JP2860545B2 - Automatic white balance correction device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic white balance correction device in an imaging device such as a video camera or an electronic still camera. [Prior Art] Various proposals have been made for automatic white balance correction devices such as video cameras at present, and there are devices using a color temperature sensor and devices using a video signal. A conventional example of an automatic white balance correction apparatus using a video signal will be described with reference to the drawings. FIG. 2 is a block diagram showing an outline of an automatic white balance correction apparatus using a video signal reported at the 1986 National Convention of the Institute of Television Engineers of Japan. 1 is an image sensor, 2 is a luminance signal / color signal generation circuit, and 3 , 4 is a gain control circuit, 5 is a dye signal generation circuit, 6 is an encoder, 7, 8 is a gate circuit, 9, 10
Is a clipping circuit, 11 is an RB signal detection circuit, 12 is an averaging circuit, 13 is a comparison amplifier, 14 is a tracking correction circuit, and the gate circuits 7, 8 to the tracking correction circuit 14 are automatic white balance correction devices. Is composed. Second
In the illustrated device, an optical signal incident on the image sensor 1 is photoelectrically converted here, extracted as an electric signal, and output to the luminance signal color signal generation circuit 2. In the luminance signal and color signal generating circuit 2, the luminance signal Y _H, color signal band luminance signal Y _L and the color signals R having luminance signal band, the color signal B is generated. The chrominance signal R and chrominance signal B are input to gain control circuits 3 and 4, respectively, where they are amplified by the control signal from the tracking correction circuit 14 and output as chrominance signal R 'and chrominance signal B', respectively. Y _L is inputted to the color difference signal generating circuit 5 with the color difference signals _{(R-Y L), (} B-
Y _L ) is generated, and the color difference signals (R-Y _L ) and (B-Y _L )
Is input to the encoder 6 together with the luminance signal Y _H, where to generate a standard television signal from said input signal, and outputs. Here, the color difference signals (R-Y _L) and (B-
Y _L ) is also input to the automatic white balance correction circuit 15. The color difference signals (R-Y _L ) and (B-Y _L ) are input to gate circuits 7 and 8, respectively, where unnecessary signals in a blanking period, color difference signals due to signal collapse during high-luminance shooting, and the like are output. Has been removed. The signals output from the gate circuits 7 and 8 are input to clip circuits 9 and 10, respectively, where the signals exceeding the level of the color difference signal within a practical color temperature range are clipped and sent to the RB signal detection circuit 11. Is output. Here, the outputs (R-Y _L ) ′ from the clip circuits 9 and 10,
The (RB) signal is detected by taking the difference of (B−Y ₂ ) ′. The averaging circuit 12 averages the (RB) signal from the RB detection circuit 11 and converts it to a DC signal. The comparison amplifier 13 compares the signal from the averaging circuit 12 with the reference voltage _Vref, and outputs a signal corresponding to the comparison to the tracking correction circuit 14. The above tracking correction circuit
At 14, based on the signal from the comparison amplifier 13, a signal for controlling the gain of the gain control circuits 3 and 4 so that white balance is corrected is generated, and the gain control circuits 3 and 4 are generated.
