- 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.