From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Detecting colored objects
Date: Wed, 30 Oct 2002 05:00:53 GMT
NNTP-Posting-Date: Tue, 29 Oct 2002 21:00:53 PST
Harry Dellamano wrote:
> wrote in message
> > I am not clear on where the 11 colors come from. Are we talking about the
> > white-tan-brown dimension of ordinary eggs, or something more subtle?
> > Color as seen by humans has 3 dimensions: Red, Green, and Blue, or
> > Hue, Saturation and Value, or some other system. Has somebody
> > documented for you what the 11 colors are? If not, you need the
> > temporary use of some equipment such as a spectrophotometer or
> > colorimeter to clarify the problem.
> > Jim W.
> Jim, thanks for replying.
> The objects are not really eggs but similar objects painted solid colors
> for easy visual identification. This must be done electronically on the fly,
> lets say moving 0.5 feet / second.
> How do I use the spectrophotometer or colorimeter to clarify the problem?
You might do a google search on machine vision.
The idea is to use three filters. I would use additive filters for
opaque objects which are red, green and blue. The filters are expensive
but are easy to obtain. With a sensor for each filter, you might set all
of the outputs equal for a standard gray card which can be obtained from
a photography shop of supply. This will approximately compensate for the
color temperature of the light source. One approach is to obtain the
three color sensor output for an object and divide each by the sum of
the three. This normalizes the sensor signals. The three numbers are
then define a point in a plane with three 120 degree axes. This is
actually overconstrained since the axes are not orthogonal. Thus you may
have a near region rather than a point. However, this is usually
sufficient to recognize color to the precision you need.
Binning by color is a common technique in industry so you may find
commercially built devices that do this.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org