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gamma.c

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/** \file gamma.c
 *
 * \author Copyright 2001 Lutz Müller <lutz@users.sf.net>
 *
 * \par License
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * \par
 * This library 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
 * Lesser General Public License for more details. 
 *
 * \par
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

#include "config.h"
#include "gamma.h"

#include <math.h>

#include <gphoto2/gphoto2-result.h>

static int
gp_gamma_correct_triple (unsigned char *table_red,
                   unsigned char *table_green,
                   unsigned char *table_blue,
                   unsigned char *data, unsigned int size)
{
      unsigned int x;

      for (x = 0; x < (size * 3); x += 3) {
            data[x + 0] = table_red  [data[x + 0]];
            data[x + 1] = table_green[data[x + 1]];
            data[x + 2] = table_blue [data[x + 2]];
      }

      return (GP_OK);
}

/**
 * \brief Gamma correction
 *
 * Corrects size pixels within the table with a given Gamma
 * correction table.
 * 
 * \param table the gamma correction table as generated by gp_gamma_fill_table()
 * \param data the data do process, both input and output
 * \param size in number of pixels (RGB byte pairs)
 *
 * \returns a gphoto error code
 */
int
00061 gp_gamma_correct_single (unsigned char *table, unsigned char *data,
                   unsigned int size)
{
      return (gp_gamma_correct_triple (table, table, table, data, size));
}

/**
 * \brief Initialize a Gamma conversion table
 * 
 * Initializes the gamma conversion table for later use by gp_gamma_correct_single().
 * Requires a 256 byte array as table.
 * \param table a 256 byte array of unsigned char
 * \param g gamma correction value
 *
 * \returns a gphoto error code
 */
int
00078 gp_gamma_fill_table (unsigned char *table, double g)
{
      unsigned int x;

      for (x = 0; x < 256; x++)
            table[x] = 255 * pow ((double) x/255., g);

      return (GP_OK);
}

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