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stardustborn
member
Reged: 11/30/07
Posts: 54
Loc: LI, New York
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I was wondering if there was any way to destretch astrophotos that have gotten the ol' oblong star effect due to poor tracking. My homemade mount doesn't have the greatest speed control - yet - I'm working on it, but polar aligment is good. Net result is some stretched images, oblong stars. I would think it easy for software to measure how out of round the stars are and then recompress the entire image. I have AIP4WIN and there are ways to measure stars eccentricity and ways to make the stars rounder but not something that would adjust the entire image. Or at least none I see or know how to use. If I could run long exposures and not worry about oblong stars, because they could be fixed it would be very cool. There must be something, seems so simple. Photoshop?
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Orion xt10i on an ugly homemade english fork eq mount
A stepper motor,wires and stuff
Push to digital circles(COL) into "The Sky"
"The Noble Turkey Observatory".... (a small shed)
http://picasaweb.google.com/stardustborn/NobleTurkeyObservatory
Orion Starblast 4.5 imaging scope
Meade DSI 2 pro mono
...and a piece of space to peer into
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Sidereus Nuncius
super member
Reged: 03/27/05
Posts: 182
Loc: Chester County, PA
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There are some techniques to correct *minor* oblong star shapes discussed in R. Scott Ireland's Photoshop Astronomy.
PixInsight has a "morphological transformation" tool; not sure if that will work.
What you are describing is images with poor tracking. That cannot be corrected with software. Have you tried shooting shorter exposures?
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Regards,
Louis Marchesi
TMB 152, WO ZSFD80 Anniversary
AP 1200GTO
SBIG ST-2000XM, CFW9, Astrodon LRGB
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yock1960
Pooh-Bah
Reged: 06/22/08
Posts: 1124
Loc: SW Ohio, USA
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Quote:
PixInsight has a "morphological transformation" tool; not sure if that will work.
It works and even better, you can mask off everthing else. You can do this in PS but it's more of a pain. It can still only go so far though, close stars will tend to merge.
Steve
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stardustborn
member
Reged: 11/30/07
Posts: 54
Loc: LI, New York
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Thanks guys. But from what I understand these processes treat the stars seperately. What I'm thinking about is something that would shrink the whole pic along the axis of stretch, the axis of stretch determined by star shape.
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Orion xt10i on an ugly homemade english fork eq mount
A stepper motor,wires and stuff
Push to digital circles(COL) into "The Sky"
"The Noble Turkey Observatory".... (a small shed)
http://picasaweb.google.com/stardustborn/NobleTurkeyObservatory
Orion Starblast 4.5 imaging scope
Meade DSI 2 pro mono
...and a piece of space to peer into
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jimarshall
sage
Reged: 03/20/07
Posts: 241
Loc: Virginia
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Have you seen this recent post?
http://tiny.cc/QLHmQ
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Jim
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Alex McConahay
sage
Reged: 08/11/08
Posts: 245
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Photoshop/Edit/Free Transform will allow one to shrink an image along an arbitrary axis. (well, actually, along either horizontal and/or vertical, but since you can use them independently, the effect is any axis one chooses.)
Alex
Alex
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stardustborn
member
Reged: 11/30/07
Posts: 54
Loc: LI, New York
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No I hadn't seen that, thanks. That's getting closer to what I'm thinking about. It still seems like there should be something more automatic. And I guess I need the expensive version of PS, frankly I have a hard time seeing myself spending what, $600 for photo editing. All I want is a tool to change the aspect ratio of all the pixels at once I think, and this should be able to bring the stars back to round. No?
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Orion xt10i on an ugly homemade english fork eq mount
A stepper motor,wires and stuff
Push to digital circles(COL) into "The Sky"
"The Noble Turkey Observatory".... (a small shed)
http://picasaweb.google.com/stardustborn/NobleTurkeyObservatory
Orion Starblast 4.5 imaging scope
Meade DSI 2 pro mono
...and a piece of space to peer into
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stardustborn
member
Reged: 11/30/07
Posts: 54
Loc: LI, New York
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Thanks Alex, That's what I was thinking about. This should work if the off center parts of the image are about the same saturation levels as the centered parts. A more problematic situation would be if the smeared areas are due to relatively infrequent excursions off the center I guess.
Now is this tool in PS Elements? I have to look into that.
Thanks again.
John
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Orion xt10i on an ugly homemade english fork eq mount
A stepper motor,wires and stuff
Push to digital circles(COL) into "The Sky"
"The Noble Turkey Observatory".... (a small shed)
http://picasaweb.google.com/stardustborn/NobleTurkeyObservatory
Orion Starblast 4.5 imaging scope
Meade DSI 2 pro mono
...and a piece of space to peer into
|
Alex McConahay
sage
Reged: 08/11/08
Posts: 245
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I do not know whether Elements has a transform, but I would suspect it would. It is not a plug-in or such with Photoshop, but a standard operating procedure. Be aware that everything in the picture is transformed. If you have a circular nebula in the middle of those stars you are shrinking or stretching, it will become an oval!!!
Also--and this is just to help clarify the question--the term "Stretching" an image already has a meaning in imaging, and it is different than the way you are using it. You are using stretching to mean pulling it along one axis or something.....a perfectly sensible meaning (unless the word was already being used to say something else). Most imagers would use the term "Stretching" to mean spreading the light values you have from the initial exposure (usually a limited range) into the whole dynamic range available to the computer or other display mode. One uses levels and curves to accomplish this, and it does not change the shape of the image.
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