JP3075888B2 - White balance adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic white balance adjusting device for a color video camera for controlling a white balance based on an image signal obtained from an image sensor.

[0002]

2. Description of the Related Art In a color video camera, it is necessary to control a white balance in order to correct a difference in wavelength distribution of light depending on a light source.

[0003] This control is performed by adjusting the gain of each color signal so that the ratio of the three primary color signals of red (hereinafter R), blue (hereinafter B) and green (hereinafter G) becomes 1: 1: 1. Will be
Generally, for example, JP-A-62-35792 (H04)
N9 / 73), the screen color difference signals RY,
A method of adjusting the gain so that the integrated value of BY becomes zero is used.

FIG. 12 is a block diagram of a white balance circuit using this method. Light that has passed through the lens group 1 including a plurality of zoom and focus lenses is
After the photoelectric conversion by the image sensor CCD2, the color separation circuit 3
Then, the three primary color signals of R, G, and B are extracted, and the G color signal is directly input to the camera process and matrix circuit 6 via the R and B amplifier circuits 4 and 5, respectively. Then, a luminance signal Y and color difference signals RY and BY for red and blue are generated and sent to the video circuit 7.

At the same time, the two color difference signals are respectively integrated by integrating circuits 17 and 18 for a sufficiently long time, and the gain control circuits 13 and 14 are controlled by the R and B amplifying circuits 4 and 4 so that the result becomes zero. Adjust the gain of 5.

[0006]

SUMMARY OF THE INVENTION The above-mentioned method is applicable to various color distributions of a screen shot by a video camera.
It is premised that if the time constants of the integration circuits 17 and 18 are lengthened, and if these color distributions are averaged, the respective color components constituting the color distributions cancel each other out and approximate a substantially white screen state. However, since feedback is always performed in the above configuration, when a subject having a biased color integration result in the screen is photographed, the white balance shifts to its complementary color side, and an unstable correction operation is performed. Has problems.

[0007] Japanese Patent Laid-Open No. 4-988 discloses a white balance adjusting device capable of performing stable correction without fluctuation. This apparatus sets an operation mode and a stop mode for white balance correction, and shifts the white balance correction from the stop mode to the operation mode only when the color difference signal obtained from the color signal exceeds a specific range.
As a result, unstable white balance correction is not performed even when a subject having a slight deviation in the color integration result in the screen is photographed.

However, when the angle of view of the lens at the time of photographing is small or the distance to the subject is short, and the effective area entering the screen is small, a large deviation occurs in the integration result of colors in the screen. It is easy to occur. Therefore, if the set value in the above-described specific range is small, the white balance correction easily shifts from the stop mode to the operation mode, and the operation becomes unstable. On the other hand, when this setting value is set to a large value, the instability due to the subject color is eliminated, but correction may not be performed even when the light source actually changes and the wavelength distribution of light changes.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a white balance adjusting apparatus for adjusting a gain of a color signal in a picked-up video signal by a gain correction amount to perform white balance adjustment. Gain control means for evaluating the screen to calculate a target value of the gain correction amount; gain correction amount increasing / decreasing means for changing the gain correction amount so as to approach the target value; and a gain correction amount falling within a predetermined range from the target value. A gain correction amount fixing means for prohibiting a change of the gain correction amount by the gain correction amount increasing and decreasing means, and a gain by the gain correction amount increasing and decreasing means when the gain correction amount when the gain is fixed exceeds the predetermined range from a target value. A gain correction amount fixing canceling means for canceling the prohibition of the change of the correction amount; obtaining an effective area in the imaging screen from the angle of view of the lens and the subject distance; and changing the size of the predetermined range according to the effective area. It is characterized by the following.

Further, as another means, a gain correction amount fixing means for inhibiting a change of the gain correction amount by the gain correction amount increasing / decreasing means when the gain correction amount falls within a predetermined range from the target value; When the level of the color difference signal exceeds a predetermined allowable range with respect to the reference level, a gain correction amount fixing release unit that releases the inhibition of the gain correction amount by the gain correction amount increasing / decreasing unit is provided. The method is characterized in that an effective area in the imaging screen is obtained by obtaining a distance, and the predetermined allowable range is changed according to the effective area.

Further, when the color difference signal obtained from the color signal changes by a predetermined amount with respect to the level at which the change of the gain correction amount by the gain correction amount changing means is prohibited, the gain correction amount by the gain correction amount changing means is changed. A gain correction amount fixing canceling means for canceling the prohibition, obtaining an angle of view of the lens and a distance to a subject to obtain an effective area in the imaging screen, and changing the predetermined amount according to the effective area. I do.

[0012]

Since the present invention is constructed as described above, if the angle of view is narrow or the distance between the objects is short, the screen does not include a sufficiently large number of objects and the color in the screen is biased. The white balance adjustment is kept in the stop mode.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram of an automatic white balance adjustment circuit of a color video camera according to the present embodiment. The light that has passed through the lens group 1 is imaged on the CCD 2, photoelectrically converted, and then extracted by the color separation circuit 3 as three primary color signals of R, G, and B. The R and B signals of these three primary color signals are input to the camera process and matrix circuit 6 together with the G signal via the R and B amplifier circuits 4 and 5, respectively. The color difference signals RY and BY are generated, supplied to the video circuit 7, and subjected to known processing. The RY and BY signals are also supplied to the selection circuit 21 at the same time.

