The SIMD quantization algorithm does not produce correct results with the fast forward integer DCT and JPEG qualities >= 98, so for now, use the non-SIMD quantization function under those circumstances.
git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/branches/1.0.x@383 632fc199-4ca6-4c93-a231-07263d6284db
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DRC
@@ -3,13 +3,21 @@
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[1] Added further protections against invalid Huffman codes.
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[2] Since the fast integer forward DCT seems to degrade for JPEG qualities
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greater than 95, TurboJPEG/OSS will now automatically use the slow integer
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forward DCT when generating JPEG images of quality 96 or greater. This
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reduces compression performance by as much as 15% for these high-quality images
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but is necessary to ensure that the images are perceptually lossless.
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[2] The algorithm used by the SIMD quantization function cannot produce correct
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results when the JPEG quality is >= 98 and the fast integer forward DCT is
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used. Thus, the non-SIMD quantization function is now used for those cases,
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and libjpeg-turbo should now produce identical output to libjpeg v6b in all
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cases.
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[3] Fixed visual artifacts in grayscale JPEG compression caused by a typo in
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[3] Despite the above, the fast integer forward DCT still degrades somewhat for
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JPEG qualities greater than 95, so TurboJPEG/OSS will now automatically use the
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slow integer forward DCT when generating JPEG images of quality 96 or greater.
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This reduces compression performance by as much as 15% for these high-quality
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images but is necessary to ensure that the images are perceptually lossless.
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It also ensures that the library can avoid the performance pitfall created by
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[2].
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[4] Fixed visual artifacts in grayscale JPEG compression caused by a typo in
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the RGB-to-chrominance lookup tables.
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@@ -102,6 +102,8 @@ test: testclean all
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./jpegut
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./cjpeg -dct int -outfile testoutint.jpg $(srcdir)/testorig.ppm
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./cjpeg -dct fast -opt -outfile testoutfst.jpg $(srcdir)/testorig.ppm
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./cjpeg -dct fast -quality 100 -opt -outfile testoutfst100.jpg $(srcdir)/testorig.ppm
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cmp $(srcdir)/testimgfst100.jpg testoutfst100.jpg
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./cjpeg -dct float -outfile testoutflt.jpg $(srcdir)/testorig.ppm
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cmp $(srcdir)/testimgint.jpg testoutint.jpg
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cmp $(srcdir)/testimgfst.jpg testoutfst.jpg
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@@ -42,6 +42,34 @@ replacing the optimized jchuff.c and jdhuff.c with their unoptimized
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counterparts from the libjpeg v6b source.
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*******************************************************************************
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** Performance pitfalls
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*******************************************************************************
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===============
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Restart Markers
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===============
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The optimized Huffman decoder in libjpeg-turbo does not handle restart markers
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in a way that makes libjpeg happy, so it is necessary to use the slow Huffman
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decoder when decompressing a JPEG image that has restart markers. This can
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cause the decompression performance to drop by as much as 20%, but the
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performance will still be much much greater than that of libjpeg v6b. Many
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consumer packages, such as PhotoShop, use restart markers when generating JPEG
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images, so images generated by those programs will experience this issue.
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===============================================
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Fast Integer Forward DCT at High Quality Levels
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===============================================
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The algorithm used by the SIMD-accelerated quantization function cannot produce
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correct results whenever the fast integer forward DCT is used along with a JPEG
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quality of 98-100. Thus, libjpeg-turbo must use the non-SIMD quantization
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function in those cases. This causes performance to drop by as much as 40%.
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It is therefore strongly advised that you use the slow integer forward DCT
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whenever encoding images with a JPEG quality of 98 or higher.
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*******************************************************************************
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** Using libjpeg-turbo
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*******************************************************************************
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18
jcdctmgr.c
18
jcdctmgr.c
@@ -4,6 +4,7 @@
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* Copyright (C) 1994-1996, Thomas G. Lane.
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* Copyright (C) 1999-2006, MIYASAKA Masaru.
