JPH02257773A - Camera system - Google Patents

Abstract

PURPOSE:To attain detection of a focal point with high accuracy by providing a signal storage element and a readout system reading a signal optionally and driving part of the system near the focal point. CONSTITUTION:After a 1st rough focal point is detected, a picture signal at the 1st focal point is stored in a signal storage element 14, and a readout system 15 outputs only a signal from the signal storage element 14 to a monitor means 17, on which a picture is displayed. A drive control system 13 drives part of the system for this period to increase the apparent resolution thereby driving an image pickup optical system 11 again at a high speed to detect the true focal point. Then the drive control system 13 restores part of the system to output the signal of the image pickup element 12 to the monitor means 17 via the readout system 15. Thus, the focus is detected for a photographer of a camera with high resolution not giving a sense of disorder near the focal point.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a camera system, specifically, a focus detection method by calculating a video signal from a subject image formed on a photoelectric conversion means such as an image sensor. The present invention also relates to a camera system capable of monitoring the video signal.

[Prior Art] As is well known, there are a large number of techniques for detecting a focused point in a camera, etc., which detects focus by calculating a video signal obtained from a subject image formed on a photoelectric conversion means such as an image sensor. There are two types of methods: a passive method that detects focus based on brightness distribution information of the subject, and an active method that projects a beam of infrared light or ultrasound onto the subject and detects focus based on the reflected signal. . Examples of passive methods include a phase difference detection method that detects the defocus direction and approximate amount of defocus from data on two optical path lengths, and a phase difference detection method that detects the defocus direction and approximate amount of defocus from data on two optical path lengths, and a phase difference detection method that detects the defocus direction and approximate amount of defocus from data on two optical path lengths. A contrast detection method is known in which the sensor is moved and, when a peak position is detected, the sensor is stopped there.

This contrast detection method focuses on the frequency components of the image, and detects the focused point by moving a part of the imaging optical system.It is classified as a mountain-climbing method, 1 frequency component method, etc., but NHK Many proposals have been made, including ``Automatic focus adjustment of television cameras using a mountain-climbing servo method'' published by Ishida et al. in Technical Report, Vol. 17, No. 1.

This proposal for "autofocusing of TV cameras using hill-climbing servo method: A adjustment" detects the definition of the screen based on the high-frequency components of the video signal, performs hill-climbing control to maximize the definition, and automatically This paper describes the principles and circuit design conditions of a device for adjusting the optical focus of a television camera. Based on measurements of the response of an experimental circuit to a two-dimensional object and simulation experiments using an analog computer, we found that the shape of the hill-climbing curve, which changes depending on the lens aperture and focal length, determines the accuracy of focusing using the hill-climbing servo system. Accuracy is improved by increasing the gain of the control system and decreasing the time constant of the time delay element.
If you choose 1 second, the height and slope of the mountain climbing curve will be 4.
It is disclosed that a focusing accuracy of 5% can be obtained for a fold change. Furthermore, it is disclosed that by using adaptive control that detects the shape of the hill-climbing curve and controls the gain of the control system, it is possible to expand the control range and improve accuracy.

Also, 1986 Television Society National Conference Materials P85
-86 In the "autofocus system for television cameras" announced by Toyota et al. on 4-7, the amount of out-of-focus is constantly changed at a constant cycle by mechanically changing the sensor side, and in response to this, the video signal is The high frequency component of is subjected to amplitude modulation, but the phase of this amplitude modulation component varies by 180 degrees depending on whether the direction of defocus is toward the front focus or the rear focus, and the amplitude becomes zero when the focus is in focus. Therefore, focusing accuracy is improved by controlling the focal position of the lens using this amplitude modulation component.

