Note: Descriptions are shown in the official language in which they were submitted.
~3fi~
TITLE OF THE INVENTION
DOT PERCENTAGE MEASURING DEVICE
BACKGROUND OF THE INVENTION
This invention relates to dot percentage measuring
devices.
The shading of a continuous tone copy such as a
photograph is expressed by using dots different in si2e
in printing. In this method~ the continuous tone copy
is photographed through a screen or a contact screen to
obtain a film called a screen negative or a screen posi-
tive in which the shading of the copy is expressed by
dots different in size, and a printing plate is formed
from this film.
A term ~Idot percentage" as used herein is a
percentage of the total area of dots with respect to a
unitary area in such a screen positive or a screen nega-
tive or a ~ot-printed matter. Accordingly, the value of
dot percentage will greatly affect the tone and gradation
of a printed matter.
When an obtained dot percentage is different from
a predetermined one, it may be corrected by subjecting
the screen positive or the screen negative to "reduc-
tion" which is one of the methods of correcting a dot
percentage. In the reduction, the photographed film is
washed with a so-called "reducer" to reduce the density
of the picture. In the case of a dot-printed matter, a
portion around a dot, which is low in density and is
called "a fringe", on the film becomes transparent by
the reduction process; that is, the dot percentage is
decreased to correct the values of the printed matter.
Thus, in printing with dots, the dot percentage is one
of the important factors which determined the quality
of a printed matter, and accordingly it is essential to
control the dot percentage throughout the printing
process from makeup to printing.
In an off-set retouch process, it is necessary to
measure dot percentages after reduction has been carried
out, and to ensure the configurations of dots, especially
whether the dots are deformed or not.
In the case where the dot area becomes considerably
smaller by excessive reduction or where measurement
-- 2
result indicates smaller dots, it is necessary that the dots
are photographed again and are compared with the previous ones.
Heretofore, dots are, in general, evaluated by visual
inspection. However, the visual inspection is disadvantageous
in that it involves personal errors and therefore it is
necessary to provide a skilled person for the visual inspection.
Since halftone-photographed dots are soft dots including
fringes, the inspector will read the size of dots including
fringes through his sense of sight, and accordingly the size
of dots thus read is larger than the real size of dots.
Furthermore, although the data actually required in
reduction process is not the absolute value of dot percentaye,
but the amount of reduction representative of the difference
~etween the dot percentage before reduction and that after
reduction, no device for indicating the amount of reduction
i has been provided in the art yet.
SUMMARY OF THE INVENTION
The present invention contemplates an apparatus
to obtain a correct dot percentage and a correct amount of
reduction by simple operation thereby to improve work
efficiency in a printing process, and to correct the effect of
fringes on a dot film with respect to light transmittivity
thereby to obtain a measurement of value with high accuracy.
It is further desirable that the apparatus of the invention
provides a correction circuit simple in construction.
Therefore, in accordance with the present invention
there is provided a dot percentage or density measuring device
of a portable type which comprises a device body, a supporting
-- 3
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arm protruding from the device body; a light receiving
cylinder fixedly secured to the end portion the supporting
arm and having a lower end face which substantially coincides
with the lower surface of the device body, means for
converting light from the light receiving cylinder into an
electrical signal, the means being incorporated in the device
body, and the light being reflected light or transmitted
light. The device further includes a display device
incorporated in the device body for displaying electrical
signal as a dot percentage or density.
The characteristic features of the present invention
will become more apparent from the following detailed
description and the appended claims when read in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings: -
The part (A) of FIG. 1 is an explanatory diagramshown a conventional dot percentage measuring device;
The part (B) of FIG. 1 is also an explanatory
diagram for a description of the operation of the measuring
device shown in the part (A) of FIG. l;
FIG. 2 is a graphical representation indicating
measurement values obtained according to a conventional
correction method;
FIG. 3 and FIG. ~ are graphical representations
each indicating light transmittivity with amount of correction;
FIG. 5 is a perspective view showing one example
of a dot percentage measuring device according to this
invention;
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Fl~. 6 is an explanatory diagram, partly as a
block diagram, showing the internal arrangement of the
measuring device shown in FIG. 5;
FIG. 7 is a perspective view showing another example
of the dot percentage measuring device according to the
invention, in which a reduction amount indicating device
is additionally provided;
FIG. 8 and FIG. 9 are explanatory diagrams, partly
as block diagrams, showing examples of the internal
arrangement of the measuring device shown in FIG. 7,
respectively;
FIG. 10 is an explanatory diagram showing another
example of the dot percentage measuring device according
to the invention;
FIGS. 11 through 14 are perspective views showing
various examples of the measuring device according to
the invention;
FIG. 15 is a sectional view taken along line V-V
in F,IG. 11;
FIGS. 16(A), 16(B) and 16(C) are vertical
sectional views showing different examples of a light receiving
cylinder;
FIGS. 17 and 18 are sectional views showing
modifications of a light receiving cylinder in FIG. 11;
FIG. 19 is a block diagram showing a signal
processing circuit;
FIG. 20 shows a positive and negative switching
circuit;
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FIG. 21 is a graphical representation optical
wavelength with light transmittivity;
FIGS. 22 through 25 are diagrams for a description
of a correction principle according to this invention;
FIG. 26 is an explanatory diagram showing another
example of the measuring device according to the invention;
FIG. 27 is a circuit diagram showing a part of the
measuring device shown in FIG. 26;
FIG. 28 through FIG. 30 are graphical representations
for a description of the operation of the measuring device
shown in FIG. 26;
FIG. 31 is a graphical representation indicating
relati.onships between dot percentages with light transmittivities
and errors in actual measurement value;
FIG. 32 is an explanatory diagram showing another
~'~ example of the measuring device according to the invention;
.FIG. 33 is a circuit diagram showing one example
of an optical detector employed in the measuring device
shown in FIG. 32;
FIG. 34 is a block diagram showing one example of
a correction circuit employed in the present invention;
FIG. 35 and FIG. 36 are explanatory diagrams
showing other examples of the measuring device according to
the invention;
FIG. 37 is a block diagram showing another example
of the correction circuit employed in the invention;
FIG. 38 is a graphical representation indicating
relationships between dot percentages and errors in actual
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measurement value in the correction circuit shown in FIG. 37;
FIG. 39 and FIG. 41 are block diagrams showing
other examples of the correction circuit employed in the
invention, respectively; and
FIG. 40 and ~'IG. 42 are graphical representations
sfiowing the correction characteristics of the correction
circuits shown in FIGS. 39 and 41, respectively.
