[gdal-dev] Feature request: gauss and other interpolations in gdalwarp

[Brent Fraser]

Jan,

   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
<Coefs>-0.111 -0.111 -0.111 -0.111 2 -0.111 -0.111 -0.111 -0.111</Coefs>
to apply sharpening to satellite imagery.

     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...

Best Regards,
Brent Fraser

On 3/28/2013 5:27 AM, Jan Hartmann wrote:
> 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.
>
> 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:
>
> http://mapserver.sara.nl/topo/triang/
>
> 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.
>
> So I would like to propose two enhancements to gdal:
>
> - add additional filters to gdalwarp, gauss and the filters mentioned 
> below.
> - 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
>
> 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.
>
> I would appreciate any kind of comment on this, positive or negative.
>
> Regards,
>
> Jan
>
> Dr. J. Hartmann
> Department of Geography
> University of Amsterdam
>
> On 03/27/2013 10:13 PM, John Twilley wrote:
>> 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!
>>
>> Jack.
>>
>> -- 
>> mathuin at gmail dot com
>>
>>
>> On Mon, Feb 18, 2013 at 8:17 AM, Jan Hartmann <j.l.h.hartmann at uva.nl 
>> <mailto:j.l.h.hartmann at uva.nl>> wrote:
>>
>>
>>     Hi devs,
>>
>>     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.
>>
>>
>>     Funding would probably no problem. The question is: can and
>>     should it be done?
>>
>>     Jan
>>
>>
>>
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