Tuesday, October 23, 2012

4K Plug-And-Play

The process of shooting and playing back 4K at home

Labels: Help Desk
The Digital Cinema standard specified by SMPTE has a resolution of 4096x2160. Working with a Canon EOS C500 and an AJA Ki Pro Quad, you can output a 4K feed from the camera into a 4K digital home theater projector.

At AbelCine, we're always trying to stay on the cutting edge of technological development in the camera world, so we often get questions about the latest cameras and workflows. Recently, a client asked about playing back 4K footage on his new Sony 4K home theater projector, which he primarily used for HD screenings. Now he wanted to be able to record 4K footage in his studio space and immediately play it back in his screening room in 4K. In other words, he wanted to treat 4K just like a standard HD system, where we can easily record and play back at full resolution. 4K RAW acquisition and workflows are pretty well established now, but this client was asking for something rather different: 4K video. The ability to both capture and immediately play back 4K footage at full resolution is still rare, even with the latest and greatest cameras, so this request was a bit more complicated than it sounds. The Canon EOS C500 camera, however, offered a unique solution to this problem and one that makes 4K a little more plug-and-play.

To understand why the C500 was the answer, I need to explain a couple of things about the current state of 4K tools and recording formats.

A RAW Deal
At the heart of this issue is the fact that most 4K acquisition is in some kind of RAW data format. Sensors are essentially black-and-white; their photosites gather light and output voltage. Color on a single-sensor camera typically is made using a filter array; RAW data stores brightness information from each photosite and color information from whatever single color it's filtered for (red, green or blue). So in RAW, each stored pixel doesn't represent all colors, just one. Video recording, on the other hand, stores each pixel with both brightness and full color information. So why don't we just always record video? Because an uncompressed video file would be a considerably larger file size than the same RAW data, especially at high bit rates like the 12- to 16-bit ranges we see in some formats. For example, a single frame of ARRIRAW in 16x9 mode would be about 7 MB; the same 12-bit DPX file (a video frame) would be around 19 MB—a pretty big difference. So the question is, if the video is derived from the RAW sensor data anyway, why bother recording in video? Well, it all comes down to your workflow.

VIDEO KILLED THE RAW WORKFLOW
With the release of the RED ONE camera a few years back, RAW capture became a reality for many productions, including television series. RED enabled 4K production at an affordable price point, but it didn't come without some caveats. RAW data needs to be processed into video to be used, which meant an extra step in post. When RED first hit the production world, this conversion step was painfully slow on most computers. RED helped speed it up with the release of their RED Rocket com-puter card, and today's software tools minimize the post issues even more. Despite all of that, the majority of television productions today are shot in video. The introduction of the ARRI ALEXA in 2010 really changed the game. The ALEXA can output high-resolution RAW, or record in HD in the popular ProRes or DNxHD compression. The latter has proven to be the choice of a large majority of television productions. The ALEXA makes a great image, but some believe that it also was the HD workflow that pushed many television shows toward the camera.

The ALEXA records in a Log mode, giving a great deal of dynamic range, and in recording qualities up to 12-bit ProRes 4444. This is a very high-quality recording mode, but is still strictly a 1920x1080 resolution. Recording in RAW is a great option, but it's not practical in terms of cost and time in post. The quality and dynamic range of the ALEXA's HD recording is good enough for television work, and has been used for theatrical releases, as well. RAW recording is still preferable for high-res finishing and recomposition options, but it's not the norm today. Is it possible to combine high-resolution recording with the relatively easy video workflow? Canon was hoping you would ask that question, and their answer is the C500.

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