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From: Toby Thain <toby@telegraphics.com.au>
Date: Wed, 17 Dec 2008 10:40:00 -0500
To: "Mitesh" <shailaj@mail.com.np>
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Cc: tiff@lists.maptools.org, 'Richard Nolde' <nrichard8@qwest.net>
Subject: Re: [Tiff] Extracting layers from a TIFF file
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On 17-Dec-08, at 7:34 AM, Mitesh wrote:

> Hello Richard and all,
>
> I need to extract the layers like in layers in psd.
>
> I looked at ImageMagick software and it can extract layers from a  
> psd file
> but not from a tiff file.
>
> Our tiff files are created in Photoshop composing of several layers  
> (50 +)
> and then saved in a tiff file.
>
> Now I have to write code to separate each layer information  
> embedded in the
> tiff file and GENERATE A SEPARATE FILE for each layer.


That's exactly what my tool does, from the PSD. Why do you have to  
save as TIFF?


> Or in other words
> decompose the combined layers

Adobe may have some information on how it encodes Photoshop layer  
data in TIFF, in the SDK.


>
> There is a confusion about multipage, layers and channels.
>
> Can somebody explain in detail what are the above?
>
> Do you all mean to say in Tiff layer data is stored as channels?

You could closely examine a TIFF produced by Photoshop. Start with  
tiffinfo...

--Toby

>
> Please explain fully and point me to the write direction.
>
>
> Thanks
> Mitesh
> -----Original Message-----
> From: tiff-bounces@lists.maptools.org
> [mailto:tiff-bounces@lists.maptools.org] On Behalf Of Richard Nolde
> Sent: Tuesday, December 16, 2008 10:49 PM
> To: tiff@lists.maptools.org
> Subject: [Tiff] Extracting layers from a TIFF file
>
> On Tue, 16 Dec 2008, Mitesh wrote
>
>>> Now it is clear to me that multi pages and layers are two different
> beasts.
>>>
>>> Now I need to extract layers from a Tiff file. How should I do it?
> Please
>>> suggest.
>> Do you know how many layers are in your TIFF file?  If you install
>> libtiff and utilities, what is the output of 'tiffinfo' when provided
>> the name of your file?
>>
>> My software (GraphicsMagick) may be useful but it only handles up to
>> four channels ("layers"), one of which must be an alpha channel.
>> There is likely other software much better at handling TIFFs with an
>> arbitrary number of channels.
>>
>> Bob
>> ======================================
>> Bob Friesenhahn
> The next version of tiffcrop has hooks that could be used to do  
> this and
> it is not limited to 4 channels. I posted a query to the list as to
> whether this would be useful and no one replied so I only  
> implemented it
> for debugging purposes.  What exactly do you mean when you say  
> extract a
> layer?  Extract the raw binary data as a data dump in binary or ASCII
> format or to a new TIFF file.  The first case can be handled with my
> debugging dump code.  The later requires some information about how
> various types of TIFF input files will be converted to output  
> files.  eg
> RGBA to RGB may not be a big deal since you are just throwing away the
> alpha channel but all current planes would have to be multiplied by  
> the
> values in the alpha channel if is is associated alpha data if I  
> remember
> correctly.  However extracting one or more input channels
> RGB[A][N1][N2]...  to one of R,G,B,A,N1,N2  requires some  
> interpretation
> of the input data and a new definition of the output file type.   
> Does a
> single channel become a 'grayscale' image and if so, what about bit
> depth conversions?  If you extract any three channels from a
> multi-spectral image, does it become RGB?  Since I doubt that there is
> any legal TIFF image type where the number of image planes is not  
> 1,3,4
> or greater than four. You probably cannot extract only two channels  
> to a
> new TIFF image.
>
> If you can define the conversions in a way that are generally accepted
> by the other members of the TIFF community, I could probably add that
> support to tiffcrop in the next release after this one.  The current
> version in CVS will be obsoleted by the version that is soon to be
> uploaded so don't bother looking at it as it has none of the code  
> you need.
>
> Richard Nolde
> Tiffcrop author
> _______________________________________________
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> http://www.remotesensing.org/libtiff/
>
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> http://lists.maptools.org/mailman/listinfo/tiff
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