JPS5841486B2 - Object image clarity detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting the sharpness of an object image suitable for application to a focusing system of an optical system in an optical device such as a camera.

For example, when trying to control the focus adjustment of the photographing optical system of an optical device such as a camera by photoelectrically detecting changes in the sharpness of the object image, an object image sharpness detection method is used. occupies an extremely large weight.

That is, the accuracy of the focus adjustment of the optical system is largely influenced by the accuracy of detecting image clarity.

By the way, various object image sharpness detection methods and devices applied to eye movement or semi-automatic focus adjustment devices of conventional cameras etc. each have two functions.

Although there are differences in effectiveness, in principle, the illuminance distribution on the image plane of the object image due to the luminous flux from the object is converted into an electrical signal by a photoelectric conversion means, and this is processed appropriately to make the object image clearer. This is to obtain information corresponding to the degree.

However, with these conventional methods, signals are processed in analog quantities, which complicates the series of information processing processes, making it difficult to process signals quickly, and it is not possible to obtain highly accurate detection results. This method has many drawbacks, such as the inability to adjust the focus, and it is very difficult to apply it to a focus adjustment method for optical equipment.

In view of the above-mentioned circumstances, the present invention focuses on the common essential elements in various conventional methods for detecting object image sharpness, fundamentally reforming their configurations, and making the present invention a central feature of modern technology. The purpose of this project is to provide a new object image sharpness detection method that can eliminate the above-mentioned drawbacks of conventional methods by introducing information processing technology using a computer and its peripheral technology. The feature is that a photoelectric conversion means consisting of a large number of photoelectric element parts is arranged at or near the imaging plane of an optical system that forms an image of an object, and the object imaged on the photoelectric conversion means is arranged. A photoelectric output signal from each of the photoelectric elements generated in response to the illuminance of the image is converted into a time-series signal by a signal time-series converter, and this is further converted into a digital signal via an analog-to-digital converter. After that, this was input to a signal processing means that employs an autocorrelation function as a function for evaluating the sharpness of the object image, and an electrical signal corresponding to the sharpness of the object image was obtained. .

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the basic structure of a specific example of the object image sharpness detection method according to the present invention.

In the figure, reference numeral 1 indicates an object such as a person to be detected due to the sharpness of its image.

Reference numeral 2 denotes an optical system that is provided to form an image of the object 1 and is movable along its optical axis.

Reference numeral 3 denotes a photoelectric conversion means consisting of a large number of independent photoelectric element portions arranged in alignment at or near the image forming plane of the optical system 2 (the detailed structure thereof will be explained in FIG. 2).

As is clear from the configuration described above, the image of the object 1 is formed on the photosensitive surface of the photoelectric conversion means 3 via the optical system 2, and the illuminance at each point of the image is converted into a photoelectric output of each photoelectric element portion. be done.

Further, as the optical system 2 moves along the optical axis direction, the sharpness of the object image on the photoelectric conversion means 3 changes, and the illuminance distribution of the image that changes accordingly is detected as a change in the photoelectric output moment by moment.

Reference numeral 4 denotes a time-series means, such as a ring counter, for converting the photoelectric outputs of the large number of photoelectric element portions obtained in this manner into time-series signals in a predetermined order.

A specific example of the time series forming means 4 will be explained with reference to FIG.

Generally, the time-series signal from the time-series forming means 4 is amplified because the object image illuminance on the photosensitive surface of the photoelectric conversion means 3 is extremely low, such as 101 ux or less, and the obtained photoelectric output is weak. The signal is amplified to an appropriate level via the converter 5, and then input to the analog-to-digital conversion circuit 6, where it is converted into a digital signal and then used as a signal processing means for converting it into an electrical output corresponding to the object image clarity. The signal is input to a small electronic computer 7 and converted into an electrical output corresponding to the object image definition, that is, image definition information.

The small electronic computer T is provided with programming capable of calculating a function for evaluating object image clarity, which will be described in detail later.
Digital time-series input, that is, illuminance at each point of the object image, is used as a variable to calculate the object image sharpness information corresponding to the adjustment state of the optical system 2 at that time. is obtained.

The function for evaluating object image clarity as described above will be referred to as an evaluation function hereinafter.

The evaluation function is schematically shown in block 8 indicated by a broken line in the figure.

