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Procedure for making room invisible.

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Theory ______________ ______________ ______________

/*Red + Green + Blue = White Color. */

If you shine a purple ( = Red + Blue) colored light on green surface, that surface should appear black ( Thanks to MechE's anno.).

i.e. a surface of any color could be made to appear black, by throwing light of appropriate color on it.

Instruments required : ______________ ______________

A room, Digital Camera, Slide Projector, Image processing Software.

Procedure.: ______________ ______________ ______________

1. Take photo of the room. ( say, of a wall, with all the household objects, with camera located at the center of the room.)

2. Using software, manipulate colors of photo using the software as described in theory. e.g. replace all green color by purple color.; replace all red color by combination of other two i.e. blue + green. This process will replace every color in the photo by the some other color which will make it appear black. White will be replaced by black color.

3.Put this new image on to slide Projector.

4. Position the projector exactly where the camera was. Project the image.

The wall and all the objects should appear invisible ( black).

______________ ______________ ______________

Patent pending.

VJW, Jul 05 2011

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       Maybe. The thing is, there are probably different kinds of inversion. Try it and see, i suppose. Another matter is the nature of the data. I think i'd like to see something like a straightforward chemical photographic negative projected onto a room.
nineteenthly, Jul 05 2011
  

       you can skip all that by shining a white light on a black surface: you'll get just as much white out of it.
FlyingToaster, Jul 05 2011
  

       To clarify the previous posters, if you shine pure red and blue light on a pure green surface, you will get black not white. Remember that the color you see is the light that is reflected off that surface, and the other colors are absorbed. If there is no green light hitting the green surface, it will reflect nothing and appear black.
MechE, Jul 05 2011
  

       OK. So the room will appear invisible (black).   

       Any new object which gets introduced will stand out, changing colo(u)rs as it is moved around the (now invisible) room.
neelandan, Jul 05 2011
  

       Well, then comes the next complexity, note the "pure" in my above. Objects, even apparent mono-colors, don't have a monochromatic response. That red vase has some green and some blue in it. There will be wavelengths where it has a very low reflectance, but these are unlikely to bear any resemblance to the colors available in a projector or similar.   

       To try to simplify: A projector can create apparent continous color by mixing sources, but it can't exclude colors the same way.
MechE, Jul 05 2011
  

       Maybe you wouldn't need to start with a photo - a video camera would give instant feedback of the error.
Ling, Jul 05 2011
  

       It sounds like it would have interesting effects but that these would not include invisibility. What i'm wondering now is if you'd end up with something like video compression artifacts when things changed, with a video camera, due to the slight delay, so for example the edges of a moving object would be more visible than the middle.
nineteenthly, Jul 05 2011
  

       Anyway, a small C4 parcel would definitely work.
Ling, Jul 05 2011
  

       Thanks to MechE: Yes, it should appear black not white. 'Have updated the idea.   

       //video camera would give instant feedback of the error// Please explain.
VJW, Jul 05 2011
  

       //Explain// Use a *projector and video camera. Any colour detected by the camera can be used to change the projected colour accordingly.   

       *Not a slide projector.**   

       **Can you still buy them?
Ling, Jul 05 2011
  

       Re my second anno, a slide projector would do better at this than a digital one, since it starts with a white light source and the slide is pan-chromatic instead of RGB. The lack of perfect filtering from the slide would still mean everything is dimly illuminated rather than completely black though.
MechE, Jul 05 2011
  

       The reason slide projecor instead of LCD projector was suggested is that idea was to to have a minimal setup.   

       Objective of this whole procedure will be what has been stated by [neelandan] above. This can be used as special effects process.   

       Projector + video camera combination by [Ling] sounds good, because then one will be able to work with moving background instead of a still one.
VJW, Jul 05 2011
  

       //slide projector would do better [...], since it starts with a white light source//   

       sp. 'white' -> 'orange'
lurch, Jul 05 2011
  

       Well, a slide projector could be made with a true white lamp, in any case.
MechE, Jul 05 2011
  

       Photographic negatives have an orange cast, due to impurities in the dye colors - which is easier to work around than actually solve.   

