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Very interesting stuff. I'm curious if this means anything in terms of good vs perfect technology or what tech wins out in practice. This process seems just pl

Very interesting stuff. I'm curious if this means anything in terms of good vs perfect technology or what tech wins out in practice. This process seems just plain better than green-screen, so why did it lose out? Is is just that green screen is good enough? Was it too hard to do this sodium vapor process with random cameras back in the day? Are sodium vapor lights bad enough in some way that practically it lost out?

buck746 3y ago
It lost because there were only 3 prisms made. It also required a lot more lot as running thru an optical splitter means at least half of your light was lost, it's not a big issue today. Modern cameras are insanely more sensitive than film was at the time. Alfred Hitchcock used this on "The Birds". In the YouTube video they got a great result even with a smaller studio than would have been used on Mary Poppins. The trick needed the screen as far back as you could get it to minimize the chance of spill, that used to be normal on blue screen before the software improved.
- kadoban 3y ago
  > It lost because there were only 3 prisms made. But it seems so much better that that shouldn't have been a blocker. Like optics isn't magic, and knowing that someone did it before should be enough incentive? Not like movies are a small or poor industry.
  - cooper_ganglia 3y ago
    I wonder if it’s just more cost effective to use a well-established tool like green screen, and then contract out all the rotoscoping clean-up to other countries for less than minimum wage?
    - kadoban 3y ago
      Yeah maybe it's something like the person choosing the camera process doesn't directly have to deal with 12 hours of roto per day, so practically it's just not something they think about.
    - 486sx33 3y ago
      I think part of the deal is that, no amount of manual intervention will allow translucent objects (like the veil) as nicely as sodium vapor lighting , also motion blur
    - bigiain 3y ago
      "and then contract out all the " blame for it's shortcomings... "Sorry boss, that's industry best practice. Nothing we can do to make sit better."
  - astrodust 3y ago
    Incentive is one thing, budget is another. Keep in mind stuff gets lost all the time, even really important things like nuclear weapon components like https://en.wikipedia.org/wiki/Fogbank https://en.wikipedia.org/wiki/Fogbank
    - kadoban 3y ago
      Fair. But looking at that story (very interesting btw, thanks), they did recreate it. So incentive does mean a lot when $$ is also available, which I'd suspect it is in movies.
      - astrodust 3y ago
        I think the US nuclear program has a much bigger budget than Disney, and if they need something, they just get it. The movie industry had cheaper options, so they went with those.
        kadoban 3y ago
        I think you're underselling Disney's budget and reach. Yes, it's probably technically smaller than the US nuclear program, but even just Disney is worth $200 billion USD, ignoring all other studios and etc. Movies are big money.
  - wbl 3y ago
    Today we could use a dichoric coating but back then I think fabrication was much harder.
    - namibj 3y ago
      Well, the technology for them is far from recent, the process control and chamber geometry design to allow the needed precision and uniform-ness at the throughout needed to not be extremely expensive, however, required cheap microprocessors for a good decade to develop the required skills in control engineers to then actually go and make a machine like this. And the computers suitable we're still triple-digits in the 80's, so this only really started to deploy to factories ~25 years ago.
tadfisher 3y ago
Practically, you could see it in the video: they had to have near-perfect lighting to avoid any 589nm spill on the subject, or they would end up with semi-transparent regions on the matte where they didn't want any. Chroma-keying is more tolerant to spill, only needs one camera with one film reel, and you don't need a special screen with special lamps and special cameras.
- kadoban 3y ago
  > Chroma-keying is more tolerant to spill, only needs one camera with one film reel, and you don't need a special screen with special lamps and special cameras. Fair on the number of films/cameras. Is normal keying actually more tolerant to spill or is it just worse so you're going to have to manually deal with spill anyway so you just live with it? I don't even have good eyes and even I sometimes see spill in actual movies, or especially in TV. Edit: I guess that's _different_ spill though. I mean you do famously need a special screen :) And you don't need _special_ lamps per se but you do have to light your greenscreen fairly well to have real success.
cladopa 3y ago
>so why did it lose out? Is is just that green screen is good enough? It looks that the problem was manufacturing the prism, as simple as that. Today you can use unusual wavelength LEDs without phosphorous to do the same thing probably way cheaper.
- namibj 3y ago
  No, LEDs are far wider than low pressure sodium, which is two about 0.1nm wide (thermal broadening, IIUC basically Doppler effect between the emitting particle and the surrounding world/containment vessel) lines 0.56nm apart. See https://lambdasys.com/uploads/LLE-2.pdf https://lambdasys.com/uploads/LLE-2.pdf for a measured spectrum that's not as coarse as the one on en-wiki where both lines are blurred together. LEDs are 10~50nm, untuned laser diodes 1~10nm. It is my understanding that it's easy to make a filter for the camera that very selectively targets this line pair, though it may entail mild optical complications as a sub-nm pass/reject bandwidth detunes from sideways angles, so lenses may need to collimate the light first before feeding the filter, and de-collimate again after.
