CD / Shutter Speed
Summary
TLDRCe script explore l'évolution de l'obtention d'images à travers le temps, des premières caméras à la technologie moderne. Il explique le fonctionnement du temps d'exposition, la naissance des obturateurs mécaniques et électroniques, et les implications artistiques et techniques de la vitesse d'obturation. Il met en lumière les défis du rolling shutter et les espoirs pour une adoption future de l'obturation globale, tout en reflétant sur l'indifférence grandissante de la société face aux progrès technologiques.
Takeaways
- 📸 La vitesse de l'obturateur dans les caméras contrôle la durée d'une exposition, similaire à la façon dont la hauteur d'une montagne a un sommet.
- 🕰️ Les premières caméras étaient des boîtes avec une ouverture pour la lentille, nécessitant une exposition à la lumière pendant une durée considérable.
- 🤖 Avec l'amélioration de la photosensibilité, les temps d'exposition ont diminué, menant à l'apparition de mécanismes pour contrôler la durée d'exposition de manière précise.
- 🎞️ L'industrie du cinéma a introduit des concepts comme l'obturateur rotatif pour répondre aux exigences de capture d'images en mouvement continu.
- 📹 L'obturateur rotatif, avec son disque à secteurs, a permis aux caméras de filmer des images en mouvement en convertissant un mouvement continu en mouvement intermittent.
- 📽️ La notion d'angle de l'obturateur est apparue dans le cinéma, mesurant l'exposition relative à la durée de vie d'un cadre de film plutôt qu'en fractions de seconde.
- 📺 L'évolution vers les capteurs électroniques a permis d'abandonner les limitations mécaniques des obturateurs, offrant des vitesses d'obturateur extrêmement rapides ou lentes.
- 📱 Les capteurs CMOS actifs ont remplacé les CCD, offrant une efficacité accrue en transformant les électrons libres en voltages et en les envoyant à l'extérieur ligne par ligne.
- 🌀 L'obturateur enroulé, présent dans presque toutes les caméras numériques modernes, peut causer des distorsions sur les objets en mouvement rapide.
- 🔍 Les défauts d'obturateur enroulé sont souvent critiqués, mais ils sont difficiles à corriger et sont de plus en plus acceptés dans la culture populaire.
- 🌐 L'obturateur global, où chaque pixel a son propre condensateur pour stocker l'exposition, est plus cher mais devient de plus en plus abordable avec les améliorations dans les processus de fabrication.
Q & A
Quelle est la signification de la vitesse d'obturation dans la photographie?
-La vitesse d'obturation est le temps pendant lequel la lumière est autorisée à atteindre la pellicule ou le capteur de la caméra. Elle est essentielle pour contrôler la quantité de lumière reçue et peut affecter la netteté et les effets de mouvement dans l'image.
Quels sont les différents types d'obturateurs mentionnés dans le script?
-Les types d'obturateurs mentionnés sont les guillotines, les obturateurs à feuilles et les obturateurs Packard.
Pourquoi les obturateurs ont-ils évolué vers des mécanismes moins traditionnels avec l'arrivée du cinéma?
-Avec l'arrivée du cinéma, les exigences rigoureuses de capturer seize images par seconde dépassaient les capacités des conceptions d'obturateurs traditionnelles. Pour remédier à cela, on a converti le mouvement continu en mouvement intermittent en utilisant des obturateurs rotatifs.
Quel est le rôle de l'angle d'obturation dans les films?
-L'angle d'obturation mesure l'exposition relative à la durée de vie d'un cadre de film, au lieu de la vitesse d'obturation qui est mesurée en fractions de seconde pour la photographie fixe. Cela permet de contrôler l'effet de mouvement et la netteté des images dans les séquences de film.
Pourquoi la vitesse d'obturation de moitié du taux de cadres est-elle devenue la norme dans le cinéma?
-La moitié du taux de cadres devient la norme car elle permet une exposition suffisante tout en évitant les effets de mouvement excessifs, et elle fonctionne bien avec le taux de cadre de 24 images par seconde qui est considéré comme idéal pour les films.
Quel changement a apporté l'âge électronique dans la capture d'images?
