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Sony Projector Gets Bright Images From Black Screen
da_foz writes "Sony has developed a new projector that can give a bright, unfaded picture without the need to eliminate ambient light. The secret is that they project onto a black screen instead of a white one. Their screen uses species filters so that white ambient light is absorbed, but the red, green, and blue light from the projector is reflected. Sony sees a possible use in home entertainment systems because of the ability to have a much bigger picture than conventional TVs as well as businesses adopting the projectors for presentations."
It probably appears black (or close to it) from the viewing angle when the projector is powered off.
It would seem that the ultimate version of this would use RGB lasers as the light source and notch filters on the screen. The narrowness of the notches would determine the depths of the black. The biggest trick would be in tuning the notch filters to reflect the off-axis, angled laser light.
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When your screen doesn't reflect so much of the ambient light anymore, you can use a projector that outputs less power. For one, this can lead to less hot projector lamps, thus a longer life for them.
It might also enable the use of lower-power technologies (LED-lasers anyone?), that might in turn make the projectors much cheaper.
Nice work by Sony
Now, is there a physicist in da house who knows how wide the reflection-band (in wavelength-terms) for R, G and B is?
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Actually, if it only reflect three specific wavelengths
then it's probably the _blackest_ thing you've ever seen.
Then nothing else is black except black holes. I bet you go bitching in stores too when they sell black pants even though they reflect some.
I bought some high-end binoculars a while back. When you're looking through all the Nikons and Swarovskis and Leicas side by side, you start to realize when your eyes feel the little zing. It isn't pure resolution that does it, and your eyes compensate rapidly enough to changes in brightness (due to objective size or quality) that you don't often perceive differences except at dusk and dawn. (The only exceptions for me were old-style tank commander Zeiss binocs. Very bright.)
But when you hit a binoc that felt right for contrast, ahhh -- those were my handful of last choices. It's like seeing the world with the slanting light at around 6:30 on a summer night -- everything just pops out, so clear, and the slight 3-D exaggeration of the binocular view brings it out just that little bit more. The optics store people said that was a pretty common reaction -- a slight edge in contrast was a huge advantage.
Sounds like this screen has that going for it. Big selling point, next to potential competitors, if they can get it around the right price point.
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Sony engineers worked from the basic principle that projectors, like all TVs and monitors, form colors by blending three primary hues: red, green and blue. They came up with a filter that allows the screen to reflect only red, green and blue light. The other light in a room, such as white incandescent or fluorescent bulbs, isn't reflected.
Man I hate it when the newspapers print stupid things. Whaddaya wanna bet they are using something like polaroid or narrow bandpass quarter wave plate filters with a similarly filtered projector? What would be cool is a fluorescent screen and a projector that uses light (UV?) outside the visible spectrum. Then the screen really could be visibly black but it would still glow when stimulated by the projector.
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The article specifies that this is for use with digital projectors. I assume the reason for this is that single chip DLP projectors don't actually project white light onto the screen. The red, green and blue components of the image cycle so fast on the screen that your eye perceives this as different shades and combinations including white. All you need to do is have the screen absorb white light while reflecting red, green and blue and there you go. This is really an ingenious use of this effect, but I wonder if it is unusable with a 3 chip DLP projector that shows all components at the same time? You would at least need a more sophisticated screen in this situation.
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If it reflects _anything_, it isn't black.
Of course it is. Every black object in the world reflects some light.
You are confusing black bodies, an abstract notion defined by physiscists which does not exist in the real, physical world, and the color black, which our eyes percieve just fine whether or not it is a shiny surface with a lot of reflection, or a matted surface with minimal (but still greater than zero) reflection. The black BMW I had the misfortune of following the other day positively glinted in the midday sun.
With light, black is defined as the abscence of color. With pigment, black is the presenece of all color (analogous to white light).
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'but Sony knows how risky it is to play "exclusive" in the market and make things incomatible from rest of the world'
Err, one word, Memory Stick, well, two words then.
As others have pointed out, a truly black screen wouldn't reflect the projector's light. And, conversely, a screen that is able to reflect the red, green, and blue light from the projector will reflect some of the ambient light, which contains some light at the projector's R, G, and B wavelengths. It's too bad the article has to describe it as "Gee whiz! it's technological magic!"...
What we need to know is: a) what percentage of white, ambient room light does the screen reflect? It's not zero, and the screen probably looks like a dark grey. b) When the projector is projecting "white" light, what fraction of that light is reflected? Not only is it less than 100%, it's probably less than a white screen would reflect.
Other things one would like to know are whether the filters that do this magic cause any visible graininess, and over what angle the reflected light is reflected.
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If Sony does license this they will want inane amounts of money for use. Betamax or Minidisc ring any bells for you?
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It seems like a feasible variation, at least to me -- keep the mostly-black coating to absorb nuisance ambient light, but allow transmission at narrow RGB wavelengths. Then backlight it with an LED screen, with the diodes tuned to the three transmission frequency ranges.
Don't know whether it's technically possible, but if it is, I bet it's in the works already.
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I'm guessing that the seccond bullet point is "High Contrast"
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Many DLP projectors, especially those targeted to the business sector, have a white section on their color wheel to increase brightness for slide presentations which tend to have a large amount of white. I imagine this screen would reduce the effectiveness of these projectors. Now the amount this reduction would be offset by the increased contrast of the screen, I wouldn't know.
Six o' one, half dozen of the other, but a little one watt bulb can illuminate a room in the absence of any other light. (I regularly use the back light of the phone to track down lost pacifiers under my daughter's crib in the middle of the night.)
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