iPhone 15 to have true log / ACES support

Discussions - Using ACES
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16

Here’s the Apple Log Profile ACES IDT based on the Apple White Paper in GLSL. The matrix values are derived from BT2020 with CIECAT02 adaptation. Maybe someone can convert it to a DCTL and compare to the reference implementation (?) in Resolve.

// Apple Log Gamma to Linear Decoding Function
float appleLogToLinear(float x)  {

    const float R_0 = -0.05641088;
    const float R_t = 0.01;
    const float c = 47.28711236;
    const float beta = 0.00964052;
    const float gamma = 0.08550479;
    const float delta = 0.69336945;
    const float P_t = c * pow(R_t - R_0, 2.0);

    if (x >= P_t) {
        return pow(2.0, (x - delta) / gamma) - beta;
    } else if (x >= 0.0 && x < P_t) {
        return sqrt(x / c) + R_0;
    } else {
        return R_0;
    }

}

// Apple Log Profile to ACES_2065-1 (AP0) Linear
vec3 IDT(vec3 AppleLog) {
  float r_lin = appleLogToLinear(AppleLog.x);
  float g_lin = appleLogToLinear(AppleLog.y);
  float b_lin = appleLogToLinear(AppleLog.z);
  vec3 oces = vec3(
    r_lin * 0.6788911506598102 + g_lin * 0.15886842237789234 + b_lin * 0.16224042703562752,
    r_lin * 0.04557083087232135 + g_lin * 0.8607127720474108 + b_lin * 0.0937163970408747,
    r_lin * -0.0004857103518124508 + g_lin * 0.025060195735059528 + b_lin * 0.9754255145687619
  );
  return oces;
}
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