Refmagefindpars: Source finding parameters for the reference image
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 settings apply only to source finding in the reference images.
These parameters control the operation of the algorithm that extracts
sources from the reference image (if specified) as called by TWEAKREG: Image Alignment.
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 parameterskysigma
. 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
and4+8
are equivalent to settingdqbits
to 12.Settingdqbits
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 ofNone
will turn off the use of image’s DQ array for source finding.In order to reverse the meaning of thedqbits
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), setdqbits
to~4+8
, or~4,8
. To obtain the same effect with anint
input value (except for 0), enter -(4+8+1)=-13. Following this convention, adqbits
string value of'~0'
would be equivalent to settingdqbits=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
andsharphi
are designed to eliminate brightness maxima that are due to bad pixels rather than to astronomical objects. Only sources with sharpness above thesharplo
value will be selected.- sharphi: float (Default = 1.0)
sharplo
andsharphi
are designed to eliminate brightness maxima that are due to bad pixels rather than to astronomical objects. Only sources with sharpness below thesharphi
value will be selected.- roundlo: float (Default = -1.0)
roundlo
androundhi
are designed to eliminate brightness maxima that are due to bad rows or columns, rather than to astronomical objects. Only sources with roundness above theroundlo
value will be selected.- roundhi: float (Default = 1.0)
roundlo
androundhi
are designed to eliminate brightness maxima that are due to bad rows or columns, rather than to astronomical objects. Only sources with roundness below theroundhi
value will be selected.
- drizzlepac.refimagefindpars.help(file=None)
Print out syntax help for running
refimagefindpars
.- Parameters:
- filestr (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.