JPS5984210A - Method and device for adjusting automatic focus - Google Patents

Abstract

PURPOSE:To adjust a focus in a short time with high precision through simple constitution by lowering the clipping level for the differentiation output of a gradational picture and making a step interval less as the clipping level is greater. CONSTITUTION:The gradational picture 1 is photodetected by a photodetector through an optical system 2, a picture signal is inputted to a differentiation circuit 4 and a clipping circuit 5, and clipped outputs are summed up by an adding circuit 6. A control circuit 10 selects the lowest clipping level among three clipping levels firstly and then selects a higher level every time when a detection signal arrives from a comparing circuit 9. The optical system 2 is moved stepwise through a driving control circuit 11 and a driving mechanism 12 at step intervals which become less as the clipping level becomes greater. The sum value, on the other hand, is compared with a threshold value by the comparing circuit 9 and sent to a detection signal control circuit 9 when greater than the threshold value. Thus, the focus adjustment is made in a short time with high precision through the simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an automatic focus adjustment method and an adjustment device for automatically adjusting the focus of an optical system with high precision.

[Technical background of the invention and its problems]

Conventionally, as a method for automatically adjusting the focal length 'Nf of an optical system used in an industrial television camera or a camera using a solid-state image sensor, etc., for example, #light image information imaged through a wander adjustment optical system is adjacent to each other. Detects the density difference between pixels,
Move the optical system to be adjusted so that this density difference is maximized (
There are also known methods that perform Fourier transform on the captured images I and III to obtain high frequency components, and perform focus adjustment according to the level of the high frequency components.

However, these methods (1) When detecting the density difference between adjacent pixels.

It is easily affected by noise, etc., and cannot perform high-precision n)M adjustment.

(11) When performing Fourier transform, because the calculation of Fourier transform is complicated? J., it takes a lot of time to adjust, and the configuration of the device becomes complicated, as the configuration of the filter for extracting high frequency components is complicated.

There are drawbacks such as.

On the other hand, as another method for automatically adjusting the focus, each time the optical axis position of the optical system to be adjusted is moved step by step at regular intervals, high-frequency components and low-frequency components of the captured image information are extracted using filters. There is a system that calculates the added value and sets the optical axis position of the optical system to be adjusted where the added value is the maximum as the focus matching position.

However, in such conventional methods, it is necessary to set the step movement interval of the optical system to be adjusted short in order to accurately detect the focus alignment position, and when the step movement interval is set short in this way, the focus When the amount of deviation is large, it takes a long time to detect the focus matching position, which has the disadvantage that the adjustment time becomes significantly longer.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic focus adjustment method and an adjustment device thereof, which can perform highly accurate adjustment in a short time even when the amount of defocus is large, has high adjustment ability, and can be realized with a simple configuration. do.

[Summary of the invention]

In order to achieve the above object, the present invention sets a plurality of clip levels different from each other for the differential output of the gray scale image information received through the harmonic 5-tuning optical system, and sets a plurality of clip levels that are different from each other, and The step movement interval is set to become smaller as each clip level increases, and each time the optical system to be adjusted is moved step by step, a grayscale image is received and the differential output of the received light information is clipped according to the clip level. The operation of determining the output added value is repeated by sequentially changing the clip level from a small level to a large level every time the added value exceeds a predetermined value predetermined for each clip level,
The position where the added value is maximum at the maximum clip level is detected and this is set as the focus matching position.

[Embodiments of the invention]

FIG. 1 is a block diagram of an automatic focus adjustment device according to an embodiment of the present invention.

