Modern frame rate standards have been with us for nearly a century. Given the fantastic new opportunity High Definition gave us to re-write the rule book, why did we not aim for a much higher viewer experience? Richard Salmon (pictured), BBC Lead Research Engineer, will challenge the very core of our understanding of television when he presents a Television and Motion Seminar in January, writes Tony Orme.
Motion representation has been largely neglected in recent years in favour of pixel resolution and aspect ratios such as 1080i and 720p. This seminar takes a look at the “I” and the “P” and investigates their real importance. To truly understand the consequence of frame rates on the viewer, we have to obtain an in-depth understanding of the psychological links affecting the human eye and brain.
When discussing image motion, many broadcast professionals tend to think of MPEG compression and cross conversion, especially between US and European 59.94/50Hz standards. If we are to provide a better viewer experience we need to consider even more fundamentally the nature of motion, why it’s so important to us and how the human mind can react to the content of different scenes.
With the advent of much improved domestic television screens, more and more motion artefacts are becoming noticeable to the home viewer. When a camera pans across a football stadium, constant switching between sharp and blurred images is regularly noticed, and this can be very disorienting, even inducing nausea-type symptoms in the viewer. Large higher scan-rate monitors can occasionally make this even more apparent.
When is a ball not a ball? When it’s a balloon! Sports events wonderfully demonstrate the very worst motion artefacts in the broadcast chain due to the high dynamic nature of the moving scenes. If you were to individually step through frames of a ball moving across a camera frame, the ball would appear to be horizontally distorted, almost balloon shaped. This provides us with a significant challenge when we want to show freeze frame images or slow motion clips.
Television standards historically have their roots in film. Most people are familiar with the fundamental workings of film; the entire film consists of millions of individual transparent photographs, back-lit and projected onto a screen in rapid succession. But did you know that when you go to the cinema you are actually seeing the film twice? To make motion as smooth and realistic as possible, the scene is shot at 24 frames per second. However, if you were to look at this using a projector running at the same speed, the film would be almost un-viewable, as the flicker would be very disturbing and probably induce a headache. To remedy this, the early pioneers of film designed the projectors to flash each photograph on the screen twice, thus increasing the frame rate to 48 frames per second and reducing flicker at the same time. It’s probably not surprising then that most computer screens run at 75 frames per second as a minimum.
Next time you go to the cinema, turn your head to one side and focus on the corner of the room but remain conscious of the film on the screen; you immediately notice a flickering in your peripheral vision. What changed? The film is still running at 48 frames a second and all you did was move your head. A similar effect could be seen on old cathode ray tube television sets running at 50 fields per second, but it is near-impossible to perceive on the new flat screen televisions running at higher interpolated frame rates.
During this experiment you might even start to feel a bit stressed or unnerved as your “fight or flight” mechanism kicks in and you prepare to take on the enemy! Our primeval instinct takes over as the highly developed motion receptors in the eye detect the movement in an instant; this is an evolutionary defensive mechanism developed from early cave man. If the cave man detected motion, maybe from a danger such as an attacking bear, he would be instantly prepared to “fight or flight”; either way he probably survived the experience, because if he didn’t he became bear food!
Television is an illusion, and from a broadcaster’s point of view we want to effectively con the human eye and brain into thinking a moving image exists. The samples of moving television and film frames offer the human eye and brain only a mere hint of the original scene; our brains invent the rest of the detail based on this and our perceptions and experiences.
No matter whether you’re an engineer or producer, new to the industry or a professional at the top of your game, understanding the nature of motion and its solutions will help you make better television and improve the viewer experience. Through his many years of BBC research Richard will encourage us to ask some very searching questions and will provide an interesting insight into the “next big thing” in broadcasting.
The RTS Television and Motion Seminar by Richard Salmon, BBC Lead Research Engineer, will take place on 18 January 2012 at Pincents Manor Hotel, Calcot, Reading. To book a place, please email firstname.lastname@example.org.
Tony Orme is a member of the RTS Thames Valley Centre committee and is producing the RTS Motion and Television Seminar.