Name
imgen - image generation
Synopsis
imgen [commands]
Description
imgen creates images with a given pattern definition and
according parameters. Since nearly all astronomical soft-
ware packages have very extended image generation capabil-
ities, imgen is deliberately limited to very simple pat-
terns. See the commands below for pattern definitions.
In all options, whenever a reference is made to pixel
coordinates, the FITS convention is used: the first image
pixel is at coordinates (1,1) in the lower left corner of
the image. Increasing x go right, increasing y go up.
Image Generation Specifications
-x value -y value
to specify the generated image size
(NAXIS1,NAXIS2). Defaults to 256x256.
-b or --bitsperpix value
to request another pixel depth than the default
one. The default output pixel type is chosen at
compilation time: it is -32 if you did not request
anything, -64 if you requested double precision
format for internal pixel representation. Possible
values correspond to pixel depth in the FITS defi-
nition: 8, 16, 32, -32, or -64.
-o or --output name
gives a name to the output image. Default is
`out.fits'.
-S name or --ref name
gives the program a reference FITS file name which
the output image will match in size. This option
may not be used together with the -x or -y options.
Theoretical Images
-a or --airy `width max dx dy'
to create an Airy pattern, of given width (in pix-
els), maximum pixel value at the peak, and given
dx, dy offset. The offset indicates where should
the real peak be situtated from the center of the
image. dx and dy are given in pixels from the cen-
ter, axes comply with the FITS standard. Enclose
the four required parameters into simple quotes.
-g or --gauss `x-center y-center sigma'
to create a gaussian pattern centered on (x-center,
y-center) of standard deviation sigma.
-l or --lorentz `x-center y-center intensity dispersion'
to create a lorentzian pattern centered on (x-cen-
ter, y-center) with intensity and dispersion
strictly positive real numbers. the formula used is
pixel value equals intensity over one plus disper-
sion times the square of the distance of the given
pixel to the center of the distribution (x-
center,y-center).
-p `m1 m2 w0 dw pixelscale'
to generate a optical transfer function for a given
telescope and camera configuration. Enclose the 5
requested parameters into simple quotes. The
parameters are respectively:
The diameter of the primary mirror of the telescope in
meters (m1).
The diameter of the secondary mirror of the telescope in
meters (m2).
The central wavelength of observation (w0) in microns.
The filter bandwidth (dw) in microns.
The pixel scale on the sky (pixelscale) in arcseconds.
All these values can be defaulted to the ESO 3.6m la Silla
telescope, which are:
m1 = 3.60 m
m2 = 1.57 m
w0 = 2.20 um
dw = 0.30 um
pixelscale = 0.05 arcseconds
An input value of -1 means: use a default value.
OTF's are square images, only the x-size parameter will be
used to set the image size, the y-parameter being dis-
carded.
An alternate form uses long options: --otf requires the
OTF. Telescope parameters are set by --m1, --m2,
--lambda0, --dlambda, and --pixelscale.
-t `m1 m2 w0 dw pixelscale'
to generate a theoretical PSF for a given telescope
configuration. See option above, parameters are
set as for OTF.
PSF's are square images, only the x-size parameter will be
used to set the image size, the y-parameter being dis-
carded.
An alternate form uses long options: --psf requires the
PSF. Telescope options are as above for OTF: --m1, --m2,
--lambda0, --dlambda and --pixelscale.
Random Patterns
-r `U min max' or --urandom `min max'
to create an image containing noise having a uni-
form probability distribution in the pixel value
interval [min,max].
-r `G mean sigma' or --grandom `mean sigma'
to create an image containing noise having a gaus-
sian probability distribution centered around mean
and having a sigma value of sigma. The default
value for sigma is 1/sqrt(2), it will be used if a
negative value is provided.
-r `L mean dispersion' or --lrandom `mean disp'
to create an image containing noise having a
lorentzian probability distribution centered around
mean with a dispersion factor being dispersion.
The default value of 1.0 will be used for
dispersion if a negative value is provided.
Binary Patterns
-d or --bdisk `x-center y-center radius'
to create a binary disk, centered in the image at
point (x-center, y-center) , having a radius of
radius. Center coordinates and radius are not
restricted to integer values. The disk is gener-
ated as white (1) on a black (0) background. The
output can only be generated in FITS 8bit/pel for-
mat. A perfectly valid alternative long options is
--bdisk `x0 y0 r'.
