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From: "Keith Buck"
Subject: Re: Detecting colored objects
Date: Wed, 30 Oct 2002 20:42:49 -0000
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
NNTP-Posting-Date: Wed, 30 Oct 2002 20:45:12 +0000
This problem was literally sorted out years ago, yet no-one seems to have
heard of the solution. You need a single photomultiplier tube and a lens
with a white light source also. For every colour that you need to detect,
you also need a sample of the same colour as a piece of card or painted
metal. This is arranged to fill the PM tubes field of view. The object to be
detected is then placed in front of the coloured card. If it is identical,
then it will not be detected as it will be identical to the background.
however if it is only slightly different in hue or saturation, then the PM
tube signal will change in one directin or another. You need some support
electronics for the PM tube and amplifiers etc and a presence detector for
Regards Keith Buck
"Adrian M Jansen" wrote in message
> Photocells are not inherently color sensitive. What you normally do is
> 2 or 3 different color light sources, and read the photo response to each
> incident color in turn. Then the 2/3 response values give you a way of
> matching the color to a table of possible colors. Its still a difficult
> problem, because you have to allow for variations in light level and
> reflectivity, but it can be done.
> Adrian Jansen email@example.com
> Design Engineer J & K Micro Systems
> Microcomputer solutions for industrial control
> "Harry Dellamano" wrote in message
> > I would like to candle eggs that have 11 possible solid colors rolling
> > an assembly line. Once the color is determined a microprocessor will
> > them into the correct bin. I do not know the best way to detect color on
> > fly. It would be nice if a photocell would put out different current
> > that can be calibrated and detected by a threshold detector. Once I get
> > the light to electronic transducer I am home free. What is the best
> > detector and light source for this job??
> > thanks
> > harry
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