Filming and grading for HDR video

High Dynamic Range (HDR) video offers much more than simply brighter whites and deeper blacks. With the ability to deliver a much greater peak brightness of up to 10,000 nits, a wider colour gamut that meets the BT.2100 standard, and the opportunity to display smoother gradients between colours and shades in 10-bit, HDR video brings a more pronounced improvement in video presentation than moving from Full HD to 4K resolution.

While an HDR compatible display is needed to grade, edit and view HDR video content, you have more freedom when it comes to recording footage for an HDR production. You can either capture an expansive dynamic range with Canon Log and grade to HDR in post, or record directly in HDR. A number of Canon professional camcorders and Canon Cinema EOS cameras offer the convenience of recording HLG and PQ formats internally, saving you post-production time and budget.

So, which Canon cameras are best for HDR video? How should you shoot with HDR deliverables in mind? And what do you need to take into account when planning an HDR workflow? Paul Atkinson, Pro Video Product Specialist at Canon Europe, explores these questions, with insights from Sonny Sheridan, Senior Colourist at top UK post-production house The Farm.

There are two basic routes to outputting in HDR: do it in-camera or do it in post. "The traditional way is to record a file with the maximum dynamic range possible, and then take it through HDR workflow later," explains Paul. "If you were to apply an HDR workflow to a smaller bitrate and a lower colour-sampled image, it's just not going to hold up well. So, you need to start off with the maximum amount of information possible. That's where shooting in Canon Log gives you the advantage."

Canon Cinema EOS cameras offer Canon Log recording, as do selected EOS mirrorless and DSLR cameras and Canon professional camcorders including the Canon XF705 and the Canon XA55/XA50. Designed to capture the widest possible dynamic range, Canon Log offers maximum flexibility when it comes to colour grading and post-processing. The popular Canon Log 3, for example, is capable of delivering a dynamic range of up to 14 stops, depending on the camera.

Even the latest Canon PTZ remote cameras have a Wide Dynamic Range Mode option with BT.709 or BT.2020 colour space applied, which could be useful if you're working to a tight deadline and don't have time to grade. But there is a 2-stop difference between Wide DR and Canon Log 3, making them very different in highlight performance. When it really needs to be HDR, "the Canon CR-N500 and CR-X500 professional PTZ cameras can also capture in Canon Log 3," says Paul. "So even our PTZ cameras are able to record that wide dynamic range for grading that will allow you to put it into an HDR output and workspace."

In many respects, acquisition for High Dynamic Range is no different to acquisition for Standard Dynamic Range. "Even if you're using one of the presets, your shooting discipline needs to stay the same," says Paul. "You're likely to be outputting in 4K for HDR, for example, so your focus needs to be spot-on, and obviously we've got things that can help with that, be it Dual Pixel CMOS AF or the Focus Assist feature for manual focus."

The in-camera exposure for HDR and SDR can be approached in a broadly similar way too. It's important to ensure the mid-tones areas are exposed correctly for both, for example. Bright areas require some consideration, though. Compared with SDR, clipped highlights in HDR can appear unnatural and painfully distracting, and it's crucial to eliminate or reduce highlight clipping when shooting for HDR so you have more flexibility to match peak white levels across different shots. Reducing the ISO can help, as can the ND filters built into many Canon Cinema EOS cameras and professional camcorders.

Lighting, metering and monitoring for HDR on set, and regularly checking the SDR to ensure that it retains your intended balance of light and dark, is often the most straightforward option. Using a Canon Reference Display that offers an HDR-SDR split-screen function, such as the Canon DP-V2421, makes this process even easier.

"The Canon XF705 can go a little bit further," Paul adds, "as it allows you to record HDR internally and simultaneously send an SDR output to an external recorder. You can tell the camera which one you're correctly exposing, and it will automatically make a gain adjustment to the other output to give you a correctly exposed image there too. So then you have your HDR and your SDR ready and available, apart from minor tweaks that you would normally do in editing as opposed to full grading."

HDR adds a layer of complexity to post-production and grading, but it also brings a new level of freedom. "It gives you more detail in the highlights, so that's where you can have fun with it," says Sonny Sheridan, who is probably best known for his work as colourist on the UK TV series Lucky Man and 24 Hours in A&E, and has won an RTS Craft & Design Award for Best Picture Enhancement. "If you're shooting someone next to a window, you can keep all the information in the scene outside the window and still have a good exposure on the person inside. That would be very difficult to achieve in SDR. You now have more details and subjects in an image to help tell the story.

"The main challenges I find in grading HDR are managing the highlights on practical lights and, for example, actors standing next to bright windows," Sonny continues. "I have to use a power window to lift the person up from the window and use a luminance key to bring the brightness down in the window. This is to get the balance right, so the person in the foreground is not overshadowed by the high luminance in the window. You need to get the balance right with how bright you go – just because you can go up to 1,000 nits, it doesn't mean you should. Sometimes the best HDR is subtle HDR."

There are additional factors to be taken into account when working out an HDR workflow, Sonny adds. "The main considerations are the source camera acquisition formats and the master delivery specifications – for example, if we are delivering in Rec 2020 or DCI-P3, Dolby Vision, HDR10, HLG and so on.

"Colour management is really important. For scripted drama there is often a single camera format involved, so I would work through a LUT from my acquisition colour space to my target. However, if there is a mix of two or more camera formats, I might choose to work in an ACES workflow so that everything will be unified in my timeline, retaining the widest latitude possible."

Several Cinema EOS cameras, including the EOS C300 Mark III and EOS C500 Mark II, natively support the ACES pipeline, making for a more efficient workflow.

Sonny says that with some workflows, doing the HDR grade before an SDR grade is a necessity – "Dolby Vision, for example, as the SDR is derived from the HDR. There are some standards that allow you to workflow SDR first, but it usually comes down to preference and what directors want to focus on as a priority."

Having to derive multiple HDR formats from a master will also determine your workflow, adds Chris Spearman, Technical Operations Manager at The Farm. "It partly depends on who the primary deliverable is for and the standards of HDR requested," he says. "For example, we can derive HDR10 deliverables from a Dolby Vision workflow quite easily, but if there are different colour gamuts between the different deliverables then we need to make sure we get that the right way round. We'll work at the standard with the widest latitude first, and ACES is a good pipeline for multi-standard deliverables.

"I think that while an increasing number of platforms support HDR, there will be more standardisation of practices," Chris continues. "We might see some standards becoming more prominent and some disappearing, and HDR tools becoming even more readily available, making HDR the new 'SDR'."

So, the future for HDR video is looking bright indeed – at least 1,000 nits.