Considerations when shooting and posting HDR for movies

Daniele Siragusano, Image Engineer, FilmLight

HDR has rapidly moved to the forefront in discussions on how to shoot and post premium content. Movies are increasingly choosing HDR as a second order deliverable and are searching for a suitable archive strategy to prepare their content for later exploitation. Prestige television projects like the recent BBC Blue Planet II are also using HDR acquisition and producing HDR deliverables.

So what does HDR bring to the table?

We tend to talk about HDR, high dynamic range, but in fact this brings several shifts in capabilities and creative aspects. First and most obvious, it increases the contrast ratio, meaning that you can have both bright highlights and deep shadows simultaneously or between scenes over time.

Another benefit is that it extends the palette of bright, saturated colours available. With HDR displays you can express bright, vivid and fluorescent colours that are simply not achievable with traditional standard dynamic range displays. This enlarges the colour palette the colourist has at hand.

But the standard dynamic HD colour volume (Rec.709) already covers most of the reflected colours in a scene. Therefore, having a greater dynamic range and colour gamut also brings some challenges for the colourist, as pictures can start to look quite unnatural if the colours are pushed too much towards the edge of the colour volume.

New colour grading tools are needed to give the colourist the right controls. Additionally, the image viewing pipeline needs to account for the implications of natural colours.

HDR not only influences the colour aspects of an image, it also introduces various other subjective effects.

Because of the greater contrast and reduced highlight compression, images are perceived as sharper. Edges that might appear relatively soft in SDR appear harder. This is seen as a major benefit in television. Genres like sport, where pictures can never be too clear or too sharp, regard HDR as a significant step forward, even on today's HD displays without the need to go to 4K.

For movies or premium drama though, directors and cinematographers are used to the language of film. For many movies that means a degree of softness, allowing light to bloom rather than to cut like a knife.

The question is: can we enjoy the benefits of detailed highlights and shadows, and rich, revealing colour palettes, without losing the ability to create cinematic moods and atmospheres?

The enhanced dynamic range also affects the perception of motion. Motion artefacts, like motion judder, are contrast sensitive. Images with higher contrast in higher frequencies will emphasise these artefacts. So it is possible that a slow panning shot that looks fine in SDR can start to judder when the image is translated to HDR.

But the most important issues relate to image composition and lighting. What looks attractive when shooting for SDR can look like a distraction in HDR. Similarly, a scene that looks interesting in HDR might look unexciting in SDR.

Practical exploration FilmLight recently took part in a one-day masterclass, organised by ARRI, in which the cinematographer Karl Walter Lindenlaub ASC lit and shot specific scenes. FilmLight was on hand, first to provide immediate viewing and correction through FilmLight's Prelight on-set software, and then to provide a final grade of the images using a full Baselight workstation. Andy Minuth, FilmLight's in-house colourist and colour workflow expert, performed the grade.

Karl Walter Lindenlaub ASC

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