JPH03287106A - Automatic focus controller - Google Patents

Abstract

PURPOSE:To perform highly accurate focus control by controlling the movement of the position of a photographic lens so that the focus evaluation arithmetic value obtained by calculating the sum of the squares of differences between electric signals obtained by respective adjacent photoelectric converting elements is maximum. CONSTITUTION:An optical image of a subject which is obtained through the photographic lens 11 is made incident on a solid image pickup element (CDD) 12 and image and focus area data specified by a focus area specification part 18 is sent to a control part 15. The control part 15 evaluates the sum of the squares of the differences between the adjacent image signals as a contrast level and controls the movement of the lens so that the evaluated value becomes maximum. A stepping motor is used as a lens moving motor 16 and driven to rotate stepwise through a motor driving control part 17 according to the lens movement control signal from the control part 15. Consequently, highly accurate focus positioning is performed for any subject image.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a CCD (Charge Coupled
The present invention relates to an automatic focus control device installed in an electronic still camera or the like using a solid-state image sensor.

[Prior art and its problems] Conventionally, the AF (autofocus) method in general cameras has been an active method that uses infrared rays or ultrasonic waves reflected from the subject, or a photoelectric conversion element that converts the subject image into an electrical signal. A passive method is in use that converts this electrical signal and evaluates the state of the goldfish based on this electrical signal.

Among the AP methods described above, one of the most excellent methods in terms of focusing accuracy and number of parts per unit is a method in which a subject image obtained through an imaging lens is photoelectrically converted and evaluated.

Here, to evaluate the subject image by photoelectrically converting it, the obtained electric signal is converted to a signal corresponding to fine image contrast through an HPF (bypass filter), and the sum of the widths of the magnitudes of this image signal is summed. In addition, the optical image obtained through the imaging lens is made incident on the photoelectric conversion unit through another lens, and the peak position of electric signal generation in this photoelectric conversion unit and the pre-determined value of the photoelectric conversion unit are determined. There are methods that evaluate the deviation from a fixed focus position.

However, in the AF method that performs focus evaluation based on the photoelectric conversion signal passed through the HPF, it is necessary to variably set the cutoff frequency of the HPF depending on, for example, the fluctuation state of the contrast of the subject, and the high viscosity It is Tanashi who performs focus control.

In addition, in the AF method that evaluates the focus position at the photoelectric conversion unit from the imaging lens through the auxiliary lens, it is not possible to directly use the electrical signal corresponding to the entire subject image (the entire focal area) as the evaluation standard, so it is difficult to achieve high precision. Focus control cannot be performed.

[Purpose of the Invention] The present invention has been made in view of the above-mentioned problems, and it is possible to achieve highly accurate focus positioning for any subject image without bypassing the imaging electric signal or adding mechanical parts. An object of the present invention is to provide an automatic focus control device that can perform the following functions.

[Summary of the Invention] In other words, the automatic focus control device according to the present invention includes an imaging lens, and a plurality of lenses that receive at least a part of an optical image of a subject through the imaging lens and generate an electric signal according to the amount of received light. a photoelectric conversion means having a photoelectric conversion element; a focus evaluation calculation means for calculating the sum of the squares of the differences in the magnitudes of electric signals obtained by each adjacent photoelectric conversion element of the photoelectric conversion means; and a focus position movement control means for controlling the movement of the position of the imaging lens so that the focus evaluation calculation value calculated by the means becomes a maximum value.

[Embodiments of the invention] An embodiment of the present invention will be described below with reference to the drawings.

Figure 1 shows the configuration of an electronic still camera equipped with an AF function. In the figure, 11 is an imaging lens;
An optical image of the subject obtained through the imaging lens 11 is incident on a solid-state imaging device (CCD) 12 . This solid-state image sensor 12 includes a large number of photoelectric conversion elements (pixels) arranged in a plane in the matrix direction, and captures an incident optical image for each pixel as a charge corresponding to the amount of incident light. The image signal of the subject image accumulated in the element 12 is serially output for each pixel and is converted into a binary value through the A/D converter 13. This A/D converter 3 is
The analog image signal for each pixel output from the solid-state image sensor 12 is binarized and converted into a digital image signal, for example, white "]"/black "O". The black binarized digital image signal is sequentially transferred to the image data memory 4 and stored as image data corresponding to the subject. Writing and reading address designation control for the image data memory 4 is performed by a control section 15, and a read data transfer bus 1.4a is connected to this control section 15.

