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gammaCorrectionTables.c

/**
 * Jitter offset table
 *
 * $Id: gammaCorrectionTables.c,v 1.3 2002/11/25 12:02:03 mein Exp $
 *
 * ***** BEGIN GPL/BL DUAL LICENSE BLOCK *****
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version. The Blender
 * Foundation also sells licenses for use in proprietary software under
 * the Blender License.  See http://www.blender.org/BL/ for information
 * about this.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 * The Original Code is Copyright (C) 2001-2002 by NaN Holding BV.
 * All rights reserved.
 *
 * The Original Code is: all of this file.
 *
 * Contributor(s): none yet.
 *
 * ***** END GPL/BL DUAL LICENSE BLOCK *****
 */

#include "gammaCorrectionTables.h"
#include <stdlib.h>
#include <math.h>
#include "render_intern.h"

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

/* There are two parts here: one for the old renderer, one for the unified   */
/* renderer. we start with the latter.                                       */

/* Default gamma. For most CRTs, gamma ranges from 2.2 to 2.5 (Foley), so    */
/* 2.35 seems appropriate enough. Experience teaches a different number      */
/* though. Old blender: 2.0. It  might be nice to make this a slider         */
#define RE_DEFAULT_GAMMA 2.0
/* This 400 is sort of based on the number of intensity levels needed for    */
/* the typical dynamic range of a medium, in this case CRTs. (Foley)         */
/* (Actually, it says the number should be between 400 and 535.)             */
#define RE_GAMMA_TABLE_SIZE 400

/* These indicate the status of the gamma lookup table --------------------- */

static float gamma_range_table[RE_GAMMA_TABLE_SIZE + 1];
static float gamfactor_table[RE_GAMMA_TABLE_SIZE];
static float inv_gamma_range_table[RE_GAMMA_TABLE_SIZE + 1];
static float inv_gamfactor_table[RE_GAMMA_TABLE_SIZE];
static float colour_domain_table[RE_GAMMA_TABLE_SIZE + 1];
static float colour_step;
static float inv_colour_step;
static float valid_gamma;
static float valid_inv_gamma;
static int   gamma_table_initialised = 0;
static int   do_gamma;
/* ------------------------------------------------------------------------- */

float gammaCorrect(float c)
{
      int i;
      float res = 0.0;
      
      i = floor(c * inv_colour_step);
      /* Clip to range [0,1]: outside, just do the complete calculation.       */
      /* We may have some performance problems here. Stretching up the LUT     */
      /* may help solve that, by exchanging LUT size for the interpolation.    */
      /* Negative colours are explicitly handled.                              */
      if (i < 0) res = -pow(abs(c), valid_gamma);
      else if (i >= RE_GAMMA_TABLE_SIZE ) res = pow(c, valid_gamma);
      else res = gamma_range_table[i] + 
                   ( (c - colour_domain_table[i]) * gamfactor_table[i]); 
      
      return res;
} /* end of float gammaCorrect(float col) */

/* ------------------------------------------------------------------------- */

float invGammaCorrect(float col)
{
      int i;
      float res = 0.0;

      i = floor(col*inv_colour_step);
      /* Negative colours are explicitly handled.                              */
      if (i < 0) res = -pow(abs(col), valid_inv_gamma);
      else if (i >= RE_GAMMA_TABLE_SIZE) res = pow(col, valid_inv_gamma);
      else res = inv_gamma_range_table[i] + 
                   ( (col - colour_domain_table[i]) * inv_gamfactor_table[i]);
                     
      return res;
} /* end of float invGammaCorrect(float col) */


/* ------------------------------------------------------------------------- */

void makeGammaTables(float gamma)
{
      /* we need two tables: one forward, one backward */
      int i;

      valid_gamma        = gamma;
      valid_inv_gamma    = 1.0 / gamma;
      colour_step        = 1.0 / RE_GAMMA_TABLE_SIZE;
      inv_colour_step    = (float) RE_GAMMA_TABLE_SIZE; 

      /* We could squeeze out the two range tables to gain some memory.        */   
      for (i = 0; i < RE_GAMMA_TABLE_SIZE; i++) {
            colour_domain_table[i]   = i * colour_step;
            gamma_range_table[i]     = pow(colour_domain_table[i],
                                                            valid_gamma);
            inv_gamma_range_table[i] = pow(colour_domain_table[i],
                                                            valid_inv_gamma);
      }

      /* The end of the table should match 1.0 carefully. In order to avoid    */
      /* rounding errors, we just set this explicitly. The last segment may    */
      /* have a different lenght than the other segments, but our              */
      /* interpolation is insensitive to that.                                 */
      colour_domain_table[RE_GAMMA_TABLE_SIZE]   = 1.0;
      gamma_range_table[RE_GAMMA_TABLE_SIZE]     = 1.0;
      inv_gamma_range_table[RE_GAMMA_TABLE_SIZE] = 1.0;

      /* To speed up calculations, we make these calc factor tables. They are  */
      /* multiplication factors used in scaling the interpolation.             */
      for (i = 0; i < RE_GAMMA_TABLE_SIZE; i++ ) {
            gamfactor_table[i] = inv_colour_step
                  * (gamma_range_table[i + 1] - gamma_range_table[i]) ;
            inv_gamfactor_table[i] = inv_colour_step
                  * (inv_gamma_range_table[i + 1] - inv_gamma_range_table[i]) ;
      }

      gamma_table_initialised = 1;
} /* end of void makeGammaTables(float gamma) */

/* ------------------------------------------------------------------------- */

int gammaTableIsInitialised(void)
{
      return gamma_table_initialised;
}

/* ------------------------------------------------------------------------- */
int doGamma()
{
      return do_gamma;
}

/* ------------------------------------------------------------------------- */

/**
 * Set/unset performing gamma corrections.
 */
void setDoGamma(int i)
{
      do_gamma = i;
}

/* eof */

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