opticam.photometers

Classes

BasePhotometer	Base class for performing photometry on OPTICAM catalogues.
AperturePhotometer	A photometer for performing aperture photometry.
OptimalPhotometer	A photometer that implements the optimal photometry method described in Naylor 1998, MNRAS, 296, 339-346.

Functions

get_optimal_weights(var, position, psf_major, ...)	Compute the optimal weight for each pixel in an image.
get_optimal_flux_and_error(image, bias_var, dark_var, ...)	Compute the optimal flux and its error.
get_growth_curve(image, x_centroid, y_centroid, r_max)	Compute the growth curve for a point in an image.

Module Contents

class opticam.photometers.BasePhotometer(forced=False, source_matching_tolerance=5.0, local_background_estimator=None)

Bases: abc.ABC

Base class for performing photometry on OPTICAM catalogues.

Parameters:

• forced (bool)

• source_matching_tolerance (float)

• local_background_estimator (opticam.background.local_background.BaseLocalBackground | Callable | None)

forced = False

source_matching_tolerance = 5.0

local_background_estimator = None

abstractmethod compute(image, bias_var, dark_var, flat_var, background_rms, cat_coords, image_coords, psf_params, read_noise)

Compute the fluxes of the catalogued sources from the given image.

Parameters

imageNDArray

The image. If self.local_background_estimator is undefined, this image will be background subtracted.

bias_varfloat | NDArray

The bias correction variance term.

dark_varfloat | NDArray

The dark noise correction variance term.

flat_varfloat | NDArray

The flat-field correction variance term.

background_rmsNDArray | None

The background RMS. May be None if self.local_background_estimator is defined.

cat_coordsNDArray

The source coordinates in the catalogue.

image_coordsNDArray | None

The source coordinates in the image. If match_sources is True, this will be used to match sources in the image to sources in the catalogue.

psf_paramsDict[str, float]

The PSF parameters for the camera used to take the image. This parameter is defined in the catalogue and has the following keys: ‘semimajor_sigma’ (in pixels), ‘semiminor_sigma’ (in pixels), and ‘orientation’ (in degrees).

read_noisefloat

The detector’s read noise.

Returns

Dict[str, List]

The photometry results.

Parameters:

• image (numpy.typing.NDArray)

• bias_var (float | numpy.typing.NDArray)

• dark_var (float | numpy.typing.NDArray)

• flat_var (float | numpy.typing.NDArray)

• background_rms (numpy.typing.NDArray | None)

• cat_coords (numpy.typing.NDArray)

• image_coords (numpy.typing.NDArray | None)

• psf_params (Dict[str, float])

• read_noise (float)

Return type:

Dict[str, List]

get_position(cat_coords, image_coords, source_index, psf_params)

Get the position of a source in an image.

Parameters

cat_coordsNDArray

The source coordinates in the catalogue.

image_coordsNDArray | None

The source coordinates in the image.

source_indexint

The source index.

psf_paramsDict[str, float]

The PSF parameters for the camera used to take the image. This parameter is defined in the catalogue and has the following keys: ‘semimajor_sigma’ (in pixels), ‘semiminor_sigma’ (in pixels), and ‘orientation’ (in degrees).

Returns

NDArray

The source coordinates.

Parameters:

• cat_coords (numpy.typing.NDArray)

• image_coords (numpy.typing.NDArray | None)

• source_index (int)

• psf_params (Dict[str, float])

Return type:

numpy.typing.NDArray | None

get_closest_source(cat_coords, image_coords, source_index, psf_params)

Given a source, find the closest source in the catalogue.

Parameters

cat_coordsNDArray

The source coordinates in the catalogue.

image_coordsNDArray | None

The source coordinates in the image.

source_indexint

The source index.

psf_paramsDict[str, float]

The PSF parameters for the camera used to take the image. This parameter is defined in the catalogue and has the following keys: ‘semimajor_sigma’ (in pixels), ‘semiminor_sigma’ (in pixels), and ‘orientation’ (in degrees).

Returns

NDArray | None

The coordinates of the closest source.

Parameters:

• cat_coords (numpy.typing.NDArray)

• image_coords (numpy.typing.NDArray | None)

• source_index (int)

• psf_params (Dict[str, float])

Return type:

numpy.typing.NDArray | None

define_results_dict()

Define a results dictionary for the photometer depending on whether local_background_estimator is defined.

