JPS6267973A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To prevent an unnaturalness on a screen from being produced by providing a means for detecting a large change of a scene on the screen and prohibiting a focusing operation. CONSTITUTION:A scene change detecting circuit 20 detects the existence of a substantial correlation before and after one field of a video signal from an image pickup means by using, for instance, a luminance signal and outputs a control signal indicating the change of a scene. This control signal resets integration circuits 7A, 7B and flip-flops 14A, 14B without relating to a reset operation by a reset signal from a frequency divider 10 and a delay circuit 11, so that finally it makes flip-flops 15A, 15B low outputs. Thereby, an AF arithmetic circuit 16 decides that a focusing and non-focusing can not be detected and prohibits a focusing operation.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an automatic focus adjustment device used in a video camera, etc., and in particular to an automatic focus adjustment device that does not cause unnaturalness on the screen at sudden scene changes. Regarding.

(Prior Art) Various methods have been proposed as automatic focusing devices suitable for video cameras. Among them, active and differential automatic focusing devices based on the principle of triangulation are explained, for example. A light projecting element that projects external light and two sets of light receiving sensors are arranged to be separated by a baseline length, and reflected light from a luminous flux projected from the light projecting element reflected by a subject is received by the two sets of light receiving sensors, Focus adjustment is performed by driving and controlling a lens group that performs a focusing operation in a photographing optical system in accordance with a relative comparison output of signals obtained by detecting these photoelectric conversion outputs.

To give an example of the above-mentioned relative comparison method of photoelectric conversion outputs, the outputs of two sets of light receiving sensors are synchronously detected in synchronization with the output of a pulse oscillator that drives a light emitting element, and the detected outputs are collected over a predetermined period of time. It integrates periodically and compares the times when these integrated waveforms exceed a predetermined level. That is, if the time difference between the times when the two sets of integral waveforms each exceed a predetermined level is within a predetermined time length, it is considered to be in focus, and if the above-mentioned time difference exceeds a predetermined time length. In this case, it is assumed that the lens group is out of focus, and depending on which of the above two sets of integral waveforms exceeds the predetermined level listed above first, the motors that drive the lens groups are turned in the forward direction or in the reverse direction. The focus is adjusted by rotating the lens in the direction of the lens.

As mentioned above, a method has been proposed in which the output signal of the imaging means itself is used without using an external ranging system, but in this method, the imaging signal obtained from the image sensor of the video camera is converted into a luminance signal in a process circuit. This luminance signal is passed through a high-pass filter to extract high-frequency components such as contour signals, the level of this extracted component is detected, and the mountain climbing control circuit is used to increase this detection level as much as possible. The lens driving circuit is controlled to drive the lens group.

(Problems to be Solved by the Invention) In the conventional automatic focus adjustment device of a video camera as described above, for example, when the scene on the screen -1- used for camera panning changes significantly, the automatic focus adjustment device A so-called twitching phenomenon occurs, causing an unnatural appearance on the screen.

The automatic focus adjustment device of the present invention prohibits the focus adjustment operation when the scene on the screen changes significantly. With the goal.

(Means for Solving the Problems) In order to achieve the following objects, the automatic focus adjustment device of the present invention provides a detection means for detecting the presence or absence of correlation between fields in image information output from an imaging means. and when a signal indicating that there is no substantial correlation between the fields is detected from the detection means, inhibiting the focus adjustment operation.
h. Here, the above-mentioned image information refers to a standard television signal such as a luminance signal or a color signal obtained from an output signal of an imaging means, or a color difference signal or an NTSC signal obtained by modulating a luminance signal and a color difference signal. It may be either.

(Function) The automatic focus adjustment device of the present invention is based on the above configuration,
Regarding the image signals output from the imaging means, whether there is a complete correlation between the previous field and the next field, or whether there is a substantial difference between the two fields, such as whether the difference between them does not exceed a predetermined limit, etc. When a signal indicating the existence of a certain correlation is detected, the focus adjustment operation continues; When a signal indicating that there is no substantial correlation between the two is detected, such as when L is less than a predetermined limit, the focusing operation is inhibited.

(Example) Examples of the automatic focus adjustment device of the present invention will be described in detail below with reference to the drawings. The following explanation will be about an embodiment in which the present invention is applied to an active differential automatic focusing device, its overall configuration, a specific example of the means for detecting the presence or absence of correlation in the embodiment, and the order of operation of the embodiment. Do it with It should be noted that the present invention can also be applied to focus adjustment devices other than the active and differential types described in "-".

(Overall configuration of an embodiment of the automatic focus adjustment 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 numeral 1 denotes a light projecting element 2A.

2B is a light receiving sensor, 3 is a pulse oscillator, the light emitting element l emits light in a pulsed manner by the oscillation pulse of the pulse oscillator 3, and the light beam reflected by the subject is sent to the two light receiving sensors 2A.
, 2B.

