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Yeah, that was pretty much my read as well. I pulled the paper down to
read it over, just haven't had the time yet.
Jim
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Personally, I played it using mplayer (which is a Linux tool) - the codec
it picked was was the FFmpeg library used there, if that's possibly of
help. I don't have any "real" Windows systems any more.
Jim
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On Tue, 10 May 2005 22:18:13 +0100, scott wrote:
> I don't see why it isn't possible. The projector is lighting one tiny
> segment of the card at a time, if it hits a red bit, the book is going to
> be lit with a red hue, very easy to pick up by the camera. Once it's
> scanned the whole card, it would be easy to build up the picture.
That's the trick, though - the projector shown in the video, unless I'm
terribly mistaken, is just a standard video projector (the type you might
plug a PC into to project it on the screen) - so the projector is in fact
lighting the entire book/card scene all at the same time.
Jim
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Among other things, Warp saw fit to write:
> Now, I have to admit I'm at a loss about how to play that .mp4 file.
> Winamp opens it ok, but plays the audio only, no video. Windows media
> player (version 9 in Windows XP) refuses to play it altogether ("Windows
> Media Player cannot play the file."). The Core Media Player does not
> recognize the format at all. The Video Inspector utility (which can be
> used to determine if codecs needed by multimedia files are installed in
> the system or not) does not recognize the format either.
mplayer in an up-to-date linux box gave no problem (other than asking to use
-nocache, and that did help). I guess it's a matter of codecs and you'd
have to find the appropriate one for your system, but I can't help in
that...)
--
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby
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Among other things, Jim Henderson saw fit to write:
>> I don't see why it isn't possible. The projector is lighting one tiny
>> segment of the card at a time, if it hits a red bit, the book is going to
>> be lit with a red hue, very easy to pick up by the camera. Once it's
>> scanned the whole card, it would be easy to build up the picture.
>
> That's the trick, though - the projector shown in the video, unless I'm
> terribly mistaken, is just a standard video projector (the type you might
> plug a PC into to project it on the screen) - so the projector is in fact
> lighting the entire book/card scene all at the same time.
As I understand it, the scene is lit "pixel by pixel", and the resolution
use for lighting is the resolution you get in the "dual image". If all the
scene is illuminated at once, it makes no sense talking about the projector
resolution. Besides, in the paper there is a figure for the card trick that
shows the different images seen by the camera when the light is sent to
different "pixels" of the card.
Anyway, I believe those projectors, like TVs and monitors, actually perform
a sweep over the screen, and we see it as a whole image due to... guess
what, persistence of vision ;-) (and maybe to screen persistence on TVs and
monitors). What would probably be needed is to slow down the scanning in
the projector or to use a very high speed camera.
--
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby
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> Anyway, I believe those projectors, like TVs and monitors, actually
> perform a sweep over the screen, and we see it as a whole image due
> to... guess what, persistence of vision ;-) (and maybe to screen
> persistence on TVs and monitors). What would probably be needed is to
> slow down the scanning in the projector or to use a very high speed
> camera.
No, those projectors use LCD panels inside, every pixel is on continuously,
and a whole line is updated at a time. So if you like it "sweeps"
downwards, but you will never see any flicker because the pixels don't "turn
off" like they do in a CRT.
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Jim Henderson wrote:
> On Tue, 10 May 2005 22:18:13 +0100, scott wrote:
>
>> I don't see why it isn't possible. The projector is lighting one
>> tiny segment of the card at a time, if it hits a red bit, the book
>> is going to be lit with a red hue, very easy to pick up by the
>> camera. Once it's scanned the whole card, it would be easy to build
>> up the picture.
>
> That's the trick, though - the projector shown in the video, unless
> I'm terribly mistaken, is just a standard video projector (the type
> you might plug a PC into to project it on the screen) - so the
> projector is in fact lighting the entire book/card scene all at the
> same time.
You are not mistaken, it is a *projector* and not a light bulb exactly so
they can light up one point at a time. They just display a black image on
the projector with one white pixel, and move that pixel about. It's the
same as having a very narrow spotlight and moving it about.
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Ah, yes, that does make a difference - after reading the paper, this makes
perfect sense. :-)
Jim
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"Jim Henderson" <nos### [at] nospam com> 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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Among other things, Jellby saw fit to write:
> Here is a physical technique to interchange the roles of a camera and a
> light-source which is reminds me of how POV-Ray calculates the rays.
I've tried implementing this in POV-Ray, see p.b.images: "Dual photography
concept testing".
--
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby
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