Output to 4. Since the negative feedback loop is configured as described above, the color difference signal subjected to the white balance correction can be supplied to the encoder 6. [Problems to be Solved by the Invention] In the conventional apparatus as described above, in a light source approximating a blank radiation formula such as sunlight or halogen lamp light, when the subject is white, the above (R-YL ₎ ) Signal, (B-
Y _L ) are both zero and white-balanced, but in the case of a light source such as a fluorescent lamp, the emission spectrum distribution is different from the blank radiation formula, so that the (R -B) Even if the signal becomes zero, the above (R-
Since the (Y _L ) signal and the (B−Y _L ) signal do not become zero, there is a problem that white balance cannot be obtained. The present invention has been made in order to solve such a problem, and provides an automatic white balance correction device that can perform a good white balance adjustment regardless of whether the illumination light source approximates Planck's radiation formula or not. The purpose is to do. [Means for Solving the Problems] To achieve the above object, an automatic white balance correction device according to the present invention provides a first signal of a difference between signal components of two color difference signals from which a color signal is obtained. Means for detecting; means for averaging a first signal from the detecting means; and a first signal adjusted equal to a DC voltage when the first signal goes to zero. A tracking correction circuit having a means for comparing with a reference voltage; a means for detecting a second signal of a sum of signal components of the two color difference signals; and averaging a second signal from the detecting means. Means, means for averaging the second signal from the detecting means, and a second reference voltage adjusted equal to the averaged signal and a DC voltage when the second signal goes to zero. And the output from the comparing means. And means for adding the output from the tracking correction circuit,
With one output from the tracking correction circuit,
By controlling the gain of the R signal and controlling the gain of the B signal to be small when R + B> 2Y _L (Y _L is a low-frequency luminance signal) by the output from the adding means, R = B <
When a 2Y _L and has a mechanism for controlling so as to increase the gain of the B signal. [Operation] With the above configuration, regardless of whether the illumination light approximates Planck's radiation formula or not,
Good automatic white balance adjustment can be performed. Embodiment FIG. 1 is a block diagram showing a main configuration of an automatic white balance correction device according to one embodiment of the present invention. First
Terminals K, L, M, and N in the figure correspond to FIG. 2 shown in the conventional apparatus, and the automatic white balance correction circuit 26 in FIG. It corresponds to the balance correction circuit 15. The apparatus of Figure 1, the outputted the color difference signals from the color difference signal generation circuit _{5 (R-Y L),} (B-Y L) terminals M, N
Are output to the RB detection circuit 16 and the Mg-G detection circuit 20 through In the RB detection circuit 16, the color difference signal (R-B
By taking the difference between (Y _L ) and (B-Y _L ), the (RB) signal as the first signal is created. Further, the Mg-G detection circuit 20 produces the (R + B-2Y _L ) signal as a second signal by taking the sum of the color difference signals (R-Y _L ) and (B-Y _L ). The averaging circuits 17 and 21 output the above output signals (R−B) from the RB detection circuit 16 and the Mg-G detection circuit 20, respectively.
B) and (R + B−2Y _L ). The comparison amplifier 18 compares the output signal from the averaging circuit 17 with the first reference voltage _Vref1 , amplifies and outputs. Here, the first reference voltage _Vref1 is adjusted to be the same as the DC voltage when the RB signal becomes zero.
In the first tracking correction circuit 19, when the output from the comparison amplifier 18 indicates R> B, a control signal for reducing the gain of the gain control circuit 3 is generated. On the contrary, when R <B, a control signal for increasing the gain of the gain control circuit 3 is generated. The comparison amplifier 22 outputs a result obtained by comparing the output signal from the averaging circuit 21 with the second reference voltage _Vref2 . Here, the second voltage V _ref2 is adjusted in the same manner as the DC voltage when the (R + B−2Y _L ) signal becomes zero. Since if the illumination light is emitted officially approximation of Planck is the R + B ÷ 2Y _L, the output signal of the comparison amplifier 22 is a certain signal level, when it is R + B> 2Y _L is the The output signal of the comparison amplifier 22 is a control signal for reducing the gain of the gain control circuit 4, R + B <2Y _L
When, the control signal for increasing the gain is output. The adder 23 is a device that adds one of the output signals from the tracking correction circuit 19 and the output signal from the comparison amplifier 22. Here, when the illumination light is a light source approximating Planck's radiation formula, the output signal from the comparison amplifier 22 is substantially constant as described above. At this time, the two signals output to the gain control circuits 3 and 4 are output. The control signal is set by the tracking correction circuit 19 and the adder 23 so as to have an optimal relationship with a change in the color temperature of the illumination light. The output signal of the Mg-G detection circuit 20 is R +
B> When showing the 2Y _L or R + B <2Y _L, the averaging circuit 21
Is different from the output signal when the illumination light approximates Planck's radiation formula. At this time, the output from the adder 23, when indicating the R + B> 2Y _L as described above, as the gain of the gain control circuit 4 is smaller, larger such characteristics when showing the R + B <2Y _L have. Then, according to the control signals from the tracking correction circuit 19 and the adder 23, the gain control circuits 3 and 4 input the gain-controlled color signals R 'and B' to the color difference signal generation circuit 5. The color-difference signal generation circuit 5 includes the R ′,
B 'signal and a color difference signal in the low frequency luminance signal _{Y L (R-Y L)} ,
(B-Y _L ) is generated and supplied to the encoder 6 and the automatic white balance correction circuit 26 described above. As described above, when the illumination light approximates Planck's radiation formula. The color difference signal, which has been appropriately white-balance corrected mainly by the tracking correction circuit 19 and when the approximation to Planck's radiation formula is not performed, is supplied to the encoder 6 by the operation of the tracking correction circuit 19 and the comparison amplifier 22. can do. Further, in the present embodiment, if the width of the output signal from the averaging circuit 21 is narrowed, and the extent to correct the white balance correctly when, for example, a fluorescent lamp (white) is the illumination light is set as the limit, An automatic white balance correction device that is not significantly affected by green leaves of trees on the screen can be configured. In the present embodiment, the configuration is such that the gain of the color signals R and B is controlled to correct the white balance.
