AIPS NRAO AIPS HELP file for MWFLT in 31DEC18



As of Thu Jul 19 0:07:33 2018


MWFLT: Applies a nonlinear low/high pass filter to an image.

INPUTS

INNAME                             Input image name (name)
INCLASS                            Input image name (class)
INSEQ             0.0     9999.0   Input image name (seq. #)
INDISK            0.0        9.0   Input image disk unit #
OUTNAME                            Output image name (name)
OUTCLASS                           Output image name (class)
OUTSEQ           -1.0     9999.0   Output image name (seq. #)
OUTDISK           0.0        9.0   Output image disk unit #.
BLC                                Bottom left corner of input
TRC                                Top right corner of input
OPCODE                             Operation codes: 'ROW '
                                   'MW  ','ALFA','MODE','NRML'
                                   ;MAX ', 'MIN '
CPARM                              1,2: Filter Box width, height
                                   ('ROW' 2: "Median" pixel
                                   3: include fraction
                                   4: >0 => Print progress
                                   5: 'ROW' pixel increment
                                   6: 'ROW' Saturation Limit
                                   7: 'ROW' Saturation Value
DPARM                              1:Data Scale, 2:Filter scale
                                   3:'NRML' background scale

HELP SECTION

MWFLT
Task:  Task which applies various high or lowpass filters to images.
       Handles blanking and data cubes.  MWFLT is based on the TAFFY
       paraform, and uses its scrolling buffer ability.  It implements
       five filters which work on a matrix of pixels surrounding and
       containing each input pixel.  The dimensions of this matrix are
       passed to the task via CPARM.
Adverbs:
  INNAME.....Input image name (name).       Standard defaults.
  INCLASS....Input image name (class).      Standard defaults.
  INSEQ......Input image name (seq. #).     0 => highest.
  INDISK.....Disk drive # of input image.   0 => any.
  OUTNAME....Output image name (name).      Standard defaults.
  OUTCLASS...Output image name (class).     Standard defaults.
  OUTSEQ.....Output image name (seq. #).    0 => highest unique.
  OUTDISK....Disk drive # of output image.  0 => highest disk
             number with sufficient space.
  BLC........Bottom right corner in input image of desired
             subimage.  Default is entire image.
  TRC........Top right corner in input image of desired
             subimage.  Default is entire image.
  OPCODE.....User specified operation code:
             'ROW' => Median window filter for rows.  Result is
                      data +/- Median filter of pixels in the
                      CPARM(1) pixels on the row surrounding and
                      containing each input point.  CPARM(2) is
                      the Nth point of the CPARM(1) pixels to
                      used for the sky.  A true median is
                      CPARM(2)=CPARM(1)/2  The output values
                      are scaled by DPARM()s (D() below):
                      output = D(1)*input + D(2)*MW(input)
                      Highpass, sky removal:  D(1)=1,D(2)=-1
                      Low pass, star removal: D(1)=0,D(2)=1
             'MW'  => Median window filter.  Result is data
                      +/- Median filter of pixels in the
                      CPARM(1)xCPARM(2) window surrounding and
                      containing each input point.
                      output = D(1)*input + D(2)*MW(input)
                      (Much slower than 'ROW')
             'MAX '=> Take maximum value in the CPARM(1)xCPARM(2)
                      window surrounding the pixel
                      output = D(1)*input + D(2)*MWMax(input)
             'MIN '=> Take minimum value in the CPARM(1)xCPARM(2)
                      window surrounding the pixel
                      output = D(1)*input + D(2)*MWMin(input)
             'ALFA'=> Alpha trim filter.  Median, but extreama
                      are excluded.  Each result point is
                      the mean of all the values in the
                      CPARM(1)xCPARM(2) window surrounding and
                      containing each input points which are
                      greater than CPARM(3) percent of the
                      values in the window and less than
                      CPARM(3) percent of the values.
                      (ie C(3)=25 => points 25 to 75  percent)
                      output = D(1) * input + D(2) * MW(input)
             'MODE'=> Mode window filter.  Similar to Median
                      except Mode used.  The mode approximated
                      as 3 times the median of the distribution
                      minus twice the mean.
             'NRML'=> Normalization filter.  This filter is an
                      extension of the alpha trim and mode
                      filters.  It is mainly used to reduce the
                      dynamic range of an image.  Each result
                      point is the sum of the square root of the
                      normalized mode of the distribution of
                      pixels and a normalization function.  This
                      function is simply the original data point
                      minus the mode of the pixels in the window
                      that are within the given alpha trim range
                      (see above) times a scale factor based on
                      the RMS of the distribution of pixels. The
                      scale factor is inversely proportional to
                      the RMS so that lighter features are
                      enhanced while brighter features are
                      reduced.  The formula is:
                        RESULT(I)=(DATA(I)-MODE(I))*(D(1)-D(2))*
                             (ABS(MODE(I))/DATAMAX)+D(2))/RMS(I)
                             + D(3)*SQRT(ABS(MODE(I)/DATAMAX))
  CPARM......CPARM(1) is the width of the window.
             For 'ROW' CPARM(1) the maximum value is the length.
                CPARM(2) is the Nth brightest value to use as
                the median. (True median is CPARM(2)=C(1)/2)
             For other opcodes CPARM(2) is the window height.
                The window values must be odd, greater than 0,
                and less than or equal 201.
             For 'ALFA' or 'NRML' CPARM(3) is the fraction of
                points in the window which define the cutoffs.
                This value must be between zero and 0.5.
                CPARM(4) specifies whether row numbers should be
                output as the task is running (-1 => no)
  DPARM......If OPCODE is not 'NRML', DPARM(1) is the scale for
                the input image in calculating the output image.
                DPARM(2) is the scale for the median.
                output = input*DPARM(1) + median*DPARM(2)
                   Median highpass, sky subtraction:
                      D(1)=1,D(2)=-1
                   Median lowpass, star removal:
                      D(1)=0,D(2)=1
                   If image is a negative, to remove sky and
                   make positive:
                      D(1)=-1,D(2)=1
                   Default: DPARM(*)=0 => DPARM(1)=1,DPARM(2)=-1

