High Dynamic Range (HDR) photography is one of the most popular forms of computational photography, but did you know you can make HDR video, too? In an HDR video, the dynamic range of a digital video camera is extended by capturing several identical images of a scene, each with a different exposure value. In post-production the multiple frames are blended together to create a single image that has a greater dynamic range than the camera can capture in a single shot. In this article you'll get an overview of how to apply HDR techniques to video capture.
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What is HDR Video?
HDR video is essentially the same as HDR photography in that you record a scene with more than one exposure and blend them together in post production in order to extend the dynamic range of the camera. HDR videography, however, differs from HDR photography in a number of significant ways.
First, the techniques used for still images don’t readily transfer over to video. In HDR photography, the camera is normally locked down on a tripod and shutter speed is adjusted between each frame. The images are taken sequentially. When there is no movement in the scene (or you are trying to blur the movement in the scene) this works well; very little changes between each exposure. If you’re filming a video, you can’t stop to lock down your camera and film the scene twice with different exposures; too many details will change between each take. No matter how skilled the actor, they won’t be able to repeat their previous performance with perfect accuracy. The different exposures need to be captured concurrently, or as close to concurrently, as possible.
Second, HDR photography has developed into it’s own field; there is a specific look associated with it. Whether that’s a good thing or not is up for debate. HDR videography is much more of a tool purely to extend the dynamic range of the camera rather than to create HDR-stylised video. HDR videos are shot as flat as possible so that they can take heavier colour grading and processing in post-production. While it’s often easy to spot a HDR image, if done well it’s almost impossible to recognise finished HDR video.
Display and Projection Problems
One of the greatest barriers to HDR video is that most TVs and cinema screens simply can’t display it. While professional movie cameras like those made by RED or ARRI have sensors with a dynamic range of thirteen or fourteen stops, most displays only have a dynamic range of between eight and ten stops. Even without using HDR techniques, any footage captured using a modern camera far exceeds what displays can show. In particular, many TVs have a great deal of trouble showing accurate black levels.
Fortunately, this looks like it might be changing. The recently launched Dolby Vision is a video standard that greatly expands the dynamic range. Films released in Dolby Vision, or display devices that can show it, can have up to 21 stops of dynamic range according to News Shooter. While Dolby Vision isn’t widely available yet—there are only a handful of cinemas and very expensive TVs capable of supporting it—over the next few years it’s likely to become a lot more popular. If you make a HDR movie now, you’ll probably be able to view it faithfully on your TV in a few years.
How to Make Your Own HDR Video
While still images can be shot at thousands of a second, movies are commonly recorded with a frame rate of 24 frames per seconds. For the cinematic look, the shutter speed used to record each frame is most commonly double the frame rate, so 1/48th of a second (or 1/50th of a second if you’re using a DSLR). If you’re interested in more details on how shutter speed affects video, check out Rob Taylor’s great article. The important take away is that, for the most part, video shutter speeds need to be a lot slower than what your camera is capable of. This means there is a time gap in between the capture of each frame that can be used to capture a second frame with a different exposure.
A Second Frame
The best way to create HDR video is with a professional camera. RED’s cinema cameras support HDRX mode: they can capture a second, under-exposed frame (the X FRAME) immediately after the first frame (the A FRAME). The additional highlight information from the X FRAME is added to the A FRAME in post production to create a flat movie with an extended dynamic range ready for colour grading. Importantly, the X FRAME is captured by modulating the shutter speed so it also affects the degree of motion blur. This means it can also be used for other creative purposes. If you’re not lucky enough to own a RED EPIC, you can rent one for your production for a fraction of the cost.
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At present, no DSLR manufacturer supports recording HDR video with their equipment. Some clever Canon fans, however, have developed the Magic Lantern custom firmware which enables it on some DSLRs. Rather than modulating the exposure with shutter speed, Magic Lantern’s solution brackets the exposure using ISO.
Tom Ellingsen has written a great tutorial on capturing HDR footage with Magic Lantern and a Canon DSLR. He talks you through the whole process, from capturing the footage to editing it in post. If you want to start experimenting with HDR video footage, it’s one of the best ways.
HDR Time Lapses
Time lapses are a topic we love to cover here on Envato Tuts+ because they blur the line between photography and videography in a really neat way. While many of the techniques used in them are more closely related to photography, the end product is a movie. HDR time lapses are something that can be captured by almost any DSLR. While it might not be a true HDR movie, it is still HDR footage.
Stefan Surmabojov has written a great tutorial on using SNS-HDR Pro to create HDR time lapses. If you’ve got a non-Canon DSLR or want a less hacky intro to HDR videography, playing around with HDR time lapses is a great option.
What the Future Holds for HDR Video
In the next few years I suspect that HDR video is going to become increasingly popular. The technology necessary to capture HDR footage will trickle down from professional movie cameras to consumer DSLRs which will open up the technique to a whole new audience. Screens with a high enough dynamic range to accurately show HDR footage will become more common place. Rest assured, we at Envato Tuts+ will keep on top of the latest developments and show you how to use them.
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