pyimcom.splitpsf.imsubtract

Routines for implementing the image subtraction step in PSF wing removal.

Functions

pltshow

Helper to determine where to save a plot.

get_wcs

Extracts the World Coordinate System from a cached file.

run_imsubtract

Main workflow for image subtraction step.

Attributes

config_file

Functions

fftconvolve_multi(in1, in2, out[, mode, nb, workers, ...])	Convolve two N-dimensional arrays using FFT.
pltshow(plt, display[, pars])	Where to save a plot.
get_wcs(cachefile)	Gets the WCS from a cached FITS file.
get_wcs_from_infile(infile)	Gets the "sub-WCS" from the FITS file. Using SlicedLowLevelWCS avoids extra axes
run_imsubtract_single(cfgdata, scaid, obsid, path, expname)	Main routine to run imsubtract on a single image.
run_imsubtract(config_file[, display, scanum, ...])	Main routine to run imsubtract.

Module Contents

fftconvolve_multi(in1, in2, out, mode='full', nb=4, workers=None, verbose=False)

Convolve two N-dimensional arrays using FFT.

This is almost a drop-in replacement for scipy.signal.fftconvolve. The big difference is that the convolution is directly added to out, rather than being a return value.

For the 2D mode = “valid” case, this splits up the data into nb blocks for the convolution. It is designed to be efficient when in1 is much smaller than in2.

Parameters:

• in1 (np.ndarray) – First input.

• in2 (np.ndarray) – Second input. Should have the same number of dimensions as in1.

• out (np.ndarray) – Location to add to the output image. Must have the right dimensions.

• mode (str, optional) – Mode; options are “full”, “valid”, and “same” (just as for the scipy functions).

• nb (int, optional) – Number of blocks to use.

• workers (int, optional) – Number of workers for the FFTs if requesting parallelism.

• verbose (bool, optional) – Whether to print the intermediate steps.

Return type:

None

pltshow(plt, display, pars={})

Where to save a plot.

Parameters:

• plt (matplotlib.pyplot) – The pyplot module to use for plotting.

• display (str or None) – Sends to file (if string), screen (None), or nowhere (if ‘/dev/null’)

• pars (dict, optional) – Parameters for saving the file. Must be provided if a file is requested.

Return type:

None

Notes

The pars dictionary contains the keys: * ‘type’ : str, currently only supports ‘window’ * ‘obsid’ : int, observation ID * ‘sca’ : int, SCA number * ‘ix’ : int, x block index * ‘iy’ : int, y block index

get_wcs(cachefile)

Gets the WCS from a cached FITS file.

If a gwcs is used, finds the attached ASDF file and reads that.

Parameters:

cachefile (str) – Name of the cached file.

Returns:

The World Coordinate System of the cached file.

Return type:

pyimcom.wcsutils.PyIMCOM_WCS

get_wcs_from_infile(infile)

Gets the “sub-WCS” from the FITS file. Using SlicedLowLevelWCS avoids extra axes which create additional complications in the WCS.

Parameters:

infile (str) – Name of the file.

Returns:

The World Coordinate System of the file with only the necessary axes.

Return type:

sub-WCS

run_imsubtract_single(cfgdata, scaid, obsid, path, expname, display=None, local_output=False, fft_workers=None, wcs_shortcut=True, max_layers=None, mmap=None)

Main routine to run imsubtract on a single image.

Parameters:

• cfgdata (Config object) – a pyimcom Config object

• scaid (int) – SCA ID for the image to be subtracted. Should be in range 1..18, inclusive.

• obsid (int) – Observation ID for the image to be subtracted.

• path (str) – Path to the directory containing the cached files.

• expname (str) – Name of the cached file (will be of the form `stem_obsid_scaid.fits’).

• display (str or None, optional) – Display location for intermediate steps.

• local_output (bool, optional) – Whether to direct the file to local output instead of the cache directory. (This will normally be the default False; it is provided only so that if more than one user runs tests at the same time, they can use True to avoid a collision.)

• fft_workers (int, optional) – Number of workers for the FFTs if requesting parallelism.

• wcs_shortcut (bool, optional) – If set, allows interpolation methods to speed up WCS computations.

• max_layers (int, optional) – Maximum number of layers to process. (For testing; default is None, which means no limit.)

• mmap (str or str-like, optional) – Directory to put temporary mmap files.

Notes

There are several options for display:

• display = None : print to screen

• display = ‘/dev/null’ : don’t save

• display = any other string : save to display+f'_{obsid}_{sca}_{ix:02d}_{iy:02d}.png'

run_imsubtract(config_file, display=None, scanum=None, local_output=False, max_img=None, workers=None, wcs_shortcut=True, max_layers=None, mmap=None)

Main routine to run imsubtract.

Parameters:

• config_file (str) – Location of a configuration file.

• display (str or None, optional) – Display location for intermediate steps.

• scanum (int or None, optional) – If not None, only run this SCA. Should be in range 1..18, inclusive. (Mostly used for parallelization.)

• local_output (bool, optional) – Whether to direct the file to local output instead of the cache directory. (This will normally be the default False; it is provided only so that if more than one user runs tests at the same time, they can use True to avoid a collision.)

• max_img (int, optional) – If provided, does computations for a maximum number of SCAs. Most users will want the default of None; this is provided mainly for testing.

• workers (int, optional) – Number of workers for the FFTs if requesting parallelism.

• wcs_shortcut (bool, optional) – If set, allows interpolation methods to speed up WCS computations.

• max_layers (int, optional) – Maximum number of layers to process. (For testing; default is None, which means no limit.)

• mmap (str or str-like, optional) – Directory to put temporary mmap files.

Notes

There are several options for display:

• display = None : print to screen

• display = ‘/dev/null’ : don’t save

• display = any other string : save to display+f'_{obsid}_{sca}_{ix:02d}_{iy:02d}.png'

config_file