Returns

Dict[str, List]

The results dictionary with keys ‘flux’, ‘flux_err’. If local_background_estimator is defined, the dictionary will also contain ‘bkg’ and ‘bkg_err’.

Return type:

Dict[str, List]

pad_results_dict(results)

Pad the results dictionary with None values for flux and flux error, and background and background error if `local_background_estimator’ is defined. This is used when a source cannot be matched or its position is invalid.

Parameters

resultsDict[str, List]

The results dictionary to pad.

Returns

Dict[str, List]

The padded results dictionary.

Parameters:

results (Dict[str, List])

Return type:

Dict[str, List]

populate_results_dict(results, phot_function, image, bias_var, dark_var, flat_var, background_rms, position, psf_params, read_noise)

Populate the results dictionary with the computed flux, flux error, and background (if applicable) using the provided photometry function.

Parameters

resultsDict[str, List]

The results dictionary to populate.

phot_functionCallable

The photometry function to use for computing the flux and flux error. This function should take the image, image error, position, and PSF parameters as arguments and return the flux and flux error, and optionally the background and background error if local_background_estimator is defined.

imageNDArray

The image.

bias_varfloat | NDArray

The bias correction variance term.

dark_varfloat | NDArray

The dark noise correction variance term.

flat_varfloat | NDArray

The flat-field correction variance term.

background_rmsNDArray | None

The background RMS. May be None if self.local_background_estimator is defined.

positionNDArray

The position of the source in the image.

psf_paramsDict[str, float]

The PSF parameters for the camera used to take the image. This parameter is defined in the catalogue and has the following keys: ‘semimajor_sigma’ (in pixels), ‘semiminor_sigma’ (in pixels), and ‘orientation’ (in degrees).

read_noisefloat

The detector’s read noise.

Returns

Dict[str, List]

The updated results dictionary with the computed flux, flux error, and background (if applicable).

Parameters:

• results (Dict[str, List])

• phot_function (Callable)

• image (numpy.typing.NDArray)

• bias_var (float | numpy.typing.NDArray[numpy.float64])

• dark_var (float | numpy.typing.NDArray[numpy.float64])

• flat_var (float | numpy.typing.NDArray[numpy.float64])

• background_rms (numpy.typing.NDArray | None)

• position (numpy.typing.NDArray)

• psf_params (Dict[str, float])

• read_noise (float)

Return type:

Dict[str, List]

get_label()

Get the label of the photometer for labelling output.

Returns

str

The label.

Return type:

str

class opticam.photometers.AperturePhotometer(semimajor_axis=None, semiminor_axis=None, orientation=None, forced=False, source_matching_tolerance=5.0, local_background_estimator=None)

Bases: BasePhotometer

A photometer for performing aperture photometry.

Parameters:

• semimajor_axis (int | None)

• semiminor_axis (int | None)

• orientation (float | None)

• forced (bool)

• source_matching_tolerance (float)

• local_background_estimator (None | opticam.background.local_background.BaseLocalBackground)

semimajor_axis = None

semiminor_axis = None

orientation = None

compute(image, bias_var, dark_var, flat_var, background_rms, cat_coords, image_coords, psf_params, read_noise)

Compute the fluxes of the catalogued sources from the given image.

Parameters

imageNDArray

The image. If self.local_background_estimator is undefined, this image will be background subtracted.

bias_varfloat | NDArray

The bias correction variance term.

dark_varfloat | NDArray

The dark noise correction variance term.

flat_varfloat | NDArray

The flat-field correction variance term scaled by the square of the calibrated image.

background_rmsNDArray | None

The background RMS. May be None if self.local_background_estimator is defined.

cat_coordsNDArray

The source coordinates in the catalogue.

image_coordsNDArray | None

The source coordinates in the image. If match_sources is True, this will be used to match sources in the image to sources in the catalogue.

psf_paramsDict[str, float]

The PSF parameters for the camera used to take the image. This parameter is defined in the catalogue and has the following keys: ‘semimajor_sigma’ (in pixels), ‘semiminor_sigma’ (in pixels), and ‘orientation’ (in degrees).

read_noisefloat

The detector’s read noise.

Returns

Dict[str, List]

The photometry results.

