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July 2004
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2004.07.21 05:28 "JPEG Compression Support", by Jean Paul Mir V
Hi,
I'm working on a C++ ATL component for TIFF conversion to PCL, PS And PDF.
Actually I have completed TiffToPCL and TiffToPS translation based on
tiff2ps and tifftopcl tools of libtiff.
Everything works fine until I started using Grayscale and Color Images using
JPEG compression. After many errors I successfully created libtiff.lib, but
when I tried to convert the file using my ATL I got so many errors regarding
unrecognized tags and so on. One of those alerts saids "Old-Style JPEG
Support is not installed"... then I enabled OJPEG compression and recompile
it again.
At this time I got an error like "..._ jpeg_reset_huff_decode
unrecognized... " or something like that...
I searched on internet and found an article saying that I would need to
patch libtiff to add OJPEG support to the library.. I could not patch the
library but I found the missing function:
GLOBAL(void)
jpeg_reset_huff_decode (register j_decompress_ptr cinfo)
{ register huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
register int ci = 0;
/* Discard encoded input bits, up to the next Byte boundary */
entropy->bitstate.bits_left &= ~7;
/* Re-initialize DC predictions to 0 */
do entropy->saved.last_dc_val[ci] = 0; while (++ci <
cinfo->comps_in_scan);
}
I just copy-paste it into jduff.c and then the compilation ends up
successfully.
Once I got the library and my DLL compiled(after Library compilation), I
tried to convert a JPEG Compressed tiff file to a PCL file and all I got is
a full of gray lines page.
Could someone tell me how could I build propertly the library with support
for JPEG and OJPEG compression ???
Thanks in advance!