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

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.

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.