JP2561239B2 - Automatic focus adjustment device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus adjusting device used for a video camera or the like, and particularly to an automatic focus adjusting device which does not cause unnaturalness on a screen at a sudden scene change. Regarding

(Prior Art) Various systems have been proposed as an automatic focusing device suitable for a video camera. Among them, an active and differential automatic focusing device based on the principle of the triangulation method will be described. A light projecting element for projecting external light and two sets of light receiving sensors are arranged at a distance of a baseline length, and a light beam projected from the light projecting element receives reflected light reflected by a subject by two sets of light receiving sensors, The focus adjustment is performed by driving and controlling the lens group that performs the focusing operation in the photographing optical system according to the relative comparison output of the signals obtained by detecting the photoelectric conversion outputs.

As an example of the relative comparison means of the photoelectric conversion outputs, the outputs of the two sets of light receiving sensors are synchronously detected in synchronization with the output of the pulse oscillator for driving the light projecting element, and the detected outputs are detected over a predetermined period. Periodically integrating, and comparing the time when these integrated waveforms exceed a predetermined level set in advance. In other words, if the time difference between the two sets of integrated waveforms exceeding a predetermined level is within a predetermined time length, it is considered to be in focus, and the time difference exceeds the predetermined time length. In this case, it is regarded that the lens is out of focus, and the motors for driving the lens groups are respectively moved in the forward direction or the reverse direction depending on which one of the above-mentioned two integrated waveforms exceeds the predetermined level first. The focus is adjusted by rotating it.

As described above, a method has been proposed in which the output signal itself of the image pickup means is used without using the external distance measurement system. In this method, the image pickup signal obtained from the image pickup element of the video camera is used as the luminance signal in the process circuit. To a color signal, and the luminance signal is filtered through a high-pass filter to extract high-frequency components such as contour signals, the level of this extracted component is detected, and the hill-climbing control circuit increases this detection level as much as possible. The lens drive circuit is controlled so as to drive the lens group.

(Problems to be Solved by the Invention) In the conventional automatic focus adjusting device for a video camera as described above, for example, when a scene on the screen is largely changed due to panning of the camera, a so-called picking phenomenon of the automatic focus adjusting device occurs. It occurs and causes unnaturalness on the screen.

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic focus adjusting device that prohibits the focus adjusting operation when the scene on the screen changes greatly so that the unnaturalness on the screen does not occur. .

(Means for Solving the Problems) In order to achieve the above object, according to the first invention of the present application, a focus adjusting means for adjusting a focus state and a color signal component in an image signal are compared between fields. Correlation detection means for detecting the presence or absence of substantial correlation between screens by doing,
Controlling the focus adjusting means based on the output of the correlation detecting means, when a signal indicating that there is no substantial correlation between fields is detected from the correlation detecting means,
And a control means for prohibiting the focus adjusting operation of the focus adjusting means.

According to the second invention of the present application, the focus adjusting means for adjusting the focus state and the color signal components in the image signal obtained by sampling the image signal at a plurality of positions in the screen are compared between fields, Correlation detection means for detecting the presence or absence of correlation of color signal components at a plurality of positions, and a signal indicating the presence or absence of a signal output by the correlation detection means indicating the presence or absence of correlation of color signal components at each of the plurality of positions If it is determined by the relative evaluation whether there is a substantial inter-screen correlation between fields, and if it is determined that there is no substantial inter-screen correlation between fields, the focus adjustment is performed. And a control means for prohibiting the focus adjustment operation of the means.

(Operation) Based on the above configuration, the automatic focus adjustment device of the present invention has a perfect correlation between the previous field and the next field in the color signal component in the image signal output from the imaging means. The focus adjustment operation is continued when a signal indicating that there is a substantial correlation between the two is detected, for example, whether it is maintained or the difference between the two does not exceed a predetermined limit, but On the other hand, there is no correlation between the two, or even if there is a certain degree of correlation, the difference between the two is more than a predetermined limit, and a signal indicating that there is no substantial correlation is detected. If this happens, the focus adjustment operation is prohibited.