A conventional dot percentage measuring device of
this type is shown in the part (a) of FIG. 1. A light
emitting section 3 is provided inside a measuring table 2
on which an object 1 to be measured such as a film is placed,
and a light receiving section 4 is movably provided above
the measuring table 2 in such a manner that it can confront
the light emitting section 3. The light receiving section 4
is made up of a cylindrical head 4a which is open at one end,
and a light receiving element 4b such as a photo-electric
conversion element. In measuring a dot percentage with this
conventional measuring device, the object 1 to be measured
is placed on the measuring table 2, and a portion to be
measured of the object 1 is positioned at the measuring section
of the device (or on the line connecting the light emitting
section 3 and the light receiving section 4). Then, the light
receiving section 4 is lowered in the direction of the heavy
arrow P to confront the light emitting section 3 as shown in
the part (B) of FIG. 1, so that the upper opening edge of the
head 4a is in close contact with the portion to be measured
of the object 1. Under the conditions that the external light
is shielded, the light emitting section 3 emits predetermined
light to irradiate the lower surface of the object 1 in the
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direction Or the sllor-ter arrow Q shown in the part (B)
of FIG. 1 so that the light receiving element 4b in the
light receiving section 4 receives l~ght passed
through the object 1, and the dot percentage of density of
the object 1 is displayed by a display section (not shown)
connected electrically to the light receiving element 4b.
However, the conventional measuring device is
disadvantageous in the following points: The construction
of the measuring device is intricate because the device is
so designed that the light receiving section is movable
towards the light emitting section as was described above.
The operation of the measuring device is intricate and
accordingly troublesome because positioning the measurement
portion of the object 1 must be carried out before measurement
and the upper opening edge of the head 4a must be brought into
close contact with the measurement portion of the object 1.
Therefore, in the case where a dot percentage of density
measured should be corrected by reduction, it is necessary to
carry out the following steps: After the object 1 is removed
from the measuring table 2 and is subjected to reduction
process by using a washing table or the like, the object 1
must be placed on the measuring table 2 again. ~his will
increase labor and decrease work efficiency.
Measurement o~ a dot percentage is carried out in
the processes of halftone photography and development also.
The dot percentage measurement can be carried out with the
aforementioned conventional measuring device; however, the
conventional measuring device is not suitable for frequently
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performing the measurement for the following reasons: Since
the llght measuring section of the conventional device is
provided at the lower portion of the case thereof, the light
measuring section is out of the operator's field of vision,
which makes it difficult to place the light measuring section
at a portion to be measured of an object. A film density
may be measured by per-forming the positioning only once;
however, in measuring a do-t percentage as described above,
the operator has to take an uncomfortable position to direct
the light measuring section to the portion to be measured. This
is undoubtedly troublesome for the operator.
Two practical methods of measuring a dot percentage
have been known in the art. In the first method, the shading
of a dot film is converted into an electrical signal by means
of, for instance, a vidicon to measure the area of a portion
of the film where the density is higher than a predetermined
value, thereby to measure the dot percentage. In the second
method, the light transmittivity of a portion to be measured
of the dot film is measured to obtain the dot percentage. The
first method is advantageous in that it is not affected by
fringes around dots and therefore its measurement can be
achieved theoretically with high accuracy; however, it is
disadvantageous in that the measuring device is bulky and
expensive, and therefore not practical. The second method
is also disadvantageous in that it is greatly affected by the
fringes, and therefore errors are liable to be involved in
measuring a halftone-photographed film having a large fringe
area.
In general, the error due to the fringe is small or
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zero with dot percentages about 0% and about 100~ and great
with a dot percentage about 50~. In order to correct this
error, in the second method, the multiplying factor of the
display section is finely adjusted, or transmission light to be
measured is subjected to photo-electric conversion, and then the
amplification factor of the resultant electrical signal is
finely adjusted. In this correction method, a film having a
known dot percentage, preferably about 5%, is prepared, and the
fine adjustment is carried out so that the measurement value
of the film coincides with the known value. With the film
subjected to this correction, the errors due to the fringe are
relatively satisfactorily corrected with dot percentages about
0~ and about 100%, but they are still great with a dot
percentage about 50~, as indicated in FIG. 2. The relation
of the dot percentage to the light transmittivity is not linear
because of the influence of fringes, that is, it is expressed
p
by a characteristic curve which is curved in the vicinity of
50~ as shown in FIGS. 3 and 4. Nevertheless, the conventional
correction method assumes that the relation of the dot
percentage to the light transmittivity is linear, and performs
fine adjustment of this straight line slope. Accordingly, in
the conventional correction method, a relatively great error
remains in the vicinity of 50% when referred to the errors at
dot percentages 0% and 100%.