-L'âge électronique a remplacé la pellicule par des capteurs électroniques tels que les tubes, puis les CCD, et enfin les capteurs CMOS. Cela a permis des vitesses d'obturation plus rapides ou plus lentes et une gestion plus efficace de l'exposition.
Quel est le problème avec les capteurs CCD mentionné dans le script?
-Les capteurs CCD ne sont pas suffisamment évolutifs pour capturer des images plus grandes et à un nombre de cadres plus élevé, ce qui est devenu nécessaire avec l'arrivée de la télévision haute définition.
Quelle est la différence entre les capteurs CMOS et les capteurs CCD?
-Les capteurs CMOS sont plus efficaces que les capteurs CCD car chaque pixel transforme ses propres électrons en tension et l'envoie à la partie du circuit où il est converti en un signal numérique, ce qui permet une exposition plus rapide et une meilleure gestion de la charge des pixels.
Qu'est-ce que le 'rolling shutter' et pourquoi est-il problématique?
-Le 'rolling shutter' est un phénomène où les lignes de pixels d'un capteur CMOS enregistrent des moments légèrement différents en raison de la lecture séquentielle des pixels. Cela peut causer des distorsions sur les objets en mouvement rapide, même si la vitesse d'obturation est rapide ou lente.
Pourquoi les obturateurs mécaniques échappent-ils généralement aux effets de 'rolling shutter'?
-Les obturateurs mécaniques échappent généralement aux effets de 'rolling shutter' car ils se déplacent à une vitesse si rapide que les distorsions ne sont pas perceptibles à l'œil nu. De plus, la position physique de l'obturator mécanique par rapport au plan focal peut également atténuer ces effets.
Quel est l'avenir de la technologie de l'obturation?
-L'avenir de la technologie de l'obturation inclut la généralisation de l'obturation globale ('global shutter') dans les capteurs CMOS, où chaque pixel a son propre condensateur pour stocker l'exposition avant lecture, offrant ainsi une image plus intégrale et moins sujette aux distorsions.
Outlines
📸 L'évolution de la vitesse d'obturation
Le paragraphe 1 explore l'histoire et l'importance de la vitesse d'obturation dans la photographie. Il commence par une introduction humoristique sur l'exposition à la lumière, suivie d'une explication technique sur le rôle de l'obturation dans la durée d'exposition. L'auteur décrit l'évolution des appareils photo, depuis les boîtes à la première lumière jusqu'aux mécanismes d'obturation modernes comme les obturations guillotine, feuilles et Packard. Il explique également comment l'industrie a adapté ces concepts aux besoins des films en mouvement, introduisant l'obturation rotative et l'angle d'obturation. Le texte se termine par une réflexion sur la transition de l'obturation mécanique à l'électronique avec l'arrivée de l'âge électronique et la conception du CCD.
📹 La naissance de l'obturation électronique et ses défis
Le paragraphe 2 se concentre sur l'obturation électronique et ses implications dans la qualité de l'image. Il décrit comment les caméras de la fin du XXe siècle, équipées de capteurs CCD, fonctionnaient avec une obturation électronique qui pouvait être ajustée en fonction des besoins. L'auteur mentionne les limites de la technologie CCD et l'introduction des capteurs CMOS, qui ont résolu les problèmes de scalabilité. Cependant, il souligne le phénomène de l'obturation enroulée (rolling shutter), qui provoque des distorsions sur les objets en mouvement rapide. Il compare les effets de l'obturation mécanique et électronique et discute des réactions variées de la communauté photographique à ce problème.
🤔 L'acceptation et l'impact de l'obturation enroulée
Dans le paragraphe 3, l'auteur aborde la perception publique de l'obturation enroulée et son impact sur l'industrie cinématographique et les artistes du VFX. Il mentionne que malgré les inconvénients et les réactions négatives, l'obturation enroulée est devenue inévitable avec l'utilisation des capteurs CMOS. L'auteur se demande si les consommateurs et les professionnels sont simplement en train d'accepter cette nouvelle normalité ou s'ils ne voient pas d'alternative. Il conclut en se demandant si l'adoption future de l'obturation globale (global shutter) rétablira l'intégrité des images ou si cela n'est pas suffisamment prioritaire pour les producteurs de caméras et les utilisateurs.