[Problems to be Solved by the Invention] However, in the focusing point detection method of this contrast detection method, which is typified by the conventionally proposed "automatic focus adjustment of a television camera using a mountain climbing servo method," it is difficult to determine the defocus direction and defocus amount. is unknown in one detection, so the in-focus position can only be detected after passing through the in-focus point while constantly scanning. Therefore, it is necessary to perform image detection many times, and in the vicinity of the in-focus point, errors such as overlapping, which occurs once passing through the in-focus point and then returning to the in-focus point, are unavoidable.

Therefore, for the photographer looking into the AF left camera viewfinder, even though the subject image within the viewfinder field of view is moving in the direction of focus, when it reaches near the in-focus point, there may be confusion such as overlap. This results in a screen that is extremely difficult to view, causing discomfort.

Furthermore, when a sensor equivalent to an SV or VTR is used as a sensor in a camera using a silver halide film, the resolution of the sensor at a focused point is low, resulting in low focusing accuracy. Therefore, if you try to increase the overall resolution, you will not be able to monitor the entire screen, or the sensor itself will become extremely large.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems, and to provide a high-resolution focal point without showing the user the overlap ( The present invention provides a camera system that performs detection.

[Means and Effects for Solving the Problems] The camera system of the present invention has an imaging element that converts subject light guided by an imaging optical system into an electrical signal, and the imaging optical system is electrically driven. A camera system comprising a focus detection means for detecting a focusing direction and a focused point of the imaging optical system based on a change in the electrical signal, wherein the camera system is configured such that the imaging optical system is in a first focused state. a signal accumulating means for accumulating the electric signal when the electrical signal is reached, and a second in-focus state that is more accurate than the first in-focus state after the signal accumulating means accumulates the electric signal; a focus detection auxiliary means for performing a focus detection operation again; an electric signal selection means for selecting either the electric signal from the image sensor or the electric signal accumulated in the signal accumulation means; and a control means for controlling the electrical signal selection means to select the accumulated electrical signals during the operation of the focus detection assisting means. This is a characteristic feature.

[Implementation example] Hereinafter, the present invention will be specifically described with reference to the drawings.

Before explaining the present invention in detail, the arrangement of the optical system in the camera when the present invention is applied to a single-lens reflex camera will be explained using FIG.

In FIG. 7, the light flux from the subject is transmitted through the photographing lens 20.
2 and is guided to a pentaprism 203 by a first mirror 204. The object light whose optical axis has been changed by the prism 203 is sent to the finder 210 via the half mirror 205.
It is designed to be guided by. On the other hand, this half mirror
The subject light reflected by the mirror 205 is guided to the AF optical system 207 via the second mirror 206, and is imaged onto the imaging probe 208. Note that the video signal taken out from this imaging cable 208 can be monitored externally.

The first mirror 204 is a quick return mirror that flips up when the release button is fully pressed, so that the light beam forms an image on the film 209.

Since the AF optical system 207 has a zoom function, the focal length can be varied during focus detection and focus direction detection. Further, the imaging cable 208 has a surface equivalent to 20 films, and allows video signals to be monitored on a monitor 212 via a monitor terminal 211.

Note that *1. The flow described in *2 is executed by the AF optical system 207.

FIG. 1 is a conceptual block diagram showing the present invention from a functional perspective. In the figure, a signal from an imaging optical system 11 is converted into an electrical signal by an imaging probe 12, and this electrical signal is sequentially taken into a signal storage element 14.

The electrical signal photoelectrically converted by the image sensor 12 is also supplied to a signal processing system 16, which processes the signal and detects a power peak corresponding to the frequency, thereby creating a first rough composite. Focus detection is performed.

After that, the image signal at the first focused point is transferred to the signal storage probe 1.
The reading system 15 outputs only the signal from the signal storage element 14 to the monitor means 17 for image display. During this period, the drive control system 13 drives a part of the system to increase the apparent resolution, and thereby drives the imaging optical system 11 again at high speed to detect the true focal point. Thereafter, a part of the system is returned to its original state by the drive control system 13, and the signal from the image sensor 12 is outputted to the monitor means 17 via the readout system 15.

