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Date: Thu, 17 Apr 2008 14:14:00 -0700
Subject: Re: [Tiff] a question about creating transparency of the image in TIFF
From: Chris Cox <ccox@adobe.com>
To: Gerben Vos <Gerben@zylab.com>, TIFF <tiff@lists.maptools.org>
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Status: RO

There are 2 types of alpha in TIFF: associated (transparency) and
unassociated (undefined extra channels).

Also, the TIFF spec. states that images with associated alpha (transparen=
cy)
must be premultiplied.

Chris



On 4/17/08 8:18 AM, "Gerben Vos" <Gerben@zylab.com> wrote:

>> =CA=EE=ED=F1=F2=E0=ED=F2=E8=ED =CB=F3=F6=EA=E8=E9 wrote:
>>> Hi.  Can anyone help me ?  How can I create transparency of the image=
 in
>>> TIFF?=20
>=20
> Frank Warmerdam wrote:
>> The conventional approach is to create an alpha sample for each pixel,=
 and
>> set it to indicate transparent pixels.
>=20
> For example, for RGB images (PhotometricInterpretation =3D 2) you can s=
et
> SamplesPerPixel to 4, and then indicate in the ExtraSamples tag that th=
e
> extra (fourth) sample is an alpha channel. Read the TIFF specification =
for
> more info.
>=20
> Gerben Vos.
>=20
> _______________________________________________
> Tiff mailing list: Tiff@lists.maptools.org
> http://lists.maptools.org/mailman/listinfo/tiff
> http://www.remotesensing.org/libtiff/


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