Mindmap
Keywords
💡Shutter speed
💡Exposition
💡Obturateur
💡Photographies sensibles
💡Cinéma
💡Obturateur rotatif
💡Angle de l'obturation
💡Taux de cadres
💡Capteur CCD
💡Capteur CMOS
💡Obturation en roulement
💡Obturation globale
Highlights
There’s no such thing as infinity in the physical world. A snapshot of the tiniest moment is a record of a period of time.
In cameras, the setting that controls the period of exposure is called shutter speed.
The earliest cameras were simple boxes with a lens, requiring long exposure times.
As photosensitivity increased, shorter exposure times reduced motion blur.
Mechanisms like guillotine, leaf, and Packard shutters replaced manual lens uncovering.
Motion pictures demanded high-speed photography beyond the capabilities of traditional shutters.
The rotary shutter was introduced for movie cameras, spinning at a constant rate.
The concept of shutter angle in cinema measures exposure relative to the life of a movie frame.
180-degrees was the standard shutter angle for cinematic art, influencing iconic movie images.
The advent of electronic age reimagined image capturing with the introduction of CCDs.
Electronic shutter speed could vary greatly, no longer limited by mechanical parts.
Active Pixel CMOS sensors allowed for more efficient image capturing by transforming electrons into voltage at the pixel level.
Rolling shutter effect causes image distortion in digital cameras due to the sensor readout sweep.
Rolling shutter is present in almost all modern footage and is considered unfixable.
Mechanical shutters can also cause rolling shutter effects, but they operate at much higher speeds, making distortion less perceptible.
Global shutter in CMOS sensors is possible but more expensive due to the need for individual capacitors for each pixel.
The future may see global shutter cameras becoming more affordable and widespread.
Despite technical advancements, many people may not care about the integrity of images, indicating a lack of incentive for further development.
Transcripts
What?
What?!
Too much exposure for you?
Well, excuse me!
[metal rattles]
[short synth jingle]
The shutter is...
Cameras need...
[exhales]
There’s no such thing as infinity in the physical world.
Just as the tallest mountain has a peak,
a snapshot of the tiniest moment
is actually a record of a period of time.
In cameras, we call the setting
that controls that period shutter speed.
Why?
As usual, because of olden times.
-[Ragtime music plays] -The earliest cameras
were just a box.
You uncovered a lens, let light accumulate inside
for a tedious amount of time,
then covered the lens back up.
This made selfies extremely challenging.
-[Camera snaps] -As the photosensitivity
of the medium inside the box increased,
exposure times decreased.
Things got less motion-blurry
but it became important to get the short timing
of the exposure just right. [mechanical clatter]
Jobs of hard working lens uncoverers
were lost to cheap, newfangled mechanisms
such as guillotine shutters,
leaf shutters and Packard shutters.
The best designs made sure to close in the opposite pattern
of how they opened,
so that every particle on the film plane
spent exactly the same amount of time in the light.
[Irish accent] But nothing could have prepared the industry
for the disruptive technology of motion pictures.
The rigorous demands of taking
upwards of sixteen photographic images per second
were beyond the capabilities of traditional shutter designs.
Luckily, there was a simple solution:
Convert spinny motion into intermittent motion.
The standard in pretty much all movie cameras
from the time of Lumiere brothers
to the century in which I began to be alive,
has been the rotary shutter:
a disc with a wedge cut out that spins at a constant rate
between the lens and the gate that lets light in.
Of course in practice, it's actually much cooler:
the wedges are doubled so the disc can spin
half as fast and it's angled 45 degrees
and has a mirror surface,
so that between exposures light is bounced
to a viewfinder, so you can see what the hell you're filming.
You might ask, "Captain, you're very smart,
but if we're now capturing continuous motion,
why do we need a shutter at all?"
Well, because it's still the past.
We're still burning discrete picture rectangles
onto a film strip
and the camera needs time in the dark for a scary claw
to advance it to the next picture-burning spot,
usually about half the time
of the whole frame capturing process.
