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Патент USA US2921985

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Jan. 19, 1960
|_. SHAPIRO ETAL
2,921,975
‘ MULTICHANNEL SCANNING SYSTEM
Filed on. 25, 1956
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INVENTORS
Lums SHAPIRU r5‘
JOHN S. RYDZ
BY
1 TTGJPIVEY
United States Patent-it)
CC
2,921,975
Patented Jan. 19, 1960
2.
three optical channels, each‘ vcor-responding - to >~ a. different
2,921,975
one of the-‘primary-colorsa- Thei lighti-values-inthese
three optical. channels-may not be the same for corre
MULTICHANNEL SCANNING SYSTEM '1
sponding picture information'in the original subject- or for
corresponding density values‘inthetseparations of the sub-.
Louis Shapiro and John S. Rydz, Haddon?eld, N.J., as
signors to Radio Corporation of America, a corpora
tion of Delaware
Application October 25, 1956, Serial No. 618,342
6 Clain'1s.. (Cl.'178—5.2) .
ject ‘being scanned. » Such differences may bedueto differ
ences .orp-necessary» ‘tolerances @in exposure and develop-1
ment of color separations-which differences mayirosult'.
in’ different density ranges‘ on ditie'rent- effects-io?'ith‘e
10 nonlinear». photographic: characteristic’ in- one separation‘
as against anothert?t» has :been' found -desirab1e,--for» example, to use thev-non-linea'r toeof‘this photographic
characteristic
order to‘ gain ‘high transmission values
This invention relates to a multichannel‘ scanning‘ 15 in the resulting, separations.) ‘ Another ‘reason for-such
differences-is that theremayvbe ditferences'between-ethe
vsystem, and particularly to phototube circuits for such
channelscin their optical» characteristics; sucheetfectsntfor
a scanning system incorporating electronic compensation
for optical distortions in the scanning systema
~ example, an: effect>like tcosineafourthlthatdis due~to the
optical geometry) -_may affect the. value of “the Callier
This invention may be used in an electronic color cor
rectionsystem, for example, of theqtypedescribeddn an 20 coe?icient. Diderent- ,densityrangesof' thephotographic‘
images in~the three'optical channels vgenerally willalso
article entitled v“Photographic and Photomechanical .As
result ‘in- diiferent distortionwaves due to » the Callier
pects of Color Correction,” by I. S. Rydz,.et al., inthe — coe?icient.
Furthermore, there mayebevsubstantiallvariar
“Sixth Annual Proceedings of the Technical Association
tionsin the value-of theCallier coe?icient withedensitye
of the Graphic Arts,” 1954, at page 139. In such a
differences.
system,-a cathode ray tube is used as a ?ying spot scanner
It ‘is? amongthe objects of this invention-to'provide:
for scanning transparencies in the form of three photo
A new and'improved multichannel‘ scanning system’
graphic color separations- of- a colored subject to be
which. includes compensations-for optical distortions in,
reproduced; these three separations relate, respectively, to ~- the
scanning system;
three primarycolors or tristimulus values. By meansof
the scanner and separate phototubes, electrical signals 30 A new and improved multichannel’ scanning system’
which: includes electronic compensation-for optical -,dis
are derived, which are proportional to the transmission
tortionsin the scanning-system and adjustments fordiffere:
characteristics, and thereby: to the color-component char
ences- in these‘distortions between‘ channels;
acteristics, of‘ corresponding picture elements or areas
In accordance with» this invention; a cathode-ray-tube
of "the color separations. These-signals are-applied to a
scanning system-isused to scan a transparency of 1a:
computer,’ which produces corrected signals represent 35
colored subject. The» transparency densityv values ;vary
ative of ink percentages to be printed. The corrected
with the primary ‘color characteristics ‘of the subject.
signals-are used-to vary‘ the light intensity of another,
The scanning system is 'mounted; within a’ light-tight
image-producing cathode ray tube and 1to expose~a> set
housing and includes a'plurality of optical channels, one
of corrected color‘separations. From the corrected color
separations,aset of printing plates is made, which plates 40 for each primary color, and a plurality of'photoelectric
receptors, one for each‘v channel.» Separatecompensating
are employed to reproduce the original subject.
circuits mounted‘ adjacent the photoreceptors~ include“ '
‘ In such a system; the transparencies maybe prepared
electronic circuits for compensating the Callier‘ coef?:
jby‘means of standard photographic techniques, which
may include the use of contact print methods. In such
contact prints, the picture information inherentlytinvolves
diffuse‘ picture densities rather than specular- densities.
cient= e?ects of- the respectivewoptical ‘channel " as well
as other optical distortions. These compensatingeciri
" cuits'include'individual signal level and "gain‘adjustments,
whereby the electrical signals corresponding to’primary
Likewise,~the sensing‘ of picture information from such
color ‘ values may" be consistentlyqrelated at both' "limits ‘of
the signal" range 'as- well 'as at, all, intermediate signal:
separations should be on- a>diffuse transmission basis.
