| Re: Plotimage and non-byte images [message #75376] |
Wed, 02 March 2011 13:56  |
wlandsman
Messages: 743
Registered: June 2000
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Senior Member |
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On Wednesday, March 2, 2011 2:06:43 PM UTC-5, le.d...@tiscali.it wrote:
> Hi all,
> I am trying to plot images using "plotimage". Nevertheless, images are
> "non-byte scaled" and the appearence is always quite weird. I have to
> spend a huge amount of time trying to find the best suited "range"...
> Do you have a smart (=quick) solution for that?
> Thanks in advance!
Have you been using the RANGE keyword to PLOTIMAGE and setting it to the minimum and maximum of the image values? Or more directly first using BYTSCl on your image?
Sometimes using the image minimum and maximum is a poor choice (e.g. if the maxima are due cosmic ray spikes in a CCD image). In that case you might want to use a histogram and select a data range such as in http://idlastro.gsfc.nasa.gov/ftp/pro/tv/sigrange.pro
If you have a large dynamic range you might consider logarithmic scaling
( http://www.astro.ucla.edu/~mperrin/IDL/sources/alogscale.pro )
--Wayne
P.S. For a long time I would switch back and forth between using Craig Markwardt's PLOTIMAGE and David Fanning's CGIMAGE (formerly TVIMAGE) because each had features that I wanted. Now with one exception CGIMAGE has all the features of PLOTIMAGE, and I hope to convince David to add the equivalent of the IMG[X/Y]RANGE keyword (to first subset the image to a specified pixel range) when he finds the time ;-)
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