From: Lindsay MacDonald <L.W.MacDonald@derby.ac.uk>
Organization: Colour & Imaging Institute
To: Color and Vision Network <cvnet@lawton.ewind.com>
Subject: Re: CVNet - query on colorimeter information
In reply to the query by Adam Reeves, we at the Colour & Imaging
Institute have an excellent visual colorimeter, custom-designed by
Dr Arthur Tarrant and manufactured by Bentham Instruments in the
UK. Primaries are three tungsten-halogen lamps filtered through
RGB medium-bandwidth filters, with intensities independently
controlled by 10-turn potentiometers (no electronics!). An optional
fourth primary permits tetrachromatic investigation, and is useful for
mesopic colour matching. The test stimulus may be any of the following:
- Fourth lamp through a narrow-band dichroic filter
- Light piped from a full-spectrum scanning monochromator
- Reflective sample illuminated by white light
- Patch on a CRT display through rear aperture
- Patch projected through second port from LCD projector
Observers look with both eyes (binocular) through a porthole
at a screen on the rear wall of the enclosure, approximately
100 cm distant, and turn the three knobs until the best visual
match is obtained. We have been using this device for two years
in our MSc Colour Imaging programme and have had very
good results. Students learn a lot by hands-on colour matching.
Results are not of national metrological accuracy, but are better
than would normally be achieved by lab demonsration equipment.
The binocular arrangement is easier to use than haploscopic
techniques, and makes observer metamerism very apparent.
The unit is table-top rather than desk-top in size, approximately
5 feet by 3 feet in footprint, and cost about UK£10K (i.e.
about US$16K) to produce, excluding the monochromatic
light source. Arthur Tarrant gave a paper on the device at
the recent Colour 2000 conference at NPL in London.
Regards,
Lindsay MacDonald
-------------------------------------------------
Lindsay W. MacDonald CEng FBCS FIEE FRSA
Professor of Multimedia Imaging
Colour & Imaging Institute, University of Derby
Kingsway House East, Derby DE22 3HL, England UK
http://colour.derby.ac.uk/colour/people/lindsay/
Tel +44 1332 593105 Fax +44 1332 622218
L.W.MacDonald@colour.derby.ac.uk
-------------------------------------------------
> From: "Adam Reeves" <Reeves@neu.edu>
> To: "Hoover Chan" <cvnet@lawton.ewind.com>
> Subject: CVNET: request for colorimeter info.
>
> Dear CVNETers,
> I am looking for a comercially available visual colorimeter.
> One one side, it should have 3 knobs for adjusting the amounts of
> three primaries, to make a visual match. The knobs should be calibrated;
> relative units are enough.
> One the other side, it should have a location to
> place a sample, to be illuminated by white light.
>
> I do NOT want any electronics, because this is for teaching,
> so the students should be able to see what they are doing.
>
> I do NOT want a Singerman apparatus, because although this shows
> mixtures of 3 primaries, it has no place for a sample or test stimulus,
> and it is entirely uncalibrated.
>
> I thought 'tintometer' would have the right euipment, but after 100 years
> they now only make electronic colorimeters.
>
> If anyone has any suggestions, I'll be deeply grateful. I don't
> look forward to having to make a bunch of lab set-ups by hand.
>
> Adam Reeves
>
> Dept. of Psychology,
> Northeastern University
> Boston MA 02115.
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