On the other hand, the imaging lens 11 is moved by a lens moving motor 16 toward an infinite focal point or toward the farthest point (the closest focusing position).
For example, a step motor is used, and the control section 1
5 through the motor drive control section 17 in response to a lens movement control signal from 5.

The control unit 15 also includes a focus area designation unit 18.
is connected. This focus area designation unit 18 designates an arbitrary subject area as the focus area when the operator looks through the finder and captures the subject, and the focus area data designated by this focus area designation unit 18 is as described above. It is sent to the control section 15. That is, when the control section 15 is given focus area data from the focus area specifying section 18, the control section 15 takes in the imaging data corresponding to the focus area from the image data memory 4, and the imaging data within the focus area is It outputs a lens movement control signal to the motor drive control section 17 so as to achieve the goldfish state, and this control section 15 includes a calculation/comparison section 1 for controlling the goldfish.
1 and 2 and 2 are connected to each other.

That is, the control unit 15 evaluates the sum of the squares of the differences between adjacent image signals as a contrast level based on image signals from a large number of pixels corresponding to the focus area, and adjusts the contrast level so that this evaluation value is maximized. This is to control the lens movement, and the contrast level evaluation calculation process and the comparison judgment process of the maximum evaluation value are performed by the above calculation and calculation.
This is carried out by the comparison section 19, and each evaluation calculation data is written into the data memory 20 and its maximum value storage section 20a. The maximum value storage section 20a stores the maximum evaluation calculation data of the contrast level as well as the lens position at the time of the evaluation calculation as step data for the lens moving motor 16.

Here, the number of pixels in the focus area is (nXm),
Assuming that each pixel position is P,), the above-mentioned contrast level evaluation calculation formula is expressed by the following formula (1).

Next, the AF function of the electronic still camera according to the second structure will be explained.

FIG. 2 is a flowchart showing the AF (autofocus) process of this electronic still camera. When the operator looks through the viewfinder, captures the subject, and specifies the focus area by pressing the release switch (not shown), for example, the specified focus Focus area data corresponding to the area is sent from the focus area specifying section 18 to the control section 15. Then, first, the control unit 15 controls the motor drive 1. The imaging lens 11 is controlled to move to the initial position (nearest and distant position) by the lens movement control signal for the shrine 17 (step Sl). Then, when the imaging data of the subject image at this lens initial position is stored in the double image data memory 14 from the solid-state imaging device 12 through the A/D converter 13, an image corresponding to the pre-designated focus area is generated. The data is read out to the control unit 15 (steps S2 and S3). Then, the control unit 15 sends the image signal for each pixel corresponding to the specified focus area to the calculation/comparison unit 9, and calculates the sum of the squares of the signal level differences between adjacent pixels as the contrast level of the focus area. The evaluation data calculated by the calculation/comparison unit 19 is transferred from the control unit 15 to the data memory 20 and written (steps S4 and S5). .

Here, the calculation/comparison unit 19 judges whether the evaluation data calculated this time is the maximum value by comparing it with the evaluation data calculated last time. Since there is no evaluation data for ``maximum evaluation value''
A determination is made that the maximum evaluation data and the corresponding lens position are written into the maximum value storage section 20a (steps S6 and S7). At this time, the control unit 15 determines whether the lens position written in the maximum value storage unit 20a has reached the infinity step. position), so the determination is "No", and the lens position is moved toward infinity by one step in the lens movement motor 16 according to the lens movement control signal from the control unit 15 (steps S8 and S9).
. Thereafter, the process 1 determination in steps S2 to S9 is repeatedly executed, and as the lens position of the imaging lens 11 is sequentially moved one step at a time in the infinity direction, the maximum of the evaluation data indicating the contrast level of the focus area is In the state where the value is updated, “No” in step S6;
In other words, if it is determined that the value of the evaluation data at the current lens position has become lower than the maximum evaluation data value (in this case, the evaluation data at the previous lens position), the difference in the drop in the evaluation data is less than the predetermined value. It is determined whether or not (steps S10 and S11). If "Yes" in this step Sll, that is, it is determined that the downward trend of the evaluation data at the current lens position with respect to the maximum evaluation data is less than a predetermined value, the lens position at this time has not reached the infinity step. Only in this case, the process returns to step S9 and further executes the one-step movement process of the imaging lens 11 and its evaluation calculation process (step 512).
).