When a dot film is subjected to reduction by using
an iron chelate group reducer, its portion subjected to the
reduction is colored yellow-brown. When this film is
measured in the second method, the light transmittivity is
affected by the colored portion, and the measured dot
., -- 10 --
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y
percentagc involvcs errors. These errors depend on the
amount of reduction, and therefore the correction cannot be
achieved by the measuring device according to the second method.
DETAILED DESCRIPTION OF THE IMVENTION
A first example of a dot percentage measuring device
according to this invention, as shown in FIG. 5, comprises
an elongated microscope section 10 to observe a test piece
6 with dots from above, and semi-cylindrical dot percentage
displaying section 20 which holds the
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middle portion o~ th~ microscope sec~ion 10 and displays
a dot percentage on a meter 22 graduated in equal in-
crement. A power swi~ch 24 and the zero-adjustment knob
25 of the ~e-ter 22 are provided on the outer wall of
the dot percentage displaying section 20. The internal
arrangement o the device is as sho~m in FIG. 6. More
specifically, the microscope section 10 comprises an
objective lens 11, a hali-mirror 12, and an eye-piece
13. The dot percentage displaying section is made up
of a photo~electric converter 23 adapted to convert the
quantity of ligh-t reflected by the half--mirror 12 into
an electrical data~ and the meter adapted to indicate
the elec-trical data on its scale graduated in equal
increment. In observing the sample, the test piece 6
is irradiated by a lamp 7 or a r.atural light.
If the dots on the test piece 6 are subjected to
reduction by using a reducer portions around the dots
are stained~ causing erroneous measurement, because it
is difficult for light from the lamp 7 to pass through
the portion thus stained 3 that is, the portions allow
light to pass therethrough in printing on a printing
plate and form no dots.
During the development of the device, the inventor
has found that light having wavelength in an infrared
ray range can pass through the stained portions, but
visible light and ultraviolet light cannot pass there-
through.
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Therefore, it is desirable that the half-mirror
12 of the microscope section 10 is made up of an inter-
ference filter which reflects th~ infrared light toward
the photo-electric converter 23 and permits the visible
light or the like to pass therethrough so that it is
directed toward the eye-piece 13. An infrared ray
passing filter may be disposed on an optical path extend-
ed from the half~-mirror 12 to the photo-electrical con-
verter. It is preferable that the photo--electric con-
verter 23 ha~ an elemcnt such as silicon photo-diode
which receives infrared rays satisfactorily. The lamp 7
may be of an infrared ray source; however, this is not
recommended because it is difficult to perform visual
inspection.
In operation~ the power switch 24 is turned on and
the test piece 6 is disposed in place below the micro-
scope section 10~ Light passed through the test piece 6
enters the objective lens 11~ and a part (or visible
light or ultraviolet light) of the output light of the
objective lens reaches the eye-piece 13, whereby the
observer 8 can evaluate the configuration of the dots on
the test piece 6. A part (or infrared light) of the
output light of the objective lens 11 is reflected in a
perpendicular direction by the half-mirror 12 to enter
the photo-electrical converter 23 where it is converted
into an electrical data corresponding to the input light
quantity. The electrical data is indicated by the meter
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22 (such as a voltmeter). As the light passed through
the test piece is proportional to the dot percentage,
the value indicated by the meter 22 is proportional to
the dot percentage r For instance, if the test piece 6
is completely black, the meter indicates 100%, and if
the test piece is transparen-t, it indicates 0~. Per-
centage indication on the meter 22 can be adjusted by
the zero-adjustment knob 25 according to the quantity
of light of the light source or the optical transmittivi-
ty of a film form the test piece.
As shown in FIG. 7, another example of the dot per-
centage measuring device is provided with a reduction
amount indicating device. In this case, a memory switch
26 is provided which temporarily stores a dot percentage
and is operated in obtaining -the amount of reduction.
The internal arrangement of the device thus organized
is as shown in FIG. 8. Its rlicroscope section 10 has an
optical system made up of an objective lens 11, a half-
mirror 12 and an eye-piece 13. Its dot percentage indi-
cating section 20 comprises a photo-electrical converter
23 for converting light reflected by the half-mirror 13
into an electrical data, an amplifier circuit 28 for
amplifying the electrical data from the photo-electrical
converter 23~ a meter 22 for indicating the output of
the amplifier circuit 28 on its scale graduated in equal
increment, a memory circuit 29 for storing the output
of the amplifier 28 upon operation of the memory switch
,
26, a comparison/subtraction circuit for subjecting the
value stored in the memory circuit 29 and the output
value of the amplifier circuit 28 to comparison and
subtraction thereby to obtain a reduction data, and a
meter 40 for indicating the output of the comparison/
subtraction ci~cuit as a reduction data or a dot per-
centage change data.
In operation, the power switch 24 is turned on,
and the test piece 6 is disposed in place below the
microscope section 10. Light passed through the test
piece 6 enters the objective lens 11, and a part (or
visible light or ultraviolet light) of the output
light of the objective lens reaches the eye-piece 13,
whereby the observer 8 can evaluate the configuration
of the dots on the test piece 6. A part (or infrared
light) of the output light of the objective lens 111
is reflected in a perpendicular direction by the half-
mirror 12 to enter the photo-electrical converter 23
where it is converted into an electrical data corres-
ponding to the input light quantity. The electrical
data is amplified by the amplifier circuit 28. The
electrical data thus amplified is indicated on the
meter 22 (such as a voltmeter). Since the light pass-
ed through the test piece is proportion to the dot per-
centage, the value indicated by the meter 22 is pro-
portional to the dot percentage.
