Step Arguments

The skymatch step uses the following optional arguments:

General sky matching parameters:

skymethod (str, default=’match’)

The sky computation algorithm to be used. Allowed values: local, global, match, global+match

match_down (boolean, default=True)

Specifies whether the sky differences should be subtracted from images with higher sky values (match_down = True) in order to match the image with the lowest sky, or sky differences should be added to the images with lower sky values to match the sky of the image with the highest sky value (match_down = False). NOTE: this argument only applies when skymethod is either match or global+match.

subtract (boolean, default=False)

Specifies whether the computed sky background values are to be subtracted from the images. The BKGSUB keyword (boolean) will be set in each output image to record whether or not the background was subtracted.

Image bounding polygon parameters:

stepsize (int, default=None)

Spacing between vertices of the images bounding polygon. The default value of None creates bounding polygons with four vertices corresponding to the corners of the image.

Sky statistics parameters:

skystat (str, default=’mode’)

Statistic to be used for sky background computations. Supported values are: mean, mode, midpt, and median.

dqbits (str, default=’~DO_NOT_USE+NON_SCIENCE’)

The DQ bit values from the input images’ DQ arrays that should be considered “good” when building masks for sky computations. See DQ flag Parameter Specification for details. The default value rejects pixels flagged as either ‘DO_NOT_USE’ or ‘NON_SCIENCE’ and considers all others to be good.

lower (float, default=None)

An optional value indicating the lower limit of usable pixel values for computing the sky. This value should be specified in the units of the input images.

upper (float, default=None)

An optional value indicating the upper limit of usable pixel values for computing the sky. This value should be specified in the units of the input images.

nclip (int, default=5)

The number of clipping iterations to use when computing sky values.

lsig (float, default=4.0)

Lower clipping limit, in sigma, used when computing the sky value.

usig (float, default=4.0)

Upper clipping limit, in sigma, used when computing the sky value.

binwidth (float, default=0.1)

Bin width, in sigma, used to sample the distribution of pixel values in order to compute the sky background using statistics that require binning, such as mode and midpt.