Since the output of the small computer 7 is a digital signal,
In order to facilitate subsequent processing, the image sharpness signal is converted back into an analog signal by the digital-to-analog conversion circuit 9 and outputs a control signal for use in focusing the optical system based on the image sharpness information. The signal is input to the optical information processing circuit 10 and converted into a signal output that can be supplied to the display means 11 or the servo motor 12 as an adjustment means for driving and controlling the optical system 2.

Upon receiving this signal output, the servo motor 12 drives and controls the optical system 2 along its optical axis using a known method.

As described above, the optical system 2 is adjusted so that the sharpness of the object image formed on the photoelectric conversion means 3 is maximized.

Therefore, if the photographing optical system 13 such as a camera is linked to the optical system 2 at this time so that its drive can be controlled by the motor 12, automatic focus adjustment of the photographing optical system can be easily achieved.

It goes without saying that the optical system 2 may also serve as the photographing optical system 13.

FIG. 2 is a diagram illustrating the form of a large number of photoelectric element portions arranged in an array suitable for use in the present invention, and FIG. A schematic configuration example of means 3 is shown.

Therefore, as the photoelectric conversion means 3, for example, a photodiode array (MOS image sensor), CCD (Char
An image sensor such as a ge CoupleaDevice (charge coupled device) may be used.

Note that the shape of the photoelectric element portion 14 and the arrangement thereof are not limited to this example, and may be circular or the like.

In the same figure, c and d are electrical wiring diagrams of each element part when a photoconductive element, a photodiode, and a solar cell are respectively used as the photoelectric element part 14, and these are connected with one pole in common, The other pole is left open so that the individual outputs can be detected.

FIG. 3 is a diagram showing an example of an embodiment of the above-mentioned signal time series generation means 4, and includes an oscillator 15 and a driver 1 for oscillating signals of appropriate frequencies from each photoelectric element portion constituting the photoelectric conversion means 3.
6 and the ring counter 17 to sequentially switch the photoelectric output of each photoelectric element portion to the output terminal 18.
It is possible to input the signal to the next stage circuit (not shown).

Arrows 19 in the figure schematically show that signals from the ring counter 17 are sent to each photoelectric element portion 14 in correspondence with each other.

FIG. 4 is a diagram for explaining the detection principle of the object image sharpness detection method of the present invention.
2, ..., n, where n is the total number of photoelectric element parts 14), the value Pj after analog-to-digital conversion of the photoelectric output of the photoelectric element part is expressed at each point of the object image by taking j on the horizontal axis. This figure shows an electrical signal corresponding to the illuminance distribution.

However, the signal distribution is shown in analog form to make the diagram easier to read.

In the figure, a signal indicated by a broken line represents a signal which has been delayed k with respect to a signal indicated by a solid line.

In other words, there is a phase difference K between the two signals.

This is provided by a delay circuit in the calculation circuit, which will be described later.

The delayed signal obtained in this manner will be expressed as Pj -.

The output of the delay circuit, which is output simultaneously with the signal Pj that is not subject to the delay of the photoelectric output of the j-th photoelectric element portion, is Pj.
− becomes.

The autocorrelation function Ak is expressed as follows using the above symbols.

However, the subscript indicates the delay. A graph of such an autocorrelation function Ak is shown in the same figure.

In the same figure, the horizontal axis shows k and the vertical axis shows Ak.As is clear from the above, since it is normalized, A when =o
The value of k is constant.

When the object image clarity is low, a value indicated by Akout in the figure is obtained, and as the image clarity increases, the value of Ak decreases to Akin.

This is based on the reasons stated earlier.

Therefore, if the value of Ak is calculated every moment and the optical system 2 is adjusted to the point where the value is minimized, a correct focus adjustment feeling can be obtained.

FIG. 5 shows an embodiment of a calculation circuit provided in the small electronic computer T to calculate the autocorrelation functions A and k in the above equations.

In the figure, numerals 6 and 9 are the aforementioned analog-to-digital conversion circuit and digital-to-analog conversion circuit, respectively, and 7, indicated by a broken line frame, is a small-sized computer.

The output of the analog-digital conversion circuit 6 is Pj,
This is branched into three systems, one of which is directly input to the multiplier 21, and the other system is input to the delay circuit 20 and receives a delay k to become Pj-.

The multiplier 21 multiplies Pj and Pj - obtained in this manner with respect to j, and outputs Pj-Pj-k.

