Subject: Re: Detecting colored objects
Date: Wed, 30 Oct 2002 00:44:02 -0500
NNTP-Posting-Date: 30 Oct 2002 05:44:15 GMT
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Harry Dellamano wrote:
> 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?
Well, I am in agreement with others who say that you need colored lights and/or
detectors with colored filters. What you would do with the instrumentation is to
clarify which filters are best, and how easily the different colors can be
discriminated. On the one hand, if your 11 "colors" were 11 shades of gray,
electronics could surely make these discriminations, but you might want such
features as a stabilized light source to make the gray measurement more
Stark color variations would be something like red, green, blue, yellow,
cyan, magenta, black, white, pink, orange, yellow-green. With these
wide-ranging color differences, you could use filters that select for the
human primaries of red (610 nm), green (540 nm), and blue (450 nm).
The filters need not be extreme narrow-band, but could be centered
on these wavelengths more or less. Or the red filter could pass all
wavelengths above a cutoff and the blue filter could pass all
wavelengths below a cutoff, so they need not be expensive filters.
The idea of the instrumentation would be to reduce trial-and-error
in choosing the filters and lights, so that you get well-separated
signals for the 11 samples. Depending on the colored objects,
it might be easiest to use more than 3 detectors.
You have an obvious issue of amplitude variability if the objects are
rolling past the detector without stopping. The more that the colors
are truly different, the more that you want to compare red versus green,
etc, and try to ignore absolute amplitude.
One way to test the reflectance in a narrow wavelength band might be
to use an LED in that band. LEDs are not lasers but emit in fairly
narrow bands. There are lots of LEDs now at different wavelengths.