/* Copyright (c) 1999 Surendar Chandra and Duke University
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by Duke University
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE
 */

/*
  Usage:
      unsigned int initialQualityFactor(struct jpeg_decompress_struct dinfo)
  
  Compile with IJG JPEG Library version 6a or higher.
 */

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#include <jpeglib.h>
#include <jinclude.h>
#include <jerror.h>

#include "common.h"

/*
  ALL_TABLE - Compute the quality factor as a average of all Quant
  table values. Usually computing the value for just a single
  representative Quant table entry is enough and so this may be safely
  undefined. 
*/
#undef ALL_TABLE

/*
  The representative index if not using ALL_TABLE. 2 seems to work best
 */
#define USE_INDEX 2

/*
  We can either use the Luminance table or Chrominance table. There
  are no chrominance tables for GrayScale JPEGs and so using Luminance 
  table is preferred
 */
#define USE_LUMINANCE_TABLE

#define DCTSIZE2 64

unsigned int initialQualityFactor(struct jpeg_decompress_struct dinfo)
{
  JQUANT_TBL *qt;
  unsigned int initQ = 0;
  unsigned int temp;
	
  /* Standard JPEG Luminance and Chrominance Quantization tables */
#ifdef USE_LUMINANCE_TABLE
  static const unsigned int std_luminance_quant_tbl[DCTSIZE2] = {
    16,  11,  10,  16,  24,  40,  51,  61,
    12,  12,  14,  19,  26,  58,  60,  55,
    14,  13,  16,  24,  40,  57,  69,  56,
    14,  17,  22,  29,  51,  87,  80,  62,
    18,  22,  37,  56,  68, 109, 103,  77,
    24,  35,  55,  64,  81, 104, 113,  92,
    49,  64,  78,  87, 103, 121, 120, 101,
    72,  92,  95,  98, 112, 100, 103,  99
  };
#else
  static const unsigned int std_chrominance_quant_tbl[DCTSIZE2] = {
    17,  18,  24,  47,  99,  99,  99,  99,
    18,  21,  26,  66,  99,  99,  99,  99,
    24,  26,  56,  99,  99,  99,  99,  99,
    47,  66,  99,  99,  99,  99,  99,  99,
    99,  99,  99,  99,  99,  99,  99,  99,
    99,  99,  99,  99,  99,  99,  99,  99,
    99,  99,  99,  99,  99,  99,  99,  99,
    99,  99,  99,  99,  99,  99,  99,  99
  };
#endif /* USE_LUMINANCE_TABLE */


#ifdef USE_LUMINANCE_TABLE
  qt = dinfo.quant_tbl_ptrs[0];
#else  /* USE_LUMINANCE_TABLE */
  qt = dinfo.quant_tbl_ptrs[1];
#endif /* USE_LUMINANCE_TABLE */

#ifdef ALL_TABLE
  for (int index=0; index < DCTSIZE2;index++) {
    temp = ((qt->quantval[index] * 100L) - 50L) / std_luminance_quant_tbl[index];
    if (temp <= 100) temp = (200 - temp) / 2; else temp = 5000 / temp;
    initQ+=temp;
  }
  initQ /= DCTSIZE2;
#else
  temp = ((qt->quantval[USE_INDEX] * 100L) - 50L) / std_luminance_quant_tbl[USE_INDEX]; 
  if (temp <= 100) temp = (200 - temp) / 2; else temp = 5000 / temp; 
  initQ = temp;
#endif /* ALL_TABLE */

  return initQ;
}

#undef DEBUG
#ifdef DEBUG

int main(int argc, char *argv[], char *envp[])
{
  FILE * infile;                /* source file */  
  struct jpeg_decompress_struct dinfo;
  struct jpeg_error_mgr jerr;
  
  if (argc != 2) {
    fprintf(stderr, "Usage: %s <JPEG image>\n", *argv);
    exit(0);
  }
    
  if ((infile = fopen(argv[1], "rb")) == NULL) {
    fprintf(stderr, "can't open %s\n", argv[1]);
    exit(0);
  }

  /* We set up the normal JPEG error routines, then override error_exit. */
  dinfo.err = jpeg_std_error(&jerr);

  jpeg_create_decompress(&dinfo);
  jpeg_stdio_src(&dinfo, infile);  
  (void) jpeg_read_header(&dinfo, TRUE);
  
  printf("JPEG Quality Factor: %d\n", initialQualityFactor(dinfo));

  jpeg_destroy_decompress(&dinfo);
  exit(0);
} 
#endif /* DEBUG */