       Having a white lamp would be a moot point. I think you're trying to drive at "full spectrum", rather than "white".
lurch, Jul 05 2011
  

       White light is the presence of the entire visible spectrum, that's what I'm calling for. That would allow a theoretical opposition lighting. It still wouldn't work perfectly, as the slide isn't going to filter anywhere near the complete input. (Look at a black projected slide, it's still brighter than the projection screen).   

       The slides themselves aren't photographic negatives, but computer processing.
MechE, Jul 06 2011
  

       //If you shine a purple ( = Red + Blue) colored light on green surface, that surface should appear black ( Thanks to MechE's anno.).   

       i.e. a surface of any color could be made to appear black, by throwing light of appropriate color on it.//   

       That's even worse than the original. You may not have read [MechE]'s annotations carefully enough. Most ordinary objects reflect some light at all wavelengths; a green object reflects some red and blue light. Your idea works better in the original version, although you'll need a bright projector, and good colour contrast, and the scene will still appear dimly lit.   

       The only way to make everything appear black is to eliminate all light.
spidermother, Jul 06 2011
  

       Yes, agreed. A green vase will have many shades of green, and some shades mixed with other primary colors, reddish green for example. It is not possible to have any real life object, with a purely monochromatic color.   

       However, how this is a problem for the idea ?
VJW, Jul 06 2011
  

       It's not a problem for the idea in its original form, so much as for the modified form (in which black replaces white).   

       Or, as Zaphod said, "It's the weird colour scheme that freaks me. Every time you try to operate one of these weird black controls, which are labeled in black on a black background, a small black light lights up black to let you know you've done it."
spidermother, Jul 06 2011
  

       Idea is not to throw a computed single monochromatic color onto a real-life green vase to make it appear black. Idea is to project an entire life-size color-altered image of vase, on to vase itself. IMO, that should take care of all complex greenish shades which the "green" vase has.
VJW, Jul 06 2011
  

       I realise that, it's just that the result won't be black; the best description might be grey, since you will cancel the colour but the result will not be very bright.   

       You should actually try this out. I think it might actually work; at least, you should get rather washed out colours. Otherwise, get some coloured LEDs and try lighting up objects with them; by playing with the amount of red, green and blue light, you should be able to make coloured objects look greyish. Remember that RGB does not perfectly reproduce human colour vision, so you won't be able to eliminate colour perfectly either.
spidermother, Jul 06 2011
  

       Maybe just build a small black hole.
cudgel, Jul 06 2011
  

       A magnesium flare, or just get everyone to close their eyes?   

       On a more technological way, just very big lcd screens on the walls and switch the pictures from flock wallpaper to shots of the outdoors.   

       Erm why would anyone want to make a room invisible, if that's not a dumb question?
not_morrison_rm, Jul 06 2011
  

       To see through the walls, to what lies beyond.
neelandan, Jul 06 2011
  

       I can't help thinking it'd be easier just to turn off the lights.
nineteenthly, Jul 06 2011
  

       I don't think "invisible" is the right term...perhaps "reduced contrast" would explain more betterer.
Ling, Jul 06 2011
  

       Another thing : Spectator's head will have to be very close to camera.   

       With some modification, this procedure can be used in special effects e.g. rocks shows such as Pink Floyd shows.   

       Imagine background being partially invisible inspite of strong light source and a moving object starkly visible in the foreground.
VJW, Jul 06 2011
  

       I like it. It would make a good special effect for a stage show. Various items, backgrounds, even characters could be grayed out in place with appropriate projected colors.
bungston, Jul 06 2011
  

       //small C4 parcel//   

       C4, to make it go away - not far, but very fast
C-41: make it appear dimly gone
C-141: Takes a while, but you can make it go far away
lurch, Jul 06 2011
  

       Of course, using a small explosive parcel to turn a room white (the original stated outcome of this idea) was done by Mr Bean.
spidermother, Jul 06 2011
  
      
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