giantrobot 3y ago
As I understand it (not an expert but interested amateur) the sodium vapor method of a matte was a cheaper version of mattes movies used to use. To make a matte they'd film the actors over a black background with normal lighting for the actors. The black was velvet or batting that didn't reflect any of the foreground lights. They'd take that film and do a bunch of exposures that would eventually create a white silhouette that would preserve a decent amount of fine detail from the foreground. That matte would be used in an optical printer to double expose the film, once with the background plate then with the foreground plate. While effective this was really expensive and time consuming. The sodium vapor light technique allowed for a very easily generated matte with a high level of detail. It however required specific lights and a lot of control over spillage from the background lighting into the foreground. It was also difficult to film from multiple angles since the lighting would need to be adjusted when the camera was repositioned. With those limitations in mind it was much cheaper and less time consuming than making mattes with multiple exposures and such. Cheaper effect shots meant more effect shots for the same size budget. With a movie like Mary Poppins that wanted a ton of effects shots the traditional method of making mattes would have been cost prohibitive. Chroma keys came about because they were much cheaper than the multiple exposure method of doing mattes. The back and foreground could be lit together and the matte could be knocked out relatively easily by applying a chroma filter when making the work print. The mattes weren't as exact and had their own limitations but they were relatively inexpensive. For video (as opposed to film) chroma keys could be done electrically by filtering and mixing the video signal. Digital mattes have a lot of flexibility. As shown in the video digital editing software has lots of toggles to help make chroma mattes look good. It's a very manual process and hard to really get right. Also as shown in the video there's some things that just do not work really well with chroma keying like translucent materials and anything with high index of refraction. They're typically a good balance of cheap and effective with a lot of known techniques to make look good.
YoshiRulz 3y ago
This was addressed at the end of the video: The main points are that it can't be used outside, or when the shot includes the subjects' legs/feet (as the ground would need to be an amber-screen as well), and on top of that, it requires a certain level of setup which some shoots can't afford.
- laserbeam 3y ago
  I don't think I've ever seen green screen used outside either. I think you can kinda use it outside... But any random cloud passing by would destroy your morale in the editing room if you're keying against green screen. Also lighting conditions change during a day and you'd have to be aware of that when keying. Not fun.
  - niccl 3y ago
    Lord of The Rings used some huge external green/blue screens. One I know of was the scene in Return of the King where there's a dead oliphaunt and, IIRC, Eowyn fighting the Witch King. But there were lots of others.
rendall 3y ago
> so why did it lose out? The video suggests that it was difficult to replicate and extremely expensive.
mrguyorama 3y ago
In modern production, an army of underpaid, un-unionized visual effects contractors who pitch lowest bidder contracts to manually retouch basically every single pixel in the film six times over is a fine price to pay for studios, while this method would require carefully planning everything ahead of time, proper scripting, and not being able to change scenes after shooting nearly as easily, and also probably involves hiring unionized labor by talented tradespeople who can say "naw that's a bad deal and a dumb idea".
rperez333 3y ago
Because it creates more problems than it solves. A movie set is expensive and moves fast – and keying is not as big of a problem as they made it out to be. For example, Niko doesn't seem to be aware of the IBK keyer (based on his comments in the VFX subreddit), which is the keyer used on almost every shot in high-budget movies. While it's not a single-click solution, it's the main tool to tackle thousands of shots with defocused edges, motion blur, and semitransparency every year. Niko deserves credit for bringing Paul's incredible experiment, but Corridor is at its core a group of entertainers, and most of them have never had experience in a large production/VFX environment. Take everything they present with a grain of salt.
WorldMaker 3y ago
Some of why it "lost out" just seems that it was a proprietary technology carefully guarded with a rather low "bus factor". Blue/Green screens and chroma-keying have been "common knowledge" for a long time, with a lot of implementations over decades, but the sodium vapor process was a more closely held secret because it was a competitive advantage. Fewer people knew how to do it. Fewer people had access to do it. Eventually those people passed on or retired and the industry "forgot" how to do it entirely. It may have been "lost" simply because not enough people were allowed to know how it worked or have access to recreating it. I think there are a lot of analogies here to find related to the software industry, such as the relationships between closed source and open source software.

