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From: Frank Warmerdam <warmerdam@pobox.com>
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To: xevit@s3os.net
Cc: tiff@remotesensing.org
Subject: Re: [Tiff] support for modify compressed tile.
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Date: Thu, 27 May 2004 15:08:46 -0400
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xevit@s3os.net wrote:
> Hello,
> I'm working on a large image viewer project.
> Currently I have a viewer that works with libtiff and supports large tiff
> tiled files, and zooms.
> 
> Now I want to implement a libtiff editor, but my problem is that when I'm
> trying to update a tile works if the image is uncompressed, but fails if
> the image is compressed ( I need compressed images ). Other problem is
> that I can have a read/write acces to the file simultaneous. To read and
> write some information.
> 
> Have you got any idea, what can I do to solve this.

Xevit,

It should be possible to open the file in "update" mode (ie. mode="r+")
to read and write on the same handle.

Re-writing compressed blocks is somewhat more problematic.  What we really
need is to keep track of freespace in the file, and to move blocks to another
location if the compressed form is larger than the existing space.  This is
a non-trivial change to make but shouldn't be insurmountable.  I don't forsee
Andrey or I implementing this though, unless you can fund some of his time or
he takes a particular interest in doing it.

If you can prepare careful patches we might be able to integrate them into the
core.

Best regards,
-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam@pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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