Collapse image along one axis, aggregating pixel values along that axis.
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 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. If not specified, no image is written
but an image analysis tool which references the output image is returned.
overwrite If output file is specified, 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 Direction plane box specification, "blcx, blcy, trcx, trcy". Only one box
may be specified. If not specified, region is used if specified. If region
is also not specified, entire directional plane unioned with any chans and
stokes specification determines the region.
region Region specification. See help par.region. Default is to not use a region.
chans Optional contiguous frequency channel number specification. Not used if
region is specified. Default is all channels.
stokes Contiguous stokes planes specification. Not used if region is specified.
Default is all stokes.
mask Mask to use. See help par.mask. Default is none.
stretch Stretch the input mask if necessary and possible. Only used if a mask is specified.
See help par.stretch.
wantreturn If true, return an image analysis tool referencing the collapsed image, if
false, return false.
This task collapses an image along a specified axis or set of axes of N pixels to a single pixel on each
specified axis. 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: 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).
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).
If outfile is not specified (or contains only white spaces), no image is written but, if wantreturn=True,
the collapsed image is still able to be accessed via the returned image analysis tool which references
the collpased image. If the returned object is not wanted it should still be captured and deleted via its
done() method. If this is not done, there is no gaurantee for when the python garbage collector will delete
it. If the returned object is wanted, it should be deleted as soon as possible for the same reasons, eg
collapsed_image = imcollapse(..., wantreturn=T)
# do things (or not) with collapsed_image and when done with object, do
collapsed_image.done()
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"
collapsed = imcollapse(imagename=imagename, outfile=outfile, function=function, axes=axis, box=box, chans=chans, wantreturn=True)
# manipulate collapsed
collapsed.done()
T
1.8.0