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Message-ID: <11848b2f0609160258if2dc9abs7c90404f51577002@mail.gmail.com>
Date: Sat, 16 Sep 2006 15:28:32 +0530
From: "Anurag Singh" <contact.anurag@gmail.com>
To: "Bob Friesenhahn" <bfriesen@simple.dallas.tx.us>
Subject: Re: [Tiff] is there alpha component present in Grayscale
	orPalettecolor image
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Cc: tiff@lists.maptools.org, Gerben Vos <Gerben@zylab.com>
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Thanks for reply..

i am using tiffcp.c for reading tiles n strips of images.

> What I am thinking is an extra data plane, not an extra column in the
> color table

then how will i get extra data plane in palette images. I want all image
data so please let me know how can i get it.

>Transparency and especially translucency are not always tied to the
>color of a pixel (which would be the effect of the extra column in the
>colortable),  rather, it is often tied to position in the image (i.e.
>vignettes around the edges)

>In that case, the advice for palette images would be the same as your
>advice for the greyscale images.

So what should i understand??  i am getting that grayscale and palette both
can have extra component. am i rt?

thanks
anurag


On 9/15/06, Bob Friesenhahn <bfriesen@simple.dallas.tx.us> wrote:

> On Fri, 15 Sep 2006, Grissom, Ed wrote:
>
> >
> > Gerben -
> >
> > For palette images, is an alpha channel explicitly forbidden by the spec
>
> > ?
> >
> > What I am thinking is an extra data plane, not an extra column in the
> > color table.
>
> Right.  An interesting issue is that libtiff requires that all samples
> be the same size so Pallete images using a small bits per sample for
> the index impose the same bits per sample restriction on the alpha
> channel.  For an 8 bits per sample image, this is not usually a
> restriction, but it becomes more so for 2 or 4 bits per sample.
>
> Associated alpha makes no sense since Pallete entries are not related
> to pixel position but associated alpha is related to pixel position.
>
> Bob
> ======================================
> Bob Friesenhahn
> bfriesen@simple.dallas.tx.us ,
> http://www.simplesystems.org/users/bfriesen/
> GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/<http://www.graphicsmagick.org/>
>
>

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<div><br>Thanks for&nbsp;reply.. </div>
<div>&nbsp;</div>
<div>i am using tiffcp.c for reading tiles n strips of images.</div>
<div>&nbsp;</div>
<div><font color="#3366ff">&gt; What I am thinking is an extra data plane, not an extra column in the<br>&gt; color table</font></div>
<div>&nbsp;</div>
<div>then how will i get extra data plane in palette images.&nbsp;I want all image data so please let me know how can i get it.</div>
<div>&nbsp;</div>
<div><font color="#3366ff">&gt;Transparency and especially translucency are not always tied to the<br>&gt;color of a pixel (which would be the effect of the extra column in the<br>&gt;colortable), &nbsp;rather, it is often tied to position in the image (
i.e.<br>&gt;vignettes around the edges)<br><br>&gt;In that case, the advice for palette images would be the same as your<br>&gt;advice for the greyscale images.</font></div>
<div><font color="#3366ff"></font>&nbsp;</div>
<div>So what should i understand??&nbsp; i am getting that grayscale and palette both can have extra component. am i rt?</div>
<div>&nbsp;</div>
<div>thanks </div>
<div>anurag</div>
<div>&nbsp;</div>
<div>&nbsp;</div>
<div><span class="gmail_quote">On 9/15/06, <b class="gmail_sendername">Bob Friesenhahn</b> &lt;<a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:bfriesen@simple.dallas.tx.us" target="_blank">bfriesen@simple.dallas.tx.us
</a>&gt; wrote:</span> </div>
<div>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">On Fri, 15 Sep 2006, Grissom, Ed wrote:<br><br>&gt;<br>&gt; Gerben -<br>&gt;<br>&gt; For palette images, is an alpha channel explicitly forbidden by the spec 
<br>&gt; ?<br>&gt;<br>&gt; What I am thinking is an extra data plane, not an extra column in the<br>&gt; color table.<br><br>Right.&nbsp;&nbsp;An interesting issue is that libtiff requires that all samples<br>be the same size so Pallete images using a small bits per sample for 
<br>the index impose the same bits per sample restriction on the alpha<br>channel.&nbsp;&nbsp;For an 8 bits per sample image, this is not usually a<br>restriction, but it becomes more so for 2 or 4 bits per sample.<br><br>Associated alpha makes no sense since Pallete entries are not related 
<br>to pixel position but associated alpha is related to pixel position.<br><br>Bob<br>======================================<br>Bob Friesenhahn<br><a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:bfriesen@simple.dallas.tx.us" target="_blank">
bfriesen@simple.dallas.tx.us </a>, <a onclick="return top.js.OpenExtLink(window,event,this)" href="http://www.simplesystems.org/users/bfriesen/" target="_blank">http://www.simplesystems.org/users/bfriesen/</a><br>GraphicsMagick Maintainer,&nbsp;&nbsp;&nbsp;&nbsp;
<a onclick="return top.js.OpenExtLink(window,event,this)" href="http://www.graphicsmagick.org/" target="_blank">http://www.GraphicsMagick.org/</a><br><br></blockquote></div><br>

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