(Example) With reference to drawings, the example of the automatic focusing device of this invention is described in detail below. The following explanation is about the embodiment to which the present invention is applied to an active and differential type automatic focus adjusting device, the overall configuration, a concrete example of the means for detecting the presence or absence of correlation in the embodiment, and the order of the operation of the embodiment. Done in.
The present invention can also be applied to focus adjusting devices other than the active and differential type.

(Overall Configuration of Embodiment of Automatic Focus Adjusting Device of the Present Invention)
(FIG. 1) FIG. 1 shows the overall configuration of an embodiment of an automatic focus adjustment device of the present invention, in which 1 is a light projecting element, 2A and 2B are light receiving sensors, 3 is a pulse oscillator, and a pulse oscillator. The light projecting element 1 emits light in a pulsed manner by the oscillation pulse of 3, and the light flux reflected by the subject is received by the two light receiving sensors 2A, 2B.

The processing circuit for the received light output photoelectrically converted by the light receiving sensors 2A and 2B is composed of A and B series. First, 4A and 4B are process circuits, which include amplifiers 5A and 5B and synchronous detectors 6A and 6B, respectively, and amplifiers 5A and 5B amplify the outputs of the light receiving sensors 4A and 4B, respectively, and the amplified output is a pulse. Synchronous detection is performed by the synchronous detectors 6A and 6B synchronized with the oscillator 3, and the detection outputs are input to the integrating circuits 7A and 7B, respectively. Reference numerals 8A and 8B are switches that reset the integrations of the integration circuits 7A and 7B, respectively, and are controlled by the cycle end signal. The cycle end signal is a signal obtained by dividing the output of the pulse oscillator 3 (FIG. 2A) by the frequency divider 10 (FIG. 2B) and delaying it by Δt by the delay circuit 11 (FIG. 2C). ) Is given via the OR gate 12.

9A and 9B are differential amplifiers, the (+) inputs of which are connected to the outputs of the integrating circuits 7A and 7B, and the (−) inputs of which are connected to the threshold potential source Vref. Therefore, the outputs of the integrator circuits 7A and 7B respectively increase with the passage of time, but when these outputs exceed the threshold value Vref, the outputs of the differential amplifiers 9A and 9B respectively become high. 13
A and 13B are AND gates, each of which is a differential amplifier 9A
And the output of 9B are input, and a fixed quantity counter 18 described later
Are commonly input via the inverter 19.

The outputs of the AND gates 13A and 13B are input to the clock terminals of the D flip-flops 14A and 14B, respectively, and the outputs of the OR gate 12 are supplied to their reset input terminals. The D flip-flops 15A and 15B have their D input terminals connected to the preceding D flip-flops 14A and 1B, respectively.
The Q outputs of 4B are respectively supplied, and their clock terminals are also supplied with the output of the frequency divider 10. Reference numeral 16 is an AF arithmetic circuit to which the Q outputs of the D flip-flops 15A and 15B are input, and the AF motor M is controlled by the output thereof. That is, if both of the two inputs are high, the AF calculation circuit 16 determines that the focus is in focus and does not send a control signal to the AF motor M.
If one of the two inputs is high and the other one is low, it is determined to be out of focus and the AF motor M is rotated in either forward or reverse direction. If it is impossible to determine the out-of-focus state, the focus adjustment operation such as stopping the AF motor M is prohibited.

Reference numeral 17 is an OR gate to which the outputs of the D flip-flops 14A and 14B are input, and 18 is a fixed amount counter to which the output of the OR gate 17 is supplied as a clock input.
The output of the frequency divider 10 is input to the reset input terminal of, and the output Qn thereof is supplied to one input terminal of the AND gates 13A and 13B via the inverter 19.

Reference numeral 20 denotes a scene change detection circuit which is an example of a means for detecting the presence or absence of correlation of image information, which is a main feature of the present invention, and its internal configuration will be described later with reference to FIGS. 2 to 4. However, the output control signal is input to the OR gate 12 together with the reset signal output from the delay circuit 11,
The output of the OR gate 12 is supplied to the reset switches 8A and 8B and the D flip-flops 14a and 14B to control the operation of the focus adjustment system shown in FIG. 1 as described later. That is, the above control signal is supplied to the reset switches 8A and 8B to reset the integrator circuits 7A and 7B when a scene change occurs, and finally reset the D flip-flops 14A and 14B to finally flip-flop 15A. , 15B Forced low output to disable AF detection operation, AF motor M
To stop.

