U.S. patent number 3,783,275 [Application Number 05/242,071] was granted by the patent office on 1974-01-01 for apparatus for the optical-electrical scanning of a drawing having a large number of points of different colors.
This patent grant is currently assigned to Firma Franz Morat GmbH. Invention is credited to Denes Nagy, Reinhold Oelmayer, Winfried Reif, Albert Seelos, Hans Joachim Stock.
United States Patent |
3,783,275 |
Oelmayer , et al. |
January 1, 1974 |
APPARATUS FOR THE OPTICAL-ELECTRICAL SCANNING OF A DRAWING HAVING A
LARGE NUMBER OF POINTS OF DIFFERENT COLORS
Abstract
Apparatus for scanning a drawing consisting of a large number of
points each of which is of a colour selected from a number of
colours, and for converting the information obtained by scanning
the points into colour signals characteristic of the individual
colours, comprising a scanning head movable relative to the drawing
having a number of optical electrical scanning elements each
responding to a definite spectral range and colour discriminators
connected to the scanning head for producing a respective colour
signal only when the analogous output signals of all the scanning
elements associated with it, or signals derived from the said
output signals, lie within an upwardly and downwardly limited
tolerance range.
Inventors: |
Oelmayer; Reinhold (Kaufbeuren,
DT), Seelos; Albert (Kaufbeuren, DT), Reif;
Winfried (Stuttgart-Rohr, DT), Nagy; Denes
(Plattenhardt, DT), Stock; Hans Joachim (Freiburg,
DT) |
Assignee: |
Firma Franz Morat GmbH
(Stuttgart, DT)
|
Family
ID: |
5805003 |
Appl.
No.: |
05/242,071 |
Filed: |
April 7, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Apr 17, 1971 [DT] |
|
|
P 21 18 720.2 |
|
Current U.S.
Class: |
250/226; 250/210;
358/515; 327/75 |
Current CPC
Class: |
G01J
3/46 (20130101); H04N 1/54 (20130101); G01J
3/51 (20130101) |
Current International
Class: |
G01J
3/46 (20060101); H04N 1/54 (20060101); G01j
003/34 () |
Field of
Search: |
;250/226,235,222,209,208
;88/14 ;307/290,235 ;356/173 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Low Cost Schmitt-Trigger made with Digital IC" by Francis et al.
Electronics Mar. 4, 1968 p. 88. .
"Level Detector . . . . Point" Electronic Design, Oct. 11, 1967 p.
98..
|
Primary Examiner: Dixon; Harold A.
Attorney, Agent or Firm: John Lezdey et al.
Claims
We claim:
1. Apparatus for scanning a drawing consisting of a large number of
points each of which is of a color selected from a number of
colors, and for converting the information obtained by scanning the
points into color signals characteristic of the individual colors,
comprising a scanning head movable relative to the drawing having a
number of optical-electrical scanning elements each responding to a
definite spectral range by producing analog output signals; at
least one electrical circuit coupled to said scanning elements for
producing derived signals by combining said output signals with
other signals; at least one color discriminator connected to said
electrical circuit, said discriminator producing a respective color
signal only when the derived signals of the electrical circuit
associated with it lie within an upwardly and downwardly limited
tolerance range; and means for upwardly and downwardly adjusting
the tolerance range.
2. Apparatus according to claim 1, including means for forming a
normalized "white" signal wherein the electrical circuits are
subtracting circuits for forming differential signals, the
differential signals being formed by subtraction of the analogous
output signals of the scanning elements from the normalized "white"
signal, and the derived signals being said differential
signals.
3. Apparatus according to claim 2, wherein one derived signal is
used for the dynamic regulation of the tolerance ranges of the
other derived signals and wherein only the other derived signals
are provided for forming the color signal.
4. Apparatus according to claim 1, wherein the electrical circuits
are first dividing circuits for forming first quotient signals, the
first quotient signals being formed by division of the analogous
output signals of at least one scanning element by the sum of the
analogous output signals of all the scanning elements, and the
derived signals being said first quotient signals.
5. Apparatus according to claim 1, wherein the electrical circuits
include first dividing circuits for forming first quotient signals,
said first quotient signals being formed by division of the
analogous output signals of at least two scanning elements by the
sum of the analogous output signals of all the scanning elements,
and further including subtracting circuits and second dividing
circuits for producing second quotient signals, the second quotient
signals being proportional to the slope of a line formed by two
definite points in the color triangle, one of these points being
fixed by the color of the background and the other point by the
color to be recognized, and the derived signals being said second
quotient signals.
6. Apparatus according to claim 5, wherein there is associated with
the second dividing circuit a means for detecting selected output
signals of the second dividing circuit.
7. Apparatus according to claim 5, wherein there is associated with
the second dividing circuit a further device by means of which such
output signals of the second dividing circuit can be distinguished
which are associated with colors of the same slope but different
intensity.
8. Apparatus according to claim 1, the means for adjusting the
tolerance ranges being voltage dividers.
9. Apparatus according to claim 8, including means for selectively
applying a fixed stabilized voltage to at least one of all the
voltage dividers.
10. Apparatus according to claim 9, including a switch by means of
which to one end of all the voltage dividers of a color
discriminator can be supplied a derived signal.
11. Apparatus according to claim 1, each derived signal being
supplied to two connected inputs of a pair of comparators, to the
other inputs of which are connected the taps of a voltage divider
for upwardly and downwardly adjusting the tolerance range.
