Created
2009 April 24
VIDEO PROCESSING
Dark frame subtraction
(From
the PLANOCCULT mailing list)
Oscar Canales Moreno recommended the program iPrep at: http://www.geocities.com/jgroveuk/iPrep.html
iPrep is an interactive image preprocessor. It deals with the correction of common long exposure imaging defects, operating on a collection of source images and allowing the selection of a variety of pre-processing algorithms. The results are visible in a preview window, allowing the processing parameters to be fine-tuned prior to saving the final results.
Features:
– Import/export image files in
– Work in colour or monochrome
– Subtract dark frames
– Apply flat frames
– Generate synthetic flats from image files
– Eradicate hot and cold pixels
– Contrast stretch
– Remove interlacing artifacts
The downloadable ZIP file contains the program iPrep.exe, and a rich text file
iPrep.rtf containing a description of its features and how to use them (you can
read this file using WordPad). You can also download a sample iPrep project,
demonstrating some of its capabilities.
Astrometry
Over
the last 5 years, precisely timed video has matured into the preferred approach
to recording observations of asteroid occultations. The passage of 2009 DD45 on
2009 March 2 was noteworthy as two observers independently recorded the
asteroid on video with the aim of obtaining astrometric positions.
Significantly, the astrometric positions derived from the videos had a positional
accuracy comparable with usual CCD astrometry. Most importantly, the time
associated with each position was determined to a far greater precision than
traditional CCD astrometry. [It was subsequently determined that the positions
reported from Siding Spring required a correction of 0.375 secs; corrections of
over 1 second were indicated for some other observatories.
For precise astrometry of fast-moving objects (that is, moving faster than
100"/minute) precisely timed video provides a number of advantages over
normal CCD astrometry - with the advantages increasing as the rate of motion
increases. Recognising that most observers involved with astrometry have little
knowledge of video techniques, and that video observers have little knowledge
of astrometry, I have put together a Video Astrometry guide. That guide is now
available on the web site of the Minor Planet Center. On the CBAT/MPC/ICQ index
page, it is in the 'Documentation' section under the new heading 'Video
Observers'. The direct link is:
http://www.cfa.
You will also see a link to 'Script for determining mini normal places'. The
script has been written by the MPC to combine positions spread over an interval
of less than two seconds into a single position. Its use is essential for video
astrometry of fast moving objects.
The guide is a 29 page document detailing the hardware, software, and
processing (including normal positions) required to obtain an astrometric
observation using video. As referenced in the MPC 'What's New' document: "A
new web service allowing video observers to derive the mini normal places
needed for submission. Documentation (PDF, 660KB) on using the service is
supplied and should be considered mandatory reading. [2009 March 30]"
As I state in the guide, I would like to acknowledge the following people who
have critiqued or otherwise assisted in putting the guide together.
John Broughton (who also suggested the possibility of performing video
astrometry on 2009 DD45 on an internet group.)
Gerhard Dangl
Dave Gault
Bill Gray
Rob McNaught
Hristo Pavlov
Gareth Williams