JP2614543B2 - 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 white balance in order to correct a difference in wavelength distribution of light depending on a light source. This control is performed in red (hereinafter R),
The ratio of the three primary color signals of blue (hereinafter B) and green (hereinafter G) is 1:
This is performed by adjusting the gain of each color signal so as to be 1: 1. Generally, for example, as disclosed in Japanese Patent Application Laid-Open No. 62-35792 (H04N9 / 73), a method is used in which the gain is adjusted so that the integral values of the color difference signals RY and BY of the screen become zero. Have been.

FIG. 2 is a block diagram of a white balance adjustment circuit using this method. In this figure, light passing through a lens 1 is photoelectrically converted by an image pickup device 2 (CCD), and then extracted by a color separation circuit 3 as R, G, and B primary color signals. The R and B signals are input to a camera process and matrix circuit 6 via an R amplifier circuit 4 and a B amplifier circuit 5, and a luminance signal Y and color difference signals RY and BY for red and blue are generated. And video circuit 7
Sent to At the same time, the two color difference signals are respectively integrated by the 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 5 so that the result becomes zero. Adjust the gain.

[0004]

The above-mentioned method is based on the rule of thumb that when a general subject is photographed, a value obtained by averaging the color difference signals of the entire screen is equivalent to a case where a completely white surface is photographed. Therefore, it is necessary for the photographing screen to include each color on average.

However, in this method, when the color of the subject itself is biased, for example, when a green grass or blue sky occupies a large area on the screen, or when a person wearing a red center is closed up. In some cases, even if the color distribution of the entire screen is averaged, a white screen state will not be obtained, and the white balance will be lost, and if such a subject is subjected to the white balance adjustment as described above, the biased color Has the disadvantage that the gain changes in the direction to cancel the white balance and the white balance shifts to the complementary color side, making it impossible to reproduce a proper color.

[0006]

The present invention is characterized in that the contrast of an image pickup screen is detected and the time constant of gain control of each color signal is changed in accordance with the contrast. It is characterized by using inference.

[0007]

Since the present invention is configured as described above, it is determined that a single-color subject occupies most of a low-contrast screen, and the time constant of the gain control is set to a large value so that the color is controlled. It is possible to prevent the white balance from shifting in the canceling direction.

[0008]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit block diagram of the automatic white balance adjusting device according to the present embodiment. In this figure, light that has passed through a lens 1 is imaged on a CCD 2 and photoelectrically converted, and then extracted by a color separation circuit 3 as R, G, and B primary color signals. R and B in these three primary color signals
The signal is input to the camera process and matrix circuit 6 together with the G signal through the R and B amplifier circuits 4 and 5, respectively.
Based on these, the luminance signal Y and the red and blue color difference signals R
-Y and BY are created, supplied to the video circuit 7, subjected to well-known processing, and recorded on a VTR or the like.

The RY and BY chrominance signals are supplied to integrating circuits 38 and 37, respectively. At the same time, the luminance signal Y passes through a high-pass filter 8 (HPF) and its high-frequency component YH Only the signal is input to the integration circuit 19. The high-frequency component YH has a property of increasing as the contrast of the screen increases, and can be used for evaluating the focus state of the TTL autofocus operation.

Each of the integration circuits 38, 37, and 19 is a digital integration circuit that integrates an input signal for one field and outputs the integrated signal for each field. Specifically, as shown in FIG. An A / D converter 31 that samples at a sampling cycle and sequentially converts the digital value;
An adder 32 for adding the output of the A / D converter to the output of the holding circuit 33 at the subsequent stage every time this new A / D converter output is issued, and a holding circuit 33 for holding the latest added output.
The contents held by the holding circuit 33 are issued as each evaluation value for each field, the holding circuit 33 is reset, and the same operation is repeated again. In this way, the integration outputs for one field of the color difference signals BY and RY are output from the integration circuits 37 and 38, respectively, to the color evaluation values b and r for each field.
And at the same time, the high-frequency component Y
An integrated output for one field of H is output as a contrast evaluation value yh for each field.

The reference level of the two color difference signals input to the integration circuits 37 and 38, that is, the zero level, is set in advance to a level obtained when a complete achromatic surface is photographed. It goes without saying that the / D conversion value can take not only a positive value but also a negative value.

The color evaluation values r and b obtained as described above
Are the gain control circuits 44 and 43 and the phase difference detection circuit 2 respectively.
The contrast evaluation value yh is input to the time constant calculation circuit 21.

The gain control circuits 44 and 43 control the amplification gains of the R and B amplification circuits 4 and 5 in the direction to make the input color evaluation values r and b zero as in FIG. That is, for example, if the color evaluation value r is a large value, the amplification gain of the R amplifier circuit 4 is reduced, and if the color evaluation value r is a small value, the amplification gain is controlled to be increased. The same applies to the relationship between the color evaluation value b and the amplification gain of the B amplifier circuit 5. Here, the time constant of the gain change in both amplifier circuits is calculated by a time constant calculation circuit 2 described later.
1 is calculated.

