MAN page from Mandrake Other XITE-3.3-3.i386.rpm

XFILTER

Section: User Commands (1)
Updated: 16 Mar 1998
Index

 

NAME

xfilter - filter image and display power spectra

 

SYNTAX

xfilter [<option>...] <inimage>

 

DESCRIPTION

An image, the logarithm of a chosen filter's discreteFourier transform magnitude, the cross-section of the latterand the output (filtered) image are displayed. Refer to theoptions described below on how to display more of theimages involved in the filtering process.

The actual filtering is performed in the Fourier domain bymultiplication of the discrete Fourier transform of the inputimage by the discrete Fourier transform of the filter.(Actually, the FFT is not directly computed, rather theFast Hartley transform is used because it is more effectivethan the FFT. The results are the same as if the FFT had beenused, except for roundoff errors.)

The filter can be chosen from a menu. The initial filter canbe chosen with the option -ftype(see below).

There are two main classes of filters available. One classcontains realizable filters, the other contains non-realizablefilters (realizable in this context means that the filters canbe implemented in finite space).

The realizable filters are "lp", "hp", "bp" and "bs". Theseare all based on the ideal Fourier transform magnitudes of thecorresponding type. For these filters, the spatial domainfilter functions are known analytically and they have infiniteextent in the spatial domain. (They have been foundanalytically by inverse Fourier transformation of the idealFourier domain filter functions.) In this application thespatial domain filter functions are multiplied by2-dimensional window functions to make them realizable. Theresulting realizable Fourier transform magnitudes aredisplayed.

The non-relizable filters are "ilp", "blp" and "elp". "ilp"is made from the ideal Fourier transform magnitude. Insteadof using the analytically correct spatial domain filterfunction, "ilp" computes the spatial domain filter functionvia inverse FFT (not equal to the inverse Fourier transformon the continuous frequency domain). This sampling in thefrequency domain (from continuous frequency to discrete pointsin the FFT) results in aliasing in the spatial domain."blp" and "elp" have also been constructed from closed-formFourier domain filter functions. The spatial-domain functionshave been found with inverse FFT.

 

OPTIONS

-low cutoff

Lower cutoff frequency, normalized by the Nyquist frequency.This means that cutoffequal to 1.0 corresponds to half thesampling frequency. cutoffcan be adjusted with a sliderafter startup. Default: 0.2.

-high cutoff

Higher cutoff frequency (normalized by the Nyquist frequency).This can be adjusted with a slider after startup.Default: 0.5.

-ftype filter-type

Type of filter. Use one of the symbols

 Full name    Short name
 ------------------------
 lowpass         lp
 highpass        hp
 bandpass        bp
 bandstop        bs
 lowpass_ideal   ilp
 butterworth_lp  blp
 exponential_lp  elp

Default: lp.

-order filter-order

For the window-based filters, this is the filter size inpixels (diameter of window function). For the Butterworthand Exponential filters, filter-orderis the parameterin the formula. For the "ideal" filter, this option has nomeaning. It can be adjusted with a slider after startup.Default: 41.

-wtype window-type

Type of window function to multiply with filter in thespatial domain. Use one of the symbols

 Full name    Short name
 -----------------------
 rectangle        r
 bartlett         b
 triangle         t
 hamming          hm
 hanning          hn

Default: hm.

-scale scale

Use this scalewhen displaying Fourier transform magnitudes.Refer to fftDisplay(3)for a description of this parameter.Default: 10 (which will give the power spectra in dB).

-logmin min

Set all values smaller than minafter logarithmiccompression (for display of Fourier magnitudes) equal to min.Default: -4.0 * scale(from option -scale).

-cmin min

Clip cross-section display of filter spectrum at min.This can be adjusted with a slider after startup.Default: -80.

-cmax max

Clip cross-section display of filter spectrum at max.This can be adjusted with a slider after startup.Default: 10.

-cminmin min

Lowest possible value for the -cmin option. Default: -200.

-cmaxmax max

Largest possible value for the -cmax option. Default: 50.

-emin min

Smallest possible eps-value for logarithmic compressionof FFT magnitude. Default: 1.0e-20.

-emax max

Largest possible eps-value for logarithmic compressionof FFT magnitude. Default: 0.5.

-ilin

Use linear scrollbar for eps in logarithmic compression ofFFT magnitude of input. Default: Logarithmic scrollbar.

-flin

Use linear scrollbar for eps in logarithmic compression ofFFT magnitude of filter. Default: Logarithmic scrollbar.

-olin

Use linear scrollbar for eps in logarithmic compression ofFFT magnitude of output. Default: Logarithmic scrollbar.

-rms

Do not calculate and display the RMS difference betweeninput and output.

-wall

Show widgets for FFT(input), filter and FFT(output) inaddition to input, output, FFT(filter) and its cross-section.

-win

Do not show widget for input.

-wfin

Do not show widget for FFT(input).

-wfilt

Do not show widget for filter.

-wffilt

Do not show widget for FFT(filter).

-wout

Do not show widget for output. Also implies option -rms.

-wfout

Do not show widget for FFT(output).

-wcross

Do not show widget for cross-section of FFT(filter).

 

RESOURCES

In order to specify resources, it is useful to knowthe hierarchy of the widgets which compose xfilter.In the notation below, indentation indicates hierarchicalstructure.