The selection circuit 21 sequentially selects one of the two color difference signals RY and BY in accordance with the selection signal S1 from the timing circuit 25 for each field. ... BY → RY →... Are output to the subsequent A / D converter 22 every field. The selection signal S
1 is created based on a vertical synchronization signal obtained from the synchronization separation circuit 24 as described later.

The A / D converter 22 outputs the color difference signals RY, B selected by the selection circuit 21 at a predetermined sampling cycle.
−Y is sampled and converted to a digital value,
This value is output to the integrator 23. By the way, the timing circuit 25 converts the image screen into an 8 × 8 image shown in FIG. 13 based on the camera process and the vertical and horizontal synchronization signals from the matrix circuit 6 and the fixed oscillator output for driving the CCD 2.
.. Are divided into four rectangular areas A11, A12, A13,..., And a switching signal S2 for extracting the output of the selection circuit 21 in each of these areas in a time-division manner is output to the integrator 23.

The integrator 23 receives the switching signal S2 and adds the A / D converted value of the output of the selection circuit 21 over one field period for each region, that is, digitally integrates every 64 regions. When the integration for the field is completed, the integrated value is stored in the memory 26 as a color evaluation value. As a result, a digital integration value of the color difference signal RY corresponding to 64 regions in a given field is obtained as 64 color evaluation values rij (i, j: 1 to 8). .
In the next field, the color difference signal B-
Since Y is selected, as a result of integration in each area of the adder 23, a digital integrated value of each area of the color difference signal BY is obtained as 64 color evaluation values bij. Thus, at the time when the integration of the two fields of the color difference signals RY and BY is completed, the values of the 64 color evaluation values rij and bij are stored in the memory 26. Thereafter, the same operation as described above is repeated, and the color evaluation value rij is provided in the next field, and the color evaluation value bij is provided in the next field.
Are sequentially updated.

The latest color evaluation value r obtained as described above
ij, bij (i, j: 1 to 8) are the screen evaluation circuit 27
Are calculated as the screen color evaluation values Vr and Vb of the entire screen of each color difference signal based on the following equations 1 and 2.

[0018]

(Equation 1)

[0019]

(Equation 2)

The equations (1) and (2) are obtained by dividing the total sum of the color evaluation values rij and bij of the 64 areas by the number of areas.
The average value for each area is calculated as the screen color evaluation value. The screen color evaluation values Vr and Vb are determined by the gain control circuit 28,
It is sent to the first evaluation value comparison circuit 30 and the second evaluation value comparison circuit 31.

The gain control circuit 28 corrects the current gains of the R and B amplifier circuits 4 and 5 to make the screen color evaluation values Vr and Vb, which are the color evaluation values of the entire screen, zero. Then, a correction value signal corresponding to the correction values Gpr and Gpb for the gain is generated and output to the correction value comparison circuit 29.

Next, the correction value comparison circuit 29, the first and second
The operation of the evaluation value comparison circuits 30 and 31 will be described.

The correction value comparison circuit 29 is configured as shown in FIG. That is, the current gain correction values Gmr and Gmb that are held in the R and B correction value memories 33 and 34 and adjust the current gains of the R and B amplifier circuits 4 and 5, and the gain correction values Gm
By evaluating the screen generated by the gain control by r and Gmb, the new correction values Gpr and Gpb obtained from the gain control circuit 28 are compared by the R correction value comparator 29a and the B correction value comparator 29b, respectively. As a result, when the R correction value comparator 29a determines that Gmr = Gpr, an H-level signal as the control signal Pr1 and Gmr ≠ Gpr
If it is determined that the control signal Pr1 is low, a low-level signal is output to the correction value increasing / decreasing circuit 35. At this time, if Gmr <Gpr, an H-level signal is output to the correction value increasing / decreasing circuit 35 as the control signal Pr2, and if Gmr> Gpr, an L-level signal is output as the control signal Pr2.

A similar determination is made in the B correction value comparator 29b. When it is determined that Gmb = Gpb, an H level signal is used as the control signal Pb1, and Gmb ≠ Gpb.
Is determined, the L-level signal is output as the control signal Pb1 to the correction value increasing / decreasing circuit 35. At this time, Gmb <
If Gpb, an H level signal is used as the control signal Pb2. If Gmb> Gpb, an L level signal is used as the control signal Pb2.
The level signal is output to the correction value increase / decrease circuit 35.

At the same time, in the R correction value comparator 29a, the absolute value of the difference between the input correction values Gmr and Gpr | Gmr-Gpr |
And the B correction value comparator 29b calculates the absolute value | Gmb-Gpb | of the difference between Gmb and Gpb.
9c.

The correction value adder 29c calculates the sum of these absolute values, that is, | Gmr-Gpr | + | Gmb-Gpb |, and the correction value comparator 29e uses a correction value threshold value calculation circuit 44 to be described later. The magnitude relationship between the calculated value and the threshold value TG stored in the correction value threshold value memory 29d is compared. As a result, when Equation 3 is satisfied, the control signal P1 is set to H
When the level signal and Expression 4 hold, an L level signal is output as the control signal P1.

