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It Took Me 30 Years to Solve This VFX Problem – Green Screen Problem [video]

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Re: It Took Me 30 Years to Solve This VFX Problem – Green Screen Problem [video]

#21

Post by wiml »

somat wrote: post #10
Springtime wrote: post #3

In an earlier video they made a couple years back about Disney's sodium vapor technique Paul Debevec suggested he was considering creating a dataset using a similar premise: filming enough perfectly masked references to be able to train models to achieve better keying. So it was interesting seeing Corridor tackle this by instead using synthetic data.

With regards to the sodium vapor process, an idea has been percolating in the back of my head ever since I saw that video. But I don't really have the budget to try it out. theory: make the mask out of non-visable light illuminate the backing screen in near Infra-Red light. (after a bit of thought I chose near-IR as opposed to near-UV for hopefully obvious reasons) point two cameras at a splitting prism with a near I…

This approach was used in the 1950s/60s with ultraviolet light (rather than IR) to create a traveling matte. I'm not sure why visible-light techniques won out. Easier to make sure that the illumination is set up correctly, maybe?

Re: It Took Me 30 Years to Solve This VFX Problem – Green Screen Problem [video]

#22

Post by meatmanek »

diacritical wrote: post #7

From ~04:10 till 05:00 they talk about sodium-vapor lights and how Disney has the exclusive rights to use it. From what I read the knowledge on how to make them is a trade secret, so it's not patented. Seems weird that it would be hard to recreate something from the 1950's. I also wonder how many hours were wasted by people who had to use inferior technology because Disney kept it secret. Cutting out animals and obje…

The lights are relatively easy to get. iirc (it's been a bit since I watched their full video on the subject[1]) the hard part to find was the splitter that sends the sodium-vapor light to one camera and everything else to another camera.

1. https://www.youtube.com/watch?v=UQuIVsNzqDk

Re: It Took Me 30 Years to Solve This VFX Problem – Green Screen Problem [video]

#24

Post by amluto »

actionfromafar wrote: post #16
somat wrote: post #10

Earlier quoted context omitted.

With regards to the sodium vapor process, an idea has been percolating in the back of my head ever since I saw that video. But I don't really have the budget to try it out. theory: make the mask out of non-visable light illuminate the backing screen in near Infra-Red light. (after a bit of thought I chose near-IR as opposed to near-UV for hopefully obvious reasons) point two cameras at a splitting prism with a near I…

I'll do you one better, which requires no special cameras (most have IR filters) nor double cameras or prisms. Shoot the scene in 48 or 96 fps. Sync the set lighting to odd frames. Every odd frame, the set lights are on. Every even frame, set lights are off. For the backing screen, do the reverse. Even frames, the backing screen is on. Odd frames, backing screen is off. There you go. Mask / normal shot / Mask normal…

Surely this makes your actors feel sick? And wouldn’t it make your motion blur look dashed and also cause artifacts at the edge of the mask if there’s a lot of motion?

Re: It Took Me 30 Years to Solve This VFX Problem – Green Screen Problem [video]

#25

Post by diacritical »

meatmanek wrote: post #22
diacritical wrote: post #7

From ~04:10 till 05:00 they talk about sodium-vapor lights and how Disney has the exclusive rights to use it. From what I read the knowledge on how to make them is a trade secret, so it's not patented. Seems weird that it would be hard to recreate something from the 1950's. I also wonder how many hours were wasted by people who had to use inferior technology because Disney kept it secret. Cutting out animals and obje…

The lights are relatively easy to get. iirc (it's been a bit since I watched their full video on the subject[1]) the hard part to find was the splitter that sends the sodium-vapor light to one camera and everything else to another camera. 1. https://www.youtube.com/watch?v=UQuIVsNzqDk

Yup, I wanted to say that the prisms are hard to recreate, not the light itself.

