STScI Logo

rmpupil mscred


NAME · PARAMETERS · DESCRIPTION · EXAMPLES · SEE_ALSO

NAME

rmpupil -- remove pupil pattern from single or multiextension data

PARAMETERS

input
List of input images or multiextension files.
output
List of corrected output images or multiextension files. If no list is specified then the input list is used, otherwise the output list must match the input list. If an input and output file are the same the output is created in a temporary file and the input is replaced after the output is completed.
pupil
List of pupil images or multiextension files. The list must either match the input list or be a single file to be used for all the input files. The pupil pattern is assumed to have a zero background.
masks
List of masks identifying pixels to ignore in the input data. Pixels to ignore have non-zero mask values. An empty list applies no bad pixel mask, a single mask applies to all input data, and a list is matched with the input list. A mask is specified by a filename or by reference to a filename given by the value of a header keyword in the input image. A header keyword reference is made with the syntax "!<keyword>" where <keyword> is the desired keyword with case ignored. For multiextension files the masks may be either a multiextension file with matching extension names or a directory of pixel list files with the extension names as the filenames.

pupilmasks
List of masks identifying pixels to ignore in the pupil image. This mask is primarily intended to restrict the amplitude calculation to the region of the pupil pattern. Pixels to ignore have non-zero mask values. The same options for specifying the masks apply as for the masks parameter. Keyword references will sought in the pupil pattern image header.
outtype = "sdiff" (sdiff|sflat)
Output type from the choices "sdiff" and "sflat". The first one scales and subtracts the pupil pattern and the second flattens the input by the pupil pattern.
ncblk = 5, nlblk = 5
Moving average block sizes for the input and pupil images. The block average size for columns and for lines are specified separately.
extfit = "im[2367]"
Extensions to use for fitting the pupil amplitude. A null string matches all extension names. Otherwise the parameter is a comma separated list of patterns which match the entire extension name. Thus, a list of extension names may be given or the pattern matching characters ? for any character or [] for a set of characters. The set may include ranges in ascii order by using hyphens; i.e. 1-3 matches the characters 1, 2, and 3. The default value is for the KPNO Mosaic at the Mayall telescope. All the selected extensions in the input files must also exist in the pupil and mask files.
logfile = ""
Filename for appending log information. If no name is specified then no log is written. Note that there is no need to use "STDOUT" since the same information is written when the verbose parameter is set.
verbose = yes
If set to yes, log information is written to the standard output. Note that this is the same information as written to the logfile specified by the logfile parameter.

DESCRIPTION

RMPUPIL determines the pupil amplitude that minimizes the weighted mean difference between an input image and a fringe image given in equation 1. The input images, specified by the input parameter, may be individual images (which includes images selected from multiextension files as explicit image extensions) or multiextension files specified by a root filename. In the latter case the image extension names selected by the extfit parameter are used for computing a global pupil amplitude for all the extensions.

The output of this task are pupil corrected images or multiextension files. When the input is a multiextension file the output is a multiextension file with all the same extensions. Note that all the extensions in the input are output regardless of which extensions are selected for fitting.

The statistic used to compute the scale is

    (1)  <(((A - <A>) - s (P - <P>)) (P - <P>))> = 0

where

    A		Input image		  (\fIinput\fR parameter)
    B		Input image background	  (\fIbackground\fR parameter)
    P		Pupil image	 	  (\fIpupil\fR parameter)
    s		Pupil amplitude scale factor

The solution of equation 1 is determined over all pixels in the image or extensions selected by the extfit parameter which are not flagged in the pixel masks specified by the masks and pupilmasks parameters. For multiextension files equation 1 is also solved separately for each extension and estimates of the pupil amplitude are shown in the log output (see examples 2 and 3). However, the final pupil amplitude is not the average of these values but the solution over all pixels. To treat image extensions as independent images the various file lists must be explicit images rather than multiextension file rootnames (see example 3).