The output of the amplifier circuit 28 is applied
- 15 _
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to the memory circuit 29 and the compariso~subtraction
circuît 30; however the OUtpUI of the memory circuit
29 is equai to the input thereof when the memory switch
26 is not operated. Accordingly, the same signals are
applied to the comparison/subtraction circuit 30, and
therefore the output of the comparison/subtraction
circuit 30 i6 zero~ which is indicated on the meter l~O.
I~ the memory switch 26 is depressed, the memory circuit
29 stores and hold the output value of the amplifier
circuit 28. As the dot percentage is varied by moving
the test piece 6 or replacing it with another one, the
amount of light passing through the test piece 6 is
varied and the output of the amplifier circuit 28 is
also varied. In this operation, as the output value of
the memory circuit 29 is maintained unchanged, the in-
puts to the comparison/subtraction circuit 30 are dif-
ferent in level from each other, and therefore an outout
signal corresponding to the difference is provided by
the circuit 30 and is indicated by the meter 40.
Thus, with the dot percentage measuring device, the
configuration of the dots can be measured by the micro-
scope section and the dot percentage can be indicated by
the meter. Furthermore, the dot reduction data or the
dot increment data can be indicated by the meter. This
will facilitatc improvement of off-set retouching process.
The memory circuit 29 is cleared by depressing the memory
switch agin.
- 16 -
Another example of the dot percentage measuring
device according to the invention will be described with
reference to E~IG. 9 in which those components which have
been previously described with reference to FIG. 8 have
therefore been similarly numbered. In this example, the
~utput of the comparison/subtraction circuit 30 is ap-
plied to a comparison amplifier 31 where it is amplified
and is then applied to the memory circuit 29. When the
memory switch 26 is not operatcd (depressed), -the input
to -the memory circuit 29 is applied, as i-t is, to the
comparison/subtraction circuit 30. Therefore, if two
inputs to the comparison/subtraction circuit 30 are
different in level~ a signal corresponding to the dif-
ference is outputted by the circuit 30 to be applied
to the meter 40~ Thus, the difference between the out-
put of the memory circuit 29 and the output of the
amplifier circuit 28 is indicated on the me+er.
Next, the memory switch 26 is depressed to connect
the output of the comp~ison amplifier 31 to the memory
circuit 29. If in this case two inputs to the comparison/
subtraction circuit 30 are different in level from each
other, a signal corresponding to this difference is out-
putted by the comparison/subtraction circuit 30 to be
applied to the comparison amplifier 31, as a result of
which the comparison amplifier 31 outputs a signal so
that the two inputs become equal to each other. If under
this condition the memory switch 26 is depressed, then
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the output signal o~ the memory circuit 29 coincides
with the output of the amplifier circuit 28. If the
memory circuit is opened, the output signal of the com-
parison amplirier 31 is not applied to the memory circuit,
and therefore the memory circuit 29 holds the output
signal value obtained when the s~itch 26 is opened.
Similarly as i.n the above-described case, as the
dot percentage is changed, -the output of the amplifier
circuit 28 is also changed. As a result, the two inputs
-to the comparison~subtraction circuit 30 become dif-
ferent from each other, and a signal corresponding to
this difference is provided, and is indicated as the
reduction data or the increment data by the meter 40.
Thus, the same effect can be obtained by this example
of the dot percentage measuring device.
Another example of the dot percentage measuring
device according to the invention, as shown in FIG. 10,
comprises: a light receiving section 54 provided inside
a measuring table 52; and a stationay light emitting
section 53 provided above the light receiving section 54
in such a manner that the former 53 confronts the latter
54. The light receiving section 54 is made up of a
cylindrical head 54a having an opening at one end, a
light receiving element 54b such as a photo-electrical
conversion element for receiving light from an object
51 to be measured (hereinafter referred to as a test
piece 51 when applicable), a pipe 54c for introducing
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light through the opening to the light receiving element
54b. The light receiving section 54 is arranged so that the
upper edge of the opening of the head 54a and accordingly
of the pipe 54c is flush with the upper surface of the
measuring table 52. Accordingly, if the test piece 51
is placed on the measuring table 52, then the lower
surface of the test piece 51 is in close contact with
the upper ed~e of the opening of the hcad and the pipe
54c. The light r-eceiving element 54b is electrically
connected to a display section 55 so that the quantity
of light passed through the test piece 51 is received
by the light receiving element 54b and displayed by the
display section 55.
In measuring the dot percentage of a test piece 51,
the test piece 51 is positioned suitably on the opening
of the head 54a and the pipe 54c. Then, light having a
predetermined intensity is a~aplied to the test piece 51
through a condenser lens 56 provided on the outlet of
the light emitting sect;on 53, so that the light receiv-
ing element 54b in the light receiving section 54 can
receive light passed through the test piece 51. The
quantity of light received by the light receiving element
54b i.s indicated on the display section 55. Since both
of the light emitting section 53 and the test piece 51
are exposed outside, the measurement is liable to be
affected by external light. In order to eliminate this
difficulty, light other than visible light, that is~
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infrared light (or ultraviolet light) is employed as
the light emitted by the light emitting section 53, an
infrared ray transmltting filter is provided on the
optical path extending from the test piece 51 to the
light receiving element 54b in the light receiving
section, and a silicon photo-diode receiving infrared
rays satisfactorily is employed as the light receiv;.ng
elemen-t. In this case, it is possible to protect the
operator's senr.e of sight from being affected by the
external lighto Furtherrnore~ in th~ case of using ultra-
violet light, it may be necessary to employ a means for
preventing the effect of visible light.
This device shown in FIG. 10 can be incorporated
in a washing table used in the reduction process. In
this case a after the test piece 51 is subjected to
reduction9 the amount of reduction can be measured im-
mediately. This will considerable improve the work
efficiency.
