aware. ☁️

pkfilter -i input.tif -o filter.tif -dx 3 -dy 3 -class 255 -f dilate -circ

🦋 Filtering in spectral/temporal domain 🦋

Now we're in a whole different dimension (literally). Calculate the median value for each pixel, calculated on a moving window of width 3 (-dz 3) over all input bands. Heads up: the output raster dataset will contain as many bands as the input raster dataset. No shrinking, no surprises. 💅

pkfilter -i input.tif -o filter_stdev.tif -dz 3 -f median

No moving window (-dz 1)? Fine. Calculate the standard deviation for each pixel, calculated on all input bands. And because there's no window, the output raster dataset will contain a single band only. One band. That's it. Periodt.

pkfilter -i input.tif -o filter_stdev.tif -dz 1 -f stdev

"Smooth" (interpolate) nodata in spectral/temporal domain (-dz 1), using a linear interpolation. Here are the interpolation types that are supported, bestie — take notes 📝:

  • akima (this one's the default, no cap)
  • linear
  • polynomial
  • cspline
  • cspline_periodic
  • akima_periodic

Please check the gsl page http://www.gnu.org/software/gsl/manual/html_node/Interpolation-Types.html for more information on the interpolation types. 🧚

pkfilter -i input.tif -o input_smoothed.tif -dz 1 -f smoothnodata -interp linear
🫶 And that's a wrap on pkfilter(1), babes! This page is from 01 January 2025, and yeah — pkfilter(1) really said "new year, same filter." Go filter something gorgeous, you absolute icon. 👑💖
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