[gdal-dev] Unwanted partial transparency when clipping

[Michael Corey]

Sure, I've uploaded samples here.

http://www.mikejcorey.com/spatial/diablo-box-sample.tif
http://www.mikejcorey.com/spatial/diablo-cutout-sample.tif

These are the same as the images created by the process I described (but 
scaled down).

To your point about specifying size in the first step -- will that make 
the process run faster, or does it do the scaling down after it builds 
the full-resolution image?

Also, I notice that my filesize always gets significantly bigger when I 
do the cutout step, which seems counter-intuitive to me since in theory 
shouldn't there be less information present once the cutout is done?

Thanks for your help!

Michael Corey


On 7/6/11 5:01 PM, Chaitanya kumar CH wrote:
> Michael,
>
> Can you provide screenshots of 
> diablo-combined-center-utm10-70pct-box.tif and 
> diablo-combined-center-utm10-70pct-cutout.tif for comparison?
>
> By the way, you can perform the actions of the two gdal_translate 
> commands in the first step with the gdal_merge.py script itself unless 
> you want to use a specific resampling algorithm.
>
> On Thu, Jul 7, 2011 at 4:28 AM, Michael Corey <mcorey at cironline.org 
> <mailto:mcorey at cironline.org>> wrote:
>
>     Hi all:
>
>     I'm using a shapefile as a clipping mask to cut out the shoreline
>     from some DOQ files that I have merged together. But when I do the
>     clipping step, I end up with unwanted semitransparency in the
>     non-clipped areas.
>
>     I'm pretty sure the problem is only with my gdalwarp step at the end.
>
>     Here's my process:
>
>     gdal_merge.py -init "255" -o diablo-combined-center-utm10.tif file
>     file file file
>
>     gdal_translate -outsize 70% 70% diablo-combined-center-utm10.tif
>     diablo-combined-center-utm10-70pct.tif
>
>     ogrinfo -al ./diablo_canyon_detail_clipper.shp
>     //Extent: (XXXX, YYYY) - (XXXX, YYYY)
>
>     gdal_translate -projwin XXXX YYYY XXXX YYYY
>     diablo-combined-center-utm10-70pct.tif
>     diablo-combined-center-utm10-70pct-box.tif
>
>     gdalwarp -co COMPRESS=DEFLATE -cutline
>     ./diablo_canyon_detail_clipper.shp
>     diablo-combined-center-utm10-70pct-box.tif
>     diablo-combined-center-utm10-70pct-cutout.tif
>
>     Can anyone help?
>
>     Thanks!
>
>     -- 
>     Michael Corey
>
>     _______________________________________________
>     gdal-dev mailing list
>     gdal-dev at lists.osgeo.org <mailto:gdal-dev at lists.osgeo.org>
>     http://lists.osgeo.org/mailman/listinfo/gdal-dev
>
>
>
>
> -- 
> Best regards,
> Chaitanya kumar CH.
> /t?a???nj?/ /k?m?r/
> +91-9494447584
> 17.2416N 80.1426E
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