IterativelySubtractedPSFPhotometry

class photutils.psf.IterativelySubtractedPSFPhotometry(group_maker, bkg_estimator, psf_model, fitshape, finder, *, fitter=<astropy.modeling.fitting.LevMarLSQFitter object>, niters=3, aperture_radius=None, extra_output_cols=None, subshape=None)

Bases: BasicPSFPhotometry

Deprecated since version 1.9.0: The IterativelySubtractedPSFPhotometry class is deprecated and may be removed in a future version. Use photutils.psf.IterativePSFPhotometry instead.

This class implements an iterative algorithm to perform point spread function photometry in crowded fields. This consists of applying a loop of find sources, make groups, fit groups, subtract groups, and then repeat until no more stars are detected or a given number of iterations is reached.

Parameters:

group_makercallable or GroupStarsBase

group_maker should be able to decide whether a given star overlaps with any other and label them as belonging to the same group. group_maker receives as input an Table object with columns named as id, x_0, y_0, in which x_0 and y_0 have the same meaning of xcentroid and ycentroid. This callable must return an Table with columns id, x_0, y_0, and group_id. The column group_id should contain integers starting from 1 that indicate which group a given source belongs to. See, e.g., DAOGroup.

bkg_estimatorcallable, instance of any BackgroundBase subclass, or None

bkg_estimator should be able to compute either a scalar background or a 2D background of a given 2D image. See, e.g., MedianBackground. If None, no background subtraction is performed.

psf_modelastropy.modeling.Fittable2DModel instance

PSF or PRF model to fit the data. Could be one of the models in this package like IntegratedGaussianPRF or any other suitable 2D model. This object needs to identify three parameters (position of center in x and y coordinates and the flux) in order to set them to suitable starting values for each fit. The names of these parameters should be given as x_0, y_0 and flux. prepare_psf_model can be used to prepare any 2D model to match this assumption.

fitshapeint or length-2 array_like

Rectangular shape around the center of a star that will be used to define the PSF-fitting region. If fitshape is a scalar then a square shape of size fitshape will be used. If fitshape has two elements, they must be in (ny, nx) order. Each element of fitshape must be an odd number.

findercallable or instance of any StarFinderBase subclasses

finder should be able to identify stars, i.e., compute a rough estimate of the centroids, in a given 2D image. finder receives as input a 2D image and returns an Table object which contains columns with names: id, xcentroid, ycentroid, and flux. In which id is an integer-valued column starting from 1, xcentroid and ycentroid are center position estimates of the sources and flux contains flux estimates of the sources. See, e.g., DAOStarFinder or IRAFStarFinder.

fitterFitter instance

Fitter object used to compute the optimized centroid positions and/or flux of the identified sources. See fitting for more details on fitters.

aperture_radiusfloat

The radius (in units of pixels) used to compute initial estimates for the fluxes of sources. If None, one FWHM will be used if it can be determined from the `psf_model.

nitersint or None

Number of iterations to perform of the loop FIND, GROUP, SUBTRACT, NSTAR. If None, iterations will proceed until no more stars remain. Note that in this case it is possible that the loop will never end if the PSF has structure that causes subtraction to create new sources infinitely.

extra_output_colslist of str, optional

List of additional columns for parameters derived by any of the intermediate fitting steps (e.g., finder), such as roundness or sharpness.

subshapeNone, int, or length-2 array_like

Rectangular shape around the center of a star that will be used to define the PSF-subtraction region. If None, then fitshape will be used. If subshape is a scalar then a square shape of size subshape will be used. If subshape has two elements, they must be in (ny, nx) order. Each element of subshape must be an odd number.

Notes

If there are problems with fitting large groups, change the parameters of the grouping algorithm to reduce the number of sources in each group or input a star_groups table that only includes the groups that are relevant (e.g., manually remove all entries that coincide with artifacts).

References

[1] Stetson, Astronomical Society of the Pacific, Publications,

(ISSN 0004-6280), vol. 99, March 1987, p. 191-222. Available at: https://ui.adsabs.harvard.edu/abs/1987PASP…99..191S/abstract

Deprecated since version 1.9.0: The IterativelySubtractedPSFPhotometry class is deprecated and may be removed in a future version. Use photutils.psf.IterativePSFPhotometry instead.

Attributes Summary

finder
niters

Methods Summary

do_photometry(image, *[, mask, ...])

Perform PSF photometry in image.

Attributes Documentation

finder

niters

Methods Documentation

do_photometry(image, *, mask=None, init_guesses=None, progress_bar=False, uncertainty=None)

Perform PSF photometry in image.

This method assumes that psf_model has centroids and flux parameters which will be fitted to the data provided in image. A compound model, in fact a sum of psf_model, will be fitted to groups of stars automatically identified by group_maker. Also, image is not assumed to be background subtracted. If init_guesses are not None then this method uses init_guesses as initial guesses for the centroids. If the centroid positions are set as fixed in the PSF model psf_model, then the optimizer will only consider the flux as a variable.

Parameters:

image2D ndarray

Image to perform photometry. Invalid data values (i.e., NaN or inf) are automatically ignored.

init_guessesTable

Table which contains the initial guesses (estimates) for the set of parameters. Columns ‘x_0’ and ‘y_0’ which represent the positions (in pixel coordinates) for each object must be present. ‘flux_0’ can also be provided to set initial fluxes. If ‘flux_0’ is not provided, aperture photometry is used to estimate initial values for the fluxes. Additional columns of the form ‘<parametername>_0’ will be used to set the initial guess for any parameters of the psf_model model that are not fixed. If init_guesses supplied with extra_output_cols the initial values are used; if the columns specified in extra_output_cols are not given in init_guesses then NaNs will be returned.

mask2D bool ndarray, optional

A boolean mask with the same shape as image, where a True value indicates the corresponding element of image is masked.

uncertainty2D ndarray, optional

Stddev uncertainty for each element in image.

Returns:

output_tableTable or None

A table with the photometry results, i.e., centroids and fluxes estimations and the initial estimates used to start the fitting process. Uncertainties on the fitted parameters are reported as columns called <paramname>_unc provided that the fitter object contains a dictionary called fit_info with the key param_cov, which contains the covariance matrix.