JPH0898200A - Video camera - Google Patents

Abstract

PURPOSE: To shift to a normal white balance state in a short time after the change of a light source by providing a white balance correcting device to increase the speed of changing the gain of a color signal faster than before the change of the light source when the change of the light source is detected. CONSTITUTION: An integrator 11 digital by integrates a color difference signal B-Y extending over one field period, and this integrated value is made a color evaluation value Vb. Similarly, the integrators 12, 13 input the integrated values of the color difference signal R-Y and a luminance signal Y to a microcomputer 14 as the color evaluation value Vr and a luminance evaluation value Vy. The microcomputer 14 monitors the variation of the luminance evaluation value Vy and he color evaluation values Vr, Vb, and when each variation exceeds each threshold, it judges that the light source was changed. Then, while the light source is not changed, and its color temperature is kept stable, the changing speed of the amplification factor of the color signal in white balance correction is made slow, and the moderate white balance correction is maintained, and when the light source is changed once, and the color temperature is changed, the changing speed is speeded up, and following this, the white balance correction to meet quicky the color temperature of the new light source is executed.

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 correction device for a color video camera which controls white balance based on an image pickup video signal obtained from an image pickup device.

[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 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) is 1: 1: 1. Be seen.
Generally, for example, JP-A-62-35792 (H04
N9 / 73), the screen color difference signal RY,
A method of adjusting the gain so that the integrated value of BY is zero is used.

FIG. 3 is a block diagram of a white balance correction circuit using this method. Light that has passed through a lens group 1 composed of a plurality of zoom and focus lenses is photoelectrically converted by a solid-state image sensor (CCD) 2, and then is separated by a color separation circuit 3 into three primary colors of R, G, and B. The G color signal is directly extracted, and the R and B color signals are input to the camera process and the matrix circuit 6 through the R amplification circuit 4 and the B amplification circuit 5, respectively, and the luminance signals Y, red and blue are respectively output. Color difference signals R-Y and B-Y are generated and sent to the video circuit 7.

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

[0006]

In the ordinary white balance correction such as the above-mentioned conventional example, the control speed of the white balance correction,
That is, the change speed of the amplification gain of the P and B amplifier circuits based on the screen evaluation is performed at a relatively slow speed so that the color of the image pickup screen does not feel uncomfortable.

If the control speed of white balance correction is suppressed to a low speed in this way, the following problems occur. For example, if you were shooting indoors with a fluorescent light source,
Due to the color temperature, a white subject looks blue under a fluorescent light, so white balance correction is applied to suppress this and control is performed to suppress the gain of the B signal. When the light source is switched to an incandescent lamp, the white color of the object appears red due to the difference in color temperature, and it is necessary to suppress this. However, if the control speed of the white balance control is set to a low speed as described above, it is not possible to quickly respond to the switching of the light source, and the image pickup screen becomes reddish for a while and becomes very unsightly.

[0008]

According to the present invention, there is provided a color signal amplifying means for changing an amplification gain of a color signal based on a color information signal in a picked-up image signal, and a variation of a color information signal level to monitor a light source. A light source change detecting means for detecting a change is provided, and when the change of the light source is detected, the speed of changing the gain of the color signal is made faster than before the change of the light source. An evaluation value detection unit that outputs the entire brightness signal level and color information signal level as a brightness evaluation value and a color evaluation value, respectively, and monitors the fluctuations in the brightness evaluation value and the color evaluation value, and the respective fluctuation amounts set the respective threshold values. It is characterized in that it comprises a light source change detecting means for judging that the light source has changed when the light source is exceeded, and when the change of the light source is detected, the speed of changing the gain of the color signal is made faster than before the change of the light source.

[0009]

Since the present invention is configured as described above, while the color temperature is stable without changing the light source, the changing speed of the amplification gain of the color signal in the white balance correction is set to a low speed to display on the screen. Maintains a gentle white balance correction that does not cause discomfort.
Once the light source is changed and the color temperature is changed, the speed of change is increased, and following this, the white balance correction that matches the color temperature of the new light source is promptly executed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an automatic white balance correction circuit of a color video camera according to this embodiment. The incident light that has passed through the lens group 1 is imaged on the solid-state image sensor (CCD) 2 and photoelectrically converted, and thereafter, R,
It is taken out as three primary color signals of G and B. The R and B signals in these three primary color signals are respectively the R and B amplifier circuits 4,
5, the signal G is input to the camera process and the matrix circuit 6 together with the G signal, and the luminance signal Y and the color difference signals R-Y and B-Y of red and blue are generated based on these signals and supplied to the video circuit 7. Well-known processing is performed. Also, Y, R-
The Y and BY signals are A / D converters 8, 9, 10 respectively.
Entered in.

