JPH04988A - White balance adjusting device - Google Patents

Abstract

PURPOSE:To stably perform white balance correction without generating fluctuation by prohibiting the change of the quantity of gain cor rection by a gain correction quantity control means when the quantity of gain correction enters within a constant range from a targeted value. CONSTITUTION:When a picture color evaluation value is changed, the quantity Gpr, Gpb of gain correction calculated at a gain control circuit 28 are changed, and the quantity of gain correction stored in each of R, B correction value memory is increased/decreased at a correction value control circuit 35 based on a comparison result at a correction value comparator 29, and when the change of the gain correction value is within a threashold value, a control signal P1 of H level is outputted. Thence, a stability discrimination circuit 32 receives the signal, and outputs a control signal P4 of H level, and the correction value control circuit 35 stops the increment/decrement of the quantity of gain correction at that time, then, the mode of white balance correction migrates to a stopping mode.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention is based on a captured video signal obtained from an image sensor.
The present invention relates to an automatic mill balance adjustment device for a color video camera that controls mill balance.

(B) Conventional Technology In a color video camera, it is necessary to control the mill balance in order to correct for differences in the wavelength distribution of light due to the light source.

This control includes red (hereinafter referred to as R), blue (hereinafter referred to as B), green (hereinafter referred to as G).
) by adjusting the gain of each color signal so that the ratio of the three primary color signals becomes 1:1:1. Generally, a method is used in which the gain is adjusted so that the integral value of the screen color difference signals R-Y and B-Y becomes zero, as shown in, for example, Japanese Patent Application Laid-Open No. 62-35792 (HO4N9/73). ing.

FIG. 12 is a block diagram of a mill balance adjustment circuit using this method.

The light that has passed through the lens (1) is transferred to an imaging device (CCD) (2).
), the color separation circuit (3) converts R, G,
The B color signal is extracted as the three primary color signals, and the G color signal is directly
Each R and B signal is transmitted through an R amplifier circuit (4) and a B amplifier circuit (5).
) is input to the camera process and matrix circuit (6), and the luminance signal Y and the red and blue color difference signals R are input to the camera process and matrix circuit (6).
-Y, B-Y are created and sent to the video circuit (7).

At the same time, the two color difference signals are respectively sent to the integrating circuit (17).
(18), the gain control circuits (13) and (14) are set to R so that the integration is performed for a sufficiently long time and the result becomes zero.
, B. The gain of each amplifier circuit (4), (5) is adjusted.

(c) Problems to be Solved by the Invention However, in the above-described configuration, since feedback is constantly working on the R and B amplification circuits, the amount of amplification gain correction tends to fluctuate depending on the subject, resulting in unstable white balance correction. There is a problem in that it is necessary to carry out

(d) Means for Solving the Problems The present invention is a white balance adjustment device that adjusts mill balance by correcting the gain of a color signal in an imaged video signal using a gain correction amount. A gain control unit that evaluates the screen and calculates a target value of the gain correction amount, and a gain correction amount increase/decrease unit that changes the gain correction amount so as to approach the target value, and the gain correction amount is within a certain range from the target value. The present invention is characterized in that when the gain correction amount increase/decrease means enters the gain correction amount, changing of the gain correction amount by the gain correction amount increase/decrease means is prohibited.

As another means, in a white balance adjustment device that performs mill balance adjustment to correct the gain of the color signal in the captured video signal, when the color difference signal obtained from the color signal falls within a predetermined specific range, the color It is characterized by having a fixed signal gain.

Also, when the color difference signal obtained from the color signal exceeds a predetermined specific range, or when the gain correction amount when the gain is fixed exceeds a certain range from the target value, the fixation of the gain of the 9 color signals is released. It is characterized by Furthermore, when the color difference signal changes by a predetermined amount with respect to the level when changing the gain correction amount by the gain correction amount increase/decrease means is prohibited, or when the color difference signal changes by a predetermined amount with respect to the level when the gain of the color signal is fixed. , is characterized by releasing the fixation of the gain of the color signal.

(E) Function Since the present invention is configured as described above, stable white balance correction without fluctuation can be performed.