Shown in FIGSo 11 through 14 are cther different
examples of the dot percentage measuring device accord-
ing to the invention. Each device is light and small so
that it can be readily operated or handled by and carried
with the operatorO These devices can measure not only
a dot percentaF,e bu-t a]so a dot densi-Ly. Each device
comprises~ a case G0 made up of the upper and lower
halves which can be separated from each other when
required; a zero-adjustment dial 62 exposed outside the
~ 20 -
case 60; a power switch 64, and a measured value dis-
playing window 66. A recess 68 (70 or 72) is formed in
one portion of the wall of the case. Cantilevered by a
supporting arm 76 in the recess is a light receiving
cylinder 74 which receives light reflected by and passed
through a -test piece.
I'he term "-test p:i.ece" as used herein is intended -to
mean an object to be rneasured having an image formed
with dots or an image of continuous tone) such as a
screen negative film, a screen positive film, a printed
material, a photographing film or the like.
In the example shown in FIG. 11, the recess 68 is
formed at one corner of the case 60. The light receiv-
ing cylinder 74 and the supporting arm 76 are provided
within the area of the recess 68, which is defined by
extending the side walls of the case. In this example,
the supporting arm and the l;.ght receiving cylinder are
so designed as to introduce light passed through the
test piece; however, they may be so designed as to intro-
duce light reflected by the test piece as shown in FIG.
16(.A). ~owever, it is necessary that the mounting
angles of the light source and the light receiving sec-
tion are such that regular reflection light is not
received. An arrangement meeting this requirement is
shown in FIGo 16tB).
In this case, the test piece 88 is an opaque print-
ed material. Optical fibers are divided into two bundles
ig~
90 and 92 by a holding mem~er 96 in a light receiving
cylinder 94. Onc 90 -the bundles of optical fibers is
directed to a ligh-t source 98 and the other 92 is direct-
ed to a ligh-t receiving element 100, in ~he case.
A reflecting mirror, a prism, a half-mirror or the
like instead of -the optical ~`ibers may be employed as
the light receiving rnealnsO FI(,. 16(C) shows a case
where a reFlecting mirror ~Ind a half-lnirror are used in
combination. In FIG. 16(C), rcference numerals 91, 93
and 95 designates -the mirror, a lens 3 and the half-
mirror, respectively.
The above-described light receiving cylinder 74 or
94 may be supported as illustrated in FIG. 17 or 18.
The construction shown in FIG. 17 or 18 is intended to
release impact which mav be applied to the light receiv-
ing cylinder during measurement.
In the arrangement show~ in FIG~ 17~ the afore-
mentioned supporting arm 76 is replaced by a shock ab-
sorber 102 such as a spring or a rubber block (not shown).
In -the case of FIG. 18, the supporting arm 76, the
light receiving cylinder 74 and a part of the upper half
of the case are formed as one unit. The part of the
upper half of the case is coupled through a hinge 104
to the other part of the upper half of the case, and a
portion, corresponding to the supporting arm, of -the one
unit is coupled to the lower half of the case with a
screw 106 through an elastic member 102 such as a spring.
In the example shown in FIG. 12, the recess 70 is
formed in the middle ~ortion of a side wall of the case,
and the light receiving cylinder 74 is held as shown in
FIG. 15, 17 or 1~ In this case also~ the light receiv-
ing cylinder 74 is positioned inwardly of the side wall
or to be flush with the side wall. It is difficult for
the operator's hand or the like to make access to the
light receivin~, cyli.nder when compared with the light
receiving cylinder in FIG. 11, and thcrefore the light
receiving cylinder is scarcely damaged. However, it
should be noted that as the recess is formed at the
corner of the case in the case of FIG. 11~ the operator
can readily hold it in his hand.
The recess 70 in FIG. 13 has the same shape as the
recess in FIG. 12, but the supporting arm in FIG. 13 is
protruded from a side wall of the recess. This arrange-
ment is employed when it is convenient in association
with an electrical circuit incorporated in the measuring
device.
In the case of FIG. 14, the recess 72 is formed in
such a manner -that it extends from the side wall of the
case to the bottom wall. In this point, the recess 72
in FIG. 14 is different from the recess 68 or 70 which
extends from the top wall of the case to the bottom wall.
In the example of FIG. 14, as the light receiving
cylinder 74 is provided below the slan-t wall of the
recess 72, it is rather difficult to see the test piece
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when compared with the above described examples. However,
the light receiving cylinder i4 is more satisfactorily
protected from damage being covered by the top wall and
the side walls.
The operation of each measuring device shown in FIGS.
11, 12~ 13 ancl 14, will be descril)ed with reference to a
signal processing circuit showrl in ~IGS. 19 and 20.
When, ligh-t passed through d transparent film 80
such as a screen positive fllm is utilized in measuring
a dot percentage, a measuring position is specified by
marking desired points of a light table 110 with round
points 112 or the like in order to eliminate the occur-
rence of a measurement error due to the fluctuation in
light intensity of the light table 110 on which the film
is placed. Then 3 a portion having a dot percentage 0%
of the test piece 80 is placed between the marks 112.
The power switch 64 is .urned onS and the zero-
adjustment dial 62 is operated so that a digital display
section 66 is set to zero (0).
Then, a portion to be measured of the test piece 80
is placed between the marks 112, and the measuring device
is placed on the portion so that the light receiving
cylinder 74 confronts that portion. Thereafter, the
operator reads a dot percentage indicated on the display
section 66. Measurement of the dot percentage is carried
out for various portions of the film and is recorded.
If the resultant data is greater than a predetermined
- 24 -
~13~9~?3
value, i-t is subjected ~o reduction process so that the
dot percentage is reduced. Tf the resultant value is
smaller than the pre~etermined value~ photographing is
carried out again.
