nuttx-apps/graphics/traveler/tools/libwld/wld_pixel2lum.c

/****************************************************************************
 * apps/graphics/traveler/tools/libwld/wld_loadpaltable.c
 * This file contains the logic that creates the range palette table that is
 * used to modify the palette with range to hit
 *
 *   Copyright (C) 2016 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/*************************************************************************
 * Included files
 *************************************************************************/

#include <math.h>

#include "wld_paltable.h"
#include "wld_color.h"

/*************************************************************************
 * Public Functions
 *************************************************************************/

/*************************************************************************
 * Function: wld_pixel2lum
 * Description: Convert a pixel value into RGB-Luminance value.
 ************************************************************************/

void wld_pixel2lum(wld_pixel_t pixel_value, color_lum_t * lum)
{
  color_rgb_t *rgb = &g_rgb_lut[pixel_value];

  /* Get the luminance associated with the RGB value */

  lum->luminance = sqrt(rgb->red   * rgb->red   +
                        rgb->green * rgb->green +
                        rgb->blue  * rgb->blue);

  /* Convert the RGB Component into unit vector + luminance */

  if (lum->luminance > 0.0)
    {
      lum->red   = rgb->red   * lum->luminance;
      lum->blue  = rgb->green * lum->luminance;
      lum->green = rgb->blue  * lum->luminance;
    }
}