The phase difference detection circuit 20 detects, as a phase difference, a deviation of both color evaluation values from a preset light source color temperature axis for each field. Next, the operation of the phase difference detection will be described in detail with reference to FIG.

The color temperature axis of the light source refers to a change in the color temperature of the illuminating light on an image pickup screen which is ideal for white balance adjustment, such as a screen where a white object occupies most or a screen including each color on average. Is defined as the change in color evaluation value for
It is represented as light source color temperature axes P and Q on the color plane of FIG. Here, the deviation between the color evaluation value of the imaging screen and the light source color temperature axis is defined as the angle formed by a straight line connecting the point at which the color evaluation value is plotted on the color plane and the origin with the light source color temperature axis. Can be. However, when r ≧ b, it is determined as an angle from the light source color temperature axis P existing in the second quadrant, and when r <b, it is determined as an angle from the light source color temperature axis Q existing in the fourth quadrant. .

For example, if the color evaluation values r and b of a certain input field are present at the point J, the phase difference θ becomes
Angle θ between the straight line connecting point J and the origin and the light source color temperature axis P
a. If the color evaluation value is at the point K, it is defined by an angle θb between a straight line connecting the point K and the origin and the light source color temperature axis.

The time constant calculation circuit 21 receives the phase difference θ and the contrast evaluation value yh, performs fuzzy inference according to the following rules, and performs R and B amplification circuits 4 and 5.
, The so-called gain control time constant is determined. [Rule 1] "If if θ is large then time constant is large" [Rule 2] "If yh is large then time constant is small" These rules are as shown in FIGS. , “Large” and “small” are defined by membership functions for input variables such as “θ” and “yh” and output variables such as “time constant g”.

Rule 1 is defined by a membership function as shown in FIGS. FIG. 4 shows a membership function for the phase difference θ as an input variable, which is a function for calculating a membership value under the condition of rule 1 that “θ is large”. A simple increasing straight line increases as the phase difference θ increases. The membership value u1 corresponding to the phase difference θ is obtained from this function. FIG. 5 is a membership function for a time constant which is an output variable of rule 1 that “the time constant is large”, and is a function including a simple increasing function. In FIG. 4, a value indicated by △ as a phase difference θ in FIG. Then, when the membership value u1 of Rule 1 is determined, this value is designated on the vertical axis indicating the membership value in FIG. 5, and the hatched portion obtained by cutting off the head of the membership function is: This is the inference result obtained by comparing rule 1 with the facts.

Rule 2 is defined by a membership function as shown in FIGS. FIG. 6 shows “yh is large”
Is a membership function for a contrast evaluation value yh as an input variable, and a contrast evaluation value y
This is a function having a simple increase straight line that increases as h increases, and a membership value u2 corresponding to the contrast evaluation value yh is obtained from this function. FIG. 7 is a membership function for a time constant which is an output variable of rule 2 that “time constant is small”, and is a function including a simple decreasing function. In FIG. 6, a value indicated by △ as a contrast evaluation value yh in FIG. Entered and the membership value u2 of rule 2
Is determined, this value is designated on the vertical axis indicating the membership value in FIG. 7, and the hatched portion obtained by cutting off the head of the membership function is obtained by illuminating Rule 2 with the fact. Inference results.

Next, a method for determining the time constant in consideration of all the two rules will be described. The hatched rectangles in FIGS. 5 and 7 are superimposed on the same coordinates as those figures, that is, on a coordinate in which the horizontal axis represents the time constant g and the vertical axis represents the membership value. The obtained function in FIG. 8 is a membership function indicating the final inference result, and the position of the center of gravity Z of the function in the horizontal axis direction is a time constant in consideration of all the conditions of the two rules. Also, instead of the method of determining the time constant at the position of the center of gravity described above, the horizontal axis of the straight line parallel to the vertical axis and halving the area of the portion surrounded by the membership function with the horizontal axis is shown. It goes without saying that the position in the axial direction can be a time constant.

Next, the effect of each rule on the white balance adjustment operation will be described. In general, when considering the relationship between the color temperature change of the light source and each color difference signal, the color temperature of the light source illuminating this screen changes on a screen where a white subject occupies most or on a screen containing each color on average. In this case, the value obtained by averaging the color difference signals of the entire screen changes like the light source color temperature axes P and Q in FIG. Therefore, these color difference signals having a phase shifted from the light source color temperature axis do not reflect the color temperature of the light source, and are preferably not considered as information when performing white balance adjustment. In other words, it can be said that a color difference signal of a screen containing a large amount of green and blue-violet colors has a large phase shift from the light source color temperature axis and is not suitable for white balance adjustment. Therefore, as the phase difference θ increases, it becomes necessary to reduce the influence of the color evaluation value on the white balance adjustment. Therefore, in rule 1, it is determined from the phase difference whether there are many green or blue-violet subjects not related to the color temperature change of the light source from the phase difference, and the color relating to the green or blue-violet subject having a large phase difference is determined. As for the evaluation value, the time constant of the gain control in the amplifier circuits 4 and 5 is increased to substantially reduce the contribution of the corresponding color evaluation value to the white balance adjustment.

