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FIELD OF THE INVENTION
This invention relates to the reproduction of color pictures by electronic
means such as are utilized in television and in scanners used in making
color separations for the printing industry.
DESCRIPTION OF THE PRIOR ART
In color television and in color printing, it is sometimes desirable to
selectively modify certain chosen colors without affecting others.
Heretofore, this capability has been provided by a non-linear matrix
device invented by Monahan et al, U.S. Pat. No. 3,558,806. The Monahan
invention has been implemented and made available to the industry by the
RCA Corporation in a device known as the Chromacomp and also by the
Philips Audio Video Systems Corporation in a device known as the Variable
Matrix. These devices permitted independent adjustment of the hue and
saturation for each of the six primary and secondary hues: red, cyan,
green, yellow, blue and magenta. In other words, the chrominance plane is
divided into six sectors, each centered on the aforesaid hues; within each
sector, the hue and saturation of the colors lying within that sector can
be altered without affecting color lying outside that sector. With the
non-linear matrix device invented by Monahan it is not possible to change
the color of one object whose color lies within one segment of the
chrominance plane without affecting the color of other objects in that
segment. Moreover, because the color of a given object usually is
represented by an area in the chrominance plane and not just a single
point, and because that area may lie in two or more adjacent segments,
adjustment of the color of that object may require coordinated adjustments
in the adjacent segments. While this can be done, it presents some
difficulty to the colorist operating the equipment.
SUMMARY OF THE INVENTION
This invention provides a capability for modification of both the luminance
and chrominance of the colors in an arbitrarily selected region of the
color space while not affecting the colors outside that region; the
selected color space region may further be delimited to an arbitrarily
selected region of the picture itself. This modification capability can be
applied independently in a multiplicity of regions.
In order to guide the colorist in his choice for the location, shape and
size for any of the color modification regions, this invention provides
several cathode ray tube displays. In one of these displays the monitor
scope, which normally displays either the original picture or the modified
version, can be blanked out except in the region selected for
modification. In another of these displays the monitor scope, or its
equivalent, shows the area in the chrominance plane of the color
modification region. In still another of these displays the monitor scope,
or its equivalent, shows the extent along the luminance axis of the color
modification region.
In the television industry there is a particular need for color
modification of picture material which is stored on color film. Typically,
this material is a composite of a number of scenes, each scene requiring
independent modification. Because of the rapidity with which one scene
changes to the next, scene-by-scene instructions for color modification
are stored in a digital computer and applied automatically as the scenes
change. This technology has been described in U.S. Pat. Nos. 3,610,815,
3,637,920 and 4,096,523. This invention can also be implemented in such
computer controlled systems; when so implemented, some of the functions
which would otherwise be implemented in apparatus can be handled by
computer software.
In color television systems, the color signals change too rapidly for
digital computer processing and storage; the digital computer is limited
to processing and storing control signals. However, color separation
scanners for the printing industry can be implemented in such a way that
the color signals pass through the computer and may be processed and
stored in digital form. Such a digital computer-scanner has been described
in U.S. Pat. No. 3,612,753. This invention can be implemented in such
systems, where the color signals are in digital form and accessible to a
digital computer; when so implemented, many of the functions which would
otherwise by implemented in apparatus can be handled by computer software.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention is described in greater detail by reference to the Figures.
FIG. I depicts the chrominance plane.
FIG. II depicts the basic embodiment of this invention.
FIG. III depicts an embodiment of the control aspects of this invention
when used with a digital computer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In color television systems, three signals, Red, Green and Blue are
generated by three camera tubes, each viewing the same picture but through
red, green and blue filters respectively. In order to provide
compatibility with monochrome reception and to facilitate transmission,
the Red, Green and Blue signals are transformed into signals Y, I and Q.
Upon reception the Y, I and Q signals are transformed back into Red, Green
and Blue signals which are then used to excite the corresponding
picturetube phosphors. These transformations are referred to as
"matrixing" and are well known to those skilled in the art.
The color of any picture element, thus, has three attributes, e.g., Red,
Green Blue or Y, I, Q, and may be thought of as being represented by a
point in a three dimensional color space. The coordinates in that space
may be taken as Red, Green, Blue or alternatively as Y, I, Q. Matrixing is
equivalent to a change in the coordinate system. The Y, I, Q coordinate
system is of particular interest because it corresponds with the human
perception of color. Y corresponds with the luminance or brightness of a
color; the I and Q axes lie in a plane of constant luminance. This plane
is known as the chrominance plane and is depicted in FIG. I. Radial
distance of the color point, 1, from the origin, 2, on this plane is known
as saturation; angular position is known as hue. The angular positions of
the primary and secondary hues, red, green, blue and cyan, magenta, yellow
are shown on the periphery of FIG. I. The chrominance boundaries of a
typical region selected for color modification are shown at UI, LI, UQ and
LQ. The corresponding boundaries for the region along the luminance axis
are designated as UY and LY but are not depicted in FIG. I.
