JPH0273784A - Image pickup device - Google Patents

Abstract

PURPOSE:To attain high speed focusing and to avoid unpleasant blur on a pickup pattern due to retrogressing of a lens by differentiating an optimum focal position from 1st and 2nd detection means. CONSTITUTION:An output of a luminance signal processing circuit 34 is fed to BPFs 42A, 42B for automatic focusing and an output of a color signal processing circuit 36 is fed to band pass filters(BPFs) 44A, 44B. A system controller 6 selects a BPF according to the detection sensitivity and the frequency component extracted by the BPF is detected by detection circuits 50, 52 and only a signal of a range finding frame is inputted to integration circuits 58, 60 through gate circuits 54, 56, and the resulting output is fetched in a system controller 66. The system controller 66 compares the present integration value with the just preceding integration value and the focusing lens is stopped at a position of the lens where the present integration value is less than the just preceding integration value. Thus, the reversing of the lens is eliminated and the pickup is applied without unpleasant feeling.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an imaging device such as a video camera.

[Conventional technology]

2. Description of the Related Art Conventionally, in imaging devices such as video cameras, automatic focusing devices are known that perform autofocusing of a photographing optical system using an output signal from an imaging element.

To briefly explain the basic principle of autofocus, a distance measurement window is set at a predetermined position on the shooting screen, and the focusing of the shooting optical system is adjusted so that the high frequency component of the signal portion corresponding to the window is maximized.・It controls the position of the lens. In other words, when the image sensor is far away from the focused state, the optical image on the imaging surface of the image sensor (especially its distance measurement window) is a blurred image with a low spatial frequency, and the signal from the distance measurement window also contains high frequency components. does not contain much. However, as the focusing lens moves closer to the in-focus position, the optical image on the imaging surface also begins to have high spatial frequency components.
Finally, at the focal point, the optical image of the imaging plane will have the highest spatial frequency components. This spatial frequency component is
Since this is reflected in the high-frequency component of the signal from the distance-measuring window, it is possible to determine whether the focal point is in focus or not based on the magnitude of the high-frequency component of the signal from the distance-measuring window.

Therefore, conventionally, a band pass filter (BPF) that passes the high frequency component at the focused point is prepared, a gate circuit extracts the signal portion corresponding to the distance measurement window from the luminance signal component of the imaging signal, and the BPF The high-frequency components are extracted by the integrator circuit and integrated by the integrator circuit. Then, the integration result of the integration circuit is compared with the integration result at the position immediately before the focusing lens, and the position where the integration value is maximum is determined to be the in-focus point. To determine whether the value is the maximum, the comparison is repeated while the integral value is increasing, and when the integral value starts to decrease, it can be determined that the previous value is the maximum. In other words, it is similar to climbing a mountain, so it is called the mountain climbing method. The focusing lens is returned to the previous position at the point when the integral value starts to decrease.

Note that normally, the BPF described above has low sensitivity when it is far away from the in-focus point, and therefore cannot determine the moving direction of the focusing lens as it approaches the in-focus point, so it has filtering characteristics at lower frequencies. One or two BPFs are provided, and these BPFs are switched as the focal point approaches.

[Problem to be solved by the invention]

Color imaging devices include single-chip, 2-Fi, and 3-chip types, but all of them first create a brightness signal, and then perform focus control using the hill-climbing control described above based on this brightness signal. Ta. In mountain climbing control, the focusing lens always passes through the -degree focused point and then returns a little, which causes some discomfort to the photographer. Further, due to the characteristics of the motor, it is extremely difficult to rapidly rotate the motor in reverse due to inertia, and therefore there is a problem that the focusing speed cannot be increased.

To solve this problem, a method has been proposed in which the focusing lens is made to vibrate minutely in the optical axis direction using a piezo element, the in-focus point is determined from the change in brightness information at that time, and the focusing lens is stopped at the in-focus point. However, this method requires a vibration actuator to minutely vibrate the focusing lens, leading to increased manufacturing costs and power consumption.

Therefore, an object of the present invention is to provide an imaging device that can obtain a faster focusing speed.

[Means to solve the problem]

The imaging device according to the present invention provides a first
a first detection means for detecting the degree of focus based on the focus detection signal of the imager; and a second detection means for detecting the degree of focus based on the second focus detection signal output from the imaging means; The present invention is characterized in that it includes a second detecting means having a different optimal focus position from the first detecting means, and means for determining focus from the first and second detecting means.

