[gdal-dev] alpha mask to data value

[Even Rouault]

Le mardi 01 avril 2014 22:14:11, William Kyngesburye a écrit :
> I've wrestled with various nodata issues in the past, now it's hitting me
> again...
> 
> I'm using Photoshop to delete collars on scanned maps, creating an alpha
> mask.  GDAL has no problem with this.  What I want to do is merge maps
> together (after rectification), then set any remaining nodata areas to
> white, RGB 255,255,255.  Just dropping the extra alpha band doesn't work
> because nodata is set to 0,0,0, which is black.  The a_nodata option in
> gdal_translate just defines what existing value in the data is nodata.
> 
> I tried using gdalwarp with the -dstnodata option which should set nodata
> values in the output to a specific value, but it carries along the alpha
> band and ignores dstnodata.
> 
>   gdalwarp -dstnodata "255 255 255" in.tif out.tif
>   Processing input file in.tif.
>   Using band 4 of source image as alpha.
>   Using band 4 of destination image as alpha.

You can perhaps try adding  -wo INIT_DEST="255,255,255,0"

> 
> 
> -----
> William Kyngesburye <kyngchaos*at*kyngchaos*dot*com>
> http://www.kyngchaos.com/
> 
> First Pogril: Why is life like sticking your head in a bucket filled with
> hyena offal? Second Pogril: I don't know.  Why IS life like sticking your
> head in a bucket filled with hyena offal? First Pogril: I don't know
> either.  Wretched, isn't it?
> -HitchHiker's Guide to the Galaxy
> 
> 
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