The colorist, the person operating an equipment embodying this invention,
selects the boundaries of the region within which he intends to make a
color modification by setting the bank of potentiometers, 3, shown in FIG.
II. If the equipment permits further delimitation of the region to a
specified area of the picture by the inclusion of potentiometer bank, 4,
and its associated comparators, 6, he would also set potentiometers, 4.
This act of setting the potentiometers establishes voltage levels which
correspond with the region boundaries UI, LI, UQ, LQ, UY, LY, UH, LH, UV,
LV, respectively.
The banks of comparators 5 and 6 determine whether the color signals Y, I,
Q on the one hand, and whether the deflection signals H, V on the other
hand, lie within the region selected. The comparators depicted here are
commercially available under the designation LM319. They have what is
termed "open collector output", i.e., if the voltage at the + input 7
exceeds the voltage at the - input 8, the condition at the output 9
relative to the reference terminal 10 will be an open circuit; if the
voltage at the + input 7 does not exceed the voltage at the - input 8, the
condition at the output 9 relative to the reference terminal 10 will be a
short circuit. Thus, if, and only if, all three color signals lie within
the boundaries of the selected region:
UY<Y<LY and UQ<Q<LQ and UI<I<LI and UH<H<LH and UV<V<LV
where H is the signal voltage corresponding to the horizontal coordinate of
a point in the picture
where V is the signal voltage corresponding to the vertical coordinate of a
point in the picture
then the gate signal 11 will be at a level of plus six volts. If, on the
other hand, any of the three color signals Q, I, Y, or any of the two
coordinate signals H, V, lie outside the boundaries of the selected
region, one or another of the comparator output terminals 9 will be short
circuited to the reference terminal 10 and the gate signal 11 will be at a
level of minus six volts. The electronic switches at 12 and 14, which are
typified by the commercially available unit designated as the CD4066A,
will be in the closed position shown when the respective control members
13 and 15 are at a potential of +6 volts; but they will be open when the
control members 13 and 15 are at a potential of -6 volts.
Control switches 19-26 which can be operated either manually or remotely by
means of relays, control the picture to be displayed on the monitor scope
17 and to be available for recording or transmission at 18. Table I lists
the monitor scope pictures as a function of the settings of control
switches 19-25. Thus, for the unmodified picture to appear on the monitor
scope 17, switches 23 and 24 are put in the left position, switch 25 is
put in the right position; as a result electronic switch 12 will be
closed, electronic switch 14 will be open, and the Q,I,Y signals alone
will appear at the input to the summation amplifiers 16 and upon the
monitor scope 17.
For a modified picture to appear on the monitor scope 17 and to be
available for transmission or recording at 18, the switches 19-25 are set
in accordance with line 2 of Table I. If the color signals Q,I,Y or the
location V,H in the picture plane are outside the selected modification
region, gate signal 11 will be at a potential of -6 volts, electronic
switch 12 will be closed, electronic switch 14 will be open, only Q,I,Y
will appear at the summation amplifiers 16 and on monitor scope 17. On the
other hand, if the color signals Q,I,Y and the location V,H in the picture
plane are inside the selected modification region, gate signal 11 will be
at a potential of +6 volts, both electronic switches 12 and 14 will be
closed, the color modification voltages MQ, MI, MY will be added to the
unmodified color signals Q,I,Y in the summation amplifiers 16, and the
modified color will appear on the monitor scope 17 and be available for
recording or transmission at 18. At this point the colorist can alter the
color within the modification region at will by adjusting the modification
potentiometer bank 26.
TABLE I
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Switch Positions
Line 19 20 21 22 23 24 25 Monitor Scope Display
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1 * * * * Lt Lt Rt Unmodified picture
2 Lt Lt Lt Lt Lt Rt Lt Modified picture
3 Lt Lt Lt Lt Lt Rt Lt Picture blanked except in
modification region
4 Rt Lt Rt Rt Rt Rt Rt Extent of modification region
in chrominance plane
5 Rt Rt Lt Rt Rt Rt Rt Extent of modification region
along luminance axis
6 * Rt Rt Lt Rt Rt Rt Extent of modification region
in picture plane
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* = Either
Lt = Left
Rt = Right
The system depicted in FIG. II is based upon analog type comparators,
switches and summation amplifiers. However, digital equivalents of these
elements are commonly available and can be used instead of their analog
counterparts. For example, SN74LS85 digital comparators can be used to
provide comparator action on digital signals; SN74LS157 data selectors can
be used as switches for digital signals; SN74LS83 binary adders can be
used to add digital signals. One or more of these digital type devices
could be used in place of the corresponding analog device of FIG. II. If
digital switching alone were to be employed using SN74LS157s, the color
modification signals would be supplied to it in digital form and the
switch outputs would be converted to analog form by digital-to-analog
converters such as the DAC-08. If digital comparators and summation
amplifiers such as the SN74LS85 and the SN74LS83 were to be used in
addition, the color video signals as well as the control voltages would be
supplied in digital form. The MATV-0811 is an example of a
state-of-the-art device for converting normal analog video voltages into
digital form.
