[Gdal-dev] Resampling with gdalwarp

[Chris G. Nicholas]

The real test is, as always, change detection. :-)

And I think (scientists out there, please correct me!) nearest-neighbor is as reasonable as anything. 

Now, it would be interesting if GDAL could have a flag where one could take the time/computation hit and do the transformation matrix for *every* pixel... (like the MODIS reproject tool; see:  http://lpdaac2.usgs.gov/landdaac/tools/ modis/info/MRT_Users_Manual.pdf)

Chris

-----Original Message-----
From:	Frank Warmerdam [mailto:warmerdam at pobox.com]
Sent:	Tue 3/16/2004 3:58 PM
To:	gdal-dev at remotesensing.org
Cc:	
Subject:	Re: [Gdal-dev] Resampling with gdalwarp
Mario Beauchamp wrote:
> Hi,
> 
> Is there something wrong with gdalwarp resampling algorithms? I have done some tests and got strange
> results which I put here: http://pages.infinit.net/starged/gdal/resampling.html
> 
> For comparison, I have put an image processed in Paint Shop Pro 7 using bilinear resampling. It's
> also strange that cubic spline give almost the same results.

Mario,

At the macro level (looking at a whole image) I would expect bilinear and
cubic convolution to be hard to differentiate unless a great deal of
resolution magnification is taking place.

I looked at the images, and it does appear that there are some differences
from the results in Paint Shop Pro, but it is impossible for me to tell
what might be causing the differences.   If you can provide the input
files, and arguments you used to process them, and the raw results from
Paint Shop Pro I could try and compare.  However, there isn't anything I
do with jpeg files since the "corruption" of the data due to jpeg
compression will in many ways dominate the effects of different resampling
algorithms.

Best regards,

-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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