Le mercredi 30 mai 2012 22:26:18, Craig Bruce a écrit :
> Even Rouault wrote:
> > There will be likely a compatibility problem if we do this, because
> > GDAL up to now writes TIFF RGBA images with EXTRASAMPLE_ASSOCALPHA
> > (pre-multiplied), but I think in most cases the data that people have
> >
Even Rouault wrote:
> There will be likely a compatibility problem if we do this, because
> GDAL up to now writes TIFF RGBA images with EXTRASAMPLE_ASSOCALPHA
> (pre-multiplied), but I think in most cases the data that people have
> feed in the GTiff driver was not pre-multiplied. So if we un-pre
Frank Warmerdam wrote:
> because it is hard to hit all the appropriate code paths safely and
> partly because the result will be lossy.
It depends on what you mean by "lossy". The value returned through the
GDAL interface won't be the literal sample value that is in a TIFF file
with associated
Le mardi 29 mai 2012 23:12:45, Frank Warmerdam a écrit :
> Craig,
>
> My opinion is that applications should assume alpha is not pre-multiplied.
> I have been hesitant to "un-premultiply" premultiplied TIFF images - partly
> because it is hard to hit all the appropriate code paths safely and partl
Craig,
My opinion is that applications should assume alpha is not pre-multiplied.
I have been hesitant to "un-premultiply" premultiplied TIFF images - partly
because it is hard to hit all the appropriate code paths safely and partly
because the result will be lossy.
Going forward GDAL should do o
Tamas Szekeres wrote:
> 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.
I think it wo
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 :
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
