[GRASSLIST:1038] Re: patched rasters

[Stuart Edwards]

Thanks (that's two I owe you, I think)

Your proposed process cleared up the fuzziness nicely but there were  
some unintended consequences.  The r.composite image had >32,000 new  
'colors'.  I used i.group and i.cluster to sample the data back to  
something reasonable.  255 was an improvement, but still too hard to  
match a color table.  Using 4 categories (the original map was  
printed in blue, brown and black on white) was a big improvement, but  
the brown and blue were indistinguishable.  Long story short, I went  
back to a graphics program to patch the two sheets and then  
reimported them.  Simple really.  Lesson learned is that patching  
scanned color graphics is better accomplished in something other than  
GRASS as a pre-process!

Stuart
_________________
On May 7, 2006, at 4:48 AM, Maciek Sieczka wrote:

> On Sat, 6 May 2006 10:24:03 -0400
> Stuart Edwards <sedwards2 at cinci.rr.com> wrote:
>
>> Hi
>>
>> Curious problem with r.patch.  I'm patching two topo maps and which
>> ever one is identified second will appear blurred on the new
>> composite image (see patch1). However, if I display them
>> independently on the same monitor, both maps are just fine (see
>> display1).  It looks like a resolution problem,
>
> The problem is palette. Your images have indexed palettes (8 bit?),  
> each
> palette is different. You would need to:
> 1. move your maps to a truecolor space
> 2. patch
> 3. transform back to indexed (to reduce the size and for Grass display
> sake, which is slow on more than 15 bit color).
>
> Maybe do it this way:
> 1. separate each maps R,G,B component with r.mapcalc # operator:
> 'map_blue=b#map'
> 2. r.patch R, G and B layers separately
> 3. r.composite them
>
> Maciek
>
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