From: Milton Aupperle <milton@outcastsoft.com>
Date: June 24, 2005 11:51:56 AM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Astro IIDC 2.01.00 on Friday June 24.
Hi Alan;
I doubt if Auto will solve that problem - unless the clouds are moving very very slowly.
Basically we have to wait until 4 frames have passed after we adjust the CCD exposure to see what change it made, and then re-adjust it in a feed back loop. Each camera is different in how long it takes before the exposure changes are applied, some are as fast as 1 frame others take up to 3 frames. To be safe we wait until 4 frames have returned before analyzing the next one. So it you would get frames that change brightness throughout your recording, especially with fast moving clouds.
And no stacking or alignment app that I know of handles dynamic change in brightness or in object shape well, especially anything FFT based.
However if you utilized the "Use Sharpness for Capture" in Astro IIDC at a reasonably high cut off level (say 10 to 20% change) while recording, it could filter all of it out for you. The Sharpness estimator is partially brightness dependent, so it would detect and eliminate the frames that change brightness or are different from your non cloud obscured "set" frame while recording.
HTH..
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
www.outcastsoft.com
On 24-Jun-05, at 11:11 AM, Alan Friedman wrote:
On Jun 23, 2005, at 7:01 PM, Milton Aupperle wrote:
Hi folks;
- Added "Auto" exposure control, which will adjust the CCD exposure
time to keep the brightness reasonably (+/- 3%) constant.
This sounds like a great addition. I ran into some processing problems this week with a reasonably high resolution stream taken under passing high clouds. The change in brightness really messed up the ability of Keith's Image Stacker to align the frames properly.
best -
Alan