] O On the other hand, in the above step Sll, rNoJ, that is,
It is determined that the value of the evaluation data corresponding to the current lens position has fallen by a predetermined value or more from the maximum evaluation data, and the imaging lens 1
When it becomes certain that the movement position of image pickup lens 11 has exceeded the in-focus position and moved to the infinity side, or rYesJ in step S12, that is, the movement position of the imaging lens 11 reaches the infinity step, the maximum value is stored. The imaging lens 11 is controlled to be moved to a lens position that is one step closer to infinity than the lens position corresponding to the maximum evaluation data stored in the section 20a, and the lens movement step width associated with subsequent lens movement processing is, for example, 10 minutes. 1, and its moving direction is switched to the near-to-far direction (steps 813, 514).

Then, the data stored in the maximum value storage section 20a is cleared (step 515).

Next, in steps 816 to 32B, the lens movement control in steps of 10 minutes in the far direction and the maximum value writing process of the evaluation calculation value are performed in steps S2 to S9.
Process 1 is executed repeatedly in the same way as the process 1 judgment.

That is, first, when the imaging data of the subject image at the lens position whose movement has been controlled in step 81B is stored in the image data memory 14 from the solid-state imaging device 12 through the A/D converter 13, a focus area specified in advance is stored. The image data corresponding to is read out to the control unit 15 (step S16, 517). Then, the control unit 15 sends the image signal for each pixel corresponding to the specified focus area to one calculation/comparison unit, and calculates the sum of the squares of the signal level differences between adjacent pixels as the contrast level of the focus area. The evaluation data calculated by the calculation/comparison unit 19 is transferred from the control unit 15 to the data memory 20 and written (steps 318, 519).
.

Here, the calculation/comparison unit 1 determines whether or not the evaluation data calculated this time is the maximum value by comparing it with the evaluation data calculated last time. At the time of the first calculation associated with ]2, since there is no evaluation data of the previous calculation, it is determined that the evaluation value is the maximum, and the maximum evaluation data and the corresponding lens position are written into the maximum value storage section 20a. (Step S20, 521).

At this time, the control unit] 5 determines whether the lens position written in the maximum value storage unit 20a has recently reached the far step, and in this case, the lens position has not yet reached the in-focus position. Since it is on the infinity side beyond the limit, the answer is "No", and the lens position is moved toward the far side by 1/10th step of the lens moving motor 16 according to the lens movement control signal from the control unit 15 (step S 22.823
).

Thereafter, the process 2 determination of steps 816 to 323 is repeatedly executed, and as the lens position of the imaging lens 11 is sequentially moved in the near-to-far direction by 1/10 steps,
In a state where the maximum value of the evaluation data indicating the contrast level of the focus area is updated, if "No" is answered in step S20, that is, the value of the evaluation data at the current lens position is the value of the maximum evaluation data (in this case, the value of the evaluation data at the current lens position is the same as that of the previous lens). If it is determined that the evaluation data has become lower than the evaluation data (evaluation data at position 3), it is determined whether the drop difference in the evaluation data is less than a predetermined value (step S24, 525). If "Yes" in this step S25, that is, it is determined that the decrease in the evaluation data at the current lens position with respect to the maximum evaluation data is less than a predetermined value, the lens position at this time has not recently reached the far step. Only in this case, the process returns to step 82B, and the process of moving the imaging lens 11 by one-tenth step and its evaluation calculation process are executed (step 522).

On the other hand, in step S25, rNoJ, that is,
When the lens was recently moved in 1/10 steps in the far direction, it was determined that the value of the evaluation data corresponding to the current lens position had fallen by a predetermined value or more from the maximum evaluation data, and the moving position of the imaging lens 11 was brought into focus. When it becomes certain that the imaging lens 11 has crossed the position and has been moved to the far side again, the imaging lens 11 is controlled to move to the lens position corresponding to the maximum evaluation data stored in the maximum value storage section 20a (step 526). As a result, the imaging lens 11 is moved to a lens position where the maximum contrast level can be obtained in the focus area, and highly accurate focusing control can be performed.

