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 19:20:55 GMT
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Viewed:
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1563 times
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...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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