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 20:11:43 GMT
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Original-From:
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John Barnes <BARNES@SENSORS.stopspamCOM>
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Viewed:
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645 times
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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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