New test results from the EBU show dynamic HDR converters can create exceptional image quality, outperforming static converters in terms of highlight compression. However, artefacts may appear in certain cases. EBU Tech Report 078 advises on what to test before use.

Currently, for live production static (mostly LUT-based) HDR to SDR converters are most commonly used. This approach creates high-quality, predictable results and is used worldwide. It could be regarded as the safe approach.

However, static converters are inherently conservative. Rather than adapting to the picture’s content, they always map an incoming pixel value to a pre-defined (static) output value. Dynamic converters are more flexible. They take into account the whole image and adapt their conversion strategy based on it. They may also take into account multiple frames and provide, for example, shot-based specific conversions.

The expectation has been that such dynamic conversions can be of higher quality than static ones and potentially could also lead to even better HDR images, because the SDR image converted from HDR determines the shading decisions in combined HDR –SDR live production; see EBU Tech Report 070. This was already noted in 2018 during the European Championships trials. A concern with dynamic converters has been to understand the circumstances under which they do NOT provide better images.

Proof of the pudding

To have a more profound understanding of the state-of-the art in dynamic conversion, the EBU Video Systems group recently organized a test with leading converter vendors. Expert viewers from both EBU Members and the vendors looked at different converted test sequences.

The results (see EBU Tech Report 078) show that dynamic converters can outperform static converters in terms of highlight compression and gamut correction, but also that they can introduce noise amplification, temporal overshoots and changes in graphics levels. A lot depends (as with static converters) on what can be assumed about the input signal.

Aside from test results, EBU Tech Report 078 also provides some advice for users who want to experiment with HDR converters for their own productions. Further work is required to understand interoperability issues between different dynamic and/or static converters. This is especially important for multilateral events, where it is important for broadcasters to match their own cameras against an incoming feed.

Members-only supplements

EBU Members can find more detailed test reports for specific converters in three supplements: EBU Tech Report 078s1 (Technicolor), 078s2 (Lynx Technik/EVIE+), 078s3 (b<>com/EVS Neuron).



HDR: high dynamic range
SDR: standard dynamic range
LUT-based: converters based on lookup tables

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