(f) Example An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit block diagram of an automatic white balance adjustment circuit according to this embodiment.

The light that has passed through the lens (1) is imaged on the CCD (2) and subjected to photoelectric conversion, after which it is sent to the color separation circuit (3) into R,
It is extracted as three primary color signals of G and H. The R and B signals among these three primary color signals are processed by R and B amplification circuits (4
)(5), it is input to the camera process and matrix circuit (6) together with the G signal, and based on these, the luminance signal (
Y) and red, front color difference signals (RY) and (B-Y), respectively
is created, supplied to the video circuit (7), and subjected to well-known processing. Moreover, each signal of (RY) (B-Y) is
At the same time, it is also supplied to the selection circuit (21).

The selection circuit (21) selects the color difference signals (R-Y), (B-Y) by the selection signal (Sl) from the timing circuit (25).
One of the two signals is sequentially selected for each field, (RY) → (B-Y) → (RY) →
...and a subsequent A/D converter (22) for each field.
is output to. Note that the selection signal (Sl) is created based on the vertical synchronization signal obtained from the synchronization separation circuit (24), as will be described later.

The A/D converter (22) receives the color difference signal (R-Y) selected by the selection circuit (21) at a predetermined sampling period.
(B-Y) is sampled and converted into a digital value, and this value is output to the integrator (23). by the way,
The timing circuit (25) receives vertical and horizontal synchronization signals from the camera process and matrix circuit (6) and the CCD (2
), the imaging screen is divided into 64 8x8 rectangular areas (All
), (A12), (A13)... (A88), that is, (Aij) (i, j = an integer of 1 to 8), and the selection circuit (21 ) A switching signal (S2) for extracting the output in time division is output to the integrator (23).

The integrator (23) receives the switching signal (S2) and adds the A/D converted values of the output of the selection circuit (21) for each region over one field period, that is, digitally integrates each of the 64 regions. When the integration for one field is completed, this integrated value is held in the memory (26) as a color evaluation value. As a result, the digital integral value of the color difference signal (R-Y) corresponding to 64 areas in a certain arbitrary field is 64 color evaluations if (ri j) ci, j:
1-8). Also, in the next field, the color difference signal (B-Y) is selected by the selection circuit (21), so as a result of the integration in each region of the integrator (23), the color difference signal (B-Y) for each region is Digital integral values are obtained as 64 color evaluation values (bij). In this way, when the integration of the two fields of color difference signals (R-Y) (B-Y) is completed, the color evaluation value (r ij) (
64×2 values of b i j) will be held in the memory (26). After this, the same operation as described above is repeated, and the color evaluation value (rij) is updated in the next field, and the color evaluation value (bij) is updated in the next field.

FIG. 14 shows the internal structure of this integrator (23) in more detail. Each A/D conversion data is transferred to the switching circuit (61)
supplied to This switching circuit (61) receives a switching signal (S2
) and add each A/D converted value prepared for each area! (Fl 1) (Fl 2) . . . (F8B), it has the role of supplying data to the adder for the region where the sampling point of the corresponding data exists. That is, if a sampling point of some arbitrary data is included in the area (All), this data is added to the adder (Fil) for the area (All).
supply to. Hereinafter, the adder (Fij) (i
j=1 to 8) are set for the area (Aij), and a total of 6
Four adders are provided. After each adder,
A holding circuit (Qij) is provided, and each added value is temporarily held in each holding circuit. The data held in each holding circuit is input to the adder again and added to the next input data. Further, each holding circuit is reset for each field based on a vertical synchronizing signal, and only the held data immediately before this reset is supplied to the memory (26). Therefore,
One set of adder and holding circuit constitutes one digital integration circuit, and a total of 64 integration circuits constitute an integrator (23).
The digital integral value is stored in memory (26) for each 64 areas from each holding circuit for each field.
is input. When the integration for one field is completed, this integrated value is held in the memory (26) as a brightness evaluation value or color evaluation value.

