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2008.02.06 17:12 "Re: Why is TIFF/zip not a default option?", by Frank Warmerdam
Bob Friesenhahn wrote:
> On Wed, 6 Feb 2008, Anders Sewerin Johansen wrote:
>>
>> Can I conclude that most recent libtiff equiped systems (e.g. systems
>> deployed or updated during the last five years) will support tiff/zip?
>
> You can't really conclude anything at all. Yesterday I fixed a bug in
> my software related to libtiff 3.6.1. People are still using these old
> versions. Some commercial OSs don't automatically update to the latest
> version with each major release because they operate on the "If it ain't
> broke ..." principle.
>
> Currently it is necessary to use defines from tiffconf.h to determine
> the libtiff build options used. Unfortunately, this is completely the
> wrong way to handle the problem. Libtiff should support a query
> function whereby an application can test to see if a library supports a
> feature at run-time.
Bob,
It is possible to detect the available codecs at runtime as I do here
in GDAL:
/* -------------------------------------------------------------------- */
/* Determine which compression codecs are available that we */
/* want to advertise. If we are using an old libtiff we won't */
/* be able to find out so we just assume all are available. */
/* -------------------------------------------------------------------- */
strcpy( szOptionalCompressItems,
" <Value>NONE</Value>" );
#if TIFFLIB_VERSION <= 20040919
strcat( szOptionalCompressItems,
" <Value>PACKBITS</Value>"
" <Value>JPEG</Value>"
" <Value>LZW</Value>"
" <Value>DEFLATE</Value>" );
#else
TIFFCodec *c, *codecs = TIFFGetConfiguredCODECs();
for( c = codecs; c->name; c++ )
{
if( c->scheme == COMPRESSION_PACKBITS )
strcat( szOptionalCompressItems,
" <Value>PACKBITS</Value>" );
else if( c->scheme == COMPRESSION_JPEG )
strcat( szOptionalCompressItems,
" <Value>JPEG</Value>" );
else if( c->scheme == COMPRESSION_LZW )
strcat( szOptionalCompressItems,
" <Value>LZW</Value>" );
else if( c->scheme == COMPRESSION_ADOBE_DEFLATE )
strcat( szOptionalCompressItems,
" <Value>DEFLATE</Value>" );
else if( c->scheme == COMPRESSION_CCITTRLE )
strcat( szOptionalCompressItems,
" <Value>CCITTRLE</Value>" );
else if( c->scheme == COMPRESSION_CCITTFAX3 )
strcat( szOptionalCompressItems,
" <Value>CCITTFAX3</Value>" );
else if( c->scheme == COMPRESSION_CCITTFAX4 )
strcat( szOptionalCompressItems,
" <Value>CCITTFAX4</Value>" );
}
_TIFFfree( codecs );
#endif
And you are absolute right about not being able to conclude anything.
If I wanted ubiquity I would not depend on Deflate or LZW compression.
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 | President OSGeo, http://osgeo.org