In this way, accuracy at the in-focus point can be improved, and it is possible to avoid giving the photographer a sense of discomfort near the in-focus point.

FIG. 2 is a concrete block system diagram of a camera system showing one embodiment of the present invention. A block system diagram showing a more detailed configuration of the signal processing circuit 103 in FIG. 2 is shown in FIG. 3 (A), and the power for the lens position at a specific frequency determined by the bandpass filter in FIG. The line diagrams are shown in Figure 4 (A) and (B
), and FIG. 5 shows detailed configurations of the DCPU 105 and image memory 106 in FIG. 2, respectively. The configuration of this embodiment will be explained below with reference to FIGS. 2 to 5.

In FIG. 2, a subject image transmitted through a photographing zoom lens 101 is converted into an electrical signal by an imaging circuit 102 and supplied to a signal processing circuit 103 and an A/D conversion circuit 104.

The signal processing circuit 103 supplies the focus detection signal divided into each spatial frequency to the main CPU (hereinafter abbreviated as MCPU) 107 . The above A/D conversion circuit 104
Then, the analog signal is converted into a digital signal and supplied to a signal processing dedicated CPU (hereinafter abbreviated as DCPU) 105.

The DCPU 105 is configured to manage bidirectional transfer of image signals to the image memory 106, image analysis, bidirectional communication with the MCPU 107, transfer of image signals to the video signal output circuit 110, and the like. Also, MCPU107
is the focus detection signal from the signal processing circuit 103, DCP
A lens drive signal is sent to the lens control circuit 109 based on the image analysis signal from U105, the lens position signal, lens aperture signal, zoom value signal, etc. from the lens control circuit 109. At the same time, the MCPU 107
05, a signal determining the content of image data to be transferred to the video signal output circuit 110 is sent.

The lens control circuit 109 has a function of monitoring the lens position, aperture position, and zoom value of the photographing zoom lens 101, and also drives the motor 108 based on a lens drive signal supplied from the MCPU 107. This motor 108 can change the lens position, aperture value, and zoom value of the photographing zoom lens 101.

FIG. 3(A) is a block system diagram showing the detailed configuration of the signal processing circuit 103 shown in FIG. 2. A plurality of circuits shown in FIG. 3(A) are combined for each spatial frequency band. A signal processing circuit 103 shown in FIG. 2 is configured. In this FIG. 3(A), the gate circuit 121
and the synchronous separation circuit 126, the imaging circuit 102 shown in FIG.
When the electrical signal photoelectrically converted is supplied, the synchronization separation circuit 126 and the gate control circuit 127 transmit a position signal for applying a gate to the analog image signal to the gate circuit 121.
Output to. The position where the gate is applied to this analog image signal can be selected arbitrarily, but as shown in Fig. 3 (B),
Generally, a position signal is generated by specifying a region 129 consisting of a plurality of pixels located at the center of the analog image 128.

The gate circuit 12 is controlled by the signal from the gate control circuit 127.
1, only a specific frequency component is extracted by a band pass filter (hereinafter abbreviated as B-P-F) 122, detected by a detection circuit 123, and integrated by an integration circuit 124. After that, the A/D conversion circuit 12
5, the data is A/D converted into a digital value and output to the MCPU 107 shown in FIG.

Figures 4 (A) and (B) show a B-P-F with a pass band in the low frequency region and a B-P-F with a pass band in the high frequency region.
FIG. 4 is a diagram showing the relationship between lens position and power for each of F. As is clear from the figure, when using B-P・F, which band-passes low frequency components, the fourth
As shown in Figure 4 (A), the power change with respect to the change in lens position is broad, whereas when using B-P・F, which band-passes high frequency components, the lens position changes as shown in Figure 4 (B). It can be seen that the power change with respect to the change in becomes sharp. B-P-F122, which band-passes such low frequency components and high frequency components (see Figure 3)
The signal that has passed is detected and integrated, then A/D converted by the A/D conversion circuit 125, and then sent to the MCPU 10 shown in FIG.
7.

