From: Alan Friedman <alan@greatarrow.com>

Date: September 26, 2005 1:57:57 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: processing comparison


Hi all -


You might have heard me ramble on about the benefits of using multiple alignment points for stacking in astro images. I thought I would upload a comparison image for you to look at.


http://groups.yahoo.com/group/Astro_IIDC/files/Lunar/tycho.proc.comp.jpg


This image of Tycho was taken in fair (5/5 pickering) seeing at the end of August. I was able to select 214 decent frames from a total of about 1100 for stacking. The right hand image shows the results of a single stack using the central mountain peaks for registration of the images. The left hand image was created using data from 30 different stacks applied into the right image. In this was, the image is "focused" on different regions gaining a modest but noticeable improvement. The improvement is most easily seen as you move away from the center of the image in these reduced images.


Here is a summary of the technique.  In the stacking software, multiple stacks are created from the same frame selection and are saved separately. In photoshop, a base layer is created from the original mountain stack and then new layers are created for the focus regions. Each focus file is opened, a selection is created around the focus for that image, the selection is feathered, copied and then pasted into a layer over the base layer. Once they are registered over the master and flattened, final processing is done and the image completed.


I like to think of this as adaptive optics for the Great Lakes. You can see the final image here:


http://www.geocities.com/alanfgag/tycho.jpg


Obviously the technique is time consuming and the improvement is subtle. It is of most advantage in lunar and solar imaging but will offer improvements in planetary imaging if you work at a large image scale (long EFL). It is not an option currently with stacking in Astro IIDC, but may be down the road so I thought I would share it here.


best,

Alan