[gdal-dev] Unwanted partial transparency when clipping

[Chaitanya kumar CH]

Michael,

It looks like both the images have the transparency issue.
Please provide the gdalinfo outputs of the rasters.

Specifying the extents in gdal_merge.py will definitely speed things up.

Scaling time has many more variables. It is probably faster in
gdal_translate. Also, gdal_translate also has more options of resampling
methods.

File size not only depends on the information to to stored but also the
encoding. Your original image was compressed more than the output image. If
you want, you can specify the compression creation options to the GDAL
programs. For tiff formats you can see that options at GTiff driver page[1].

[1]: http://www.gdal.org/frmt_gtiff.html

On Thu, Jul 7, 2011 at 6:05 AM, Michael Corey <mcorey at cironline.org> wrote:

> **
> 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>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
>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>>
>
>
>
> --
> Best regards,
> Chaitanya kumar CH.
> /tʃaɪθənjə/ /kʊmɑr/
> +91-9494447584
> 17.2416N 80.1426E
>
>
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>



-- 
Best regards,
Chaitanya kumar CH.
/tʃaɪθənjə/ /kʊmɑr/
+91-9494447584
17.2416N 80.1426E
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