[gdal-dev] mapfile config options - scan directory

[Jan Hartmann]

Hi all,

What is the relationship between the "PER_DATASET_ALPHA" mask of the RGB 
bands in a raster dataset, and the Alpha Channel? I created a four-band 
tiff file with gdalwarp from an RGB original. On creation, the fourth 
band has all values set to 255, and the whole picture is visible. 
However, when setting parts of the fourth band to zero with 
gdal_rasterize, everything remains visible. Could that be caused by the 
Mask Flags of the first three channels, and, if so, what can I do about it?

Band 1 Block=4016x1 Type=Byte, ColorInterp=Red
   Mask Flags: PER_DATASET ALPHA
Band 2 Block=4016x1 Type=Byte, ColorInterp=Green
   Mask Flags: PER_DATASET ALPHA
Band 3 Block=4016x1 Type=Byte, ColorInterp=Blue
   Mask Flags: PER_DATASET ALPHA
Band 4 Block=4016x1 Type=Byte, ColorInterp=Alpha

Jan
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