The latest color evaluation value (rij) (b
ij) (], j1 to 8) are sent to the screen evaluation circuit (27), and are calculated as color evaluation values (Vr) (vb) of the entire screen of each color difference signal based on the following equations (1) and (2). be done.

i=I J=1 i=1 3=1 These equations (1) and (2) calculate the color evaluation value (ri
j) (bij) is divided by the number of regions, and the average value for one region is calculated as the screen color evaluation value. This screen color evaluation value (Vr) (Vb) is sent to a gain control circuit (28), a first evaluation value comparison circuit (30), and a second evaluation value comparison circuit (31).

In the gain control circuit (28), the R and B amplifier circuit (4) (
5) to make the screen color evaluation value (V r) (V b), which is the color evaluation value of the entire screen, zero, a correction value (Gpr) (Gpb) is added to the current gain.
), and generates a correction value signal corresponding to the correction value comparison circuit (2
9).

Next, the operations of the correction value comparison circuit (29) and the first and second evaluation value comparison circuits (30) and (31) will be explained.

The correction value comparison circuit (29) is constructed as shown in FIG. That is, the current gain correction values (Gmr) (Gmb) that are held in the R and B correction value memories (33) and (34) and are adjusting the current gains of the R and B amplifier circuits (4) and (5). , the correction value (Gpr) obtained from the gain control circuit (28) (
Gpb) are compared by an R correction value comparator (29a) and a B correction value comparator (29b), respectively. As a result, in the R correction value comparator (29a), (G mr) = (G
pr), an H level signal is sent as the control signal (Prl), and (G mr)≠(G pr
), the control signal (Prl) is L.
A level signal is output to the correction value increase/decrease circuit (35).

At this time, if (Gmr) < (Gpr), an H level signal is used as the control signal (Pr2), and (Gmr
) > (Gpr), an L level signal is output as the control signal (Pr2) to the correction value increase/decrease circuit (35). A similar judgment is made in the B correction value comparator (29b), and when it is judged that (Gmb) = (Gpb), an H level signal is sent as the control signal (Pbl), and (Gmb)≠ If it is determined that (G pb), an L level signal is output as a control signal (Pbl) to the correction value increase/decrease circuit (35), and at this time (Gmb) <
(Gpb), an H level signal is used as the control signal (Pb2), and (Gmb) > (Gpb)
If so, an L level signal is outputted as a control signal (pb2) to the correction value increase/decrease circuit (35). At the same time, in the R correction value comparator (29a), each input correction value (Gmr)
(Gpr) difference, lGmr-Gprl, and the B correction value comparator (29b), (G mb) (G p
b) difference, lGmb-G pb l, is calculated and both are sent to the correction value adder (29C). Correction value adder (29
In c), the sum Gmr - Gpr l +l Gmb - Gpb is calculated, and the correction value comparator (29e) compares the magnitude relationship with the threshold value (TG) stored in advance in the correction value threshold memory (29d). be done. As a result, Gmr −Gpr l + l Gmb−−Gpb l
When ≦TG (3), H is used as the control signal (Pl).
The level signal is also Gmr-Gprl + l Gmb-Gpbl > TG
At the time of (4), an L level signal is output as the control signal (Pl).

The first evaluation value comparison circuit (30) is configured as shown in FIG. First, the first R evaluation value subtractor (30a) uses the screen color evaluation value (Vr) output from the screen evaluation circuit (27) and the R reference value (
In addition, the first B evaluation value subtracter (30b) calculates the difference between the screen color evaluation value (vb) and the B reference value (1Vr−Vlrl) stored in the B reference value memory (30d) in advance.
(2) The difference from IVb-Vlbl is calculated, and both are sent to the first evaluation value adder (30e). The first evaluation value adder (30e) calculates the sum V r −V lr + V b −V lb, and the first evaluation value comparator (30g) stores the first evaluation value threshold memory (30f) in advance. The threshold value stored in (
Tvl) is compared in size. As a result, Vr-Vlrl + l Vb Vlbl≦Tvl
At the time of (5), an H level signal is used as the control signal (P2), and Vr-Vlrl + l Vb-Vlbl > Tvl
At the time of (6), an L level signal is output as the control signal (P2).

