INTERP may be used to remove bad portions of an image. It works by
replacing the bad pixels with a polynomial fit to several pixels on either
side of the bad part. It is an inherently one-dimensional interpolation,
in that it will only interpolate either along a column or along a rows.
Hence if you have a bad column you want to get rid of, specify the COL
keyword. If you need to replace a bad row, use ROW. Note that ONE of
these two keywords MUST be specified. The region across which the
interpolation is done is specified by defining a box containing the
region. A list of boxes may be given via the BOX= keyword, in case you want
to remove a number of bad columns (or rows) from an image. An alternate
form uses the MASK keyword. When this is used the program searches the
image for the first masked pixel, continues until the next unmasked pixel,
and interpolates across this region. Then it proceeds until it finds the
next masked pixel, and repeats the process until no more masked pixels have
been found. Note that the BOX= and MASK keywords are incompatible; use
only one or the other.
The order of the interpolation-polynomial is given with the ORD=n
keyword. The default is ORD=0, so that the bad pixels are replaced simply
by the average of the adjacent pixels. This works fine for flat images, but
when interpolating across stars or spectra ORD=2 works much better (higher
orders up to 6 are allowed but are rarely needed). The user can change the
number of pixels to be used in the fit by the AVE= keyword. AVE pixels at
each side of the bad region are used in the fit. The value of AVE has to
be at least (ORD+1)/2, if a smaller value is given, the order of the
interpolation-polynomial will be reduced to the highest allowed order. The
default value is AVE=1; in other words, replaces the bad pixels with the
line (or the average if ORD=0) defined by the pair of adjacent pixels (one
pixel on either side) of the bad region.
<#5053#>Examples:<#5053#>