opticam.noise

Functions

get_source_photons(N_source, gain)	Get the number of source photons.
get_sky_photons_per_pixel(n_sky, gain)	Get the number of sky photons per pixel.
get_sky_stderr(N_source, N_pix, n_sky, gain)	Get the standard error (in magnitudes) of the sky noise.
get_shot_stderr(N_source, gain)	Get the standard error (in magnitudes) of the shot noise.
get_dark_stderr(N_source, N_pix, dark_flux, gain)	Get the standard error (in magnitudes) of the dark current noise.
get_read_stderr(N_source, N_pix, gain)	Get the standard error (in magnitudes) of the readout noise.
snr(N_source, N_pix, n_sky, dark_flux, gain)	The (simplified) S/N ratio equation or CCD Equation (see Chapter 4.4 of Handbook of CCD Astronomy by Howell, 2006).
snr_stderr(N_source, N_pix, n_sky, dark_flux, gain)	The standard error (in magnitudes) on the CCD Equation (see Chapter 4.4 of Handbook of CCD Astronomy by Howell,
get_noise_params(file, catalog, background, psf_params)	Get the noise values of a science image.
get_snrs(file, background, catalog, psf_params)	Get the S/N ratios for the cataloged sources in a science image.
characterise_noise(file, background, catalog, psf_params)	Characterise the expected noise from an image and compare it to the measured noise for a number of cataloged

Module Contents

opticam.noise.get_source_photons(N_source, gain)

Get the number of source photons.

Parameters

N_sourcefloat | NDArray

The number of source counts.

gainfloat

The gain.

Returns

float

The number of source photons.

Parameters:

• N_source (float | numpy.typing.NDArray)

• gain (float)

Return type:

float | numpy.typing.NDArray

opticam.noise.get_sky_photons_per_pixel(n_sky, gain)

Get the number of sky photons per pixel.

Parameters

n_skyfloat

The sky counts per pixel.

gainfloat

The gain.

Returns

float

The number of sky photons per pixel.

Parameters:

• n_sky (float)

• gain (float)

Return type:

float

opticam.noise.get_sky_stderr(N_source, N_pix, n_sky, gain)

Get the standard error (in magnitudes) of the sky noise.

Parameters

N_sourcefloat

The total number of source counts.

N_pixint

The number of aperture pixels.

n_skyfloat

The number of sky counts per pixel.

gain: float

The detector gain.

Returns

float

The standard error (in magnitudes) of the sky noise.

Parameters:

• N_source (float)

• N_pix (float)

• n_sky (float)

• gain (float)

Return type:

float

opticam.noise.get_shot_stderr(N_source, gain)

Get the standard error (in magnitudes) of the shot noise.

Parameters

N_sourcefloat

The total number of source counts.

gain: float

The detector gain.

Returns

float

The standard error (in magnitudes) of the shot noise.

Parameters:

• N_source (float)

• gain (float)

Return type:

float

opticam.noise.get_dark_stderr(N_source, N_pix, dark_flux, gain)

Get the standard error (in magnitudes) of the dark current noise.

Parameters

N_sourceQuantity

The total number of source counts.

N_pixint

The number of aperture pixels.

dark_currQuantity

The number of dark current electrons per pixel per unit time.

t_exp: Quantity

The exposure time.

gain: Quantity

The detector gain.

Returns

float

The standard error (in magnitudes) of the dark current noise.

Parameters:

• N_source (float)

• N_pix (float)

• dark_flux (float)

• gain (float)

Return type:

float

opticam.noise.get_read_stderr(N_source, N_pix, gain)

Get the standard error (in magnitudes) of the readout noise.

Parameters

N_sourcefloat

The total number of source counts.

N_pixfloat

The number of aperture pixels.

gain: float

The detector gain.

Returns

float

The standard error (in magnitudes) of the readout noise.

Parameters:

• N_source (float)

• N_pix (float)

• gain (float)

Return type:

float

opticam.noise.snr(N_source, N_pix, n_sky, dark_flux, gain)

The (simplified) S/N ratio equation or CCD Equation (see Chapter 4.4 of Handbook of CCD Astronomy by Howell, 2006).

Parameters

N_sourcefloat | NDArray

The total number of source counts.

N_pixint

The number of aperture pixels.

n_skyfloat

The number of sky counts per pixel.

dark_fluxfloat

The dark current’s “flux” contribution per pixel.

gain: float

The detector gain.

Returns

float | NDArray

The S/N ratio.

Parameters:

• N_source (float | numpy.typing.NDArray)

• N_pix (float)

• n_sky (float)

• dark_flux (float)

• gain (float)

Return type:

float | numpy.typing.NDArray

opticam.noise.snr_stderr(N_source, N_pix, n_sky, dark_flux, gain)

The standard error (in magnitudes) on the CCD Equation (see Chapter 4.4 of Handbook of CCD Astronomy by Howell, 2006).

Parameters

N_sourcefloat | NDArray

The total number of source counts.

N_pixfloat

The number of aperture pixels.

n_skyfloat

The number of sky counts per pixel.

dark_fluxfloat

The dark current’s “flux” contribution per pixel.

gain: float

The detector gain.

Returns

float | NDArray

The standard error (in magnitudes) on the S/N ratio.

Parameters:

• N_source (float | numpy.typing.NDArray)

• N_pix (float)

• n_sky (float)

• dark_flux (float)

• gain (float)

Return type:

float | numpy.typing.NDArray

opticam.noise.get_noise_params(file, catalog, background, psf_params)

Get the noise values of a science image.

Parameters

filestr

The path to the science image.

catalogQTable

The source catalog corresponding to the science image.

backgroundBaseBackground | Callable

The background estimator.

psf_paramsDict[str, float]

The PSF parameters.

Returns

Tuple[NDArray, NDArray, float, float, float, float]

The fluxes, flux errors, number of aperture pixels, backgorund counts/pixel, dark flux, and gain.

Parameters:

• file (str)

• catalog (astropy.table.QTable)

• background (opticam.background.global_background.BaseBackground | Callable)

• psf_params (Dict[str, float])

Return type:

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

opticam.noise.get_snrs(file, background, catalog, psf_params)

Get the S/N ratios for the cataloged sources in a science image.

Parameters

filestr

The path to the science image.

backgroundBaseBackground | Callable

The background estimator.

catalogQTable

The source catalog corresponding to the science image.

psf_paramsDict[str, float]

The PSF parameters.

Returns

NDArray

The S/N for each source. Sources are ordered as they appear in catalog.

Parameters:

• file (str)

• background (opticam.background.global_background.BaseBackground | Callable)

• catalog (astropy.table.QTable)

• psf_params (Dict[str, float])

Return type:

numpy.typing.NDArray

opticam.noise.characterise_noise(file, background, catalog, psf_params)

Characterise the expected noise from an image and compare it to the measured noise for a number of cataloged sources.

Parameters

filestr

The file path to the science image.

backgroundBaseBackground | Callable

The background estimator.

catalogQTable

The source catalog corresponding to the science image.

psf_paramsDict[str, float]

The PSF parameters.

Returns

Dict[str, NDArray]

The noies properties.

Parameters:

• file (str)

• background (opticam.background.global_background.BaseBackground | Callable)

• catalog (astropy.table.QTable)

• psf_params (Dict[str, float])

Return type:

Dict[str, numpy.typing.NDArray]