FIG. 5 is a block system diagram showing a more detailed configuration of the DCPU 105 and image memory 106 shown in FIG. 2 above. In the figure, the first image signal RAM 131 that saves the image signal converts the digital signal from the A/D conversion circuit 104 (see FIG. 2) input into its input terminal into the MC
The data is saved based on the control signal of the PU 107. This first
The image signal stored in the image signal RAM 131 is supplied to and saved in the second image signal RAM 132 for saving the image signal via the control section 130, which is composed of, for example, an analog switch. This second image signal RAM1
32 performs vertical and horizontal Fourier transform 13 based on control signals supplied from the MCPU 107 (see FIG. 2).
3. Processing such as data binarization 1342, center of gravity detection 135, and image comparison 136 is performed at high speed, and the results are sent to the MCPU 107.

First image signal RAM 131 for saving the above image signal
The image signal read out from the image memory 1 shown in FIG.
It is also supplied to 06. This image memory 106 includes a first memory 106a that stores image signals saved prior to the start of the focus detection operation, and a first memory 106a that stores image signals during the focus detection operation, and as a result, the most recent image signal is stored. and a second memory 106b. Further, the control unit 130 supplies the image signal output from either the first image signal RAM 131 or the image memory 106 to the second image signal RAM 132 based on a control signal from the MCPU 107, or supplies the image signal to the second image signal RAM 132. It operates as a changeover switch for selecting whether or not to supply to the output circuit (see FIG. 2) 110.

Next, the operation of this embodiment configured as described above will be explained below based on the flowchart shown in FIG. This FIG. 6 shows M consisting of steps 81 to S16 in the center of the figure
The flow of the CPU 107 is shown in step S21 on the left side of the diagram.
The flow of the DCPU 105 consisting of steps S25 to S25 is shown on the right side of the figure.
3 is a flowchart from AF start to focus determination showing the flowcharts shown in FIG. 3 in parallel.

When the camera operation starts, the process advances to step S21, where the DCPU 105 performs normal image signal processing. That is, normally the A/D conversion circuit 104 shown in FIG.
The image signal converted into a digital value is taken into the first image signal RAMI 31 shown in FIG.
(See Figure 1) for continuous display on the monitor.

When a release button (not shown) is pressed, the process advances to step S1 and the AF operation signal is turned on.

Then, the process advances to step S22, and the DCPU 105 reads the first image signal RAM at the moment this AF operation signal is turned on.
Video signal output circuit 1 for the image signal taken into l31
10 and stores it in the first memory 106a of the image memory 106.

Then, the image signal stored in the first memory 106a is outputted to the video signal output circuit 110 to be output to the monitor means 1.
Display the image on 7. An image signal supplied after the image signal when the AF operation signal is on, which is stored in the first memory 106a, is written into the second memory 106b. The image signal stored in this second memory 10'6b is
It is rewritten each time so that the latest image signal is always stored.

That is, a new image signal is input to the second memory 106b of the image memory 106, and the new image signal is already input to the second memory 106b of the image memory 106.
Although the image signal recorded in 6b is erased and written, it is not output to the video signal output circuit 110. As described above, the image signal output to the output circuit 110 is stored in the first memory 106 prior to the start of this focus detection operation.
This is the image signal saved in g.

The above is the DCPU 10 when the AF operation signal is turned on.
5, the operation of the signal processing circuit 103 in step S31 and the operation of the MCPU in step S2 are as follows.
The operation of 107 will be explained.

Proceeding to step S31, the B-P-F 122 of the signal processing circuit 103 shown in FIG. 3(A) performs "power detection" of a specific frequency whose passband is defined. At the same time, when the process proceeds to step S2, the MCPU 107 commands "AF motor drive", whereby the photographing lens is driven by a minute amount. Then, in step S3, the first focusing "direction detection" is performed after the photographic lens is moved by a minute amount.