The fitting defined by equation 1 is improved by smoothing when the data and pupil pattern include noise, such as occurs when it is derived from observational data. The images may be smoothed by a moving block average with block sizes specified by the parameters ncblk and nlblk .

There are two types of output from the task selected by the outtype parameter. When the type is "sdiff" the output is "A - s * P". When the type is "sflat" the output is "A / (f * P + 1)" where

    (2)  f = s / b = s / (<A> - s * <P>)

The quantity b is an estimate of the background outside the pupil pattern. The derived quantities f and b are printed in the log output under the keywords "flatscale" and "flatbkg".

While the observed pupil pattern is basically a scattered (additive) light effect it must be removed in a two step process when it also appears in the flat field data. In the first step the pattern is removed from the flat field data using the "sflat" option. This separates the underlying relative responses of the pixels. After this corrected flat field is applied to the object data the pupil pattern is then removed as additive light using the "sdiff" option. Generally the pupil pattern image is derived before each step. A pupil pattern is first derived from data which has not been flat fielded, in other words from the flat field data itself. Then, after the object data has been flat fielded by the corrected flat field, a new pupil pattern is extracted from a sky flat field produced from the flat fielded object data.

A key to obtaining the best match between the pupil pattern and the input data is to use masks for the input and the pattern. The mask for the input data identifies bad data and objects in the input image. The task nproto.objmasks is recommended for creating the masks. When removing the pattern from flat field data the mask may be absent or identify regions where the flat field response significantly distorts the pattern, such as regions of very low or non-linear response or dust patterns.

The pattern mask restricts the data used to determine the pupil amplitude to where the pupil pattern is located. The two masks can be combined into one mask but it may be easier to use two separate masks since the pattern mask will often be independent of the data or even the date of observation.

The masks specified by the masks and pupilmasks parameters may be in any of the supported masks formats. As of IRAF V2.12 this includes pixel list (.pl) files and FITS "type=mask" extensions. When the input is a multiextension file, the selected extension names are appended to the mask filename to select masks with the same extension name. If a mask file of the form "name[ext]" is not found the task will treat the filename as a directory of pixel list files and select the filename corresponding to the extension name; i.e. "name/ext.pl".

In addition to the pupil corrected image, log output to the terminal is produced when verbose is "yes" and log output to a specified file is produced by setting logfile . The output is the same for both. Because this task is a simple script calling the task patfit the log output contains some additional information not described here. See the help page for patfit for details.

The output image will also contain a record of the operation performed under the keyword RMPUPIL as in the following example.

    RMPUPIL  = 'o262 - 0.80696 pupil'

EXAMPLES

1. Pupil removal from a single image, "o262". The input image is processed to produce a mask, "objmask262", of the objects and bad pixels (see nproto.objmasks ). A pupil mask, "pupilmask", has been created at the same time as the pupil pattern image, "pupil".

    cl> rmpupil o262 fo262 pupil objmask262 pupilmask=pupilmask
    RMPUPIL: NOAO/IRAF V2.11EXPORT ... 18-Jan-2002
      input = o262
      pattern = pupil
      weight = pupil
        ncblk = 5
        nlblk = 5
      input background = <input>
      pattern background = <pattern>
      weight background = <weight>
      input mask = objmask262
      pattern mask = pupilmask
      output = fo262
      outtype = sdiff
      <input> = 7650.
      <pattern> = 0.1554
      <weight> = 0.1554
      scale = 0.807
	fo262 = o262 - 0.80696 pupil

2. The same example but with multiextension files. In this case the object mask may either be a multiextension file of mask type extensions (V2.12 and later) or a directory "objmask262" with files im1.pl, im2.pl, etc. This shows fitting the pupil only in the set of extensions where parts of the pupil pattern are found and then creating an output with all the extensions.

