Optics: measuring and testing – By shade or color – Tristimulus examination
Patent
1981-06-19
1985-05-21
McGraw, Vincent P.
Optics: measuring and testing
By shade or color
Tristimulus examination
356406, 356223, 356227, G01N 2125, G01J 142, G01J 144
Patent
active
045182582
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a colour analyser comprising an indicating instrument consisting of three light scales. The principal purpose of the instrument is to present an indication of a necessary color correction, for colour recording or reproduction purposes. The field of application comprises, among other things, colour photography and colour television.
The embodiment as described is principally designed for use in combination with an enlarger for enlarging colour negatives and transparencies. Such enlargers are usually equipped with three continuously variable colour correction filters. The colour analyser provides a means to determine which correction filters have to be engaged and to what density, to correct for the colour imbalance in the negative or transparency used. Besides this, a time determining circuit may be added to the analyser, for indicating the correct exposure time for a print or an enlargement.
Colour analysers are usually provided with one light sensitive cell. Blue, green and red filters can subsequently be placed in front of this cell, for measuring the respective yellow, magenta and cyan corrections. A suchlike embodiment has been described in U.S. Pat. No. 4,125,330. A disadvantage of this measuring method is the time consuming process of the sequential colour switching and measuring, and also the fact that due to counter absorptions in the correction filters one or two repeated complete measuring cycles are required. These disadvantages are offset in the embodiment of my invention because it is provided with at least three measuring cells, the signals of these cells being simultaneously transmitted.
Another colour analyser with three different cells is known from U.S. Pat. No. 3,819,275. A disadvantage of last said analyser, and equally of other known embodiments lies in the necessity to read one or more measuring instruments. The operator is asked to read and interpret three quantities in order to get to a correct filter setting, for every exposure again, with the added difficulty of being in a darkroom. My invention reduces the complicacy of the measurement in a new way, namely by indicating the filters by a lighted colour star, presenting in each case an image of one or two vectors of coloured light, describing the complete colour circle.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a representation of three rows of light emitting diodes which form the colour star.
FIG. 2 is a block diagram of the preferred embodiment of the invention.
The colour star thereby exists of three rows of coloured light sources, such as light emitting diodes, each row in an appropriate colour, and placed under mutual angles of 120 degrees, i.e. as indicated in FIG. 1.
From one glance the operator can tell which filter knobs to engage at the enlarger, because the analyser indicates them by coloured lights. These coloured lights are extinguished gradually as the operator increases the filter density, until all lights are completely darkened when the correct density is reached.
The indicators may consist of any number of lights and the indication needs no linear relation to the corresponding filter density. As it only needs to show an accurate zero indication it may minimally comprise only one light per indicator. Hence it follows that the colour star is more than a simple system of three indicating instruments. It is actually a single instrument, showing a vectorial indication of the colour inbalance. Therefor the colour star can only function together with its specially designed signal processor unit. This unit converts the three originally measured signals into three other signals, that provide an immediately recognisable indication for the correction filters needed, if displayed vectorially.
The operation of a colour analyser according to my invention will be described hereunder in conjunction with the block diagram of FIG. 2.
Its four measuring cells 1, 2, 3, and 4 may be either photodiodes or photomultiplier tubes. The cells are provided with respective blue, green, orange-red, and dark red filters.
REFERENCES:
patent: 2203036 (1940-06-01), Van Briessen et al.
patent: 3097563 (1963-07-01), Weisglass
patent: 3408142 (1968-10-01), Hunt et al.
patent: 3819275 (1974-06-01), Aimi et al.
patent: 4025190 (1977-05-01), Hughes
patent: 4125330 (1978-11-01), Schild
patent: 4140391 (1979-02-01), Laciak et al.
patent: 4194838 (1980-03-01), Bey et al.
McGraw Vincent P.
Turner S. A.
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