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# hlg

Extended dynamic range (EDR) metadata for the Hybrid Log-Gamma (HLG) transfer function.

```
class var hlg: CAEDRMetadata { get }
```

## Discussion

Your content should be scene referred and encoded with the ITU-R BT.2100-2 Hybrid Log Gamma (HLG) opto-electrical transfer function (OETF). The system applies the opto-optical transfer function (OOTF) based on peak display brightness and ambient lighting. If you’re rendering to a [`CAMetalLayer`](/documentation/QuartzCore/CAMetalLayer) with a linear colorspace (for floating point EDR layers), you must apply the HLG inverse OETF without normalization, to provide a nominal range of `[0, 12]`.

For more information on HLG, see <https://www.itu.int/rec/R-REC-BT.2100>.

---

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