HDR Input and Output

Introduction

In this documentation, we will talk about working with HDR (High Dynamic Range) inputs and outputs using Aximmetry.

What is HDR?

Dynamic Range

Before we talk about HDR, we must talk about what Dynamic Range is.
The range between the brightest and darkest values that we can capture or display is called Dynamic Range. Dynamic Range is measured in stops.
Our eyes have about 20-21 stops of Dynamic Range.
When capturing images with a camera, this range is reduced, very high-end cameras have around 14 stops of dynamic range.
Most displays are working in SDR (Standard Dynamic Range), which has about 6 stops.
The higher the Dynamic Range, the more details you can preserve in your images.
The following images show the difference in Dynamic Range in photos:

You can see that the upper (HDR) image preserved more details at different exposure values than the lower (SDR) image.:

Displaying SDR / HDR Content

Monitors and TVs can not show as high brightness as the real-life object would show.
SDR content is typically displayed at 200 nits. Nits are units of the brightness of monitors and TVs.

However, there are some monitors and TVs that are capable of displaying HDR content.

HDR allows much higher brightness levels than SDR. This makes images keep more details in both dark and bright parts of the image.
HDR content can be displayed at the maximum of your display device's capabilities.
What peak brightness your device is capable of displaying should be listed on the manufacturer's website.
Max brightness is usually measured in either NITs or cd/m2. 
NOTE: 1 NIT = 1 cd/m2

HDR Rendering in Aximmetry

Setting the Rendering Pipeline

By default, Aximmetry is rendering in the sRGB Gamma pipeline that is only suitable for SDR content creation.
For HDR results, you should switch to sRGB Linear.
NOTE: You can still create SDR content in the sRGB Linear pipeline. In this case, the maximum brightness intensity should be set to 1, which is equal to the maximum brightness of SDR content.

To do this, go to File/Properties and in the pop-up window choose Rendering and set the rendering pipeline to sRGB Linear:

Aximmetry by default renders in full HDR, meaning that the brightness levels are not restricted by the software during calculations.
However, HDR output also depends on your output screen, the screen must be capable of displaying HDR content.
In Aximmetry, brightness values can be converted into nits using this equation: Aximmetry brightness 1=80 nits.

HDR Preview

Previews are rendered by default in SDR. If you wish to have your previews rendered in HDR too, you should turn on the HDR Render property in the PREVIEW MONITOR OUTPUT control panel on the CAMERAS control board:

Tone Mapping

As Aximmetry renders in full HDR, you can create brightness levels that your device is not capable of displaying and those parts of the image that exceed your display's capabilities would all become completely white, leading to a loss in details and overbright images.
To countermeasure this, you can use Tone Mapping in Aximmetry. Tone Mapping is an operation during which we map a range of color values into another range. In this case, from a higher dynamic range to a lower dynamic range.
NOTE: You can learn more about Tone Mapping here.

Tone mapping in itself is not mandatory to do. But if your scene's brightness is higher than the device on which it is going to be displayed, then we recommend using it to avoid loss of details.

When working with SDR output and/or display, your Max Out Lum setting should be set to 1 in the Tone Mapper.
NOTE: You should leave the Max Out Lum In Nits property turned off.

When working with HDR output, your Max Out Lum setting should be set to the maximum brightness of your display device.
In this case, we suggest using Nits for setting the value by turning on the Max Out Lum In Nits property.

You can check your maximum brightness in the device's manual.

HDR Rendering in Unreal Engine

Unreal Engine Setup for Virtual and Tracked Camera and LED WALL Production

By default, Unreal renders in HDR and applies tone mapping resulting in SDR content. We want Unreal not to apply Tone Mapping and output HDR content.
To do so, open the Project Settings and search for Frame Buffer. Find the Frame Buffer Pixel Format setting and set it to Float RGBA:

Restart and recook your scene.

In Aximmetry

NOTE: Unreal Engine does not do Tone Mapping for HDR output, if you wish to you can do it inside Aximmetry.

