type t = [ | `Reserved0| `Bt709| `Unspecified| `Reserved| `Gamma22| `Gamma28| `Smpte170m| `Smpte240m| `Linear| `Log| `Log_sqrt| `Iec61966_2_4| `Bt1361_ecg| `Iec61966_2_1| `Bt2020_10| `Bt2020_12| `Smpte2084| `Smptest2084| `Smpte428| `Smptest428_1| `Arib_std_b67
]val from_name : string -> t option