JPEGView/Independent JPEG Group/jcparam.c

/*
 * jcparam.c
 *
 * Copyright (C) 1991-1994, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains optional default-setting code for the JPEG compressor.
 * Applications do not have to use this file, but those that don't use it
 * must know a lot more about the innards of the JPEG code.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"


/*
 * Quantization table setup routines
 */

GLOBAL void
jpeg_add_quant_table (j_compress_ptr cinfo, int which_tbl,
		      const unsigned int *basic_table,
		      int scale_factor, boolean force_baseline)
/* Define a quantization table equal to the basic_table times
 * a scale factor (given as a percentage).
 * If force_baseline is TRUE, the computed quantization table entries
 * are limited to 1..255 for JPEG baseline compatibility.
 */
{
  JQUANT_TBL ** qtblptr = & cinfo->quant_tbl_ptrs[which_tbl];
  int i;
  long temp;

  /* Safety check to ensure start_compress not called yet. */
  if (cinfo->global_state != CSTATE_START)
    ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);

  if (*qtblptr == NULL)
    *qtblptr = jpeg_alloc_quant_table((j_common_ptr) cinfo);

  for (i = 0; i < DCTSIZE2; i++) {
    temp = ((long) basic_table[i] * scale_factor + 50L) / 100L;
    /* limit the values to the valid range */
    if (temp <= 0L) temp = 1L;
#if BITS_IN_JSAMPLE == 8
    if (temp > 32767L) temp = 32767L; /* limit quant vals to 'short' */
#else
    if (temp > 65535L) temp = 65535L; /* quant vals are 'UINT16' */
#endif
    if (force_baseline && temp > 255L)
      temp = 255L;		/* limit to baseline range if requested */
    (*qtblptr)->quantval[i] = (UINT16) temp;
  }

  /* Initialize sent_table FALSE so table will be written to JPEG file. */
  (*qtblptr)->sent_table = FALSE;
}


GLOBAL void
jpeg_set_linear_quality (j_compress_ptr cinfo, int scale_factor,
			 boolean force_baseline)
/* Set or change the 'quality' (quantization) setting, using default tables
 * and a straight percentage-scaling quality scale.  In most cases it's better
 * to use jpeg_set_quality (below); this entry point is provided for
 * applications that insist on a linear percentage scaling.
 */
{
  /* This is the sample quantization table given in the JPEG spec section K.1,
   * but expressed in zigzag order (as are all of our quant. tables).
   * The spec says that the values given produce "good" quality, and
   * when divided by 2, "very good" quality.
   */
  static const unsigned int std_luminance_quant_tbl[DCTSIZE2] = {
    16,  11,  12,  14,  12,  10,  16,  14,
    13,  14,  18,  17,  16,  19,  24,  40,
    26,  24,  22,  22,  24,  49,  35,  37,
    29,  40,  58,  51,  61,  60,  57,  51,
    56,  55,  64,  72,  92,  78,  64,  68,
    87,  69,  55,  56,  80, 109,  81,  87,
    95,  98, 103, 104, 103,  62,  77, 113,
    121, 112, 100, 120,  92, 101, 103,  99
    };
  static const unsigned int std_chrominance_quant_tbl[DCTSIZE2] = {
    17,  18,  18,  24,  21,  24,  47,  26,
    26,  47,  99,  66,  56,  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,  99,  99,  99,  99,
    99,  99,  99,  99,  99,  99,  99,  99
    };

  /* Set up two quantization tables using the specified scaling */
  jpeg_add_quant_table(cinfo, 0, std_luminance_quant_tbl,
		       scale_factor, force_baseline);
  jpeg_add_quant_table(cinfo, 1, std_chrominance_quant_tbl,
		       scale_factor, force_baseline);
}


GLOBAL int
jpeg_quality_scaling (int quality)
/* Convert a user-specified quality rating to a percentage scaling factor
 * for an underlying quantization table, using our recommended scaling curve.
 * The input 'quality' factor should be 0 (terrible) to 100 (very good).
 */
{
  /* Safety limit on quality factor.  Convert 0 to 1 to avoid zero divide. */
  if (quality <= 0) quality = 1;
  if (quality > 100) quality = 100;

  /* The ba