measurement_images

class ByKeyword(key)

Bases: object

Callable that can be used to split an ImageGroup by a keyword value (i.e. FILTER).

Parameters

key (str) – FITS header keyword (i.e. FILTER)

See also

ImageGroup.split

class ByPattern(key, pattern)

Bases: object

Callable that can be used to split an ImageGroup by a keyword value (i.e. FILTER), applying a regular expression and using the first matching group as key.

Parameters

  • key (str) – FITS header keyword

  • pattern (str) – Regular expression. The first matching group will be used as grouping key.

See also

ImageGroup.split

class FitsFile(*args: Any, **kwargs: Any)

Bases: _SourceXtractorPy.

class ImageGroup(**kwargs)

Bases: object

Models the grouping of images. Measurement can not be made directly on instances of this type. The configuration must be “frozen” before creating a MeasurementGroup

See also

MeasurementGroup

add_images(images)

Add new images to the group.

Parameters

images (list of, or a single, MeasurementImage) –

Raises

ValueError – If the group has been split, no new images can be added.

add_subgroup(name, group)

Add a subgroup to a group.

Parameters

  • name (str) – The new of the new group

  • group (ImageGroup) –

is_leaf()
Returns

True if the group is a leaf group

Return type

bool

print(prefix='', show_images=False, file=<_io.TextIOWrapper name='<stderr>' mode='w' encoding='UTF-8'>)

Print a human-readable representation of the group.

Parameters

  • prefix (str) – Print each line with this prefix. Used internally for indentation.

  • show_images (bool) – Show the images belonging to a leaf group.

  • file (file object) – Where to print the representation. Defaults to sys.stderr

split(grouping_method)

Splits the group in various subgroups, applying a filter on the contained images. If the group has already been split, applies the split to each subgroup.

Parameters

grouping_method (callable) – A callable that receives as a parameter the list of contained images, and returns a list of tuples, with the grouping key value, and the list of grouped images belonging to the given key.

See also

ByKeyword, ByPattern

Raises

ValueError – If some images have not been grouped by the callable.

class MeasurementGroup(image_group, is_subgroup=False)

Bases: object

Once an instance of this class is created from an ImageGroup, its configuration is “frozen”. i.e. no new images can be added, or no new grouping applied.

Parameters

image_group (ImageGroup) –

is_leaf()
Returns

True if the group is a leaf group

Return type

bool

print(prefix='', show_images=False, file=<_io.TextIOWrapper name='<stderr>' mode='w' encoding='UTF-8'>)

Print a human-readable representation of the group.

Parameters

  • prefix (str) – Print each line with this prefix. Used internally for indentation.

  • show_images (bool) – Show the images belonging to a leaf group.

  • file (file object) – Where to print the representation. Defaults to sys.stderr

class MeasurementImage(*args: Any, **kwargs: Any)

Bases: _SourceXtractorPy.

A MeasurementImage is the processing unit for SourceXtractor++. Measurements and model fitting can be done over one, or many, of them. It models the image, plus its associated weight file, PSF, etc.

Parameters

  • fits_file (str or FitsFile object) – The path to a FITS image, or an instance of FitsFile

  • psf_file (str) – The path to a PSF. It can be either a FITS image, or a PSFEx model.

  • weight_file (str or FitsFile) – The path to a FITS image with the pixel weights, or an instance of FitsFile

  • gain (float) – Image gain. If None, gain_keyword will be used instead.

  • gain_keyword (str) – Keyword for the header containing the gain.

  • saturation (float) – Saturation value. If None, saturation_keyword will be used instead.

  • saturation_keyword (str) – Keyword for the header containing the saturation value.

  • flux_scale (float) – Flux scaling. Each pixel value will be multiplied by this. If None, flux_scale_keyword will be used instead.

  • flux_scale_keyword (str) – Keyword for the header containing the flux scaling.

  • weight_type (str) –

    The type of the weight image. It must be one of:

    • none

      The image itself is used to compute internally a constant variance (default)

    • background

      The image itself is used to compute internally a variance map

    • rms

      The weight image must contain a weight-map in units of absolute standard deviations (in ADUs per pixel).

    • variance

      The weight image must contain a weight-map in units of relative variance.

    • weight

      The weight image must contain a weight-map in units of relative weights. The data are converted to variance units.

  • weight_absolute (bool) – If False, the weight map will be scaled according to an absolute variance map built from the image itself.

  • weight_scaling (float) – Apply an scaling to the weight map.

  • weight_threshold (float) – Pixels with weights beyond this value are treated just like pixels discarded by the masking process.

  • constant_background (float) – If set a constant background of that value is assumed for the image instead of using automatic detection

  • image_hdu (int) – For multi-extension FITS file specifies the HDU number for the image. Default 0 (primary HDU)

  • psf_hdu (int) – For multi-extension FITS file specifies the HDU number for the psf. Defaults to the same value as image_hdu

  • weight_hdu (int) – For multi-extension FITS file specifies the HDU number for the weight. Defaults to the same value as image_hdu

load_fits_image(image, psf=None, weight=None, **kwargs)

Creates an image group with the images of a (possibly multi-HDU) single FITS file.

If image is multi-hdu, psf and weight can either be multi hdu or lists of individual files.

In any case, they are matched in order and HDUs not containing images (two dimensional arrays) are ignored.

Parameters

  • image – The filename of the FITS file containing the image(s)

  • psf – psf file or list of psf files

  • weight – FITS file for the weight image or a list of such files

Returns

A ImageGroup representing the images

load_fits_images(images, psfs=None, weights=None, **kwargs)

Creates an image group for the given images.

Parameters

  • images (list of str) –

    A list of relative paths to the images FITS files. Can also be single string in which case,

    this function acts like load_fits_image

  • psfs (list of str) – A list of relative paths to the PSF FITS files (optional). It must match the length of image_list or be None.

  • weights (list of str) – A list of relative paths to the weight files (optional). It must match the length of image_list or be None.

Returns

A ImageGroup representing the images

Return type

ImageGroup

Raises

ValueError – In case of mismatched list of files

print_measurement_images(file=<_io.TextIOWrapper name='<stderr>' mode='w' encoding='UTF-8'>)

Print a human-readable representation of the configured measurement images.

Parameters

file (file object) – Where to print the representation. Defaults to sys.stderr