JPS63109686A - Automatic tracing circuit for white balance of color video camera - Google Patents

Abstract

PURPOSE:To attain photographing with an appropriate white balance, by providing 3rd and 4th comparator circuits to which output signals of 1st and 2nd integration circuits are supplied and by which said output signals and reference level signals are compared, and an exclusive 'OR' circuit to which the output signal of each comparator circuit is supplied. CONSTITUTION:Regardless of color temperature, logic of the output signals at respective output terminals of comparators 21 and 22 is such that the logic of one output signal is 'L' when the logic of the other output signal is 'H', and vice versa. Therefore, the output signal of an exclusive 'OR' circuit 23 becomes 'H' in logic and a start/stop controlling circuit 24 sets up-down circuits 8 and 16 and counters 9 and 17 to operable states. Therefore, when a whole picture becomes green of lawns in a state where white balance is maintained, gain controlling circuits 2 and 11 are held at the gains immediately before the whole picture turns to green and photographing can be carried out without spoiling the white balance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an automatic white balance tracking circuit for a color video camera that automatically adjusts white balance using a color difference signal obtained from a video signal.

(Prior art) Color video cameras need to adjust the white balance according to the light source to be photographed, and there are methods to do this, such as using a color filter, using a color temperature sensor,
There are some that use imaging signals.

Among these, those that utilize an imaging signal use an imaging lens to obtain the color temperature of the light source illuminating the subject, and have the advantage of a simple structure.

FIG. 4 is a block diagram of a conventional white balance automatic tracking circuit of a color video camera that utilizes such an image signal.

In the figure, an input terminal 30 is supplied with a blue primary color signal B obtained from an imaging signal, and this signal is supplied to a matrix circuit 32 via a gain control circuit 31 whose gain is externally controlled. A matrix circuit 32 generates a color difference signal (B-YL). Here, YL is a low-band luminance signal obtained by passing the luminance signal through a 0.8 MH2 low-pass filter.

This color difference signal (B-YL) is compared with a reference level in an auto-white circuit 33, and a control signal corresponding to the difference is obtained. The gain of the gain control circuit 31 is controlled by this control signal.

On the other hand, the red primary color signal obtained from the imaging signal supplied to the input terminal 34 is supplied to the matrix circuit 36 via the gain control circuit 35, where a color difference signal (R-YL) is obtained. (R-YL) is compared with a reference level signal in an auto-white circuit 37, and a control signal corresponding to the difference is obtained. The gain of the gain control circuit 35 is controlled by this control signal.

The imaging signals are outputted from the matrix circuits 32 and 36 through output terminals 38 and 39, subjected to signal processing by a modulation circuit (not shown), etc., and then taken out of the video camera.

The white balance automatic tracking circuit of a conventional color video camera with such a configuration takes advantage of the fact that the integral value of color over one screen is usually almost white; If the white level deviates from the set white level,
The color temperature is corrected based on the assumption that the color temperature of the light source for photographing has changed.

Figure 2 is an explanatory diagram, and the vertical axis is the color difference signal (R-YL
), the horizontal axis is the color difference signal (B-YL), and the curve P passing through the intersections of quadrants 1 and 2 and the axes in FIG. 2 is the color temperature axis (blackbody radiation axis). This color temperature axis P indicates that the color temperature can be controlled on the color temperature axis P by controlling the color difference signals (B-YL) and (R-YL) to account for the difference in color temperature.

Here, if the color temperature at the time of shooting becomes high while the white balance is well-balanced, the color temperature at this time will be located in the fourth quadrant on the color temperature axis P in Figure 2, and the color difference in the shooting signal will be signal(
It can be seen that the color difference signal (B-YL) increases and the color difference signal (R-YL) decreases.

Therefore, the auto white circuit 33 uses a color difference signal (B-YL).
) is increased from the set white level, and the gain control circuit 31 is controlled in accordance with the amount of increase to reduce the gain of the blue primary color signal B to control white balance.

On the other hand, with respect to the red primary color signal R, the white balance is adjusted by increasing the gain of the gain control circuit 35 based on the same logic.

On the other hand, if the color temperature becomes low at the time of shooting, the color temperature at this time will be located in the ① quadrant on the color temperature axis P in Fig. 2,
The gain of the gain control circuit 31 increases and the gain of the gain control circuit 35 decreases based on the same logic as when the color temperature becomes high.