             'NRML', DPARM(1) is the maximum RMS to be in
             the output image, DPARM(2) is the minimum RMS
             to be in the output image, and DPARM(3) is the
             weight of the square root of the background in
             the calculation of the output image.

EXPLAIN SECTION

MWFLT:  Task which applies Median Filters
DOCUMENTOR: Glen Langston, Thad A. Polk/Don Wells NRAO.
RELATED PROGRAMS:  All AIPS image tasks.

                          PURPOSE


     MWFLT is designed to apply lowpass or highpass filters to images.
It uses the 'scrolling buffer' concept with space for a 201-row buffer.
It allows a framework which allows the implementation of any operator
which depends on the pixels within a window of user specified size.
MWFLT can handle up to 7 dimensional images and supports blanking.  A
subimage of the
input image may be selected.

     Since optical images often do not have correct coordinate info,
MWFLT also will update the coordinate type increment, reference pixel
and reference location via the CPARM adverb.  If the input image has
blanks for the axis types, the axis type is assume to be a tangent
projection of Ra and Dec.

               DETAILS ABOUT SPECIFIC OPCODES

ROW:  Median filter of data in one row.  Considerably faster than MW.
       CPARM(1) is the width of the median filter (no maximum).
       CPARM(2) is the Nth value of the sorted list of pixels to use as
       the filter output.  A true median is CPARM(2)=CPARM(1)/2.  If the
       image is full of objects, then the sky is better subtracted by a
       smaller CPARM(2).  For negative images, make CPARM(2) bigger.
MW:   Median window filter.  The median calculation uses a two
       dimensional merge sort algorithm to keep all the pixels within
       the window in sorted order.  The result is the pixel value in the
       middle of this sorted array.
MAX:  Uses the MW code, but returns the max in the window
MIN:  Uses the MW code, but returns the min in the window
       See L Rudnick, (2002), PASP, 114, 427 for uses that may be made
       of this simple filter.  Larry recommends setting CPARM(1) and
       CPARM(2) to at least 3x beam extent in pixels and DPARM = 0,1.
       Then run OPCODE='MIN' on the input image and OPCODE='MAX' on the
       output of 'min' to get all emission larger than 3x beam.  This
       can be subtracted from the original image with COMB to get only
       more compact emission.
ALFA: Alpha-trimmed mean filter, which is formed by taking the average
       of a subset of the data points in the window. The subset is
       defined as all those data points greater than CPARM(3) percent of
       the data and less than CPARM(3) percent of the data.
MODE: Mode filter.  The mode of the distribution is approximated as 3
       times the median of the distribution minus twice the mean.  In
       addition, outliers of the distribution are excluded by
       calculating the standard deviation of the sample and using the
       Chauvenet rule to calculate a normal distribution cutoff value
       for the sample.  Only those pixels whose values are between the
       two cutoff limits are allowed to enter the median, mean, and
       standard deviation calculations.  This result is a much closer
       estimate of the true background than is the mean.
NRML: Normalization filter.  It calculates the result as the sum of the
       square root of the mode of the distribution and a normalization
       function.  This function is simply the original data point minus
       the mode of the pixels in the window that are within the given
       alpha trim range times a scale factor that is inversely
       proportional to the r.m.s. of the distribution of pixels.  This
       operator is mainly useful in reducing the dynamic range of images
       while enhancing lighter features.

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