Here is a post repeated from the AIP4WIN newsgroup. Richard Berry, co-author of AIP4WIN, gives a step by step guide for creating rotation difference images that bring out the jet structure detail inside the central condensation of Comet 17P. Samples 17P images from high-end amateurs using this technique are collected at the Utah Astro wiki current events page under C17P and the "From the web" section. This procedure is simple enough to be implemented with any imaging processing package used by club members. Difference image links collected on Utah Astro wiki. See entries using term shows "detail": http://www.utahastronomy.com/Current_observing_events#From_the_web - Kurt ====== By Richard Berry 11-7-2007 Improved Larson-Sekanina routine... Message #7949 of 7953 Hi-- Compound processes like Larson-Sekanina are easily built from more basic processes. I followed the following procedure: 1) Start with a high-SNR original image at a fairly large image scale. 2) Use the Star Image Tool to determine the centroid of the nucleus. 3) Use the Translate-Rotate-Shift Tool to rotate the original image clockwise around the centroid. Rotation angles from 1 to 5 degrees work well, but experiment. The tool creates a new rotated image. 4) Use the Translate-Rotate-Shift Tool to rotate the original image counter-clockwise around the centroid by the same angle. The tool creates another new rotated image. 5) Use the Multi-Image>Image Math Tool to average the two rotated image together. This creates an image with doubled stars. You can delete the two rotated images now, since you won't need them again. 5a) Optional: Use the Wavelet Spatial Filter to smooth the averaged image. Set scale 1 to 0, scale 2 to 0, and scale 3 to 0.5. This removes noise and produces a slightly better-looking result. 6) Use the Multi-Image>Image Math Tool to subtract the averaged image from the original image. The result is a Larson-Sekanina rotational difference image. 7) Use the Image Display Control to find appropriate Black/White display values. These will have opposite signs, i.e., -100 and +100. 8) Use the Brightness Scaling Tool to linearly scale the image from the Black/White stretch into the range 0 to 65635, then export the image as a 16-bit TIFF file. I think of AIP4Win as a toolbox of functions and procedures that can be combined and daisy-chained into powerful (and highly repeatable) image processing routines. The newest Larson-Sekanina image from Nov 4 is posted at: <http://www.wvi.com/~rberry/astronomy/cometholmes/cometholmes.htm> --Richard ==================== _______________________________________________ Sent via CSolutions - http://www.csolutions.net