In this way, if the subject is a subject whose integral value on the screen is white, it is possible to cope with changes in color temperature. However, if the entire screen is a solid green subject, such as a lawn, while the white balance is well-balanced, the color difference signal ( R-YL) and (8-YL) both decrease.

Therefore, the auto white circuits 33 and 37 detect this and operate to increase the gains of the gain control circuits 31 and 35 even though the white balance is correct, so the white balance shifts to the magenta side. As a result, the white balance is disrupted, and green becomes white and white becomes magenta.

Conversely, if the entire screen is magenta, the white balance will be disrupted, causing white to turn green and magenta to white.

(Problems to be Solved by the Invention) As mentioned above, the white balance automatic tracking circuit of the conventional color video camera has a problem in that the entire screen is colored close to green or magenta even though the white balance is correct. There is a problem in that when photographing objects with similar colors, the white balance is reversed and the colors shift to magenta and green, respectively.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides first and second solutions.
a first gain control circuit to which the primary color signals of are respectively supplied and whose gain can be controlled externally; A first matrix circuit and a second matrix circuit that generate color difference signals between the respective output signals of the gain control circuit and the low-band luminance signal, and integrate the respective output signals of the first and second matrix circuits. a first integrating circuit and a second integrating circuit;
a first comparator circuit that compares each output signal of the integrating circuit with a reference level signal; a second comparator circuit whose output characteristics are opposite to that of the first comparator circuit; and the first and second comparator circuits. a first control signal generation circuit and a second control signal generation circuit for controlling the gains of the first and second gain control circuits by respective output signals of the first and second integration circuits; a third comparison circuit and a fourth comparison circuit to which respective output signals are supplied and which are compared with the reference level signal; and an exclusive OR to which respective output signals of the third and fourth comparison circuits are supplied. circuit and an output signal of the exclusive OR circuit is provided to provide the first and second control credit circuits.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the white balance automatic tracking circuit for a color video camera according to the first invention. In the figure, to explain from the main blocks, 1 is an input terminal to which a red primary color signal R and a blue primary color signal B are supplied, and the signal supplied to this input terminal 1 is transmitted via a process circuit a. The auto white circuit is supplied with
The output signal of this auto white circuit is the process circuit a.
is applied with feedback to control the gain in the output circuit a.

Furthermore, the level is clamped in the auto white circuit and the signal passes through a low pass filter. , +1 iIl
The signal generator circuit is used to control the auto white circuit.

Next, more specific configurations of the process circuit a1, auto white circuit b, and control signal generation circuit C will be described.

The signal supplied to the input terminal 1 is supplied to one input terminal of the switch circuit 4 via the gain control circuit 2 and the matrix circuit 3 of the process circuit a serially, and the output signal of one of the switch circuits 4 is The signal is supplied to the negative terminal of the comparator 7 through the clamp circuit 5 and the low-pass filter 6 of the white circuit, respectively.

The output signal of the comparator 7 is supplied to the control t[I terminal of the gain control circuit 2 via an up/down control circuit 8, a counter 9, and an A/D converter 10 in series.

Further, the signal from the input terminal 1 is supplied to the other input terminal of the switch circuit 4 via a gain control circuit 11 and a matrix circuit 12 in series. The other output signal of the switch circuit 4 is supplied to the negative input terminal of a comparator 15 through a clamp circuit 13 and a low-pass filter 14 of the auto-white circuit, respectively.

The output signal of the comparator 15 is supplied to the control terminal of the gain control circuit 11 via an up/down control circuit 16, a counter 17, and an A/D converter 18 in series.

Furthermore, the output signal of a clamp circuit 19 whose input terminal is grounded via a capacitor C is supplied via a low-pass filter 20 to each positive input terminal of the comparators 7 and 15.

The output signal of this filter 20 is supplied to the respective positive input terminals of comparators 21 and 22 of the control signal generation circuit C, and the output signals of the filters 6 and 14 are supplied to the negative input terminals of the comparators 21 and 22. are supplied respectively.

