From: Milton Aupperle <milton@outcastsoft.com>
Date: April 20, 2005 12:51:01 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Jupiter Sharpness Comparison
Hi Alan;
On 20-Apr-05, at 12:13 PM, Alan Friedman wrote:
Nice images! Thanks for posting the interesting report.
Choosing the right amount of sharpening is a very challenging craft. It reminds of asking for directions on the subway and getting the response "just get of at the stop before me..." - by the time you're done you realize you should've stopped a while back.
I don't see much difference in detail between the images - the increased crispness seems to be at the expense of increased granulation? But I am also very sensitive to over sharpening because I am a prime offender.
It's not a huge difference and sharpening will always increase noise levels. The key with my technique is to reduce noise on the CCD side by keeping the Brightness/Gains as low as possible. At high gains subtle detail gets lost in the noise and then all sharpening will do is amplify the noise.
Also sharp focus is a hugely important issue too. I have a few movies I took before this one (using the moon for focusing) that weren't quite as sharp and the white spots to the upper left of the red spot are basically gone in those images.
My technique usually produces a number of streams for luminance (4-8 or so) which I process separately and then restack for the final image. I sharpen these preliminary stacks for detail just past the optimum point - slightly grainy - and allow the final stacking to average and lessen the noise. This is of course a very tedious process in Keith's Image Stacker.
The above is what Astro IIDC does - but for each frame in your Stack is sharpened and then aligned/stacked.
I need to make the time to learn how to accomplish the same techniques in ASTRO IIDC - my first attempts with the beta did not work out right. The images were not aligned correctly - perhaps because it drifted too much during the capture?
It's hard to say exactly without more information, for example the method (Planetary or Lunar/Solar) used and what CI % you used for the sharpness selector. Also a sample of the images used as source would be helpful too. Some of my lunar images at really long focal lengths (5+ meters) were drifting 70 to 100 pixels by the time 1000 frames had been collected and they aligned fine.
Also the Planetary/Lunar option is a bit misleading. Planetary works good for smaller disk sizes, but since your Saturn images are really large, you probably would be better off using Lunar/Solar which aligns using an edge detection method rather than the simple planetary centroid method.
The other possibility could be that the "pixel align" finnish is getting tripped up because the disk of saturn is basically featureless (at least for a 32x32 pixel comparsion block) and with high gain / noise levels it may be thinking the noise it's seeing is "features". If it does not see any "significant" variance in the images it disables this fine tuning automagically, but I may have to add an option to turn it off manually for these cases.
Hope That helps..
Milton J. Aupperle
President
ASC - Aupperle Services and Contracting
Mac Software (Drivers, Components and Application) Specialist
#1005 - 815 14th Avenue. S.W.
Calgary Alberta Canada T2R0N5
1-(403)-229-9456
milton@outcastsoft.com
www.outcastsoft.com
Alan
On Apr 20, 2005, at 1:44 PM, milton_aupperle wrote:
Hi folks;
I had very good stable skies last night as the jet stream shifted way
north of me into the North West Territories and Arctic. So I managed
to get some good shots of Jupiter (with GSR) and Luna last night -
accumulating another 9 gigabytes of 16 bit video movies.
Since I finally had some decent shots of Jupiter to work with, I ran
the same movie through Astro IIDC for stacking and alignment, and then
varied the pre sharpness amount in each run from none to extreme.
Astro IIDC has the ability to sharpen each frame before stacking and
aligning them - which in theory should help accentuate subtle features
as long as the CCD gain noise isn't too high.
You can read about it and see the (subtle) difference that it makes in
the Jup_Comp_050419.jpg file in the Planetary folder. The 16 bit tiff
is a little bit easier to see the subtle differences too.
One thing I'm now more convinced of now is that 16 bit planetary
imaging does make a difference for very subtle features. However to
take advantage of it you need very good seeing conditions (and have to
stay in 16 processing from start to finnish) - otherwise
it may not be worth the money.
TTYL..
Milton J. Aupperle
President
ASC - Aupperle Services and Contracting
Mac Software (Drivers, Components and Application) Specialist
#1005 - 815 14th Avenue. S.W.
Calgary Alberta Canada T2R0N5
1-(403)-229-9456
milton@outcastsoft.com
www.outcastsoft.com
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