HDR in Pixotope

Introduction

High-dynamic-range video (HDR video) describes video having a dynamic range and gamut greater than that of standard-dynamic-range video (SDR video).

The process of HDR video involves capture, production, content/encoding and display. HDR capture and displays are capable of much brighter whites and an overall much higher contrast ratio. To accommodate this, HDR encoding standards allow for a higher maximum luminance and use at least a 10-bit dynamic range in order to maintain precision across this extended range.

While technically "HDR" refers strictly to the ratio between the maximum and minimum luminance, the term "HDR video" is commonly understood to imply wide color gamut (WCG) as well.

The goal

The goal of HDR (high-dynamic-range) and WCG (wide color gamut) is to:

• increase image quality

• achieve more natural looking images

• approach towards photorealism

Additionally, it allows for:

• linear compositing, which greatly enhances realism when combining graphics and video

Learn more about Linear space compositing

What HDR requires

• an HDR capable camera

  • to capture many more f-stops in a single exposure than a traditional video camera (greater dynamic range)

• an HDR-ready transportation medium

  • to ensure optimal bandwidth and compatibility without losing extra information captured by HDR cameras

  • to encode the video into a format that can transport and store the HDR values, such as various LOG formats (sLog, clog, vlog), HLG and PQ.

• an HDR-ready color management system

  • to ensure that the captured light information is interpreted, processed and encoded in a predictable and correct way

• an HDR display

  • to show brighter highlights without compromising shadows and details

  • to accurately judge what you see

HDR in Pixotope

For most broadcast productions, there are 2 flavors of HDR that are most common:

1. Camera native LOG formats that capture HDR dynamic range and wide gamut.

   1. Example formats would be:

      • For Sony: I S-Log3 - S-Gamut3.Cine

      • For Arri:  LogC(E400) - Wide Gamut

      • For Canon: Canon-Log3 - Cinema Gamut Daylight/Tungsten

      • For Panasonic: Panasonic - V-log - V-Gamut

      • For RED:  REDlogFilm - REDcolor4 

   2. Hybrid Log Gamma (HLG)

      • HLG exists in several different flavors, especially on the camera side. Optimally you would have a colorspace conversion specifically for how the footage was encoded, but in practice this is not readily available, so using a single standard HLG conversion is sufficient for now.

As the workflows for LOG formats are better understood and standardized than the various HLG formats, we highly recommend shooting and outputting the graphics in LOG format, with conversion to HLG/PQ downstream if possible.

Regardless, the workflow in Pixotope is the same:

1. Use the same color conversion on inputs and outputs, unless you specifically need to create an SDR output for preview. 

   • Ie. Your camera feed is encoded in sLOG , so your main output should also be configured as sLOG to ensure that all colors in the video plate are unchanged, and that the graphics are tonemapped in the same manner. However, the sLog will look very flat on a rec709 monitor so that if you can not convert it in the monitor or using an external conversion device, Pixotope can convert the signal to Rec709 by choosing that as your output space.

   • Similarly, on your PC monitor, the image will look “wrong” (typically very low contrast) if you do not use a preview display conversion in the Editor. If you have an HDR monitor, choose the appropriate HDR lookup (ie. PQ/HLG) or if the monitor does not support HDR; chose an sRGB preview, that will convert the HDR signal to SDR for preview

   • For HLG input / outputs, use the “Rec.2020 HLG (1000 nits)” ODT

2. When outputting HDR on SDI, make sure the SDI signal range is set appropriately (see section on SDI signal range).

3. Turn off “Film” tonemapper

   • The LOG formats will all heavily tonemap the content

   • HLG has a less aggressive tonemapping, but it is highly recommended that you do not use the “Film” tonemapper, and rather rely on the built in curve and light accordingly.

4. Preferably work with a scope to ensure that the white levels of your graphics are set appropriately. 

   • This is particularly important when working with motion graphics elements, such as Logos, where specific color and value is often desirable. 

   • As an example, in HLG a 75% marker on a waveform monitor references HDR Reference White (100%) which is also diffuse white and Graphics White. That means that values above 75% will be super bright values that are brighter than reference white.

   • In general, it is highly recommended that users familiarize themselves with the “Guidance for operational practices in HDR television production” documentation (ITU-R BT.2048-7 ): https://www.itu.int/pub/R-REP-BT.2408-7-2023

5. When using inverse ODTs for converting input video into linear space, you can “up convert” an SDR signal to HDR. It will be a relatively crude approximation, but it can give some of the nice effects of HDR when doing compositing, even for output.