The following hierarchy is constructed when the defaultresources/options for widget layout is used.

The widgets of class XfwfButton can be replaced by classCommand (from the Athena widget set) by using the ximage(3)option -widgetsetor corresponding application resource.

xfilter (class XFilter)

  popup                   (class TransientShell)
    dialog                (class Dialog)
      label               (class Label)
      command             (class Command)
  colorsmenu              (class SimpleMenu)
    menuLabel             (class SmeBSB)
    backgroundcol         (class SmeBSB)
    Work-map              (class SmeBSB)
    colorsep              (class SmeLine)
    White - 256           (class SmeBSB)
    Black - 256           (class SmeBSB)
    Red - 256             (class SmeBSB)
    Green - 256           (class SmeBSB)
    Blue - 256            (class SmeBSB)
    Spectrum - 256        (class SmeBSB)
    Hue - 256             (class SmeBSB)
    Rainbow - 256         (class SmeBSB)
  overlaysmenu            (class SimpleMenu)
    menuLabel             (class SmeBSB)
    backgroundovl         (class SmeBSB)
    Std-overlay           (class SmeBSB)
    colorsep              (class SmeLine)
    White - mono          (class SmeBSB)
    Black - mono          (class SmeBSB)
  optionsmenu             (class SimpleMenu)
    menuLabel             (class SmeBSB)
    optionsmenusep        (class SmeLine)
    optionsmenuentry      (class SmeBSB)
    optionsmenuentry      (class SmeBSB)
    optionsmenuentry      (class SmeBSB)
    optionsmenusep        (class SmeLine)
    optionsmenuentry      (class SmeBSB)
    optionsmenuentry      (class SmeBSB)
    optionsmenuentry      (class SmeBSB)
  toolsmenu               (class SimpleMenu)
    menuLabel             (class SmeBSB)
    imageinfo             (class SmeBSB)
    histogram             (class SmeBSB)
    slice                 (class SmeBSB)
  inimageShell            (class TopLevelShell)
    imageForm             (class ImageForm)
      menubar             (class XfwfMenuBar)
        colors            (class XfwfPullDown)
        tools             (class XfwfPullDown)
        options           (class XfwfPullDown)
      image               (class Image)
  xfilter control panel   (class TopLevelShell)
    topContainer          (class Form)
      Filter type         (class Label)
      Filter-menu         (class MenuButton)
        Filter-menu       (class SimpleMenu)
          lowpass         (class SmeBSB)
          highpass        (class SmeBSB)
          bandpass        (class SmeBSB)
          bandstop        (class SmeBSB)
          lowpass_ideal   (class SmeBSB)
          butterworth_lp  (class SmeBSB)
          exponential_lp  (class SmeBSB)
      Low cutoff          (class Label)
      lowPrompt           (class XfwfPrompt)
      lowScroll           (class Scrollbar)
      High cutoff         (class Label)
      highPrompt          (class XfwfPrompt)
      highScroll          (class Scrollbar)
      Filter order        (class Label)
      orderPrompt         (class XfwfPrompt)
      orderScroll         (class Scrollbar)
      Window type         (class Label)
      Window-menu         (class MenuButton)
        Window-menu       (class SimpleMenu)
          rectangle       (class SmeBSB)
          bartlett        (class SmeBSB)
          triangle        (class SmeBSB)
          hamming         (class SmeBSB)
          hanning         (class SmeBSB)
      rmsDiff             (class Label)
      fInimageEpsLabel    (class Label)
      fInimageEpsPrompt   (class XfwfPrompt)
      fInimageEpsScroll   (class Scrollbar)
      fFiltimageEpsLabel  (class Label)
      fFiltimageEpsPrompt (class XfwfPrompt)
      fFiltimageEpsScroll (class Scrollbar)
      fOutimageEpsLabel   (class Label)
      fOutimageEpsPrompt  (class XfwfPrompt)
      fOutimageEpsScroll  (class Scrollbar)
      crossMinLabel       (class Label)
      crossMinPrompt      (class XfwfPrompt)
      crossMinScroll      (class Scrollbar)
      crossMaxLabel       (class Label)
      crossMaxPrompt      (class XfwfPrompt)
      crossMaxScroll      (class Scrollbar)
      read inimage        (class XfwfButton)
      save outimage       (class XfwfButton)
      save filter         (class XfwfButton)
      quit                (class XfwfButton)

Six additional image widgets belong to the hierarchy. Theirdescription is exactly like the one for inimageShell above,except that the resource instance names of the TopLevelShellwidget is f_inimageShell, filtimageShell, f_filtimageShell,filtcrossShell, outimageShell and f_outimageShell.

 

SEE ALSO

lowpass(1),highpass(1),bandpass(1),bandstop(1),lowpassIdeal(1),butterworth(1),exponential(1),fft2d(1),fht2d(1),ht2ft(1),fhtPower(1),logarithm(1),ximage(3),Image(3)

 

FILES

$XITE_HOME/etc/app_defaults/XFilter

 

AUTHOR

Svein Bře, Ifi, UiO

 

DOC

Svein Bře

 

ID

$Id: xfilter.c,v 1.45 1997/07/29 08:58:16 svein Exp $

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Index

NAME

SYNTAX

DESCRIPTION

OPTIONS

RESOURCES

SEE ALSO

FILES

AUTHOR

DOC

ID

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