However, a scanning system- suchas that mentioned
above operates by applyingfocused rays of light to the 50 steps; Thesecompensatedprimary-color signals-are ap
pliedeto and combined in a-suitable electronic device;
separations. Collection of- the'transmitted portions of
The foregoing and other objects, ; the‘ advantages and '
this light is on a geometric ray basis, which results,
' novel features'of thisyinvention, as well as the invention
essentially, in only the specularly transmitted compo
itself both’ as-to its organization 'and mode of "operation,
nents = being: received by the phototubes;
maybe best understood from‘the following "description,
Photographic density measured by specular methods
when read inconnection withthe accompanying draw
ing, in which-like references refer to like parts,’ and in'
results in different measured values of density from that
using diffuse methods‘. The relationship between diffuse
densityand specular density -may be approximated by
the Callier coe?icient. The basic relationship‘between
transmission and‘density is that density is equal to the
log of the reciprocal of the transmission. Accordingly,
the transmission measurements made on a specular basis
incorporate non-linearities which correspond to the de
parture from diffuse density.‘
It has also been ‘found that, in a scanning system
of‘ theiaforementioned‘type, an appreciable amount of
spurious ambient light is present. Thisspurious light
isdueto' mechanisms such as ?are light in the cathode
ray tube and:light,scattering:by various optical compo
which:
Figure ll is‘a schematic optical and electrical ‘diagram
69
of a-multichannel, scanning-system embodying;the inven-;_
tion;
Figure 2 is a schematic circuit diagram of'a phototube
circuit embodying this‘invention that may be used in_the
system of Figureil; and
Figure 3 is an idealized graph of the transfer character~.
istics of different portions of the system ‘of Figures .1 and
2.
A cathode ray tube ltl'is used as a ?ying, spot kinescope
to provide a scanning light spot. - The-light spot is formed -
nents; This spurious-lighthas beenfoundto be a sub 70 on a phosphor-screen ~12 depositedonthe‘insidesurface
of the kinescope faceplate 14.7 Vertical and horizontal
stantial percentage of the'scanning light.
In'-;the;v aforementioned scanning system, there. are
de?ection coils 16 and-18; resoectively,_.areprovidedwto;
produce .:-vertical. and horizontal:de?ections- rof-z' the_ light’
2,921,975
3
4
duce a set of corrected photographic separations that may
spot, thereby forming a raster on the screen 12 of the
tube 10. ' Appropriate de?ection circuits 17 and 19 are
be used to make printed plates to reproduce the original
connected to the de?ection coils 16, 18. A beam focusing
subject.
system (not'shown) is also provided.
.
A light-tight housing 21 encloses the cathode ray tube
10 and the remainder of the scanning system that is now
described. The scanning light spot formed at the phos
phor screen 12 is directed to corresponding areas of-three
.
In Figure 2, an electronic circuit is shown that may be
used for the phototube 52 and phototube circuit 64 of
Figure l. The phototube circuits 66 and 68 are generally
the same as that shown in Figure 2 except as noted here
inafter. , In Figure 2, the phototube 52 is shown'as a
photomultiplier, having an anode 76, a cathode 78, and
transparencies 20, 22, 24 may be monochrome separation 10 ten dynode stages. An adjustable resistor 80 is connected
between the cathode 78 and /a source'of negative operat
positives of a colored subject, which positives are pre
ing potential. A load resistor 82 is connected between
pared trom negatives that are exposed, for example,
the anode ‘76 and a potentiometer 84, which is used to
through red, green, and blue ?lters, respectively. The
adjust the operatingpotential applied to the anode 76.
optical channels respectively associated with these separa
tions may be identi?ed by the associated primary color 15 Operation of the photomultiplier 52v is based on ten
cascaded dynode stages, which operate on the principle
of the ?lter and are referenced by the corresponding
or‘ secondary emission. The gain of each such stage is
letters R, G, and B. The optical paths from the object
determined by the voltage existing across the stage. Adja
plane of the kinescope faceplate 14 to the transparencies
cent dynode steps are connected by resistors 86, which
20, 22, 24 are by way of separate imaging lenses 26, 28,
30. The imaging lenses 26, 28, 30 may be substantially 20 form a voltage divider network between the last stage
uncorrected separation transparencies 20, 22, 24. These
identical and of the symmetrical type. Where operated
and the cathode '78.
