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/* GIMP - The GNU Image Manipulation Program
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* Copyright (C) 1995 Spencer Kimball and Peter Mattis
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* Copyright (C) 2007 Raphaël Quinet <raphael@gimp.org>
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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#include <glib/gstdio.h>
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#include "jpeg-quality.h"
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* Note that although 0 is a valid quality for IJG's JPEG library, the
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* baseline quantization tables for quality 0 and 1 are identical (all
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* divisors are set to the maximum value 255). So 0 can be used here
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* to flag unusual settings.
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/* sum of the luminance divisors for quality = 0..100 (IJG standard tables) */
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static gint std_luminance_sum[101] =
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16320, 16315, 15946, 15277, 14655, 14073, 13623, 13230, 12859, 12560, 12240,
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11861, 11456, 11081, 10714, 10360, 10027, 9679, 9368, 9056, 8680, 8331,
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7995, 7668, 7376, 7084, 6823, 6562, 6345, 6125, 5939, 5756, 5571,
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5421, 5240, 5086, 4976, 4829, 4719, 4616, 4463, 4393, 4280, 4166,
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4092, 3980, 3909, 3835, 3755, 3688, 3621, 3541, 3467, 3396, 3323,
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3247, 3170, 3096, 3021, 2952, 2874, 2804, 2727, 2657, 2583, 2509,
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2437, 2362, 2290, 2211, 2136, 2068, 1996, 1915, 1858, 1773, 1692,
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1620, 1552, 1477, 1398, 1326, 1251, 1179, 1109, 1031, 961, 884,
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814, 736, 667, 592, 518, 441, 369, 292, 221, 151, 86,
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/* sum of the chrominance divisors for quality = 0..100 (IJG standard tables) */
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static gint std_chrominance_sum[101] =
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16320, 16320, 16320, 16218, 16010, 15731, 15523, 15369, 15245, 15110, 14985,
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14864, 14754, 14635, 14526, 14429, 14346, 14267, 14204, 13790, 13121, 12511,
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11954, 11453, 11010, 10567, 10175, 9787, 9455, 9122, 8844, 8565, 8288,
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8114, 7841, 7616, 7447, 7227, 7060, 6897, 6672, 6562, 6396, 6226,
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6116, 5948, 5838, 5729, 5614, 5505, 5396, 5281, 5172, 5062, 4947,
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4837, 4726, 4614, 4506, 4395, 4282, 4173, 4061, 3950, 3839, 3727,
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3617, 3505, 3394, 3284, 3169, 3060, 2949, 2836, 2780, 2669, 2556,
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2445, 2336, 2221, 2111, 2000, 1888, 1778, 1666, 1555, 1444, 1332,
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1223, 1110, 999, 891, 779, 668, 558, 443, 333, 224, 115,
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* jpeg_detect_quality:
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* @cinfo: a pointer to a JPEG decompressor info.
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* Returns the exact or estimated quality value that was used to save
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* the JPEG image by analyzing the quantization table divisors.
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* If an exact match for the IJG quantization tables is found, then a
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* quality setting in the range 1..100 is returned. If the quality
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* can only be estimated, then a negative number in the range -1..-100
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* is returned; its absolute value represents the maximum IJG quality
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* setting to use. If the quality cannot be reliably determined, then
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* This function must be called after jpeg_read_header() so that
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* @cinfo contains the quantization tables read from the DQT markers
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* Return Value: the JPEG quality setting in the range 1..100, -1..-100 or 0.
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jpeg_detect_quality (struct jpeg_decompress_struct *cinfo)
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/* files using CMYK or having 4 quantization tables are unusual */
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if (!cinfo || cinfo->output_components > 3 || cinfo->quant_tbl_ptrs[3])
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/* Most files use table 0 for luminance divisors (Y) and table 1 for
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* chrominance divisors (Cb and Cr). Some files use separate tables
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* for Cb and Cr, so table 2 may also be used.
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for (t = 0; t < 3; t++)
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if (cinfo->quant_tbl_ptrs[t])
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for (i = 0; i < DCTSIZE2; i++)
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sum[t] += cinfo->quant_tbl_ptrs[t]->quantval[i];
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if (cinfo->output_components > 1)
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if (sum[0] < 64 || sum[1] < 64)
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/* compare with the chrominance table having the lowest sum */
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if (sum[1] < sum[2] || sum[2] <= 0)
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sums = sum[0] + sum[1];
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sums = sum[0] + sum[2];
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while (sums > std_luminance_sum[q] + std_chrominance_sum[q])
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if (sum[0] == std_luminance_sum[q] && sum[1] == std_chrominance_sum[q])
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while (sum[0] > std_luminance_sum[q])
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if (sum[0] == std_luminance_sum[q])
added
removed
plug-ins/jpeg/jpeg-quality.c
