Why 4K

Ever since the launch of RED Digital Cinema, 4K imagery has become an industry buzzword. The concept stems from 35mm film post, where the digital scan of a film frame at 4K is considered full resolution and a 2K scan to be half resolution. In the proper used of the term, 4K only refers to frame dimensions, although it is frequently and incorrectly used as an expression of visual resolution or perceived sharpness. There is no single 4K size, since it varies with how it is used and the related aspect ratio. For example, full aperture film 4K is 4096 x 3112 pixels, while academy aperture 4K is 3656 x 2664. The RED One and EPIC use several different frame sizes. Most displays use the Quad HD standard of 3840 x 2160 (a multiple of 1920 x 1080) while the Digital Cinema Projection standard is 4096 x 2160 for 4K and 2048 x 1080 for 2K. The DCP standard is a “container” specification, which means the 2.40:1 or 1.85:1 film aspects are fit within these dimensions and the difference padded with black pixels.

Thanks to the latest interest in stereo 3D films, 4K-capable projection systems have been installed in many theaters. The same system that can display two full bandwidth 2K signals can also be used to project a single 4K image. Even YouTube offers some 4K content, so larger-than-HD production, post and distribution has quickly gone from the lab to reality. For now though, most distribution is still predominantly 1920 x 1080 HD or a slightly larger 2K film size.

Large sensors

The 4K discussion starts at sensor size. Camera manufacturers have adopted larger sensors to emulate the look of film for characteristics such as resolution, optics and dynamic range. Although different sensors may be of a similar physical dimension, they don’t all use the same number of pixels. A RED EPIC and a Canon 7D use similarly sized sensors, but the resulting pixels are quite different. Three measurements come into play: the actual dimensions, the maximum area of light-receiving pixels (photosites) and the actual output size of recorded frames. One manufacturer might use fewer, but larger photosites, while another might use more pixels of a smaller size that are more densely packed. There is a very loose correlation between actual pixel size, resolution and sensitivity. Larger pixels yield more stops and smaller pixels give you more resolution, but that’s not an absolute. RED has shown with EPIC that it is possible to have both.

The biggest visual attraction to large-sensor cameras appears to be the optical characteristics they offer – namely a shallower depth of field (DoF).  Depth of field is a function of aperture and focal length. Larger sensors don’t inherently create shallow depth of field and out-of-focus backgrounds. Because larger sensors require a different selection of lenses for equivalent focal lengths compared with standard 2/3-inch video cameras, a shallower depth of field is easier to achieve and thus makes these cameras the preferred creative tool. Even if you work with a camera today that doesn’t provide a 4K output, you are still gaining the benefits of this engineering. If your target format is HD, you will get similar results – as it relates to these optical characteristics – regardless of whether you use a RED, an ARRI ALEXA or an HDSLR.

Camera choices

Quite a few large-sensor cameras have entered the market in the past few years. Typically these use a so-called Super 35MM-sized sensor. This means it’s of a dimension comparable to a frame of 3-perf 35MM motion picture film. Some examples are the RED One, RED EPIC, ARRI ALEXA, Sony F65, Sony F35, Sony F3 and Canon 7D among others. That list has just grown to include the brand new Canon EOS C300 and the RED SCARLET-X. Plus, there are other variations, such as the Canon EOS 5D Mark II and EOS 1D X (even bigger sensors) and the Panasonic AF100 (Micro Four Thirds format). Most of these deliver an output of 1920 x 1080, regardless of the sensor. RED, of course, sports up to 5K frame sizes and the ALEXA can also generate a 2880 x 1620 output, when ARRIRAW is used.

This year was the first time that the industry at large has started to take 4K seriously, with new 4K cameras and post solutions. Sony introduced the F65, which incorporates a 20-megapixel 8K sensor. Like other CMOS sensors, the F65 uses a Bayer light filtering pattern, but unlike the other cameras, Sony has deployed more green photosites – one for each pixel in the 4K image. Today, this 8K sensor can yield 4K, 2K and HD images. The F65 will be Sony’s successor to the F35 and become a sought-after tool for TV series and feature film work, challenging RED and ARRI.

