| Re: Combining rgb fits files [message #53292] |
Fri, 06 April 2007 09:46 |
Christopher Thom
Messages: 66
Registered: October 2006
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Member |
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Quoth Amanda:
> I have 3 seperate fits files in red, green and blue and I think I need
> to combine them before I can do anything with them. When I look at
> them individually, they seem blank. I tried using the rgb to tiff
> procedure in idl but its still mostly blank with a small bit of it
> white. I got the data from the Faulkes telescope and the star I want
> shows up in the jpeg image. I'm trying to get light curves of variable
> stars from fits files. I don't know what I can do with a tiff file
> even if it did show up properly. I'm still not very good at this stuff
> so any help would be appreciated.
In addition to the advice that others have suggested, if you are really
looking at fits files, then an easier way to do a quick-look is to
download and use ds9, the "standard" fits viewer used in astronomy. It is
far more flexible (and easier to use) than the "tv" commands in idl.
http://hea-www.harvard.edu/RD/ds9/
And if you are after light curves, I see no reason that you would combine
rgb (are they really rgb? Not UBV filters?) images before attempting the
photometry. What is your aim in combining the images?
cheers
chris
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| Re: Combining rgb fits files [message #53306 is a reply to message #53305] |
Thu, 05 April 2007 06:41  |
Paolo Grigis
Messages: 171
Registered: December 2003
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Senior Member |
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Well, whatever it is you are doing, you should check first
if it works with a single color image.
If the image looks blank, either it is, or you are not scaling
it correctly when viewing it. A bit of experiment with scaling
should clear the issue. If max(image) is equal min(image), then
it is really blank, so you'll have to get better data first...
Also it seems to me that you are confusing FITS with tiffs...
Ciao,
Paolo
Amanda wrote:
> I have 3 seperate fits files in red, green and blue and I think I need
> to combine them before I can do anything with them. When I look at
> them individually, they seem blank. I tried using the rgb to tiff
> procedure in idl but its still mostly blank with a small bit of it
> white. I got the data from the Faulkes telescope and the star I want
> shows up in the jpeg image. I'm trying to get light curves of variable
> stars from fits files. I don't know what I can do with a tiff file
> even if it did show up properly. I'm still not very good at this stuff
> so any help would be appreciated.
> Thanks.
>
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| Re: Combining rgb fits files [message #53307 is a reply to message #53306] |
Thu, 05 April 2007 07:30 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Amanda writes:
> I have 3 seperate fits files in red, green and blue and I think I need
> to combine them before I can do anything with them. When I look at
> them individually, they seem blank. I tried using the rgb to tiff
> procedure in idl but its still mostly blank with a small bit of it
> white. I got the data from the Faulkes telescope and the star I want
> shows up in the jpeg image. I'm trying to get light curves of variable
> stars from fits files. I don't know what I can do with a tiff file
> even if it did show up properly. I'm still not very good at this stuff
> so any help would be appreciated.
Alas, three blank images stuck together will probably
result in a thick blank image. :-(
I'd download XSTRETCH and try to figure out exactly
why these images are blank. Astronomy images are
often perverse and the hyperbolic sine and log
stretches available in XSTRETCH are helpful in
extracting data from the images.
http://www.dfanning.com/programs/xstretch.zip
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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