[Qgis-user] Rasters alpha channel black instead of transparent

[Pedro Venâncio]

Hello everyone,

I was cutting some rasters in the same way I did several times in the past, adding the alpha channel to ensure transparency:

gdalwarp -of GTiff -r lanczos -dstalpha -cutline shapefile.shp raster_input.tif raster_output.tif

However, now the area that would appear transparent, is shown in black on QGIS 1.7 (and 1.8 dev), as you can see in the picture attached.

I've tried other software and it open the image with transparency in these areas. 
Images that I've cut in the past and opened correctly in QGIS, now are black instead of transparent.

Why is this happening? It is an option that can be changed?

Thanks!

Best regards,
Pedro Venâncio
-------------- next part --------------
A non-text attachment was scrubbed...
Name: alpha_channel.jpg
Type: image/jpeg
Size: 71354 bytes
Desc: not available
URL: <http://lists.osgeo.org/pipermail/qgis-user/attachments/20110830/b2b9fbec/attachment.jpg>