[0027]

(Equation 3)

[0028]

(Equation 4)

The first evaluation value comparison circuit 30 is configured as shown in FIG. First, in the first R evaluation value subtractor 30a, the absolute value | Vr-V1r | of the difference between the screen color evaluation value Vr output from the screen evaluation circuit 27 and the R reference value V1r previously stored in the R reference value memory 30c. , And the first B evaluation value subtractor 30
b, the screen color evaluation value Vb and the B reference value memory 30d are stored in advance.
Absolute value | Vb− of the difference from the B reference value V1b stored in
V1b | is sent to the first evaluation value adder 30e.

The first evaluation value adder 30e calculates the sum of
| Vr−V1r | + | Vb−V1b | is calculated in the first evaluation value comparator 30g by a first evaluation value threshold calculation circuit 45 described later, and stored in the first evaluation value threshold memory 30f. The magnitude relationship with the threshold value TV1 is compared.
As a result, when the expression 5 is satisfied, an H-level signal is output as the control signal P2, and when the expression 6 is satisfied, an L-level signal is output as the control signal P2.

[0031]

(Equation 5)

[0032]

(Equation 6)

The second evaluation value comparison circuit 31 is configured as shown in FIG. First, in the second R evaluation value subtractor 31a, the absolute value | Vr−V2r | of the difference between the screen color evaluation value Vr output from the screen evaluation circuit 27 and the R evaluation value V2r previously stored in the R evaluation value memory 31c. Is the second B evaluation value subtractor 31
b, the screen color evaluation value Vb and the B evaluation value memory 31d are stored in advance.
Absolute value | Vb− of the difference from B evaluation value V2b stored in
V2b | is sent to the second evaluation value adder 31e.

The second evaluation value adder 31e calculates the sum of
That is, | Vr−V2r | + | Vb−V2b | is calculated, and the second
In the evaluation value comparator 31g, a second evaluation value threshold value calculation circuit 46, which will be described later, calculates the second evaluation value threshold value memory 31.
The magnitude relationship with the threshold value TV2 stored in f is compared. As a result, an H-level signal is output as the control signal P3 when the equation 7 holds, and an L-level signal is output as the control signal P3 when the equation 8 holds.

[0035]

(Equation 7)

[0036]

(Equation 8)

Here, a method of calculating the correction value threshold value TG, the first evaluation value threshold value TV1, and the second evaluation value threshold value TV2 will be described. Reference numeral 140 denotes a well-known zoom mechanism used in a general video camera, which changes a focal length of a lens system of the entire camera by displacing a zoom lens in the lens group 1 to obtain a desired zoom range from a wide-angle to a telephoto zoom range. Can be selected. The zoom mechanism 14
From 0, a signal indicating the lens position of the zoom lens is output to the angle-of-view detection circuit 141 at the subsequent stage.

The angle-of-view detecting circuit 141 receives the position signal of the zoom lens, detects the position in the zoom area at this time, and determines the horizontal position of the screen from the relationship between the zoom position and the angle of view shown in FIG. The angle of view Rw (in radians) and the angle of view RL in the vertical direction are calculated. By the way, as is obvious in FIG. 11, as the zoom position is on the wide angle side, the angles of view Rw, R
L increases.

Reference numeral 142 denotes a well-known focus mechanism which measures the distance to the subject using infrared rays or the like, and moves the focusing lens of the lens group 1 in the optical axis direction in accordance with the subject distance to bring the lens into a focused state. The information on the subject distance L obtained by the focus mechanism is input to an effective area calculation circuit 143 at the subsequent stage.

In the effective area calculation circuit 143, the view angles Rw and RL from the view angle detection circuit 141 and the focus mechanism 14
An effective amount (area) of all subjects (all objects projected on the entire screen including the main subject and the background) included in the screen is calculated based on the subject distance L from 2. Specifically, the effective area S is obtained by Expression 9.

[0041]

(Equation 9)

In this equation, Rw × L indicates the effective length of all subjects in the horizontal direction, and RL × L indicates the effective length of all subjects in the vertical direction. The effective area S thus obtained is calculated by using a threshold value calculation circuit for correction value 144, a threshold value calculation circuit for first evaluation value 145,
And the second evaluation value threshold value calculation circuit 46.

The correction value threshold value calculation circuit 44 calculates a correction value threshold value TG based on the input effective area S by using equation (10). Here, FIG. 14 illustrates the relationship of Expression 10.

[0044]

(Equation 10)

Further, the first evaluation value threshold value calculating circuit 45 calculates the first evaluation value threshold value TV1 according to the equation 11 based on the input effective area S. Here, FIG. 15 illustrates the relationship of Expression 11.

[0046]

[Equation 11]

Further, the second evaluation value threshold value calculating circuit 46 calculates the second evaluation value threshold value TV2 by the equation 12 based on the input effective area S. Here, FIG. 16 shows the relationship of Expression 12.

[0048]

(Equation 12)

As described above, the effective area S
Each threshold value is set to be proportionally larger as becomes smaller. This is because, as the effective area S decreases, the types of subjects included in the screen are limited, and the colors in the screen are likely to be biased. This is to prevent them from moving to the side.