On the other hand, in the case of density measure-
ment, the zero~ad~ustment is performed directly on the
light table and bc-cweerl the marks, and -then a portion
to be measurecl of the tesl: piece is placed between -the
marks for measurement.
In the case where the test piece 88 is an opaque
printed material~ the test piece is placed on a flat
surface other than the light table, and the measurement
is performed with the measuring device having the light
receiving cylinder 94 shown in FIG. 16 similarly as in
the above-described measurement.
Referring to FIG. 19, a DC component extracting
filter is a circuit for eliminating light flickering due
to AC power supply to improve the measurement accuracy.
A negative and positive change-over switch 114 is provid-
ed in a circuit as shown in FIG. 20, so as to read
negative and positive values. If the switch 114 is turn-
ed on, a positive dot percent or density is displayed,
and if it is turned off, a negative dot percent or
density is di.splayed.
An electric source 116 is a battery incorporated in
the casej however~ it may be provided outside the case
so that it is connected through a cord to the measuring
- 25 -
~3~ 3
device.
If a dot percentage is measured~ a dot density can
be calculated ~rom the dot percentage. In contrast, if
a dot density is measured, a dot percentage can be
calculated from the dot density.
Factors causing errors in dot percentage measure-
men-t using ligh-t transmittivity may be decrease in light
transmittivity due to fringe and due to the coloring of
yellow-brown in reduction process. The decrease in
light transmittivity due to fringe is substantially
constant if the conditions of halftone photography and
development are constant, and it can be corrected with
a predetermined value. However, as the light trans-
mittivity is further decreased by reduction, it has been
difficult to accurately correct the light transmittivity
of a halftone film subjected to reduction. The result
of measuring the spectral light transmittivity of a
portion which has been colored brown by reduction with a
iron chelate group reducer is as indicated in FIG. 21.
As is apparent from FIG. 21, the spectral light trans-
mittivity is such that light in the ultraviolet ray range
scarcely passes through the brown portion; the transmit-
tivity of light in the visible ray range is abruptly
increase, and the transmittivity of light in the infrared
ray range is more than 80%. Accordingly~ the dot per-
centage measurement with light in the ultraviolet ray
range or the visible ray range is greatly affected by
- 26 -
6.~
the portion colored by reductionO However~ the dot per-
centage measurement with li~ht in the infrared ra~ range
is less effected by such a portion. This will become
more apparent from FIGS. '2, 23, 24 and 25.
A first instance is shown in ~IGS. 22 and 23, in
which an iodine lamp is employed as the light source,
and a silicon photo-diode is used as the light receiving
section. A seconcl instance is sho~n in FIGS. 24 and 25,
in which in addition to the componen-ts cmployed in the
first instance an optical filter for cutting off the
light in the ul-traviolet ray range and the light in the
visible ray range is additionaily providedO Each of
FIGS. 22 and 24 indicates the relative sensitivity
characteristic of the detecting section with respect to
the wavelength of transmitted light. Each of FIGS. 23
and 25 indicates the characteristic of an error caused
by reduction. As is clear from these graphical represen-
tations, the first instance is most sensitive to the
light in the infrared ray range and is also sensitive to
the visible lighto Thereforeg the first instance is
affected by the portion colored by reduction process,
and accordingly~ the measurement error is increased as
the amount of reduction is increased. In the second
instance, the optical filter is added to the first
instance so as to decrease the sensitivity oE the detect-
ing section to the ultraviolet light and the visible
light. In the case of the second instance~ the dot
~ 27
percentage measurement is scarcely affected by the por-
tion colored by reduction proeess, and the increment of
the measuremen-t error due to the increase of the amount
of reduction is suppressed as shown in FIG. 25. The
same effect can be also obtained by using a light source
which does not cmit ultraviolet light ~nd visible light.
Thus, if, aftcr the influence o~ the reduction is elimi-
nated to stabillze the altlourlt of error, a function
having a charac-teristic as shown in FIG. 4 (the charac-
teristic being such that the light transmittivity is
small or zero at about 0% and 100%, and is maximal at
about 50%) is generated to be added 9 as a correction
datag to the light transmittivity or a data related
thereto, then a dot percentage can be obtained with high
accuracy.
The arrangement of a device performing such an
operation as described above is as shown in FIG. 26.
In the device shown in FIG. 26, light from a light
source 121 passes throu~h a test piece 122, and is intro-
duced through a lens system 123 and a filter 124 to a
photo-electrical converter 125, which output an electri-
cal data corresponding to the quantity of light passed
through the test piece. As the filter 124 allows only
infrared light to pass therethrough, the influence of
reduction can be eliminated. The outpu-t of the photo-
electrical converter 125 is amplified to the operating
level of a correction circuit 124 connected thereto.
'
- :
After the above described correction is carried out~ the
dot percentagSe is displayed on a display device 128.
Where an AC li,ght source is used as the light source 121,
it is preferable to insert a circuit (not shown) adapted
to prevent light flickering between the amplifier 126
and the correction circuit :L27.
In general, the amount oE fringe is substantially
constant if the conditions of halftone photography and
development are f:ixed. Therefore, the i.nfluence of
fringe can be correc-ted by presetting a correc-tion data.
