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.help fixpix Aug96 proto
.ih
NAME
fixpix -- fix pixels identified by a bad pixel mask, image, or file
.ih
USAGE
.nf
fixpix images masks
.fi
.ih
PARAMETERS
.ls images
List of two dimensional images to be "fixed" (modified) by
linear interpolation.
.le
.ls masks
List of bad pixel masks, images, or files (collectively called masks)
identifying the bad pixels. The list of masks must either match the
list of input images in number or a single mask may be specified to apply
to all images. The special name "BPM" may be specified to select a mask
specified by the header keyword "BPM" in the input image. The possible
mask formats are given in the DESCRIPTION section.
.le
.ls linterp = "INDEF", cinterp = "INDEF"
Normally interpolation is performed across the narrowest dimension spanning
the bad pixels with interpolation along image lines if the two dimensions are
equal. However specific values in the mask may be used to
identify the desired interpolation direction. The value in the mask
specifying line interpolation is given by the \fIlinterp\fR parameter and
the value specifying column interpolation is given by the \fIcinterp\fR
parameter. Any values which are do not match one of these parameters
results in interpolation along the narrowest dimension. Note that a
text file mask always has 2 for pixels with narrow dimension along
lines and 3 for pixels with narrow dimension along columns.
.le
.ls verbose = no
If this parameter is set to yes a line identifying each image and
associated mask is printed. If the \fIpixels\fR parameter is
set then a list of the pixels modified is also printed.
.le
.ls pixels = no
List the pixels modified? This is only done if this parameters and
the \fIverbose\fR parameter are set.
.le
.ih
DESCRIPTION
Pixels in a list of images identified by bad pixel masks, images, or text
files (collectively called masks here) are replaced by linear interpolation
along lines or columns using the nearest good pixels. The list of input
images, specified by the \fIimages\fR parameter, are matched with a list of
masks, specified by the \fImasks\fR parameter. The list of masks must
match the list of input images or a single mask name may be given to apply
to all input images. The special mask name "BPM" may be used to
select a mask name given in the input image header under the keyword
"BPM".
There are three types of masks which may be used. The preferred type
is a bad pixel mask given as a "pixel list" image. Pixel list images
have the extension ".pl" signifying a special compact file of integer
values ideal for identifying sets of pixels. For a bad pixel mask the
good pixels have a value of zero and bad pixels have positive integer
values.
The second type is any image format. The image will be internally
converted to a bad pixel mask. Note that real image values will be
truncated to integers. Again good pixels will have values of zero and bad
pixels will have positive values.
The final format is a text file with lines giving the integer coordinates
of a single pixel or a rectangular region. A single pixel is specified by
a column and line number. A region is specified by a starting column, an
ending column, a starting line, and an ending line. Internally this file
is turned into a bad pixel mask of the size of the input image with values
of zero for non-specified pixels, a value of two for pixels with narrowest
interpolation direction along lines, and three for pixels with narrowest
interpolation direction along columns.
As noted previously, bad pixels are "fixed" by replacing them with values
by linear interpolation to the nearest pixels not identified as bad.
Normally interpolation is performed across the narrowest dimension spanning
bad pixels with interpolation along image lines if the two dimensions are
equal. However specific values in the mask may be used to identify the
desired interpolation direction. The value in the mask specifying line
interpolation is given by the \fIlinterp\fR parameter and the value
specifying column interpolation is given by the \fIcinterp\fR parameter.
Any values which are do not match one of these parameters results in
interpolation along the narrowest dimension. Note that a text file mask
always has 1 for pixels with narrow dimension along lines and 2 for pixels
with narrow dimension along columns.
The \fIverbose\fR allows printing a line giving the task name, the
image name, and the mask name. In addition, if the \fIpixels\fR
parameter is set the pixels modified are listed. The list of pixels
consists of the column and line of the pixel, the original
and replaced pixel values, and the column and line of the one or two
pixels used for the interpolation. If the bad pixel region has no
pixels at one end, that is there are bad pixels all the way to one edge
of the image, then the single pixel used is printed.
Normally the input images and the masks will have the same dimension.
However, this task matches bad pixels in the masks with the input images
based on physical coordinates. Thus, the mask image may be bigger or
smaller than the input image and image sections may be used with either
the input images or the bad pixel mask or image mask images. If the
input image is the result of extracting a subsection of a bigger image
the coordinates of the pixels will be those of the original image
and the matching coordinates of the mask will be applied. This has
the effect of allowing image sections to be applied to images having
a bad pixel mask specified in the image and still having the bad pixel
mask be valid.
Mask images may be made in a variety of ways. Any task which produces
and modifies image values may be used. Some useful tasks are
\fBimexpr, imreplace, imcopy,\fR and \fBmkpattern\fR. If a new image
is specified with the explicit ".pl" extension then the pixel mask
format is produced. Two other ways to make masks are with the
tasks \fBtext2mask\fR and \fBccdmask\fR. The former uses an input
text file consisting of rectangular region. This is the old
"fixpix" format. The task \fBccdmask\fR is specialized to make a mask
of bad pixels from flat fields or, even better, from the ratio of
two flat fields of different exposure levels.
.ih
EXAMPLES
1. A list of images have bad pixel masks defined in the image header.
To replace the bad pixels by interpolation along the narrowest
dimension:
.nf
cl> fixpix obj* BPM
.fi
2. A simple mask of 0s and 1s defines bad columns in spectral data
with dispersion along the lines. To interpolate along the lines:
.nf
cl> fixpix spec00*h ccdmask linterp=1 v+
FIXPIX: image spec001.imh with mask ccdmask
FIXPIX: image spec002.imh with mask ccdmask
...
.fi
3. A text file of bad pixels is used and the modified pixels are printed
with:
.nf
cl> type mask.dat
1 2 1 1
25 26 25 25
26 27 27 27
49 50 50 50
10 10
20 21 20 20
cl> fixpix myimage mask.dat v+ p+
FIXPIX: image myimage with mask mask.dat
1 1 1. 1. 1 2
2 1 1. 1. 2 2
10 10 1. 1. 9 10 11 10
20 20 1. 1. 20 19 20 21
21 20 1. 1. 21 19 21 21
25 25 1. 1. 25 24 25 26
26 25 1. 1. 26 26 26 28
26 27 1. 1. 26 26 26 28
27 27 1. 1. 27 26 27 28
49 50 1. 1. 49 49
50 50 1. 1. 50 49
.fi
4. Because a text file input automatically sets the mask values to
2 or 3 you may need to set the linterp and cinterp parameters to
force the direction. In particular, to apply FIXPIX to a 1D image,
say a spectrum, if you have regions described by ranges in columns
the mask interpolation values will be assigned as 3. This means
it is trying to interpolation between line 0 and line 2 which is
obviously not what is intended. To make this work set linterp to
3:
.nf
cl> fixpix myimage mask.dat linterp=3
.fi
.ih
REVISIONS
.ls FIXPIX V2.11
This task replaces the old task (now obsolete.ofixpix) and works with the
more general pixel mask facilities. It also provides greater flexibility
in choosing the interpolation direction.
.le
.ih
SEE ALSO
epix, imedit, ccdproc, text2mask, obsolete.ofixpix
.endhelp
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