autowisp.image_calibration.overscan_methods module

Class Inheritance Diagram

A collection of overscan correction methods (see Calibrator class docs).

class autowisp.image_calibration.overscan_methods.Base(**configuration)

Bases: ABC, Processor

The minimal intefrace that must be provided by overscan methods.

abstractmethod __call__(*, raw_fname, raw_hdu, overscans, image_area, gain, split_channels=None)

Return the overscan correction and its variance for the given image.

Parameters:

• raw_fname – The raw image(s) for which to find the overscan correction. Should be dictionary of filenames if processing multi-channel dataset that is split in different files.

• raw_hdu – The HDU to read from the raw file. Int or dict indexed by channel name.

• overscans – A list of the areas on the image to use when determining the overscan correction. Each area is specified as dict(xmin = <int>, xmax = <int>, ymin = <int>, ymax = <int>) For multi-channel data the coordinates are for the un-split image.

• image_area – The area in raw_image for which to calculate the overscan correction. The format is the same as a single overscan area.

• gain – The value of the gain to assume for the raw image (electrons/ADU).

• split_channels – See Calibrator.

Returns:

Dictionary with items:

• correction: A 2-D numpy array with the same resolution

  as the image_area giving the correction to subtract from each pixel.

• variance: An estimate of the variance in the

  overscan_correction entries (in ADU).

Return type:

dict

abstractmethod document_in_fits_header(header)

Document last overscan correction by updating given FITS header.

class autowisp.image_calibration.overscan_methods.Median(reject_threshold=5.0, max_reject_iterations=10, min_pixels=100, require_convergence=False)

Bases: Base

Correction is median of all overscan pixels with iterative outlier reject.

The correction is computed as the median of all overscan pixels. After that, pixels that are too far from the median are excluded and the process starts from the beginning until no pixels are rejected or the maximum number of rejection iterations is reached.

Public attributes exactly match the __init__() arguments.

__call__(*, raw_image, overscans, image_area, gain, split_channels=None)

See Base.__call__

__init__(reject_threshold=5.0, max_reject_iterations=10, min_pixels=100, require_convergence=False)

Create a median ovescan correction method.

Parameters:

• reject_threshold – Pixels that differ by more than reject_threshold standard deviations from the median are rejected at each iteration.

• max_reject_iterations – The maximum number of outlier rejection iterations to perform. If this limit is reached, either the latest result is accepted, or an exception is raised depending on require_convergence.

• require_convergence – If this is False and the maximum number of rejection iterations is reached, the last median computed is the accepted result. If this is True, hitting the max_reject_iterations limit throws an exception.

• min_pixels – If iterative rejection drives the number of acceptable pixels below this value an exception is raised.

Returns:

None

Notes

Initializes the following private attributes to None, which indicate the state of the last overscan correction calculation:

_last_num_reject_iter: The number of rejection iterations

used by the last overscan correction calculation.

_last_num_pixels: The number of unrejected pixels the last

overscan correction was based on.

_last_converged: Did the last overscan calculation converge?

document_in_fits_header(header)

Document the last calculated overscan correction to header.

Notes

Adds the following keywords to the header:

OVSCNMTD = Iterative rejection median
           / Overscan correction method

OVSCREJM = ###
           / Maximum number of allowed overscan rejection
           iterations.

OVSCMINP = ###
           / Minimum number of pixels to base correction on

OVSCREJI = ###
           / Number of overscan rejection iterations applied

OVSCNPIX = ###
           / Actual number of pixels used to calc overscan

OVSCCONV = T/F
           / Did the last overscan correction converge

Parameters:

header – The FITS header to add the keywords to.

Returns:

None