146 lines
5.0 KiB
C
146 lines
5.0 KiB
C
/**
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* Jitter offset table
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*
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* $Id$
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*
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* ***** BEGIN GPL LICENSE BLOCK *****
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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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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*
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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 Foundation,
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* Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* The Original Code is Copyright (C) 2001-2002 by NaN Holding BV.
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* All rights reserved.
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*
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* The Original Code is: all of this file.
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*
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* Contributor(s): none yet.
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*
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* ***** END GPL LICENSE BLOCK *****
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*/
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#include "gammaCorrectionTables.h"
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#include <stdlib.h>
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#include <math.h>
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#ifdef HAVE_CONFIG_H
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#include <config.h>
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#endif
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/* WARNING; optimized, cannot be used to do gamma(invgamma()) and expect */
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/* result remain identical (ton) */
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/* gamma is only used here for correcting adding colors or alpha */
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#define RE_DEFAULT_GAMMA 2.0
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/* This 400 is sort of based on the number of intensity levels needed for */
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/* the typical dynamic range of a medium, in this case CRTs. (Foley) */
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/* (Actually, it says the number should be between 400 and 535.) */
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#define RE_GAMMA_TABLE_SIZE 400
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/* These indicate the status of the gamma lookup table --------------------- */
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static float gamma_range_table[RE_GAMMA_TABLE_SIZE + 1];
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static float gamfactor_table[RE_GAMMA_TABLE_SIZE];
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static float inv_gamma_range_table[RE_GAMMA_TABLE_SIZE + 1];
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static float inv_gamfactor_table[RE_GAMMA_TABLE_SIZE];
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static float color_domain_table[RE_GAMMA_TABLE_SIZE + 1];
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static float color_step;
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static float inv_color_step;
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static float valid_gamma;
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static float valid_inv_gamma;
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/* ------------------------------------------------------------------------- */
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float gammaCorrect(float c)
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{
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int i;
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float res = 0.0;
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i = floor(c * inv_color_step);
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/* Clip to range [0,1]: outside, just do the complete calculation. */
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/* We may have some performance problems here. Stretching up the LUT */
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/* may help solve that, by exchanging LUT size for the interpolation. */
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/* Negative colors are explicitly handled. */
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if (i < 0) res = -pow(abs(c), valid_gamma);
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else if (i >= RE_GAMMA_TABLE_SIZE ) res = pow(c, valid_gamma);
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else res = gamma_range_table[i] +
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( (c - color_domain_table[i]) * gamfactor_table[i]);
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return res;
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} /* end of float gammaCorrect(float col) */
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/* ------------------------------------------------------------------------- */
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float invGammaCorrect(float col)
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{
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int i;
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float res = 0.0;
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i = floor(col*inv_color_step);
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/* Negative colors are explicitly handled. */
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if (i < 0) res = -pow(abs(col), valid_inv_gamma);
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else if (i >= RE_GAMMA_TABLE_SIZE) res = pow(col, valid_inv_gamma);
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else res = inv_gamma_range_table[i] +
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( (col - color_domain_table[i]) * inv_gamfactor_table[i]);
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return res;
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} /* end of float invGammaCorrect(float col) */
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/* ------------------------------------------------------------------------- */
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void makeGammaTables(float gamma)
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{
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/* we need two tables: one forward, one backward */
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int i;
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valid_gamma = gamma;
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valid_inv_gamma = 1.0 / gamma;
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color_step = 1.0 / RE_GAMMA_TABLE_SIZE;
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inv_color_step = (float) RE_GAMMA_TABLE_SIZE;
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/* We could squeeze out the two range tables to gain some memory. */
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for (i = 0; i < RE_GAMMA_TABLE_SIZE; i++) {
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color_domain_table[i] = i * color_step;
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gamma_range_table[i] = pow(color_domain_table[i],
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valid_gamma);
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inv_gamma_range_table[i] = pow(color_domain_table[i],
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valid_inv_gamma);
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}
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/* The end of the table should match 1.0 carefully. In order to avoid */
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/* rounding errors, we just set this explicitly. The last segment may */
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/* have a different lenght than the other segments, but our */
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/* interpolation is insensitive to that. */
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color_domain_table[RE_GAMMA_TABLE_SIZE] = 1.0;
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gamma_range_table[RE_GAMMA_TABLE_SIZE] = 1.0;
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inv_gamma_range_table[RE_GAMMA_TABLE_SIZE] = 1.0;
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/* To speed up calculations, we make these calc factor tables. They are */
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/* multiplication factors used in scaling the interpolation. */
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for (i = 0; i < RE_GAMMA_TABLE_SIZE; i++ ) {
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gamfactor_table[i] = inv_color_step
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* (gamma_range_table[i + 1] - gamma_range_table[i]) ;
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inv_gamfactor_table[i] = inv_color_step
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* (inv_gamma_range_table[i + 1] - inv_gamma_range_table[i]) ;
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}
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} /* end of void makeGammaTables(float gamma) */
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/* ------------------------------------------------------------------------- */
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/* eof */
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