November 3rd became a day for competing press events when Canon and RED Digital Cinema both launched their newest offerings. Canon introduced the Cinema EOS line of cameras designed for professional, cinematic work. The first products seem to be straight out of the lineage that stems from Canon’s original XL1 or maybe even the Scoopic 16MM film camera. The launch was complete with a short Bladerunner-esque demo film produced by Stargate Studios along with a new film shot by Vincent Laforet (the photographer who launch the 5D revolution with his short film Reverie)  called Möbius.

The Canon EOS C300 and EOS C300 PL use an 8.3MP CMOS Super 35MM-sized sensor (3840 x 2160 pixels). For now, these only record at 1920 x 1080 (or 1280 x 720 overcranked) using the Canon XF codec. So, while the sensor is a 4K sensor, the resulting images are standard HD. The difference between this and the way Canon’s HDSLRs record is a more advanced downsampling technology, which delivers the full pixel information from the sensor to the recorded frame without line-skipping and excessive aliasing.

RED launched SCARLET-X to a fan base that has been chomping at the bit for years waiting for some version of this product. It’s far from the original concept of SCARLET as a high-end “soccer mom” camera (fixed lens, 2/3” sensor, 3K resolution with a $3,000 price tag). In fact, SCARLET-X is, for all intents and purposes, an “EPIC Lite”. It has a higher price than the original SCARLET concept, but also vastly superior specs and capabilities. Unlike the Canon release, it delivers 4K recorded motion images (plus 5K stills) and features some of the developing EPIC features, like HDRx (high dynamic range imagery).

If you think that 4K is only a high-end game, take a look at JVC. This year JVC has toured a number of prototype 4K cameras based on a proprietary new LSI chip technology that can record a single 3840 x 2160 image or two 1920 x 1080 streams for the left and right eye views of a stereo 3D recording. The GY-HMZ1U is derivative of this technology and uses dual 3.32MP CMOS sensors for stereo 3D and 2D recordings.

Post at 4K

Naturally the “heavy iron” systems from Quantel and Autodesk have been capable of post at 4K sizes for some time; however, 4K is now within the grasp of most desktop editors. Grass Valley EDIUS, Adobe Premiere Pro and Apple Final Cut Pro X all support editing with 4K media and 4K timelines. Premiere Pro even includes native camera raw support for RED’s .r3d format at up to EPIC’s 5K frames. Avid just released its 6.0 version (Media Composer 6, Symphony 6 and NewsCutter 10), which includes native support for RED One and EPIC raw media. For now, edited sequences are still limited to 1920 x 1080 as a maximum size. For as little as $299 for FCP X and RED’s free REDCINE-X (or REDCINE-X PRO) media management and transcoding tool, you, too, can be editing with relative ease on DCP-compliant 4K timelines.

Software is easy, but what about hardware? Both AJA and Blackmagic Design have announced 4K solutions using the KONA 3G or Decklink 4K cards. Each uses four HD-SDI connections to feed four quadrants of a 4K display or projector at up to 4096 x 2160 sizes. At NAB, AJA previewed for the press its upcoming 5K technology, code-named “Riker”. This is a multi-format I/O system in development for SD up to 5K sizes, complete with a high-quality, built-in hardware scaler. According to AJA, it will be capable of handling high-frame-rate 2K stereo 3D images at up to 60Hz per eye and 4K stereo 3D at up to 24/30Hz per eye.

Even if you don’t own such a display, 27″ and 30″ computer monitors, such as an Apple Cinema Display, feature native display resolutions of up to 2560 x 1600 pixels. Sony and Christie both manufacture a number of 4K projection and display solutions. In keeping with its plans to round out a complete 4K ecosystem, RED continues in the development of REDRAY PRO, a 4K player designed specifically for RED media.

Written for DV magazine (NewBay Media, LLC)

©2011 Oliver Peters

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