The second evaluation value comparison circuit (31) is configured as shown in FIG. First, the second R evaluation value subtractor (31a) uses the screen color evaluation value (Vr) output from the screen evaluation circuit (27) and the R evaluation value (Vr) stored in advance in the R evaluation value memo 'J (31c). 2r), IVr-V2rl is also the second B
The evaluation value subtracter (31b) calculates the difference between the screen color evaluation value (Vb) and the B evaluation value (V2b) stored in the B evaluation value memory (31d) in advance, ]Vb−V2bl, and both It is sent to the 2-evaluation value adder (31e). The second evaluation value adder (31e) calculates the sum Vr-V2r (Vb-V2b), and the second evaluation value comparator (31g) calculates the sum Vr-V2r, which is stored in the second evaluation i threshold memory (31f) in advance. The magnitude relationship with the threshold value (Tv2) is compared. As a result, Vr-V2rl + l Vb-V2bl≦Tv2
At the time of (7), an H level signal is used as the control signal (P3), and Vr-V2rl+IVb-V2bl>Tv2 (8)
At this time, an L level signal is output as the control signal (P3).

As described above, each control signal (PI) (P2) (P3) output from the correction value comparator (29), the first evaluation value comparison circuit (30), and the second evaluation value comparison circuit (31) is as follows: Both are input to the stability determination circuit (32).

The stability determination circuit (32) is configured as shown in FIG. 5, and control signals (PI) (P2) (P3) are input to the OR gate (51). The switch (52) is a fixed contact (52a) or an OR gate (51) to which a control signal (Pl) is applied.
) has a function of selectively connecting the fixed contact (52b) coupled to the output terminal and the fixed contact (52c) coupled to the output terminal, and the switching thereof is controlled by the output control signal (P4) generated at the output terminal. , the fixed contact (52b) side when the signal (P4) is at H level, and the fixed contact (52b) side when the signal (P4) is at L level.
52a) side.

Next, the operation of the stability determination circuit (32) will be explained. First, the H level control signal (PI) is detected by the stability determination circuit (32).
), the output of the OR game (51) will always be at H level, so no matter which fixed contact the switch (52) is at first, the output control signal (P4) will be at H level. , the switch (52) eventually changes to the fixed contact (52).
b) will be connected to the side. In this state, as long as at least one of the control signals (PI) (P2) (P3) is at H level, the output control signal (P4) is at H level. Next, the control signal (PI) (P2) (both at L level) (
P3) is input to the stability determination circuit (32),
Since the output of the OR gate (51) becomes L level, the output control signal (P4) becomes L level, and the switch (52)
will be connected to the fixed contact (52a) side.

In this state, as long as the control signal (Pl) is at L level,
The output control signal (P4) becomes L level.

That is, when the equation (3) is established in the correction value comparison circuit (29), the stability determination circuit (32) issues an H level output control signal (P4), and this H level control signal (P4) is output.
4) serves as a white balance stop signal as described later.

On the other hand, in the correction value comparison circuit (29), equation (4) is
When equation (6) holds true in the first evaluation value comparison circuit (30) and equation (8) holds true in the second evaluation value comparison circuit (31), the stability determination circuit (32) controls the L level. signal (P4), and this L level control signal (P4) is output.
4] acts as a white balance operation signal.

This control signal (P4) is sent to the second evaluation value comparison circuit (31).
, and is input to the correction value increase/decrease circuit (35).

In the second evaluation value comparison circuit (31), an edge detector (31
h) receives this control signal (P4).

The edge detector (31h) 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 and stores the R evaluation value memory (31C) and the B evaluation value memory (31C).
The screen color evaluation value (Vr) (Vb) is allowed to pass through the memory (31c) (31cl) and the screen color evaluation value immediately after passing is stored in the memory (31c) (31d).

Therefore, when the mill 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 respectively set in the R evaluation value memory (3).
]c) and B evaluation value memory (31d).

