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<div class="moz-cite-prefix">Jan,<br>
<br>
I can't speak the development request, but you may be able to do
some sharpening using the <Kernel> object in a VRT. I've
used<br>
<Coefs>-0.111 -0.111 -0.111 -0.111 2 -0.111 -0.111 -0.111
-0.111</Coefs><br>
to apply sharpening to satellite imagery.<br>
<br>
And a few years ago I found that using wavelet compression on
scanned topographic maps when downsampling made the text more
readable (preserves edges more). I used ECW back then, but I
suspect JPEG2000 may do it as well...<br>
<pre class="moz-signature" cols="72">Best Regards,
Brent Fraser</pre>
On 3/28/2013 5:27 AM, Jan Hartmann wrote:<br>
</div>
<blockquote cite="mid:5154290F.2020402@uva.nl" type="cite">
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<font face="Times New Roman, Times, serif">Perhaps I should
clarify a bit what I meant, I haven't had any reactions until
now, positive or negative, and it is important for me.<br>
<br>
I use Gdalwarp and gdaladdo extensively for goereferencing and
tiling large historical maps serieses (raster scans). To display
them efficiently, I need to create layers at different scale
levels, e.g. if the original maps have a pixel size of 10
meters, I need to resample them to rasters with pixel sizes of
20, 40, 80 , 160, 320 and 640 meters, and tile all those maps
appropriately. So the original maps have to be resampled quite
drastically. In Gdalwarp there is no adequeate resampling
algorithm, and you end up with very grainy map at those lower
resolutions. Gdaladdo has several more algorithms, with gauss in
many cases the most efficient. However, even with the gauss
filter, maps resampled at very low resolutions turn out too
hazy. For an example see the 1930 map of the Netherlands:<br>
<br>
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charset=ISO-8859-1">
<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="http://mapserver.sara.nl/topo/triang/">http://mapserver.sara.nl/topo/triang/</a><br>
<br>
If you zoom in to more detailed levels, you'll see the way the
image sharpens. For the effect on black-white image choose the
TMK-map (1850) with the top-center button. Filters like "unsharp
mask" would perform much better in these cases.<br>
<br>
So I would like to propose two enhancements to gdal:<br>
<br>
- add additional filters to gdalwarp, gauss and the filters
mentioned below.<br>
- implement more filters for gdalwarp and gdaladdo, e.g.
"unsharp mask", or the "mode" filter asked by Jack below.
Perhaps even add the possibility to specify parameters, like in
ImageMagick<br>
<br>
I don't know how difficult is, and whether the gdal devs would
find this really an improvement for gdal. I could do this with
some ImageMagick or Gimp scripts, but it would be a kludge. As
we are going to georeference the complete cadastral and
topographical map base of the Netherlands from 1832 to 1994 the
next few years (millions of map-scans), this exentsion of gdal
would come in very handy. And funding it will really be no
problem at all.<br>
<br>
I would appreciate any kind of comment on this, positive or
negative.<br>
<br>
Regards,<br>
<br>
Jan<br>
<br>
Dr. J. Hartmann<br>
Department of Geography<br>
University of Amsterdam <br>
<br>
</font>
<div class="moz-cite-prefix">On 03/27/2013 10:13 PM, John Twilley
wrote:<br>
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cite="mid:CAEUMa-f0pqvnVLDisp3kUKHA4ovvtc+m-qsQosvX9cXEeDjnaw@mail.gmail.com"
type="cite">
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<div dir="ltr">I'm interested in this feature request as well.
Adding the mode resampling algorithm to gdalwarp would be
very beneficial to my projects, right up there with being able
to access the warp API from Python. Is this at all possible?
Should I submit a feature request on Trac, or what? Just let
me know!
<div> <br>
</div>
<div>Jack.</div>
</div>
<div class="gmail_extra"><br clear="all">
<div>-- <br>
mathuin at gmail dot com</div>
<br>
<br>
<div class="gmail_quote">On Mon, Feb 18, 2013 at 8:17 AM, Jan
Hartmann <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:j.l.h.hartmann@uva.nl" target="_blank">j.l.h.hartmann@uva.nl</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF"> <br>
<div> <font face="Times New Roman, Times, serif">Hi
devs,<br>
<br>
Would it be possible to add gauss and other
interpolations to gdalwarp? At the moment I
georeference large scans to 2000*2000 tiles at the
most detailed scale, and then create 2000*2000 tiles
at resolutions of 2, 4 6 etc times the original
scale, using gdaladdo and gauss or other
interpolations. It would help immensely if I could
do that directly with gdalwarp.
<div class="im"><br>
<br>
Funding would probably no problem. The question
is: can and should it be done?<br>
<br>
Jan <br>
</div>
</font> <br>
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<br>
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