JPH0124396B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention displays the white balance adjustment status of a color television camera on the subject monitor screen of the viewfinder, thereby allowing the camera operator to know whether the white balance is correct or incorrect. This invention relates to a white balance operation display method that allows easy identification.

When using a color television camera outdoors, the white balance is adjusted using outside light, but when the camera is brought indoors, the white balance must be re-calibrated under the new environment. Since the color temperature of outdoor light and indoor lighting is different, the resulting image output will have a reddish tinge overall, resulting in noticeable "color shift" and a decrease in the quality of the reproduced image. In this way, adjusting the white balance of a color television camera is one of the important preparatory operations before use.

Conventionally, methods for achieving white balance depend on the lighting conditions in the environment in which the television camera is used, such as
If the usage environment is indoors, a white subject is illuminated and imaged in that condition, and the resulting signals indicating the white part of the red (R) signal, green (G) signal, and blue (B) signal are obtained. When the condition that the level is the highest is met, the white balance button is pressed and the gain of the process amplifier for each color signal is automatically controlled and set to match the levels of the three color signals and installed in the viewfinder of the television camera. The indicator light was turned on when the three color signal levels matched to notify the camera operator that the white balance adjustment was complete.

However, such a method has the following drawbacks.

In other words, when adjusting the white balance, if a subject adjacent to a white subject with an electrical signal level higher than this enters the imaging field of view, the white balance circuit will operate with that high level signal. Even if a white object is imaged during a photo shoot, the image output signal does not reproduce it as white, resulting in a "color shift" that makes it difficult to see, and the image quality inevitably deteriorates.

Although this kind of situation can be avoided if the camera operator is careful, there is a fear that operators who are too absorbed in operating the camera often overlook it, and in fact, based on such cases, Image quality often deteriorates.

Conventionally, the completion of white balance adjustment has only been indicated by an indicator light, and that indicator light may turn on once white balance adjustment is complete, regardless of the incorrect imaging field of view as described above. This is also due to the fact that camera operators tend to rely too much on the indicator light.

From the viewpoint that such human erroneous operations cannot be prevented unless the camera operator always pays attention to the above-mentioned problems, the present invention provides that the camera operator does not necessarily need to perform the operations. A display pattern is superimposed and projected on the white-balanced subject part on the viewfinder's video screen that needs to be viewed in a form that allows the image of this part to be visually confirmed, In a color television camera comprising an automatic white balance circuit that uses a specific color signal among the three color signals as a reference and matches the level of other color signals to the reference color signal level, the automatic white balance A display signal from a display signal generator is extracted by an extraction signal having a timing and time width corresponding to a color signal whose level is matched by a circuit, and this extracted display signal is supplied to a viewfinder of the color television camera. By superimposing the image on the video signal, the display pattern is superimposed and displayed on the screen of the viewfinder at the location extracted for white balance, so that the image of this location can be visually confirmed. That is.

FIG. 1 shows a well-known automatic white balance circuit in a three-tube color television camera.

In the same figure, when adjusting the white balance,
If a white subject, which is the standard for white balance, is illuminated with the illumination light from light source 2, white subject 1
The reflected light passes through the imaging lens 3 and is separated into three color lights of red (R), green (G), and blue (B) by the three-color separation optical system 4, and enters the respective image sensors 5, 6, and 7. . The three color lights are photoelectrically converted by each image sensor 5, 6, and 7, and each red (R), green (G), and blue (B) video signal (hereinafter referred to as "R signal, G signal, B signal,
It is called "signal". ) and amplified by process amplifiers 8, 9 and 10, respectively.

It is assumed that the respective color signal levels at this time have the relationships shown by dotted lines a, b, and c in FIG.

These three color signals are guided to each differential amplifier 11, 12 including a peak value detection circuit as shown in the figure, and when the push button switch of the auto white control circuit (not shown) is pressed, each differential amplifier 11, 12 is guided to each differential amplifier 11, 12 including a peak value detection circuit. , the R and B signals are compared with the G signal as a reference, and the comparison outputs are fed back to the process amplifiers 8 and 10, so that the B and R signals become the G signal as shown by the solid line in FIG. The gain of each amplifier 8, 10 is automatically controlled to match the level of the white balance, and the camera operator lights up the indicator light 13 provided in the viewfinder to notify the camera operator that the white balance adjustment is complete. is informed. The gain of each amplifier 8, 10 is maintained as is when the camera operator releases the push button switch.

