I guess you want the key deleting the background, like green screen. That fore, you must understand how chroma keying works.
The composition of dust works just a chromakey filter in aftereffects, but in real time: it detects a certain color key. What you have to do, as done while doing green screen in filming, is, as the name says, use a green screen (Or actually any screen of a certain color as long it is lighted to be balanced, and you don't have that color in the foreground). In that case, you can annulate the background. Another way is you are in front of a white screen which is illuminated (but not you,) by UV-light, so you can filter the whole surface out. OR another way is you take a snapshot of background and eliminate it.
I am not to clear, I know, not even in other languages, so have a look at https://en.wikipedia.org/wiki/Chroma_key to see what I mean.
Greetings
I guess you want the key deleting the background, like green screen. That fore, you must understand how chroma keying works. The composition of dust works just a chromakey filter in aftereffects, but in real time: it detects a certain color key. What you have to do, as done while doing green screen in filming, is, as the name says, use a green screen (Or actually any screen of a certain color as long it is lighted to be balanced, and you don't have that color in the foreground). In that case, you can annulate the background. Another way is you are in front of a white screen which is illuminated (but not you,) by UV-light, so you can filter the whole surface out. OR another way is you take a snapshot of background and eliminate it. I am not to clear, I know, not even in other languages, so have a look at https://en.wikipedia.org/wiki/Chroma_key to see what I mean. Greetings