A processing circuit for the light receiving output photoelectrically converted by the light receiving sensors 2A and 2B consists of two series A and B. First, 4A and 4B are process circuits including amplifiers 5A and 5B and synchronous detectors 6A and 6B, respectively.
amplify the outputs of the light receiving sensors 4A and 4B, respectively,
Its amplified output is transmitted by a synchronous detector 6 which is synchronized with the pulse oscillator 3.
A and 6B perform synchronous detection, respectively, and the detected outputs are input to integration circuits 7A and 7B, respectively.

8A and 8B are switches that reset the integration of the integration circuits 7A and 7B, respectively, and are controlled by the cycle end r signal. The above-mentioned cycle end signal is a signal obtained by dividing the output of the pulse oscillator 3 (a) by the frequency divider 10 (b) in the same figure and delaying it by Δt by the detour 11 (C in the same figure). ) is given through Or Game]・12.

9A and 9B are differential amplifiers whose (+) inputs are connected to the outputs of the 1A circuits 7A and 7B, respectively, and whose (=) inputs are connected to the threshold (tj potential source V ref ). Therefore, the outputs of the integrating circuits 7A and 7B increase over time, but when these outputs exceed the threshold Vref, the outputs of the differential amplifiers 9A and 9B increase.
The outputs of each go high. 13A and 13B are AND gates, to which the outputs of differential amplifiers 9A and 9B are inputted, respectively, and the output of a partial quantity counter 18, which will be described later, is commonly inputted via an inverter 19.

The outputs of the gates 13A and 13B are input to the clock terminals of D flip-flops 14A and 14B, respectively, and the output of the OR gate 12 is supplied to their reset input terminals, respectively. D flip flop 15
A and 15B have their D input terminals supplied with the Q outputs of the previous-stage D flip-flops 14A and 14B, respectively, and their clock terminals with both the output of the frequency divider 10. 16 is a D flip-flop 15A,
This is an AF calculation circuit into which the Q output of 15B is input, and the AF momo-M is controlled by the output. That is, A.F.
If the two manual forces are both high, the arithmetic circuit 16 determines that the focus is in focus and does not send a control signal to AF Momo-M.
If one of the manual forces is high and the other is low, it is determined that the focus is out of focus and the AF Momo-M is rotated in either the forward or reverse direction.If both of the two human forces are low, the focus is determined to be out of focus. For example, if it is impossible to determine focus, AF Momo-M may be stopped.
The camera is configured to prohibit equifocal adjustment operations that cause the lens to move.

17 is an OR gate to which the outputs of the D flip-flops 14A and 14B are input; 18 is a partial quantity counter to which the output of 17 is supplied as a clock;
The output of the frequency divider 10 is input to the reset input terminal of the counter 18, and the output Qn is outputted via the inverter 19.
The signals are supplied to one input terminal of each of the analogue games 13A and 13B.

Reference numeral 20 denotes a scene change detection circuit, which is an example of 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, and the output of the OR gate 12 is supplied to the reset switches 8A and 8B and the D flip-flops 14A and 14B, and the first Controls the operation of the focus adjustment system shown in the figure. That is, the above control signal is supplied to the reset switches 8A and 8B, and when a scene change occurs, the integration circuits 7A and 7B are reset, and by resetting the D flip-flops 14A and 14B, the flip-flop 15A is finally reset. , 15B are forcibly set to low output to disable the AF detection operation and stop the AF MOMO-M.

(Specific examples of means for detecting the presence or absence of correlation in the embodiment of the present invention) (Figs. 3 to 5) Figs. 3 to 5 show the scenes of Fig. 1 as means for detecting the presence or absence of correlation. Specific examples of the turning point detection circuit 20 will be shown, and these examples detect whether there is a correlation between one field before and after one field of an image signal output from an imaging means of a video camera.

Among these circuits, Fig. 3 detects a scene change using the luminance signal in the output signal of the imaging means, and 31 in the figure is a process circuit that detects the color signal output from the imaging means. (R,G.

B) is converted into a luminance signal Y and a color difference signal (R-
Y), (B-Y). The output intermediate signal (hereinafter referred to as Y signal) of the process circuit 31 is inputted to a difference circuit 33 on one side via a delay circuit 32 and directly on the other side to detect the difference between both signals, and this difference signal is used as appropriate. For example, the integration circuit 34 integrates (adds) the iH force at the timing of the vertical synchronization signal, and the integrated iH force is applied to the comparator 3.
5 and is compared with a predetermined level. That is, the difference between the Y signal of the current field and the Y signal of one field before is detected and compared with a predetermined level.