under a condition of unit-magni?cation, a symmetrical
lens has a minimum distortion. Symmetrical lenses hav
ing ?at ?elds are used, in order that these lenses may be
the grid of a triode 88. The cathode of the triode 88 is
connected to the cathode of a second triode 2% and,
'
‘
The anode of the photomultiplier 521's connected to
positioned in parallel planes, and the color separations 25 also, through _a common cathode resistor 92 to a source
of negative, potential. The two triodes $8, 90 form a
may also be positioned in parallel planes. The lenses
direct-coupled differential ampli?er 59. A feedback volt
26, 28, 30 are‘ adjustably mounted in the frame 38 by
age is applied to the grid of the tube 9%. The anode of
‘appropriate means (not shown) for adjustment along the
the tube 90 is-connected through a load resistor 94 to
of the lenses 26, 28, 30 may be adjusted to vary the 30 a source of positive operating potential and, also, to a’
high-gain ampli?er 96. This ampli?er 96 may be a
intensity of the imaged light spot. An appropriate imag
direct-coupled ampli?er stage of the same type as that of
ing system is described in the patent U.S. No. 2,740,832.
the ampli?er 89, and serves merely to supply additional
The color separations 20, 22, 24 are mounted in sup
gain that maybe needed and to position the voltage at
porting frames 40, 42, 44, respectively. Separate three
vpoint register mechanisms (not shown) are used in the 35 an appropriate level. The output of the ampli?er 96
is applied to the grid of a triode 98. The‘ cathode imframes 40,42, 44 to position the separations in planes
edance of the tube 98 includes, in'pait, the series combi
parallel to the principal plane of theassociated lenses
nation of resistors 100 and 102. A feedback network
26, 28, 30, respectively. Additional means (not shown)
from the cathode of the tube 98 is by way of a‘ series
may be provided in each frame 40, 42, 44 for adjusting
the separations transversely of the optical paths, and for 40 combination of resistors‘ 104 and 106. The junction
of these resistors 104,106 is'connected to the grid of
rotating each separation around the central axis of the
respective optical paths. The aperture stops (not shown)
associated paths.
The light passing through the color separations 20, 22,
the differential-ampli?er tube 90; the other terminal
of the resistor 106 is connected to a reference potential
shown as ground.
,
24 is collected by separate condenser lenses 46, 48, 50
and directed to separate phototubes 52, 54, 56,’respec 45 A non-linear diode compensating network is connected
in shunt to the cathode resistor 100 to form the remainder ‘
tively. Optical integrating spheres 58, 60, 62 may be
of the cathode impedance for the tube 98. This com
used to collect the light passing through the transparencies
pensating network includes a diode 108, the'anode of
which is connected to the cathode of the tube 98, and
The electricaloutputs of the phototubes 52, 54, 56 are 50 the cathode of which is connected through an adjustable.
20, 22, 24 and to direct it to the associated phototubes
52, 54, 56.
-
‘
~
respectively appliedv to phototube circuits 64, 66, and 68.
The outputs of the circuits 64, 66, and 68 are applied to
a device 70 for combining the signals from those circuits.
In the aforementioned color-correction system, this de
resistor 110 to an adjustable tap on a resistor 112. The
resistor 112 is connected between the junction 114 and
a source of positive voltage. A second diode 116 is
connected in a similar manner between the cathode of
vice 70 may be a color-correction computer such as the 55 the tube 98 and‘ a terminal of an adjustable resistor 118.
The other terminal of the resistor 118 is connected to
the adjustable tap of a resistor 120, which is connected
between the junction 114 and the positive voltage source.
signals corresponding to colored ink values that may be
The anode of the tube 98 is connected by way of a
used to reproduce the original subject. These output sig
‘ nals from the color-corrector 70 may be applied to a re 60 resistor 120 to a source of positive operating potential.
one described in the patent US. No. 2,434,561. The
outputs of this color-corrector device 7 0 may be electrical
corder 72 for exposing corrected photographic‘ separations
that may be used in making printed plates for reproducing
the original subject. An appropriate form of recorder
This resistor 120 may be a current-summing resistor in
a color-correction computer 70, such as that described in
the aforementioned patent, US. No. 2,434,561.v In'that
computer system, the inputs to the computer are currents,
72 that includes another cathode ray tube system is de
scribed in the patent US. No. 2,740,828.
65 say from the tube 98 (and from corresponding tubes of
the phototube circuits 66 and 68 for the other channels).
The overall operation of the system of Figure l is as
If the color-corrector system that is used requires a volt
follows: The scanner operates to derive electrical signals
age input,.the resistor 120 may be used as a load resistor,
in accordance with the color characteristics of an original
and the anode voltage of the tube 98 would be taken as
subject. These color characteristics are represented by
transparency density values in the separations 20, 22, and 70 the desired voltage. '
.