[Effect]

By differentiating the optimum in-focus position using the first and second detection means, the photographed image can be kept within the in-focus range without retracting the focusing lens. Therefore, the focusing speed can be increased, and unpleasant blurring of the photographic screen due to the lens retreating can be eliminated.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

Fig. 1 is a block diagram of the configuration of an embodiment of the present invention, Fig. 2 shows the frequency distribution of the luminance signal and chrominance signal when they are focused in a two-chip camera, and Fig. 3 shows the integrated output of high frequency components with respect to the lens position. . First, the basic principle of this embodiment will be explained with reference to FIGS. 2 and 3. As a BPF for focus determination, a center frequency fy is prepared for the luminance signal, and a center frequency fcO is prepared for the chrominance signal. Characteristic P of the diagram
,,becomes a PC. That is, the color signal characteristic PC changes smoothly with respect to the lens position, and the focusing accuracy is loose, so the focusing range is wide. On the other hand, the characteristic P of the luminance signal changes sharply with respect to the lens position, and the focusing accuracy is strict, so the focusing range is narrow. Therefore, in this embodiment, as shown in the characteristics P, PC in FIG. 3, the luminance signal imaging device and the color signal imaging device Set the positional relationship of the elements.

For example, position the focusing lens ■, ■.

If you move the lens position ■ and then pay attention to the color signal, you will notice that the integrated output at lens position ■ is smaller than the integral output at lens position ■, and lens position ■ is determined to be the in-focus point.
The lens position (3) is still within the focusing range when viewed from the luminance signal. Both image sensors are arranged at such positions.

FIG. 1 will be explained. 10 is a shadow optical system, 12 is an infrared cut filter, 14 is a light splitter consisting of a prism, 1
6.18 is crystal LPF (low pass filter), 2
0 is a color filter, 22 is a luminance signal image sensor, 2
4 is an image sensor for color signals, 26.28 is a 378 circuit that performs double correlation sampling etc. to remove 1/f noise of the image sensor 22.24, 30.32 is a gamma correction circuit, 3
4 is a luminance signal processing circuit that performs processing such as level balance (LB) and white knee, 36 is a color signal processing circuit that performs processing such as white balance, and 38 is a synchronizing signal to the output of the luminance signal processing circuit 34. This is an adder for adding.

A luminance signal is obtained from the adder 38, and the color signal processing circuit 36
to the color difference signal RY.

B-Y is obtained. Reference numeral 40 denotes a pulse generation circuit that supplies drive signals to the image pickup elements 22, 24 and sampling clocks for the S/H circuits 26, 28. The above-mentioned portions have a known configuration as a normal two-chip imaging device.

In addition, 42A is a BPF with filtering characteristics at the center frequency f shown in FIG. A BPF with filtering characteristics at frequency re, 44B is a BP with filtering characteristics at a wider or lower center frequency.
It is F. That is, near the in-focus point, BPF42A, 44A
BPF42 is used in low-sensitivity areas far from the focal point.
B.

44B is used. 46 and 48 are changeover switches for this purpose. 50.52 is a detection circuit; 54 and 56 are gate circuits that pass the signal portion corresponding to the ranging frame according to the gate signal from the pulse generation circuit 40; and 58.60 is an integral that integrates the output of the gate circuit 54.56. circuit, 62.64
is an A/D converter, and 66 is a system controller. A system controller 66 controls switching of switches 46,48. An actuator 68 drives a focusing lens (not shown) of the optical system 10 according to instructions from the system controller 66.

The incident light of the optical system 10 passes through a filter 12 and a light splitter 14.
is incident on the image sensor 22.24 through the image sensor 22.24.
24 outputs a corresponding electrical signal. Image sensor 22.2
4 has 1/f noise removed by the S/H circuit 22.4, and is input to the luminance signal processing circuit 34 and color signal processing circuit 36 via gamma correction circuits 30 and 32, respectively. The signal processed by the luminance signal processing circuit 34, such as level balance and white knee, is applied to an adder 38, where a synchronization signal is added, and a luminance signal Y is generated. Further, the color signal processing circuit 36 performs processing such as white balance and outputs color difference signals RY and BY.

For automatic focusing operation, the output of the luminance signal processing circuit 34 is applied to the BPF 42A, 42B, and the output of the luminance signal processing circuit 36 is applied to the BPF 42A, 42B.
The output of is applied to BPF44A, 44B. The system controller 66 switches the switch 46.4 according to the detection sensitivity.
Switch 8 to BPF42A, 44A; 42B, 44B
Select.

The frequency components extracted by the BPFs 42A, 44A; 42B, 44B are detected by the detection circuit 50.52, and only the signal in the distance measurement frame is detected by the gate circuit 54.56 by the integration circuit 5.
Entered at 8.60. The output of the integrating circuit 58.60 is A
/D converters 62 and 64 and incorporated into system controller 66. The system controller 66 compares the current integral value with the previous integral value and stops the focusing lens at the lens position where the current integral value is less than the previous integral value.

For example, if the lens is currently in the position corresponding to ■ in Figure 3,
Start focusing and rotate the lens ■,■.

Suppose we move it as... When viewed from the color signal, the integrated output at the lens position ■ is smaller than the integral output from the lens position ■, and the lens position ■ is determined to be the in-focus point, but when viewed from the luminance signal, the lens position ■ is determined to be the focal point. is still within the in-focus range. In this way, both ↑most image elements are arranged. Therefore, it is sufficient to stop driving the lens at the lens position (2) without returning the lens to the position (2).

