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offsets stsdas.analysis.dither



offsets -- Builds a set of 4 cross-correlation images from a single multi-group WFPC image and a multi-group reference WFPC image.


offsets image refimage output


image [file name list/template]
List of input 4-group WFPC images.
refimage [file name]
Input 4-group WFPC reference image.
output [file name list/template]
List of base names for the output cross-correlation images. For each entry in the input list, 4 cross-correlation images are generated. Each of these images will have its name built by appending "_gN" to the base name, where N is the group number.
(coeffs = "header") [string]
Geometrical correction coefficient type used by the drizzle task. Acceptable values are "header" and "". The empty value implies that no geometrical correction takes place.
(cdriz = "") [pset]
Pset with crossdriz parameters.
(tempdir = "tmp$") [path name]
Path to directory where temporary images and tables are kept.
(verbose = yes) [boolean]
Print log of what is beign done ?


This task is a simple script that calls the crossdriz task 4 times in sequence, to process the 4 groups in a single WFPC image. It supports image lists/templates as well. In this case the input and output lists must be paired (one output image for each input image). Only one reference image can be input, and the resulting cross-correlation images will all be in reference to that single image.

This task is appropriate when one has WFPC2 images which are shifted with respect to one another, or shifted and rotated by at most a small angle.


The following line takes the output files from precor (which appends _obj to input file names) and cross-correlates images from positions 2,3,4 with an image from position 1. The output file naming convention chosen here displays the images used in the cross-correlation. The default settings are used, so the images will be drizzled before cross-correlation. This is appropriate in the case of WFPC2 when the likely shifts are more than a few pixels, and geometric distortion in WFPC2 will therefore reduce the cross-correlation if not removed.

di> offset pos2_obj,pos3_obj,pos4_obj pos1_obj pos2x1,pos3x1,pos4x1



This task was written by I.Busko in collaboration with A. Fruchter



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