"Jim Henderson" <nos### [at] nospamcom> wrote in message
news:pan### [at] nospamcom
> Ah, yes, that does make a difference - after reading the paper,
> this makes perfect sense. :-)

Projectors are often used to capture 3D data using a normal camera.  If you 
place the projector and camera at slightly different positions, you can then 
project special patterns using the projector.  For example, if you project a 
series of images using the projector:

11110000      11001100     10101010
11110000 -->  11001100 --> 10101010  (1=white)
11110000      11001100     10101010  (0=black)

Then record the three images the camera sees in monochrome.  For each pixel 
in the camera, it will have three values (one from each frame), this is 
effectively a 3-bit number that will tell you which line on the projector is 
lighting that pixel.  Using some simple geometry you can then work out the 
distance of that point from the camera (because you know the position of the 
camera and the projector, and the angle that the light came out / went into 
each).

Do this for every pixel and you have a height-field of your scene built up 
very quickly.  If you projector has 1024 vertical lines, you only need 
project and record 10 frames to get the height-field, that's less than 1 
second.

Do the whole process at several different known locations and you start to 
build up a very detailed 3D map very quickly...

Projectors are almost cheap enough now for me to not feel guilty buying one 
for home use :-)

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