Parameters:

• image (numpy.typing.NDArray)

• bias_var (float | numpy.typing.NDArray)

• dark_var (float | numpy.typing.NDArray)

• flat_var (float | numpy.typing.NDArray)

• background_rms (numpy.typing.NDArray | None)

• cat_coords (numpy.typing.NDArray)

• image_coords (numpy.typing.NDArray | None)

• psf_params (Dict[str, float])

• read_noise (float)

Return type:

Dict[str, List]

compute_aperture_flux(image, bias_var, dark_var, flat_var, background_rms, position, psf_params, read_noise)

Compute the aperture flux of a source in the image.

Parameters

imageNDArray

The image.

bias_varfloat | NDArray

The bias correction variance term.

dark_varfloat | NDArray

The dark noise correction variance term.

flat_varfloat | NDArray

The flat-field correction variance term scaled by the square of the calibrated image.

background_rmsNDArray | None

The background RMS. May be None if self.local_background_estimator is defined.

positionNDArray

The position of the source.

psf_paramsDict[str, float]

The PSF parameters for the camera used to take the image. This parameter is defined in the catalogue and has the following keys: ‘semimajor_sigma’ (in pixels), ‘semiminor_sigma’ (in pixels), and ‘orientation’ (in degrees).

read_noisefloat

The instrument’s read noise.

Returns

Tuple[float, float] | Tuple[float, float, float, float, float]

The flux and its error. If local_background_estimator is defined, the local background and its error are also returned.

Parameters:

• image (numpy.typing.NDArray)

• bias_var (float | numpy.typing.NDArray)

• dark_var (float | numpy.typing.NDArray)

• flat_var (float | numpy.typing.NDArray)

• background_rms (numpy.typing.NDArray | None)

• position (numpy.typing.NDArray)

• psf_params (Dict[str, float])

• read_noise (float)

Return type:

Tuple[float, float] | Tuple[float, float, float, float]

get_aperture(position, psf_params)

Parameters:

• position (numpy.typing.NDArray)

• psf_params (Dict[str, float])

Return type:

photutils.aperture.EllipticalAperture

get_aperture_area(psf_params)

Get the area of the aperture.

Parameters

psf_paramsDict[str, float],

The PSF parameters.

Returns

float

The area of the aperture.

Parameters:

psf_params (Dict[str, float])

Return type:

float

class opticam.photometers.OptimalPhotometer(forced=False, source_matching_tolerance=5.0, local_background_estimator=None)

Bases: BasePhotometer

A photometer that implements the optimal photometry method described in Naylor 1998, MNRAS, 296, 339-346.

Parameters:

• forced (bool)

• source_matching_tolerance (float)

• local_background_estimator (opticam.background.local_background.BaseLocalBackground | Callable | None)

compute(image, bias_var, dark_var, flat_var, background_rms, cat_coords, image_coords, psf_params, read_noise)

Compute the fluxes of the catalogued sources from the given image.

Parameters

imageNDArray

The image. If self.local_background_estimator is undefined, this image will be background subtracted.

bias_varfloat | NDArray

The bias correction variance term.

dark_varfloat | NDArray

The dark noise correction variance term.

flat_varfloat | NDArray

The flat-field correction variance term scaled by the square of the calibrated image.

background_rmsNDArray | None

The background RMS. May be None if self.local_background_estimator is defined.

cat_coordsNDArray

The source coordinates in the catalogue.

image_coordsNDArray | None

The source coordinates in the image. If match_sources is True, this will be used to match sources in the image to sources in the catalogue.

psf_paramsDict[str, float]

The PSF parameters for the camera used to take the image. This parameter is defined in the catalogue and has the following keys: ‘semimajor_sigma’ (in pixels), ‘semiminor_sigma’ (in pixels), and ‘orientation’ (in degrees).

read_noisefloat

The detector’s read noise.

Returns

Dict[str, List]

The photometry results.

Parameters:

• image (numpy.typing.NDArray)

• bias_var (float | numpy.typing.NDArray[numpy.float64])

• dark_var (float | numpy.typing.NDArray[numpy.float64])

• flat_var (float | numpy.typing.NDArray[numpy.float64])

• background_rms (numpy.typing.NDArray | None)

• cat_coords (numpy.typing.NDArray)

• image_coords (numpy.typing.NDArray | None)

• psf_params (Dict[str, float])

• read_noise (float)

Return type:

Dict[str, List]

compute_optimal_flux(image, bias_var, dark_var, flat_var, background_rms, position, psf_params, read_noise)

Compute the optimal flux of a source in the image as described in Naylor 1998, MNRAS, 296, 339-346.