Other methods, for example, a configuration in which a low-frequency luminance signal is added to or subtracted from a color difference signal at a certain rate can be easily implemented. Further, the gate circuits 7 and 8 and the clip circuits 9 and 10 of the conventional example can be easily added to the present invention. In this embodiment, the control signal applied to the gain control circuit is obtained by adding the output signal from the tracking correction circuit 19 and the output signal of the comparison amplifier 22 by the adder 23. Instead of the control circuit 4, a gain control signal from the adder 23 may be used for the gain control circuit 3. [Effects of the Invention] As described above, the automatic white balance correction device of the present invention detects the first signal of the difference between the signal components of the two color difference signals obtained from the color signals, and the detecting device. And means for comparing the averaged signal with a first reference voltage adjusted equal to the DC voltage when said first signal goes to zero. A tracking correction circuit, a means for detecting a second signal of the sum of the signal components of the two color difference signals, a means for averaging the second signal from the detection means, and a signal from the detection means. Means for averaging the second signal;
Means for comparing the averaged signal with a second reference voltage adjusted to be equal to the DC voltage when the second signal becomes zero; and an output from the comparing means and a signal from the tracking correction circuit. Means for controlling the gain of the R signal by one output from the tracking correction circuit, and R + B> 2Y _L (Y _L is a low-frequency luminance signal by the output from the means for adding. ), The gain of the B signal is controlled to be small, and R + B <2Y _L
In the case of, the gain of the B signal is controlled to be large, and the white balance can be corrected well regardless of whether the illumination light approximates Planck's radiation formula or not.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG.
FIG. 1 is a block diagram showing a configuration of a conventional example. In the figure, 1: Image sensor 2: Luminance signal color generation circuit 3, 4: Gain control circuit 5: Color difference signal generation circuit 6: Encoder 16: R-B signal detection circuit 17, 21: Averaging circuit 18, 22: Comparison Amplifier 19: Tracking correction circuit 20: Mg-G detection circuit 23: Adder

Claims (1)

(57) [Claims] In an automatic white balance correction device for performing white balance correction by feedback-controlling the gain of a color signal obtained from an image sensor, a first difference between signal components of two color difference signals obtained from the color signal is obtained. Means for detecting a signal, means for averaging a first signal from the detecting means, and the averaged signal;
A tracking correction circuit having a means for comparing a DC voltage when the signal becomes zero with a first reference voltage adjusted to be equal to zero, and further a second signal of a sum of signal components of the two color difference signals. Means for detecting, means for averaging the second signal from the detecting means, and a second reference adjusted equal to the averaged signal and the DC voltage when the second signal goes to zero. A means for comparing the output from the tracking correction circuit with an output from the comparison means and an output from the tracking correction circuit, and controlling the gain of the R signal by one output from the tracking correction circuit; the output from said means for adding, controls so as to reduce the gain of the B signal when _{R + B> 2Y L (Y} L is the luminance signal of low frequency) is the gain of the B signal when a R + B <2Y _L To make it big Automatic white balance correction apparatus and controls.