buck746 3y ago

It lost because there were only 3 prisms made. It also required a lot more lot as running thru an optical splitter means at least half of your light was lost, it's not a big issue today. Modern cameras are insanely more sensitive than film was at the time. Alfred Hitchcock used this on "The Birds". In the YouTube video they got a great result even with a smaller studio than would have been used on Mary Poppins. The trick needed the screen as far back as you could get it to minimize the chance of spill, that used to be normal on blue screen before the software improved.

kadoban 3y ago
> It lost because there were only 3 prisms made. But it seems so much better that that shouldn't have been a blocker. Like optics isn't magic, and knowing that someone did it before should be enough incentive? Not like movies are a small or poor industry.
- cooper_ganglia 3y ago
  I wonder if it’s just more cost effective to use a well-established tool like green screen, and then contract out all the rotoscoping clean-up to other countries for less than minimum wage?
  - kadoban 3y ago
    Yeah maybe it's something like the person choosing the camera process doesn't directly have to deal with 12 hours of roto per day, so practically it's just not something they think about.
  - 486sx33 3y ago
    I think part of the deal is that, no amount of manual intervention will allow translucent objects (like the veil) as nicely as sodium vapor lighting , also motion blur
  - bigiain 3y ago
    "and then contract out all the " blame for it's shortcomings... "Sorry boss, that's industry best practice. Nothing we can do to make sit better."
- astrodust 3y ago
  Incentive is one thing, budget is another. Keep in mind stuff gets lost all the time, even really important things like nuclear weapon components like https://en.wikipedia.org/wiki/Fogbank https://en.wikipedia.org/wiki/Fogbank
  - kadoban 3y ago
    Fair. But looking at that story (very interesting btw, thanks), they did recreate it. So incentive does mean a lot when $$ is also available, which I'd suspect it is in movies.
    - astrodust 3y ago
      I think the US nuclear program has a much bigger budget than Disney, and if they need something, they just get it. The movie industry had cheaper options, so they went with those.
      - kadoban 3y ago
        I think you're underselling Disney's budget and reach. Yes, it's probably technically smaller than the US nuclear program, but even just Disney is worth $200 billion USD, ignoring all other studios and etc. Movies are big money.
- wbl 3y ago
  Today we could use a dichoric coating but back then I think fabrication was much harder.
  - namibj 3y ago
    Well, the technology for them is far from recent, the process control and chamber geometry design to allow the needed precision and uniform-ness at the throughout needed to not be extremely expensive, however, required cheap microprocessors for a good decade to develop the required skills in control engineers to then actually go and make a machine like this. And the computers suitable we're still triple-digits in the 80's, so this only really started to deploy to factories ~25 years ago.

tadfisher 3y ago

Practically, you could see it in the video: they had to have near-perfect lighting to avoid any 589nm spill on the subject, or they would end up with semi-transparent regions on the matte where they didn't want any. Chroma-keying is more tolerant to spill, only needs one camera with one film reel, and you don't need a special screen with special lamps and special cameras.

kadoban 3y ago
> Chroma-keying is more tolerant to spill, only needs one camera with one film reel, and you don't need a special screen with special lamps and special cameras. Fair on the number of films/cameras. Is normal keying actually more tolerant to spill or is it just worse so you're going to have to manually deal with spill anyway so you just live with it? I don't even have good eyes and even I sometimes see spill in actual movies, or especially in TV. Edit: I guess that's _different_ spill though. I mean you do famously need a special screen :) And you don't need _special_ lamps per se but you do have to light your greenscreen fairly well to have real success.

cladopa 3y ago

>so why did it lose out? Is is just that green screen is good enough? It looks that the problem was manufacturing the prism, as simple as that. Today you can use unusual wavelength LEDs without phosphorous to do the same thing probably way cheaper.

namibj 3y ago
No, LEDs are far wider than low pressure sodium, which is two about 0.1nm wide (thermal broadening, IIUC basically Doppler effect between the emitting particle and the surrounding world/containment vessel) lines 0.56nm apart. See https://lambdasys.com/uploads/LLE-2.pdf https://lambdasys.com/uploads/LLE-2.pdf for a measured spectrum that's not as coarse as the one on en-wiki where both lines are blurred together. LEDs are 10~50nm, untuned laser diodes 1~10nm. It is my understanding that it's easy to make a filter for the camera that very selectively targets this line pair, though it may entail mild optical complications as a sub-nm pass/reject bandwidth detunes from sideways angles, so lenses may need to collimate the light first before feeding the filter, and de-collimate again after.