    cl> rmpupil o262 fo262 pupil objmask262 pupilmask=pupilmask
    RMPUPIL: NOAO/IRAF V2.11EXPORT ... 15-Jan-2002
      input = o262
      pattern = pupil
      weight = pupil
        ncblk = 5
        nlblk = 5
      input background = <input>
      pattern background = <pattern>
      weight background = <weight>
      input mask = objmask262
      pattern mask = pupilmask
      output = fo262
      outtype = sdiff
	o262[im2]: 0.8103
	o262[im3]: 0.8235
	o262[im6]: 0.8365
	o262[im7]: 0.7584
      <input> = 7650.
      <pattern> = 0.5208
      <weight> = 0.5208
      scale = 0.8095
	fo262[im1] = o262[im1] - 0.80953 pupil[im1]
	fo262[im2] = o262[im2] - 0.80953 pupil[im2]
	fo262[im3] = o262[im3] - 0.80953 pupil[im3]
	fo262[im4] = o262[im4] - 0.80953 pupil[im4]
	fo262[im5] = o262[im5] - 0.80953 pupil[im5]
	fo262[im6] = o262[im6] - 0.80953 pupil[im6]
	fo262[im7] = o262[im7] - 0.80953 pupil[im7]
	fo262[im8] = o262[im8] - 0.80953 pupil[im8]

3. The same multextension example treating the extensions as independent images. Note that in this case the mask is actually objmask262/im1.pl but is referenced as objmask262[im1] (the other form could also be used).

    cl> dpar rmpupil
    rmpupil.input = "o262[im2],o262[im3],o262[im6],o262[im7]"
    rmpupil.output = "fo262[im2],fo262[im3,append],...
    rmpupil.pupil = "pupil[im2],pupil[im3],...
    rmpupil.masks = "objmask262[im2],objmask262[im3],...
    rmpupil.patternmasks = "pupilmask[im2],pupilmask[im3],...
    rmpupil.outtype = "sdiff"
    rmpupil.ncblk = 5
    rmpupil.nlblk = 5
    rmpupil.extfit = ""
    rmpupil.logfile = "logfile"
    rmpupil.verbose = yes
    rmpupil.mode = "ql"
    # EOF
    cl> rmpupil
    List of input images (o262[im2],o262[im3],...
    List of output corrected images (fo262[im2],fo262[im3,append],...
    Pupil or list of pupil patterns (pupil[im2],...
    List of object/bad data masks (objmask262[im2],...
    RMPUPIL: NOAO/IRAF V2.11EXPORT ... 18-Jan-2002
      input = o262[im2]
      pattern = pupil[im2]
      weight = pupil[im2]
        ncblk = 5
        nlblk = 5
      input background = <input>
      pattern background = <pattern>
      weight background = <weight>
      input mask = objmask262[im2]
      pattern mask = pupilmask[im2]
      output = fo262[im2]
      outtype = sdiff
      <input> = 7340.
      <pattern> = 0.1587
      <weight> = 0.1587
      scale = 0.8088
	fo262[im2] = o262[im2] - 0.80883 pupil[im2]
    RMPUPIL: NOAO/IRAF V2.11EXPORT ... 18-Jan-2002
      input = o262[im3]
      pattern = pupil[im3]
      weight = pupil[im3]
        ncblk = 5
        nlblk = 5
      input background = <input>
      pattern background = <pattern>
      weight background = <weight>
      input mask = objmask262[im3]
      pattern mask = pupilmask[im3]
      output = fo262[im3,append]
      outtype = sdiff
      <input> = 7299.
      <pattern> = -0.3147
      <weight> = -0.3147
      scale = 0.7948
	fo262[im3,append] = o262[im3] - 0.79481 pupil[im3]
    ...

Note that in this case an output multiextension file is built from the individual outputs by using the "append" syntax of the FITS image kernel.

SEE ALSO

nproto.objmasks, patfit, rmfringe, irmpupil


Source Code · Search Form · STSDAS