seepsf psfimage image
psfimage
The list of input PSF images computed by the PSF task.
Each PSF image consists of the parameters of a 2D analytic function
stored in the image header and an optional sampled lookup table of residuals
from that fit stored in the image pixels.
image
The list of output PSF images consisting of the sum of the analytic function
and the residuals in the lookup table. There must be one output PSF image
for each input PSF image.
dimension = INDEF
The dimensions of the output PSF image. By default image is a 2D image
with dimensions of N by N where N = 2 * nint (psfrad / scale) + 1 with the
same scale as the original image from which psfimage was derived.
Psfrad is the PSF fitting radius stored in the psfimage image
header parameter "PSFRAD". Scale is the image scale stored in
the image header parameter "SCALE".
xpsf = INDEF
The x coordinate of the output PSF.
Xpsf is only used if psfimage was computed
with the variable PSF parameter varorder in the DAOPARS task
set to > 0.
ypsf = INDEF
The y coordinate of the output PSF.
Ypsf is only used if psfimage was computed
with the variable PSF parameter varorder in the DAOPARS task
set to > 0.
magnitude = INDEF
The intensity scale of the output PSF. By default the intensity scale
is set by the magnitude of the first star
used by the PSF task to compute psfimage.
This parameter is stored in the keyword "PSFMAG" in psfimage.
SEEPSF takes the input PSF psfimage computed by the PSF task, consisting of the parameters of a 2D analytic function stored in the image header and an optional lookup table of residuals from the fit stored in the image pixels, and computes an output PSF, image, consisting of the sum of the analytic function and the residuals.
By default image is a 2D image of dimensions N by N where N = 2 * nint (psfrad) + 1 and the scale of image is the same as the scale of the original image from which psfimage was derived. If dimension is greater or less than N then the output PSF is block-averaged or subsampled with respect to the original image. Psfrad is the value of the psf radius parameter in the task DAOPARS used to compute psfimage and is stored in the psfimage header parameter "PSFRAD".
If psfimage was computed with the variable PSF parameter varorder set to > 0, then image is computed at a point (xpsf, ypsf) defined relative to the original image. By default image is computed at the centroid of the PSF defined by the psfimage header parameters "XPSF" and "YPSF".
The intensity scale of image is determined by the value of magnitude relative to the magnitude of the PSF. By default the output PSF has the magnitude of the first PSF star stored in the psfimage header parameter "PSFMAG".
SEEPSF is most commonly used for visualizing the PSF in image scale coordinates and checking the form of any variability as a function of position. However image can also be used as input to other image processing program, for example it might be used as the kernel in a convolution operation.
1. Compute the output PSF in image scale coordinates of PSF function for image N4147.
da> seepsf n4147.psf.3 n4147psf
2. Compute the output PSF in image scale coordinates of the variable PSF for the image m92b at position (113.63,50.48) pixels relative to the original image.
da> seepsf m92b.psf.2 m92psf xpsf=113.63 ypsf=50.48
psf,