QGIS and RGBA Geotiffs

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QGIS and RGBA Geotiffs

Harry G. McGavran Jr.

I have a utility that trims the collars of Geotiffs by translating the
indexed colormap Geotiff into an RGBA Geotiff with the Collar made
transparent via the alpha channel in the tiff.

The GIMP and other image viewers honor the alpha channel and the Geotiffs
made with this utility do in fact have transparent collars.

I'm running QGIS 0.7.4 under Ubuntu Dapper and it very nicely will load
raster Geotiffs and place them correctly based on the Geotiff coordinates --
BUT -- the collars on the Geotiffs overlay adjoining maps so the image
isn't very useful -- AND -- unfortunately, if I do the same thing
except use the RGBA transparent collar Geotiffs, QGIS doesn't honor the
alpha channel in the RGBA Geotiff so the collars still overlay the adjacent

Other image viewers seem to honor tiff RGBA alpha channels.  Is there
any hope we will see this in QGIS????

If so, the fact that QGIS overlays raster layers positioned correctly
based on Geotiff coordinates doesn't help.  If QGIS honored the RGBA
alpha channel, then one could easily join adjacent Geotiffs with QGIS
and the transparent collar utility.


Harry G. McGavran, Jr.

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