12. Apparatus according to claim 11, wherein each comparator is
followed by a verification element which indicates the presence or
non-presence of an output signal at the comparator.
13. Apparatus according to claim 11, wherein each color
discriminator has an AND element coupled to said comparators for
producing the color signal.
14. Apparatus, according to claim 1, including means for measuring
the analog output signals at the scanning elements.
15. Apparatus according to claim 1, including preamplifiers with
variable amplification factors connected between each scanning
element and the color discriminator.
16. The apparatus according to claim 1, wherein there are provided
three scanning elements for the colors blue, green and red.
17. Apparatus for scanning a drawing consisting of a large number
of points each of which is of a color selected from a number of
colors, and for converting the information obtained by scanning the
points into color signals characteristic of the individual colors,
comprising a scanning head movable relative to the drawing having a
number of optical-electrical scanning elements each responding to a
definite spectral range; preamplifiers with variable amplification
factors coupled to said scanning elements; color discriminators
connected to the preamplifiers for producing a respective color
signal only when the analogous output signals of all the
preamplifiers associated with it lie within an upwardly and
downwardly limited tolerance range; and means for upwardly and
downwardly adjusting the tolerance range.
18. The apparatus according to claim 17, wherein said
discriminators include pairs of comparators, two inputs of the
comparators of each pair being connected and also connected to a
preamplifier and the other inputs of the comparators of each pair
being connected to the taps of a voltage divider for upwardly and
downwardly adjusting the tolerance ranges; and wherein the outputs
of said comparators are connected to the inputs of an AND gate
which produces a color signal only when all comparators produce an
output signal.
19. The apparatus according to claim 18, including means for
selectively applying a fixed stabilized voltage to at least one end
of all the voltage dividers.
20. The apparatus according to claim 18, including a switch for
selectively applying to at least one end of all the voltage
dividers a fixed stabilized voltage or the output of one of the
preamplifiers, respectively.
Description
The invention concerns apparatus for the optical-electrical
scanning of a drawing consisting of a large number of points each
of which is of a colour selected from a number of colours, and for
the conversion of the information obtained by scanning the points
into electrical colour signals characteristic of the individual
colours.
Apparatus of this kind is known for example from British Pat.
specifications Nos. 1,170,947 and 1,190,600, and comprises a
scanning head movable relative to the drawing and having a number
of optical-electrical scanning elements, each responsive to a
definite spectral range, and which are followed by colour
discriminators for the production of a respective colour
signal.
A serious disadvantage of such apparatus is that for producing the
drawing only very definite colours may be used in order to permit
clear and reproducible recognition of these colours. Also when the
quality of the colour applied to the drawing paper fluctuates
considerably or when, owing to poor covering power of the colour,
the generally white colour of the drawing paper shows through with
varying intensity the apparatus is liable to operate incorrectly.
It is in fact also already known from British Pat. specification
No. 1,190,600 to eliminate partly by dynamic regulation the errors
caused by fluctuations in the illumination intensity and/or the
distance of the scanning head or the source of light from the
drawing being scanned, but the number of usable colours is not
thereby increased.
In the known apparatus, the scanning head comprises for example
three phototransistors, in front of each of which is placed a
respective colour filter (for example blue, green and red) and each
of which is followed by an amplifier. By adjusting the threshold
value of these amplifiers, it is possible, if definite colours are
used (for example blue, green and red), to ensure that in scanning
these colours only one of the amplifiers delivers an output signal
and thus produces a definite colour signal. In the use of a number
of similar colours (for example two different red colours),
however, difficulties occur because the reflection or transmission
maxima of the two similar colours may overlap, depending on the
colour application and colour covering power, in such a manner that
satisfactory recognition of the two colours is no longer possible.
The same difficulties arise if, for example, the colours blue,
green, red, turquoise, violet and yellow are used, because in this
case, it is necessary to ensure that the so-called mixed colours
turquoise, violet and yellow have high reflection or transmission
factors just where two of the individual colours blue, green or red
have a maximum.
Limitation to only a few colours is undesirable because, on the one
hand, the known apparatus is required for example in the knitting
and weaving arts, to prepare control strips for the electronic
control of knitting or weaving machines by means of which goods are
made, having a pattern identical with the scanned drawing and as
multicoloured as possible, and because, on the other hand, the
patterns drawn by the designer in the special colours frequently
give quite a different impression from the finished knitted or
woven goods, whose colours only in seldom cases agree with the
colours required for the drawing.
According to this invention there is provided apparatus for
scanning a drawing consisting of a large number of points each of
which is of a colour selected from a number of colours, and for
converting the information obtained by scanning the points into
colour signals characteristic of the individual colours, comprising
a scanning head movable relative to the drawing having a number of
optical-electrical scanning elements each responding to a definite
spectral range and colour discriminators connected to the scanning
head for producing a respective colour signal only when the
analogous output signals of all the scanning elements associated
with it, or signals derived from the said output signals, lie
within an upwardly and downwardly limited tolerance range. The
tolerance ranges are preferably upwardly and downwardly
adjustable.
The invention provides the important advantage that any two colours
can be differentiated from each other by means of a single scanning
element if their tolerance ranges do not overlap. For increasing
the accuracy, reproducibility and number of the colours used,
however, for scanning each one colour there are used for example
three scanning elements each having three associated tolerance
ranges, so that each colour is recognised when the output signals
of the three scanning elements lie in the three fixed tolerance
ranges. It is sufficient, therefore, if the output signals of at
least one scanning element are associated with different tolerance
ranges.
