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Welcome to Filmmaker IQ.com - I'm John Hess and today we'll dive into the history of frame rates.
Let's establish a basic truth about film. Nothing in the movies is real
The sets are fake, the actors are pretending and reciting lines written for them, even
the very essence of moving pictures is a lie - There's nothing moving, it's all an optical illusion.
Take for instance this spinning wheel of circles - it looks like it's moving clockwise but
if we compare each frame of this animation, we see that actually nothing is moving at
all. We're just turning off circles sequentially but when we flash these illustrations one
after the other our brains create a sense of movement.
This is called the Phi Phenomenon first described by Max Wertheimer in Gestalt psychology in
1912. The human brain can perceive about 10-12 individual frames per second. Faster than
that and our brains blend the images together into motion.
So we've found our first frame rate - anything higher than 12 frames a second. Simple, right?
Well not so fast...
With film we need to stop the projection as we load up each frame otherwise we'll have
a blurry mess. But Playing back 12 frames per second with 12 intermittent periods of
black as the film advances will create an intolerable amount of flicker. How fast do
you need to flash the images on screen to make the flicker disappear? According to
Thomas Edison - the magic number is 46 times per second. At 46 frames per second, our persistence
of vision kicks in and we won't notice the screen going dark between every frame.
But 46 frames per second meant you had to run through a lot of film and that stuff isn't cheap.
Film projectionists came up with a unique solution - let's flash the same frame
on the screen more than once.
Using double or triple bladed shutters, you could up the frame rate projected without
running more film. Playing back a 16 frames per second film using a triple bladed shutter,
we would flash each frame 3 times for a total of 48 frames per second - just above Edison's recommendation
And that's our first commonly used frame rate for silent film - 16 frames per second.
Or there abouts. The inconsistency of silent film frame rates have driven film historians
and preservationists nuts, Early 20th century cameras and projectors were hand cranked and
cinematographers would undercrank or overcrank the camera for effect, D.W. Griffith was notorious
for undercranking his shots, shooting as low as 12 frames per second. Even Edison ignored
his recommediation. Exhibitors also played fast and loose with the frame rate sometimes
playing films back faster so they could squeeze in one extra showing at the end of the day. In reality, silent film
frame rates could range anywhere from 14 to 26 frames per second but that was okay as
it didn't really ruin the effect of motion pictures.
That is until Sound came into the picture.
The introduction of sound was one of the most drastic technological and artistic changes
in all of motion picture history. Because sound was recorded as an optical track that
ran alongside the film strip, recording and playing back film had to be kept at a very
strict and even frame rate - and that frame rate would be established internationally
in 1929 as 24 frames per second.
Why 24? Well they found that the audio track just didn't have enough fidelity on a 16 frames
per second system. Using 48 projected frames as our goal, they stepped up the next factorial
- a 24 frame per second projection using a double bladed shutter to keep to desired 48
projected frames per second
Why 24 and not 23 or 25? Well that comes down to basic math. 24 is number that can easily
be divided 2, 3, 4, 6, and 8. So an editor can know right off the bad that half a second
is 12 frames. A third is 8 frames, a quarter is 6 frames and so on.
Why not a higher number like 30 or 32 which also have the same factors. Like I said
earlier, this stuff ain't cheap. 24 frames was just the lowest easily divisible number
that would work for sound.
Ironically, the need for a consistent 24 frames per second created headaches in the
sound department. The first sound cameras with their whirling electric motors were very noisy - forcing
camera operators to shoot from a soundproof booth through a window.
Technology and design did eventually catch up, but the 24 frames per second frame rate
is still very much with us today - almost culturally ingrained into what we come to
expect from the cinematic experience.
Television had to deal with the same flicker issues that plagued motion picture film - but
flashing the same frame on screen was not an option that was technologically feasible.
Engineers more concerned about bandwidth, something they were trying to conserve with
over-the-air television broadcast.
The solution was developed independently by German Telefunken engineer Fritz Schr'ter
in 1930 and in the US by RCA engineer Randall C. Ballard in 1932. To conserve bandwitdth
and avoid flickering - each frame would be Interlaced - that is broken down into two
alternating fields - an upper and a lower field. Each field would be created on the
screen one after the other in a comb like pattern. In order to eliminate intermodulation
- or a beating distortion caused by hum generated in the electrical current, the refresh rate
was set to that of the AC power- in the United States, 60 hertz - so that each field
is created in a 60th of a second resulting in a full 30 frames per second.
But the story gets more complicated with the introduction of color.
In 1948, the FCC put a moratorium on new television broadcast licenses as it tried to figure out
what to do with the newly available UHF spectrum. The idea was introduce a new color system
utilizing this higher frequency bandwidth and let the older VHF channels which the older
tv sets could access die off. While they were trying to figure out what to do, TV sales went through the
roof exploding from 1 million sets to just over 10 million in matter of a few years.
The idea of letting older VHF TV stations die off became impractical.
So now the race was on to create a color standard that was compatible with older black and white
set. The NTSC, the board that created the first US TV standards, reconvened with RCA
leading the way using a system first outlined by Georges Valensi in 1938. Breaking the image
down into luminance and chrominance, broadcasters could embed a color signal as a subcarrier
in the television signal. New color TVs could pick up and interpret this color subcarrier
which would just be ignored by the older black and white TV sets.
So far so good - but there was a small problem. The bandwidth used by the color subcarrier
could potentially interfere with the audio signal causing intermodular beating. The solution
would be to reduce the frame rate by a factor of .1% phasing the color and audio signals
so that they would never full match up.
In December 1953, the FCC adopted the RCA system for color broadcast and we go from
60 fields per second, down to 59.94 fields per second - for an effective
29.97 full frames per second.
In a mathematically ingenious way of creating a signal for both color and black and white
television sets, we have these odd ball frame rates that are still a big part of modern
broadcasting standards.
But that's only if you live in a country that uses the NTSC standard. In 1963 German television
manufacturer Telefunken released PAL to the European broadcasting union with regular broadcasts
in PAL starting in 1967. PAL was an format designed to solve the color problems that plagued
NTSC and would work with the 50 hertz AC power used in Europe and elsewhere in the world.
PAL along with a similar format SECAM run at 50i for an effective 25 frames per second.
So how do we get the cinematic 24 frames a second to fit 60i video stream for say watching
movies on video.
Let’s walk through this process -
First the 24 frames per second film is slowed down by 0.1% giving us 23.976 frames per second.
Now if we do the math we see that we need to make 4 frames of 23.976 fit into 5 frames
of 29.97
We do this spitting up the frames into fields using a 3:2 pulldown. The first frame is captured
onto three fields - the upper, lower and then upper field - that’s one and one half frames.
Then the next frame is captured on the following two fields, lower field and then upper. The
next frame fills up the lower, then following upper and lower with the last frame filling
the upper and lower. So we have 3 fields, 2 fields 3 fields 2 fields .
That’s your 3:2, 3:2 cadence.
Unfortunately this process isn’t perfect with resulting video stream
having Telecine Judders every 3 frames which
is especially noticeable on long slow camera movements.
Reverse Telecine or Reverse 3:2 pulldown are technologies that work backgrounds, constructing
a true 23.976 or 24p video stream from the 3:2 pulldown 60i footage.
Most modern digital cameras can avoid
the telecine process altogether and record 23.976 or straight 24 frame rates natively on to the hard drive
but there are some workflows that run video through HDMI cables which are rated for 60i, may still
utilize the 3:2 pull down.
For telecining film onto PAL or SECAM’s 25 frames per second, the process is much simpler
Using a 2:2 Pulldown, the 24 frame per second footage is sped up by 4% and each
frame is transfered onto two fields - an upper and lower field. The increased speed raises
the pitch of the audio by a noticeable 0.679 semitones or a little more than a quarter
step musically but can be adjusted down using a pitch shifter.
24 frames has been the standard for narrative film for nearly a century now. But enterprising
filmmakers have tried to push the temporal resolution or frame rate higher - trying to
reduce motion blur to create smoother and more realistic look.
One of the notable experiments in high frame rate is Showscan - a 70mm format developed
by Visual Effects Wizard Douglas Trumbull - who’s famous for developing many of the
visual effects for Stanley Kubrick’s 2001: A Space Odyssey. Running at 60 frames per
second, Showscan created a stronger biometric response in test audiences, but the process
just never found use in narrative film - being used mainly in motion simulator rides.
More recently Trumbull has worked on a digital Showscan - shooting at 120 frames per second
and adjusting the play back anywhere from 24 to 120 frames depending on the needs of the shot.
But audiences just haven’t been warm to high frame rate in narrative film - the most
recent experiment was Peter Jackson’s “The Hobbit” presented in 48 frames per second.
Variety reviewed the film and complained that the “human actors seemed overlit and amplified
in a way that many compared to modern sports broadcasts or daytime television.
One projectionist complained that "it looked like a made-for-TV movie"
But filmmakers at the technological bleeding edge, people like Peter Jackson or James Cameron, still push for higher frame rates.
Will the future of narrative filmmaking leave 24p behind? The technology is already here - the
new 4K standards are capable of up to 120 frames per second. While these high frame
rates may be great for recreating the immediacy of sports broadcasts or really good 3D or for video games
- to this filmmaker there’s just something cinematic about the cadence of 24 frames per second. For all
it’s drawbacks in clarity and motion blur It’s just how we grew up watching movies.
Maybe the next generation will grow up high frame rates and
see 60p the new cinematic look - or maybe not.
Frame rate is engine behind the cinematic lie - the magic trick that allows us to enter
a world not quite real but real enough.
A simple defining number shaped by psychology, economics and clever engineering all in
service to the act of telling stories. So use it. Use that engine and go make something
great. I’m John Hess and I’ll see you at FilmmakerIQ.com