The resistor 102 in the cathode network of the tube 98
24. The electrical signals from the scanner are applied
is a small resistor used to sample the current in the
to the color-corrector 70, which, in turn, deriveselectrical
cathode network and to provide a voltage at the junction
signals corresponding to ink values that would reproduce
13.4 proportional to that current. This voltage at the
generally the original colored subject. The signals from
junction
114 is applied to a resistor 122 of a resistor
75
the color corrector 70 are applied to a recorder 72 to pro- >
5
2,921,975
matrix 127 .thatalso{includes-resistors 124 and 126.. The
resultsfrom thehigh forward gain of the feedback .loop
being controlled'or reduced by the usual. feedback‘, factor
resistorsi'l24 ‘and-1'26 ‘receive at one terminal correspond
ingvoltages from the phototube circuits 66 and 68015 the
green and blue channels, respectively. The other ter
minals. of Ithe resistors .122, 124,. and 126'are connected
due to, the action of the ‘beta network. Where such‘ con—
trolby the.beta.network is impaired or delayed by'stray.
capacitanceslthe forward section of the feedback loop,
together at a junction ‘128: the.voltage at the junction
128"is'l"proporti0nal to a weighted sum of the voltages re
withiits. high; gain, ampli?es the high frequency portion
of vthe signal. and produces an effect of high frequency
peaking... This condition permitsthe entire non-linear di
suitable resistor values, the voltage at the junction 128 is 10 odecompensating network to be positioned outsideof the
circuits64, 66,‘an,d '68 at any convenient location remote
proportional ‘to a luminance function of the compensated
fromthe scanner housing 21;‘ any stray capacitance due
primary-‘color signals. Such‘ aluminance-function signal,
to such?remote .positioning tends to addto the overall
may'be'used 'for' deriving a neutral or black-printer .cor
high
frequency response of the phototube circuit. If
rected""sig'nal in ‘combination with the colored-ink cor
high
frequency peaking tends to be excessive, _it_can be
rected signals Qder'ived 'bymeans. of the color'corrector 70. 15
reducedqby variousappropriate means, suchas ‘control
The phototube circuit of Figure 2 operates generally
of the -frequency ch'aracteristicof theforward .sectionof
asféll'oWstThe current drawn by the photomultiplier 52
the feedback-loop.» Each phototubecircuit. 64,. 66, 68. is
is proportional‘to the intensity of the light recei'ved'by
ceived"by,theseresistors 122, .124,‘ 126, the values of the
resistors determiningthe weights of the voltages. With
acomplete 'unit that. provides a highlyiprecisecurrent ,or
the photomultiplier (which light intensity isproportional
to"the;*lig‘ht~"transmitted’"by the transparency 20).‘ The 2.0 voltagewoutput. at ..a low. impedance. level. , . All- ,of .. the
necessary controls, thegain. adjustment 80, .the_D,.-C.flevel
anode‘volt‘ag'e; which‘is developedacross'th'e load resistor
adjustmentl..84,land theadjustable resistors of.the..com-.
82',‘»i's" applied to~the grid of the differential ampli?er tube
pensating network, may , be ; positioned remotelyjoutsider
88;’ the'grid'of 'tlieiother tube 90 receives a'feedback volt-.
age at "a="proper "level; by way; of‘ the feedback ‘resistor
c‘ombihation'104f‘106‘.‘ An ' error‘signal ‘is developed-atv
of ‘the -scanner housing 21 without any deleterious ,e?ects
on. the operations, ,
the ‘ahodeof’the-‘tube~'90"which‘ is " proportional‘ vto the
25 'Reference. istmadestothe idealizedmgraph of'Figure 3
difference between‘ the'photomultipli'er anode "voltage and
the ‘feedbaclc‘volt‘age: This‘erronsignal is ampli?ed in
thediife‘rehtial"ampli?er‘89; and further ampli?ed 'in the
pensating for. the non.—linear. transfercharacteristic,of- the
red opticalJCh'a'nneLin ,the scanner-.ofFigureJL The
to explain the operation of the diodemetwork in com
ampli?er‘96 and‘applie'd to the grid'of the tube 98. The 3.0 abscissaof the graphofFigure 3 is aset of equal-density
gray-scalesteps ranging from an extreme of highest .den-.
sityor blackpB', .tottheeothertextreme of-Jowest density
?er~-"s‘ta‘ges"89 and 96' drive ‘the tube"98;' which operates
or,white,~W.. One-set~-.of.ordinates plotted». againstthis
like‘ a‘cat'hod'e‘follower. The tube 98‘is driven to produce
tubei'98io?erates'eas iaecurrent: ampli?er. The two "ampli'-'
a~volta7ge“at~its1cathode such-that ‘the ‘feedback 'voltage
at the grid of the'tu'bef90 becomessubstanti'a'lly equal
tovthe photomultiplier-1anode'voltage applied to the grid
of-Y‘the: tube 885! ' Thus,‘ the feedback‘ circuit operates to
developiat the‘ cathode of vthe tube 98 a voltage propor->
grayigscale abscissais a set of transmission valuesfor such
35
agravseale..- Theicurve.130§is.'a.graph illustrating the
ideal logarithmic relationship between transmission. and
density, .with .both‘transmissionand. density being diffuse,
that? .lS.Z..~ '
v
tionalt'ofthe photomultiplier anode-voltage. ‘This voltage
l;
at ‘the cathode‘ of the tubee‘98' is at a substantially higher
T .. .
