film

[stayvisualfilms]

As is clear (I hope) from the above top graphic, if you apply the 180 rule to exposure when doing video, the frame is exposed for half of it’s lifetime.

Say you have chosen 25p (25 frames per second) for your video recording. Using the 180 rule you’ll set your exposure to 1/50th and you’re capturing half of the action that takes place during your frames lifetime.

In other words, Choosing 25 frames per second means you’re sending 1 frame to the viewer every 1/25th second. If you expose for 1/50th second, you’re exposing only half the lifetime for each frame.

So let’s say a car travels 40km / hour. That’s 11 meters per second and half a meter per 1/25th second. So if you expose for 1/50th second, every 1/25th second, your actually recording a car 1/4 of a meter for every frame and skipping the other 1/4 meter. So you see, now you are recording video with gaps. (see 2nd graphic).

Ok, So now let’s look at what happens if you run 25p for your video and expose for say 1/100th of a second. That means that you’re exposing 1/4 of the time and leaving 3/4 of the frame time unused. If a car travels 50cm in 1/25th of a second, then 1/100th of a second will only capture 12.5cm. 

One frame will show 12.5cm of movement (blurred), then the next frame will show another 12.5cm and so on, with the beginning of each frame starting 37.5 cm from the end of the last shown distance (see 3rd graphic)

You see?

In all cases you are missing part of the footage :)

In the case of 1/100th of a second exposure you are missing 3/4 of the action that happened during the one frame time (1/25th sec), in which case your eye could start to see jerky footage.

The 180 rule is a rule of thumb that makes it kind of acceptable to watch, with your brain making up for the missing information.

Why can’t we have full frame exposure?

[stayvisualfilms]

A Sense of Perception

Our inner world, what we hear, what we see, what we perceive through our noses and our tactile sense is an interpretation of the natural phenomena as they exists outside us. For example: when we see a bird, what we are actually perceiving is light reflected off certain colours of a birds feathers, the light travels in waves with different frequencies representing different colours. We may hear a sound of a specific species of bird and we are perceiving fluctuations in waves of air that vibrate at a certain rate. Combinations of these air vibrations constitute a signature structure peculiar to a species of bird. When we perceive these sights and sounds, our organs of perception are only the first step in a series of processing steps that take place as the said sights and sounds travel to and through our brains. The end product is an image of a bird and the sound of a birdcall. We don’t know exactly what our brain does to the incoming information in order to create the end product, but we do know that the audio visual end product in our brains is quite different from the original sight and sound before perception. Our brains “make sense” of the raw perception data that our sense organs deliver. The process of making sense is involuntary and necessary and has developed over hundreds of thousands of years. One of the things our brains excel at is creating patterns. That is: recognising co-relationships and cause and effect sequences. Once it recognises a pattern it can conceptualise that into an object and put a label on it. When it sees this pattern again, it associates with the label etc. The result is that our brains complement a lot of the perceived information with existing pattern information to create end products, birds in our example.

So… long story short our brains “make up” a lot of the information based on what’s been seen before. It’s easier that way. When we’re learning something new the learning curve we experience, is the brain not being able to relate to existing information and have to create new labels, concepts, objects and products.

Now if we take the example of film. 24 frames per second being illuminated 48 times per second by a two blade projector shutter or 72 times per second by three blade shutter, the brain has to work to fuse the images together into motion. The brain can perceive individual images up to the rate of about 15 images per second at which point the flicker fusion threshold is reached and the images are “blurred” into motion.

The fact that 24 frames per second has been the standard film frame rate for so many years is no accident. It was dependent on the flicker fusion threshold as well as economic factors such as the price of celluloid (film). From a cost benefit point of view it makes sense to standardise a low as possible frame rate but not lower than the flicker fusion threshold.