Parameters

imageNDArray

The image.

bias_varfloat | NDArray

The bias correction variance term.

dark_varfloat | NDArray

The dark noise correction variance term.

flat_varfloat | NDArray

The flat-field correction variance term scaled by the square of the calibrated image.

background_rmsNDArray | None

The background RMS. May be None if self.local_background_estimator is defined.

positionNDArray

The position of the source in the image, given as (y, x) coordinates.

psf_paramsDict[str, float]

The PSF parameters for the camera used to take the image. This parameter is defined in the catalogue and has the following keys: ‘semimajor_sigma’ (in pixels), ‘semiminor_sigma’ (in pixels), and ‘orientation’ (in degrees).

read_noisefloat

The instrument’s read noise.

Returns

Tuple[float, float] | Tuple[float, float, float, float]

The flux and flux error. If local_background_estimator is defined, the background and its error are also returned.

Parameters:

• image (numpy.typing.NDArray)

• bias_var (float | numpy.typing.NDArray[numpy.float64])

• dark_var (float | numpy.typing.NDArray[numpy.float64])

• flat_var (float | numpy.typing.NDArray[numpy.float64])

• background_rms (numpy.typing.NDArray | None)

• position (numpy.typing.NDArray)

• psf_params (Dict[str, float])

• read_noise (float)

Return type:

Tuple[float, float] | Tuple[float, float, float, float]

opticam.photometers.get_optimal_weights(var, position, psf_major, psf_minor, psf_orientation)

Compute the optimal weight for each pixel in an image.

Parameters

varNDArray[np.float64]

The variance image.

positionNDArray[np.float64]

The position of the source.

psf_majorfloat

The semi-major axis of the PSF.

psf_minorfloat

The semi-minor axis of the PSF.

psf_orientationfloat

The orientation of the PSF in degrees.

Returns

Tuple[NDArray[np.float64], float]

The weights and the normalisation constant.

Parameters:

• var (numpy.typing.NDArray[numpy.float64])

• position (numpy.typing.NDArray[numpy.float64])

• psf_major (float)

• psf_minor (float)

• psf_orientation (float)

Return type:

Tuple[numpy.typing.NDArray[numpy.float64], float]

opticam.photometers.get_optimal_flux_and_error(image, bias_var, dark_var, flat_var, background_rms, read_noise, position, psf_params)

Compute the optimal flux and its error.

Parameters

imageNDArray[np.float64]

The background-subtracted image.

bias_varfloat | NDArray

The bias correction variance term.

dark_varfloat | NDArray

The dark noise correction variance term.

flat_varfloat | NDArray

The flat-field correction variance term scaled by the square of the calibrated image.

background_rmsfloat | NDArray[np.float64]

The background RMS. May be a scalar value or an NDArray with the same shape as image.

read_noisefloat

The instrument’s read noise.

positionNDArray[np.float64]

The source position [x, y].

psf_paramsDict[str, float]

The PSF parameters.

Returns

Tuple[float, float]

The flux and its corresponding error.

Parameters:

• image (numpy.typing.NDArray[numpy.float64])

• bias_var (float | numpy.typing.NDArray[numpy.float64])

• dark_var (float | numpy.typing.NDArray[numpy.float64])

• flat_var (float | numpy.typing.NDArray[numpy.float64])

• background_rms (float | numpy.typing.NDArray[numpy.float64])

• read_noise (float)

• position (numpy.typing.NDArray[numpy.float64])

• psf_params (Dict[str, float])

Return type:

Tuple[float, float]

opticam.photometers.get_growth_curve(image, x_centroid, y_centroid, r_max)

Compute the growth curve for a point in an image.

Parameters

imageNDArray

The image.

x_centroidfloat

The x centroid of the point.

y_centroidfloat

The y centroid of the point.

r_maxint

The maximum radius in pixels.

Returns

Tuple[NDArray, NDArray]

_description_

Parameters:

• image (numpy.typing.NDArray)

• x_centroid (float)

• y_centroid (float)

• r_max (int)

Return type:

Tuple[numpy.typing.NDArray, numpy.typing.NDArray]