Re: [Geoserver-users] Support for alpha band in GeoTIFF?

[Ryan H. <rya...@ng...>]

On Nov 16, 2007, at 1:59 PM, Ryan Hofschneider wrote:

> I've been having some difficulty in getting a 2-band 8-bit grayscale
> plus 8-bit alpha GeoTIFF to render correctly. Depending on the actual
> values in the alpha layer, an exception gets thrown and the server
> returns a blank PNG.
>
> Is anyone successfully using GeoServer with a similar data set?

Replying to my own message...

The GeoTIFF that was giving me problems was generated with GDAL with  
the ALPHA=YES option (as described at http://www.gdal.org/frmt_gtiff.html) 
.

If this option is not indicated, then GeoServer will render images as  
expected.

For the GeoTIFF that works, gdalinfo will describe the TIFF bands as:
Band 1 Block=1440x5 Type=Byte, ColorInterp=Gray
Band 2 Block=1440x5 Type=Byte, ColorInterp=Undefined

For the GeoTIFF that doesn't work, gdalinfo indicates:
Band 1 Block=1440x5 Type=Byte, ColorInterp=Gray
Band 2 Block=1440x5 Type=Byte, ColorInterp=Alpha

Cheers,
Ryan