Therefore, when a television camera with the white balance adjusted in this manner captures an image of the same white subject, a white signal will be obtained regardless of the color temperature of the light source.

In the figure, 9 is a process amplifier for a specific color signal, that is, a G signal in this case, and 15 is an encoder for forming a color television signal of a desired system, the output of which is sent to a terminal 16. taken from.

However, when performing white balance in this way, if there is an unnecessary light source 14 with higher brightness and color near the white subject 1 or another unnecessary subject 14 within the imaging field of view, The imaging output at that time is the other subject 14.
Assuming that the subject is a bluish subject, as shown in A, B, and C of Fig. 3, a pair of signals S, W, and S corresponding to a bluish subject and a white subject, respectively, are generated for each color signal. ', W'·S'', W'' are extracted, and the level of the B signal S of the signal S corresponding to the bluish subject is higher than that of the B signal W of the white subject.

Under these conditions, when the white balance adjustment circuit explained earlier operates to detect the maximum level of the three color signals, the white balance circuit (Figure 1) outputs the G signal W' corresponding to the white object shown in Figure B. The high-level B signal S corresponding to the bluish subject shown in A in the same figure was compared with the reference, and as a result, the gain of the B signal amplifier 8 was lowered, resulting in a bluish color as shown in the figure. Automatic control is performed so that the levels of the subject B signal S and the white subject's G and R signals W' and W'' match. Furthermore, in this state, it is assumed that the white balance adjustment has been completed, and the indicator light 1 is
3 lights up. If you take an image of a white subject with a color television camera without noticing such malfunction of the white balance circuit, the image will be output as a reddish color.

In order to prevent such a situation, in the present invention, when adjusting the white balance, in order to make the camera operator aware that the white balance is being adjusted by a subject other than a white subject, the corresponding part on the screen of the Viewfinder is displayed. A visually appropriate display pattern, such as a zebra pattern, is superimposed on the display.

FIG. 4 is a block diagram of an embodiment of the present invention method using a part of the known white balance display circuit 17. The input terminals 21, 22, and 23 are R, G, and B signal output terminals 18, 19, and 20 of the well-known white balance circuit shown in FIG. Lead the color signal.

Each of these color signals is sent to each level detector 2.
4, 25, and 26 to hold the peak value, the level detector 25 detects the peak value in addition to the comparators 27 and 28 configured to output the input signal if the level difference is within a predetermined tolerance range. Based on the value-held G signal, the level detector 2
The peak value hold R signal and G signal from 4 and 25 are compared in level, and the indicator lamp 13 is turned on based on the comparison output signal, thereby indicating the operating state of the white balance.

However, as described in detail earlier, in the circuit 17, when there is a high-brightness object other than a white object within the imaging field of view, the white balance circuit 17 malfunctions as shown in FIG. There is a risk that the adjustment completion display may be displayed.

Therefore, in the system of the present invention, as shown in the embodiment of FIG. 4, for example, the R, G, and B signals derived from the white balance circuit of FIG. Each color signal from the white balance circuit (FIG. 1) is branched and taken out from 23 and led to an amplitude selection mixing circuit 30.

The amplitude selection mixing circuit 30 may have the function of outputting only the input signal with the highest amplitude among the plurality of input signals when the plurality of input signals are input at the same timing. , will be explained assuming that a NAM circuit (non-addition mixed circuit) is used.

Now, the color signals S, W・S′, based on the malfunction of the white balance circuit (Fig. 1) as shown in Fig. 2,
Assuming that W'・S'', W'' are input to the NAM circuit 30, S, S', and S'' are signals at the same timing, so the highest level S is the B of the bluish subject. The signal is also W of a white subject,
Regarding W' and W'', either W' or W'' is similarly selected and the output signal shown in FIG. 5A is output. That is, signals W' and W'' corresponding to the B signal S from a bluish subject and the G signal or R signal from a white subject are extracted with a timing relationship related to the positions of these two subjects. The output signal is led to a comparator 31, and its level is compared with the peak value held G signal from the G signal level detector 25 used as a reference signal in the white balance display circuit 17 as a reference (indicated by L in FIG. 5A). Then, with the comparison output, the extracted signals M, N
(Figure 5B). Since this extracted signal is obtained by selecting a color signal with white balance as explained earlier, it has a timing and time width corresponding to the selected and extracted color signal. That is clear.