Here, if the correlation with the field before the l field is perfect, the output will be zero even if the above difference signal is integrated, or if the correlation as described above is obtained to some extent, the above integrated output will be Although it does not exceed a predetermined level, if this integral output exceeds a predetermined level, it is determined that the correlation has collapsed, and a control signal indicating a scene change 11 for the next field is output to the OR gate 12 in FIG. The signal is used as a reset signal as described above.

The circuit shown in FIG. 4 detects a scene change scale by detecting the ratio of a specific color signal output from the imaging means. In the figure, 41 and 42 are integration circuits that integrate the G signal component and B signal component output from the imaging means for an l field period under the control of the vertical synchronization signal, and the ratio of their integrated outputs is divided by It is determined by the circuit 43. The difference between the value of the ratio of this integral output and the value of the ratio of the integral output one field before is detected by means such as a delay circuit 44 and a difference circuit 45, and the detected output is compared with a predetermined level by a comparator 46, If this is above a predetermined level, a scene change signal is input to the or game (or game) 12 in FIG.

The circuit shown in Fig. 5 is a further development of the circuit shown in Fig. 3, which extracts image information from only a few places on the screen as samples, and checks whether or not there is a correlation with the previous field for each sample. It is then determined whether to continue the focus adjustment operation or to prohibit it based on the relative evaluation of the correlation in these samples. for example,
As shown in Figure 6, the n1 line in a part of the screen, the n2 line in the center, and the n3 line in the lower part are taken as samples,
The presence or absence of correlation between the Y signals on each of these sample lines is detected. If no correlation is obtained for all of the n1 to n3 lines, it is determined that there is no correlation for the entire screen, and in this case, the scene has changed significantly due to camera shake, so focus adjustment is prohibited only in this case. 1t-do. On the contrary, the correlation is broken only on the n2 line, but the nl
If there is a correlation between line n2 and line n3, it is determined that only the image signal of line n2-1- has changed due to, for example, movement of the subject, and the focus adjustment operation is continued.

In FIG. 5, 51a to 51c are mono multivibrators (M, M, ), each of which delays a vertical synchronizing signal corresponding to the line n1 + n2 + n3 to create a gate pulse.

52a to 52c are gate circuits, and process circuits 31
The Y signal being outputted is extracted by the above gate pulse. Similar to the circuit shown in FIG. 3, the extracted Y signal is detected for each line by means such as delay circuits 53a to 53c and difference circuits 54a to 54c to detect the difference between the extracted Y signal and the Y signal of the line one field before. be done. These difference signals are integrated by integrating circuits 55a to 55c, and each comparator 56
A to 56c are compared with a predetermined level. Comparator 56a~
Based on the relative evaluation of the output of the comparators 56c, it is determined whether to continue the focus adjustment operation or to prohibit it. Here, the outputs of the comparators 56a to 56c are input to the AND gate 57. , shows an example in which a scene change signal is output to the OR gate 12 of FIG. 1 only when its output is high. In this example, the integrating circuit 55a
A scene change signal is output only when all the outputs of ~55c are above a predetermined level, and the focus adjustment operation is prohibited, but even if one of the outputs of the above integration circuit does not exceed a predetermined level. If so, the focusing operation continues. The above-mentioned method of creating the turn signal from the number of sample lines and the output signal of the comparator is merely an example, and many other variations are possible.

(Operation of the embodiment of the automatic focus adjustment device of the present invention) (First
2) Next, the operation of the device shown in FIG. 1 will be explained with reference also to FIG. 2.

FIG. 2a shows the output pulse of the pulse oscillator 3 in FIG. ), this delayed signal is applied to the reset switches 8A, 8B to reset the corresponding integration circuits 7A, 7B. Integrating circuits 7A and 7B start integrating operation again after being reset, and their output increases with time (d in the same figure).
As shown in the figure, in the control cycle of
t, and then the integrated output of the other series (assumed to be the B series here) becomes the threshold voltage V at time tBt.
ref is exceeded, and the time difference between time tAt and time EBt is longer than a predetermined time length (for example, To described later).

The output of the differential amplifier 9A becomes high at time tAx, but since the output Qn of the counter 18 has not yet become high at this time, the output of the AND gate 13A to which this is input via the input/hatter 19 becomes t. , becomes high after 1.

As a result, the output Q of the D flip-flop 14A at the next stage becomes high, as shown in e of the figure, until the next set pulse (C of the figure) is input. This high output is inputted to the clock terminal of the partial amount counter 18 via the D terminal of the next-stage flip-flop 15A and the OR gate 17, and the counter 18 has its Qn output set to high after a certain period of time To (FIG. ), and is reset by the output of the frequency divider 10 (b in the figure).

