ACES Fitting

ACESFitting.cpp

// Mostly code from https://github.com/ampas/aces-dev

Vec3 ACES_RRT( Vec3 aces )
{
  // --- Glow module --- //
  float saturation = rgb_2_saturation( aces);
  float ycIn = rgb_2_yc( aces);
  float s = sigmoid_shaper( (saturation - 0.4f) / 0.2f);
  float addedGlow = 1.0f + glow_fwd( ycIn, RRT_GLOW_GAIN * s, RRT_GLOW_MID);

  aces = mult_f_f3( addedGlow, aces);

  // --- Red modifier --- //
  float hue = rgb_2_hue( aces);
  float centeredHue = center_hue( hue, RRT_RED_HUE);
  float hueWeight = cubic_basis_shaper( centeredHue, RRT_RED_WIDTH);

  aces[0] = aces[0] + hueWeight * saturation * (RRT_RED_PIVOT - aces[0]) * (1.0f - RRT_RED_SCALE);

  // --- ACES to RGB rendering space --- //
  aces = clamp( aces, 0.0f, HALF_POS_INF);  // avoids saturated negative colors from becoming positive in the matrix

  Vec3 rgbPre = mult_f3_f33( aces, AP0_2_AP1_MAT);

  rgbPre = clamp( rgbPre, 0.0f, HALF_MAX);

  // --- Global desaturation --- //
  rgbPre = mult_f3_f33( rgbPre, RRT_SAT_MAT);

  // --- Apply the tonescale independently in rendering-space RGB --- //
  Vec3 rgbPost;
  rgbPost[0] = segmented_spline_c5_fwd( rgbPre[0]);
  rgbPost[1] = segmented_spline_c5_fwd( rgbPre[1]);
  rgbPost[2] = segmented_spline_c5_fwd( rgbPre[2]);

  // --- RGB rendering space to OCES --- //
  Vec3 rgbOces = mult_f3_f33( rgbPost, AP1_2_AP0_MAT);

  return rgbOces;
}

Vec3 ACES_ODT( Vec3 oces )
{
  // OCES to RGB rendering space
  Vec3 rgbPre = mult_f3_f33( oces, AP0_2_AP1_MAT);

  // Apply the tonescale independently in rendering-space RGB
  Vec3 rgbPost;
  rgbPost[0] = segmented_spline_c9_fwd( rgbPre[0]);
  rgbPost[1] = segmented_spline_c9_fwd( rgbPre[1]);
  rgbPost[2] = segmented_spline_c9_fwd( rgbPre[2]);

  // Scale luminance to linear code value
  Vec3 linearCV;
  linearCV[0] = Y_2_linCV( rgbPost[0], CINEMA_WHITE, CINEMA_BLACK);
  linearCV[1] = Y_2_linCV( rgbPost[1], CINEMA_WHITE, CINEMA_BLACK);
  linearCV[2] = Y_2_linCV( rgbPost[2], CINEMA_WHITE, CINEMA_BLACK);

  // Apply gamma adjustment to compensate for dim surround
  linearCV = darkSurround_to_dimSurround( linearCV);

  // Apply desaturation to compensate for luminance difference
  linearCV = mult_f3_f33( linearCV, ODT_SAT_MAT);

  // Convert to display primary encoding
  // Rendering space RGB to XYZ
  Vec3 XYZ = mult_f3_f33( linearCV, AP1_2_XYZ_MAT);

  // Apply CAT from ACES white point to assumed observer adapted white point
  //XYZ = mult_f3_f33( XYZ, D60_2_D65_CAT );

  // CIE XYZ to display primaries
  linearCV = mult_f3_f33( XYZ, XYZ_2_DISPLAY_PRI_MAT);

  // Handle out-of-gamut values
  // Clip values < 0 or > 1 (i.e. projecting outside the display primaries)
  linearCV = clamp( linearCV, 0.0f, 1.0f);

  return linearCV;
}