light seen by camera but not eye?

omega42

A bit of a strange one

I'm wondering is there any type of light or other substance that doesn't show up to the naked eye but can be seen by a filter or lens.

What I am thinking is it possible to project a light on a wall that the human eye cant see i.e. UV or infra-red but when viewed through a camera the wall would show up a colour that could be used for cromakeying in post?

Any help would be great

Omega

af_thefragile

Most camera sensors have infra-red filters although most cameras will be able to see in the infra-red range so if you use an infra-red filter (one that only allows infra-red light to pass) you can capture images in the infrared spectrum.

Anyway croma key won't work the way you're saying. Humans emit infra red radiation so if the camera was to capture IR, it'ld capture the person too, which would be no use for chromakeying. I don't think cameras are very good at capturing UV either and UV is usually absorbed by most objects to give a bright enough image. There's a reason green is used for cromakeying. It's the colour furthest away from human skintone which makes it easy to distinguish it from a human subject and key in. Blue was used in the day of film because flim particles reacting to blue light had the finest grain so you could say it gave the best resolution to key in and blue too is fairly distinct from human skin tones for the software to distinguish between the blue background and the human subject.

So yeah if you wanna do cromakey work, it'll be much easier and simply to simply buy a green screen or pain the wall green or something.

omega42

Thanks for the reply

I know the limit of cromakey, what I'm trying to achieve is the wall have 1 image on it but key in another image in post, I don't want the subject to know their in front of a greenscreen