-- New Image Registration Task

New Image Registration Task

A new task for registering 1 and 2 dimensional images using cross-correlation techniques, xregister, has been released with IRAF 2.10.3BETA. xregister computes the x and y shifts required to register a list of input images to a reference image by finding the position of the peak of the input image reference image cross-correlation function, then performs the shift. xregister is designed to register 1 and 2 dimensional images which have the same size and pixel scale, are shifted relative to each other by simple translations in x and y, and contain at least one feature in common that will produce a peak in the computed cross-correlation function. These features may be point sources like stars, extended sources with well-defined centers like galaxies, or diffuse features like HII regions.

xregister permits the user to define starting x and y shifts either by inputting them directly or by inputting the coordinates in each image of a feature common to all the images, to fit and subtract the background before computing the cross-correlation function, to compute the cross-correlation function directly or using fourier techniques, and to compute the position of the peak of the cross-correlation function using a variety of algorithms. The user can also select the interpolant type and boundary extensions algorithm to be used to compute the shifted output image.

xregister can be run non-interactively or interactively. In non-interactive mode the parameters are set at task startup and the input images are processed sequentially. In interactive mode the user can mark the regions to be used to compute the cross-correlation function on the image display, define the initial shifts from the reference image to the input image on the image display, show or set the data and algorithm parameters, compute, recompute, and plot the cross-correlation function, experiment with the various peak fitting algorithms, and overlay row and column plots of the input and reference images with and without the initial or computed shifts factored in.

xregister is installed in the images package. Users who have not yet upgraded to IRAF 2.10.3BETA or who are running IRAF on platforms for which IRAF 2.10.3BETA is not yet available, can acquire the new task by retrieving and installing the external layered package nmisc from our FTP archive.

Lindsey Davis

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