In an advantageous embodiment of the invention, the scanning
elements are followed by subtracting circuits for forming
differential signals, the differential signals resulting from the
subtraction of the analogous output signals of the scanning
elements from a normalised "white" signal.
The formation of differential signals is considered expedient for
the following considerations. It will be assumed that three
scanning elements are provided by means of which the blue, green
and red proportions of a colour drawn on a white background are
measured, and that the scanning elements are followed by
preamplifiers which in the scanning of the white background lead to
normalised output signals of + 1 volt. If with the three scanning
elements a colour is scanned, which with full covering power, i.e.,
when the white backing does not show through, produces output
signals of 0.2 volt for the blue portion, 0.6 volt for the green
portion and 0.9 volt for the red portion, then in the case of half
the covering power, i.e., when the white ground colour half shows
through, these signals amount to about 0.6, 0.8 and 0.9 volt
respectively. In the case of no covering power at all, i.e., when
practically only the white background colour shows through, these
signals on the contrary amount to + 1 volt each. The differences
between the said output signals with full covering power and the
normalised "white" voltage is therefore 0.8, 0.4 and 0.1 volt
respectively and in the case of half the covering power, on the
contrary, 0.4, 0.2 and 0.05 volt, respectively. In the case of both
full covering power and half the covering power, the differential
signals are in the proportions 100:50:12.5, whereas the analogous
output signals in the case of full covering power are in the
proportions 22:66:100 and in the case of half the covering power
they are in the proportions 63:84:100. The ratios of the
differential signals, therefore, remain practically constant,
despite the different covering powers, so that different degrees of
covering power have no substantial influence, whereas the ratios of
the analogous output signals vary relatively considerably, so that
the tolerance ranges would have to be made so wide that only a few
colours could be used side by side.
In a further preferred embodiment of the invention, the scanning
elements are followed by dividing circuits for forming quotient
signals, the quotient signals from the division of the analogous
output signals of at least one scanning element being given by the
sum of the analogous signals of the scanning elements. This circuit
offers the advantage that fixed factors, resulting for example from
fluctuations of temperature, mains voltage, air humidity or for
example by ageing, become negligibly small after division and cause
only small errors. The quotient method, in addition, has the
advantage that with the use of three scanning elements sensitive to
blue, green and red, in general only the quotient signals of two
scanning elements need be evaluated, because the sum of all three
quotient signals is always unity.
Finally, a particularly preferred embodiment of the invention is
provided by the dividing circuits being followed by further
subtracting and dividing circuits for forming quotient signals, the
quotient signals being proportional to the slope of a line through
two points in the colour triangle, and one of these points being
fixed by the colour of the background and the other by the colour
to be recognised. This circuit has the advantage that relatively
narrow tolerance ranges can be assigned to the slopes of the
colours, which in the colour triangle are theoretically equal for
all possible degrees of covering power, so that the number of
usable colours is very large.
The invention will be described in more detail, by way of example,
with reference to the accompanying drawings, in which:
FIG. 1 shows apparatus embodying the invention for ensuring
recognition of a number of colours;
FIG. 2 shows diagrammatically the tolerance ranges of a number of
colours scannable by means of three scanning elements;
FIG. 3 shows part of an embodiment of the invention for the
production of differential signals;
FIG. 4 shows a circuit arrangement, modified in comparison with
FIG. 1, for varying the tolerance ranges;
FIGS. 5 and 6 show part of embodiments of the invention for the
production of quotient signals; and
FIG. 7 shows diagrammatically the incorporation of all colours in a
colour triangle.
In the embodiment of the invention shown in FIG. 1, of which only
the parts essential for understanding are shown, altogether three
scanning elements 31b (blue channel), 31g (green channel) and 31r
(red channel) are provided, which for example may consist of
photocells, photodiodes or phototransistors, and are accommodated
in a scanning head, not shown, which can be moved relative to the
drawing to be scanned, also not shown.
The drawing consists for example of white squared paper, the
squares being filled in with different colours, so that a pattern
of the type of a screen pattern is produced. Between the drawing
and the scanning elements 31, there are provided, also within the
scanning head, colour filters or dichroic mirrors, so that there
impinges on each scanning element only the light of a relatively
narrow spectral range (for example, blue, green, and red).
Connected to the outputs are the three inputs of a number of colour
discriminators 411, 412 and 413 of which only the colour
discriminator 411 is shown in detail in FIG. 1. Connected to each
input is an operational amplifier 33, connected as non-inverting
preamplifier, to the negative input of which there is connected a
voltage divider 35,37 having a fixed and an adjustable resistance,
by means of which the amplification factor of the preamplifier 33
can be adjusted. The outputs of the preamplifiers 33 can be
connected by means of a push switch 38, individually or jointly, to
voltmeters 39, it being assumed that the points B1 and B2, G1 and
G2 and R1 and R2, respectively, are in each case connected
together. For ease of description, the suffixes b (blue), g (green)
and r (red) will be omitted from reference numerals where the
description applies to all three channels.
The colour discriminators comprise as essential parts three
comparators 43b1, 43b2 and 43g1, 43g2 and 43r1, 43r2, respectively,
and an AND element 451, whose six inputs are connected to the
outputs of the six comparators 43. The comparators consist of
antiparallel-connected differential amplifiers having two inputs.
