[gdal-dev] GDAL alpha channels

[Tamas Szekeres]

I have added a ticked for such an issue long ago, but I don't remember
what would be the expected solution.
http://trac.osgeo.org/gdal/ticket/2279

There should be an external config option to instruct the driver which
representation should be used.

Best regards,

Tamas



2012/5/29 Craig Bruce <csbruce at cubewerx.com>:
> I have run into a problem using GDAL to read TIFF images with a alpha
> channels.  GDAL returns the source TIFF sample values verbatim regardless
> of whether the alpha channel is associated (pre-multiplied) or unassociated
> within the TIFF image samples.  (In each alpha model, the same pixel
> value with the same alpha value will have different sample values.)
>
> GDAL does not appear to enforce a specific alpha model in its interface
> (pre-multiplied or non-pre-multiplied) and does not appear to offer any
> indication of which is currently being used.  This creates a dead end as
> far as the GDAL interface goes.  My system and most image formats (e.g.,
> PNG) use the non-pre-multiplied alpha model.  TIFF can use either.
>
> What is a user supposed to do about this?
>
> --------------------------+----------------------+--------------------------
> Dr. Craig S. Bruce        | Ph 819-771-8303 x205 |             CubeWerx Inc.
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