Furthermore, as can be seen from Fig. 3, in the composite characteristic P y +P e of the characteristic P and the characteristic PC, the peak of the characteristic Py (the focal point of the luminance signal) and the peak of the characteristic PC (the focal point of the chrominance signal) are There is a peak in the middle of the integrator circuit 58.
Even if the lens position where the weighted or unweighted sum of the 56 outputs starts to decrease is detected and the focusing lens is stopped at that position, the luminance signal (and, of course, the chrominance signal)
An in-focus state can be obtained for.

In the embodiment shown in FIG. 1, the color difference signal RY is used as the color signal, but of course the color difference signal B-Y may also be used.

Moreover, the characteristics Py! of the image sensor 22 for brightness signals are shown by the broken line in FIG. The same effect can be obtained even if it is placed at a position corresponding to .

FIG. 4 shows a block diagram of another embodiment of the present invention.

In this embodiment, a luminance signal is created from the output of the color signal image sensor 24 and used for focus determination. 70 is a brightness generation circuit that creates a brightness signal from the signal (for example, R, G, B signal) output from the gamma correction circuit 32, and 72 is a brightness signal processing circuit that performs brightness signal processing on the output of the brightness generation circuit. be.

The luminance signal processing circuit 72 has the same function as the luminance signal processing circuit 34. Then, the output of the luminance signal processing circuit 72 is BP
Apply to F74A and 74B.

Assuming that the output of the luminance signal processing circuit 34 is yl and the output of the luminance signal processing circuit 72 is y2, the frequency distribution at the time of focusing is as shown in FIG. The center frequency of BPF74A is fy! in Figure 5. The BPF 74B has a wider pass band on the lower frequency side than the BPF 74A, or has filtering characteristics at a lower center frequency. FIG. 6 shows changes in the integral values of the outputs of the BPFs 42A and 74A with respect to the lens position. R9 indicates the characteristic of the luminance signal y1, R2 indicates the characteristic with respect to Yt, and R1+RZ indicates the characteristic with respect to the sum of the integral value regarding the luminance signal y1 and the integral value regarding the luminance signal y2. In the case of the luminance signal y2, the focusing characteristic R2 is steeper than that of the color signal, and the focusing characteristic R of the luminance signal y1 reaches its peak at a position slightly past the peak.
Image sensors 22 and 24 are arranged. Therefore, the image sensor 22 may be arranged so that the characteristic R1 is represented by the broken line with respect to the characteristic R2.

The focusing operation is basically the same as in the case of FIG. This embodiment has the advantage that the focusing characteristic of the luminance signal y2 is steeper than that of the color signal, and it is easier to make a focus judgment as a whole.

Note that the amount of deviation of the imaging elements 22 and 24 from the focusing lens is quite small and does not pose a problem in practice. Further, since the color signal has a lower band and lower sensitivity than the luminance signal, it is possible to shift the position of the image pickup device sufficiently within the permissible range.

〔Effect of the invention〕

As can be easily understood from the above description, according to the present invention, unlike conventional mountain climbing control, there is no need to slightly retract the focusing lens in order to position the focusing lens at the focal point. Therefore, the time required to reach focus can be shortened, and since the lens does not move backwards, images can be drawn without discomfort. Further, since it is not necessary to use a special actuator such as a piezo element for optical path modulation, power consumption can be saved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the configuration of one embodiment of the present invention, FIGS. 2 and 3 are characteristic diagrams of FIG. 1, FIG. 4 is a block diagram of the configuration of another embodiment of the present invention, and FIGS. FIG. 6 is a characteristic diagram of FIG. 4. 10.-Photographing optical system 12-Infrared cassette filter 14
- Light splitter 16.18 - Crystal LPF 20 - Color filter 22 - Luminance signal imaging element 24 - Color signal imaging element 34.72 - Luminance signal processing circuit 36
- Color signal processing circuit 40 - Pulse generation circuit 50.52
-Detection circuit 54,56-Gate circuit, 58.60-
Integrating circuit 66--System controller 68
-Actuator 70-Brightness signal generation circuit

Claims (3)

[Claims] (1) A first detection means that detects the degree of focus based on a first focus detection signal output from the image pickup means, and a second focus detection signal output from the image pickup means. A second detecting means that detects the degree of focus and has a different optimal focus position from the first detecting means, and a means for determining focus from the first and second detecting means. An imaging device characterized by: (2) The imaging means includes a plurality of imaging elements, and the first
Claim No. (1), characterized in that the and second focus detection signals are output from separate image sensors.
The imaging device described in section. (3) An imaging device comprising a luminance signal imaging means and a chrominance signal imaging means, in which the optimum focus point is determined by the output signal of the luminance signal imaging means and the output signal of the chrominance signal imaging means. An imaging device characterized in that both imaging means are arranged so that the optimum focus point is shifted within an allowable focusing range.