Such a correcti.on data can be obtained by adding the
data shown in FIG. 4 to the electrical data proportional
to the light transmittivityO
A circuit for generating the above-described cor-
rection data~ as shown in FIG. 27, is made up of oper-
ational amplifiers OPl and OP2, a diode D and resistors
Rl through R5. The output Vr of the operational ampli-
fier OPl is changed in amplification factor at the input
voltage RlR22 VB as shown in FIG. 28, that is its
characteristic curve is as a polygonal line. If the
voltage Vr having such a characteristic and the input
voltage Vs is subjected to addition in a suitable ratio
in the operational amplifier OP2, then a signal approxi-
mating the amount of correction can be obtained as indi
cated in FIG~ 29. That is~ if the input voltage Vs is
employed as an electrical signal proportional to the
light transmittivity, VD may be employed as an electrical
- 29 -
~3L3`~
signal approxlm-~ing -the ~mount of correction for the
light transmittivity (FIG. 4).
If this corrcction signal is added in a suitable
ratio to the signal proportional to the light transmit-
tivity as shown in FIG. 30~ -then the value of light
transmittivity in the vicinity of 50% can be corrected
as desired without affecting the values at 0% and 100%.
The value V0 is -thc aforeMentioned amount of correction
to be prese-t.
FIG. 31 shows an actually measured curve to indi-
cate what errors the dot percentage measurement utiliz-
ing light transrnittivity include. That is, the curve is
obtained by avera~ing the test results of about thirty
samples. The amount of error is defined as follows:
A measurement value obtained according to the above~
described method is employed as a reference value. The
amount cc deviation of a valle caiculated from Equation
Ap = (1 - T) X 100% (where Ap is the dot percentage, and
T is the ligh-t transmittivity) from the reference value
is the amount of error. The one-dot chain line indicates
a correction func-tion with a polygonal line which has
one refraction point so that the amounts of error at dot
percentages Ap 5%~ 45% and 100o coincide with one another.
The correction function indicated by the one-dot chain
line includes relatîvely great errors more than 1% in
the vicinity of Ap 70 - 90%. This error may be reduced
by providing the refraction point in the vicinity of Ap
- 30 -
55 - 60%., however in this CaSe 3 an error more than 1%
is caused in the vicinity of Ap 35 _ 45c~. Therefore,
in order to improve -the accuracy, it is necessary to
increase the number of refraction points. The dotted
line in FIG. 31 has an additional refraction point at Ap
80% in order to reduc( the errors in the vicinity of Ap
70 - 90%. That is, the dotted line inclicates a poly-
goncll line having 1:wo refraction ~oints to approximate
the actually measured curve (solid line). However, if
the number oE re~raction poin-ts is incr~ased, the number
of adjustment points is increased. For instance in the
case where two refraction points are provided, as each
adjustment point to be set for approximation has to
specify three point positions in a plane, six factors
are involved~ which make the setting of a polygonal line
for correction intricate.
As ~ result of investigation of a number of actual-
ly measured value, in the following embodiment of the
invention is employed the fact that when the dot percen-
tage of a screen film is measured by using the light
transmittivity of the film, a characteristic curve for
converting light -transmittivity into dot percentage can
be relatively readily approximated with a quadratic
function with high accuracy.
In this embodiment, it is preferably to use a light
source free of flickering and drift in the quantity of
light emitted t'nereby, such as iodine lamp driven by a
-- 31 -
,,
stable DC source. Af-ter passing through a test piece
or a halftone fllm 133 the light emitted by the light
source ent~-rs an aperture mechanism 134. The aperture
mechanism operates to increase or decrease the cross
sec-tional area of -the optical path according to the
variation in light intensity of the light source 1311
-thereby to correct a measurement error due to the vari-
ation in liht: interlsi-ty of the light source. For
instance in the case of using as tllc test piece a film
having a dot percentage ~%, the aperture mechanism 134
is controlled so that a display device 135 indicates
zero. Alternatively the aperture mechanism may be con-
trolled as followsO That is, by using a film whose dot
percentage is known~ preferably about 5%~ the aperture
mechanism is controlled so that the display device 135
shows that dot percentage. An optical detector 136
receives light passed throu~h the aperture mechanism 134
and converts it in-to an electrical signal T proportional
to the quantity of light thus received. A pho-toelectric
tube~ a photoconductive element or a photodiode is
employed as the optical detector 136.
FIG~ 33 shows one example of the optical detector
136 whi.ch is made up of a photodiode 261. ~he photo-
diode 261 is connectcd between the positive and negagive
input terminals oE an operational amplifier 262~ and a
feedback resis-tor is connected between the input and
output terminals oE the operational amplifier 262.
I`he ~ ctric.l signal T provided by the optical
detector 136 is proportion tn the average transmittivity
of the measuremen-t portion of the film~ and the propor-
tion factor is adjusted by the aperture mechanism 134.
The electrical signal T is applied to an correction
circuit 137 which operates to correct the measurement
error at about 50% which rnay be caused by the effect
of fringe~ and an error due to a ghost dot. FIG. 34
is a block diagram showing one example of the correc-
tion circuit 137. :[f in this circuit the input T is
represented by an exprcssion (O~T<l), then its correc-
tion outpu-t Tc can be expressed by the following Equation
(1):
Tc = alT - a2Tm ....... ,....... ,... (1)
After being multiplied by the factor al in a scale-
factor element 271j the input T is applied to one input
terminal of an adder 272. In addition J after being
converted into log T in a logarit~n converter 273, the
input T is multiplied by the factor m in a scale-factor
element 274. The output m log T of the scale-factor
element 274 is converted into a value Tm by an inverse
logarithm converter 275, the output of which is multi-
plied by the factor -a2 in a scale-factor element 276.