giantrobot 3y ago

As I understand it (not an expert but interested amateur) the sodium vapor method of a matte was a cheaper version of mattes movies used to use. To make a matte they'd film the actors over a black background with normal lighting for the actors. The black was velvet or batting that didn't reflect any of the foreground lights. They'd take that film and do a bunch of exposures that would eventually create a white silhouette that would preserve a decent amount of fine detail from the foreground. That matte would be used in an optical printer to double expose the film, once with the background plate then with the foreground plate. While effective this was really expensive and time consuming. The sodium vapor light technique allowed for a very easily generated matte with a high level of detail. It however required specific lights and a lot of control over spillage from the background lighting into the foreground. It was also difficult to film from multiple angles since the lighting would need to be adjusted when the camera was repositioned. With those limitations in mind it was much cheaper and less time consuming than making mattes with multiple exposures and such. Cheaper effect shots meant more effect shots for the same size budget. With a movie like Mary Poppins that wanted a ton of effects shots the traditional method of making mattes would have been cost prohibitive. Chroma keys came about because they were much cheaper than the multiple exposure method of doing mattes. The back and foreground could be lit together and the matte could be knocked out relatively easily by applying a chroma filter when making the work print. The mattes weren't as exact and had their own limitations but they were relatively inexpensive. For video (as opposed to film) chroma keys could be done electrically by filtering and mixing the video signal. Digital mattes have a lot of flexibility. As shown in the video digital editing software has lots of toggles to help make chroma mattes look good. It's a very manual process and hard to really get right. Also as shown in the video there's some things that just do not work really well with chroma keying like translucent materials and anything with high index of refraction. They're typically a good balance of cheap and effective with a lot of known techniques to make look good.

YoshiRulz 3y ago

This was addressed at the end of the video: The main points are that it can't be used outside, or when the shot includes the subjects' legs/feet (as the ground would need to be an amber-screen as well), and on top of that, it requires a certain level of setup which some shoots can't afford.

laserbeam 3y ago
I don't think I've ever seen green screen used outside either. I think you can kinda use it outside... But any random cloud passing by would destroy your morale in the editing room if you're keying against green screen. Also lighting conditions change during a day and you'd have to be aware of that when keying. Not fun.
- niccl 3y ago
  Lord of The Rings used some huge external green/blue screens. One I know of was the scene in Return of the King where there's a dead oliphaunt and, IIRC, Eowyn fighting the Witch King. But there were lots of others.

rendall 3y ago

> so why did it lose out? The video suggests that it was difficult to replicate and extremely expensive.

mrguyorama 3y ago

In modern production, an army of underpaid, un-unionized visual effects contractors who pitch lowest bidder contracts to manually retouch basically every single pixel in the film six times over is a fine price to pay for studios, while this method would require carefully planning everything ahead of time, proper scripting, and not being able to change scenes after shooting nearly as easily, and also probably involves hiring unionized labor by talented tradespeople who can say "naw that's a bad deal and a dumb idea".

rperez333 3y ago

Because it creates more problems than it solves. A movie set is expensive and moves fast – and keying is not as big of a problem as they made it out to be. For example, Niko doesn't seem to be aware of the IBK keyer (based on his comments in the VFX subreddit), which is the keyer used on almost every shot in high-budget movies. While it's not a single-click solution, it's the main tool to tackle thousands of shots with defocused edges, motion blur, and semitransparency every year. Niko deserves credit for bringing Paul's incredible experiment, but Corridor is at its core a group of entertainers, and most of them have never had experience in a large production/VFX environment. Take everything they present with a grain of salt.

WorldMaker 3y ago

Some of why it "lost out" just seems that it was a proprietary technology carefully guarded with a rather low "bus factor". Blue/Green screens and chroma-keying have been "common knowledge" for a long time, with a lot of implementations over decades, but the sodium vapor process was a more closely held secret because it was a competitive advantage. Fewer people knew how to do it. Fewer people had access to do it. Eventually those people passed on or retired and the industry "forgot" how to do it entirely. It may have been "lost" simply because not enough people were allowed to know how it worked or have access to recreating it. I think there are a lot of analogies here to find related to the software industry, such as the relationships between closed source and open source software.