Therefore, each of the coefficients Atg, TG0, Atv1, TV10 and Atv in the equations (10), (11) and (12)
2. The TV 20 is set in advance based on actual measurement values obtained by experiments.

The threshold value TG set by the above equation (10) is stored in the correction value threshold value memory 2 of the correction value comparison circuit 29.
9d to update the contents of this memory. Similarly, the threshold value TV1 set by Expression 11 updates the contents of the first evaluation value threshold memory 30f of the first evaluation value comparison circuit 30, and the threshold value TV2 set by Expression 12 is used as the second evaluation value comparison circuit. 31 is updated.

The results compared by the correction value comparison circuit 29, the first evaluation value comparison circuit 30, and the second evaluation value comparison circuit 31 are input to the stability determination circuit 32 as control signals P1, P2, and P3. You.

The stability determination circuit 32 is configured as shown in FIG.
Control signals P1, P2, and P3 are input to OR gate 51. The switch 52 has a function of selectively connecting the fixed contact 52a to which the control signal P1 is applied or the fixed contact 52b connected to the output of the OR gate 51 and the fixed contact 52c connected to the output terminal. The switching is controlled by the output control signal P4 generated at the time of (1), and the signal P4 is connected to the fixed contact 52b when the signal P4 is at the H level and to the fixed contact 52a when the signal P4 is at the L level.

Next, the operation of the stability determination circuit 32 will be described. First, the control signal P1 at the H level is supplied to the stability determination circuit 3
2, the output of the OR gate 51 always goes to the H level, so that the output control signal P4 goes to the H level regardless of which of the fixed contacts the switch 52 initially has,
Eventually, the switch 52 will be connected to the fixed contact 52b. In this state, as long as at least one of the control signals P1, P2, and P3 is at the H level, the output control signal P4 is at the H level. Next, assuming that the control signals P1, P2, and P3, all of which are at L level, are input to the stability determination circuit 32, the output of the OR gate 51 is at L level, so that the output control signal P4 is at L level, and the switch 52 is connected to the fixed contact 52a side. In this state, as long as control signal P1 is at L level, output control signal P4 is at L level.

That is, when equation 3 is satisfied in the correction value comparison circuit 29, the stability determination circuit 32 generates an H level output control signal P4, and this H level control signal P4 functions as a white balance stop signal as described later. .

On the other hand, in the correction value comparison circuit 29,
In the first evaluation value comparison circuit 30, Equation 6 is
When both of the expressions 8 are satisfied in the evaluation value comparison circuit 31, the stability determination circuit 32 generates an L level control signal P4, and the L level control signal P4 functions as a white balance operation signal.

The control signal P4 is input to the second evaluation value comparison circuit 31 and the correction value increase / decrease circuit 35. In the second evaluation value comparison circuit 31, the edge detector 31h receives this control signal P4 as shown in FIG. Edge detector 31
h emits a pulse only when the control signal P4 changes from L level to H level. When the switch 31i receives this pulse, it closes the switch, allows the screen color evaluation values Vr and Vb to pass to the R evaluation value memory 31c and the B evaluation value memory 31d, and allows the memories 31c and 31d to pass the screen immediately after the passage. The values of the R evaluation value V2r and the B evaluation value V2b are updated with the color evaluation value.

Therefore, when the white balance correction shifts from the operation mode to the stop mode, that is, when the operation mode ends, the screen color evaluation values Vr and Vb are stored in the R evaluation value memory 3 respectively.
1c and B evaluation value memory 31d store R evaluation values V2r and B
It will be stored as the evaluation value V2b.

FIG. 6 shows the configuration of the correction value increase / decrease circuit 35 which receives the current gain correction amounts Gmr, Gmb and the control signals Pr1, Pr2, Pb1, Pb2. That is, the correction value increasing / decreasing circuit 35 includes six switches and R and B increasing circuits 46, 4
8, R and B reduction circuits 47 and 49.
The switches 40 and 41 are switched by a control signal P4, a signal indicating the gain correction amount Gmr is applied to the contact 40c, the fixed contact 40a is connected to the output terminal 35a, and the fixed contact 40b is connected to the contact 42c of the switch 42. It is connected. The switch 42 is controlled to be switched by a control signal Pr1, and the fixed contact 42a is connected to the output terminal 35a, and the fixed contact 42b is connected to the contact 44c of the switch 44. The switch 44 is controlled to be switched by a control signal Pr2, and the fixed contacts 44a and 44b are connected to R increase and R decrease circuits 46 and 47, respectively. Here, the outputs of the R increase and R decrease circuits 46 and 47 are led to the output terminal 35a.

Similarly, the contact 41c of the switch 41
A signal indicating the gain correction amount Gmb is applied, and the fixed contact 41a
Is the output terminal 35b, and the fixed contact 41b is the switch 4
3 is connected to the contact 43c. The switch 43 is controlled to be switched by the control signal Pb1, the fixed contact 43a is connected to the output terminal 35b, and the fixed contact 43b is connected to the switch 45.
Is connected to the contact 45c. The switch 45 is controlled to be switched by the control signal Pb2, and the fixed contacts 45a,
5b is connected to B increase and B decrease circuits 48 and 49, respectively. Here, the outputs of the B increase and B decrease circuits 48 and 49 are led to the output terminal 35b.