If the focusing direction is detected by the operation in step S3 above, the process proceeds to step S6 to turn off the AF operation signal, and if the focusing direction cannot be detected, the process proceeds to step S4 where the MCPU 107 directs the AF operation signal to the DCPU 105. Sends a “data processing signal”.

When the DCPU 105 receives this data processing signal, it processes the first memory 10 of the image memory 106 shown in FIG.
6a and the image signals stored in the second memory 106b are transferred to the second image signal RAM 132, and the RAM 132 performs data processing such as Fourier expansion.

Based on this processed data, the process proceeds to step S5 and the MC
The second focusing "direction detection" is performed by the PU 107, and if the "direction detection" is achieved, the process proceeds to step S6 above and "A" is detected.
The F operation signal is turned off, and if the focusing direction is not determined by this second focusing direction detection, the next step S7 is performed.
Proceed to.

The reason why the focusing direction is not determined even in the second focusing direction detection described above is often because the subject image has no contrast at all, so the aperture information and lens information are used.

The process returns to step S2 and "AF motor drive" is performed until the predetermined drive mmx of the AF motor determined by the distance information etc. is reached. Then, the first and second focusing "direction detection" is repeated, but when the AF motor drive reaches the predetermined drive QMx without "direction detection", the process jumps to step S16 and the AF motor is moved to the "predetermined direction". Stop at that position and end.

The first focusing “direction detection” in step S3 above;
When "direction detection" is performed during the second focusing "direction detection" in step S5, and as a result, "AF operation signal is turned off" in step S6, the process proceeds to step S24. In this step S24, the DCPU 105 The first memory 106a and the second memory 106 shown in FIG. 5 above
After deleting the image/i number saved in each of "b", the image signal saved in the first image signal RAM 131 is output to the video signal output circuit 110 to be displayed on the monitor, and the normal operation is resumed. Become.

In parallel with the operation of the DCPU 105 in step S24, the MCPU 107 performs the "AF" operation in step S8.
In step S32, the signal processing circuit 103 performs "power detection" at a specific spatial frequency associated with the movement of the photographing lens by the "AF motor drive". Then, as shown in FIGS. ), the mountain of power accompanying the movement of the lens position, that is, the in-focus point, is determined by "focus 1" indicating the first in-focus state in step S9.
If in-focus 1'' cannot be obtained, that is, if the power continues to increase as the photographing lens is moved in one direction, the in-focus point has not yet been reached, so step S24.S8.S described above
Return to step 32 and repeat these steps until "focus 1" is detected.

“Focus 1” in step S9 has poor focusing accuracy, but
At the same time as this is detected, the AF motor is stopped and the process proceeds to step SIO, where the "focusing operation signal is turned on". Then,
The DCPU 105 transfers the image signal at focus 1 from the first image signal RAM 131 to the first memory 106a in step S25, and outputs the contents of this first memory 106a to the video signal output circuit 110. Display on monitor.

The first memory 106a in this step S25 is a signal storage means as referred to in the claims, and the image signal outputted to the video signal output circuit 110 is stored in the step S25.
The flow of switching from the first image signal RAM 131 to the first memory 106a in step S25 is an electrical signal selection means.

Further, when proceeding to step Sll, the MCPU 107 drives the zoom motor 108 (see FIG. 2) to
The angle of view is expanded 3/2 times so that the center part 129 corresponding to 2/3 of the viewfinder field frame 128 shown in Figure (B) is captured in the entire image pickup circuit 102 (see Figure 2). . Normally, the main subject is almost included in 2/3 of the screen, so by further miniaturizing this part and performing power detection, focus detection with improved accuracy is attempted.

Step S12. S33 is the step S8゜S32 described above.
This is the same flow as explained in ``driving the AF motor'' and ``detecting power''. Proceeding to step 313, it is checked whether "focus 2°" indicating the second focusing state has been reached. According to the enlargement, the focusing accuracy is improved compared to "Focus 1" in step S9. Until "Focus 2" in step S1B is established, step S12.
S33 is repeated, and when the image is focused, the process proceeds to step S14.

