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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]

#51
post #32
post #24

Earlier quoted context omitted.

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?

Incandescent and fluorescent lights already flicker at your AC power frequency. Just gotta be higher than that

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

#52
post #32
post #24

Earlier quoted context omitted.

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?

Incandescent and fluorescent lights already flicker at your AC power frequency. Just gotta be higher than that

phosphors and capacitors are a thing that mask that, so is high frequency switching way above this rate…

Anyway, an old HN submission I still use when buying light bulbs: https://news.ycombinator.com/item?id=14023196

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

#53

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…

This is called “ghost frame” and already exists in Red cameras and virtual production wall tools like Disguise.

You need to basically timecode/genlock the greenscreen "illumination LEDs" to the camera so the greenscreen lights up only exactly at every other frame. Not sure if there exists any off the shelf solution which can do that but if not it can't be super hard to cobble together.

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

#54

Earlier quoted context omitted.

I fully agree but I think for them making it possible to cut corners during production is the whole point. Think about it: The choice is between 5 minutes of work plus a one time purchase of a decent GPU and a big room with a complex lighting setup with a post supervisor present. Now, quality of the end result will not be the same, for sure. You and me would opt for the quality setup whenever we can, but many others…

If you're on such a low production budget that you just physically do not have the lamps to light a screen, then you really have to ask if green screen is the right option. Maybe flip it and shoot black limbo so you do not need lights, and the lights you do have can be better used as key lights for separation. You also don't have to worry about the color cast from your light screen. Essentially, you just need a garba…

Sometimes the cost is human expertise. If the tech allows you to get stuff done with less competent staff, it's a win.

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

#55
post #24

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?

Feel sick? Possibly. People are more or less sensitive to imperceptable flicker.

Artifacts?

I bet that can be remedied by interpolating a new frame between every mask frame. Plus, when you mix it down to 24fps you can introduce as much motion blur and shutter angle "emulation" as you want.

Motion blur can also be very forgiving. You are more likely to notice artifacts in still or slow moving scenes and then the problem goes away.

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

#56
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…

Corridor Crew cover this in one of their VFX breakdowns where I can't remember the film but it was supposed to be filmed on a rapidly rotating platfom.

There were a large number of lights around it and each one was blinked on for an instant while the camera shot at an insanely high frame rate - something like 288 frames per second with twelve lights.

This meant that after the fact you could pick any one of the twelve frames for that 1/24th of a second, to choose the angle the light was hitting at.

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

#57

The sad thing about this is the problems encountered during post from the production team saying "fix it post" during the shoot. I've been on set for green screen shoots where the lighting was not done properly. I watched the gaffer walk across the set taking readings from his meter before saying the lighting was good. I flip on the waveform and told him it was not even (which never goes down well when camera dept te…

their green screen is good. that has nothing to do with this video.

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

#58
post #24

Earlier quoted context omitted.

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.

You mean do strobe, strobe, strobe, strobe, pause, pause, pause, pause? I bet that's at least as bad as holding the source on for the first four intervals and then off for the latter four intervals.

In any case, if you actually have a scene bright for 1/24th of a second and then dark for 1/24th of a second, repeating, you're well within photosensitive epilepsy range. Don't do that to your actors unless you've discussed it with them and with your insurance company first.

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

#59

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…

Even if it had been patented, patents from the 1950s would have long expired. In fact, patents from 2005 would have expired - the US patent term is only 20 years.

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

#60
As far as alternatives, I wonder if anyone has tried a screen that cycles through colors in a known sequence. Using this modulating-color screen, it might actually be easier to separate the subject because you get around the "green shirt over green screen" problem. You might even be able to use a time sampling to correct the light cast on the subject from the screen as you would have a full spectrum of response.

I could also imagine using polarized light as the backdrop as well.

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