level 1 than th'atr-from- i‘ the » photomultiplier ~ and i may " be
Thercurve 132i: is; a, graph'nof-zthe transmission “values
used2 to 'operatee'the‘ diode network at desirably‘ high‘volt'
age‘ levelsw.
for’ the‘. gray. scale .-steps nwithz a iconstantiCallier. effect as-.
sumed; that is, the-curve ~132-.is--based on specular trans
For cathode voltages-Y of "the tube98~below acertain
magnitude, the diodes 108 and 116 are biasedo?‘ in the 45 mission measurements; in which :not all of the trans
back directiomby the voltages at the adjustable tapsiof
thevresistors'» 112 ‘and 120. Consequently, the'anode
cathodecurrent-in the circuit ‘of the tube 98 (which cur;
renta'is' aifurlction of-‘the cathode resistance) ‘is'propore
tional'tto‘ itslcatho'demvoltage and, thus, to the photo
multiplier‘anodeevoltager Asthe photomultiplier anode
voltage-=increases;'a level‘w‘is reached ‘at :which the cathode
voltageeofitlfe-?tube98"exceeds the bias voltage applied
mitted lightais-received-thy itheaphototube 52. ' Theratio.
‘ of {the specular1density;t0;:the:di?use density is known,
as the: Gal-lienécoef?cient, 'rwhichicoe?icient ‘for- the: curve
132....is'assumedto be substantially constant at. a value of
50 about». la-3.~ The*curvei-;134<Yis -.an idealized graph of the
‘ actual itransfer characteristic :of .- one :of
theichannels in
the scanning-,1 systemm» This graph=~ 1134 includes: effects
other rthanr-those ,-.represented>.§by the ;Callier ,coe?‘icient,
tothe" cathode of the diod'e108, and that diode 108 con-. 55 other. .effeets- .suclmas espuriouszlighta due ; to cathode: ray
tube'l?am- light {and slight-w ‘scattering: by. optical compo
ducts's...‘ The?‘ diode 108,- whenlconducting; connects‘the
resistorsi'l'lo‘ands-1125 in circuit with‘ thecathode resistor
nents. This .-spurious.-light has :beemfound ‘to ~ bepapproxi
100 to‘-provide-ieffectively- a shunt" resistance to that
matelyconstant :overtherange: of scanned densities. The
cathode resist0r=~100£ The-setting of~the resistor'110
curve 134smay: be ,‘derived by'scanning a: standard ' gray
scale. transparency and: measuring; the: current ~ values in
efféctivelyidetermines the amount of compensating cur
rentrthroughbthe diode-108. -The combinedcathode re 60 the tube 98 with the diode networlo: disconnected from
sistance with‘the diode ">108 ‘conducting is decreased such
as=tohincrease~fthe cathode currentin the tube 9.8." A
g the circuit.
Two other. curvem136: and-138 tinzFigure 3 are plotted
similaraaddit-ional-change in the voltage-current char-v
on; theztsame grayr-scale.v abscissa coordinate as - the - curves
acteristici‘ofthe circuit‘of'the tube 98. isproduced when
th'elcath'ode‘voltaget-of'thetube'98 exceeds the bias ap
pli'edlto the cathode of the diode 116.
130; 132,‘ 134,-.-;but< on: i a. :different- "ordinate scale "corre
65 sponding; to the anode-cathode- currenta-in the tube‘ 98.
The ordinate-~.scale:of-thecurves.136, 138~is also cali
_ Th'e-overall‘phototube‘circuit of Figure .2'may, be con-
brated: as-“transmission’i in termsiof normalized ink
sidered>ias a-feedback‘loop‘that includes a non-linear
values'used- by theecomputerv, in;twhichw0% ink is white
circ'uiti element‘ (namely,v the circuits . of the- diodes . 108
and 100% ink is black.
The/position“ of' this ' non-linear. circuit' element in the
tion, and .is, ineffect,v the~:curve-~134 -on :a- di?erent ordi
nate. scale. The;:eurve-.-138. is-the compensated-transfer
The curve 136 is the'actual
and§1'16)‘-'ii'1~the'feedback'or beta network of the loop. 70 transfer’ characteristic-1oftthe:‘system without. compensa
feedbacke'vloop results effectively in an inversion offth'e
characteristic.o?'thephototubeicircuit10f Figure'2 due to
etreeezoa ‘frequency=peaking. effect‘. This inversion effect. 75 they .operation of :the: compensating network ‘ provided by
the..diodes '108.rand1.1'16;.- Thisscompensated curve 138
- effect-bf’stray‘capacitances from a frequency-deteriorating
assists‘
graphic density (and resulting small light losses during
is substantially the same as the ideal transmission-density '
The diode compensating circuit may be set up as fol
lows: The potentiometer 84 is adjusted to set the value
scanning) in this toe region. There may be different
density ranges in the three separations’which would pro
duce substantial variations in gray-scale slope due to the
of the photomultiplier anode voltage for minimum photo
tube current; this setting corresponds to the black limit
of the density range and, also, to the maximum value
in Callier coefficient and ‘vary the compensation required
between channels. The photographic emulsion charac
graph 136 in Figure 3. The output-current values shown
in the different channels. In addition, variations in the
value of the Callier coe?icient between channels may
characteristic
130.
