Subject:
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Re: Color images? (was: Re: digital camera entirely made of mindstorms?)
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 28 Sep 2000 20:44:15 GMT
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Viewed:
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1763 times
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I have some tri-colored LEDs I bought last year. They were really expensive (I
think $15 each), but they are very cool. They have three leads, and they can
make any combination of reds greens and blues. I can't remember where I got
them, but there are probably several suppliers now. There are also some
dazzlingly bright white LEDs on the market now.
In lugnet.robotics, David C. Pyatt writes:
> ...and you are going to share this great sensor, aren't you? :)
>
> Dave
>
> In lugnet.robotics, John Barnes writes:
> > I have been experimenting, on and off, with a "better light sensor"
> > for the RCX. No offense meant to Lego or any of the more purist
> > Legoists, but I indulge myself in designing various other sensors
> > for RCX use.
> >
> > In the course of that indulgence, I have been working on a color sensor.
> > It is conceptually similar to the Lego light sensor in that it supplies
> > its own light, but in my case it has four LEDs, a red, green, blue and IR.
> > It has a standard silicon sensor (phototransistor) and it energizes each
> > LED in turn as well as sampling with no light. It can therefore subtract
> > the background level from each of the four levels from the LEDs. It uses
> > the return from the IR to decide if an object is present and then measures
> > the signal from each color to decide upon a color value to return to the
> > RCX. 0 - 9 is no object in range, 10 - 89 encodes the spectrum and
> > 90+ is returned for white. It all seemed quite easy to start off with except
> > for the one thing that seems to be dogging this thread;
> >
> > The typical phototransistor seems to have quite a poor response from
> > green though the blue. In my case, the response to green and blue
> > is about one tenth what it is at red and about 1/25 what it is at IR. It
> > varies from one device type to another however.
> >
> > The other observation is that the colors produced by the average color • printer
> > don't behave the same as those embedded in materials like Lego bricks.
> > I have a spectrum printed on strip of paper wrapped around a large Lego
> > tire which I rotate to use as a continuously varying color source for
> > testing. Its
> > green and lego brick green which look the same do not have similar properties
> > when illuminated by my LED system. So if you are planning on trying to use a
> > color printer to make color filters for your camera, you may not get quite
> > the results
> > you're expecting ... or is it the LED light ? .....
> >
> > JB
> >
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