This device transfers a grayscale image 1 for focus adjustment to an optical system 2 to be adjusted.
The received light image signal 6- is received by a light receiver 3 via a differential circuit 4, and then clipped by a clip circuit 5 and guided to an adder circuit 6. This adding circuit 6 adds the clip output of the clipping circuit 5 outside the entire area of the grayscale image. In the adjustment device of this embodiment, the addition result of the addition circuit 6 is selectively guided to the maximum value detection circuit 8 or the comparison circuit 9 through the selection circuit 7. The maximum value detection circuit 8 compares a register 81 that temporarily stores the addition result each time the addition result is obtained, and the value stored in this register 81 and the addition value derived from the selection circuit 7 at the next timing. a comparator 82 which outputs a maximum value detection signal when the added value from the selection circuit 7 becomes smaller than the stored value in the register 81;
It is composed of. On the other hand, the comparison circuit 9 sets the sum value of the threshold setting circuit 9 which selectively generates a plurality of threshold values and the addition circuit 6 supplied by the selection circuit 7 using the threshold setting circuit 91. a comparator 92 that compares it with a set threshold and issues a detection signal when this threshold is exceeded;
It is composed of.

The adjustment device of this embodiment also includes a control circuit 10 that controls a series of adjustment operations. These 10 control circuits perform the following 11 operations. The control operation is as follows: (1) Three types of clip levels with different levels can be set in the clip circuit 5, and at the start of adjustment, the smallest clip level is first set among the three types of clip levels, and thereafter the comparison circuit 5 A control operation in which the clip level set in the clip circuit 5 is sequentially changed to a higher level each time a detection signal arrives from the clip circuit 5.

(ii> Different step intervals are set for each clip level set in (i), and the step feed signal for moving the 11υ adjustment optical system 2 in steps at these step intervals is sent to the drive control circuit 1 at a constant cycle. control to drive the drive mechanism 12 and move the optical system 2 to be adjusted step by step.By the way, the step interval set for each clip level is such that the force is reduced as the clip level increases. determined.

(3) A predetermined threshold level is set for each clip level set in (1), and information indicating these threshold levels (threshold information) is sent to the threshold setting circuit 91 of the comparison circuit 9. A control operation for specifying a threshold value generated by this threshold setting circuit 91.

(IV) Only when the clip level set in the clip circuit 5 is the maximum, the gate circuit 13 is opened and the addition end signal generated in the adder circuit 6 is supplied to the selection circuit 7, whereby the selection circuit 7 is set to the maximum level. Control operation to switch to the value detection circuit 8 side and supply the addition output to the maximum value detection circuit 8. Note that while the gate circuit 13 is closed, that is, when the clip level set in the clip circuit 5 is between the minimum level and the intermediate level, the selection circuit 7 selects the comparator circuit 911!
1, and the addition output is led to the comparator circuit 9.

It is.

9- Note that the drive control circuit 11 stops the operation of the moving mechanism 12 at 1V when the detection signal is generated from the maximum value detection circuit 8, or stops the operation after one step interval has elapsed. At this time, the judgment as to whether to stop or go backward is to find the difference between the added output value at 1G where the maximum value is detected and the added output value at the previous step position.
If the difference is larger than a predetermined amount, it is caused to move back, and if it is smaller, it is caused to stop at the same position. In the case of a roundabout, it is also possible to set the step interval small and set the backtracking amount in small increments, depending on the value of the above-mentioned difference. This can be easily achieved by using, for example, a step motor as the drive source of the drive mechanism.

Next, the operation of the apparatus configured as above will be explained according to the adjustment procedure.

Note that FIG. 2 is a diagram showing the main signal waveforms of the circuit, and FIG.
The figure shows the addition output for the focal position shift amount of the optical system to be adjusted, where ■, (P), and θ are the clip levels CLI, CL2, . 10 is a length curve corresponding to CL3. First, the drive mechanism 12 is set in the optical system 2 to be adjusted, and in this state, a start signal (not shown) is given to the control circuit 10.

Then, first, the control circuit 10 sends three types of clip levels to the clip circuit 5 (CLI, CL2 .
CL3 ), the minimum clip level CLI is set, and a predetermined threshold value (Ll in FIG. 3) corresponding to the clip level CLI is set in the threshold setting circuit 9 of the comparator circuit 9. Ru. Then, from the control circuit 10 to the drive control circuit 11, the optical system 2 to be adjusted is
A step sending signal is supplied at a predetermined timing to move the step in steps.