Next, the operation of the correction value increasing / decreasing circuit 35 will be described. First, when the H-level control signal P4 is input to the switches 40 and 41, that is, when the white balance correction is in the stop mode, the switch 40 is set to the fixed contact 4
0a, and the switch 41 is on the fixed contact 41a, and the values Gmr, Gmb stored in the R correction value memory 33 and the B correction value memory 34 are used as gain correction values Gr, Gb.
Are output to the output terminals 35a and 35b to adjust the gains of the R and B amplifier circuits 4 and 5, respectively. Next, the control signal P4
Is at the L level, that is, when the white balance is in the operation mode, the switch 40 is on the fixed contact 40b side, the switch 41 is on the fixed contact 41b side, and the R correction value memory 33 and the B correction value Correction value G stored in memory 34
mr and Gmb are input to the switches 42 and 43, respectively.

When the control signal Pr1 is at the H level, that is, when the correction value comparison circuit 29 determines that Gmr = Gpr, the switch 42 is on the fixed contact 42a side, and the value stored in the R correction value memory 33 is The signal is output as it is as the gain correction value Gr, and the gain of the R amplifier circuit 4 is adjusted. Next, when the control signal Pr1 becomes L level, that is, when the correction value comparison circuit 29 determines that Gmr ≠ Gpr, the switch 42 is on the fixed contact 42b side and the R correction value memory 33
Is input to the switch 44. On the other hand, the switch 43 performs the same operation as the switch 42. When the control signal Pb1 is at the H level,
The value stored in the correction value memory 34 is directly output as the gain correction value Gb, and when the control signal Pb1 becomes L level, the value stored in the B correction value memory 34 is:
Input to switch 45.

When the control signal Pr2 is at the H level, that is, when the correction value comparison circuit 29 determines that Gmr <Gpr, the switch 44 is at the fixed contact 44a side and the correction value stored in the R correction value memory 33 is set. Gmr is an R increasing circuit 46
, And a predetermined constant amount value r0 is added and output as a gain correction value Gr. That is, Gr = Gmr + r
It becomes 0. When the control signal Pr2 becomes L level,
That is, when the correction value comparison circuit 29 determines that Gmr> Gpr, the switch 44 is on the fixed contact 44b side, and the correction value Gmr is input to the R reduction circuit 47, and the fixed amount value r0
Is subtracted and output as a gain correction value Gr, that is, G
Assuming that r = Gmr-r0, the gain of the R amplifier circuit 4 is adjusted. On the other hand, the switch 45 performs the same operation as the switch 44, and when the control signal Pb2 is at the H level,
To the correction value Gmb stored in the correction value memory 34, a fixed amount value b0 is added by a B increasing circuit 48 and the control signal Pmb
When b2 becomes L level, the correction value Gmb is subtracted from the fixed amount value b0 by the B reduction circuit 49 to obtain the gain correction value Gb.
And adjusts the gain of the B amplification circuit 5.

The R and B gain correction values Gr and Gb output from the correction value increase / decrease circuit 35 are stored in the R correction value memory 3.
3 and the B correction value memory 34 again, and in the next field, are used as the current correction values Gmr and Gmb for white balance adjustment. Therefore, the R and B correction value memories 33,
34 are output terminals 35a, 35b for each field.
Will be changed by the correction value from.

In the R amplifier circuit 4, the gain when amplifying the R signal changes in accordance with the gain correction amount Gr. When the correction value Gr is zero, the gain is fixed at 1, and the correction value Gr changes in the positive direction. Then, the gain increases, and if it changes in the negative direction, the gain decreases. Similarly, in the B amplifier circuit 5, the gain correction amount Gb
, The amplification gain of the B signal changes in accordance with, and the gain is fixed to 1 when Gb = 0.

The operation of each of the above-described circuits will be described with reference to FIGS.
An example in which a screen like that described above is photographed will be described.

First, the operation when the white balance control shifts from the operation mode to the stop mode on the screen of FIG. 17 will be described. Now, suppose that the gain correction values Gmr, which are stored in the R correction value memory 33 and the B correction value memory 34, respectively,
It is assumed that the amplification gains of the R amplification circuit 4 and the B amplification circuit 5 are controlled by Gmb, and a proper white balance is obtained.
Here, for example, when the screen color evaluation value changes due to the switching of the illumination light from the fluorescent lamp to the incandescent lamp, the gain control circuit 2
The gain correction amounts Gpr and Gpb calculated in FIG. 8 change as shown in FIG. 7, and based on the comparison result in the correction value comparison circuit 29, the correction value increase / decrease circuit 35 stores the R and B correction value memories 33 and 34 respectively. When the stored gain correction amount is increased or decreased and changed from Gmr, Gmb to Gmr ', Gmb', the relationship of Equation 3 is established,
An H-level control signal P1 is output. In FIG. 7, the range in which the relationship of Expression 3 is established is a square area surrounded by a chain line 100 centered on Gpr and Gpb. The size of the square depends on the threshold TG itself, and is set to a value by which the correction value threshold calculating circuit 44 can determine that the gain of the white balance adjustment may be fixed in the current effective area of the imaging screen. I have. When the stability determination circuit 32 receives this and outputs the H-level control signal P4, the correction value increase / decrease circuit 35 stops increasing / decreasing the gain correction amount, and the white balance correction enters a stop mode.

