[Gdal-dev] gdalwarp Transparency Question

[Reinaldo Escada Chohfi]

Frank,

I downloaded and installed FWTools 1.0.0 Win.  The gdalwarp transparency 
problem did not happen with this new version.  I tested on two images that 
I would get blue spots on the overlapping areas.  The new version did the 
transparency without the blue spots.  I'll let you know if it happens with 
other mosaics.

Thanks a lot.

Reinaldo.

At 03:37 PM 6/5/2006, Frank Warmerdam wrote:
>Reinaldo Escada Chohfi wrote:
>>Hello,
>>I'm runing gdalwarp (FWTools 1.0.0a7) to mosaic geotiff images because 
>>the images are large and I run into memory problems with gdal_merge.
>>I get some strange results in several mosaics in the overlapping areas 
>>between images.  I use -srcnodata 0 to have gdalwarp do the transparency 
>>in these overlapping areas.
>>My question is, if am using -scrnodata 0, will the transparency be made 
>>when all 3 pixel values are 0, 0, 0 (RGB) or whenever any of the bands 
>>has a pixel value equal to 0?  It looks like I get a transparency only in 
>>the Blue, sometimes only in the Red or Green bands and the image has 
>>blue, red or green spots.  Do I have to use -scrnodata value "0 0 0" in 
>>order to get transparency only when RGB are equal to 0, 0, 0?
>>Thanks in advance for the help.
>
>Reinaldo,
>
>Looking at the code, it seems I implemented UNIFIED_SRC_NODATA as the
>default for gdalwarp circa September 2005.  A quick checks shows FWTools
>1.0.0a7 as being built in early November of 2005.  So it should include this.
>
>The UNIFIED_SRC_NODATA enabling forces gdalwarp to only consider a pixel as
>nodata if the values match for all bands.  So, gdalwarp *should* do what
>you want already.  That it is not may be a bug in one or more of the
>warping logic cases.
>
>Could you first try a newer FWTools and see if the problem persists?  If it
>does, could you submit a bug report detailing how to reproduce your problem?
>
>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    | President OSGF, http://osgeo.org
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