Re: It Took Me 30 Years to Solve This VFX Problem – Green Screen Problem [video]

#26

Post by aidenn0 »

meatmanek wrote: post #22
diacritical wrote: post #7

From ~04:10 till 05:00 they talk about sodium-vapor lights and how Disney has the exclusive rights to use it. From what I read the knowledge on how to make them is a trade secret, so it's not patented. Seems weird that it would be hard to recreate something from the 1950's. I also wonder how many hours were wasted by people who had to use inferior technology because Disney kept it secret. Cutting out animals and obje…

The lights are relatively easy to get. iirc (it's been a bit since I watched their full video on the subject[1]) the hard part to find was the splitter that sends the sodium-vapor light to one camera and everything else to another camera. 1. https://www.youtube.com/watch?v=UQuIVsNzqDk

It would seem to me to be relatively easy to build something like that if you're okay shooting with effectively a full stop less light (just split the image with a half-silvered reflector and use a dichroic filter to pass the sodium-vapor light one one side.

The splitter would have to be behind the lens, so it would require a custom camera setup (probably a longer lens-to-sensor distance than most lenses are designed for too), but I can't think of any other issues.

Re: It Took Me 30 Years to Solve This VFX Problem – Green Screen Problem [video]

#27

Post by throwway120385 »

amluto wrote: post #24
actionfromafar wrote: post #16

Earlier quoted context omitted.

I'll do you one better, which requires no special cameras (most have IR filters) nor double cameras or prisms. Shoot the scene in 48 or 96 fps. Sync the set lighting to odd frames. Every odd frame, the set lights are on. Every even frame, set lights are off. For the backing screen, do the reverse. Even frames, the backing screen is on. Odd frames, backing screen is off. There you go. Mask / normal shot / Mask normal…

Surely this makes your actors feel sick? And wouldn’t it make your motion blur look dashed and also cause artifacts at the edge of the mask if there’s a lot of motion?

You could strobe at some multiple of the sensor frame rate as long as your strobes are continuous through the integration period of the sensor and the lighting fades very quickly. This probably wouldn't work with incandescents but people strobe LEDs a lot to boost the instantaneous illumination without going past the continuous power rating in the datasheet.

Re: It Took Me 30 Years to Solve This VFX Problem – Green Screen Problem [video]

#28

Post by throwway120385 »

somat wrote: post #13
diacritical wrote: post #11

Earlier quoted context omitted.

Don't humans and other warm objects also radiate IR?

That is far-IR, thermal stuff, Near-IR, 700 nanometer-ish is right below red in human vision. Camera sensors can pick up a little near-IR so they have have a filter to block it. If that filter was removed and a filter to block visable light was used in place you would have a camera that can only see non-visable light. Poorly, the camera was not engineered to operate in this bandwidth, but it might be good enough for…

You can actually dimly perceive near-IR LEDs -- they'll glow slightly red in darkness.

Re: It Took Me 30 Years to Solve This VFX Problem – Green Screen Problem [video]

#29

Post by tekacs »

ralusek wrote: post #9

I'm a software engineer that, like the vast majority of you, uses AI/agents in my workflow every day. That being said, I have to admit that it feels a little weird to hear someone who does not write code say that they built something, without even mentioning that they had an agent build it (unless I missed that).

Worth bearing in mind that people in VFX are often relatively technical.

From their own 'LLM handover' doc: https://github.com/nikopueringer/CorridorKey/blob/main/docs/...

> Be Proactive: The user is highly technical (a VFX professional/coder). Skip basic tutorials and dive straight into advanced implementation, but be sure to document math thoroughly.

Re: It Took Me 30 Years to Solve This VFX Problem – Green Screen Problem [video]

#30

Post by CharlesW »

amelius wrote: post #23

There's still a bug: the glass with water does not distort the checker pattern in the background at 24:12.

When you watch the video it becomes pretty clear why it wouldn't be able to do that, although it's fun to think about how a future iteration or alternative might be able to credibly (if you don't look too hard) mimic that someday.
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