The resultant value -a2Tm is applied to the other input
terminal of the adder 272. As a result, the correction
signal Tc in Equa-tion (1) described above is obtained
as the output of the adder 272. The signal Tc
i9~3
represen~ativc of -the correction transmittîvity is calcu-
lated into an do-t percentage Ap by a calculation circuit
133 in accordance with the following Equation (2):
Ap = (1 - Tc) x 100 ........... (2)
The signal Ap proportional to the dot percentage
of the test piece is displayed as "orvi by a display device
135 when it is ~ero (0), and as "100%~' when 100. Thus,
the corrected dot percentage of` the -tcst piece 133 can
be ol)tained.
FIG. 35 is a block didgrclm shotJing another example
of the measuring device according to the invention, in
wh:ich light emitted by the light source flickers as in
the case of a fluorescent lamp in a light table. In order
to eliminate the effect of this flickering a DC component
extracting filter 139 or a low-pass filter is employed.
Thus~ the output signal of an optical detector 136 is
applied to a correction circlit 137 after its AC com-
ponents have been removed by the DC component extracting
filter 139. In this case) as the output of the correction
circuit 137 is not linear to its output, a value obtained
by inputting the DC component of a signal including an
AC component does not coincide with a signal obtained by
inputting the same signal directly to the correc-tion
circui-t 137. Therefore, it is necessary to provide the
DC component extracting filter 139 before the correction
circuit 137~
FIG. 36 shows another example of the measuring
- 3~ -
.... ~ .
device in ~hich no aperture mechanism is employed. In
this example it is necessarv that the signal is increas-
ed or decreased to a predetermined level by performing
gain control by a gain coll-tro] circuit 140 in the front
stage of a correcti.on ci.rcuit 137, and is then applied
-to the correction circuit 137. In this case also, as the
characteristic of the correc-tion circuit 137 is not
linear, the output signal of the correction circuit 137
which is obtai.ned by inputting a signal multiplied by a
constant to the correction circuit 137 is different from
the value which is obtained by multiplying by the same
constant the output of the correction circuit 137 ob-
tained by inputting the signal, as it is~ to the correc-
tion circuit 137. Therefore~ it is necessary to perform
the gain control in the front stage of the correction
circuit 1370 A multi-revolution type variable resistor
may be employed in the gain ~ontrol circuit 1~0 in FIG.
36. However~ this variable resistor is expensive and
bulky, and accordingly it is not preferable to employ
it in a small measuring device in -the view point of a
space available. Therefore~ in the case of the small
measuring device~ it is necessary to use a variable
resistor which is readily available and can over all the
range with one revolution. However, there is a problem
to be solved. That is, in the case of the small measur-
ing device which uses a light table as its light source,
its necessary adjustment range is relatively large,
-- _5 --
three to four times in gairl ratio/ because the quantity
of light ~rom tn~ light table fluctuates greatly.
Accordingly~ if it: is int~nded to cover all the adjust-
ment range with only one revolution of the sma~l variable
resistor, then i-t is rather difficult to perform fine
adjustment. Thusj it is preferable to employ a thread-
feed mechanism For -the aperture mechanism and to use a
multi-revolution type variable resistor with which the
line adjustmen-t can be pcrformed covering all the adjust-
ment range, in the small measuring device.
If the measuring device shown in FIG. 36 is so
designed that the gain control circuit 140 is provided
with at least two adjustment ranges w~.ich are suitably
selected by an externally provided change over switch~
then the adjustment can be performed more readily.
The measuring device shown in FI5S. 32, 35 and 36
have been described with ref-rence to the case where the
correction is performed according to Equation (1).
However~ the accuracy c~n be increased if the following
Equation (3) in which the number of terms is increased
is employed-
n
Tc = ~ aiT i ................... (3)
Shown in FIG. 37 is an example of a correction cir-
cuit which perEorm such a function. FIG. 37 will become
more apparent when referred to FIG. 34.
- 36 -
1136~3
An examplt~ of such a correction is illustra-ted in
FIG. 38 whi.ch may be compared with FIG. 310 In this
case, the iollowlng correction function is employed:
Tc - 1.23T - 0.2T ...... ,....... ~ (4~
In FIG. 38, an actually measured curve is indicated by
the one-dot chain line. The number of factors required
to be determined for correction is only three: factors
m, a1 and a2; however, the obtained approximation is
considerably fine as is apparent from the graphical re-
presentation in FIG. 38.
FIG. 39 shows a block diagram of a device adapted
to perform the above-described correction~ the device
being so designed that the adjustment can be readily
achieved.
In this method 9 a signal T representative of a
transmittivity which has reached a predetermined level
through gain control is multiplied by a factor a to
provide a value aT., whereby correction as to a base film
density and a ghost dot is carried out 9 and the follow-
ing function which becomes zero with T = 0.1, and
maximal with T ~ 0.5 is generated:
T Tm ............... ,....... ..(5)
The function is multiplied by a factor ~ and result
is added to the aforementioned aT, so as to obtain a
signal Tc as to the transmittivity which is corrected
at its middle portion. Then, the following calculation
- 37 -
~L136~g~
is carried ou-t, to obtain d signal Ap proportional to the
dot pere~ent~ ge,
Ap = (1 - Ic) x 100 .~ ... (6)
The parts (A) and (B~ of FlGo 40 show eorreetion eurves
obtained by such a process as deseribed above.
A eireui-t shown in FIG. ~il carries out correction
similar to those described with referenee to FIG. 39.
In this method, a por-tion (~T - 1 is noL- aL`feeted. Cor-
reetion eurves o~)t:.lin( d in tllis method are as shown in
the parts ~A) ancl (B) oL~ ~'`I(`,. 42. One oi:` the merits of
this me thod resides in that , as the r'actor c~ is ad justed
ini-tially in signal proeessing, the cireuit for multiply-
ing the fae-tor c~ ean be replaeed by the aperture meeha-
nism and the gclin eontrol eireuit.
-- 38 --
