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NRAO Home > CASA > CASA Task Reference Manual |
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0.1.36 imcollapse
Requires:
Synopsis
Collapse image along one axis, aggregating pixel values along that axis.
Arguments
Inputs |
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imagename |
| Name of the input image
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| allowed: | string |
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| Default: |
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function |
| Aggregate function to apply. This can be set one of flux,
max, mean, median, min, rms, stdev, sum, variance.
Must be specified.
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| allowed: | string |
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| Default: |
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axes |
| Zero-based axis number(s) or minimal match strings to
collapse.
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| allowed: | variant |
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| Default: | [0] |
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outfile |
| Name of output CASA image. Must be specified.
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| allowed: | string |
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| Default: |
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box |
| Rectangular region to select in direction plane. Default
is to use the entire direction plane.
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| allowed: | string |
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| Default: |
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region |
| Region selection. Default is to use the full image.
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| allowed: | string |
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| Default: |
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chans |
| Channels to use. Default is to use all channels.
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| allowed: | string |
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| Default: |
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stokes |
| Stokes planes to use. Default is to use all Stokes planes.
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| allowed: | string |
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| Default: |
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mask |
| Mask to use. Default is none.
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| allowed: | string |
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| Default: |
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overwrite |
| Overwrite exisitng ouput file if it exists?
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| allowed: | bool |
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| Default: | False |
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stretch |
| Stretch the mask if necessary and possible?
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| allowed: | bool |
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| Default: | False |
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bool
Example
PARAMETER SUMMARY
imagename Name of the input (CASA, FITS, MIRIAD) image
function Function used to compute aggregation of pixel values along the collapsed
axis. Supported functions are flux, max, mean, median, min, rms, stdev,
sum, variance. Minimum match is supported for the function parameter (eg,
function="r" will compute the rms of the pixel values).
axis Zero-based axis number(s) or minimal match strings to compress.
outfile Name of output CASA image. Must be specified.
overwrite Controls if an already existing file by the
same name can be overwritten. If true, the user is not prompted, the file
if it exists is automatically overwritten.
box Rectangular region to select in direction plane.
for details. Default is to use the entire direction plane.
region Region selection. Default is to use
the full image.
chans Channels to use. Default is to use
all channels.
stokes Stokes planes to use. Default is to use
all Stokes planes.
mask Mask to use. Default is none.
stretch Stretch the input mask if necessary and possible. Only used if a mask is specified.
This task collapses an image along a specified axis or set of axes of N pixels to a single pixel on each
specified axis. Both float valued and complex valued images are supported. It computes the specified
aggregate function for pixel values along the specified axes
and places those values in the single remaining plane of those axes in the output image. It returns
an image analysis tool containing the newly created collapsed image if wantreturn=True. Choices of
aggregate functions are: flux (see below for constraints), max, mean, median, min, rms, stdev, sum, variance. Minimal unique match is
supported for the function parameter (eg, function="r" will compute the rms of the pixel values, "med"
will compute the median).
If one specifies function=’flux’, the following constraints must be true:
1. The image must have a direction coordinate,
2. The image must have at least one beam,
3. The specified axes must be exactly the direction coordinate axes,
4. Only one of the non-directional axes may be non-degenerate,
5. The iamge brightness unit must be conformant with x*yJy/beam, where x is an optional unit (such as km/s for moments images)
and y is an optional SI prefix.
Axes can be specified as a single integer or array of integers indicating the zero-based axes along
which to collapse the image. Axes may also be specified as a single or array of strings which minimally
and uniquely match (ignoring case) world axes names in the image (eg "dec" or ["ri, "d"] for
collapsing along the declination axis or along the right ascension and declination axes, respectively).
The reference pixel of the collapsed axis is set to 0 and its reference value is set to the mean
of the the first and last values of that axis in the specified region of the input image.
# myimage.im is a 512x512x128x4 (ra,dec,freq,stokes) image
imagename = "myimage.im"
# collapse a subimage of it along its spectral axis avoiding the 8 edge
# channels at each end of the band, computing the mean value of the pixels
# resulting image is 256x256x1x4 in size.
outfile="collapse_spec_mean.im"
function="mean"
axis=2
box="127,127,383,383"
chans="8~119"
imcollapse(imagename=imagename, outfile=outfile, function=function, axes=axis, box=box, chans=chans)
More information about CASA may be found at the
CASA web page
Copyright © 2016 Associated Universities Inc., Washington, D.C.
This code is available under the terms of the GNU General Public Lincense
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