So two distinct things, the frame rate
(how many pictures are taken per second)
and shutter speed (how much of one picture's time slot is spent
actually capturing the light)
are cleverly mechanically synced up.
This is where we get the cinematic concept
of shutter angle, measuring exposure relative to
the life of a movie frame,
as opposed to the primitive still photography idea
of shutter speed, measured in fractions of a second.
You just have to get used to conceptualizing
slices of a hypothetical pie as a percentage
of an arbitrary unit of time.
Like a novelty Japanese watch.
As movie cameras improved,
it was possible to just barely increase the shutter angle
to around 200 degrees.
Of course it could always be decreased,
so you could artistically symbolize the carnage
of an ancient Roman battle with sharp staccato frames.
But if you wanted to symbolize the delirious aftermath
of the ancient Roman battle with blurry, streaky long exposures,
you had to actually lower the frame rate.
But honestly, no one wanted to dig into the camera
to switch the little disc.
You had to tell the rental house in advance...
180-degrees was fine.
Aside from specialty high-speed cameras
that used crazy things like a rotary prism
to expose continuously sliding film,
exposure time of half the frame rate
became the unspoken standard in cinematic art.
And since the world agrees that 24 frames per second
is the best frame rate,
all the most iconic images in our collective movie memories,
from Star Wars to... Star Wars,
are built out of 1/48th of a second moments in time
held on screen for twice that long.
And now it's time to forget all that
because the concept of capturing images was completely reimagined
in the electronic age.
Film was out
and the capture medium became...
tubes, which... we don't have time for that.
But eventually, it became something like film again:
an array of photosensitive silicon pixels on a chip.
This was the CCD.
Now the shutter wasn't a shutter at all,
but a decision about how long to let the pixels
get bombarded by photons
globally, all at once,
before having them pass the loose electrons
they collected to each other, down the array,
like a bucket brigade,
to be transformed into voltage fluctuations
that could be read out as a video signal.
Unshackled from mechanical parts
electronic shutter speed could now be crazy fast
or crazy slow,
even the entire duration of a frame!
Well, almost.
This is a DSR-370,
the sickest early 2000s broadcast camera
a superhero could afford straight outta’ space college.
Look at its adorable little "1/2-inch type" CCD.
There are actually 3 of them in there,
but don't worry about that.
Like all North American cameras of the time,
it was hardwired to shoot in standard definition
at 29.97 frames
- or 59.94 interlaced fields - per second.
The idea of making the shutter
even faster than that refresh rate
seemed silly most of the time.
But if you really wanted to change it,
to avoid flicker when shooting a CRT monitor or something,
there was a physical switch to engage the electronic shutter
Then you could set it in either fractions of a second
or more precisely in hertz.
Note that the slowest you could set it was 60.4 Hz.
It's not true 360-degree shutter
because you needed that tiny bit of time
to read out all the pixels and reset them
for the next exposure.
The more pixels there are, the longer that process takes.
And that's the problem with CCDs.
They weren't scalable enough.
When the OtherSpawn of Omega Draconis gifted Earth
the corrupting technology of High Definition Television
in early 21st century,
humanity suddenly needed a cheaper way
to capture much larger images
at increasingly obnoxious frame
Enter Active Pixel CMOS sensors.
In these, each pixel transforms its own loose electrons
into a voltage and sends it off, a row at a time,
to the part of the chip
where it's converted to a digital signal.
This is much more efficient because...
why should these freed pixels above be idling
and taking bathroom breaks
when they could already be capturing the next image!
As one exposure rolls off the chip,
the next can start rolling in.
You know, like a sort of...
[gasps] Oh, no.
-Rolling shutter!!! -[boulder rumbles]
We've all seen them:
skewed, wobbly or completely scrambled images
that happen in digital cameras
because that CMOS sensor readout sweep means
consecutive rows of pixels capture slightly different
moments in time.
Whether the shutter speed is long or short,
the sweep is always the same
and fast-moving objects are bound to be distorted.
At first glance it seems like something you could
compensate for in post
by shifting the rows back into alignment...
until you realize that the shift varies
depending on the speed of the motion.