The remaining one line of Pj is input to the first accumulator 22, where the algebraic sum of j is taken and ΣPj is output.

On the other hand, the output j=1 of the multiplier 21, Pj-Pj-, is input to the second accumulator 23, where the algebraic sum for j is taken, and Σ Pj-
Pj −k j=1 is output.

First accumulator 22 and second accumulator 2
The output of 3 is input to the divider 24, where it is calculated and output as Ak, and the calculated value of the correlation function is obtained.

The calculated value of the correlation function obtained in this way is converted into an analog quantity according to the thread shown in FIG. It will be served.

As described above, the object image sharpness detection method of the present invention includes:
Information on object image sharpness is obtained by performing calculations using the property of autocorrelation, and by digitally processing changes in the object image at each point, the signal-to-noise ratio is greatly improved.
It is possible to obtain accurate image sharpness information.

Needless to say, the autocorrelation function is a function that expresses the degree of correlation between the same signals when there is a phase difference between them. However, when the object image is poorly defined, the electric signal based on the photoelectric output of the photoelectric conversion means has a high frequency. Since the signal does not contain many components and does not have many sudden changes, when autocorrelation is taken with a phase difference, the degree of correlation becomes relatively high.

On the other hand, when the sharpness of the object image is high, the above-mentioned degree of correlation decreases because the signal contains many high-frequency components and changes rapidly.

Therefore, if a predetermined delay is set when processing the electrical signal, that is, the image sharpness information, and an autocorrelation is taken between the delayed signal and the non-delayed signal, the image sharpness can be improved. When is maximum, the degree of correlation is minimum, and a value corresponding to this is calculated by a small electronic computer.

In the method of the present invention, through the information processing process described above, the object image sharpness can be detected with extremely high sensitivity, and the focus of the photographing optical system can be adjusted based on the obtained image sharpness information. However, since most of the information processing process is performed using digital signals, the information is lost due to noise, as is well known in information theory.

There is much less information than in analog processing, so when processing the electrical output from a low-light object image,
It becomes possible to satisfactorily overcome the problem of the signal-to-noise ratio, which always appears as a difficult technical barrier.

According to the present invention, since it is possible to equip the computer with a program suitable for extracting information on object image clarity with the highest sensitivity, it is possible to detect image clarity with high sensitivity. As an additional function, it is not only possible to extract information on the object brightness level and use it for exposure control of optical equipment such as cameras, but also to perform simple object pattern recognition, and even extract video signals of the object image itself. , processing, etc., various effects that were impossible with conventional methods can be easily achieved, and for this reason, if necessary, even the system control function of the system camera, which is currently being widely used, can be achieved. It is something that can be given.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of a specific example of the object image sharpness detection method according to the present invention, and FIG. 2 is a schematic diagram showing a specific configuration example of a photoelectric conversion means suitable for use in the present invention. In the figure, a is an example of a configuration in which a photoelectric conversion means is constructed by arranging a large number of charging element portions each having a small area vertically and horizontally, and b is an example of the configuration. c and d are electrical connection diagrams of the respective element parts when a photoconductive element, a photodiode, and a solar cell are used as the photoelectric element parts, respectively. FIG. 3 is a block diagram of an embodiment of a signal time-series means suitable for use in the present invention. FIG. 4 is a diagram for explaining the detection principle of the method according to the present invention, and FIG. 5 is a block diagram of a specific example of a circuit for calculating image sharpness information suitable for use in the present invention. 2... Optical system, 3... Photoelectric conversion means, 4... Signal time series conversion means, 6... Analog-digital conversion means, 7... Signal processing means, 8... Object image evaluation function for evaluating the sharpness of the image, 12...adjustment means, 13.
...Photographing optical system, 14...Photoelectric element part, 15...
Oscillator, 16... Driver, 17-... Ring counter, 20... Delay circuit, 21... Multiplier, 22,2
3...Accumulator, 24...Divider.

Claims (1)

[Scope of Claims] 1. A step of scanning an image of an object formed by an imaging optical system to obtain an illuminance signal for each of n pixels of the image, and converting each illuminance signal into a digital signal P. (j is a number for distinguishing each of the above n pixels), and by performing the calculation expressed by the following formula using the digital signal P, on the predetermined scanning plane of the image. (where k is a constant smaller than n).