Name
photfits - photometry measurement
Synopsis
photfits [options] <cubes...>
Description
photfits computes the flux in ADU inside a specified disk
in an image. photfits can also estimate the background
inside a ring cented on the same point, given an internal
and external radius.
photfits accepts jokers on the command-line, it will com-
pute the photometry at the indicated point in all planes
of all given cubes.
photfits can also try to detect by itself all bright peaks
in an image, by using the same algorithm implemented in
detpeak.
Photometry Options
-x x_center -y y_center
specifies a center for the disk within which the
photometry will be computed (can be floating point
values). These options are useless when using auto-
matic peak detection.
-r radius
specifies a radius in which the flux will be com-
puted (can be a floating point value).
-b 'r_int r_ext'
specifies the internal and external radii for the
background estimation. The center of the ring will
be the same as the above disk center.
-m to require a background estimation with a median
filtering, default method uses a direct average.
Peak Detection Options
-d Activate automatic peak detection.
-f r1 r2 r3
Specify 3 radii for fine positioning after initial
detection. See the detpeak man page about how to
set this option and the related algorithm.
-l Use this option to smear out the image with a low-
pass filter before launching peak detection.
-s threshold
Specify a threshold value for a sigma detection of
the peaks.
Algorithm
For the flux computation, The output is simply the sum of
all pixel values found to be within the disk (including
the border). If a background had been estimated per pixel,
it is then subtracted from each pixel before accumulation.
For background estimation, 2 methods are offered. In both
cases, a list of all pixels found to be in the ring is
first constructed. The difference between the average
(default) and the median (-m option) is the following:
In the case of an average estimation, the background is
simply estimated as the average pixel value of the pixels
found in the ring.
In the case of the median estimation, the found pixel val-
ues are first sorted, the background is then estimated as
an average of the 3 or 4 central values in the sorted
array (whether the number of found pixels is odd or even).
This method h.PPs getting rid of spurious pixel values
that can occur in the ring. Note that in this case, a
minimum of 60 pixels has to be found to perform a back-
ground estimation.
Example
photfits -x 127.45 -y 131.65 -r 5.12 -b '5.2 20.4' -m
*.fits
would compute a flux in a circle centered on (127.45
131.65), of radius 5.12, and estimate a background in a
ring centered on the same point with radii (5.2 20.4)
using a median method.
Files
Files shall all comply with FITS format
See Also
encircl, stcube, strehl, fwhm, detpeak
Bugs
It would be nice to have other means of defining the zone
into which the background is estimated.
To be added: the possibility to give a list of disks in
which the flux has to be estimated, with a list of associ-
ated background definitions.