[guide-user] Contrast of FITS image

Jan Manek Dec 3, 1999

At 21:00 2.12.1999 +0100, Jost Jahn wrote:
>A question: How can the contrast of a FITS file changed?

In earlier version worked following (but in recent version of Guide doesn't
work either of the described methods :-( )

>Q: I've loaded some RealSky/DSS images; how can I alter their contrast
>and brightness?
>
>
> A: There is an undocumented way to do this. Once it is described, you
>will perhaps understand why it is undocumented...
>
> What you have to do is to first right-click on a corner of the image
>you want to adjust. You'll get a short dialog box describing the image,
>plus a comment such as "Contrast: 1500 to 12000". This means that a
>pixel value of 1500 is shown as pure black, one of 12000 as pure white,
>and shades of gray are used in between.
>
> Now hit Shift-F8. You'll be prompted to "Enter filename:" Instead,
>enter (for example) "3000,8000". The result will be that the range in
>which gray-scales are used will be narrowed a bit; i.e., contrast will
>be increased. Similarly, "1000,10000" would brighten the image; raising
>both numbers, such as "3000,18000", would darken it; and so on.
>
> This clumsy method is intended to simplify testing for a non-clumsy
>method, as soon as I figure out what that method will be (and as soon
>as I have time to add it in). In the meantime... it _does_ work, ugly
>though it is!
>
> One slight problem will be that, the next time you load an image,
>it will appear with the default contrast of 1500 to 12000. To change
>this, use a text editor to load the file ENVIRON.DAT. One line in
>this file reads:
>
>
>CONTRAST=1500,12000
>
>
> As you might expect, changing this line will change the default
>contrast in new RealSky/DSS images.

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Jan Manek
Stefanik Observatory Private :
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