Then, the drive mechanism 12 moves the adjusted optical system 2 to the third position.
As shown in the figure, the image is moved stepwise from the initial position P to A and B at relatively large step intervals Wl, and at each of these positions A and B, a grayscale image is transmitted to the light receiver 3 via the optical system 2 to be adjusted. 1 of light is received. The received light IIf+I image signal obtained by this light reception is differentiated, for example, as shown in FIG. 2 BS, and then the absolute value is taken as shown in FIG. 2 C8, and then clipped by the clipping circuit 5 according to the clip level CLI. Ru. Then, the clipped outputs are added by an adder circuit 6, and the added output is sent by a selector circuit 7 to a comparator circuit 9, where it is compared with a threshold value L1. As a result of the comparison, if the value of the addition output is equal to or greater than the threshold value at B in FIG. 3, a detection signal is generated from the comparator circuit 9 at this point, and the control The circuit 1o changes the clip level of the clip circuit 5 from CLI to CL2. At the same time, the threshold level is changed to the level L2 corresponding to the clip level CL2, and the step interval W2 (W2 (W
In l), a step feed signal is supplied to move the optical system 2 to be adjusted in steps.

Therefore, the adjusted optical system 2 now has a step interval W
2 each at smaller intervals than W1, for example in Fig. 3 C and D.
, E, and move to each of these positions C, D,
At every E, the light receiver 3 receives a grayscale image.

The received light image signal AS obtained by the light receiver 3 is
As in the case of the positions A and H, the absolute values are taken by the differentiating circuit 4, and then the absolute values are taken by the clipping circuit 5 according to the clipping level CL2 as shown in FIG. 2DS2.
The signals are clipped as shown in FIG. 2 and added by an adding circuit 6. Therefore, the added value obtained in this way has more image noise and light receiver 3 than in the case of the clip level CLI.
This reduces unstable factors such as uneven sensitivity and uneven illumination. Then, the added value is compared with a threshold level L2 in a comparator circuit 9, and when the added value exceeds the threshold level L2, a detection signal is generated from the comparator circuit 9. When this detection signal is generated, the control circuit 10 causes the clip circuit 5 to
The clip level 1cL2 is changed to the highest CL3, the date circuit 13 is opened, and the selection circuit 7 is switched to the maximum value detection circuit 8 side. 13- A step feed signal for moving the adjusted optical system 2 in steps at a step interval W3 (W3 (W2 (Wl)) corresponding to the clip level CL3 is supplied to the drive control circuit 1 at regular intervals. .Then, the optical system 2 to be adjusted is moved at very short intervals, for example, in Fig. 3 F, G, H,
Step movement as I, and each of these positions F,
G, H.

The differential output C8 of the received light image signal obtained every time (2) is clipped by the clipping circuit 5 according to the largest lip level CL3 as shown in FIG. 2 DS3, and added by the adding circuit 6. Therefore, the added value obtained in this manner has significantly fewer unstable factors than the clip levels CLI and CL2. The added value obtained in this way is then sent to the selection circuit 7 by the thickest value detection circuit 8.
The maximum value is detected here. As a result, if there is a maximum value between positions H and I as shown in FIG. 3, for example, a maximum value detection signal is generated at position I and supplied to the drive control circuit 11. As a result, when the drive 14-control circuit 11 receives the maximum value detection signal,
The difference between the added value at the position ■ inputted via a route not shown and the added value at the position H one step before is calculated, and based on this difference, it is determined whether to stop the adjusted optical system 2 by position machining or return it to the position H. The position after the completion of the operation is determined as the focus matching position of the optical system 2 to be adjusted.

