Re-creating Disney's sodium vapor process [video]

>brighter infrared lights to compensate if necessary

I am guessing that that is dangerous to human health because infrared fails to elicit the flinch reaction that too-strong visible light does.

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.

"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."

Near infrared isn't generated by random environmental objects. You're thinking of far infrared. Infrared is a big spectrum, much larger than the visible spectrum.

It may be generated by lights but could be filtered out. It is generated by the Sun, but so is the sodium wavelength. The technique would work indoors just as well as the sodium one, but with important advantages. I think it could even work pretty well outdoors if you used a wavelength that is mostly filtered out of sunlight by the atmosphere, or maybe two different wavelengths in two channels simultaneously.

Near-infrared penetrates very well. The same intensity is much safer, up till you get to the levels of radiation that are dangerous regardless of how they're distributed in your tissues.

That's one of the things that makes it suitable for thermal nano cancer therapies. You

(1) Create a nanoparticle with a gold core of the right size that it excites when exposed to near-infrared radiation (the far end of "near" is ideal),

(2) Coat it with something that's hopefully less toxic than the cancer because the gold nanoparticles are pretty reactive (silica was popular last I checked, though I'm not convinced that's actually safe, and there hasn't been much testing on it),

(3) Coat that in something that binds to the right antigens,

(4) Inject that into the patient so that you'll eventually have a tumor rich in these nanoparticles while the rest of the body has a very low concentration,

(5) Shine an intense near-infrared beam at the nanoparticles. It safely penetrates body and causes minimal heating, instead depositing all its energy at the tumor, selectively cooking just the bits of tissue you don't want anymore.

It's yet another way to make mice immortal, but human testing is a long ways off. The hard parts are (2) and (3), along with the (4a) I didn't mention where most of these things don't want to stay "nano" in most chemical environments, and the solution they're suspended in is usually also not ideally suited to being injected into living mammals who would like to retain that "living" property.