The system depicted in FIG. II is capable of modifying color in only one
selected region. By additional banks of potentiometers 3, 4, 26,
additional banks of comparators 5, 6, additional electronic switches 12,
14, and by appropriate changes in switches 19-25, a multiplicity of
regions can be established and independent color modifications made in
each region.
In addition, Red, Green, Blue instead of Q,I,Y signals may be operated upon
while correction and control can be exerted in terms of Q,I,Y. This can be
accomplished by the use of appropriate matrixing circuits to transform the
voltage levels from potentiometer banks 3, 4, 26 into the Red, Green, Blue
equivalents. Moreover, for convenience to the colorist, the upper and
lower boundaries to a region may be obtained by the addition and
subtraction of voltages derived from controls specifying window
parameters; window parameters being the mean and difference of the upper
and lower boundaries.
In the foregoing description relating to FIG. II, the color space region
and the picture plane region, which are described in terms of upper and
lower boundaries for Q, I, Y, V and H, are a rectangular parallelopiped in
color space and a rectangle in the picture plane. These particular shapes
for the regional boundaries result not only from the fact tht Q, I, Y, V
and H are rectangular coordinate systems in their respective spaces but
also from the particular circuitry chosen for illustration. Alternative
shapes for the regional boundaries are possible. For instance, a region in
color space with ovoid boundaries and a region in the picture plane with
oval boundaries could be implemented with hardware or software no more
complicted to design or build than that required for regions with
rectangular boundaries. The size and location of these regions would still
be defined by the same upper and lower boundaries for Q, I, Y, V and H;
these are now recognized to be values of these coordinates at the
intersection of the regional boundaries with the coordinate axes.
Some of these circuit elaborations may become inordinately extensive and
the large number of controls may become conducive to operating errors. In
that case, a digital computer may be used advantageously to reduce the
amount of circuitry and the number of controls. FIG. III illustrates how
control may be exerted by means of a digital computer; it depicts a
typical control panel. Only one joystick control, 27, is employed. The
joystick function is determined by which one of the control buttons 28-34
is depressed; these functions are listed in Table II.
TABLE II
______________________________________
Button Joystick Function
______________________________________
28 Move center of modification region ih chrominance
plane
29 Change dimensions of modification region in
chrominance plane
30 Change center and extent of modification region
along luminance axis
31 Change center of modification region in picture
plane
32 Change dimensions of modification region in
picture plane
33 Change chrominance correction in modification
region
34 Change luminance correction in modification
region
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At most, only one of the control buttons may be depressed at a given time,
the one depressed being indicated by backlighting. The joystick 27 can be
moved up or down, right or left. The up-down component of motion controls
a multiple position switch; the right-left component of motion controls
another multiple position switch. In operation, the joystick 27 controls
the rate and direction with which the computer is to change the function
designated by the depressed control button. For instance, if control
button 28 has been depressed, the position of joystick 27 will be
interpreted by the computer as an order to move the color modification
region in the chrominance plane; if joystick 27 is in its center position
there will be no motion; if off center the color modification region will
move in the direction that the joystick 27 is displaced and at a rate
proportional to the distance that the joystick 27 is displaced from the
center. The computer, by sensing the switch closures actuated by the
control buttons 28-34 and the joystick 27, makes all of the necessary
computations to change the color modification region boundaries. Buttons
35-37 enable the colorist to select the color modification channel by
depressing the appropriate button momentarily. Button 35 resets the
channel number to one; button 36 advances the channel number by one;
button 37 decreases the channel number by one. Buttons 38-40 enable the
colorist to select the picture to be displayed on the monitor scope. Only
one of these buttons may be depressed at a given time, the one being
depressed being indicated by backlighting.
Since the control panel described by reference to FIG. III operates, in the
main, by instituting changes, it is most desirable that the colorist be
given displays which depict the current situation. While this can be
provided largely by the monitor scope 17 as described earlier, it may be
preferable to confine the monitor scope to showing only the original,
blanked and corrected pictures, and to provide another scope display as at
41 on FIG. III. Scope 41 shows the selected region on the chrominance
plane 42, the selected region along the luminance axis 43, the selected
region on the picture plane 44, the number of the current channel 45, and
the total numbers of channels in current use 46.
The computer software and hardware necessary to implement the functions
described in connection with FIG. III are well known to those skilled in
the art of computer systems and need not be elaborated upon.
* * * * *
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