The output of the preamplifier 33b is connected to the inverting
input of the comparator 43b1 and to the non-inverting input of the
comparator 43b2, the output of the preamplifier 33g is connected to
the inverting input of the comparator 43g1 and to the non-inverting
input of the comparator 43g2, and finally the output of the
preamplifier 33r is connected to the inverting input of the
comparator 43r1 and to the non-inverting input of the comparator
43r2.
Furthermore, there is associated wth each group of comparators
43b,g,r, a respective voltage divider 47,48,49,50, each voltage
divider having an adjustable resistance 49. The positive ends of
these voltage dividers are connected to the output of an
operational amplifier 51, connected as non-inverting amplifier,
while their negative ends are earthed. The positive inputs of the
comparators 43b1, 43g1 and 43r1 are in each case connected to the
junction of the resistances 47 and 48, while the negative inputs of
the comparators 43b2, 43g2 and 43r2 are connected in each case to
the junction of the resistances 49 and 50.
The operational amplifier 51 is connectable by its non-inverting
input, by way of the contact 4 of a switch 53 and two resistances
55 and 57, to the positive terminal of a battery. The junction of
the resistances 55 and 57 is earthed via a Zener diode 59, whose
anode is connected by a resistance 61 also to the contact 4 of the
switch 53. The inverting input of the operational amplifier 51 is
connected to the tap of a voltage divider 63,65, by means of which
the operational amplifier 51 is adjusted to a fixed amplification
factor of 2 for example. The resistances 55,57 and 61 thus reduce
the positive working voltage to a voltage, stabilised by the Zener
diode, of for example 4 volts which, in the position of the switch
53 shown in FIG. 1, results in a potential of 8 volts at the output
of the operational amplifier 51. The non-inverting input of the
operational amplifier 51 may, however, be connected by means of the
switch 53 (positions 1, 2 or 3) also directly to an output of the
preamplifiers 33.
The outputs of the comparators 43 are connected by suitable
decoupling elements to the base of respective switching transistors
67, in whose collector-emitter circuits are connected respective
lamps 69, indicated merely diagrammatically in FIG. 1.
The mode of operation of the arrangement described is as follows.
First of all, a point of the drawing is brought below the scanning
head such that it is fully covered by the three scanning elements
31. According to the colour of the point under the scanning head,
there is obtained equal or different portions of the spectral
ranges associated with the scanning elements 31, this being shown
by the potentials of different magnitudes at the outputs of the
preamplifiers 33. The switch 53 is in position 4, so that a
potential of 8 volts is applied to the positive ends of the voltage
dividers 47 to 50.
On the assumption that the resistances 47,49 and 50 all have for
example a value of 10 k.OMEGA., while the resistances 48 have a
value of 0.82 k.OMEGA., the non-inverting inputs of comparators
43b1, 43g1 and 43r1, by adjustment of the resistances 49, can be
connected to potentials of between about 4.16 and 5.40 volts, while
the inverting inputs of the comparators 43b2, 43g2 and 43r2 are
connected correspondingly to potentials of between about 3.84 and
2.60 volts. Consequently, the comparators 43b1, 43g1 and 43r1
deliver output signals only when the output potentials of the
preamplifiers 33 lie below a maximum potential of from 4.16 to 5.40
volts, while the comparators 43b2, 43g2 and 43r2 deliver output
signals only when the output potentials of the preamplifiers 33 lie
above a minimum potential of 3.84 to 2.60 volts.
In the adjustment of the colour discriminator 411, the resistance
49b is first adjusted to "zero" value, so that the output potential
of the amplifier 33b must lie between 3.84 and 4.16 volts if both
lamps 69b are to light up. If the colour portion associated with
the scanning element 31b is relatively small, the output potential
of the preamplifier 33 is increased by means of the resistance 37b
until it lies in the said tolerance range of 4 volts .+-. 2 percent
and the lamps 69b light up. The same adjustment is then made with
the preamplifiers 33g and 33r until finally the lamps 69g and 69r
also light up. Lighting up of all the lamps means that there occurs
at the output of the AND element 451 a colour signal which is
characteristic of the colour under the scanning head.
Normally, in scanning each point of the drawing with the same
colour, a colour signal ought now to occur at the output of the AND
element 451. Owing to the different colour covering power and the
different colour application, however, in practice this is only
rarely the case within the said tolerance limits of .+-. 2 percent.
Consequently, for adjusting the colour discriminator 411 with the
three scanning elements 31. preferably a number of points of the
same colour with particularly good and particularly poor properties
are picked up and the tolerance ranges are adjusted by means of the
resistances 49 such that scanning of all points of the same colour
leads to a colour signal at the AND element 451, which can be
checked by the lighting up of the lamps 69. According to
requirement or experience, the output potential of the
preamplifiers can be applied by means of the resistances 37 to the
middle of the tolerance range or can be adjusted
unsymmetrically.
The outputs of the scanning elements 31 may be connected to a
number of colour discriminators 412, 413, etc., which are of the
same construction as the colour discriminators 411. These further
colour discriminators in FIG. 1 are shown diagrammatically in block
71, which for example has seven outputs, which together with the
output of the AND element 451 are connected to the eight inputs E1
to E8 of a logical circuit 73 in which a definite code signal can
be formed for each colour. The seven colour discriminators
accommodated in block 71, as was described above with reference to
the colour discriminator 411, are adjusted to points having other
colours, whereby correspondingly other tolerance ranges are
obtained. If a number of colour discriminators 411, 412, 413, etc.,
are used, it is sufficient if these differ from each other in at
least one tolerance range. The tolerance ranges may be of different
sizes, especially also within the same colour discriminator, and
for the weak colour portions may be larger than for the strong
colour portions.