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* Copyright 2009 Pierre Ossman <ossman@cendio.se> for Cendio AB
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* Copyright (C) 2011 D. R. Commander
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README file.
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*
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@@ -39,6 +40,8 @@ typedef JMETHOD(void, float_quantize_method_ptr,
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(JCOEFPTR coef_block, FAST_FLOAT * divisors,
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FAST_FLOAT * workspace));
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METHODDEF(void) quantize (JCOEFPTR, DCTELEM *, DCTELEM *);
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typedef struct {
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struct jpeg_forward_dct pub; /* public fields */
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@@ -160,7 +163,7 @@ flss (UINT16 val)
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* of in a consecutive manner, yet again in order to allow SIMD
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* routines.
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*/
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LOCAL(void)
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LOCAL(int)
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compute_reciprocal (UINT16 divisor, DCTELEM * dtbl)
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{
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UDCTELEM2 fq, fr;
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@@ -189,6 +192,9 @@ compute_reciprocal (UINT16 divisor, DCTELEM * dtbl)
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dtbl[DCTSIZE2 * 1] = (DCTELEM) c; /* correction + roundfactor */
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dtbl[DCTSIZE2 * 2] = (DCTELEM) (1 << (sizeof(DCTELEM)*8*2 - r)); /* scale */
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dtbl[DCTSIZE2 * 3] = (DCTELEM) r - sizeof(DCTELEM)*8; /* shift */
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if(r <= 16) return 0;
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else return 1;
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}
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/*
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@@ -232,7 +238,9 @@ start_pass_fdctmgr (j_compress_ptr cinfo)
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}
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dtbl = fdct->divisors[qtblno];
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for (i = 0; i < DCTSIZE2; i++) {
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compute_reciprocal(qtbl->quantval[i] << 3, &dtbl[i]);
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if(!compute_reciprocal(qtbl->quantval[i] << 3, &dtbl[i])
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&& fdct->quantize == jsimd_quantize)
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fdct->quantize = quantize;
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}
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break;
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#endif
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@@ -266,10 +274,12 @@ start_pass_fdctmgr (j_compress_ptr cinfo)
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}
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dtbl = fdct->divisors[qtblno];
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for (i = 0; i < DCTSIZE2; i++) {
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compute_reciprocal(
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if(!compute_reciprocal(
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DESCALE(MULTIPLY16V16((INT32) qtbl->quantval[i],
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(INT32) aanscales[i]),
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CONST_BITS-3), &dtbl[i]);
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CONST_BITS-3), &dtbl[i])
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&& fdct->quantize == jsimd_quantize)
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fdct->quantize = quantize;
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}
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}
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break;
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BIN
testimgfst100.jpg
Normal file
BIN
testimgfst100.jpg
Normal file
Binary file not shown.
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After Width: | Height: | Size: 18 KiB |
@@ -248,9 +248,11 @@ test: testclean $(ODIR)/cjpeg.exe $(ODIR)/djpeg.exe $(ODIR)/jpegtran.exe \
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cd $(ODIR); ./jpegut
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$(ODIR)/cjpeg -dct int -outfile $(ODIR)/testoutint.jpg testorig.ppm
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$(ODIR)/cjpeg -dct fast -opt -outfile $(ODIR)/testoutfst.jpg testorig.ppm
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$(ODIR)/cjpeg -dct fast -quality 100 -opt -outfile $(ODIR)/testoutfst100.jpg testorig.ppm
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$(ODIR)/cjpeg -dct float -outfile $(ODIR)/testoutflt.jpg testorig.ppm
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cmp testimgint.jpg $(ODIR)/testoutint.jpg
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cmp testimgfst.jpg $(ODIR)/testoutfst.jpg
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cmp testimgfst100.jpg $(ODIR)/testoutfst100.jpg
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cmp testimgflt.jpg $(ODIR)/testoutflt.jpg
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$(ODIR)/djpeg -dct int -fast -ppm -outfile $(ODIR)/testoutint.ppm testorig.jpg
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$(ODIR)/djpeg -dct fast -ppm -outfile $(ODIR)/testoutfst.ppm testorig.jpg
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