,
a
-
1
Callier coet?cient as well as possible appreciable changes
teristics may vary from time to time, and 'it may be
of current in the tube 98. This setting of the potentiom- '
advantageous to use ditterent emulsions (for example,
eter 84 may be such as to provide an output current of
about 5 milliamperes in the tube 98 as shown for the 10 to gain certain spectral'responses) for the separations
in Figure 3 are consistent with the circuit parameters ‘
presented in Figure 2 to illustrate an operative embodi
ment of the circuit.
result from cosine fourth effects due to some of the sep
' arations being positioned off the‘ illumination axis in an
‘
The adjustment of the resistor 80 determines, by volt 15 arrangement such as isshown in Figure 1.' For these
reasons, it may be necessary to adjust the phototube
age division with the dynode resistors 86, the cathode
circuits individually for each set of separations to be
voltage of the photomultiplier 52. Thus, the setting of
scanned.
the resistor ‘80, after the potentiometer 84 is set, deter
Such readjustment of the phototube circuits isrgen
mines the operating voltage across the photomultiplier
and, thereby, the gain of the photomultiplier (that is, 20 erally the same as that described above. The adjustment
of the. potentiometer 84 ‘provides the direct-voltage input
the change in photomultiplier current for a given change
levelv adjustment and, thereby, the directeoutput-current
in received light); The adjustment of the resistor 80
level for the black end of the transmission range. The
may be used to adjust the value of output current through
' alignment of the three channels in this manner at the
the tube 98 for the white extreme of the density range;
this may be approximately 2.5 milliamperes as shown in 25 same direct current output level for.black tends to-match
Figure 3 for the curve 136.
'
theblack end of a common neutral axis for the three
'
With the adjustments 84 and 80. set in this manner,
channels. The gain adjustment of the photomultiplier 52
the phototube circuit requires no compensation for the
extreme gray-scale steps at the white end of the range;
by means of the resistor 80 serves to match up the three
concurrent in this region from the white limit to about
the point 140. The adjustment of the resistor 112 deter
mines the bias voltage applied to the cathode of the diode
108 and, thus, the output-current value at which this
diode 108 starts to conduct. As shown in Figure v3, this
output-current value at which the diode 108 starts to
adjustment of the resistors 110, 112, 118, 120, ensures
channels for the white end of the neutral axis. The
for, as shown in Figure 3, the curves 136 and 138 are 30 adjustment of the diode compensating network, through
that the intermediate gray-scale steps are congruent.
Thus, these adjustments together tend to preserve a com
mon neutral axis for all three channels.
7
e
‘In accordance with-this invention, a new and improved
multichannel scanning system is provided. This system
conduct, represented by the point 140, is a little less than ' includes phototube circuits ‘that incorporate electronic
compensation for optical distortions in the scanning sys~
4 milliamperes. The adjustment of'the resistor 110 de
termines the amount of compensating current drawn by v40 tern. These circuits also include means to'adjust for dif
ferences in the distortions between the channels and, there~
the diodeplltlS and, thus, the slope of the curve 138 for
by, to insure that the output signals of these phototube
the region between the points 140 and 142. In a similar
manner, the resistor 120 is adjusted to permit the diode
116 to start to conduct when the output current exceeds
about 5.5 milliamperes (point 142 in Figure 3); the ad
justment of the resistor 118 determines the slope of the 45
curve 138 for values of output current in excess of 5.5
milliamperes to the black limit of 7 milliamperes.
circuits are aligned at the limits of'their ranges, and are
congruent at intermediate gray-scale steps.
