C_Color_Balance.dctl

/* 
 Color Balance

 Version 004
 
 - Use perceptual luminance.
 - Optimize performance.
 
****************************************************************************************/


__CONSTANT__ int ZOOM          = 1;   // Increase to ZOOM into the shadows.
__CONSTANT__ int SAMPLE        = 16;  // Lower for more accuracy, raise for better performance.
__CONSTANT__ int PANEL_COUNT   = 26;  // Defines the number of horizontal panels (25 max or increase arrays)
__CONSTANT__ int PANEL_SPACING = 20;  // The larger the number the smaller the height of the panels. 

__DEVICE__ float perceptual(float3 x)
{
  x.x = x.x <= 0.081f ? x.x / 4.5f : _powf((x.x + 0.099f)/1.099f, 1.0f/0.45f);
  x.y = x.y <= 0.081f ? x.y / 4.5f : _powf((x.y + 0.099f)/1.099f, 1.0f/0.45f);
  x.z = x.z <= 0.081f ? x.z / 4.5f : _powf((x.z + 0.099f)/1.099f, 1.0f/0.45f);

  return x.x * 0.2126f + x.y * 0.7152f + x.z * 0.0722f;  
}								

__DEVICE__ float3 transform(int p_Width, int p_Height, int p_X, int p_Y, __TEXTURE__ p_TexR, __TEXTURE__ p_TexG, __TEXTURE__ p_TexB)
{
    const int panel_width  = (int) p_Width / PANEL_COUNT;
    const int panel_height = (int) p_Height / PANEL_SPACING;
    const int panel_zoom   = PANEL_COUNT * ZOOM;
    
    if (p_Y < panel_height * ((float) PANEL_SPACING - 1.5f))
      return make_float3(_tex2D(p_TexR, p_X, p_Y),
                         _tex2D(p_TexG, p_X, p_Y),
                         _tex2D(p_TexB, p_X, p_Y));      
    else 
    {
      float R[26]   = {0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,
                       0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,
                       0.0f,0.0f,0.0f,0.0f,0.0f,0.0f};
      float G[26]   = {0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,
                       0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,
                       0.0f,0.0f,0.0f,0.0f,0.0f,0.0f};
      float B[26]   = {0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,
                       0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,
                       0.0f,0.0f,0.0f,0.0f,0.0f,0.0f};
      int   SUM[26] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
      
      for (int i = SAMPLE-1; i < p_Width; i+=SAMPLE)
        for (int j = (SAMPLE/2)-1; j < p_Height; j+=SAMPLE/2)
        {
           float3 x = make_float3(_tex2D(p_TexR, i, j),
                                  _tex2D(p_TexG, i, j),
                                  _tex2D(p_TexB, i, j));
           const int idx = (int) (perceptual(x) * panel_zoom);
           if (idx >= 0 && idx < PANEL_COUNT)
           {
              R[idx] += x.x;
              G[idx] += x.y;
              B[idx] += x.z;
              SUM[idx]++;
           }
        }

      int idx = (int) p_X / panel_width;
      if (p_Y < panel_height*(PANEL_SPACING - 1))
      {
         float level = (float) (2*idx+1) / (2*panel_zoom);
         float p = level <= 0.018f ? level * 4.5f : 1.099f *_powf(level,0.45f) - 0.099f;
         return make_float3(p,p,p);
      }
      else
        if (SUM[idx] >= 1)          
          return make_float3(R[idx]/SUM[idx],G[idx]/SUM[idx],B[idx]/SUM[idx]);
        else
          if (p_Y % 2)
              return make_float3(0.3f,0.2f,0.1f);
          else
              return make_float3(0.1f,0.2f,0.3f);
    }  
}