The A / D converter 8 samples the color difference signal BY at a predetermined sampling frequency to convert the color difference signal BY into a digital value, and then inputs the digital value to the integrator 11 in the subsequent stage, and similarly, A
The / D converter 9 converts the color difference signal RY and the A / D converter 10 converts the luminance signal Y into a digital value, and the integrator 1 respectively.
Supply to 2 and 13.

The integrator 11 obtains the sum of the color difference signals B-Y converted into digital values in one field period, that is, digitally integrates over one field period, and the integrated value is used as a color evaluation value Vb in a microcomputer (microcomputer). ) 14 is input. Similarly, the integrators 12 and 13 digitally integrate the color difference signal RY and the luminance signal Y, which are converted into digital values, over one field period,
The integrated value is input to the microcomputer 14 as the color difference signal Vr and the brightness evaluation value Vy.

The reference level of the color difference signals input to the A / D converters 8 and 9, that is, the zero level, is set to a level obtained when a perfect achromatic surface is photographed, and accordingly, the digital level is set. The converted color difference signals are not only positive values but also negative values, and the digital integration operation specifically adds their absolute values for positive values, and conversely for negative values. The absolute value will be subtracted.

The microcomputer 14 uses the latest brightness evaluation value Vy,
After obtaining the color evaluation values Vr and Vb, the white balance correction operation is executed for each field based on the color evaluation values Vr and Vb, and the R and B gain control signals are supplied to the R and B amplification circuits 4 and 5. It emits and adjusts each amplification gain. Below, FIG.
The flow chart will be described.

In step 50, integrators 11, 12, 1
Each evaluation value from 3 is taken in.

In step 51, it is judged whether or not the high speed flag, which is a flag for increasing the control speed of the white balance control, is in the set state. If it is in the set state, the process jumps to step 56 and the reset state is set. If step 52
The series of steps from 55 to 55 are executed.

In step 52, whether or not the absolute value of the change amount with respect to the old luminance evaluation value Vy0 obtained one field before the latest luminance evaluation value Vy obtained by the screen evaluation of the latest field is not less than the threshold value a, That is, it is determined whether or not the expression 1 is established, and in step 53, the old color evaluation values Vr0, Vb0 obtained one field before the latest both-color evaluation values Vr, Vb obtained by the screen evaluation of the latest field are determined. Whether or not the absolute value of the sum of the respective variation amounts with respect to
It is determined whether or not holds.

[0018]

[Equation 1]

│Vy-Vyo│ ≧ a

[0020]

[Equation 2]

| (Vr−Vro) + (Vb−Vbo) | ≧ c When both equations 1 and 2 are satisfied in these steps 52 and 53, that is, the average brightness of the entire screen of the latest field. The signal level greatly changes as compared with that in the previous field, the absolute value of the change amount becomes the threshold value a or more, and the average color difference signal RY of the entire screen of the latest field,
If the level of BY changes greatly compared to the value one field before and the absolute value of the sum of the respective changes is equal to or greater than the threshold value c, it is determined that the light source at the time of shooting has changed, and the high-speed flag is determined in step 55. Is set.

The thresholds a and c are values that can be taken as the absolute value of the change amount of the brightness evaluation value and the absolute value of the sum of the change amounts of the two color evaluation values when it is considered that the change of the light source has surely occurred. , Is set in advance by an experiment.

If neither of the above two equations holds, or if at least one of the two equations does not hold, it is determined that the light source does not change during photographing, and the high speed flag is cleared in step 54.

In step 56, the control speed is changed during white balance correction according to the state of the high speed flag. If the high speed flag is in the reset state, step 5 is executed.
As a result of the determination of 2, 53, it is determined that the light source has not changed from the previous field to the current field, and the process proceeds to step 57.

In step 57, the white balance correction is executed while keeping the control speed low. Here, the white balance correction operation is performed in the direction of R, in the direction in which both the color evaluation values Vr and Vb become zero.
By changing the level of the B gain control signal, the R and B amplifier circuits 4,
5 is output. At this time, when it is necessary to raise the level of the R signal, the level of the R gain control signal is set to a predetermined value m.
And the amplification gain of the R signal in the R amplifier circuit 4 increases by a predetermined amount M. On the contrary, when it is necessary to decrease the level of the R signal, the level of the R gain control signal is decreased by a predetermined value m, and the amplification gain of the R signal in the R amplification circuit 4 is decreased by a predetermined amount M accordingly. To do. Similarly,
When the level of the B signal needs to be increased, the level of the B gain control signal is increased by a predetermined value m, and the amplification gain of the B signal in the B amplification circuit 5 is increased by a predetermined amount M accordingly. On the contrary, when it is necessary to decrease the level of the B signal, the level of the B gain control signal is decreased by a predetermined value m, and the amplification gain of the B signal in the B amplification circuit 5 is increased by a predetermined amount M accordingly. To do. If there is no change in the shooting environment such as the light source due to the white balance correction and there is no change in the subject, the gains of the B amplifier circuits 4 and 5 are adjusted from the start of correction to the optimum state for each field as needed. It gradually changes by a predetermined value m.