Thus, the gain correction value is increased by the increase circuits 46 and 48.
Alternatively, the R or B increasing circuits 4 and 5 gradually change the gain in the decreasing circuits 47 and 49 to perform white balance adjustment. If the change in the gain correction value falls within the threshold value TG for each field, the white balance adjustment is performed. In order to suppress the fluctuation, the gain correction amount is stopped from increasing or decreasing, the gain correction value immediately before the stop is maintained, and the gains of the R and B increase circuits 4 and 5 are fixed to a constant gain determined by the correction value. You. Note that the correction value at this time is kept stored in the R and B correction value memories 33 and 34 while the stop mode is maintained. In other words, the gain of the R and B increasing circuits 4 and 5 during the stop mode is fixed by the correction value immediately before the stop mode held in the memory.

Next, the operation of the white balance adjustment when shifting from the stop mode to the operation mode will be described.

Now, suppose that the gain correction values Gmr, Gm stored in the R correction value memory 33 and the B correction value memory 34, respectively.
It is assumed that the amplification gains of the R amplification circuit 4 and the B amplification circuit 5 are controlled by mb, and a proper white balance is obtained. Here, the gain correction amount obtained based on the screen color evaluation value is shown in FIG.
It is not necessary to change the gain correction amount as long as Gpr 'and Gpb' change from Gmr and Gmb within a certain range surrounded by a dashed line 100, that is, within a range where Equation 3 holds. Is determined.

However, when the illumination light is switched again from the incandescent lamp to the fluorescent lamp, the gain correction amounts Gpr, Gpb change as Gpr ", Gpb", and when the equation 4 is satisfied, the gain correction value Gr, If Gb is fixed to the correction values Gmr and Gmb held in the memories 33 and 34, it is determined that an appropriate white balance cannot be obtained, and the correction value comparison circuit 29
A level control signal P1 is output.

Next, for a similar change in the screen color evaluation value,
The operation performed by the first evaluation value comparison circuit 30 will be described. First, when a proper white balance is obtained, the screen color evaluation values Vr and Vb are changed to V1r and V1b like Vr 'and Vb' in FIG.
As long as the value changes within the range of the dashed line 101 depending on the threshold value TV1, that is, within the range where Expression 5 holds, it is not determined that the screen color evaluation value has changed. However, the screen color evaluation value changes as Vr "and Vb" due to the change in the light source, and when the expression 6 is satisfied, the first evaluation value comparison circuit 30 outputs the control signal P2 at L level. You.

Here, the reference values V1r and V1b are set in advance to the screen color evaluation values of the respective color difference signals when a completely achromatic subject in which the entire screen is white is photographed. The color difference signals RY and BY output from the & matrix circuit 6 have the reference values V1r and V1b both set to zero when a completely achromatic subject is photographed. Therefore, in Equation 5, | Vr-V1
r | is a value indicating the degree of departure from the zero level of the color difference signal RY, in other words, how far it is from the achromatic color. Similarly, | Vb-V1b | is the value of the color difference signal BY from the zero level. This is a value indicating the degree of separation, and the sum of the two indicates the degree of separation of the entire screen from white. Therefore, by setting the threshold value TV1 as an allowable width of an appropriate white balance, if Expression 5 is satisfied, the imaging screen is within an allowable range where it can be determined that an appropriate white balance adjustment is realized. It is not necessary to operate, and if Equation 6 is satisfied, the imaging screen exceeds the allowable range in which it can be determined that proper white balance adjustment is already realized, and immediately starts white balance adjustment accompanying increase or decrease of the gain correction value. Mode.

Further, for a similar change in the screen color evaluation value,
The operation performed by the second evaluation value comparison circuit 31 will be described. R correction value memory 31c and B correction value memory 31d
The screen color evaluation values when the white balance correction enters the stop mode are stored as R and B evaluation values V2r and V2b, and the screen color evaluation value V newly calculated by the screen evaluation is stored in the table.
r and Vb are V2r and V2b like Vr 'and Vb' in FIG.
As long as the value changes within the range of the dashed line 102 depending on the threshold value TV2, that is, within the range where Expression 7 holds, it is not determined that the screen color evaluation value has changed.

However, when the screen color evaluation value changes as Vr ″ and Vb ″ due to the change in the light source and the equation 8 is satisfied, the L-level control signal P3 is output from the second evaluation value comparison circuit 31. Is output.

Here, the threshold value TV2 is set so that the change of the current screen color evaluation values Vr and Vb with respect to the screen color evaluation values V2r and V2b when entering the stop mode does not require the white balance adjustment by increasing or decreasing the gain. This is a value for setting an allowable range that can be determined, and is set by the second evaluation value threshold value calculation circuit 46 to a value that can determine that the gain of the white balance may be fixed in the effective area of the current imaging screen.