-R or --brect `llx lly urx ury'
to create a binary rectangle, of lower left corner
situated in (llx, lly) and upper right corner situ-
ated in (urx, ury). The given corners are included
in the rectangle. The rectangle is generated as
white (1) on a black (0) background. The output can
only be generated in FITS 8bit/pel format. A per-
fectly valid alternative long option is --brect
`llx lly urx ury'.
-u or --uniform value
to create a uniform (flat) image of given pixel
value.
--poly2 `c0 c1 c2 c3 c4 c5'
This option will create an image of a 2nd degree
polynomial in x and y. The coefficients given are
in the following order:
c[0] * x^2
c[1] * y^2
c[2] * x * y
c[3] * x
c[4] * y
c[5] * 1
The coordinate system used for the polynomial is the one
used by the FITS convention: pixel (1,1) is at the bottom
left of the image, x-axis increasing from left to right
and y-axis increasing from bottom to top.
-P or --polygon filename
This option allows to create binary maps that con-
tain polygons. This option expects a filename in
input on the command-line. This file contains the
definition of all the polygons that should be cre-
ated in the binary map. The format is the follow-
ing:
* The polygon definition file is an ASCII file.
* In this file, blank lines or lines starting with a
hash (#) are simply ignored (comments).
* Polygons are given by an ordered list of vertices.
Each vertice is defined by a set of two coordinates
in floating-point or integer format (both are sup-
ported). The polygon is drawn starting from the
first point given in the list (from left to right),
ending with the last point on the line and coming
back to the first point.
* Polygons must have at least 3 vertices. Special
cases are not tested, e.g. when all points are
aligned.
Here is an example of a polygon definition file, defining
some rectangles in a 256x256 binary map:
#
# Example of polygon definition file.
#
128 10 246 128 128 246 10 128
10 10 90 10 90 90 10 90
150 30 210 40 210 240 150 230
20.4 217.25 82.31 233.98 68.67 195.2 32.0 175.6 14 190
# end of file
To create the binary map from this file (assuming you
named it poly.def), use:
% imgen -P poly.def
Files
Input/output files shall all comply with FITS format.
Examples
To create an image of size 512x512 containing pixels hav-
ing all the same pixel value: 19.97, named `dummy.fits',
and a pixel resolution of -32 (IEEE floating point values,
usually the default pixel depth) you would type:
% imgen -u 19.97 -o dummy.fits -x 512 -y 512
To create an Airy pattern in an image of size 64x64, pixel
depth of 8 bits/pixel, centered at (-10,+15) from the
image center (in this case on pixel 22,47), with a width
of 11 pixels and a maximum pixel value of 1000.0, having
the default output name `out.fits', you would type:
% imgen -a `11 1000.0 -10 +15' -b 8 -x 64 -y 64
To create an image containing a 2d gaussian signal cen-
tered on pixel 125,135 with a sigma being 5.0, an image of
size of 256x256 (default) and a pixel depth of -32
bits/pixel (default), named `gauss.fits', you would type:
% imgen -g `125 135 5.0' -o gauss.fits
To create an image containing a 2d lorentzian signal cen-
tered on pixel 128,128, an image size of 256x256
(default), an intensity of 50.0, a dispersion factor of
1.414, a pixel depth of -32 (default), and a default file
name ('out.fits'), you would type:
% imgen -l `128 128 50.0 1.414'
To create an image containing uniform random noise with
pixel values between -10.0 and 10.0, with all default val-
ues:
% imgen -r `U -10.0 10.0'
To create an image containing noise with a gaussian proba-
bility density centered around 1.0, a sigma value of 6.0,
with all default values:
% imgen -r `G 1.0 6.0'
To create an image containing noise with a lorentzian
probability density centered around 1.0, a dispersion
value of 50.0, with all default values:
% imgen -r `L 1.0 50.0'
To create an OTF for a telescope having a primary mirror
of 8.2m diameter, a secondary of 2.4m diameter, at
lambda0=2.2 microns, and dlambda 0.1 microns, and a pixel
scale of 0.2 arcsec/pixel, with all default values:
% imgen -p `8.2 2.4 2.2 0.1 0.2'
See Also
ccube, setpix