As described above, in this embodiment, in a range where the amount of focal position shift at the start of adjustment is relatively large, the clip level for the differential output is set to a small value CL1, and the step movement interval of the optical system to be adjusted 2 is set to be large. Then, each time the added value of the clip output exceeds a predetermined threshold, the clip level is set to CL2. As I gradually changed the value to CL3 and made the step movement interval finer,
In a range where the focus position shift amount is large, the focus alignment position can be approached in a short time with large steps, and in a range close to the focus alignment position, highly accurate alignment can be performed with extremely few unstable elements. Therefore, highly accurate adjustment is possible in a short time. First, the circuit configuration has the advantage of being relatively simple compared to conventional circuits.

Note that the present invention is not limited to the above embodiments.

For example, the clip level is not limited to three levels, but may be two levels, four levels or more, and the step movement interval at that time may also be set as appropriate according to requests. However, the control circuit may be constructed using a microcomputer, and other configurations of the maximum value detection circuit, the comparison circuit, and the drive section of the optical system to be adjusted may be within the scope of the present invention. It can be implemented with various modifications.

〔Effect of the invention〕

As described in detail above, the present invention sets the clip level of the differential output small at the start of adjustment and sets the step interval large to shorten the adjustment time, and increases the clip level as the adjustment progresses to eliminate unstable factors. In addition, the clip level change, the step interval change, and the threshold value change are synchronized with each other and controlled by a control unit.

Therefore, according to the present invention, even when the amount of defocus is large, highly accurate adjustment can be performed in a short time.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram of an automatic focus adjustment device according to an embodiment of the present invention, FIGS. 2 and 3 are used to explain the operation of the device shown in FIG. 1, and FIG. The waveform diagram in FIG. 3 is a characteristic diagram showing changes in the addition force with respect to the amount of defocus. 2... Optical system to be adjusted, 4... Differentiating circuit, 5... Clipping circuit, 6... Adding circuit, 8... Maximum value detection circuit, 9... Comparing circuit. 17-112Figure 3Ja

Claims (2)

[Claims] (1) An automatic system that receives a grayscale image through the optical system to be adjusted each time the optical axis position of the optical system to be adjusted is moved step by step, and detects the focus alignment position of the optical system to be adjusted from the differential output of the received light information. In the focus adjustment method, a plurality of mutually different clip levels are set for the differential output, and step movement intervals of the adjusted optical system are determined to become smaller as each of the clip levels increases, and the adjusted optical system is adjusted. Each time the step is moved, light is received, the differential output of the received light information is clipped according to the clip level, and the added value of the clipped output is calculated until the added value exceeds a predetermined value predetermined for each clip level. For each novel, the clip level is changed sequentially from a small level to a large level and this is repeated, and in the case of a maximum clip of 1 novel, the position where the added value is maximum is detected and this is set as the focus alignment position. An automatic focus adjustment method featuring: (2) Every time the optical axis position of the optical system to be adjusted is moved step by step by the drive unit, a grayscale image is received by the light receiving means via the optical system to be adjusted, and this received light output is differentiated by a differentiating circuit. In an automatic focus adjustment device that detects a focus alignment position of an optical system to be adjusted from an output, a clip circuit that clips the differential output from the differential circuit, and one of a plurality of clip levels is selected for the clip circuit. a threshold information control circuit that generates predetermined threshold information for each clip level set by the clip control circuit; and a threshold information control circuit that generates predetermined threshold information for each clip level set by the clip control circuit; A step control signal is generated which is determined to reduce the step movement interval of the optical system to be adjusted as the clip l/pel increases, and this signal drives the drive unit to move the optical system to be adjusted in steps. a step control circuit for adding the clipped outputs of the above-mentioned rip circuit; a comparison circuit that issues a clip level change signal when the value exceeds the threshold value and changes the clip level set by the clip control circuit to a thicker one; and a maximum value detection circuit that operates only when the addition output is set, detects the maximum value of the addition output output from the addition circuit, and causes the drive unit to stop the adjusted optical system at the position where the maximum value is detected. An automatic focus adjustment device characterized by: