|Human Eye Frames Per Second|
02/21/2001 10:30:00 AM MST Albuquerque, Nm
By Dustin D. Brand; Owner AMO
How many frames per second can our wonderful eyes see?
This article is dedicated to a friend of mine, Mike.|
There is a common misconception in human thinking that our eyes can
only interpret 30 Frames Per Second. This misconception dates back to
the first human films where in fact a horse was filmed proving actually
that at certain points they were resting on a single leg during running.
These early films evolved to run at 24 Frames Per Second, which has
been the standard for close to a century.
A Movie theater film running at 24 FPS (Frames Per Second) has an
explanation. A Movie theater uses a projector and is projected on a
large screen, thus each frame is shown on the screen all at once.
Because Human Eyes are capable of implementing motion blur, and since the
frames of a movie are being drawn all at once, motion blur is
implemented in such few frames, which results in a lifelike perceptual
picture. I'll explain the Human Eye and how it works in detail later on
in this multi-page article.
Now since the first CRT TV was released, televisions have been running
at 30 Frames Per Second. TV's in homes today use the standard 60Hz
(Hertz) refresh rate. This equates to 60/2 which equals 30 Frames Per
Second. A TV works by drawing each horizontal line of resolution piece
by piece using an electron gun to react with the phosphors on the TV
screen. Secondly, because the frame rate is 1/2 the refresh rate,
transitions between frames go a lot smoother. Without going into detail
and making this a 30 page article discussing advanced physics, I think
you'll understand those points.
Moving on now with the frame rate. Motion blur again is a very
important part to making videos look seamless. With motion blur, those
two refreshes per frame give the impression of two frames to our eyes.
This makes a really well encoded DVD look absolutely incredible. Another
factor to consider is that neither movies or videos dip in frame rate
when it comes to complex scenes. With no frame rate drops, the action is
Computer Games and their industry driving use of Frames Per Second
It's easy to understand the TV and Movies and the technology behind
them. Computers are much more complex. The most complex being the actual
physiology /neuro-ethology of the visual system. Computer Monitors of a
smaller size are much more expensive in cost related to a TV CRT
(Cathode Ray Tube). This is because the phosphors and the dot pitch of
Computer Monitors are much smaller and much more close together making
much greater detail and much higher resolutions possible. Your Computer
Monitor also refreshes much more rapidly, and if you look at your
monitor through your peripheral vision you can actually watch these
lines being drawn on your screen. You can also observe this technology
difference by watching TV where a monitor is in the background on the
A frame or scene on a computer is first setup by your video card in a
frame buffer. The frame/image is then sent to the RAMDAC (Random Access
Memory Digital-Analog-Convertor) for final display on your display
device. Liquid Crystal Displays, and FPD Plasma displays use a higher
quality strictly digital representation, so the transfer of information,
in this case a scene is much quicker. After the scene has been sent to
the monitor it is perfectly rendered and displayed. One thing is missing
however, the faster you do this, and the more frames you plan on
sending to the screen per second, the better your hardware needs to be.
Computer Programmers and Computer Game Developers which have been
working strictly with Computers can't reproduce motion blur in these
scenes. Even though 30 Frames are displaying per second the scenes don't
look as smooth as on a TV. Well that is until we get to more than 30
NVIDIA a computer video card maker who recently purchased 3dFx another
computer video card maker just finished a GPU (Graphics Processing
Unit) for the XBOX from Microsoft. Increasing amounts of rendering
capabilities and memory as well as more transistors and instructions per
second equate to more frames per second in a Computer Video Game or on
Computer Displays in general. There is no motion blur, so the transition
from frame to frame is not as smooth as in movies, that is at 30 FPS.
In example, NVIDIA/3dfx put out a demo that runs half the screen at 30
fps, and the other half at 60 fps. The results? - there is a definite
difference between the two scenes; 60 fps looking much better and
smoother than the 30 fps.
Even if you could put motion blur into games, it would be a waste. The
Human Eye perceives information continuously, we do not perceive the
world through frames. You could say we perceive the external visual
world through streams, and only lose it when our eyes blink. In games,
an implemented motion blur would cause the game to behave erratically;
the programming wouldn't be as precise. An example would be playing a
game like Unreal Tournament, if there was motion blur used, there would
be problems calculating the exact position of an object (another
player), so it would be really tough to hit something with your weapon.
With motion blur in a game, the object in question would not really
exist in any of the places where the "blur" is positioned, that is the
object wouldn't exist at exactly coordiante XYZ. With exact frames,
those without blur, each pixel, each object is exactly where it should
be in the set space and time.
The overwhelming solution to a more realistic game play, or computer
video has been to push the human eye past the misconception of only
being able to perceive 30 FPS. Pushing the Human Eye past 30 FPS to 60
FPS and even 120 FPS is possible, ask the video card manufacturers, an
eye doctor, or a Physiologist. We as humans CAN and DO see more than 60
frames a second.
With Computer Video Cards and computer programming, the actual frame
rate can vary. Microsoft came up with a great way to handle this by
being able to lock the frame rate when they were building one of their
games (Flight Simulator).
The Human Eye and it's real capabilities - tahDA!
This is where this article gets even longer, but read on, please. I
will explain to you how the Human Eye can perceive much past the mis
conception of 30 FPS and well past 60 FPS, even surpassing 200 FPS.
We humans see light when its focused onto the retina of the eye by the
lens. Light rays are perceived by our eyes as light enters - well, at
the speed of light. I must stress the fact again that we live in an
infinite world where information is continuously streamed to us. Our
retinas interpret light in several ways with two types of cells; the
rods and the cones. Our rods and cells are responsible for all aspects
of receiving the focused light rays from our retinas. In fact, rods and
cones are the cells on the surface of the retina, and a lack thereof is a
leading cause of blindness.
Calculations such as intensity, color, and position (relative to the
cell on the retina) are all forms of information transmitted by our
retinas to our optic nerves. The optic nerve in turn sends this data
through its pipeline (at the nerve impulse speed), on to the Visual
Cortex portion of our Brains where it is interpreted.
Rods are the simpler of the two cell types, as it really only
interprets "dim light". Since Rods are light intensity specific cells,
they respond very fast, and to this day rival the quickest response time
of the fastest computer. Rods control the amount of neurotransmitter
released which is basically the amount of light that is stimulating the
rod at that precise moment. Scientific study has proven upon microscopic
examination of the retina that there is a much greater concentration of
rods along the outer edges. One simple experiment taught to students
studying the eye is to go out at night and look at the stars (preferably
the Orion constellation) out of your peripheral vision (side view).
Pick out a faint star from your periphery and then look at it directly.
The star should disappear, and when you again turn and look at it from
the periphery, it will pop back into view.
Cones are the second retina specialized cell type, and these
are much more complex. Cones on our retinas are the RGB inputs that
computer monitors and graphics use. The three basic parts to them absorb
different wavelengths of light and release differing amounts of
different neurotransmitters depending on the wavelength and intensity of
that light. Think of our cones as RGB computer equivalants, and as such
each cone has three receptors that receive red, green, or blue in the
wavelength spectrum. Depending on the intensity of each wavelength, each
receptor will release varying levels of neurotransmittor on through the
optic nerve, and in the case of some colors, no neurotransmitter. Due
to cones inherent 3 receptor nature vs 1, their response time is less
than a rods due to the cones complex nature.
Our Optic nerves are the visual information highway by which our lens,
then retina with the specialized cells transmit the visual data on to
our Brains Visual Cortex for interpretation. This all begins with a
nerve impulse in the optic nerve triggered by rhodospin in the retina,
which takes all of a picosecond to occur. A picosecond is one trillionth
of a second, so in reality, theoretically, we can calculate our eyes
"response time" and then on to theoretical frames per second (but I
won't even go there now). Keep reading.
The optic nerves average in length from 2 to 3 centimeters, so its a
short trip to reach our Visual Cortex. Ok, so like the data on the
internet, the data traveling in our optic nerves eventually reaches its
destination, in this case, the Visual Cortex - the
Unfortunately, neuroscience only goes so far in understanding exactly
how our visual cortex, in such a small place, can produce such amazing
images unlike anything a computer can currently create. We only know so
much, but scientists have theorised the visual cortex being a sort of
filter, and blendor, to stream the information into our conciousness.
We're bound to learn, in many more years time, just how much we've
underestimated our own abilities as humans once again. Ontogoney
recapitulates phylogeny (history repeats itself).
There are many examples to differentiate how the Human Visual System
operates differently than say, an Eagles. One of these examples includes
a snowflake, but let me create a new one.
You're in an airplane flying looking down at all the tiny cars and
buildings. You are in a fast moving object, but distance and speed place
you above the objects below. Now, lets pretend that a plane going 100
times as fast quickly flys below you, it was a blur wasn't it?
Regardless of any objects speed, it maintains a fixed position in
space time. If the plane that just flew by was only going say, 1 times
faster than you, you probably would have been able to see it. Since your
incredible auto focus eye had been concentrated on the ground before it
flew below, your visual cortex made the decision that it was there, but
well, moving really fast, and not as important. A really fast camera
with a really fast shutter speed would have been able to capture the
plane in full detail. Not to limit our eyes ability, since we did see
the plane, but we didn't issolate the frame, we streamed it relative to
the last object we were looking at, the ground, moving slowing below.
Our eyes, technically, are the most advanced auto focus system around -
they even make the cameras look weak. Using the same scenario with an
Eagle in the passenger seat, the Eagle, due to its eyes only using Rods,
and its distance to its visual cortex being 1/16 of ours wouldn't have
seen as much blur in the plane. However, from what we understand of the
Visual Cortex, and Rods and Cones, even Eagles can see dizzy blurry
objects at times.
What is often called motion blur, is really how our unique vision
handles motion, in a stream, not in a frame by frame. If our eyes only
saw frames (IE: 30 images a second), like a single lens reflex camera,
we'd see images pop in and out of existance and that would really be
annoying and not as advantagous to us in our three dimensional space and
So how can you test how many Frames Per Second we as Humans can see?
My favorite test to mention to people is simply to look around their
environment, then back at their TV, or monitor. How much more detail do
you see vs your monitors? You see depth, shading, a wider array of
colors, and its all streamed to you. Sure, we're smart enough to use a
24 frame movie and piece it together, and sure we can make real of video
footage filmed in NTSC or PAL, but can you imagine the devices in the
You can also do the more technical and less imaginative tests above,
including the star gazing, and this tv/monitor test. A TV running at
only 30 FPS is picking up a Computer monitor in the background in its
view, and with the 30 FPS TV Output you see the screen refreshes on the
computer monitor running at 60 FPS. This actually leads to eyestrain
with computer monitors but has everything to do with lower refresh
rates, and not higher.
Don't underestimate your own eyes Buddy...
We as humans have a very advanced visual system, please understand
that a computer with all it's processor strength still doesn't match our
own brain, or the complexity of a single Deoxyribonucleic Acid strand.
While some animals out there have sharper vision than us humans, there
is usually something given up with it - for eagles there is color, and
for owls it is the inability to move the eye in its socket. With our
outstanding human visual, we can see in billions of colors (although it
has been tested that women see as much as 30% more colors than men do.
Our eyes can indeed perceive well over 200 frames per second from a
simple little display device (mainly so low because of current hardware,
not our own limits). Our eyes are also highly movable, able to focus
in as close as an inch, or as far as infinity, and have the ability to
change focus faster than the most complex and expensive high speed auto
focus cameras. Our Human Visual system receives data constantly and is
able to decode it nearly instantaneously. With our field of view being
170 degrees, and our fine focus being nearly 30 degrees, our eyes are
still more advanced than even the most advanced visual technology in
So what is the answer to how many frames per second should we be
looking for? If current science is a clue, its somewhere in sync with
full saturation of our Visual Cortex, just like in real life. That
number my friend - is - well - way up there with what we know about our
eyes and brains.
It used to be, well, anything over 30 FPS is too much. (Is that why
you're here, by chance?) :) Then, for a while it was, anything over 60
is sufficient. After even more new video cards, it became 72 FPS. Now,
new monitors, new display types like organic LEDS, and FPDs offer to
raise the bar even higher. Current LCD monitors response rates are
nearing the microsecond barrier, much better than millisecond, and
equating to even more FPS.
If this old United States Air Force study is any clue to you, we've
only scratched the surface in not only knowing our FPS limits, and
coming up with hardware that can match, or even approach them.
The USAF, in testing their pilots for visual response time, used a
simple test to see if the pilots could distinguish small changes in
light. In their experiment a picture of an aircraft was flashed on a
screen in a dark room at 1/220th of a second. Pilots were consistently
able to "see" the afterimage as well as identify the aircraft. This
simple and specific situation not only proves the ability to percieve 1
image within 1/220 of a second, but the ability to interpret higher FPS.
|so, just how many frames per second can our human eye see past 100?||
In my previous article (Human Eye Frames Per Second),
I mentioned I'd have another to settle once and for all just how many
frames per second our human eye is capable of seeing, so here we are.|
If you havn't read my first article, do so now, it's quite lengthy,
but worth your time in learning, plus it's enough foundation to start
Motion Blur is so important in movies and TV programming
In my first article, I mentioned how important motion blur is
pertaining to frames per second. On Computers, this is essentially
non-existant. Motion blur in movies, which run at 24 frames per second
are designed for the big screen projector, which blasts movies to the
screen, each frame in it's entirety in the widescreen format one frame
at a time. Because each frame is filmed in a certain way, motion blur
is used, meaning the frames are not perfectly clear, they contain blur.
The blur used in todays movies will eventually be replaced by
completely digital movies (on very expensive screens, I should know, I
worked with the technology at age 16), and with the advent of computer
animation in movies, the process of replacing the blur on the film in
movies is becoming more and more inevitable.
Computer's don't work this way (with blur that is), and essentially
neither does anything digital. With digital, you either have an exact
perfectly clear image, or an exact perfectly blur image like in movies.
From the transition from movies to the TV, or DVD digital, an extra 4
frames are added each second in a method called frame mixing, just to
match correctly the device it's being displayed on, your TV.
NTSC(American) and PAL(european) use different kinds of TV formats, each
with different refresh rates and resolutions. 640x480 for NTSC and
800x600 lines for PAL. With HDTV, everything is digital, and
essentially 60 frames now, but most of these broadcasts use frame
mixing, and until 2006 you won't need to trash your regular TV, though
it may be a good idea now.
As many of you know, pause a DVD film movie during movement, or if you
can a TV with your VCR and you'll see the blur (unless the image is
static to begin with). Pause an animation DVD, or a cartoon on TV and
you won't see the blur. Why is this so? Filmed movies, and Filmed TV
shows work by bluring their subjects, actors, actresses, whatever.
Filmed movies and TV are not taking a PERFECT snapshot image of the
subject, each image is a blur, and a blur to the next giving the
impression that everything is moving seemlessly (if nothing is moving in
the scene, you can see a static image). In an animation or a cartoon,
each frame or image of the 24/30 frames per second is perfect, there is
no blur in the image - EVER.
I touched very briefly on Auto Focus Cameras, and even the best most
expensive cameras not even coming close to matching the capabilities of
our human eye in focusing. The professional cameras you see reporters
with are capable of taking pictures of EXTREMELY fast moving objects in
perfectly still quality at and above 1/4000 of a second. What does a
camera being able to take 4000 pictures in a second prove?
Our infinitely seamless world.
Professional cameras can take perfectly still pictures without any
blur, and like in the case of video cameras, pictures with blur. So
where is the limit? How quick can we take a picture, and how slow can
we take a picture? SLOW time progressed pictures have been taken,
you've probably seem them at night where all the cars tail lights are in
a streak. You've probably also seen the "Photo finish" camera's take
the winning tell tale sign of a close horse race. What all of this
really means is that unless we slow time, or speed it up, there isn't
any blur in our world. That is of course unless you're drunk, the room
is spinning, or you're on some LSD trip. Ok besides that.
Images in our world are infinitely streamed to us as I've said before.
Living in this 3rd dimension as we do, our eyes able us to see
depth/periphery, we can focus in very close, and as far as infinity. So
is there really a limit to how many frames per second we can really see
with our eyes?
Our limit, is there one?
Until someone proves me, all the scientists, optometrists, and the
like wrong, there is no limit to how many frames per second our human
eye can see. Theoretical limit yes, proven limit, NO.
Think for just a second how dumb it would be to push the limit on
video displays, devices and the like if our eyes couldn't tell the
difference between an HDTV and a plain old TV or a Computer monitor and a
Plasma display. Ok, in that second how many times do you think your
eye "framed" this screen? The number of times the screen refreshed?
Nope, the number of times your eye streamed this page to you, it's a
number that is potentially infinite, or at least until we understand the
complexity of our own mind. Just know that this number is much, much
higher than what your monitor is capable of currently displaying to you,
that is matching your own interpretation.
Our Brain is smart enough however to "exact" 24 frames into motion,
isn't it ignorant to say we can't distinguish 400, or even 4000 into
motion? Heh the skies the limit, oh wait, then space...oh wait. Give
us more, we notice the difference from 30-60, the difference from
60-120. It is possible the closer we get to our limit, be there one,
the harder it is to get there, and there is a theory about this.
Someone is across the room. Take one full step towards them. Now 1
half step towards them, then 1 half step of a half step, on and on until
your 1 half of each movement you take. Will you ever get there? That
my friend is open to debate, but in the mean time, will you take one
step towards me?
The Human Eye perceiving 220 Frames Per second has been proven, game
developers, video card manufacturers, and monitor manufacturers all
admit they've only scratched the surface of Frames Per Second. With a
high quality non-interlaced display (like plasma or a large LCD FPD) and
a nice video card capable of HDTV resolution, you can today see well
above 120 FPS with a matching refresh rate. With some refresh rates as
high as 400Hz on some non-interlaced displays, that display is capable
of 400 FPS alone. Without the refresh rate in the way, and the right
hardware capable of such fast rendering (frame buffer), it is possible
to display as cameras are possible of recording 44,000 Frames Per
Second. Imagine just for a moment if your display device were to be
strictly governed by the input it was receiving. This is the case with
computer video cards and displays in a way with adjustable resolutions,
color depth, and refresh rates.
Test your limit, you tell me...
Look at your TV, or ANY image device, then look at the device not
looking at the image it is displaying, for example the TV itself, or the
Monitor itself. Tell me the image on the screen is more clear, more
presise than the image of the TV or the monitor itself. You can't,
that's why the more frames per second, the better, and the closer to
reality it really appears to us. With 3d holograms right around the
corner, the FPS subject or maybe 3DFPS will become even more important.
The real limit is in the viewing device, not our eyes.
The real limits here are evidenced by the viewing device, not our
eyes, we can consistently pick up the flicker to prove that point. In
Movies the screen is larger than life, and each screen is drawn
instantaneously by the projector, but that doesn't mean you can't see
the dust or scratches on each frame. With NTSC and PAL/SECAM TV's, each
line is drawn, piece by piece (odd, then even lines) for each frame and
refreshes at the Hertz. The frames displaying because of this is
exactly the hertz divided by 2 or (odd line 1 hertz then even line 1
hertz). Do a search for high-speed video cameras and you'll find some
capable of 44,000+ frames per second, that should give you a clue.
CRT's be it PC monitors or TV's have to refresh with rates, known as
the Hertz. Eye fatigue can happen because of the probe or line effect
that happens after prolonged viewing, yes your eye sees this. Switch to
your Periphery vision like I gave an example for in my first article
and you can see the refresh rate. 60Hz and 50Hz also happens to be the
frequency of the main power of the countries that use these Hertz in the
TV refresh rates. Because of the way the technology works, by drawing
each line individually, your Frame Rate/Refresh rate (not your FPS) is
tied to your FPS. If something is running at 60 FPS however your
monitor is at 60 Hertz and is interlaced, which TV's are locked at,
you're seeing 30 Frames Per Second. However, if you have a nice
computer monitor (NON-INTERLACED), and it's set to 120Hertz (72+ is
considered "flicker free"), and your video is running at 120 Frames Per
Second, you're seeing exactly 120 Frames Per Second. You may have heard
that LCD's or Liquid Crystal Displays are "flicker free". LCD displays
are capable of showing their FPS in a refresh rate, much like
non-interlaced monitors are, example 75 Hertz is capable of 75 Frames
Per Second. Technically, because an LCD pixel/transistors is either
true or false, this technology is not only better, but faster than an
electron gun on a phosphor like in a CRT, thus virtually eliminating
Technically speaking: NTSC has 525 scan lines repeated 29.97 times per
second = 33.37 msec/frame or roughly 30 Frames Per Second at 60Hz
BECAUSE it's INTERLACED.
Technically speaking: PAL has 625 scan lines repeated 25 times per
second = 40 msec/frame or exactly 25 Frames Per Second at 50Hz BECAUSE
So how does 60Hertz relate in HDTV's? Well, with progressive scanning
(the XBOX supports this with it's NVidia GPU), each frame is drawn on
each pass meaning 60Hz supports 60 Frames Per Second, but as you've
learned although the hertz and FPS are related, the hertz of the display
does not necessarily mean that it is the frames per second. Frames per
second are determined by the display device and how it draws each
frame. Normal TV's don't support progressive Scan and thus redraws half
the screen on each pass, first draws the odd lines (interlaced), then
the even = 30 Frames Per Second maximum.
As you've seen, it's not our human eyes, it's the display. More on
this is the fact between interlaced and non-interlaced monitors. All
computer CRT monitors are now made non-interlaced (and have been for
quite some time), meaning the entire frame is refreshed at the refresh
rate or Hertz. The frame is scanned all at once, thus the refresh rate
can equal the Frames Per Second, but the Frames Per Second isn't going
to go past the Refresh Rate because it's not possible on the display.
Just because a video card is pushing 200 Frames Per Second, your display
may be at 100Hz meaning it's only refreshing 100 times per second.
Thus, the big misconception that our eyes can only see 30 frames or 60
frames per second is purely due to the fact that the mainstream
displays can only show this, not that our eyes can't see more. For the
time being, the frames per second capable of any display device isn't
even close to the phrase "more than meets the eye".
Definitions of relevance:
CRT Cathode Ray Tube - The tube or flat tube making up a TV
which utilizes an electron gun to manipulate phosphors at the front of
the tube for varying color.
NTSC originally developed in the United States by a committee called the National Television Standards Committee (525 lines).
PAL standing for Phase Alternate Lines (625 lines)
FPS - Frames Per Second - A Frame consists of an image completely drawn to a viewing device, example: Monitor