FIG. 2 indicates diagrammatically the possibilities for colour
scanning presented by the use of the apparatus described with
reference to FIG. 1. There are indicated along the ordinate at the
wavelengths 4,200, 5500 and 6,800 A tolerance ranges to which the
three scanning elements 31 in different colour discriminators are
adjusted, as expressed by the potentials at the inputs of the
preamplifiers 33 with the tolerances ranges referred back to the
said potentials. The ranges I to IV combine with the ranges V to
VIII to form a plurality of scannable colours, the lengths A to M
always indicating the tolerance ranges.
For example, let the ranges I and V be associated with the colour 1
and the range I and VII be associated with the colour 2. This would
mean that the colour discriminators 411 and 412 associated with
these colours have two common tolerance ranges, i.e., A and D,
which however clearly differ from each other in the third tolerance
range F or H. In the circuit diagram shown in FIG. 1, this means
that the comparators 43b and 43g respond in the scanning of colour
1 and also in the scanning of colour 2, while the comparators 43r
in the case of one colour discriminator respond only in scanning of
the colour 1 and in the case of the other colour discriminator,
respond only on scanning of the colour 2, so that only one colour
is associated with each colour discriminator.
It follows further from FIG. 2 that colours, which for example are
composed from the ranges III, V; III, VII and IV, VIII can also be
used very well side by side, since they differ relatively strongly
from one another in at least one tolerance range. On the other
hand, the colours composed for example from the ranges I, VI or II,
V or II, VII cannot be scanned so well side by side, although they
also differ from one another in at least one tolerance range. In
the case of these colours, however, slight fluctuations in
illumination or fluctuations in the scanning head/drawing distance
or illumination lamp/drawing distance can lead to overlapping of
the tolerance ranges and hence to errors.
To remove this disadvantage also, an adjustment is provided which
ensures that such fluctuations act in the same proportion on all
existing comparators 43, so that the relative distance of the
tolerance ranges is maintained. As shown in FIG. 1, switch 53 after
calibration of the colour discriminator 411 can be switched to one
of the contacts 1, 2 or 3, whereby instead of the stabilised
potential of 4 volts, a potential is now applied to the positive
ends of the resistances 47 which is dependent on the output
potential of one of the preamplifiers 33. By operating the push
switch 38, it is possible to ascertain how the output potentials of
the preamplifiers 33 behave in the said fluctuations. According to
this behaviour, after calibration is concluded, switch 53 can be
switched over to the output of the desired preamplifier 33, so that
in the case of subsequent fluctuations during scanning, the
tolerance ranges are also correspondingly shifted, and the output
potentials at the preamplifiers 33 remain in the adjusted tolerance
range despite possible considerable fluctuations. It will often be
preferable to switch the switch 53 to the output of that
preamplifier 33 which delivers the strongest output signal for the
same adjustment of the resistances. The effect of the adjustment is
shown by line K2 in FIG. 2, which indicates the shift of the line
K1, drawn through the centres of the tolerances ranges C, E and H,
when the amplification is increased.
FIG. 3 shows a device whereby it is not the analogous output
signals delivered by the preamplifiers 33, but signals derived from
the said output signals which are associated with the tolerance
range described with reference to FIG. 1, the derived signals being
defined as differential signals between normalised "white" signals
and the output signals of the preamplifiers 33.
For forming the differential signals, subtracting circuits 75 are
provided as shown in FIG. 3, the points B3, G3 and R3 of the
circuit of FIG. 3 being connected to the points B1, G1 and R1, and
the points B4, G4 and R4 of the circuit of FIG. 3 being connected
to the points B2, G2 and R2 of the circuit of FIG. 1. The outputs
of the preamplifiers 33 are in this way connected to inputs of a
respective store unit 77, to whose other inputs timing signals are
supplied by a lead 79. The outputs of the store units 77 are
connected to resistances 81, whose other ends are connected in
common to the inverting input of an operational amplifier 83, and
in addition are connected to the output of the latter by a
resistance 85. The non-inverting input of the operational amplifier
83 is earthed. The junctions between the store units 77 and the
resistances 81 are connected to the contacts 1 of three switches
87, which are switchable in common. The movable contacts of these
switches 87 are each connected to a respective voltmeter 89, the
other sides of which voltmeters are earthed.
The output of the operational amplifier 83 is connected to a
voltage divider of each of the subtracting circuits 75. Each
voltage divider comprises three series-connected resistances 91, 93
and 95, the resistances 95 being adjustable in common and being
connected by their free ends to the outputs of respective
amplifiers 97. The outputs of the preamplifiers 33 and the
junctions of the resistances 91 and 93 are connected to the
inverting inputs of the operational amplifiers 97 by resistances
99b, 99g and 99r, while their non-inverting inputs are earthed. The
outputs of the operational amplifiers 97 lead on the one hand
through the points B4, G4 and R4 to the comparators 43 (FIG. 1)
and, on the other hand, can be connected either to a further set of
voltmeters or by matching circuits, not shown, to the contents 2 of
the switches 87, so that the output signals of the operational
amplifiers 97 can also be measured by means of the voltmeters
89.
The device described operates as follows. Before commencing
automatic scanning of the drawing, the scanning elements 31 (FIG.
