Bob Pank looks at shooting 4K TV

Bob Pank#

Author: Bob Pank#

Published 1st November 2013

by Bob Pank
Issue 82 - October 2013
Not unexpectedly IBC was full of buzz and products for 4K the new image format for television. This is generally taken to be a 2x2 version of HDTVs 1920 x 1080, i.e. defining a 3840 x 2160 pixel picture. But there is nothing new about big pictures like this. Back in late 2004 a draft of the Digital Cinema Initiatives (DCI) Digital Cinema System Specification included the two picture sizes of 2048 x 1080 and 4096 x 2160 pixels referred to as 2K and 4K. So, give or take a few pixels, 4K sized images are nothing new; its just that now we are talking about television rather than cinema where it is already well established.
In the years leading up to the DCI Specification there was an ongoing debate about the number of pixels needed to render the full definition of a 35mm film frame. After all, the new medium must be at least as good as the one it replaces. It could be shown that a 4K scan of a 35mm original camera negative frame (a full frame (biggest possible) image being 24.92 x 18.67mm, Cinemascope 21.95 x 18.60mm) looked sharper than a 2K one. But then, after the film had been optically copied via interpositives and internegatives, and then distributed on release prints that went to the cinemas the resolution was generally significantly lower than 2K. So DCI images at 2K showed an immediate improvement in the cinemas and the format was used in virtually all digital cinemas... for a few years.

But 4K was not forgotten. Many film movies were scanned at 4K resolution and the format became available on digital cameras. The provision of transport/networks, compression, storage and other technologies continued to develop and 4K looked less and less of a burden. Then it started to be projected in digital cinemas. The result provides a sharper, clearer image for the audience to appreciate on the big screen. Now technology allows 4K, a picture that looks great in cinemas, to be viewed in homes as 4KTV. And yes, you will need a big screen to fully appreciate it!
Changing the resolution of the images has knock-on effects. Digital cameras for movies were required to provide the film look. Im not sure if this included scratches, dust, weaves and grain but to many it meant being able to use a shallow depth of focus especially on close-ups. And so it was that film sized imagers became de rigueur for digital movie cameras (it also applies to the HDSLR range of cameras that again have sensors at or around the 35mm film size). That, at least, can provide a part of the established film look but does it belong in the TV look?
No is does not. Such shots may be fine for drama in cinemas, which is mostly what they show, and for drama on TV, but news and, especially sport, as well as other TV genres generally much prefer a deep field of focus. So, for example, most or all of the players on a football pitch can be in focus at the same time pretty much as it would appear if you were there. In most cases it can be argued that the shallow field of focus is not natural and the deep is more like our normal perception. So far 4K camera technology still seems to be stuck in movie mode while a new bread of 4K cameras for TV needs to be based on the much smaller imaging sensors at around the half-inch diagonal size, as is widely used in TV today. Other knock-on benefits would be a resulting reduction of the size of the camera body and lens assembly, which would be very welcome especially on location shoots and OBs.

Manufacturers have been slow off the mark, promoting superb massive 4KTV screens without providing for the appropriate needs for the cameras. There are plenty of 4K cameras with 35mm-like sized sensors, but very few with half-inch sensors. Sony has recently introduced a new 4K-for-TV camera onto the market. The PXW-Z100, which features a 1/2.33-inch Exmor CMOS sensor, shoots 4K at 50p or 60p. The company describes this as its latest step in expanding the 4K world to everyone, from high-end cinema to corporate and event productions. The camera is said to include a fixed 4K-compatible high-performance G Lens, weighs less than 3kg and uses the XAVC recording format. Based on the same shooting ergonomics as a conventional handheld professional camcorder, 4K content can be recorded without extra equipment. Although 4KTV is still not widely distributed its camera footage certainly has its uses in post production. It can be down-converted to produce high quality 1080p or to provide a high quality HD zoom-in.
This camera is a welcome step but, of course, a whole new range of broadcast 4KTV cameras based around half-inch (or there about) sensors is needed. And there is more. Focusing all the image detail needed to provide full 4K definition onto the small sensor is also a challenge. While modern fabrication technology is well able to deliver the required number of photo sites in a small area of a CMOS silicon chip, the extreme accuracy required from the camera optics, the lens and its assembly, may be the factor that has held back the arrival of the professional half-inch 4K camera.

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