(Specific Example of Correlation Presence / Absence Detecting Means in the Embodiment of the Present Invention) (FIGS. 3 to 5) FIGS. 3 to 5 show the scene of FIG. 1 as a correlation presence / absence detecting means. Specific examples of the transition detecting circuit 20 are shown. These examples detect the presence or absence of the correlation between one field before and one field after the image signal output from the image pickup means of the video camera.

Of these circuits, FIG. 3 is a circuit for detecting a scene transition by utilizing a luminance signal in the output signal of the image pickup means, and 31 is a process circuit, which is a color signal output from the image pickup means. (R, G, B) is a luminance signal Y by known means
And color difference signals (RY) and (BY). The output luminance signal (hereinafter referred to as Y signal) of the process circuit 31 is
Via the delay circuit 32 on the one hand and directly on the other hand,
The difference between the two signals is detected by being input to the difference circuit 33, the difference signal is integrated (added) by the integrator circuit 34 at an appropriate timing, for example, the timing of the vertical synchronization signal, and the integrated output is output by the comparator 35 at a predetermined level. Compared to. That is, the difference between the Y signal of the current field and the Y signal of the previous field is detected and compared with a predetermined level.

Here, if the correlation with one field before is completely taken, the output is zero even if the difference signal is integrated, or if the above correlation is taken to some extent, the integrated output is at a predetermined level. However, if this integrated output is above a predetermined level, it is determined that the correlation has broken down, and a control signal indicating a scene change in the next field is output to the OR gate 12 in FIG. Is used as a reset signal.

The circuit shown in FIG. 4 detects a scene change signal by detecting a ratio of a specific color signal in the output of the image pickup means. In the figure, reference numerals 41 and 42 denote integrating circuits for integrating the G signal component and the B signal component in the output of the image pickup means for one field period under the control of the vertical synchronizing signal, respectively, and the ratio of the integrated outputs is divided. Required by circuit 43. The difference between the value of the ratio of the integrated output and the value of the ratio of the integrated output one field before is detected by means such as the delay circuit 44 and the difference circuit 45,
The detected output is compared with a predetermined level by the comparator 46, and if it is higher than the predetermined level, the scene change signal is output to the OR gate 12 in FIG.

The circuit shown in FIG. 5 is a further development of the circuit shown in FIG. 3, in which only image information at several points on the screen is taken out as a sample, and whether or not there is correlation with the previous field for each sample is determined. The detection is performed and the relative evaluation of the correlation in these samples is used to determine whether to continue the focusing operation or to prohibit the focusing operation. For example, as shown in FIG. 6, the upper n ₁ line, the central n ₂ line, and the lower n ₃ line in the screen are used as samples, and the presence or absence of correlation of the Y signal in each of these sample lines is detected.
If no correlation is obtained for all n _{1 to} n ₃ lines, it is determined that there is no correlation for the entire screen.In this case, the scene has changed significantly due to camera shake, etc. Prohibit On the contrary, if the correlation is broken only in the n ₂ line, but there is a correlation in the n ₁ and n ₃ lines, it is determined that only the image signal on the n ₂ line is changed due to, for example, the movement of the copy. Then, the focus adjustment operation is continued.

In FIG. 5, reference numerals 51a to 51c are mono-multivibrators (MM), each of which delays a vertical synchronizing signal corresponding to the lines n ₁ , n ₂ and n ₃ to create a gate pulse. Reference numerals 52a to 52c are gate circuits which extract the Y signal in the output of the process circuit 31 by the above gate pulse. The extracted Y signal is delayed by the delay circuit 53 as in the circuit of FIG.
The means such as a to 53c and the difference circuits 54a to 54c detect the difference from the Y signal of the line one field before for each line. These difference signals are integrated by integrating circuits 55a to 55c, and compared with a predetermined level by comparators 56a to 56c, respectively. Based on the relative evaluation of the outputs of the comparators 56a to 56c, it is determined whether to continue the focus adjustment operation or prohibit the focus adjustment operation.
The output of ~ 56c is input to the AND gate 57, and the scene change signal is output to the OR gate 12 in FIG. 1 only when the output is high. In this example, the scene change signal is output only when the outputs of the integrating circuits 55a to 55c are all above a predetermined level, and the focus adjustment operation is prohibited, but the output of the integrating circuit does not exceed the predetermined level. If there is even one thing, the focus adjustment operation is continued. The above method of creating the transition signal from the number of sample lines and the output signal of the comparator is merely an example, and many other modifications are possible.

(Operation of the embodiment of the automatic focus adjusting device of the present invention) (Figs. 1 and 2) Next, the operation of the device of Fig. 1 will be described with reference to Fig. 2 as well.

FIG. 2a shows the output pulse of the pulse oscillator 3 of FIG. 1, which is divided by the frequency divider 10 (FIG. 2b) and delayed by the delay circuit 11 by the minute time Δt (FIG. 2c). ). This delay signal is applied to the reset switches 8A and 8B to reset the corresponding integrating circuits 7A and 7B. After resetting, the integrating circuits 7A and 7B start the integrating operation again, and the output thereof increases with time (d in the figure), but in the first control cycle, as shown in the figure, first, one of the series (here, A the integral output time t _A1 of the a series) and then with the other sequence (here at the integration output is assumed to be B-series) t _B1,
Each exceeds the threshold voltage Vref, and time t _A1 and time t
_{It is} assumed that the time difference from _B1 is longer than a predetermined time length (for example, T ₀ described later).

Although the output of the differential amplifier 9A becomes high at time t _A1 , the output Qn of the counter 18 is not yet high at this time, so that the output of the AND gate 13A input through the inverter 19 is t _A1. After that, it goes high. As a result, the output Q of the D flip-flop 14A at the next stage becomes high until the next reset pulse (c in the same figure) is input as shown in FIG. This high output is input to the clock terminal of the fixed amount counter 18 via the D terminal of the next-stage flip-flop 15A and the OR gate 17, and the Qn output of the counter 18 becomes high after a fixed time T ₀ (see FIG. ), And reset by the output of the frequency divider 10 (b in the same figure).

Here, in the first control cycle, the time point t _B1 at which the integrated output of the B series exceeds the threshold value Vref is the time point t _B1 as described above.
After the lapse of the above-mentioned fixed time length T ₀ from _A1 , but at the time point
Since the Qn output of the counter 18 at t _B1 is high, it is input via the inverter 19 to the AND gate 13B.
Will go low even if the output of the differential amplifier 9B is high. Therefore, the output of the B series D flip-flop 14B is also low.

As described above, in the first control cycle, the output of the A-series flip-flop 14A is high, while the output of the B-series D flip-flop 14B is low, and these output signals are the flip-flops of the next stage. Since they are input to the D terminals of the amplifiers 15A and 15B, their outputs become high and low respectively (h and i in the same figure), and these signals are detected by the AF operation circuit 1
Entered in 6. Here, the AF calculation circuit 16 determines whether the two inputs are high, one is high and the other is low, or both are low, as described above. Since it is configured to perform in-focus or in-focus / out-of-focus determinations and perform predetermined operations respectively, in the above case, it is determined to be out-of-focus and time t _A1 The AF motor M is rotated in either the forward or reverse direction to move the lens group that performs the focusing operation on the optical axis in the focusing direction, depending on which of the above and the time t _B1 comes first.

Next, in the second control cycle in the in-focus state, as shown in FIG. 2d, the time points t _A2 and t _{B2 at} which the outputs of the two integrating circuits 7A and 7B exceed the threshold voltage Vref, respectively. The time difference of is different from the first control cycle and is shorter than the constant time length T ₀ . Therefore, the output of the A-series flip-flop 14A becomes high at the time point t _A2 as in the first control cycle, but the B-series flip-flop 14B is
Is different from that of the first control cycle,
It goes high at time t _B2 before the time T ₀ has elapsed from time t _A2 . Since the output of the flip-flop 14A (e in the figure) and the output of the flip-flop 14B (g in the figure) are input to the D terminals of the flip-flops 15A and 15B, respectively, the outputs of these flip-flops become high. As described above, the AF calculation circuit 16 does not send a control signal to the AF motor M when it judges that the lens is in focus, and the lens group that performs the focus operation stops at the position at that time, and the automatic focus adjustment is performed. The device is maintained in the focusing state (focusing state) corresponding to its position.

Here, when the control signal is output from the scene change detection circuit 20 of FIG. 1 as described above, this control signal indicates the reset operation by the reset signal from the frequency divider 10 and the delay circuit 11. Irrespectively resets both the integration circuits 7A and 7B and resets both the flip-flops 14A and 14B, so that both the flip-flops 15A and 15B finally output low. As a result, the AF calculation circuit 16 determines that focusing / non-focusing cannot be detected, and the AF motor M
The stop signal is transmitted to and the focus adjustment operation is prohibited. Then, if the control signal from the scene change detection circuit 20 is turned off, the focus adjustment operation is reunited, but as an alternative, the stop signal to the AF motor is continued for a certain time even if the control signal is turned off. The focus adjusting operation may be restarted after the stop signal is turned off.

(Effects of the Invention) As described above, according to the present application, based on the color signal component in the image signal output from the image pickup unit, or at a plurality of positions on the screen, between the previous field and the next field. When a signal indicating that there is no substantial correlation is detected, the focus adjustment operation is prohibited.Therefore, the so-called picking phenomenon of the automatic focus adjustment device that occurs at a sudden scene transition is prevented, and Focus adjustment that does not cause unnaturalness can be performed.

Also, since the color signal component in the image signal is used to detect the correlation of the image signal, it is not erroneously detected that the correlation has changed due to the change in brightness, and the low brightness state and high brightness state Therefore, even if the detection by the brightness is not reliable, the correlation can be detected by using the color signal component.

Further, by using the color signal component, the characteristics of the subject can be detected from the pattern and hue unique to the subject, and the correlation detection accuracy can be further improved as compared with the correlation detection based on the luminance alone.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall construction of an embodiment of the automatic focus adjusting device of the present invention, and FIGS. 2a to 2i are operation timing charts for explaining the operation of the device of FIG. 1, FIG. 3, and FIG. 5 and 5 are block diagrams showing details of the scene change detection circuit in the apparatus of FIG. 1, and FIG. 6 is a diagram showing sample lines for explaining the operation of the circuit of FIG. Description of code 3: pulse oscillator, 7A, 7B: integrating circuit, 8A, 8B: reset switch, 9A, 9B: differential amplifier, 10: frequency divider, 11: delay circuit, 1
2: OR gate, 13A, 13B: AND gate, 14A, 14B, 15A, 15
B: D flip-flop, 16: AF operation circuit, 17: OR gate, 18: Constant amount counter, 19: Inverter, 20: Scene change detection circuit, 31: Process circuit, 32,44,53a, 53b, 53c:
Delay circuit, 33,45,54a, 54b, 54c: Difference circuit, 34,55a, 55b, 5
5c: integrating circuit, 35, 46, 56a, 56b, 56c: comparator, 41: B signal component integrating circuit, 42: G signal component integrating circuit, 43: division circuit, 51
a, 51b, 51c: Mono multivibrator, 52a, 52b, 52c: Gate circuit, 57: AND gate, M: AF motor.

 ─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-58-129878 (JP, A) JP-A-60-132473 (JP, A) JP-A-54-161825 (JP, A) JP-A-59- 66271 (JP, A)

Claims (2)

(57) [Claims] 1. A focus adjusting means for adjusting a focus state, a correlation detecting means for detecting the presence or absence of substantial inter-screen correlation by comparing color signal components in an image signal between fields, and the correlation. Controlling the focus adjusting means based on the output of the detecting means, when a signal indicating that there is no substantial correlation between the fields is detected from the correlation detecting means,
An automatic focus adjusting device comprising: a control unit that prohibits a focus adjusting operation of the focus adjusting unit. 2. A focus adjustment means for adjusting a focus state, and a color signal component at a plurality of positions by comparing color signal components in an image signal and a sampled image signal at a plurality of positions in the screen between fields. Correlation detection means for detecting the presence or absence of the correlation, and between the fields by the relative evaluation of the signal indicating the presence or absence of the signal indicating the correlation of the color signal components at each of the plurality of positions output by the correlation detection means It is determined whether there is substantial inter-screen correlation, and if it is determined that there is no substantial inter-screen correlation between fields, the focus adjustment operation of the focus adjustment means is performed. An automatic focus adjusting device comprising: a prohibiting control means.