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Date: Fri, 1 Apr 2005 10:08:26 +0200
From: Jean-Yves Le Ridant <jean-yves.leridant@culture.gouv.fr>
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Subject: Re[3]: [Tiff] tif_jpeg.c and 12bit JPEG Files
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Status:   

Hello Bob,

Tuesday, March 29, 2005, 6:08:24 PM, you wrote:


BF> To me, the 16-bit JSAMPLE is really only a performance impact for 
BF> 8-bit users who expect to memcpy() directly to and from libjpeg's 
BF> buffers.  Applications which iterate through the JSAMPLE array in 
BF> order to copy to/from their own format should see little performance
BF> difference.

I'm currently, downloading-installing cygwin's tiff and jpeg material,
- I was'nt aware ... :-((( - and getting a global survey of differences
of both tiffwin32, cygwin tiff and jpeg, from 'pure' libtiff et v6b.

At this point, so not knowning what is exactely done in each case,
I also have great doubt about real impact of "few and long" memcpys
vs iterations in a general case, and especially when writing
files.
The more side effect I imagine, if for writers processing 'big'
tile(s), ( temp alloc of rawsize * 2 and optimized hufftbl per jpeg frame )
and eventual .... system bootleneck. "comme on dit ici".

The optimized two pass mode imposed ( at runtime )
to 12 bits samples in ijgv6b can safely be inhibited.
I had the use of such practice ...
it worked with 12 bits chunck ...
choosen ...
in study case :-)

--
Jean-Yves


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