What is claimed is:
,
I
1. In a color correctionlsystem, the combination of a
multichannel scanning system for deriving color compo
nent signals in accordance with the color component
characteristics of a subject; and color correction means
To summarize: The adjustment of the potentiometer
for combining said signals; said multichannel scanning
84 adjusts the minimum brightness or black level- of the
output current; the resistor 80 adjusts the maximum 50 system comprising means for producing a moving light
spot over a raster, said light spot producing means in
brightness or white level of the output current; the re
cluding a cathode ray tube; a plurality of optical chan
sistors 112, 120 are used to adjust the points at which
the slope of the curve 138 changes; and the settings of
nels, each of said channels being associated with a dif
' ferent component color and including a different photo
the resistors 110, 118 determine the slope of that curve
receptor for producing electrical signals vvariable over a
138.’ The phototube circuits 66 and 68 of the other
range‘ in accordance with the light received, and a dif
channels are individually adjusted in a similar manner;
ferent lens means for specularly directing to the as
generally, the limits of the output-current range,'and
sociatedv photoreceptor the light from said light spot that
the curve of the compensated vcharacteristic are the same
passes through a transparent photographic subject having
1
,
Generally, it may be necessary to make such adjust 60 di?use density’ values that vary with said color compo
nent characteristics; and a plurality of electronic circuits
ments of the phototube circuits 64, 66, 68 every time a
each connected to receive the signals produced by a dif
different photographic subject is scanned. In order for
ferent one of said photoreceptors, each of said circuits
the computer 70 or for the luminance signal circuit 127
individually including; a ?rst means for adjusting the
to combine properly the signals from the three channels,
it is necessary to have complete congruence of all the 65 signal level of the circuit output at one limit of the signal
range, a second means different from said ?rst means
gray-scale steps for the three primary-color signals.
for adjusting the gain of the circuit, and an adjustable
However, such congruence may not exist for a number
for all three channels.
of reasons:
.
nonlinear compensating network adapted to in?uence the
output ,of saidcircuit over a portion of its operating range
development of color separations may result in different 70 ‘for compensating said signals for differences in the asso—
ciated channel between diffuse and specular density values,
density ranges as well as in di?erent patterns of distor
whereby the outputs of said circuits are variable over the
tion of the gray scale for the three separations and asso
same range of values and corresponding intermediate out
ciated optical channels. For example, it has been foundv
Differences or necessary tolerances in the exposure and
desirable to use a part of a non-linear toe of the photo
i put values represent substantially the same diifuse density
graphic characteristic to take advantage of the low photo 75 values.
3,921,976
2.5 A multichannel scanning. system: :comprising,means_.,
for .producingra movingli'ghtspot. .over .azraster, said light
spot“ producing, means ~ including. a .cathode ray tube; .a .
plurality-of optical-channels‘, each of . said channels . being
1.0;
erent .lens means. .for._.d-irecting .to. the: associated ..color..
separation thevlighttof saidjlight sp'ot .andfo'rspecu_larl‘,'/v
directing, to the. associated .photoceptor, the light that
passes'through.theassociated color separation; and a pin
associated with a different primary color and including 5 rality ofelectronic circuits each connected to receive the
a different photoreceptor._.for.producing electrical. signals
signals produced" by a different one [of said ' 'photo
variable over ‘a' range ‘in accordance with‘ the light re
receptors, .eachof said circuits individually including a
ceived, separate-meansfforaspeeularly"directing to the as
non=linear..fee'dbackl arrangement for compensatingisaid
sociatedtphotoreceptor the light fromusaid lightrspo-ti that
signals for di?er'ences in the. associated "path'between- dif
passes through a transparent, photographic subjects-having
fuse and specularjdensity values and for photographic
di?fuse density vvalues that varywith- coloricharacteristics;
non-linearities .offth'e' associateda separation, ‘a ?rst adjust?
and a plurality of electronic circuits each connected to
ingmeans .for- adjusting ‘the ‘circuit output level .at- one‘
receive the signalssproducedaby aidiffe‘rent one of said
limit. of the signal range, and-a second adjusting means
photoreceptors, .each. of said. circuits. individually includ
different fromvsaid ?rst adjusting means for adjustingth'e
ing: ., a. non-linear .compensat-ing network for influencing ~ 15;
g‘ainof thefcircuits, whereby ‘corresponding range limits
the‘ operation of‘ the circuit over a. portion~of thesignal
of ~ the. outputs: and “corresponding intermediate output
range for compensating said signals for differences in‘ the
steps from each of said ‘circuits relate to the same diffils'e
associated channel between diffuse and specular density
density values.
values, ?rst means for adjusting the output signal level
5. In a system for obtaining color corrected records
of said circuit at one limit of the signal range, and sec
from
a plurality of transparent photographic separations
ond means different from said ?rst means for adjusting
having
diffuse density values that vary with associated
the gain of the circuit, whereby each of said electronic
color component characteristics of a subject, the com—
circuits is adjustable so that corresponding range limits
bination of a multichannel scanning system for deriving
of the output signals from said circuits and correspond
v color component signals in accordance with the color
ing intermediate signal steps relating to the same diffuse 25 component characteristics of said subject, said multi
density values are substantially the same.
