| grey scale [message #12520] |
Wed, 12 August 1998 00:00  |
Harry Reisig
Messages: 6
Registered: July 1998
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Junior Member |
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Howdy -
Does anyone know if there is a grey-scale color table on IDL 5.0.2 (for
PowerMac)? I need to publish some tvscl images (currently being viewed with
color table 4) in grey-scale.
I imagine that there is one posted somewhere, but I don't know where.
Thanks
Harry
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| Re: grey scale [message #12550 is a reply to message #12520] |
Wed, 19 August 1998 00:00  |
Richard Meyer
Messages: 1
Registered: August 1998
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Junior Member |
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Harry Reisig wrote:
> We tried loadct, 0 - but it is not publishing quality. Is there another
> grey scale that give sharper images? We are trying to print color images,
> which gives a lot of information that is lost in ct 0.
it's still there but you don't see it. Your problem is not IDL-specific. Human
eyes cannot distinguish many more than 16 different grey tones. If you stick to
grey scales, you should try some modifications to the linear scale you load by
loadct,0.
1. Apply a gamma correction (interactively by the IDL-routine xloadct). The
response function of the human eye is not linear. That's why digital cameras
and displays often have gamma correction (ca. 0.7).
2. Analyze your data! The plotting routine tvscl reduces the scale to the range
of your data, but overshooters may still occupy a large range of your scale,
reducing contrast for the more interesting data. Cut off these by e.g.
"tvscl,image <0. >11." or make a histogram equaliztion.
3. Optimize the scale to the specific data. If you like to see certain
structures in your image, try to give your greyscale maximum slope in the
interesting ranges (interactively by modifying functions with xloadct). Also
think about /|/|/|/| -like functions. But this makes assigning values
impossible!
Schoene Gruesse / Kind Regards,
Richard Meyer
____________________________________________________,_______ ___________
/|
DLR-Institut fuer Physik der Atmosphaere / |
Oberpfaffenhofen ,---/--|---,
D-82234 Wessling / / / /
Germany '---|--/---'
| /
tel.: +49-8153-28-2571 |/ DLR
fax.: +49-8153-28-1841 '
mailto:Richard.Meyer@dlr.de http://www.op.dlr.de/ipa/
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