In this way, the correction value comparison circuit 29 calculates
However, it is confirmed that Expression 6 is satisfied by the first evaluation value comparison circuit 30 and Expression 8 is further satisfied by the second evaluation value comparison circuit 31, and the control signals P1, P2, and P3 at L level are output. , The stability determination circuit 32 receives the L level control signal P4
Is output, the correction value increase / decrease circuit 35 starts increasing / decreasing the gain correction amount, and the white balance correction enters the operation mode.

In other words, the condition that the white balance correction enters the operation mode from the stop mode is that the gain correction values Gpr and Gpb calculated from the evaluation of the screen are maintained as the actual correction values Gr and Gb while the stop mode is continued. Correction values Gmr, G
mb, and the screen color evaluation values Vr and Vb are changed by a threshold TV1 or more from a reference value set in advance when a completely achromatic subject is photographed. When all three conditions that the values Vr and Vb change to the threshold TV2 or more with respect to the values at the time of entering the stop mode are satisfied at the same time, it is no longer possible to obtain an appropriate white balance in the stop mode. It becomes.

Next, the operation in the case of photographing a screen as shown in FIG. 18 in which the human face in FIG. 17 is zoomed up will be described.

When the human face occupies a large part of the screen as shown in FIG. 18, the red component in the screen color evaluation value increases, and the gain correction amounts Gpr and Gpb obtained based on this become:
It changes like Gpr3 and Gpb3 in FIG. Assuming that the threshold value for the correction value remains within the range of the dashed line 100 in FIG. 8, Expression 4 holds, and the correction value comparison circuit 29 outputs the L-level control signal P1. However, as the human face is zoomed up, the effective area S calculated by the effective area calculation circuit 43 decreases, and the correction value threshold TG calculated by the correction value threshold calculation circuit 44 increases based on the effective area S. Accordingly, the range of the dashed line 100 becomes larger as the range surrounded by the solid line 110. Therefore, the gain correction amounts Gpr and Gpb obtained based on the screen color evaluation values are Gpr3 and Gp3.
Even if it changes like b3, Equation 3 still holds, and the control signal P1 at H level is output from the correction value comparison circuit 29.

The screen color evaluation value input to the first evaluation value comparison circuit 30 is also represented by a chain line 10 like Vr3 and Vb3 in FIG.
1, but with the decrease in the effective area S,
Since the first evaluation value threshold value TV1 has increased and the range of the chain line 101 has increased to the range surrounded by the solid line 111, Equation 5 holds, and the first evaluation value comparison circuit 30
The level control signal P2 is output.

Further, the screen color evaluation value input to the second evaluation value comparison circuit 31 is also represented by a chain line 1 like Vr3 and Vb3 in FIG.
02, the second evaluation value threshold value TV2 increases as the effective area S decreases.
, The expression 7 holds, and the second evaluation value comparison circuit 31 outputs the H-level control signal P3.

As described above, if all of the control signals P1, P2, and P3 are maintained at the H level, or if any one of them is maintained at the H level, the control signal P4 becomes the H level and the white balance adjustment is performed. , The stop mode is maintained.

As described above, by changing the size of each threshold value according to the effective area S of the screen, a white balance correction operation that is hardly affected by the color of the subject can be realized.

In the above embodiment, the focus mechanism 42
Employs a so-called distance measuring method for measuring the distance to a subject using infrared rays, but is not particularly limited to this method, and the present applicant has already filed Japanese Patent Application No. 62-29493.
As proposed in No. 8, the high-frequency component of the luminance signal of the captured video signal is maximized at the in-focus position, and the high-frequency component is integrated for each field to obtain a focus. An evaluation value may be calculated, and the focus lens may be displaced to a position where the focus evaluation value becomes the maximum. A so-called TTL method may be used. In this case, the lens position of the focus lens at the time of focusing is also determined. The indicated information is supplied to the subsequent effective area calculation circuit 43 as information indicating the subject distance.

In the above-described embodiment, the A / D converter 22 and the integrator 23 are commonly used for digitally integrating and extracting the levels of the two color difference signals RY and BY for each area. Although the integrated value of each signal could only be updated in two field periods, if the A / D converter and the integrator were provided exclusively for each signal, each signal level would be one field. Needless to say, it can be updated on a field-by-field basis. Further, it goes without saying that the operation of a series of circuit blocks from the screen evaluation circuit 27 to the correction value increase / decrease circuit 35 in FIG. 1 can be processed by software using a microcomputer.

[0087]

As described above, according to the present invention, the angle of view is small, or the distance to the subject is short, and a sufficient number of subjects are not included in the screen. When the white balance adjustment occurs, it is difficult for the white balance adjustment to shift from the stop mode to the operation mode, the white balance adjustment based on the screen evaluation is prohibited, and the white balance is shifted to the complementary color side, and the appropriate white balance is adjusted. Reduce the occurrence of inconveniences that cannot be obtained.

[Brief description of the drawings]

FIG. 1 is an overall circuit block diagram of an embodiment of the present invention.

FIG. 2 is a circuit block diagram of a correction value comparison circuit 29 according to one embodiment of the present invention.

FIG. 3 is a circuit block diagram of a first evaluation value comparison circuit 30 according to one embodiment of the present invention.

FIG. 4 is a circuit block diagram of a second evaluation value comparison circuit 31 according to one embodiment of the present invention.