The extracted signals M and N obtained in this way are such that the level of the G signal used as the reference signal by the comparator 31 is NAM
Since it changes in accordance with the level fluctuation of the input signal of the circuit 30, even if the input signal level is extremely low, it can be reliably extracted without malfunctioning.

In this embodiment, the gate circuit 3 uses the extracted signals M and N obtained in this way as gate signals.
3, and gate the display signal from the display signal generator 32 to extract the display signal of the part corresponding to the bluish subject part and the white subject part, which are the subject of white balance adjustment. can do.

In the method of the present invention, the display signal extracted in this way is guided to the mixer 34 and superimposed on the video signal for the viewfinder, so that it is possible to visually confirm the area where the white balance is maintained on the video screen of the viewfinder. In this embodiment, the display signal extracted by the gate circuit 33 is used to display the display pattern in a superimposed manner. Furthermore, the white balance display circuit 17
The comparison output signals from the comparators 27 and 28 are converted into gate signals and guided to the mixer 35 via a gate circuit 35 configured to gate them. Therefore, in this embodiment, the display signal pattern appears in the bluish subject and white subject areas on the image plane of the viewfinder only while the white balance display circuit 17 is operating, so that the image of the viewfinder is A camera operator during observation can easily recognize a malfunction in the white balance circuit.

Note that the display signal generator 32 in this embodiment
is synchronized with a drive signal for driving the image sensor (5, 6, and 7 in FIG. 1), and is configured to perform an oscillation operation in conjunction with a white balance control push button (not shown). . In addition, it is desirable that the pattern of the display signal has a shape that stands out visually.For example, in this example, a zebra pattern (diagonal striped pattern) is adopted.For this purpose, a signal with the subcarrier frequency stepped down to 1/4 is used as a video signal on the TV. The display signal is superimposed on the digital signal. In the figure, numeral 36 indicates an input terminal for a video signal for the view finder, and 37 indicates a video signal supply terminal for the view finder.

As described above, according to the method of the present invention, on the image of the viewfinder of a color television camera, a display pattern in a form that makes it possible to perceive the image of this area is superimposed on the area where white balance is being maintained. Moreover, if the white balance circuit is activated by a color signal from a part other than the subject for which white balance should be taken, the display signal will also appear in the part of the subject, so the camera operator can detect malfunctions in the white balance circuit. This can be noticed immediately, and is extremely useful in preventing camera operator errors caused by malfunctions of the white balance circuit, which are easily overlooked by conventional indicators.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of a known white balance circuit in a color television camera, Figure 2 is an explanation diagram of its operation, Figure 3 is an illustration of a malfunction of the white balance circuit, and Figure 4 is a known white balance circuit diagram of a color television camera. FIG. 5 is a block diagram of an embodiment of the present invention in which the system of the present invention is added to a balance display circuit, and FIG. 5 is an explanatory diagram of the operation of the embodiment of the present invention shown in FIG. 13... Indicator light, 17... White balance display circuit, 24, 25, 26... Level detector for red, green, and blue signals, 27, 28... Comparator, 30... Non-addition mixing circuit, 31... Comparator, 32... display signal generator, 33, 35... gate circuit, 34... mixer.

Claims (1)

[Claims] 1. In a color television camera equipped with an automatic white balance circuit that uses a specific color signal among the three color signals as a reference to match the levels of other color signals with the reference color signal level, The peak value of the color signal is held, and the color signal whose level has been matched by the automatic white balance circuit is supplied to the non-addition mixing circuit to detect the color signal with the highest amplitude, and this color signal is supplied to the comparison circuit. to generate an extraction signal by comparing it with the peak value of the reference color signal, extract a display signal from the display signal generator using this extraction signal, and apply the extracted display signal to the display of the color television camera. By superimposing it on the video signal supplied to the view finder, a display pattern is superimposed and displayed on the screen of the view finder in a state extracted for white balance so that the image of this area can be visually checked. A white balance operation display method characterized by: