JPH0410887A - White balance adjusting device - Google Patents

Abstract

PURPOSE:To reduce possibility that deviation is generated in colors within a screen and that white balance is deviated to the complementary color side of it by spending much time for screen evaluation with using a color information signal and executing the screen evaluation with the more color information signals. CONSTITUTION:The effective quantity of the whole object included in a screen is calculated based on angles of view RW and RL from an angles of view detecting circuit 21 and object distance from a focusing mechanism 22 in an effective area calculating circuit 23. An obtained effective area S is transmitted to an integrating circuits 117 and 118 to integrate respective color-difference signals in the same way as integrating circuits 17 and 18 and the integrating circuits are constituted so that the time constant of them may become long as the effective area S becomes small and may become infinite when the effective area S is under a fixed threshold value. Thus, it is reduced that deviation is generated in colors within the screen and that white balance is deviated to the complementary color side of it since the sufficiently many objects are included in the screen owing to the small angles of view or the short distance of the objects.

Description

[Detailed description of the invention] (a) Industrial application field The present invention is based on a captured video signal obtained from an image sensor.
The present invention relates to an automatic white balance adjustment device for a color video camera that controls white balance.

(b) Conventional technology In a color video camera, it is necessary to perform self-balance control in order to correct for differences in the wavelength distribution of light depending on 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). It is being

FIG. 2 is a block diagram of a white 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,
It is extracted as H three primary color signals. R amplifier circuit (4)
, B amplifier circuit (5), and is input to the camera process and matrix circuit (6), where a luminance signal Y and red and blue color difference signals R-Y and B-Y are generated and sent to the video circuit. .

At the same time, the two color difference signals are respectively sent to the integrating circuit (17).
At step (18), the gain control circuits (13) and (14) control the gains of the R and B amplifier circuits (4) and (5) so that the integration is performed for a predetermined time and the results are both zero. Emit a gain adjustment signal to adjust.

Note that the reference level, ie, the zero level, of each color difference signal mentioned above is set in advance to the signal level obtained when an object whose entire screen is achromatic is photographed.

(c) Problems to be Solved by the Invention The above-mentioned method takes measures such as increasing the time constants of the integrating circuits (17) and (18) to accommodate the various color distributions of the screen photographed by the video camera. It is assumed that if these color distributions are averaged, each color component making up the color distribution cancels each other out, and a nearly perfect screen state can be approximated.

However, if the angle of view of the lens is narrow or the distance to the subject is short, the effective area that can fit into the screen becomes small, and the result of integrating colors within the screen is likely to be biased.

For example, when taking a close-up of a person wearing a red sweater, even if the color distribution of the entire screen is averaged, the screen will not be white and the balance will be disrupted. If you adjust the mill balance like this,
This has the disadvantage that the gain changes in a direction that cancels out the biased color, and the white balance shifts to the complementary color side, making it impossible to reproduce colors appropriately.

(d) Means for Solving the Problems The present invention performs white balance adjustment based on the color information signal in the captured video signal, and detects the angle of view of the imaging lens and the distance to the subject, and adjusts these by detecting the angle of view of the imaging lens and the distance to the subject. The feature is that the effective area of the subject in the screen is calculated from the value, and based on the result, the adjustment speed of white balance adjustment is changed in multiple stages, or the white balance adjustment is canceled using the current color information signal. shall be.

(E) Function Since the present invention is configured as described above, the colors within the screen may be biased because the angle of view is narrow or the distance between the objects is short and the screen does not include a sufficient number of objects. , to reduce the shift of the white balance toward its complementary color.

(f) Examples 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 mill balance adjustment circuit according to this embodiment. Note that in the drawings, explanations of parts that are the same as those in the conventional example will be omitted.

(20) is a well-known zoom mechanism used in general video cameras, and by displacing the zoom lens that makes up this zoom mechanism, the focal length of the entire lens system of the camera is changed, and the range from wide-angle to telephoto is changed. It becomes possible to select a desired angle of view from the zoom area.

The view angle detection circuit (21) detects the position of the zoom lens, detects the position in the zoom area at that time, and detects the position of the zoom lens at that time.
The horizontal viewing angle (RW) (unit: radian) and vertical viewing angle (RL) of the screen are calculated from the relationship shown in the figure. by the way,
In FIG. 4, it goes without saying that the closer the zoom position is to the wide-angle side, the larger the angle of view (RW) (RL) becomes.

(22) is a well-known focusing mechanism that measures the distance to the subject using infrared rays or the like, and moves the lens (1) forward or backward in the optical axis direction according to this subject distance to bring it into focus.
Information on the object distance (L) obtained by this focus mechanism is input to the effective area calculation circuit (23) at the subsequent stage.

In the effective area calculation circuit (23), the angle of view detection circuit (21)
interior angle (RW) (RL) and focus mechanism (
22), the effective amount (area) of all objects included in the screen (everything displayed on the entire screen including the main object and the background) is calculated. Specifically, the effective area (S) is determined by the following formula.

S= (RwXL)

The effective area (S) obtained in this way is sent to the integration circuits (117) (118) that integrate each color difference signal, similar to the integration circuits (17) and (18) in FIG. Vary the constant. That is, the integration circuit (117)i
ls) is configured such that the time constant becomes longer as the effective area (S) becomes smaller, and the time constant becomes infinite when the effective area (S) is less than a predetermined threshold. still,
Since the effective area of the predetermined threshold value is extremely small, it is recognized that appropriate white balance adjustment is difficult in screen evaluation, and is set in advance based on experimental data.

As a result, if the effective area is small and the reliability of the integral value of the color difference signal is low, by increasing the integration time, it is possible to judge whether the white balance is appropriate based on more information. As a result, the response of gain adjustment based on screen evaluation can be slowed down. Also, the effective area (
If S) is below a predetermined threshold, the time constant becomes infinite and no change is obtained in the integration result, and the gain control circuit (13
) (14) is maintained in a state based on the result of the previous screen evaluation.

Moreover, as shown in FIG. 3, instead of inputting the output of the effective area calculation circuit (23) to the integrating circuits (17) (18) to control the time constant, the gain control circuit (13) shown in FIG.
Similarly to (14), the time constant is sent to the gain control circuits (113) (114) that control the gains of the R and B amplification circuits (4) and (5), and changes the amplification gain factor of each of R and B. It is also possible to regulate That is, as the effective area (S) becomes smaller, the change in gain is slowed down, and the change is stopped when the effective area (S) becomes smaller than a predetermined threshold. For example, by controlling the gain control circuits (113) and (114), the amount of change in gain per unit time in the standard effective area (So) is controlled by (
go), the amount of change in gain (g) per unit time in the effective area (S) calculated by the calculation circuit (23) is g
"go x (S/S.)". As a result, the time required to change the gain by the amount of correction to the current gain determined based on the integration result increases as the effective area becomes smaller. As a result, the response of gain adjustment can be slowed down.Also, the effective area (S)
When is less than a predetermined threshold, it is assumed that there is not enough area to perform mill balance adjustment based on screen evaluation, and the change in gain is stopped by setting g=Q.

In this way, it is possible to expect the same effects as in the above-described embodiments.

It goes without saying that the operations of each of the circuits described above can be processed by software using a microconvenience.

(G) Effects of the Invention According to the present invention, as described above, when it is determined that there are not enough objects in the screen because the angle of view is narrow and the distance between the objects is short, the color information signal is By spending more time on screen evaluation using color information signals, the screen will be evaluated more often using color information signals, which will reduce the risk that the colors on the screen will be biased and the mill balance will shift to the complementary color side. be done.

[Brief explanation of drawings]

Fig. 1 is a circuit block diagram of one embodiment of the present invention, Fig. 3 is a circuit block diagram of another embodiment, Fig. 4 is a diagram showing the relationship between the zoom position and the angle of view, and Fig. 2 is a diagram of the conventional example. FIG. (23)...Execution area calculation circuit.

Claims (3)

[Claims] (1) In a white balance adjustment device that performs control by varying the gain of each color signal based on the color information signal in the captured image signal, the angle of view of the lens and the distance to the subject are obtained, and the 1. A white balance circuit comprising: an effective area detecting section for determining an effective area; and a time constant for gain control being changed in accordance with the effective area. (2) The white balance adjustment device according to item 1, wherein the time constant is made longer as the effective area becomes smaller. (3) The white balance adjustment device according to item 1, wherein the control is stopped when the effective area falls below a predetermined value.