[gdal-dev] Automatically creating an Alpha mask for a RGB raster to extract the backgound? (magic wand style)

[Even Rouault]

On mardi 29 janvier 2019 15:49:40 CET Idan Miara wrote:
> Hi Even,
> 
> Thanks! it does solve most of the problem!
> 
> The only issue that I think is left is that nearblack scans from the
> borders till it reaches a valid data point and stops there.
> So in case of diagonal zigzag cutting (or background in holes) there will
> be still background left inside the zigzags or holes.
> 
> A solution could be to add a parameter for a different scanning mode,
> instead of 4 scans from the borders till the first data point, do one or
> two scans (horizontal/vertical) and in each scan cover the whole
> scanline/row so we won't miss background trapped inside holes.

Yes an additional flag would be needed ("-interior" ?) since there are 
situations where you could have zero values inside the raster (lakes, etc) 
that you don't want to treat as nodata.

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