4K or not 4K – that is the Question!

 

A producer’s guide to the pros and cons of shooting in 4K

What is 4K?

Whether a video format is either 'standard' or 'high definition' has always been a moving target. A continual game of leapfrog saw resolutions rise from 35 horizontal scan lines to 100, then from 405 to 625 lines in 1963. The modern era welcomed a standardisation of 625 as the PAL system, but debate soon began over what would constitute the new high definition. Today's definition of HD (1920 x 1080) has been 20 years in development.

Now the next generation of HD is 4K resolution (4096 x 2730), which the CEA is calling Ultra HD is forecast to become the next standard for programme acquisition, delivery and broadcast.

This new VMI article investigates the positives and pitfalls of shooting in 4K and most importantly what you need to know if you want to shoot and produce a programme in 4K.

Why 4K?

Acquisition, post-production and delivery is now fully HD (1920 x 1080) but modern technology now delivers even greater resolutions and 4K has become a practical production format.

There are a number of advantages of adopting 4K acquisition now:

Today's Reality

In spite of the clear advantages of acquiring in 4K, very few productions are actually shot in 4K. For most, 4:2:2 or 4:4:4 HD codecs have been good enough for dramas and many features.

The increased camera costs, storage requirements and editing power required by 4K is, at the moment, causing DoPs to hesitate before jumping in... However, there is no doubt that 4K will happen in a big way, very soon.

Shooting in 4K

Rather than jumping head first into 4K digital production, many are using existing tools to transition towards higher resolution content creation.

ARRI

ARRI Alexa. The ARRI Alexa is not a 4K camera but it does have a 3.5K sensor. As well as recording on-board to SxS cards in 1080, its de-bayered RAW output can be recorded on external devicesat 2800 x 2160 - almost 3K. These RAW files offer improved dynamic latitude for excellent highlight control, as well as greatly increased resolution. Skyfall was shot by Roger Deakins using the Arri RAW 2K+ workflow, with the output recorded by a Codex device. Versions were prepared for 4K cinemas with the files simply up-converted and it looked fantastic!

“Celluloid 4K”

Arri’s official 4K position is that they have made some of the best film cameras yet and film is, in their opinion, still the best acquisition medium for 4K.

Their argument is that if productions want to shoot in 4K, then modern film stocks already facilitate this resolution. As the digital intermediate and telecine post production workflow is very established, producers can continue to shoot and edit film as usual. Because film cameras and stocks are very well established, there is no fear of incompatible or outdated digital standards, as may be the case with new 4K digital formats. Arri's own laser system prints digitally onto film, enabling the highest resolutions to be written back to celluloid: a great way of viewing, publishing and archiving 4K footage.

Native 4K Digital Cameras Systems

RED

RED EPIC and RED SCARLET 

RED was the initial trailblazer on the march to 4K. Although the RED One was initially unstable at full resolution, it has been improved over time and both the latest RED EPIC and RED SCARLET cameras shoot 4K very happily onto solid-state drives which mount inside the camera. This latest generation of RED cameras effectively share a common 4K architecture and shoot reliably at 4K without incident.  However, many of the slow motion frame rates of the EPIC are not available on the SCARLET, and the EPIC is also capable of shooting at 5K.  Material shot on either camera will perfectly match if required.

RED uses a native RAW capture format called REDCODE, which is a process that requires de-Bayering in order to use captured 4K material.  This may lengthen the post-production or “digital developing process”, but in exchange, these files have all the benefits of the non-destructive editing workflow that has become a standard with high-end digital still cameras. Furthermore, the development of the RED Rocket acceleration PCI card and faster computers means that this is no longer a long process.

It is a massive advantage that RED can record 4K on-board, unlike other systems which currently require external recorders.  RED users should note however, that as REDCODE RAW files are massive, so media cards will need to be offloaded frequently onto large on-set archive devices.

Sony

Sony F65 Sony entered the race with the introduction of the F65 camera in 2012.  This camera has a native 8K image sensor down-scaled to 4K in order to fight visual artefacts and the de-Bayering process. Its large size, compared with RED EPIC and Alexa, is similar to traditional 35mm cameras. As well as not being very portable, it suffers from very high power needs. Also, its high price and the massive files that it generates, has meant that the camera has struggled to achieve market penetration. Possibly the camera is ‘too good’ and even a little ahead of its time – only time will tell but it is still an excellent camera.

 

 

 

Sony FS-700 Sony has also introduced a little brother called the FS700 which will support 4K acquisition using a suitable off board recorder in a short while. The 4K off-board recording  system has now been announced but we do not yet know if this will record de-Bayered 4K or require this in post.  This is an important distinction, as this can be a very laborious post production process.