In some cases you could use
sophisticated tracking and remapping,
but there's still nothing you can do about that.
Or that.
Rolling shutter is unfixable
and present in almost all modern footage.
Some hate the artifact
because it used to not be a thing and now it is.
Others don't care because they grew up with it
and think this looks fine.
And a select few are gradually driven to madness
by a simple question:
"Captain, all mechanical shutters
are literally rolling shutters.
They all travel across the image,
sometimes in exactly the same pattern
as an electronic shutter.
How come they don't cause the rolling shutter effect?"
The answer is...
they kinda do.
Mechanical shutter curtains and CMOS sensor readouts
move at a constant rate
regardless of the shutter speed setting
and faster speeds are achieved by
more closely staggering the mechanisms
that start and end exposure,
narrowing it to a slit.
It’s just that in most stills cameras
available to most people today
the mechanical shutter fires...
way faster.
So fast, you usually just
can’t perceive the distortion with the naked eye.
Another factor in why even
a narrow angle rotary disc shutter
seems to avoid rolling shutter artifacts
is a little thing called the lens.
It’s there to focus light perfectly on the focal plane.
But the shutter is way out in front.
Here, the light is still unfocused,
and any disruptions to it appear diffused.
It’s the same reason changing the aperture inside the lens
doesn’t show up as an actual iris in the image,
but as an overall change in brightness.
Of course, it’s a matter of proportion.
In very old, large format cameras,
where a giant shutter was near a giant glass plate
and moved relatively slowly,
it actually did cause a funny kind of rolling shutter.
Some even say it’s where we got the classic concept
of cartoon speed distortion.
But even for modern stills photographers,
with their lightning-fast focal plane shutter DSLRs,
the physical position of the tiny curtain
makes a difference.
It's funny, some cameras do this hybrid thing
called "Electronic First Curtain Shutter"
where the exposure is started by the sensor,
then the mechanical shutter closes to end it,
and the optical discrepancy between the two
has a weird effect on “bokeh,”
the blobby bright spots in out-of-focus areas
that photographers are obsessed with.
And it's hilarious to see them cry about it,
"Oh, my bokeh! My precious bokeh!
Look what's happened to it, oh no!"
[chuckles]
Despite what experts on Reddit say,
it seems like in general, people are bothered
by rolling shutter defects.
Consumers comment on it whenever they see it.
Folksy educators make videos about it.
VFX artists hate how it makes tracking and compositing
less accurate.
And yet, we're forced to just accept it.
I’m not saying it’s a conspiracy...
I’m just saying...
The CMOS sensor was initially commercialized
by a guy from NASA JPL
who started a company
that got bought by another company,
renamed, then sold to a semiconductor giant
which itself rebranded,
and now supplies sensors to the most popular
line of professional cinema cameras in the world,
which all have rolling shutter!
To be fair, they did try a mechanical shutter version,
but it didn’t catch on.
And to be even more fair,
not all rolling shutter is created equal.
The actual readout speed of different sensors varies a lot.
Nerds who test new cameras have ways of measuring it
in milliseconds.
And while in some cameras it spans
almost the duration of a frame,
a few of the best ones have rolling shutter so minimal,
it rivals mechanical shutter.
But it’s perfectly possible to expose the whole frame at once,
to have “global shutter” in a CMOS sensor.
Every pixel just needs its own capacitor
to store the exposure until it can be read out.
That makes it more expensive.
But as manufacturing processes improve,
it is becoming... almost affordable.
Before you know it, global shutter cameras
will be in phones and we might finally
get back to the integrity of images we had
in the early 1900s.
Imagine:
Global adoption of global shutter.
Although...
Most people don’t care,
so there’s not a ton of incentive for it.
[outro music plays]
There’s not a ton of incentives for anything anymore.
Ever feel that?
It’s like... we finished a video game
and now it’s the end credits.
But we keep mashing the controller
like it does something.
It’s the credits, man.
[music transforms into a melody from ‘Sonic 2’]
It’s the part in the Sonic 2 credits medley
-where the drums go -[taps in time with drum solo]
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