2003.04.28 15:39 "Re: old jpeg", by Andrey Kiselev
Is somebody can tell me with wich version of jpeg libraries, I can read tiff image encoded with old jpeg algo?
You need libjpeg version 6B from ftp://ftp.uu.net:/graphics/jpeg/. To be able to compile libtiff with OJPEG support this library must be patched:
*** jdhuff.c.orig Mon Oct 20 17:51:10 1997
--- jdhuff.c Sun Nov 11 17:33:58 2001
***************
*** 648,651 ****
--- 648,683 ----
for (i = 0; i < NUM_HUFF_TBLS; i++) {
entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
}
}
+
+ /*
+ * BEWARE OF KLUDGE: This subroutine is a hack for decoding illegal JPEG-in-
+ * TIFF encapsulations produced by Microsoft's Wang Imaging
+ * for Windows application with the public-domain TIFF Library. Based upon an
+ * examination of selected output files, this program apparently divides a JPEG
+ * bit-stream into consecutive horizontal TIFF "strips", such that the JPEG
+ * encoder's/decoder's DC coefficients for each image component are reset before
+ * each "strip". Moreover, a "strip" is not necessarily encoded in a multiple
+ * of 8 bits, so one must sometimes discard 1-7 bits at the end of each "strip"
+ * for alignment to the next input-Byte storage boundary. IJG JPEG Library
+ * decoder state is not normally exposed to client applications, so this sub-
+ * routine provides the TIFF Library with a "hook" to make these corrections.
+ * It should be called after "jpeg_start_decompress()" and before
+ * "jpeg_finish_decompress()", just before decoding each "strip" using
+ * "jpeg_read_raw_data()" or "jpeg_read_scanlines()".
+ *
+ * This kludge is not sanctioned or supported by the Independent JPEG Group, and
+ * future changes to the IJG JPEG Library might invalidate it. Do not send bug
+ * reports about this code to IJG developers. Instead, contact the author for
+ * advice: Scott B. Marovich <marovich@hpl.hp.com>, Hewlett-Packard Labs, 6/01.
+ */
+ 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);
+ }
Andrey V. Kiselev
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