 

 

 

 

 

Sony F-55 New on the scene for delivery in January 2013 are two modular 16-bit 4K cameras. Importantly, like the Alexa, The Sony F55 has a global shutter to eliminate the rolling shutter effect. The F-55 camera offers simultaneous compressed HD, 2K and (in the future) 4K recording on internal high-speed SxS PRO+memory cards and RAW 2K/4K recordingon AXSM memory cards using a bolt-on AXS-R5 recorder. With this device attached, the F55 delivers at astonishing 240 fps in RAW 2K and 60 fps in RAW 4K. (Be aware that SxS Pro Plus cards are a brand new development for 2013!).  The Sony F-55 and F-5 can integrate with the AXS-R5 external recorder.  This recorder actually docks with the cameras by means of a large multi-pin connector, so it won’t feel like you are using an external recorder at all. 

 

Sony F-5 The second camera, the F5, is also a potent high frame rate 4K camera but uses an electronic shutter. Recording internally to SxS cards limits the user to 10-bit HD or 2K resolutions.  If however you use the optional new XAVC recorder, this opens up 16-bit RAW 2K & 4K capture. It can also take compressed high speed 2K shots at up-to 120 fps onto SxS cards or uncompressed onto the AXS-R5 external recorder, which as already mentioned, docks to the camera for fully integrated operation.

 

Canon

Canon C-500 After its great success with the large sensor C300 HD large sensor camera, Canon released the C500 for release in late 2012.  Almost identical to the C300, even sharing the same 4K sensor, it offers identical performance for on-board HD acquisition.  However, as with the FS700 and similar cameras, as it only records HD using its on-board acquisition system, so once again, if you want to acquire 4K, you be required to use an external recorder.  

 

 

 

 

JVC

JVC also deserves a special mention here as they have recently released a prosumer 1/2” chip camera that records highly compressed 4K on-board to multiple SD cards. The camera has the unusual capability of low latency live 4K output via four HDMI terminals. Its small sensor size makes its low light capabilities questionable but for its price, it's a great innovation.

 

 

 

Other 4K image capture cameras do exist – either in development or as specialist cameras - but the above lists the major contenders just now.

 

 

4K External Recorders

Most cameras require an external recorder to capture uncompressed 4K RAW files. The RED, Sony and Canon 4K cameras are all equipped with SDI ports that connect with external 4K recorders. An important note is that the external recorder will de-Bayer the image recorded, a great help in post-production.

The main options are:

Sony

Sony SRR1 Sony's SRR1 SRMaster is optimized for HD recording into the SR format compressed at up-to 880Mb/s or at higher bitrates uncompressed.

 

 

 

 

 

 

 

Sony AXS-R5  Designed for the Sony F55 and F5, the new AXS-R5 promises the ability to record 16-bit RAW 2K/4K images onto new AXSM cards. Featuring the potential for 240fps 2K recording, it has generated a lot of attention.  The Sony F-55 and F-5 can integrate with the AXS-R5 external recorder.  This recorder actually docks with the cameras by means of a large multi-pin connector, so it won’t feel like you are using an external recorder at all but at present, it does not offer integration to any other models of camera.

 

 

 

 

 

 

Convergent Design

Gemini RAW Recorder  Gemini RAW can record 4K RAW files (at up-to 120 fps), and simultaneously capture a second HD feed uncompressd or in Avid DNxHD. Perhaps more importantly, it can capture a camera output as a 4K RAW file and as a proxy file at the same time – perfect for offline editing workflows. The company's well-established Gemini 444 is certified for ARRI RAW, including 4:3 anamorphic compatibility. Support for Canon's Cinema RAW is on its way.

 

 

Codex Digital

Coded S Recorder  The Onboard S Recorder can ingest ARRI RAW ( 60fps 16:9 and 48fps 4:3), Canon Cinema RAW (at up-to 120fps) and uncompressed HD or wavelet encoded HD material - plus audio and metadata. At 1.1kg, it is an ideal partner for smaller cameras, such as the Canon C500.

 

 

 

 

 

STwo

STwo OB-1  OB-1 records 3K ARRI RAW with variable frame rate support. It has the power to record up-to 36 minutes of DPX files and is designed to be rugged enough for any shooting environment.

 

 

 

AJA

AJA Ki Pro Quad  With Thunderbolt connectivity, the Ki Pro Quad is built for speed. Accordingly, it records 10-bit (as opposed to 12-bit) 4K video as ProRes files. The workflow into post production is therefore fast, but with a slight compromise in image quality compared with RAW formats.

 

 

 

 

 

 

Sensor Difficulties

Before RED exploded onto the market with the RED One 4K camera, digital image sensors did not have an image sensor size with a higher resolution than 1920 x 1080 HD. Interestingly, early HD cameras actually recorded lower resolutions than this but the gold standard was always to achieve a recorded image size of 1920x1080.