The configuration of the correction value increase/decrease circuit (35) that receives the current gain correction value (Gmr) (Gmb) and control signal (Prl) (Pr2) (Pbl) (Pb2) (P4) is as shown in Figure 6. . That is, the correction value increase/decrease circuit (35) is composed of six switches, R and B increase circuits (46) (48), and R and B decrease circuits (47) (49). Switches (40) and (41) are controlled by a control signal (P4), and a gain correction value (G mr
) is applied, the fixed contact (40a) is connected to the output terminal (35a), and the fixed contact (40b) is connected to the switch (
42) is connected to the contact (42c). switch(
42) is switched and controlled by a control signal (P r 1 ), the fixed contact (42a) is connected to the output terminal (35a), and the fixed contact (42b) is connected to the contact (44) of the switch (44).
C) is connected to pz. The switch (44) is switched and controlled by the control signal (Pr2), and has a fixed contact (44a).
) (44b) are R increase and R decrease circuits (46) (4
7). Here, R increase and decrease circuit (
46) (47) The output is led to the output terminal (35a).

Similarly, a signal indicating the gain correction value (G mb) is applied to the contact (41c) of the switch (41), and the fixed contact (
41a) is connected to the output terminal (35b), and the fixed contact (4l
b) is connected to the contact (43c) of the switch (43). The switch (43) is switched and controlled by the control signal (Pbl), and the fixed contact (43a) is connected to the output terminal (3
5b), and the fixed contact (43b) is the switch (45)
is connected to the contact (45c). Switch (45)
are switched and controlled by the control signal (Pb2), and the fixed contacts (45a) and (45b) are connected to the R increase and R decrease circuits (
48) (49).

Here, the R increase and decrease circuit (48) (49) output is:
It is led out to the output terminal (35b).

Next, the operation of the correction value increase/decrease circuit (35) will be explained.

First, when the I-rubel control signal (P4) is input to the switch (40) and switch (41), that is, when the mill balance correction is in the stop mode, the switch (40) is on the fixed contact (40a) side. In addition, the switch (41) is located on the fixed contact (41a) side, and the value (Gmr) stored in the R correction value memory (33) and the B correction value memory (34) is
(Gmb) is the gain correction value (G r) (G
b) is output to the output terminals (35a) (35b), and adjusts the gains of the R and B amplifier circuits (4) and (5).

Next, when the control signal (P4) becomes L level, that is, when the mill balance is in the operation mode, the switch (40) is set to the fixed contact (40b) side, and the switch (41) is set to the fixed contact (41b) side. side, R correction value memory (33) and B
The correction value (Gmr
) (Gmb) are input to switches (42) and (43), respectively.

When the control signal (Prl) is at H level, the switch (42) is set to (G mr) in the correction value comparison circuit (29).
= (G pr), the fixed contact (42a
) side and stored in the R correction value memory (33) is output as is as the gain correction value (Gr),
Adjust the gain of the amplifier circuit (4). Next, the control signal (Pr
l) becomes L level, that is, when the correction value comparison circuit (29
), when it is determined that (G mr)≠(G pr), the switch (42) is on the fixed contact (42b) side, and the correction value (G mr) stored in the R correction value memory (33) is
mr) is input to the switch (44). On the other hand, the switch (43) also operates in the same way as the switch (42), and when the control signal (Pbl) is at H level, the value stored in the B correction value memory (34) is directly used as the gain correction value (Gb ), and the control signal (Pbl) is output as L.
When the level is reached, the correction value (G mb) stored in the B correction value memory (34) is input to the switch (45).

The switch (44) operates when the control signal (Pr2) is at H level, that is, in the correction value comparison circuit (29), (Gmr) <
(Gpr), the fixed contact (44a)
The correction value (G mr) stored in the R correction value memory (33) is input to the R increase circuit (46), and a preset constant value (ro) is added to the gain correction value. (Gr). That is, G r =Gmr+
r O. Further, when the control signal (Pr2) becomes L level, that is, in the correction value comparison circuit (29) (Gm
r) > (G pr), the switch (
44) is on the fixed contact (44b) side, and the correction value (G m
r) is input to the R reduction circuit (47), and the constant value (r
o) is subtracted and output as a gain correction value (Gr),
That is, the gain of the R amplifier circuit (4) is adjusted by setting Gr=Gmr-ro. On the other hand, the switch (45) also operates in the same way as the switch (44), and the control signal (pbx
) is at H level, the correction value (G mb) value stored in the B correction value memory (34) is
8), a constant value (bo) is added, and the control signal (P
b2) becomes L level, the correction value (G mb)
is a B reduction circuit (49), from which a fixed amount value (bo) is subtracted and output as a gain correction value (Gb), which is then sent to a B amplification circuit (49).
5) Adjust the gain.