On the other hand, the rule 2 is that the subject of various colors is mixed in the photographing screen and the contrast evaluation value yh becomes large when there are many boundaries between the subjects, and conversely, the subject of a single color is displayed on the screen. Utilizing the fact that it becomes smaller when it occupies a large part, it is determined whether or not the shooting screen contains each color on the basis of the contrast evaluation value.If the contrast evaluation value is large, the time constant is reduced. The purpose is to make the effect of the corresponding color evaluation value on the white balance adjustment appear immediately.

The time constant g calculated in this manner is input to gain control circuits 43 and 44, and adjusts the time required to reduce the color evaluation value integrated by the integration circuits 37 and 38 to zero.
That is, as shown in FIG.
When the amplification gain for the red color signal is G1, when it is necessary to change the amplification gain to G2 in order to make the next calculated color evaluation value r in the next field zero, this G1 The time required to change the amplification gain from G to G2 is proportional to the time constant g, and when the time constant g is small,
For example, as shown by the straight line X1 in FIG. 10, the gain change rate increases and a steep gain change occurs, and the time required to change from G1 to G2 is as small as T1. Therefore, the R amplifying circuit 4 reacts sensitively with emphasis on the newly calculated color evaluation value r.

On the other hand, when the time constant g is large, for example,
As shown by the straight line X2 in FIG. 10, the gain change rate decreases and a gradual gain change occurs. The time required for the change from G1 to G2 is one field period (= 1 horizontal scanning period = 1 / 60S).
T2 which is longer than EC). Therefore, the R amplifier circuit 4 does not react sensitively according to the newly calculated color evaluation value r, and one field elapses before the gain reaches G2, and the gain based on the color evaluation value of the next field is further increased. And the gain G2 is not reached. As a result, the contribution of the color evaluation value r to the white balance adjustment in a field having a large time constant is reduced, and the white balance adjustment is temporarily stopped. Even if an inconvenient imaging screen occurs, the time constant during this time increases, and the influence of this screen is reduced. In particular, when the time constant g is an extremely large value, it is considered that the screen is inappropriate for performing the white balance adjustment based on the screen evaluation, and the membership function is devised. The change in gain can also be stopped.

As described above, it is determined whether or not an imaged screen is suitable for white balance adjustment by screen evaluation by fuzzy inference using the phase difference θ and the contrast evaluation value yh as inputs. By increasing the time constant of the amplification gain change of each color signal based on the color evaluation value obtained from the screen, it is possible to make it difficult to execute the white balance adjustment based on the color evaluation value.

It goes without saying that the operation of each circuit described above can be processed by software using a microcomputer as shown in the flowchart of FIG.
Note that, in FIG.
8 and 19, step 51 is the operation of the phase difference detection circuit 20, step 52 is the time constant calculation circuit 21, step 5
Reference numeral 3 denotes an operation of the gain control circuits 43 and 44, and a series of these operations is executed in one field cycle.

The color evaluation values r and b and the contrast evaluation value yh used simultaneously by the phase difference detection circuit 20, the time constant calculation circuit 21, and the gain control circuits 43 and 44 are obtained from the video signal of the same field. It was done.

[0029]

As described above, according to the present invention, even when a single-color subject occupies a large area on the image pickup screen and the color of the entire screen is biased, the white balance is canceled in the direction to cancel the single color. Appropriate white balance adjustment can be realized without shifting.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of one embodiment of the present invention.

FIG. 2 is a circuit block diagram of a conventional example.

FIG. 3 is a diagram illustrating a light source color temperature axis.

FIG. 4 is a membership function showing a relationship between a phase difference of rule 1 and a membership value.

FIG. 5 is a membership function showing a relationship between a time constant of rule 1 and a membership value.

FIG. 6 is a membership function showing a relationship between a contrast evaluation value of rule 2 and a membership value.

FIG. 7 is a membership function showing the relationship between the time constant of rule 2 and the membership value.

FIG. 8 is a membership function of a final inference result.

FIG. 9 is a block diagram of a main circuit of FIG. 1;

FIG. 10 is a diagram illustrating a relationship between gain control and a time constant.

FIG. 11 is a flowchart showing the function of FIG. 1;

[Explanation of symbols]

 4 R amplifying circuit 5 B amplifying circuit 19, 37, 38 Integrating circuit 20 Phase difference detecting circuit 21 Time constant calculating circuit 43, 44 Gain control circuit

Claims (2)

(57) [Claims] 1. A gain control means for controlling a gain of each color signal based on a color information signal in a captured video signal, and a contrast evaluation for outputting a high frequency component level of a luminance signal in the video signal as a contrast evaluation value. A white balance adjusting device comprising a value detecting means, wherein the time constant of the gain control is gradually reduced as the contrast evaluation value increases. 2. The method according to claim 1, wherein fuzzy inference is used to determine the time constant based on the contrast evaluation value.
Item 3. A white balance adjusting device according to item 1.