[Geotiff] processing no data in GeoTIFF

[maphew (matt wilkie)]

Hi Rainer,

>   I have to process a number of tiles and have to identify no data areas.
> The TIFF images are 24BIT and the "no data" area is a black and a WHITE area
> in a tile.
>  
>   I would like to identify all tiles (filenames), which have a cluster of at
> least 4 pixels in one (white) or the other (black) color. 

maybe in two passes for each image? one pass assigning white and the 
second assigning black as nodata?

another option might be to use gdalwarp but without re-projecting,  as 
it can take multiple arguments for nodata (-srcnodata) 
http://gdal.maptools.org/gdalwarp.html

cheers,

-mtt