1) are adjusted to a white point of the drawing. This corresponds
to a condition which always arises when a colour, for example blue,
has been applied so thinly to the background that its covering
power may be equated to a minimum value of "zero." The inputs of
the store units 77 are thus supplied with analogue signals which in
scanning, give a white point. For storing these signals, a key may
be provided, on the operation of which, timing signals are supplied
to the store units by the lead 79. The output signals of the store
units 77 are then increased or decreased by adjustment of the
resistances 37 until all three voltmeters 89 give a full deflection
or, if they are calibrated in percentages, stand at 100 percent. A
voltage of exactly + 1 volt may correspond for example to this
value of 100 percent.
The potentials adjusted at the outputs of the three storage units
77 are averaged by means of the three resistances 81. The averaged
potential is inverted by the operational amplifier 83 so that a
voltage of, for example, exactly - 1 volt appears at its output if
the ratio of the resistance 85 to the parallel circuit of the
resistances 81 is equal to 1:1.
The second extreme condition is then adjusted by the scanning
elements 31 being directed to one of the colour points having
optimum covering power associated with the said colour
discriminator, at which point, therefore, the white colour of the
background shows through as little as possible. For this case,
there appears at the outputs of the preamplfiers 33 analogue
signals which, in the embodiment of FIG. 1, would lie within the
tolerance ranges adjusted for the corresponding colour
discriminator. In the embodiment of FIG. 2, however, it is not
these positive signals but their differential signals which are
used for the "white" signals stored in the store units 77. The
formation of the differential signals is obtained by supplying to
the inverting input of the operational amplifiers 97, on the one
hand, directly those analogue signals corresponding to the colour
portions of the colour just scanned, and on the other hand, by way
of the resistances 91, the inverted "white" signals formed at the
output of the operational amplifier 83, while at the same time the
output signals of the operational amplifiers 97 are returned by way
of the adjustable resistances 95 and the resistances 93 also to the
inverting inputs of the operational amplifiers 97. Potentials are
formed, therefore, at the outputs of the operational amplifiers 97
which compensate by countercurrents the currents flowing through
the resistances 91 to the amplifier inputs, the said
countercurrents flowing through the resistances 93 as long as no
signals are applied to the preamplifiers 33. If resistances 91 and
93 with values of 10 k.OMEGA. each are used, there is formed at the
resistances 93 a voltage of + 1 volt corresponding to the positive
"white" voltage. If, on the contrary, for example a potential of +
0.2 volt is applied to the point B3 and if the resistance 99b is
also 10 k.OMEGA., the countercurrent to be supplied by the output
of amplifier 97b is reduced by the current flowing through the
resistance 99b, so that at the resistance 93b there is now only a
voltage drop equal to the difference between the "white" voltage
and the voltage at the point B3, and in the said example amounts to
+ 0.8 volt.
The potentials appearing at the output of the three operational
amplifiers 97 are measured and compared with one another by means
of the voltmeters 89. The maximum potential at the three amplifier
outputs, by adjustment of the resistance 95, which fixes the
amplification factor of the operational ampliifer 97, is brought to
an arbitrarily normalised value of 100 percent, which in the
example selected amounts to + 1 volt at the output of the operation
amplifier 97b. In the example selected, therefore, after the
normalising process, all operational amplifiers 97 have an
amplification factor of 1.25, since the three resistances 95 are
coupled mechanically together. Advantageously, the voltmeters 89
are calibrated in percentages, so that the value of 100 percent can
be read off directly on the voltmeter 89b.
The outputs B4, G4 and R4 of the circuit of FIG. 3 are connected to
the inputs of the comparators 43. In using the circuit of FIG. 3,
therefore, a signal will always appear at the output of the AND
element 451 when the conditions of the three differential signals
are in a certain ratio to one another.
In a further embodiment of the invention, the points B4, G4 and R4
are not connected to the points B2, G2 and R2 of the circuit of
FIG. 1, but to the points B5, G5 and R5 of the circuit of FIG. 4.
According to FIG. 4, the point B5 is connected to the non-inverting
input of an operational amplifier 101 and in addition by a
resistance 103 to the inverting input of an operational amplifier
105, whose non-inverting input is earthed and whose output is
connected to its inverting input by a resistance 106. The inverting
input of the operational amplifier 101 is earthed by a resistance
107 and is connected to its output by a resistance 109. The outputs
of both operational amplifiers 101 and 105 are connected together
by two leads 111 and 113, which, as shown in FIG. 4, are connected
together by four pairs of resistances 115,117; 119,121; 123,125;
127,129. The resistances 117, 119, 125 and 127 have an adjustable
tap. The taps of resistances 117 and 125 are connected respectively
to the non-inverting inputs of comparators 131 and 133 and the
tappings of the resistances 119 and 127 are connected to the
inverting inputs of comparators 135 and 137, respectively. The
inverting inputs of the comparators 131 and 133 and the
non-inverting inputs of the comparators 135 and 137 are connected
to the points G5 and R5, respectively.
The outputs G6, G7, R6 and R7 of the comparators lead by means of
suitable switching circuits to the AND element 451 (FIG. 1), which
gives an output signal when the differential signal supplied to the
inputs G5 and R5 lie within the tolerance ranges adjusted at the
resistances 117, 119, 125 and 127.