That was then, this is now. We are no longer bound by the limitations of the days of celluloid film. We are now living in an age where frames per second and shutter speeds are dictated by CPU power. Todays cameras are computers that expose a sensor X amount of times per second for an X fraction of a second each time. The 180 degree rule states that shutter speed should be double the amount of the frame rate. Shooting at 24 frames, this means a shutter speed of 1/48th second, 25 frames 1/50th, etc. Why do camera operators, DPs, filmmakers abide by this rule? Not all of them do in fact. But for the most part it’s because they are complying with convention and viewer conditioning. Shooting at other frame rates with different exposure times causes a disruptive experience for the viewer. For example shooting at 24 frames but with an exposure of 100th  of a second will make the footage look less flowing, whereas 24 frames with a shutter speed of 24th of a second would possibly look too blurry. With the current technological capability it should be possible to shoot at high frame rates (200, 300) per second with high shutter speeds to achieve a more realistic and less stylised viewer experience, however viewer conditioning needs to catch up. In time we will and when we do we’ll think back to those good old days of the “cine look” as we now look at the steam engine (humble beginnings)

[stayvisualfilms]

Frames per second debate

Why would we shoot at 24, 25 or 30 frames per second? 24 frames is an evolved standard. It goes right back to when film was born and very low frame rates were pervasive. 24 frames evolved as a standard because it’s the slowest frame rate at which the human eye no longer discerns the jerkiness of slower frame rates. Driven by the limitations of the time, a best bang for buck was chosen to represent moving pictures. 24 frames was the solution to a problem.

Enter TV and tv standards. TV is electrical and dependent on the frequency of the electricity signal to render its pictures without interference. Electrical frequency 60 Hz (USA, Japan) did not display 24 frames very well, hence 30 frames. The same in Europe for 50 Hz, hence 25 frames.

Human conditioning. 1. Back in the days of Johan Sebastian (Bach) the ears of the public were not used to dissonance as much as we are today. When Bach composed for the “well tempered” tuning there was a lot of criticism that went back to how it felt on the ears. 2. When Digital audio came around the same thing happened. Over the years the public's ears had grown used to listening to vinyl, first on 78's then on 33 rpm. The perception of audio from those media emphasised certain characteristics of sound and ingrained them. When our senses perceive sound our brains complement, this leads to expectations and we call it conditioning. 3. Over time we have become accustomed to viewing video and film at 24 frames per second. Anything that is viewed at a considerably different frame rate than 24, causes our brains to balk for a moment, it needs to reassess. What we see does not comply with what we expect. Conditioning has everything to do with the phenomena as they are before we perceived them and how we experience them after our brains have processed them.

Consuming media causes emotions. Emotions are closely linked to the very details of our perceptions.

A sense of perception: Fantasy and reality In many ways viewing a movie can be seen as a means of escape from reality. The question here is: does escape from reality mean that what we view must seem different from reality. In many games, films, images and soundscapes we try to achieve an as close as possible likeness to reality. Does that mean that our feeling of escape is less? In other words, if the level of reality approaches 100%, does that mean that our ability to escape has decreased? Or in other words … is our feeling of escape from reality dependent on how illusory the video game is. Or in other words … Can we say that the more Virtual reality resembles reality the less we like it?

My answer to the above is a definite No! The more we can emulate reality, the greater the escape. It’s the knowledge that we are emulating, a meta layer of knowing, that makes what we are experiencing, an escape. This is not to say that something abstract can’t evoke feeling. It can! And what if, during our experience, we cross over from VR to R? In other words at some point during the experience, we forget that we are in an emulation of reality…? Then so much the better, the greater the escape. The more we are “born again” when we come out of it.

So to video I say: Bring on the fast frame rates. It’s only through the limitations of technology that we have been streamlined to experience slower frame rates as “the standard”, “acceptable”, and finally “preferable”. Now those limitations are disappearing, the representation of reality is nearing reality itself and that allows our brains to experience with ever more fullness the reproductions of sound and vision. Paradoxically, now we have digital sound, we have listened to mp3 as a standard for reproducing music for a long time, however that’s only temporary and largely internet bandwidth induced. Over time we’ll all be listening to vastly superior reproduction of sound and vision and we’ll be looking back at the 20th century saying “how could we have believed in 24 frames per second, it will be synonymous with ancient, inferior quality. The sexiness of vinyl and “cinematographic look” today are purely nostalgia, harking back to a day where things were simpler… the world is rapidly moving on. Embrace the new… Bring it on!