FIG. 5 is a circuit block diagram of a stability determination circuit 32 according to one embodiment of the present invention.

FIG. 6 is a circuit block diagram of a correction value increasing / decreasing circuit 35 according to one embodiment of the present invention.

FIG. 7 is a diagram illustrating a change in a gain correction amount at the time of transition from an operation mode to a stop mode according to an embodiment of the present invention.

FIG. 8 is a diagram illustrating a change in a threshold TG according to an embodiment of the present invention.

FIG. 9 is a diagram illustrating a change in a threshold value TV1 according to an embodiment of the present invention.

FIG. 10 is a diagram illustrating a change in a threshold value TV2 according to an embodiment of the present invention.

FIG. 11 is a diagram illustrating a relationship between a zoom position and an angle of view.

FIG. 12 is a circuit block diagram of a conventional example.

FIG. 13 is a diagram illustrating area division according to an embodiment of the present invention.

FIG. 14 is a characteristic diagram showing a relationship between an effective area of a screen and a threshold TG for a correction value.

FIG. 15 is a characteristic diagram showing a relationship between an effective area of a screen and a first evaluation value threshold value TV1.

FIG. 16 is a characteristic diagram showing a relationship between an effective area of a screen and a second evaluation value threshold value TV2.

FIG. 17 is a diagram illustrating an imaging screen in a state where the angle of view is wide.

FIG. 18 is a diagram illustrating an imaging screen in a state where the angle of view is narrow.

[Explanation of symbols]

 28 Gain control circuit 35 Correction value increase / decrease circuit 40 Switch 41 Switch 141 View angle detection circuit 142 Focus mechanism

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-988 (JP, A) JP-A-4-10887 (JP, A) JP-A-3-270394 (JP, A) JP-A 64-64 60088 (JP, A) JP-A-5-122719 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 9/73 H04N 9/04

Claims (3)

(57) [Claims] 1. A white balance adjustment in which a gain of a color signal in an image pickup video signal obtained by photoelectrically converting incident light from a subject incident via a lens is corrected by a gain correction amount to perform white balance adjustment. In the apparatus, a gain control means for evaluating an imaging screen based on an imaged video signal to calculate target values Gpr and Gpb of gain correction amounts, and gain correction for changing the gain correction amounts Gmr and Gmb so as to approach the target values Means for increasing or decreasing the amount, when the gain correction amount falls within a predetermined range from the target value,
Changing the gain correction amount by the gain correction amount increasing / decreasing means is prohibited, and when the gain correction amount exceeds the predetermined range from the target value while the change is prohibited, the change of the gain correction amount by the gain correction amount increasing / decreasing means is prohibited. Control means for canceling the prohibition, angle-of-view detecting means for detecting the angle of view of the imaging screen by the lens, and object distance detecting means for detecting the distance to the object and outputting as object distance information, A white balance adjusting device, wherein an effective area in an imaging screen is obtained from the subject distance information, and the size of the predetermined range is changed according to the effective area. 2. A white balance adjustment in which a gain of a color signal in an image pickup video signal obtained by photoelectrically converting incident light from a subject incident through a lens is corrected by a gain correction amount to perform white balance adjustment. In the apparatus, a gain control means for evaluating an imaging screen based on an imaged video signal to calculate target values Gpr and Gpb of gain correction amounts, and gain correction for changing the gain correction amounts Gmr and Gmb so as to approach the target values Means for increasing or decreasing the amount, when the gain correction amount falls within a predetermined range from the target value,
Changing the gain correction amount by the gain correction amount increasing / decreasing unit is prohibited, and when the level of the color difference signal in the captured video signal exceeds a predetermined allowable range from a predetermined reference level, the gain correction amount by the gain correction amount increasing / decreasing unit is increased. Control means for canceling the prohibition of the change of the amount, angle-of-view detecting means for detecting the angle of view of the imaging screen by the lens, and subject distance detecting means for detecting the distance to the subject and outputting it as subject distance information, A white balance adjustment device, wherein an effective area in an imaging screen is obtained from the angle of view and the subject distance information, and the size of the predetermined allowable range is changed according to the effective area. 3. A white balance adjustment in which a gain of a color signal in an imaged video signal obtained by photoelectrically converting incident light from a subject incident through a lens is corrected by a gain correction amount to perform white balance adjustment. In the apparatus, a gain control means for evaluating an imaging screen based on an imaged video signal to calculate target values Gpr and Gpb of gain correction amounts, and gain correction for changing the gain correction amounts Gmr and Gmb so as to approach the target values Means for increasing or decreasing the amount, when the gain correction amount falls within a predetermined range from the target value,
The change of the gain correction amount by the gain correction amount increasing / decreasing unit is prohibited, and the color difference signal in the captured video signal exceeds a predetermined allowable range with respect to the level when the gain correction amount changing unit is prohibited from changing the gain correction amount. A control unit for canceling the prohibition of the change of the gain correction amount by the gain correction amount increasing / decreasing unit; an angle-of-view detecting unit detecting the angle of view of the imaging screen by the lens; It is provided with subject distance detecting means for outputting as distance information, obtaining an effective area in an imaging screen from the angle of view and the subject distance information, and changing a size of the predetermined allowable range according to the effective area. White balance adjustment device.