As distinct from FIG. 1, in thee circuit of FIG. 4, the tolerance
ranges can be adjusted independently of one another and
independently of the centre of the tolerance ranges. In addition,
only two groups of comparators are provided, while the strongest
output signal at the output of the amplifiers 97, in the example
selected the output signal of the operational amplifier 97b, is
supplied to the two amplifiers 101 and 105. The end voltages of the
tolerance ranges are fixed by the output signals of the two
operational amplifiers 101 and 105, in a manner similar to that
whereby this is achieved by the operational amplifier 51 in the
circuit of FIG. 1. The operational amplifiers 101 and 105,
therefore, undertake regulation, i.e., for the case where the
potential at the point B5 has not reached or has exceeded the
normalised value of 100 percent, the end voltages of the tolerance
ranges are varied accordingly. If, for example, in the case of
illumination which is too weak, the differential signal at the
point B5 is only 50 percent of the normalised value, the end
potentials of the tolerance ranges will be correspondingly 50
percent lower.
The adjustable resistances 117, 119, 125 and 127 are advantageously
calibrated in percentages and have such values that the tolerance
ranges of the two differential signals appearing at the inputs G5
and R5 can be adjusted relative to the strongest signal at the
input B5 between about 0 and 150 percent at the resistances 117 and
125 or between about -50 and +100 percent at the resistances 119
and 127.
Finally, in the embodiment of FIG. 4, as in the embodiment of FIG.
1, three groups of comparators may likewise be provided. In that
case, however, the signal appearing at the point B5 would have to
be regulated, by an additional regulating circuit, to a constant
value of 100 percent, as is described for example in British Pat.
specification No. 1,190,600. Finally, suitable switches may be
provided for always connecting to the point B5 the strongest output
signal of the three operational amplifiers 97.
A further embodiment of the invention is obtained if the points B1,
G1 and R1 are connected to the points B8, G8 and R8 of the circuit
of FIG. 5, and its points B9 and G9 are connected to two of the
three points G2, B2 or R2 of the circuit of FIG. 1. The circuit of
FIG. 5 has as essential components two dividing circuits 139 and
141, as well as an adding circuit 143. The analogue signals
delivered by the preamplifiers are added in the adding circuit 143,
while the quotients of the signal delivered by a preamplifier and
the sum of signals delivered by all three preamplifiers is formed
in the dividing circuits 139, 141. The quotient signals appearing
at the points B9 and G9 are evaluated in FIG. 1 by groups, each
consisting of two comparators with an adjustable tolerance
range.
With FIG. 5, altogether only two groups of comparators are required
since the sum of the three quotient signals B/(B + G + R), G/(B + G
+ R) and R/(B + G + R) is always equal to 1, and this formula is
merely confirmed by the third group of comparators, but no
additional property of the scanned colour would be found.
The quotient formation precludes for example errors which, due to
external factors, such as temperature, illumination or voltage
fluctuations, are formed by variations in the absolute value of the
signals delivered by the preamplifiers. If it is assumed, for
example, that due to a variation in illumination, the output
signals of the preamplifiers 33 instead of the values B, G and R
have the values kB, kG or kR, where k is any constant which acts on
all three colour portions in substantially the same manner, then
this constant k is eliminated in the formation of the
quotients.
A further embodiment of the invention is obtained by connecting the
points B1, G1 and R1 of the circuit of FIG. 1 to the points B8, G8
and R8 of the circuit of FIG. 5, and the points B9, G9 and I of the
circuit of FIG. 5 to the points B10, G10 and I of the circuit of
FIG. 6. The point B10 is connected to a subtracting circuit 145 and
the point G10 to a subtracting circuit 147. In these subtracting
circuits 145 and 147, the differences between the quantities formed
according to FIG. 5, b = B/(B + G + R) and g = G/(B + G + R)
respectively and fixed base values are formed; the significance of
these quantities will be described later with reference to FIG. 7.
The output signals of the subtracting circuits 145 and 147 are
supplied to a dividing circuit 149, in which the absolute value of
the quotient (g - g.sub.B)/(b - b.sub.B) is formed.
The output signal of the dividing circuit 149 is evaluated by means
of two comparators 151 and 153 as in the embodiments described so
far, it being possible to fix at the point 155 the upper limit and
at the point 157 the lower limit of a tolerance range. By means of
an AND element 159 following the comparators, signals thus arrive
at one input of a further AND element 161 only when both
comparators 151 and 153 deliver an output signal, i.e., when he
output signal of the dividing circuit lies in the fixed tolerance
range.
There is supplied to a further input of the AND element 161 by way
of a switch 163 a positive output signal of a coding unit 165,
whose inputs are connected to the outputs of the subtracting
circuits 145, 147. There is ascertained by means of the coding unit
whether the differential signals formed in the subtracting circuits
145, 147 have a positive or negative sign.
In this way, it is possible to adjust manually whether the signal
appearing at the output F1 of the AND element 161, of which signal
only the absolute value is formed in the dividing circuit, should
have a positive value or a negative value. Thus, by means of the
circuit of FIG. 6 it is possible to recognize according to the
position of the switch 163 two colours with which are associated
signals having the same absolute value but different signs.
Finally, it is possible to supply to a third input of the AND
element 161 also the sum signal B + G + R, formed in the adding
circuit 143 (FIG. 5), by way of comparators 167 and 169 with
adjustable tolerance range, and by way of an AND element 171. It is
thereby possible to distinguish from one another colours whose
quotient signals have the same sign and the same absolute value,
but a different total intensity.
