JPS6194484A - Color camera - Google Patents

Abstract

PURPOSE:To obtain a white balanced video signal when a power source is turned on by generating a write pulse with the aid of an AGC signal of a video camera. CONSTITUTION:Due to a rise when a power source is turned on, a DC potential obtained by smoothing the AGC output signal rises a little later. The output signal is inverted 8, and given to an NAND gate 11. Also, the smoothed DC potential is converted into a prescribed potential by an integration circuit 9, and the converted output is inverted 20 and given to the gate 11. Then, the write pulse is formed in the output of the gate 11, and supplied to an automatic white balance correcting circuit 13. The write pulse forms a closed loop in the correcting circuit 13 with a synchronizing signal as a clock pulse, and a white balance error is detected and corrected by comparing the mean of a color difference signal with a reference voltage, thereby storing the state.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a color camera having an automatic white balance correction circuit using a digital memory.The present invention relates to a color camera having an automatic white balance correction circuit using a digital memory. It is intended to be obtained.

Conventional configuration and its problems When a white subject is illuminated with daylight and then with light from a 2700 K tungsten bulb, physical photometry shows that the spectral distribution is very different, but in both cases It doesn't look very different.

This is the color adaptation of the human eye. Since video cameras use physical photometry, corrections that correspond to the chromatic adaptation of the human eye are required. Therefore, it is necessary for a video camera to always reproduce the correct white color when capturing an image of a white subject under any lighting conditions, and this adjustment is called white balance adjustment.

Currently, white balance adjustment is automated by using LSI in the memory section. This made it possible to easily and accurately adjust the white balance, which had previously been difficult for ordinary users to manually operate color video cameras, and in a short amount of time.

The configuration and operation of a conventional white balance correction circuit will be described below with reference to FIG. The conventional method is configured so that the color difference signal automatically becomes zero by photographing a white subject and making adjustments. As shown in FIG. 1, this automatic white balance system consists of a gain control circuit 1 which controls the gain of color signals (R, B). The luminance low-frequency signal YL and the color difference signal (
R-YL, B-YL) 2. Subtraction circuit 21 for obtaining the color difference signal over the vertical period 3. Smoothing circuit for smoothing the color difference signal over the vertical period Reference voltage (
a comparator 4 for comparison with the zero level of the color difference signal; an up/down counter 5 for down-amplifying according to the positive and negative polarity outputs of the comparator; It consists of a D/A converter 6 that converts up/down outputs into analog values, and forms a negative feedback loop by controlling the gain of the gain control circuit with the output of the D/A converter.

The write switch 7 operates a negative feedback loop.

The negative feedback loop including the digital circuit operates to converge when the up/down counter repeats two values (white balance state), and then stores the count of the up/down counter. Therefore, when a white subject is imaged and the negative feedback loop is activated, a white-balanced state (
By turning the color difference signal to zero level and then turning off the negative feedback loop, it is possible to maintain a white balanced state and capture an image.

The above-described white balance system has the disadvantage that even if the system is equipped with a bank-up function, the white balance cannot be maintained when the next time an image is taken of a different subject than the previous one after the power is turned off. Therefore, when the power is turned on, the write switch must be operated. This makes it difficult for general users to operate the color video camera. In addition, there are many cases where problems have occurred due to forgetting to press the AWC switch.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems and provides a video camera having a system that allows white balance to be adjusted without pressing a write switch when the power is turned on.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention generates a write pulse from an AGC output signal of a video camera to obtain a video signal with a good white balance when the power is turned on.

Description of examples The configuration of the present invention will be explained below with reference to FIG.

7. Smoothing circuit that detects DC potential from the output signal of the AGC circuit of the video camera. 8. A first switch circuit into which the smoothed DC potential can be input. Integrating circuit that delays the smoothed DC potential for a certain period of time9. The second input via the integrating circuit
Switch circuit 10° 1st. 2nd switch circuit 8, 1o
gate circuit 11 to which the output signal of is input. Write switch connected to the output terminal of the gate circuit 12. Automatic white balance correction using a digital memory that uses the synchronization signal as a clock pulse to form a closed loop using write pulses, detects and corrects white balance errors by comparing the average value of the color difference signal and the reference voltage, and then stores the status. circuit 13
It's more structured.

Next, the process up to the generation of the write pulse will be explained according to the timing chart of FIG. 3. First, to achieve white balance, the automatic white balance correction circuit must be activated after the power is turned on and a camera signal is generated. Therefore, here, when the 0 power source is turned on to generate a write pulse using the AGC output of the camera signal, the power source rises as shown in 14, and the DC potential obtained by smoothing the AGC output signal rises with a delay as shown in 16. The output signal of the first switch circuit whose output signal is input is 16. The output signal of the product circuit which inputs the smoothing circuit output signal is 17. The output signal of the second switch circuit which inputs the output signal is 18. NA of 16 inverted signals and 18 signals
A write pulse 19 is formed by the ND. According to experiments, it is appropriate that the time constant tt of the integrating circuit is 2o~300m5.

Effects of the Invention As described above, when the present invention is used, the write switch always operates when the power is turned on, the white balance correction circuit operates, and a video camera signal with a well-balanced white can be obtained. In other words, the old complaints about not being able to maintain white balance due to forgetting to press the AWC switch, as in the conventional example, do not occur at all.

If you want to further improve the white balance, or if you are concerned about whether the white balance is correct, you can operate the white balance correction circuit again by manually pressing the AV'/C switch.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a conventional white balance correction circuit.
FIG. 2 is a block diagram showing a color camera according to an embodiment of the present invention, and FIG. 3 is a timing chart of the same embodiment. 7... Smoothing circuit, 8, 10... SW circuit, 9... Integrating circuit, 11... Gate circuit, 12... Switch, 13...White balance correction circuit.

Claims (2)

[Claims] (1) A smoothing circuit that detects a DC potential that rises in response to an output signal after power is turned on, a first switch circuit that receives the DC potential smoothed by the smoothing circuit, and an integration circuit that receives the DC potential. a second switch circuit to which the output signal integrated by the integrating circuit is input; a gate circuit to which the output signals of the first and second switch circuits are input; and a gate circuit connected to the output terminal of the gate circuit. A color camera comprising a white balance correction circuit and an operation switch. (2) Claim 1, characterized in that the output signal for detecting the smoothed DC potential is an AGC output.
Color camera as described in section.