Here, in the first control cycle, the time point tBz at which the integrated output of the B series exceeds the threshold value Vref is after a partial time length To has elapsed from the time point tAz, as described above. Since the Qn output of the counter 18 at time tBt is high, the output of the AND gate 13B to which it is input via the inverter 19 becomes low even if the output of the differential amplifier 9B is NO. 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 transmitted to the next stage 7. Lipflop 15A and 15
Since these signals are input to the D terminal of B, their outputs become high and low, respectively (I in the figure), and these signals are input to the AF calculation circuit 16. Here, AF calculation circuit 1
6 is whether both of those two people are high, or one is high,
Depending on whether the other one is low or both are low, it will be in focus, out of focus, or in focus and out, as described above.
Since it is configured to determine that out-of-focus is impossible and perform a predetermined operation, in the above case, it is determined that out-of-focus is determined and which of time tAt and time tBx comes first. The AF motor M is rotated in either the forward or reverse direction depending on the presence of the lens, and the lens group that performs the focusing operation is moved along its front axis in the focusing direction.

Next, in the second control cycle, which is the focused state,
As shown in FIG. 2d, the time tA when the outputs of the two integrating circuits 7A and 7B each exceed the threshold voltage V ref
The time difference between tB2 and tB2 is different from the first control cycle and is shorter than the partial time length TO. Therefore, the output of the A-series flip-flop 14A goes high at time tA2, which is the same as in the first control cycle, but the output of the B-series flip-flop 14B (g in the figure) becomes high at time tA2. Unlike a cycle, a partial time length To from time tA2
goes high at time tB2 before . The output of flip-flop 14A (e in the figure) and the output of flip-flop 14B (g in the figure) are input to the D terminals of flip-flops 15A and 15B, respectively, so the outputs of these flip-flops both become high. , A.F.
As described above, the arithmetic circuit 16 determines that the lens group is in focus, does not send a control signal to the AF motor M, and performs one focusing operation.The lens group stops at the position at that point, and the automatic focus adjustment device Focus adjustment state (focus state) corresponding to that position
will be maintained.

Here, when the aforementioned control signal is output from the scene change 1 detection circuit 20 in FIG. Integrating circuits 7A, 7 regardless of operation
B together, and flip-flops 14A, 1
In order to reset both flip-flops 15A and 15B, both flip-flops 15A and 15B are finally set to low output. This allows A
The F calculation circuit 16 determines that the focus detection 111 is impossible, and transfers a stop signal to the AF momo-M, for example, to inhibit the focus adjustment operation. Then, when the control signal from the scene change 1 detection circuit 20 is turned off, the focus adjustment operation is restarted, but as an alternative, even if the control signal is turned off, the AF motor M is not operated for a fixed period of time. The stop 1 signal may be continuously supplied and the focusing operation may be resumed after the stop 1 signal is turned off.

(Effects of the Invention) As described above, according to the present invention, there is a signal indicating that there is no substantial correlation between the previous field and the next field in the image signal output from the imaging means. When detected, the focus adjustment operation is prohibited, which prevents the so-called twitching phenomenon of the automatic focus adjustment device that occurs when a sudden scene changes, etc., and enables focus adjustment that does not cause unnaturalness on the screen. It can be carried out.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the automatic focusing device of the present invention, FIGS. Figures 1 and 5 show scene change 1 in the device shown in Figure 1, respectively.
FIG. 6 is a block diagram showing details of the detection circuit, and FIG. 6 is a diagram showing sample lines for explaining the operation of the circuit of FIG. 5. Explanation of symbols 3: Pulse oscillator, 7A, 7B: Integrating circuit, 8A,
8B: Reset switch, 9A, 9B: Differential amplifier,
10: Frequency divider, 11: Delay circuit, 12 NOR gate, 1
3A, 13B: AND gate, 14A, 14B, 15A
, 15B: D flip-flop, 16: AF calculation circuit,
17: OR gate, 18 constant star counter, 19: Inverter, 20: Scene change (1 detection circuit, 31: Process circuit, 32, 44.53a, 53b, 53c: Delay circuit, 33, 45.54a, 54b, 54c : differential circuit,
34, 55a, 55b, 55c: Integrating circuit, 35, 46
．． 56a, 56b, 56c: comparator, 41: B signal component integration circuit, 42: G signal component integration circuit, 43: division circuit, 51a, 51b. 51c: Mono multivibrator, 52a, 52b
, 52c: Gate circuit, 57: AND gate, M:
AF motor. Diagram 2

Claims (2)

[Claims] (1) A detection means for detecting the presence or absence of correlation between fields in the image information output from the imaging means, and when a signal indicating that there is no substantial correlation between the fields is detected from the detection means. , and means for inhibiting a focusing operation. (2) The detection means is means for detecting the presence or absence of correlation between fields for each of a plurality of samples on the screen, and the means for inhibiting the focus adjustment operation is for each sample among the plurality of samples. Claims including means for determining whether to inhibit a focusing operation by relative evaluation of signals indicating the presence or absence of correlation between fields (
1) The automatic focus adjustment device described above.