Then, the output signals of comparators 21 and 22 are Ex −
The signal is supplied via an exclusive OR (OR) circuit 23 to a start/stop control circuit 24 in the auto white circuit. The output signal of this start/stop control circuit 24 is transmitted to the up/down control circuit 8.16 and the counters 9, 17.
are supplied respectively.

Note that the output signal of the switch circuit 4 is output from the output terminals 25 and 26.
A photographic signal is extracted by the camera and sent to the outside of the video camera via a modulation circuit (not shown) or the like.

The operation of one embodiment of the white balance automatic tracking circuit for the color video camera of the first invention having the above configuration will be described.

The input terminal 1 is alternately supplied with a red primary color signal R and a blue primary color signal B obtained from a solid path (dynamic element, signal processing circuit, bandpass filter, etc. not shown), and this signal is simultaneously supplied to control circuits 2 and 11;
The gain is controlled by the output signals of the D/A converters 10 and 18, and this will be explained later.

Matrix circuits 3 and 12 each receive color difference signals <
B-YL) and (R-YL). Here, Y
L is a low-band luminance signal obtained by passing the luminance signal through a 0.8 MHz low-pass filter.

The switch circuit 4 receives color difference signals (B-Y
L) and (R-YL), one of them is delayed by one horizontal synchronization period, and the color difference signals (B-YL) and (R-YL) are
) are simultaneously sent out from each output terminal.

After the color difference signal (B-YL) is clamped by a clamp circuit 5, the color signal for one screen is integrated by a low-pass filter 6. Comparator 7 outputs the integrated color difference signal (B
-YL) and the reference level signal from the filter 20, and if the color difference signal (B-YL) is larger than the reference level signal, a logic logic signal is sent out, and in the opposite case, a logic H signal is sent out.

When the output signal of the comparator 7 sends out a logical signal, the up/down control circuit 8 receives this and decreases the count of the counter 9. The count of the counter 9 is converted into an analog value by the D/A converter 10, and the gain of the gain control circuit 2 is reduced to reduce the level of the blue primary color signal B.

Conversely, when the output signal of the comparator 7 is logic H, the level of the blue primary color signal B acts to increase.

Next, the color difference signal (R-YL) from the switch circuit 4 is
After being clamped in the same way as the color difference signal (B-YL), the signal for one screen is integrated and compared with the reference level signal by the comparator 15, and if the color difference signal (R-YL) is larger than the reference level signal. In the opposite case to the comparator 7, it sends out a logic H signal, and in the opposite case, it sends out a logic low signal.

Similar to the case of the comparator 7, the output signal of the comparator 15 is converted into an analog signal by the D/A converter 18 to control the gain control circuit 11, but the gain control circuit 11 has a characteristic opposite to that of the gain control circuit 2. It is. That is, D/
As the output signal of the A converter 18 increases, the gain of the gain control circuit 11 decreases, and as the output signal of the D/A converter 18 decreases, the gain increases.

The above explanations are all based on the assumption that the start/stop control circuit 24 is in the start state.

Here, if the white balance is correct and the color temperature at WJr becomes high, the color difference signals (B-YL) and (R-YL) due to the shooting signal at this time are on the color temperature axis in Figure 2. It can be seen that the color difference signal (B-YL) of the photographing signal increases and the color difference signal (R-YL) decreases.

Therefore, as explained above, the gain of the gain control circuit 2 decreases, the level of the blue primary color signal B decreases, the gain of the gain control circuit 11 increases, and the level of the red primary color signal R increases. Correct the white balance.

This time, if the color temperature of the subject becomes lower when photographing, the image signal at this time will be located in the second quadrant on the color temperature axis P in Fig. 2, and the color difference signal (B-YL) will decrease, Color difference signal (
R-YL) increases. Therefore, since the situation is completely opposite to the case where the color temperature is high, the gain of the gain control circuit 2 is increased,
It operates to increase the level of the color difference signal (B-YL), reduce the gain of the gain control circuit 11, and decrease the level of the color difference signal (R-YL).

As mentioned above, whether the color temperature becomes high or low, the output signals of the respective output terminals of the comparators 21 and 22 are such that when one is logic H, the other is logic, and when one is logic, the other is logic. is logic H, so Ex -OR circuit 23
The output signal becomes logic H, and the start/stop control circuit 24 controls the up/down circuits 8, 16 and the counters 9, 1.
7 is ready for operation.

