Re: Congrid problem

[Paul van Delst <pvandelst(at)ncep.noaa.gov>]

Jonathan Joseph wrote:
> 
> I'm running IDL 5.3 on HP-UX and seeing the following
> problem with congrid.  I have a byte image that has large areas
> of a particular solid color (a background color).
> I rescale the image to be larger using congrid with the
> /interp flag set.  My nice solid areas of the background color,
> which I would still expect to see unspoiled, now have artifacts
> in them with value background_color - 1.  This looks like a
> bug.  What's going on?
> 
> Here's an example that show's the problem:
> 
> IDL> a = bytarr(100,100) + 155b
> IDL> b = congrid(a,140,140,/interp)
> IDL> print, min(b), max(b)
>  154 155
> IDL> w = where(b eq 154, count)
> IDL> print,count
>         3703
> IDL> tvscl, b eq 154   ;shows strange pattern of lines and dots
> 
> I would expect b in this example to be filled only with value 155.
> Is this a bug or is there some other reason I am seeing this behavior?
> 
> BTW: I see the exact same behavior with INT instead of BYTE.
> 
> Thanks.
> 
> -Jonathan

IDL> print, !version
{ x86 linux unix 5.4.1 Jan 16 2001      32      32}
IDL> a = bytarr(100,100) + 155b
IDL> b = congrid(a,140,140,/interp)
% Compiled module: CONGRID.
IDL> print, min(b), max(b)
 155 155
IDL> w = where(b eq 154, count)
IDL> print,count
           0


-- 
Paul van Delst           A little learning is a dangerous thing;
CIMSS @ NOAA/NCEP        Drink deep, or taste not the Pierian spring;
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pvandelst@ncep.noaa.gov                   Alexander Pope.