channel scanning system comprising means for producing
3. In a system for obtaining color corrected records
a moving light spot over a raster, said light spot producing
from a plurality of transparent photographic separations
means including a cathode ray tube; means for supporting
having diffuse density values that vary with associated ‘
a plurality of said color separations associated with dif
color component chracteristics of a subject, the combina
ferent
component colors; a plurality of optical paths,
tion of a multichannel scanning system for deriving color
each of said paths including a different photoreceptor for
component signals in accordance with the color com
producing voltages variable over a range in accordance
ponent characteristics of said subject, said multichannel
with
the light received, and a different lens means for
scanning system comprising means for producing a mov
directing to the associated color separation the light of
ing light spot over a raster, said light spot producing 35 said
light spot and for specularly directing to the associ~
means, including a cathode ray tube; means for support
ated
photoreceptor the light that passes through the asso
ing a plurality of said color separations associated with
ciated
color separation; and a plurality of electronic cir
different component colors; a plurality of optical paths
cuits each connected to receive the signals produced by a
each including an individual photoreceptor for producing
different one of said photoreceptors, each of said circuits
electrical signals variable over a range in accordance
individually
including a non-linear compensating arrange
with the light received, and an individual lens means
ment for compensating said signals for differences in the
for directing to the associated color separation the light
associated path between diffuse and specular density
of said light spot and for specularly directing to the
values,
said compensating arrangement including an im
associated photoreceptor the light that passes through the
associated color separation; and a plurality of electronic 5 pedance means and a plurality of unilateral impedance
combinations connected in parallel with said impedance
circuits each connected to receive the signals produced by
means
to provide a resultant impedance network with
a different one of said photoreceptors, each of said cir
said impedance means, said impedance network having
cuits individually including: a non-linear compensating
different impedance values at different voltages applied
network adapted to influence the operation of the as
thereto, each of said electronic circuits further including
sociated electronic circuit over a portion of its operating
a feedback circuit responsive to the voltage from the asso
range to compensate said signals for differences in the
associated path between diffuse and specular density
values, ?rst adjusting means for adjusting the output sig
nal level of the circuit at one limit of the signal range,
and second adjusting means different from said ?rst ad
justing means for adjusting the gain of the circuit, where
by corresponding range limits of the outputs of the signals
from said circuits and corresponding intermediate signal
ciated photoreceptor for applying an ampli?ed voltage
to the associated impedance network, ?rst adjustable
means for adjusting the output level of the circuit at one
limit of the signal range, and second adjustable means
for adjusting the gain of the circuit, whereby correspond
ing range limits of the outputs from said circuits and
corresponding intermediate output steps relate to sub
stantially the same diffuse density values.
steps relating to the same diffuse density values are sub
6. In a system for obtaining color corrected records
stantially the same.
60 from a plurality of transparent photographic separations
4. vIn a system for obtaining color corrected records
from a plurality of transparent photographic separations
having diffuse density values that vary with associated
color component characteristics of a subject, the combi
nation of a multichannel scanning system for deriving
color component signals in accordance with the color
component characteristics of said subject, said multi
channel scanning system comprising means for producing
a moving light spot over a raster, said light spot produc
having diffuse density values that vary with associated
color component characteristics of a subject, the combina
tion of a multichannel scanning system for deriving color
component signals in accordance with the color com
ponent characteristics of said subject, said multichannel
scanning system comprising means for producing a moving
light spot over a raster, said light spot producing means
including a cathode ray tube; means for supporting a
plurality of said color separations associated with dif
porting a plurality of said. color separations associated 70 ferent component colors; a plurality of optical paths, each
of said paths including a different photomultiplier circuit
with different component colors; a plurality of optical
for
producing voltages variable over a range in accord
paths, each of said paths including a different photo
ance with the light received, and a different lens means for
receptor for producing electrical signals‘ variable over a
directing to the associated color separation the light of
range in accordance with the light received, and a dif
said light spot and for specularly directing to the associ
ing means including a cathode ray tube; means for sup
2,921,975
11
.
ated photomultiplier the light that passes through the
associated color separation; and a plurality of electronic
circuits each connected to receive the signal voltages pro
other limit of the light received, whereby corresponding
range limits of the signals from said circuits andlinter
mediate signal steps in corresponding circuits relating to
duced by a di?erent one of said photomultipliers, each of
said circuits individually including an adjustable non
the same diffuse density values are substantially the same.
linear compensating network for compensating said signal
voltages for di?erences in the associated path between
diffuse and specular density values and for photographic
References Cited in the ?le of this patent
UNITED STATES. PATENTS
non-linearities of the associated separation; each said
photomultiplier circuit individually including a ?rst ad 10
justable means for adjusting the voltage level at one of
the photomultiplier electrodes to set the voltage level cor-,
responding to one limit of the light received, and a second
adjustable means different from said ?rst adjustable means _
2,710,889
2,721,892
Tobias _______________ __ June 14, 1955
Yule _________________ __ Oct. 25, 1955
2,740,828
Haynes __'__-_ __________ __ Apr. 3, 1956
OTHER ‘REFERENCES
vFrayne et al.: Densitometers for Control of Color
for adjusting the voltage level across the photomultiplier 15 Motion-Picture Film Processing, February 1955, Journal
of the SMPTE, vol. 64, pages 67~68.
electrodes to set the voltage level corresponding to the
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