Also, in steps 82 to S9 above, the imaging lens]
As the lens position No. 1 is sequentially moved one step at a time toward infinity, the maximum value of the evaluation data indicating the contrast level of the focus area is updated. When the position reaches the infinity step, the imaging lens 11 is moved to a position one step before the infinity step (step 527). Then, the lens movement width is changed to, for example, 1/10 steps, and steps 315 to 5
In the process 1 judgment of 2B, 1/10 step movement control of the imaging lens 11 during one step before infinity and its evaluation calculation control are executed (step 528).

After this, in step S25, it is determined that the value of the evaluation data corresponding to the current lens position has fallen by a predetermined value or more from the maximum evaluation data in rNoJ, that is, in lens mobility 5 in 1/10 steps toward infinity. and it is certain that the moving position of the imaging lens 11 has exceeded the goldfish position, or "Yes" is determined in step S22.
That is, when the moving position of the imaging lens 11 reaches the infinite step, the imaging lens 11 is controlled to move to the lens position corresponding to the maximum evaluation data stored in the maximum value storage section 20a (step 526). In this case as well, the imaging lens 11 is moved to a lens position where the maximum contrast I/last level can be obtained in the focus area, and highly accurate focusing control can be performed.

On the other hand, if the lens position corresponding to the maximum evaluation data written in the maximum value storage section 20a is the closest position to the initial setting position when executing the process 2 judgment of steps 81 to S12, After the lens is moved by one step toward infinity in step 813, the lens movement direction and its movement width are switched in step 33.4, and in steps 815 to 682B, the imaging lens 11 is moved in one step to the nearest distance. 1/10 step movement control and its evaluation calculation control are executed. In this case as well, the maximum evaluation data and its lens position are found in step S22 or S25 as described above, and the imaging lens 11 is moved and set in step S26 to the lens position where the maximum contrast level is obtained in the focus area. become.

Therefore, according to the electronic still camera equipped with the AF function configured as described above, based on image signals from a large number of pixels corresponding to the focus area, the sum of the squares of the differences between adjacent image signals is evaluated as the contrast level, Since the lens movement control is performed so that this evaluation value is maximized, it is possible to always perform stable and highly accurate focus positioning for all subject images.

In the above embodiment, the configuration was described for obtaining a monochrome image signal, but when obtaining a color image signal, the same 7 evaluations as above were performed based on the luminance signal obtained from the color CCD through the image signal processing circuit. All you have to do is perform arithmetic processing.

[Effects of the Invention] As described above, the present invention includes an imaging lens and a plurality of photoelectrons that receive at least part of an optical image of a subject through the imaging lens and generate electrical signals according to the amount of received light. A photoelectric conversion means having a conversion element, a focus evaluation calculation means for calculating the sum of the squares of differences in the magnitudes of electric signals obtained by each adjacent photoelectric conversion element of the photoelectric conversion means, and a focus evaluation calculation means. Since it is configured to include a focus position movement control means for controlling the movement of the position of the imaging lens so that the calculated focus evaluation calculation value becomes the maximum value, bypass processing of the imaging electric signal and addition of mechanical parts are performed. Therefore, it is possible to provide an automatic focus control device that can perform highly accurate focus positioning for any subject image.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an electronic still camera equipped with an AF function according to an embodiment of the automatic focus control device of the present invention, and FIG. 2 is a flowchart showing AF processing by the electronic still 8 camera. 11... Imaging lens, 12... Solid-state imaging device, 13
... A/D converter, 14... Image data memory, 15... Control unit, 16... Lens movement motor, 1
7... Motor drive control unit, 18... Focus area designation unit, 19... Calculation/comparison unit, 2o... Data memory, 20a... Maximum value storage unit.

Claims (1)

[Scope of Claims] An imaging lens; a photoelectric conversion means having a plurality of photoelectric conversion elements that receive at least a part of an optical image of a subject through the imaging lens and generate electrical signals according to the amount of received light; a focus evaluation calculation means for calculating the sum of the squares of the differences in the magnitudes of electric signals obtained by each adjacent photoelectric conversion element of the photoelectric conversion means; an automatic focus control device comprising: a focus position movement control means for controlling the movement of the position of the imaging lens so that the focus position of the image pickup lens is adjusted to the desired value;