The mode of operation of the circuit described with reference to
FIGS. 5 and 6 follows from FIG. 7, showing diagrammatically the
usual colour triangle 173. Along the abscissa axis are plotted the
values r = R/(B + G + R) and on the ordinate axis the values g =
G/(B + G + R). The values of r and g give the red or green portion
of a colour point referred to the total intensity. Because b + g +
r = 1, the blue component b = R/(B + G + R) need not be considered
separately. The colour triangle 173 forms an area comprising all
possible colours and colour combinations. The colour triangle 173
in addition is enclosed by a line 175, along which the wavelength
of the colours is plotted between 4,000 and 7,000 A. The point
denoted by 177 with the coordinates r = 0.33 and g = 0.33 (and
correspondingly b = 0.33) corresponds to the colour white, or,
depending on the total intensity, different shades of grey up to
the colour black; white, black and grey points, therefore, can be
differentiated not by their position in the colour triangle, but
only by their total intensity (output I in FIG. 5). The point 177
is termed the base point.
If there is drawn on a white, grey or black background a colour
which leads to a point 179 on the line 175, this means that this
colour has been applied with optimum covering power, i.e., it
transmits or possesses an infinitesimally small "white" portion.
Substantially, the coordinates r = 0.44 and g = 0.56 are associated
with the point 179. If one advances from the point 179 towards the
base point 177, this means that the "white" portion of the colour
is constantly increased or the covering power of the colour becomes
even smaller, until finally at the point 177, the "white" portion
is practically 100 percent, or the covering power is practically
"zero." For the operation of the present apparatus, it is important
that over all possible degrees of covering power, i.e., from the
point 179 with the strongest covering power to the point 177 with
the weakest covering power, a straight line drawn for example
through the two points 177 and 179 with constant slope is
characteristic of each colour. The slope of these straight lines is
formed with the circuit of FIGS. 5 and 6, and is used for
recognising a definite colour.
To ensure that no errors can be produced by slight external
influences, a colour is recognised in FIGS. 5 and 6 when the
straight line associated with it in the colour triangle 173 lies
within a tolerance region 181. The quadrant in which the straight
line should lie is fixed by the coding unit 165, with reference to
the base point 177, since for example in the first quadrant a
yellow colour is obtained (tolerance range 181), in the third
quadrant, on the contrary, for the same value of the output signal
of the dividing circuit 149, a blue colour is obtained (tolerance
range 183).
Many modifications can be made to the apparatus described. More
particularly, the form of the different amplifier stages or
comparators, of the switches and verification or check elements
(e.g., lamps 69) is in itself optional, provided only that, for the
purpose of recognising a colour with certainty, at least one
variable tolerance range can be adjusted. Also the number of
scanning elements selected for each colour discriminator or the
number of colour discriminators themselves is freely selectable. In
individual cases, a single scanning element per colour
discriminator is in itself sufficient for distinguishing a number
of colours with certainty. According to FIG. 2, it is possible, for
example, to connect to a scanning element sensitive to "blue" three
colour discriminators with the tolerance ranges A, L and C. If
tolerance ranges narrower than .+-. 2 percent are desired, the
resistances 48 may be omitted. The lower tolerance limit can also
be fixed at 0 volt by switches which bridge the resistances 50.
The special advantage of all embodiments described is to be seen in
the fact that, on the one hand for making a drawing, a number of
colours with similar properties may be used, and on the other hand,
these colours may be selected from an almost unlimited number of
colours, without specific reflection or transmission factors being
required.
In the embodiments of FIGS. 4 to 6, which of the two colour
portions is used for evaluation is optional and in the individual
case depends on which colour portions lead to strong, readily
evaluatable signals. Thus, for example, in FIG. 4 it is indicated
that only green and red colour portions are evaluated, whereas
according to FIGS. 5 and 6 blue and green colour portions are
evaluated. In addition, it follows from the description of FIG. 7
that instead of using the values r and g, colour triangles are also
obtained with the values r and b or g and b. Furthermore, in the
embodiment of FIG. 3, the manner in which the timing signals
supplied over the lead 79 are produced depends on the device for
scanning the drawing. If, for example, this is a device according
to British Pat. specifications No. 1,170,947 or 1,190,600, it is
advantageous, after scanning a line of the drawing, to carry the
scanning head over the white margin of the background and at that
moment to produce a timing pulse by means of a contact, not shown.
If, on the contrary, the drawing to be scanned is clamped for
example to the periphery of a rotating drum, then also by means of
a suitable contact a timing pulse can be released when the scanning
head is situated over a part of the drum periphery covered by the
background but not by the pattern. In both cases, before renewed
scanning of a line, the "white" or "base" signal, characteristic of
the background used will thereby be stored in the store units 77
for the duration of the scanning of a line.
Finally, the apparatus is also not limited to the colour of the
background of the drawing. As follows from FIG. 7, in the circuits
of FIGS. 5 and 6, it is immaterial whether a white, grey or black
background is used. It is also possible to use a background with a
light blue, red or green undertone. In such cases, the base point
for example is shifted to the place marked 185 in FIG. 7, so that
only the zero point of the coordinate system selected is altered,
and the circuit of FIG. 6 has merely to be adjusted to a new base
point (b.sub.B, g.sub.B, r.sub.B). For this purpose, the
subtracting circuits 145, 147 have suitable potentiometers. A
correct adjustment always occurs when the output signals of the
subtracting circuits 145, 147 disappear when the background is
being scanned. In the circuit of FIG. 5, the colour of the
background plays no part because it is the intensities of the
individual colour portions, divided by the total intensity, which
are evaluated. In connection with the signals appearing at the
output I, there is finally the possibility of distinguishing
colours which certainly lie on the same straight lines in the
colour triangle according to FIG. 7, but are characterised by
different degrees of covering power or different mixtures with
white colour.
* * * * *