The R and B gain correction values (Gr) (Gb) output from the correction value increase/decrease circuit (35) are stored again in the R correction value memory (33) and the B correction value memory (34). , the next field is the current correction value (Gmr) (
Gmb) is used for white balance adjustment. Therefore,
The contents of the R and B correction value memories (33) and (34) are updated with the correction values from the output terminals (35a) and (35b) for each field.

In the R amplifier circuit (4), R
The gain when amplifying the signal changes, and when the correction value (Gr) is zero, the gain is fixed at 1. If the correction value (Gr) changes in the positive direction, the gain increases, and if it changes in the negative direction, the gain increases. The gain will be smaller. Similarly, in the B amplifier circuit (5), the amplification gain of the B signal changes according to the gain correction value (Gb), and Gb=
When the voltage is O, the gain is fixed to 1.

The operation of each circuit described so far will be explained using actual white balance correction as an example.

First, an explanation will be given of the operation when the mill balance correction shifts from the operation mode to the stop mode.

Now, the R correction value memory (33) and the B correction value memory (34)
) Gain correction value (Gmr) stored in each (G
mb), the amplification gains of the R amplifier circuit (4) and the B amplifier circuit (5) are controlled, and it is assumed that a proper mill balance is achieved. When the screen color evaluation value changes here, the gain correction amount (Gpr) calculated by the gain control circuit (28)
(Gpb) changes as shown in Figure 7, and the correction value comparison circuit (2
Based on the comparison result in step 9), the gain correction amount stored in each of the R and B correction value memories is increased or decreased by the correction value increase/decrease circuit (35), and from (Gmr) (Gmb) to (Gmr
') (Gmb'), the relationship in equation (3) is established, and an H-level control signal (Pl) is output. In FIG. 7, the range where the relationship of equation (3) holds is a square (dashed line) region centered on (G pr) (G pb). Also, the size of this square depends on the threshold value (TG) itself, and this threshold value (TG) is
The white balance gain is set to a value that allows it to be determined that it is okay to fix the gain of the white balance based on actual values measured in actual photography. The stability determination circuit (32) receives this and outputs an H level control signal (
P4), the correction value increase/decrease circuit (35) stops increasing/decreasing the gain correction amount, and the mill balance correction enters the stop mode.

In this way, the gain correction value is increased by increasing circuits (46) (48) or decreasing circuits (47) (49), and the R or B amplifier circuits (4) (5) gradually change the gain to perform white balance adjustment. The gain correction value change for each field is the threshold (TG
), the increase/decrease of the gain correction value is stopped in order to suppress fluctuation in white balance adjustment, and the gain correction value immediately before this stop is maintained, and the R and B amplifier circuits (4) (5)
The gain of is fixed to a constant gain determined by this correction value. Note that the correction values at this time will continue to be held in the R and B correction value memories (33) and (34) while the stop mode continues.

In other words, the R and B amplifier circuits (4) while continuing in the stop mode with the correction values immediately before the stop mode held in this memory.
The gain in (5) will be fixed.

Next, the operation when the mill balance correction shifts from the stop mode to the operation mode will be explained.

Now, R correction value memory (33) and B correction value memo 17 (3)
4) Gain correction value (Gtar) stored in each
(Gmb), R amplifier circuit (4) and B amplifier circuit (5)
Assume that the amplification gain of is controlled and a proper white balance is achieved. Here, the gain correction values obtained based on the screen color evaluation value are (Gpr") and (Gpb") in Fig. 9.
It is determined that there is no need to change the gain correction amount as long as it changes within a constant range from (G mr) and (G mb), that is, within a range where equation (3) holds true. .

However, the gain correction amount (Gpr) (Gpb) is (Gp
When the gain correction value (Gr) (Gb
) is the correction value (
Gmr) (Gmb), it is judged that proper mill balance cannot be obtained, and the correction value comparison circuit (29)
An L level control signal (Pl) is output from.

