Re: Function BYTSCL

[davidf(at)dfanning.com (David Fanning)]

Steffen Kernchen (steffen.kernchen@student.uni-magdeburg.de) writes:
 
> I´m just starting with IDL, so here is my first question:   ;-)
> 
> what function(s) can I use instead of BYTSCL?
> I have an array and I want to transform it to get a better contrast.
> But I should NOT use BYTSCL....  :(

Alright, enough time has passed that Seffen has
probably passed or failed the final. Here is
my take on what BYTSCL does:

   FUNCTION Daves_Bytscl, array, Top=maxVal
   minVal = 0.
   IF N_Elements(maxVal) EQ 0 THEN maxVal = 255. ELSE maxVal = Float(maxVal)
   minVec = Min(array, Max=maxVec)
   sf = [((minVal * maxVec)-(maxVal * minVec)) / $
      (maxVec - minVec), (maxVal - minVal) / (maxVec - minVec)]
   RETURN, Byte(array*sf[1] + sf[0])
   END

To test it:

   IDL> array = Dist(150, 150)
   IDL> Window, XSize=450, YSize=150
   IDL> TV, array, 0
   IDL> TV, Daves_BytScl(array), 1
   IDL> TV, BytScl(array), 2

Cheers,

David

-- 
David Fanning, Ph.D.
Fanning Software Consulting
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