Simple aperture photometry:¶
- -L, --input-list <input coordinate list file>
- Name of the input coordinate list file.
- --col-xy <colx>,<coly>
- Column indices for centroid coordinates. The coordinates read from this
file follows the native coordinating scheme (which is not the same as e.g.
in IRAF), namely the lower-left corner of the lower-left pixel has the
coordinate of (0,0) while the center of the lower-left pixel has the
coordinate of (0.5,0.5). Programs like IRAF use the coordinate (1,1) for
the center of the lower-left pixel.
- --col-ap <A1>,<A2>,...
- Column indices for various apertures. In each such column, there must be
three colon-separated number, for the radius of the aperture, inner radius
for the background annulus and the thickness of the annulus, respectively.
This option is not mandatory, all of the objects can be measured with the
same set of apertures, see also -a|--apertures for more
- --col-id <identifier column>
- Column index for object identifier.
- --col-mag, --col-magnitude <magnitude column>
- Column index for reference magnitude.
- --col-col, --col-color <color column>
- Column index for photometric color.
- --col-err, --col-error <magnitude error column>
- Column index for magnitude uncertainty.
- -z, --zoom <zoom level>
- Mutiply both the input centroid coordinates and aperture/annulusradii by
the given integer factor.
- --serial <serial>
- Serial identifier for the whole photometry procedure. Can be any arbitrary
string and used only in the formatted output (see -F|--format for
- -F, --format, --format-output
- List of output format tags. The formatted (user-friendly) output
photometry contains a few columns containing the data related to the
object, which followed by a the per-aperture photometry results. See
"Format tags" for the list of format tags used here.
- --nan <nan-string>
- String which is used to denote bad photometry. By default, objects on
which photometry cannot be performed (due to various reasons, e.g. the
object is off from the image, the background level cannot be determined or
there are bad pixels in the aperture itself), are marked by a simple dash
('-') in the output file.
- -M, --input-mask <image file>
- Input mask file to co-add to the mask of the input image. Useful for
marking pixels to be ignored from the photometry process beyond the ones
which are previously marked in the input image.
- -a, --aperture, --apertures <list of circular
- List of circular apertures to be involved in the photometry. Each circular
aperture is defined by three numbers: the radius of the aperture, and the
inner radius and "thickness" of the annulus used for sky
background estimation. The aperture specifications must be spearated by
commas while these three numbers must be separated by colons. E.g. to
perform aperture photometry on a series of apertures with a radius of 1.5,
2.0 and 2.5 pixels, where all of the annuli have an inner and outer radius
of 6.5 and 12 pixels (i.e. the thickness is 5.5 pixels), one should write
1.5:6.5:5.5,2.0:6.5:5.5,2.5:6.5:5.5 as an argument for this option.
- -a, --aperture, --apertures <list of simple
- List of polygon shaped apertures. Polygons can only be simple (i.e.
non-intersection) or weakly simple polygons which are defined throughout
the form of P[x1,y1,...,xn,yn] or polygon[x1,y1,...,xn,yn]. The
(x,y)=(0,0) point always refer to the aperture centroid as read from the
input list (see --input-list above). There are two types of
pre-defined simple polygons which is useful in astronomical image
processing. The first definition is Q[R,n,alpha] or regular[R,n,alpha]
which implies a regular polygon having n sides and an area equivalent to a
circle with a radius of R and the polygon is rotated w.r.t the xy-plane by
"alpha" degrees. In the asymptotic limit of n -> infinity,
this aperture is equivalent to a circular aperture. The second type is
T[R,n,dx,dy] or trail[R,n,dx,dy] where this definition implies a nearly
oval racetrack-shaped aperture with a curvature radius of R, a net length
of L=sqrt(dx^2+dy^2), the round part is approximated by a regular n-gon
and the whole shape is rotated w.r.t the x+ axis as defined by the (dx,dy)
vector. In the limit of L -> 0, this shape is equivalent to the
aperture definition of regular[R,n,alpha]. The trail[....] shape is useful
to perform photometry on asteroid or meteoroid trails. One should note
that circular and polygon aperture definitions cannot be mixed. In
addition, it should be noted that in case of polygon-shaped apertures, the
second definition implies the inner edge of the background area and the
third definition implies the outer edge of the background area. For
instance, the aperture 3:5:5 can be ideal for point sources, the aperture
trail[3,16,3.0,4.0]:trail[5,16,3.0,4.0]:trail[10,16,3.0,4.0] can be
optimal for a asteroid trail on the same image that has a net length of
5.0 pixels and parallel with the vector (3.0,4.0). In this case, the
equivalent radius of the third part is set to 10 which is equivalent to
the 5+5=10 pixels of the radius of the outer annulus in the definition of
- -g, --gain, --gain-poly <gain polynomial>
- The polynomial describing the gain level throughout the image. Altough
during the image readout process, the electron <-> ADU conversion
ratio has a fixed value, during the calibration process when the
vignetting is strong, the ADU levels may substantially change. The
comma-separated numbers in the gain polynomial should denote the
coefficients for the monomials 1, x, y, 1/2x^2, xy, ... (the standard
order for 2 dimensional polynomial coefficients), where x and y are the
normalized coordinates (i.e. zero at the center of the image, x = +/- 1 at
the right/left edge of the image and y is scaled appropriately keeping the
aspect ratio). Note that the number of coefficients should be 1, 3, 6, 10,
... and so on, for zeroth, first, second, third... order variations,
respectively.Specifying zero or negative gain will imply an
"infinitely large" gain, thus data are treated as being affected
only by instrumental noise and lack intrinsic photon noise.
- --gain-vmin <minimal gain>
- The minimal value for the gain level. If the polynomial describing the
spatial gain variations is evaluated on the regular image domain and
yielded a smaller value than this given number, this will be used as gain
level. In certain optical systems, the vignetting can be well described by
second-order polynomial coefficients except at the very corners of the
image. In such a situation this minimal gain is quite useful.
- --mag-flux <mag>,<flux>
- Magnitude - flux conversion level. The specified magnitude will be
equivalent to the specified flux level.
- --sky-fit <sky fitting parameters>
- This argument is followed by a set of parameters for the sky (i.e.
background level) fitting algorithm. See "Sky fitting
parameters" below for more details.
- --aperture-mask-ignore <list of masks>
- This switch is followed by a space separated list of standard masks which
should be ignored if such a pixel is marked so in the aperutre. In
practice, it might be useful to put saturated objects into the set of
- -o, --output <output photometry file>
- Name of the output file containing the results of the aperture photometry.
The format and content of this file can be arbitrarily set, see
- --output-raw-photometry <output raw photometry>
- Name of the output file containing the all of the low-level photometric
information in a fixed format. From this file, one can derive all of the
quantities which are written to the "normal" output photometry
file. The main purpose of this file is to be an input for image
subtraction based photometry, i.e. the photometric information for the
reference image is supposed to be stored in this format and the successive
calls of `fiphot` on the subtracted residual images read this information
in order to derive the final photometric information. See the subsection
"Photometry on subtracted/convolved images" about more details
on the image subtraction based photometry.
Note that the literal "auto" argument can also be used
after the -g|--gain switch. In this case, `fiphot` tries to figure
out the gain polynomial from the GAINPOLY and GAIN keywords (in this order)
as well as the minimal value for the gain from the GAINVMIN keyword.