Next, the operation performed by the first evaluation value comparison circuit (30) in response to a similar change in screen color evaluation value will be described. First, when the mill is properly balanced, the screen color evaluation value (Vr
)(Vb) is (Vr”)(Vb”) in Figure 10 (
Vlr) (Vlb) to a certain range (threshold 1i (TV
It is not determined that the screen color evaluation value has changed as long as the screen color evaluation value changes within the range indicated by the chain line depending on I), that is, within the range where equation (5) holds true. However, the screen color evaluation value is (Vr
') (Vb') and the equation (6) is established, the first evaluation value comparison circuit (30) outputs L
A level control signal (P2) is output.

Here, the reference value (Vlr) (Vlb) is set in advance to the screen color evaluation value of each color difference signal when photographing a completely achromatic subject where the entire screen is white. & The reference values (Vlr) (Vlb) of the color difference signals (R-Y) (B-Y) output from the matrix circuit (6) are both set to zero when a completely achromatic subject is photographed. It turns out. Therefore, in equation (5), IVr-Vlrl is a value indicating the degree of deviation of the color difference signal (R-Y) from the zero level, in other words, how far it is from an achromatic color, and similarly l Vb- Vlbl is a value indicating the degree of departure from the zero level of the color difference signal (B-Y), and the sum of both indicates the degree of departure from white for the entire screen.

Therefore, by setting the threshold value (Tvl) as an allowable range for proper mill balance, if equation (5) is satisfied, the imaging screen is within the allowable range where it can be determined that proper mill balance has been achieved. There is no need to operate the mill balance adjustment, and if equation (6) holds true, the imaging screen will no longer be able to determine that an appropriate mill balance has been achieved, and the gain correction value will be increased or decreased immediately. This means that it is necessary to make the accompanying mill balance adjustment the operating mode.

Furthermore, the operation performed by the second evaluation value comparison circuit (31) in response to a similar change in screen color evaluation value will be explained. In the R correction value memory (31c) and the B correction value memory (31d), the screen color evaluation values when the mill balance correction enters the stop mode are stored as (V2r) (V2b).
Screen color evaluation value (Vr) newly calculated by screen evaluation
(Vb) is within a certain range (the range of dashed lines depending on the threshold (TV2)) from (V 2r) (V 2b) like (Vr") (Vb") in FIG. )
As long as the screen color evaluation value changes within the range that holds true, it is not determined that the screen color evaluation value has changed. However, when the screen color evaluation value changes as (Vr') (vb') and the equation (8) comes to hold, the second evaluation value comparison circuit (31) outputs an L level control signal. (P3) is output.

Here, the threshold value (TV2) is the change in the current screen color evaluation value (Vr) (Vb) relative to the screen color evaluation value (V2r) (V2b) when entering the stop mode, which causes white balance adjustment by gain increase/decrease. This is a value for setting a permissible range within which it is determined that there is no need to perform this process, and is set in advance based on actual measured values through experiments.

In this way, the correction value comparison circuit (29) uses equation (4), the first evaluation value comparison circuit (30) uses equation (6), and the second evaluation value comparison circuit (31) uses equation (8). It is confirmed that the formula holds, and both control signals (PI) and (P
2) When (P3) is output and the stability determination circuit (32) receives it and outputs the L level control signal (P4), the correction value increase/decrease circuit (35) starts increasing/decreasing the gain correction amount. , white balance correction enters operation mode. In other words, the condition for white balance correction to change from stop mode to operation mode is the gain correction value (Gpr) (
Gpb) is in stop mode, the actual correction value (Gr) (
Correction value maintained as (Gb) (Gmr) (Gmb)
, the screen color evaluation value (Vr) (Vb) changes by more than the threshold value (TG), and the degree to which the screen color evaluation value (Vr) (Vb) deviates from the achromatic color becomes greater than the threshold value (TV 1 ), and the screen color evaluation value (
When the three conditions that Vr) (Vb) change by more than the threshold value (TV2) with respect to the value at the time of entering the stop mode are satisfied at the same time, it is no longer possible to obtain an appropriate mill balance in the stop mode. It is in operation mode as a chick.

Further, it is also possible to shift to the operation mode if any one of the three conditions described above is satisfied.