If the high speed flag is set,
The process moves from step 56 to step 58. In step 58, it is determined whether both absolute values of both color evaluation values are below the threshold value K. Here, the threshold value K is a color evaluation value obtained when the white balance correction operation that has been executed so far is sufficiently effective and is considered to have come close to the optimum white balance state, based on experiments in advance. It is set. If it is determined in step 58 that the absolute value of both color evaluation values is less than the threshold value K, the correction has been made considerably, and if the subsequent correction is performed at high speed, the optimum value may be exceeded. As a result, the high speed flag is cleared in step 59, and then the white balance correction is executed in step 60 with the control speed reduced to the same as in step 57.

When the absolute values of both color evaluation values both exceed the threshold value K or one of them exceeds the threshold value K in step 58, it is judged that the white balance correction is far from the optimum state.
In step 61, the control speed is increased and white balance correction is executed.

This high-speed white balance correction is different from the low-speed correction in that the R and B gain control signals are output to the R and B amplifier circuits 4 and 5 in the directions in which both the color evaluation values Vr and Vb become zero. However, at this time, if it is necessary to raise the level of the R signal, the level of the R gain control signal is changed to raise it by a predetermined value n larger than the predetermined value m. The amplification gain of the R signal is increased by a predetermined amount N larger than the predetermined amount M. On the contrary, when it is necessary to lower the level of the R signal, the level of the R gain control signal is lowered by a predetermined value n, and the R in the R amplifier circuit 4 is accordingly reduced.
The amplification gain of the signal drops by a predetermined amount N. Similarly, when it is necessary to raise the level of the B signal, the level of the B gain control signal is raised by a predetermined value n, and along with this, B
The amplification gain of the B signal in the amplifier circuit 5 increases by a predetermined amount N. On the contrary, when it is necessary to decrease the level of the B signal, the level of the B gain control signal is decreased by a predetermined value n,
Along with this, the amplification gain of the B signal in the B amplification circuit 5 drops by a predetermined amount N. It should be noted that if the predetermined amount N is twice the predetermined amount M, it means that the control speed at high speed becomes twice as high as at low speed.

When the white balance correction at high speed or low speed is completed in this way, in step 62, the old color evaluation values Vr0, Vb0 are changed by the color evaluation values Vr, Vb for the white balance correction in the next field. , The old brightness evaluation value Vy0 is changed by the brightness evaluation value Vy.

Next, the operation of the microcomputer 14 will be described with reference to a specific example along the flow chart of FIG.

First, when the video camera enters a shooting state indoors under a fluorescent light source and white balance correction is started, the brightness and color evaluation values in the first field are taken into the microcomputer 14. In this initial state, the high speed flag is configured to start from the set state, and the process proceeds from step 51 to step 56 and then to step 58. Immediately after the start of the white balance correction, the white balance correction state is still far from the optimum state, and therefore the white balance correction is executed at high speed in step 61. Thereafter, the white balance correction is executed at high speed through the same steps, and the amplification gain of the R or B amplification circuits 4 and 5 gradually changes by a predetermined amount n for each field. In particular, since the light source is a fluorescent lamp, the gain of the B amplifier circuit 5 is controlled to be suppressed.

After a few fields have passed in this way, the effect of high-speed white balance correction up to this point will bring it to an optimum state to some extent, and the absolute value of both color evaluation values will fall below the threshold value K, and a step 58 will be executed in a certain field. Then, the process proceeds from step 59 to step 59, the high speed flag is cleared, the white balance correction is executed at low speed in step 60, and the amplification gains of the R and B signals are changed by a predetermined amount M as needed. Actually, the white balance correction is finely adjusted.

Then, after the next field, step 5
The process proceeds from step 1 to step 52. These steps 52 and 53 detect that the light source has changed. If the light source is still a fluorescent lamp, no brightness change is confirmed in step 52 and the process moves to step 54 to clear the high speed flag. Then, after step 56, the process proceeds to step 57, and low-speed white balance correction is continued.

Further, if the brightness of the fluorescent lamp, which is the light source, simply rises during this low-speed white balance correction, the luminance change of | Vy-Vy0 | becomes the threshold value a or more in the judgment of step 52. However, since no color change can be confirmed in step 53, the process also proceeds to step 54, and the low-speed white balance correction is continued as in the case described above.

Further, when the indoor photography is switched to the outdoor photography during the low speed white balance correction and the light source is changed from the fluorescent lamp to the sunlight, the luminance change is confirmed in step 52 in the field immediately after this change. And step 53
Then, the change in color is confirmed, and the process moves to step 55 to set the high speed flag. Therefore, the process proceeds to step 58 through step 56.

Immediately after the light source changes from fluorescent light to sunlight, the blue color is suppressed by the correction so far, and conversely, the screen becomes reddish due to the color temperature of the sunlight. Immediately after that, the white balance state is far from the optimum state, so that both color evaluation values do not fall below the threshold value K.

Therefore, the process proceeds to step 61 to restart the high-speed white balance correction, and in the subsequent fields, jumps from step 51 to step 56, and after step 58, the high-speed correction is continued at step 61. , White balance correction is quickly performed until it is optimal for shooting under sunlight, and when it approaches a fairly optimal state, the process moves from step 58 to step 59, the high speed flag is cleared, and low speed correction is performed again. It

As described above, even if the light source is suddenly switched to sunlight under the condition that the white balance state is sufficiently stabilized by coping with the color temperature of the fluorescent lamp and the gradual white balance correction is performed. Since the correction is switched to the high speed immediately, the time when the screen becomes reddish and unsightly due to the change of the light source can be minimized. Further, when the light source changes from the sunlight to the fluorescent lamp, the same can be dealt with, and in this case, the generation time of the bluish and unsightly screen immediately after the switching of the light source can be minimized. Further, it is possible to similarly deal with the switching of the light sources having different color temperatures such as switching from the fluorescent lamp to the incandescent lamp.

In the above embodiment, the A / D converter and the integrator are provided for each of the luminance signal Y and the color difference signals RY and BY, so that both the luminance evaluation value and both color evaluation values are 1.
Although it was updated for each field, the A / D converter and the integrator are shared as a single unit, and the luminance and the color difference signals are selectively sequentially input to the A / D converter and the integrator for each field. It is also possible to do so. In this case, the brightness evaluation value and the two-color evaluation value are updated every three fields,
It is necessary to arrange a memory in the subsequent stage of the integrator to hold each evaluation value until it is updated.

Further, the judgment in step 53 for confirming the color change is not necessarily limited to the method for judging whether or not the expression 2 is established, but the judgment is made for each color evaluation value, that is, the number. It may be possible to determine whether or not the two expressions shown in FIG. The threshold value d is the absolute value of the change amount of each color evaluation value when the change of the light source can be considered to be certain, and is set in advance by an experiment like the threshold value c.

[0041]

[Equation 3]

| Vr-Vro | ≧ d | Vb-Vbo | ≧ d

[0043]

As described above, according to the present invention, while the light source is stable without change, the changing speed of the amplification gain of the color signal in the white balance correction is set to a low speed so that the screen does not feel uncomfortable. The gentle white balance correction is maintained, the change speed is accelerated once the light source changes and the color temperature changes, and the white balance correction that matches the color temperature of the new light source is quickly executed following this. It is possible to shift to the normal white balance state in a short time after the change of the light source.

[Brief description of drawings]

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

FIG. 2 is an overall flowchart of one embodiment of the present invention.

FIG. 3 is a block diagram of a conventional example of the present invention.

[Explanation of symbols]

 4 R amplifier 5 B amplifier 11 integrator 12 integrator 13 integrator 14 microcomputer

Claims (2)

[Claims] 1. A color signal amplifying means for changing an amplification gain of a color signal based on a color information signal in a picked-up image signal, and a light source change detecting means for monitoring a change of a color information signal level to detect a change of a light source. The output of the light source change detection means is supplied to the color signal amplification means, and when a change of the light source is detected, the speed of changing the gain of the color signal is made faster than before the change of the light source. A video camera equipped with a white balance correction device. 2. A video camera equipped with a white balance correction device for controlling the amplification gain of a color signal based on a color information signal in a picked-up video signal, and a brightness evaluation value for outputting a brightness signal level of the entire screen as a brightness evaluation value. A detection unit, a color evaluation value detection unit that outputs the color information signal level of the entire screen as a color evaluation value, and a change amount of each of the brightness evaluation value and the color evaluation value is monitored by monitoring the change of the brightness evaluation value and the color evaluation value. Light source change detection means that determines that the light source has changed when the respective thresholds have been exceeded, and that when the change in the light source is detected, the speed at which the gain of the color signal is changed is made faster than before the change of the light source. Characteristic video camera.