Interestingly, the reason that scientists and technicians created the 1920 x 1080 image size is that it matched the resolvability of our eyes under common viewing distances and screen sizes at the time (which equals, I am told, an observer 1/3 way from the front of the Odeon Marble Arch with a screen size of 60’!). Independently, researchers also found that it was a good size for capturing an image with the least amount of artefacts such as moiré and aliasing and so it became the standard for HD acquisition and delivery.

Cameras were introduced with large CMOS sensors compared with a traditional CCD. The result is that motion artefacts became apparent for two reasons.  Firstly, the jello

effect started to be seen when using CMOS sensors with a slow rolling shutter, so different parts of an image will capture at different times (compared to CCDs with an electronic shutter which exposes the entire image simultaneously). This effect causes vertical lines to tilt when you pan the camera. However, over time, manufacturers have found ways to compensate for this and so this has ceased to be such a problem. The second reason motion artefacts became apparent is because sensors designed for high resolution stills were being used for lower resolution motion images.  If these sensors did not utilize all pixels for their lower resolution motion images, sensor technologies designed to minimize artefacts such as aliasing and moiré were no longer effective.  One technology in particular is the optical low-pass filter (OLPF), which is essential for creating natural-looking images.  Both of these effects started becoming apparent with the Canon 5D MkII.

New strategies have been employed for reducing aliasing and moiré artefacts by restructuring sensors into new configurations. The Canon C300 employs two 1920x1080 streams carefully restructured into a 4K sensor, whereas Sony produces its F65 with 2 x 4K sensors placed on top of each other (one at a 45˚ angle) to effectively create an 8K sensor. In a similar vein, the latest RED cameras have sensors greater than 4K to achieve higher-quality, super-sampled images.

Storage Concerns

Storage and handling massive files is a real issue. Hopefully the price of drives and solid-state storage will improve in the future but the reality of transferring huge amounts of data is not a problem which is going to disappear quickly, as data hungry cameras generate ever larger amounts of data media.

The Glass

With an ever-greater pixel count, the quality of the optics becomes a much more important consideration. Consequently, Zeiss and Cooke have been able to capitalise on their exceptional quality. Cooke states that its S4 lenses are rated for not just HD and 2K but also 4K, 8K, 16K…  While 16K claims may be far-fetched, DSLR lenses or Zeiss Compact Primes

can't be expected to perform with the same quality, resolution and performance as Zeiss MasterPrimes or Cooke S4 lenses. Lenses are pushed really hard when working with a wide-open iris; any defect is highlighted. So lens choice becomes a very important consideration when shooting in resolutions above 2K.

Conclusion of 4K

Who needs 4K?  HD home projectors with a 6ft screen looks great. Will 4K actually make such a difference?

RED claims that with their 5K Mysterium-X sensor, productions can zoom in about 800% in post-production, a very handy tool to have for visual effects and chroma key work. The increased resolution also allows for better keying and rotoscoping, as first noticed when Doctor Who began testing with HD.

The downside is the need for a very powerful workstation to handle the data throughput and processing.

A more practical problem is that it will probably be a while before everyone at home owns a 4K screen at home to be able to appreciate the higher resolution images. In Japan and Korea, the advancement of digital broadcast has created such fierce competition they have already started experimenting with 4K broadcast streaming, so 4K HD broadcasting is perhaps just a matter of time now.

A small number of our clients are now shooting 4K and finishing in HD, to permit re-versioning in 4K in the future and making their library future-proof.  Movies shot on film will just need to be rescanned in 4K to be finished in 4K, as we already know that film can handle 4K, but many digital acquisition formats will simply fall out of favour should the 4K migration happen.

Another issue is that 4K might not be the end of the road for the resolution race.  8K sensors already exist in the Sony F-65, though 8K capture is still some way off.  Perhaps, although Ultra HD 4K is being adopted by the consumer Industry, wholescale migration might wait until 8K becomes a practical delivery format.

Whilst shooting 4K will help producers to deliver much higher resolution images, the one question that no one can answer is whether this will actually produce more aesthetically pleasing images. 4K pictures are incredibly sharp and our experience is that DoPs, when faced with incredibly sharp images, often choose to degrade their pictures by introducing some kind of softening filters to make their pictures look… well, more filmic!

The hard reality is that 4K is here. Some are embracing it and others are avoiding it. If you choose to go down the 4K route, you will undoubtedly give your clients additional capabilities in post-production such as zooming-in and better VFX. Your pictures will be future-proofed for 4K projection (until 8K arrives, at least). And, you're likely to be ahead of the competition.

 

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Barry Bassett and Gerard Botha. VMI
November 2012.

 

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