Imagefindpars: Source finding parameters

This interface provides a mechanism for setting the parameters used by the built-in source finding algorithm based on the published algorithms used by DAOFIND.

These parameters control the operation of the algorithm that extracts sources from the image as called by TWEAKREG: Alignment of Images. The algorithm implemented follows the concepts defined by DAOFIND (without actually using any DAOFIND code).

Attributes:
computesig: bool (Default = True)

This parameter controls whether or not to automatically compute a sigma value to be used for object identification. If set to True, then the value computed will override any user input for the parameter skysigma. The automatic sigma value gets computed from each input exposure as:

\sigma = \sqrt{2\left|mode\right|}

This single value will then be used for object identification for all input exposures.

skysigma: float (Default = 0.0)

The standard deviation of the sky pixels. This value will only be used if computesig is False.

conv_width: float (Default = 3.5)

The convolution kernel width in pixels. Recommended values (~2x the PSF FWHM): ACS/WFC & WFC3/UVIS ~3.5 pix and WFC3/IR ~2.5 pix.

peakmin: float, None (Default = None)

This parameter allows the user to select only those sources whose peak value (in the units of the input image) is greater than this value.

peakmax: float, None (Default = None)

This parameter allows the user to select only those sources whose peak value (in the units of the input image) is less than this value.

threshold: float (Default = 4.0)

The object detection threshold above the local background in units of sigma.

nsigma: float (Default = 1.5)

The semi-major axis of the Gaussian convolution kernel used to compute the density enhancement and mean density images in Gaussian sigma.

ratio: float (Default = 1.0)

The ratio of the sigma of the Gaussian convolution kernel along the minor axis direction to the sigma along the major axis direction. For a circularly-symmetric kernel use ratio = 1.0.

theta: float (Default = 0.0)

The position angle (degrees) of the major axis of the Gaussian convolution kernel. Theta is measured counter-clockwise from the x axis.

fluxmin: float, None (Default = None)

This parameter allows the user to select only those sources whose total flux (in the units of the input image) is greater than this value.

fluxmax: float, None (Default = None)

This parameter allows the user to select only those sources whose total flux (in the units of the input image) is less than this value.

dqbits: int, str, None, optional (Default = None)

Integer sum of all the DQ bit values from the input image’s DQ array that should be considered “good” when building masks for source finding. For example, if pixels in the DQ array can be combinations of 1, 2, 4, and 8 flags and one wants to consider DQ “defects” having flags 2 and 4 as being acceptable for source finding, then dqbits should be set to 2+4=6. Then a DQ pixel having values 2,4, or 6 will be considered a good pixel, while a DQ pixel with a value, e.g., 1+2=3, 4+8=12, etc. will be flagged as a “bad” pixel.

Alternatively, one can enter a comma- or ‘+’-separated list of integer bit flags that should be added to obtain the final “good” bits. For example, both 4,8 and 4+8 are equivalent to setting dqbits to 12.

Setting dqbits to 0 will make all non-zero pixels in the DQ mask to be considered “bad” pixels, and the corresponding image pixels will not be used for source finding.
The default value of None will turn off the use of image’s DQ array for source finding.
In order to reverse the meaning of the dqbits parameter from indicating values of the “good” DQ flags to indicating the “bad” DQ flags, prepend ‘~’ to the string value. For example, in order not to use pixels with DQ flags 4 and 8 for source finding and to consider as “good” all other pixels (regardless of their DQ flag), set dqbits to ~4+8, or ~4,8. To obtain the same effect with an int input value (except for 0), enter -(4+8+1)=-9. Following this convention, a dqbits string value of '~0' would be equivalent to setting dqbits=None.
use_sharp_round: bool (Default = False)

This parameter controls whether or not to enable selection of sources based on their sharpness and roundness statistics.

sharplo: float (Default = 0.2)

sharplo and sharphi are designed to eliminate brightness maxima that are due to bad pixels rather than to astronomical objects. Only sources with sharpness above the sharplo value will be selected.

sharphi: float (Default = 1.0)

sharplo and sharphi are designed to eliminate brightness maxima that are due to bad pixels rather than to astronomical objects. Only sources with sharpness below the sharphi value will be selected.

roundlo: float (Default = -1.0)

roundlo and roundhi are designed to eliminate brightness maxima that are due to bad rows or columns, rather than to astronomical objects. Only sources with roundness above the roundlo value will be selected.

roundhi: float (Default = 1.0)

roundlo and roundhi are designed to eliminate brightness maxima that are due to bad rows or columns, rather than to astronomical objects. Only sources with roundness below the roundhi value will be selected.

drizzlepac.imagefindpars.getHelpAsString(docstring=False, show_ver=True)

return useful help from a file in the script directory called __taskname__.help

drizzlepac.imagefindpars.help(file=None)

Print out syntax help for running astrodrizzle

Parameters:

file : str (Default = None)

If given, write out help to the filename specified by this parameter Any previously existing file with this name will be deleted before writing out the help.