Note that in this embodiment, the A/D converter (22) and the integrator (
23) is commonly used to digitally integrate and extract the levels of the two color difference signals (R-Y) (BY) for each region, and the integrated value of each signal can only be updated in two-field cycles. However, it goes without saying that if an A/D converter and an integrator are provided exclusively for each signal, each signal level can be updated for each field.

By the way, in the above-mentioned embodiment, one condition for shifting the mill balance correction to the stop mode is that the deviation of the correction values (Gpr) (Gpb) calculated from the screen evaluation results is within the allowable range. determined solely by
In addition to this, when the control signal (P2) becomes H level, that is, the reference value (Vlr) of the screen color evaluation value (Vr) (Vb)
) By adding the condition that the degree of departure from (Vlb) is within the permissible range, it is possible to more reliably judge whether or not to enter the stop mode. According to this condition, as shown in Figure 8, the screen color evaluation value when proper white balance is achieved is (Vr) (Vb), and as the screen changes here, the screen color evaluation value becomes ( When the screen color evaluation value becomes (Vr") (Vb") by controlling the amplification gain of each of R and B, equation (5) is established. However, when it enters the range indicated by the chain line depending on the threshold value (TVI), an H level control signal (P2) is generated.

In this case, as shown in Fig. 15, the stability determination circuit (30)
In A, the control signal (Pi) (P2) is powered by two people.
By leading the output of the ND gate (50) to the fixed contact (52a), it becomes possible to shift to the stop mode only when both of the above two conditions are satisfied.

Furthermore, it is also possible to control transition to the stop mode only under newly added conditions.

(G) Effects of the Invention As described above, according to the present invention, more stable white balance correction without fluctuation is possible.

[Brief explanation of drawings]

FIG. 1 is an overall circuit block diagram of an embodiment of the present invention; FIGS. 2, 3, 4, 5, 6, and 14 are circuit block diagrams of the same essential parts; Figure, Figure 8, Figure 9, Figure 10
11 is an explanatory diagram at the time of mode transition, FIG. 15 is a block diagram of main parts of another embodiment, FIG. 12 is a circuit block diagram of a conventional example, and FIG. 13 is an explanatory diagram of area division. (27)...Screen evaluation circuit, (28)...Gain control circuit, (29)...Correction value comparison circuit, (30)...First evaluation value comparison circuit, (31)...First evaluation value comparison circuit 2 evaluation value comparison circuit, (32)... stability determination circuit, (35)... correction value increase/decrease circuit, (4)... R amplifier circuit, (5)... B amplifier circuit

Claims (6)

[Claims] (1) In a white balance adjustment device that adjusts white balance by correcting the gain of a color signal in a captured video signal using a gain correction amount, a target value for the gain correction amount is determined by evaluating the imaging screen based on the color signal. a gain control means for calculating, and a gain correction amount increase/decrease means for changing the gain correction amount so as to approach the target value, and when the gain correction amount falls within a certain range from the target value, the gain correction amount increase/decrease means A white balance adjustment device characterized in that changing a gain correction amount is prohibited. (2) In a white balance adjustment device that performs white balance adjustment to correct the gain of the color signal in the captured video signal, when the color difference signal obtained from the color signal falls within a predetermined specific range, the gain of the color signal is adjusted. A white balance adjusting device characterized in that the white balance is fixed. (3) When the color difference signal obtained from the color signal exceeds a predetermined specific range, the prohibition of changing the gain correction amount by the gain correction amount increase/decrease means is canceled. Balance adjustment device. (4) gain control means that evaluates the imaging screen based on the color signal and calculates the target value of the gain correction amount; 3. The white balance adjustment device according to claim 2, wherein the white balance adjustment device releases fixation of the gain. (5) The white balance adjustment device according to item 1, wherein the white balance adjustment device releases the prohibition when the color difference signal changes by a predetermined amount from the level at which change of the gain correction amount by the gain correction amount increase/decrease means is prohibited. . (6) The white balance adjustment device according to item 2, wherein the fixation of the gain of the color signal is released when the color difference signal changes by a predetermined amount with respect to the level when the gain of the color signal is fixed.