Here, with the white balance correct, the entire screen is
For example, when the grass is all green, the green is located in G of quadrant ① in Fig. 2, and the color difference signal (R-
YL) and (B-YL) both decrease.

Therefore, if left as is, the gains of the gain control circuits 2 and 11 would work to increase, causing the white balance to collapse.In order to prevent this, the control signal generation circuit C is activated. It has become.

That is, since the color difference signals (B-YL) and (R-YL) have decreased with respect to the reference level signal, the comparators 21 and 22 both send out logical H signals, and the Ex-OR circuit 23 sends out logical H signals. In response to this logic signal, the start/stop control circuit 24 stops the up/down control circuit 8.16 and the counter 9.17, respectively, and holds the value at that time.

Therefore, the gain control circuits 2 and 11 are maintained at the gain just before the entire screen becomes solid green, allowing photography to be performed without disturbing the white balance.

Next, when the white balance is correct and you shoot a subject whose entire screen is magenta, the magenta color is located in M a of the engraver's quadrant in Figure 2, so the image signal is Since the color difference signals (B-Y) and (R-Y) increase, the comparators 21 and 22 both send out logical signals, and the EX-OR circuit 23 sends out logical signals. Start-stop control circuit 2
2 is an up/down control circuit 8, 16 and a counter 9,
17, respectively, and hold the values at that time.

Therefore, the gain control circuits 2 and 11 are maintained at the gain just before the entire screen becomes magenta, making it possible to take pictures without disturbing the white balance.

FIG. 3 shows a block diagram of an embodiment of an automatic white balance tracking circuit for a color video camera according to the second invention. The difference from FIG. 1 is that an adder circuit d is provided that adds the two output signals of the auto white circuit in FIG. 1, and the output signal of this adder circuit d controls the gain of the gain control circuit 2.11. It is configured to do so. Therefore, the same components as those in FIG. 1 will be described with the same reference numerals.

As explained above, the second invention also adjusts the white balance when the integral value of the entire screen deviates from the white level, since the integral value of the entire screen to be photographed is generally white. The integral value for the entire screen is not near the color temperature axis P shown in Figure 2, for example, red (R in quadrant ■ in Figure 2) or cyan (CY in quadrant ■ in Figure 2)
It is a more effective invention if

Here, if the entire screen to be photographed is almost red, the position of the red color is away from the primary color temperature axis P shown in Fig. 2 and close to the color difference axis (R-YL), and the position of the red color is away from the color difference axis (B-YL).
It is located in R, which is further away.

In other words, the color difference signal (B-YL) is better than the color difference signal (R-YL).
) is closer to the set white level.

Therefore, the color difference signal (B-YL) converges to the set value faster. This depends on whether the up/down control circuit 8.16 and the counters 9, 17 converge to the white level one step at a time in response to the clock signal.

If the color difference signal (B-YL) quickly converges to the set value in this way, the levels of the two input signals of the comparator 7 will be almost the same, and the output signal of the comparator 21 can only be logical or H, so at the critical point. The output signal of is in an unstable state of logic or H. At this time, the color difference signal (R-YL) that is the input signal to the comparator 22 does not yet match the set white level, so the comparator 2
Since the output signal of comparator 2 is a logic high, if comparator 2
When the output signal of 2 becomes logical, it is still a color difference signal (R-Y
Although L) has not converged to the white level, E
The output signal of the X-OR circuit 23 becomes logical and maintains the gain of the gain control circuit 2.11. Then, when the output signal of the comparator 21 becomes logic H again, the operation of the gain control circuit 11 resumes and converges to the white level, but there may be a time delay or the white level may not be reached midway.

However, an embodiment of the white balance automatic tracking circuit for a color video camera according to the second invention is provided with an adder circuit d, so that if the object to be photographed is red as described above, D. Since the output signals of the /A converters 10 and 18 are summed, they are averaged and located on the color temperature axis P.

If it is located on the color temperature axis P in this way, the influence on the color will be smaller than if it is located away from the color temperature axis P, and the white balance can be controlled quickly when the screen is switched.

Note that the reset circuit 27 shown in each of FIGS. 1 and 3 sets the white balance to the middle of the color temperature control range when the power is turned on to the white balance automatic tracking circuit of the color video camera of the present invention. The output signal of the D/A converter 10.18 is set to approximately 4300'''K.

(Effects of the Invention) According to the present invention, even if the integral value of the color of the entire screen is a subject consisting of green and magenta colors and colors in their vicinity, the white balance is maintained by maintaining the white balance immediately before the subject. It has the feature that it prevents the color temperature from shifting from the color temperature axis (blackbody radiation axis), enables photography with an appropriate white balance, and allows photography of the correct colors.

In addition to this, in the second invention, even if the integral value of the entire screen is a subject consisting of red, cyan, or colors in their vicinity, the color temperature axis will not be locked at a location where the color balance is disrupted. Since the color temperature is corrected to the point close to the blackbody radiation axis, it is possible to create shadows with less color shift, and
It has the advantage of being able to smoothly track the white balance for the next screen.

[Brief explanation of the drawing]

1 and 3 are block system diagrams of respective embodiments of the first and second inventions of the white balance automatic tracking circuit for a color video camera according to the present invention, FIG. 2 is an explanatory diagram, and FIG. The reason is the block diagram of the white balance automatic tracking circuit of a conventional color video camera. DESCRIPTION OF SYMBOLS 1... Input terminal, 2... First gain control circuit, 3.
... first matrix circuit, 6 ... low-pass filter (first integration circuit), 7 ... comparator (first comparison circuit), 8.16 ... up-down control circuit, 9
．． 17...Counter, 10.18...D/A converter, 11...Second gain control circuit, 12...Second
matrix circuit, 14... low pass filter (second integration circuit), 15... comparator (second comparison circuit), 21... comparator (third comparison circuit),
22... Comparator (fourth comparison circuit), 23...
- Ex-OR circuit (exclusive OR circuit), a...process circuit, b...auto white circuit, C...control signal generation circuit, d...addition circuit.

Claims (2)

[Claims] (1) A first gain control circuit to which the first and second primary color signals are respectively supplied and whose gain can be controlled externally, and a second gain control circuit whose control characteristics are opposite to the first gain control circuit. , a first matrix circuit and a second matrix circuit that generate color difference signals between the output signals of the first and second gain control circuits and the low-band luminance signal, and the first and second matrix circuits. a first integrating circuit and a second integrating circuit that integrate respective output signals of the first and second integrating circuits; a first comparing circuit and a second integrating circuit that compare the respective output signals of the first and second integrating circuits with a reference level signal; a second comparator circuit whose output characteristics are opposite to that of the first comparator circuit; a first control signal generation circuit, a second control signal generation circuit, a third comparison circuit and a fourth comparison circuit to which respective output signals of the first and second integration circuits are supplied and compared with the reference level signal; The comparison circuit and this third and fourth
an exclusive OR circuit to which respective output signals of the comparison circuits are supplied; and a control circuit to which the output signals of the exclusive OR circuit are supplied to control the first and second control signal generation circuits. A white balance automatic tracking circuit for a color video camera. (2) A first gain control circuit to which the first and second primary color signals are respectively supplied and whose gain can be controlled externally, and a second gain control circuit whose control characteristics are opposite to those of the first gain control circuit. , a first matrix circuit and a second matrix circuit that generate color difference signals between the output signals of the first and second gain control circuits and the low-band luminance signal, and the first and second matrix circuits. a first integrating circuit and a second integrating circuit that integrate respective output signals of the first and second integrating circuits; a first comparing circuit and a second integrating circuit that compare the respective output signals of the first and second integrating circuits with a reference level signal; a second comparator circuit whose output characteristics are opposite to that of the first comparator circuit; A first control signal generation circuit and a second control signal generation circuit, and the output signals of the first and second control signal generation circuits are added and the control signals are sent to the first and second gain control circuits, respectively. an addition circuit; a third comparison circuit and a fourth comparison circuit to which respective output signals of the first and second integration circuits are supplied and which are compared with the reference level signal; and the third and fourth comparison circuits. an exclusive OR circuit to which respective output signals of the circuits are supplied; and a control circuit to which the output signals of the exclusive OR circuit are supplied to control the first and second control signal generation circuits. A white balance automatic tracking circuit for a color video camera.