With Virtual Camera, go to the CAMERAS control board.
With Tracked Camera, go to the INPUTS control board.
With LED Walls, go to the LEDWALLS control board,
and find the HDR panel:

In the Pin Values window turn it on: 

You should then adjust the Tone Mapping values.
You can learn more about tone mapping here: Tone Mapping Methods.
NOTE: You should adjust these values to the device on which the content is going to be displayed.

Unreal Engine Setup for AR Production

By default, Unreal renders in HDR and applies tone mapping, which results in SDR content. We want Unreal not to apply Tone Mapping and output HDR content.
To do so, open the Project Settings and search for Frame Buffer. Find the Frame Buffer Pixel Format setting and set it to Float RGBA:

In Aximmetry

NOTE: Unreal Engine does not do Tone Mapping for HDR output, if you wish to you can do it inside Aximmetry.

Go to the INPUTS control board and find the TONE MAP module:

You should then adjust the Tone Mapping values.
You can learn more about tone mapping here: Tone Mapping Methods.
NOTE: You should adjust these values to the device on which the content is going to be displayed.
NOTE: Any content generated inside Aximmetry and mixed with Unreal’s HDR content (such as by connecting it to the Overlays pin of the camera compound) will not be rendered and mixed in HDR by default. To render this content in HDR, refer to the HDR Rendering in Aximmetry section, especially the information about setting the rendering pipeline to sRGB Linear.

Inputs and Outputs

Inputs

If the input is not HDR, no settings need to be changed.

If the input is HDR, follow these instructions:

• In your Input Devices, make sure to set your input to 10-bit:
  
  
  
• In the Input panel, set the In Color Space parameter to match your camera’s output. Typically, this will be Rec.2100 PQ (Perceptual Quantizer) or Rec.2100 HLG (Hybrid Log-Gamma).
• Set the In Gamma Curve parameter to Color Space.
  
  
  

• For LED wall camera compounds, HDR is automatically enabled for Inputs when the HDR panel is set to Active within the camera compound.
  When HDR is not enabled for an Input, the color range is limited to a maximum value of 1.0.
  
  NOTE: This feature is not supported for green screen camera compounds. If you require HDR Input functionality for green screen setups, please contact us.
  NOTE: Similarly, in the Flow Editor, Video Input and Video Player modules include HDR Out pins to enable HDR.

  
  

• In Unreal AR camera compounds, HDR Input can be enabled in the Tone Map panel:
  

Outputs

When it comes to outputs, there are a few settings that you should change depending on your output method:

• SDI

  • When working with SDI output, set the output to 10-bit:
    
    

  • You can also set the Color space here.
    NOTE: You should set it to one of the supported HDR Color Spaces as detailed here.
    
    
    
• HDMI / DP
  • When using an HDMI or DisplayPort (DP) cable, Windows will automatically convert the video signal to the Rec. 2100 PQ color space.
  • Make sure that your Windows display settings are correct and that HDR is turned on:
    
    
    
• Previews
  • Both full-screen monitor outputs and preview panels of the Aximmetry Composer support HDR output as long as your Windows display settings are correct and HDR is enabled, as in the above image.
    NOTE: The peeking values of pins function in the Flow Editor (CTRL + Mouse) do not support HDR output. 

Supported HDR Color Spaces

Here you can find all supported HDR codecs:

• Rec.2100 Perceptual Quantizer (PQ)
  • Brightness is stored in nit
  • HDR10 uses this codec, therefore, it is supported by most TVs, Monitors, and the Windows OS.
• Rec.2100 Hybrid Log-Gamma (HLG)
  • 1 unit is typically the top of SDR capabilities, which is 200 nit
• Sony S-Gamut3/S-Log3
• Sony S-Gamut3.Cine/S-Log3
• Panasonic V-Gamut/V-Log
• REDWideGamutRGB/Log3G10