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jam m, 195@
iled July 25, 1946
Patented Jan. 10,_ 1950
Franklin C. Williams, Rochester, N. Y., assignor
to Eastman Kodak Company, Rochester, N. Y.,
a corporation of New Jersey
Application July 25, 1946, Serial No. 686,171
2 Claims. (Cl. 235-61)
This invention relates to the electrical deter
presses one desired quantity in terms of three
mination of the sum of several products and more
particularly to a simple linear coordinate trans
directly measurable quantities.
These equations are solved electrically by set
fer computing method and device.
ting up potentials corresponding to the constants
Whenever it is necessary to make a large num
pertaining to the dyes involved, dividing these
ber of linear transfers between two related sets
potentials by factors representing the densities
of two or more related coordinates, the manual
and noting the resulting combined potential.
labor involved is considerable and, of course, sub
This resulting potential may be numerically
ject to occasional error. The primary object of
equal, in volts, to the desired quantity in density.
the present invention is to provide a method and
Referring to Fig. 1, there is shown a poten
apparatus whereby such computations may be 10 tiometer
I'll connected across the terminals of a
made electrically and the answer read directly.
Other objects and advantages of the invention
will become apparent frOm the following descrip
tion when read in connection with the accom 15
panying drawing in which:
Fig. 1 is a wiring diagram showing a simple de
linearly-wound potential divider H, such as a
linear radio volume control, having a sliding con
tact arm l2, the high voltage end of the divider
H being connected to an adjustable contact l3
on the potentiometer l0. Voltage is supplied to
the potentiometer IE) from any suitable source
vice illustrating the principle of the invention;
such as a battery I4. A high impedance volt
Fig. 2 is a wiring diagram of an arrangement 20 meter l5, which may be a vacuum-tube voltmeter,
is connected between the zero-end terminal of
permitting determinations to be made in rapid
the divider H and its contact arm l2 to indi
cate the resulting voltage.
One ?eld in which the invention ?nds great
The principle of the invention will become
usefulness is in specifying the sensitometric char
clear if it is assumed that the equation to be
acteristics of subtractive process color ?lm where 25 solved is simply C=aDr. First calibrate by set
it is desirable to determine the three individual
ting the contact arm l2 at 1.0, as shown, and ad
dye densities from measurements made of the
the contact !3 until the voltmeter reads “a”
entire composite three-dye image and the in
volts. Now if the contact arm I2 is set at any
vention will be described as applied in this ?eld.
value of Dr, the voltmeter ['5 will read directly
If the density of a composite three-dye image
c=d-Dr. Now if three entirely independent de
to each of three essentially monochromatic radia
vices such as shown in Fig. 1 are adjusted to yield
tions, usually of red, green and blue light, is
voltages equal to aDr, bDg, and CDb and connected
measured, data is obtained from which the equiv
in series, the voltage sum as read by the volt
alent density of each individual dye may be com
meter Will be
puted. The computation is a linear three-dimen 35
sional coordinate transfer and in accordance with
the invention is done electrically.
Such a series arrangement is shown in Fig. 2. If
Each of the three measurable densities to the
I) or c is negative, the polarity of the applied po
above-mentioned monochromatic radiations is
tential can be reverse .
the sum of contributions of all three dyes. From 40
The arrangement shown in Fig. 2 in addition
known characteristics of these dyes individually,
provides for rapid shifting from determination of
equations can be derived expressing the indi
C to the determination of M and then Y. This is
vidual components in terms of the measurements
possible because all that is needed for the shift
of the whole and may be expressed as
is to change the potentials to correspond to a’, b’,
45 and c’ and then to a", b”, and c" and the same
potentiometers can be used since the di?erent po
where Dr, Dg, and Db are the densities of the
whole image to the three radiations and a, b, etc.
are constants pertaining to one particular set
of dyes and the density units employed. This
is a coordinate transfer system‘ from the coordi
tentials are not required at the same time. Thus
as shown in Fig. 2 the potential divider I l is
connected in series with additional potential di
viders l6 and I‘! having contact arms l8 and I9,
respectively, for setting up the values for Dg and
Db. Also, the potentiometer In is provided with ad
ditional taps 20 and 2| corresponding to a,’ and a",
nate set Dr, D1; and Db to the linearly related set
C, M and Y. Thus each of these equations ex- 55 respectively, which are selectively connectable to
the divider II by means of a switch 22 carried by
a shaft 23 having a, control knob 24. Similarly,
the divider I6 has a supply potentiometer 25 hav
ing three taps 25, 21, and 28 corresponding to the
coefficients b, b’, and b”, respectively, which are
selectively connectable to the divider it by a
switch 29 carried by the shaft 23. In the same
manner, a third potentiometer 38 has three taps
3|, 32, and 33 representing the coef?cients c, c’,
and 0", respectively, and adapted to be connected
to light complemental in color to the respective
dyes to provide electric potentials representative
of the products of said transmission character
istic times the respective density factors, and
measuring the algebraic sum of the potentials so
2. In a device for determining the equivalent
density of each of the dyes in a composite three
dye subtractive image from the density of the
to the divider I‘! by a selecting switch 34 carried 10' composite image to each of three substantially
monochromatic radiations complemental in color
to the three dyes, the coef?cients of each of the
three dyes to each of the three radiations being
Ill, 25, and 30 may be adjustable to set up the
known, three voltage dividers in serial relation
proper coefficients when a different set of dyes is
involved, it is preferred for the sake of accuracy 15 ship each adjustable to correspond to the den
by the shaft 23.
Although the several taps to the potentiometers
to have the taps ?xed and use a different set of
potentiometers for each set of dyes. This requires
a predetermined voltage across the potentiom
eters and it may be obtained by test, but prefer
ably a set of regulated voltage power supplies 35
is employed.
With the device above described, the density
readings of a composite color image to red, green,
sity of the image to a different one of the three
radiations, each of the voltage dividers having '
an associated potentiometer provided with three
?xed taps corresponding respectively to the three
coe?icients of the three dyes to the same different
one of the three radiations, switching means for
selectively connecting to the dividers the taps of
the potentiometers corresponding to the meth
cients of any one of the three dyes, and means for
and ll and the equivalent densities C, M, and Y 25 indicating the total voltage across the three divid
and blue light are set up on the dividers ll, l5,
read on the voltmeter !5 in rapid succession by
suitable manipulation of the knob 24.
While a speci?c device has been described in
detail to disclose the invention, it will be readily
apparent to those skilled in the art that many 30 The foliowing references are of record in the
modi?cations will suggest themselves and all such
?le of this ‘patent:
modi?cations are intended to be included within
the scope of the appended claims.
I claim:
1. The method of determining the equivalent 35
density of a dye in a composite three-dye subtrac
tive image which comprises setting up three elec
tric potentials corresponding respectively to the
transmission characteristics of the three subtrac 40
tive dyes, dividing each such potential by a factor
representing the density of the composite image
Martin __________ __ June 3, 1941
Swartzel, ‘Jr ______ __ June 11, 1946
Wilcox __________ __ Mai: 11, 1947
Country ,
Sweden __________ __ Oct. 19, 1943
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