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/**
* Jitter offset table
*
* $Id$
*
* ***** BEGIN GPL 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.
*
* 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, 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 LICENSE BLOCK *****
*/
#include "gammaCorrectionTables.h"
#include <stdlib.h>
#include <math.h>
/* WARNING; optimized, cannot be used to do gamma(invgamma()) and expect */
/* result remain identical (ton) */
/* gamma is only used here for correcting adding colors or alpha */
#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 color_domain_table[RE_GAMMA_TABLE_SIZE + 1];
static float color_step;
static float inv_color_step;
static float valid_gamma;
static float valid_inv_gamma;
/* ------------------------------------------------------------------------- */
float gammaCorrect(float c)
{
int i;
float res = 0.0;
i = floor(c * inv_color_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 colors 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 - color_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_color_step);
/* Negative colors 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 - color_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;
color_step = 1.0 / RE_GAMMA_TABLE_SIZE;
inv_color_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++) {
color_domain_table[i] = i * color_step;
gamma_range_table[i] = pow(color_domain_table[i],
valid_gamma);
inv_gamma_range_table[i] = pow(color_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 length than the other segments, but our */
/* interpolation is insensitive to that. */
color_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_color_step
* (gamma_range_table[i + 1] - gamma_range_table[i]) ;
inv_gamfactor_table[i] = inv_color_step
* (inv_gamma_range_table[i + 1] - inv_gamma_range_table[i]) ;
}
} /* end of void makeGammaTables(float gamma) */
/* ------------------------------------------------------------------------- */
/* eof */
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