BT709

scene_referred=true：

    if (x < 4.5f * REC709_BETA)
        x = x / 4.5f;
    else
        x = powf((x + (REC709_ALPHA - 1.0f)) / REC709_ALPHA, 1.0f / 0.45f);

    return x;

scene_referred=false: 2.4

iec61966-2-1 (SRGB)

    if (x < 12.92f * SRGB_BETA)
        x = x / 12.92f;
    else
        x = powf((x + (SRGB_ALPHA - 1.0f)) / SRGB_ALPHA, 2.4f);

    return x;

iec61966-2-4 (xvycc)

scene_referred=true：

    if (x < 4.5f * REC709_BETA)
        x = x / 4.5f;
    else
        x = powf((x + (REC709_ALPHA - 1.0f)) / REC709_ALPHA, 1.0f / 0.45f);

    return x;
}

scene_referred=false：

    if (x < 0.0f || x > 1.0f)
        return copysign(rec_709_inverse_oetf(std::fabs(x)), x);//1/0.45
    else
        return copysign(rec_1886_eotf(std::fabs(x)), x);//2.4