The History of Frame Rates

What is the Phi Phenomenon?

The Phi Phenomenon is when our brains create the sense of movement with an animation or a motion picture. It was first described by Max Wertheimer in 1912. The human brain can perceive about 10 – 12 fps, anything higher our brains blend the images together.

What is the significance of 12fps?

12fps was the first frame rate. Playing back 12 frames per second with 12 intermittent periods of black as the film advances will create an intolerable amount of flicker. To make the flicker of black Thomas Edison says the number is 46 frames per second.

What is over-cranking?

Over-cranking is recording a faster frame rate than final projection.

What is under-cranking?

Under-cranking is recording a slower frame rate than final projection.

What impact did the introduction of sound have on frame rate?

Sound was a huge technological achievement that changed film in a drastic way. Frame rate had to be kept at a strict frame rate and that was established in 1929 as 24 frames per second. It was 24 frames per second because the sound track didn’t have the fidelity on a 16 frames per second system. They used a 24 frame per second projection using a double bladed shutter to keep to desired 48 projected frames per second.

Give as much rationale as you can for why 24 became the international frame rate

24fps became the international frame rate because it was cheapest option rather than going to 30 or 32fps.

What issues surrounded bandwidth?

The issues that surrounded bandwidth was that the bandwidth used by the colour subcarrier which could potentially interfere with the audio signal causing intermodular beating. The solution to this would be to reduce the frame rate by 0.1% so this made frame rate 29.97fps.

What was interlacing?

Interlacing is when the picture it split into the upper field and lower field. Each field would be created on the screen one after the other in a comb like pattern.

How was the challenge of intermodulation tackled?

In order to beat intermodulation, or a beating distortion caused by the hum generated in the electrical current, the refresh rate was set to that of the AC power – in the United States, 60 hertz.

What is the significance of 60 hertz and how does it relate to 30 frames per second?

60 hertz equals to 60 frames per second. By this the screen will have a full 30 frames per second.

What is the difference between VHF and UHF?

VHF (30-300 MHz) was the old black and white television sets and UHF (300 – 3,000 MHz) was trying to introduce colour to the television sets.   

How was colour standard arrived at?

The would break down the colour into luminance and chrominance, broadcasters could embed a colour signal as a subcarrier in the television signal. New colour TVs could pick up and interpret this colour subcarrier which would be ignored by the older black and white TV sets.

What challenge did bandwidth present to achieving a colour standard and how was this problem overcome?

The bandwidth used by the colour subcarrier could potentially interfere with the audio signal causing intermodular beating. The solution to this would be to reduce the frame rate by .1% phasing the colour and audio signals so they would never fully match up.

What was the fields per second ratio that was eventually developed as the standard in colour and what was the resulting frames per second ratio?

The go from 60 fields per second down to 59.94 fields per second and 29.97 full frames per second.

What is PAL and why was it developed?

PAL was a format to solve the colour problems that plagued NTSC and would work with the 50 Hertz AC power used in Europe and everywhere else in the world.

What are the fields per second and frames per second ratios of PAL and SECAM?

PAL along with a similar format run at 50i for an effective 25 frames per second.

     A) Produce a step by step guide to explain how we get from the 24 frames per second of film to a 60i video stream to be able to watch celluloid movies on video?

First of all, the 24 frames per second film is slowed down by 0.1% giving up 23.976 frames per second.

If we need to make 4 frames of 23.976 to fit into 5 frames of 29.97. They did this by splitting the frames into fields using a 3:2 pull-down. 

The first frame is captured onto three fields – the upper, lower and then upper field – that’s one and one half frames. The next frame is captured on the following two fields, lower field and then upper. 

The next frame after that fills up the lower, then following upper and lower with the last frame filling the upper and lower field.

     B) What are the issues with the various conversions?

This still resulted in video streaming having Telecine judders every 3 frames which is especially noticeable on long slow camera movements.

How does modern digital camera avoid the telecine process and with what effect?

Modern digital camera avoided the telecine process as they record 23.976 or straight 24 frame rates natively on to the hard drive but there are some workflows that run through HDMI cables which are rated for 60i.

How are 24fps films telecining onto SECAM or PAL fps?

For telecining film onto PAL or SECAM’s the process was much simpler. They used a 2:2 pulldown, the 24 frames per second footage was sped up by 4% and each frame is transferred onto two fields – an upper and a lower field. The increased speed raises the pitch of the audio by a noticeable 0.679 semitones or a little more than a quarter.

Explain high frame rates and temporal resolution

24fps has been the standard for narrative film for nearly a century now. But enterprising filmmakers have tried to push temporal resolution or frame rate higher – trying to reduce the motion blur to create smoother and more realistic look to the film.

What are the issues with higher frame rates in narrative filmmaking?

Audiences have warmed up to high frame rates in narrative filmmaking, the most recent example of a film with high frame rates is Peter Jackson’s ‘The Hobbit’. This film was shot in 48 frames per second and audiences did not agree with how it looked, they complained that the “human actors seemed over-lit and amplified”, another reviewer complained that “it looked like a made-for-TV movie”. Filmmakers like Peter Jackson or James Cameron, push for higher frame rates.