NAME

seepsf -- convert a sampled PSF lookup table to a PSF image

USAGE

seepsf psfimage image

PARAMETERS

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 .

DESCRIPTION

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.

EXAMPLES

1. Compute the output PSF in image scale coordinates of PSF function for image dev$ypix.

    da> seepsf ypix.psf.3 ypixpsf

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

TIME REQUIREMENTS

BUGS

SEE ALSO

datapars,daopars,psf