Image Scaling
Phil Nelson wrote on Apr 14, 2009
I have images taken with two different cameras. The plate scales of the two sets of images are different (one camera has a scale of 1.6 arcmin/pixel while the other has a scale of 1.21 arcmin/pixel). I need to create a mosaic of the sky with these two images sets. The question is, how do I "scale" them so that the image scale is the same in both sets of images?
(An alternate way of looking at this issue... Two images overlap. One image was taken with the 1.6 arcmin/pixel plate scale and the other at the 1.21. The same two stars in the overlap region are the same distance (in arcminutes) apart on the sky but different distances (in pixels) on the two images. To truly overlap the images and create the mosaic, the pixel distance needs to be the same...)
Is/are there an IRAF package(s) that does this?
(An alternate way of looking at this issue... Two images overlap. One image was taken with the 1.6 arcmin/pixel plate scale and the other at the 1.21. The same two stars in the overlap region are the same distance (in arcminutes) apart on the sky but different distances (in pixels) on the two images. To truly overlap the images and create the mosaic, the pixel distance needs to be the same...)
Is/are there an IRAF package(s) that does this?
Mike Fitzpatrick wrote on Apr 14, 2009
Mike Fitzpatrick wrote on Apr 14, 2009
Sorry for the forgotten reply.
IMCOMBINE is the primary task you'll need, however it assumes the input images are on the same scale and not rotated with respect to one another. The 'offsets' parameter can be used to automatically determine the offsets from the image WCS and the output image will be large enough for the combined image with non-overlapping regions simply set to zero. Since you're images do have a scale difference, see the MAGNIFY task as a way to interpolate one image so the pixels are the same size as the reference, magnification factor should be a simple ratio of the two scales. The ROTATE task can be used to arbitrarily rotate an image if you know the relative rotation between the images.
Lastly, if you have the MSCRED package installed, the MSCIMAGE task can automate much of this process for you. In any case, experiment with some of these tasks and post back if you still have questions.
-Mike
IMCOMBINE is the primary task you'll need, however it assumes the input images are on the same scale and not rotated with respect to one another. The 'offsets' parameter can be used to automatically determine the offsets from the image WCS and the output image will be large enough for the combined image with non-overlapping regions simply set to zero. Since you're images do have a scale difference, see the MAGNIFY task as a way to interpolate one image so the pixels are the same size as the reference, magnification factor should be a simple ratio of the two scales. The ROTATE task can be used to arbitrarily rotate an image if you know the relative rotation between the images.
Lastly, if you have the MSCRED package installed, the MSCIMAGE task can automate much of this process for you. In any case, experiment with some of these tasks and post back if you still have questions.
-Mike
Last post on Apr 14, 2009