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# SDR/HDR Signalling

SDR/HDR signalling ensures that downstream devices interpret the video signal correctly and apply the
appropriate display characteristics (for example, brightness, contrast, and colour gamut).

In most cases, the signalling information is extracted from the incoming transport stream. If this
metadata is missing or incomplete, you can override it and explicitly specify the desired dynamic
range signalling.

The **Dynamic range signalling** setting does not perform any dynamic range conversion of the decoded
video. It only defines the signalling metadata embedded in the outgoing video stream.

## Dynamic Range and Color Standards

SDR and HDR describe the luminance range and transfer characteristics of a video, not the chromaticity
or color primaries. ITU-R recommendations BT.601, BT.709, and BT.2020 define those color primaries and
colorimetry independently of dynamic range. BT.601 covers SD, with distinct primary sets for 525-line
(NTSC) and 625-line (PAL) systems; BT.709’s HD primaries match BT.601’s 625-line variant; BT.2020 covers
the wider gamut used for UHD and HDR.

| Video Format | Dynamic Range   | Color Standard |
| ------------ | --------------- | -------------- |
| SD           | SDR             | BT.601         |
| HD           | SDR             | BT.709         |
| HD           | HDR (PQ or HLG) | BT.2020        |
| UHD          | HDR (PQ or HLG) | BT.2020        |

In practice, HDR workflows typically use BT.2020 as the color container because modern displays and delivery
systems support wider gamuts, but this is a pairing choice rather than a strict requirement.

## Dynamic Range Signalling

### Supported Signalling Options

The two most commonly used HDR transfer functions are **PQ (SMPTE ST 2084)** and **HLG (ITU-R BT.2100)**
and so these are available when selecting the **Dynamic range signalling** in the Receiver service
configuration.

| Dynamic range signalling option | Dynamic range signalled on the output           | Color standard signalled on the output |
| ------------------------------- | ----------------------------------------------- | -------------------------------------- |
| Follow input                    | -                                               | -                                      |
| SDR (BT.709)                    | SDR                                             | BT.709                                 |
| SDR (BT.2020)                   | SDR                                             | BT.2020                                |
| HDR HLG10                       | HDR HLG transfer function with 10-bit precision | BT.2020                                |
| HDR PQ10                        | HDR PQ transfer function with 10-bit precision  | BT.2020                                |

Notes on the **Follow input** selection:

* By default, a new Receiver service outputs video signalling SDR (BT.709).

* When a dynamic range standard is successfully extracted, the output video signals the extracted
  standard.

* When the dynamic range standard is lost, the last extracted standard continues to be signalled
  on the output video.

* If the video input is lost, the last decoded standard continues to be signalled on the output
  video, and outputs video according to the Video fail mode selection.

* Follow input will automatically follow any conversions made with HDR to SDR conversion
  so it will be unnecessary to manually override and select SDR.

### Configuring Dynamic Range Signalling

To manually set the standard to be used for SDR or HDR signalling follow the steps below:

* On the Home page, select the RECEIVER item from the required feed, then click  to edit.

* In the Parameters window, select the Output tab.

* Select the tab for the required output type, for example SDI 1.

* Select the appropriate setting from the Dynamic range signalling
  drop-down menu:

Select Follow input to extract the video format from the incoming transport stream and
embed into the output video.

* Select one of the SDR or HDR standards to override the incoming format and
  embed into the output video.

* Click Save and Continue to apply change.