The flow of "driving the AF motor" and "detecting power" in steps S12 and S33 after enlarging the angle of view by zooming in step Sll corresponds to the focus detection auxiliary means as referred to in the claims.

In step S14, the zoom motor is driven again to return the photographing angle of view to the state before step Sll, and then the process proceeds to step S15, where the focusing operation signal is turned off. Then, in step S26, the DCPU 105 returns the image signal output to the video signal output circuit 110 to the signal saved in the first image signal RAM 131 (see FIG. 5), and then ends the process.

That is, steps Sll, S12. Focus 2, which is more accurate than Focus 1°, is achieved by the focus detection assisting means provided by S33.
The gist of the present invention is that the in-focus point is detected with ", and the image signal at "in-focus 1" is displayed on the monitor during the focusing operation to detect this "in-focus 2". As a result, it is possible to improve the focusing accuracy at the focal point, and it is also possible to eliminate the discomfort felt by the photographer in the vicinity of the focal point.

As described above, in this embodiment, a smooth and highly accurate focus detection method is provided to the camera operator by digitally processing the signal and storing it in memory. This can also be achieved by storing it in memory. Furthermore, it goes without saying that a zoom lens drive for improving focusing accuracy may be inserted just before the imaging circuit.

[Effects of the Invention] As described above, according to the present invention, more accurate focusing can be achieved by having a signal storage element and a means for arbitrarily reading out signals, and further by driving a part of the system near the in-focus point. In addition to making focus detection possible, remarkable effects such as being able to detect a focus point without giving the user confusion such as overlap in the vicinity of the focus point are exhibited.

[Brief explanation of drawings]

FIG. 1 is a conceptual block diagram showing the camera system of the present invention from a functional perspective. FIG. 2 is a concrete block diagram of the camera system showing an embodiment of the present invention. ) is a block system diagram showing the detailed configuration of the signal processing circuit in FIG. 2 above, and FIG. 3(B) is a block diagram showing the detailed configuration of the signal processing circuit in FIG. The front view, Figures 4 (^) and (B) are
This is a characteristic diagram plotting the power against the lens position at a specific frequency determined by B-P-F in FIG. 3(A) above.
) are diagrams showing the high frequency mode, FIG. 5 is a block system diagram showing the detailed configuration of the DCPU and image memory in FIG. 2, and FIG.
Flowchart for explaining the operation in the figure. FIG. 7 is a layout diagram of the optical system in the camera when the present invention is applied to a single-lens reflex camera. 11... Imaging optical system (focus detection means) 1
2... Imaging probe (focus detection means) 13.
...... Drive control system (focus detection means) 14...
......Signal storage element (signal storage means) 15...
...... Readout system (selection means and control means) 16 ...... Signal processing system (focus detection means) 1
7...Monitoring means

Claims (2)

[Claims] (1) It has an image sensor that converts the subject light guided by the imaging optical system into an electrical signal, and the focusing direction of the imaging optical system is determined based on the change in the electrical signal caused by electrically driving the imaging optical system. and a focus detection means for detecting an in-focus point, the camera system comprising: a signal accumulation means for accumulating the electric signal when the imaging optical system reaches a first focus state. , a focus detection auxiliary means for performing a focus detection operation again after the signal accumulation means accumulates the electric signal, in order to obtain a second focus state that is more accurate than the first focus state; an electric signal selection means for selecting either the electric signal from the image sensor or the electric signal accumulated in the signal accumulation means; a monitor means for visualizing the selected electric signal; and the focus detection aid. A camera system comprising: control means for controlling the electric signal selection means to select the accumulated electric signal while the means is in operation. (2) The camera system according to claim 1, wherein the focus detection auxiliary means causes the focusing point detection operation to be performed again after moving a part of the imaging optical system to the long focal point side.