JPS5841485B2 - 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, which is suitable for application to a focusing system of an optical system in an optical device such as a camera.

For example, in optical equipment such as cameras, there is no method for detecting object image clarity, except for controlling the focus adjustment of the photographing optical system by photoelectrically detecting changes in the sharpness of the object image. It 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 automatic or semi-automatic focus adjustment devices of conventional cameras etc. have differences in their configurations, operations, and effects, but in principle, The illuminance distribution of the image of the object image due to the luminous flux of is converted into an electrical signal by photoelectric conversion means,
By appropriately processing this information, information corresponding to the sharpness of the object image can be obtained.

However, in these conventional methods, the signal is processed in analog quantities2, which makes the series of information processing complicated, and not only is the signal processing not quick, but the detection result is not accurate. This method has many drawbacks, such as the inability to obtain a focal point, and it has been 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 object image sharpness detection methods, fundamentally reforming their configurations, and making the present invention a central feature of modern technology. By introducing computer-based information processing technology and its peripheral technology, we aim to provide a new object image sharpness detection method that can overcome the above-mentioned drawbacks of conventional methods. The feature is that a photoelectric conversion means consisting of a large number of photoelectric elements is arranged at or near the imaging plane of an optical system that forms an image of an object, and the illuminance of the object image on the photoelectric conversion means is adjusted. The correspondingly generated photoelectric output signals of the respective element parts are converted into time-series signals by the signal time-series conversion means, and further converted into digitized signals via the analog-digital conversion means. is inputted into a signal processing means that employs a root mean square function as a function for evaluating the sharpness of the object image, thereby obtaining an electrical signal corresponding to the sharpness of the object image.

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, 1 is an object such as a person whose image sharpness is to be detected.

Alternatively, it is an optical system provided to form an image of the object 1 and 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 on or near the imaging plane of the optical system 2.

(The detailed configuration 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 determined by the photoelectric output of each photoelectric element. is converted to

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 moment by moment as a change in the photoelectric output.

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

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

The time-series signal from the time-series forming means 4 is generally increased 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 therefore the obtained photoelectric output is weak. It is amplified to an appropriate level via a widening device 5, and then an analog-to-digital conversion circuit 6.
After being manually converted into a digital signal, it is input to a small electronic computer 7 serving as a signal processing means for converting it into an electrical output corresponding to the object image clarity, and an electrical output corresponding to the object image clarity, i.e. Converted to image sharpness information.

The above-mentioned small-sized computer I is provided with programming that can calculate a function for evaluating object image clarity, which will be described in detail later. Calculations are performed moment by moment using the serialization signal, that is, the illumination intensity at each point of the object image as a variable, and image sharpness information corresponding to the adjustment state of the optical system 2 at that time is obtained.

The function for evaluating object visibility 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 used for focusing the optical system based on the image sharpness information. The signal is inputted to the degree 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.

The servo motor 12 receiving this signal output drives and controls the optical system 2 along its optical axis by a known method, and the display means 11 displays a clear image of the object based on the above signal output. It will display degrees or object distance.

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 the 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 be configured to 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 (NOS image sensor), a CCD (Ch
Image sensors such as argeCoupledDevices (charge coupled devices) may be used.

Note that the shape of the photoelectric element portion 14 and their arrangement form are as follows:
The shape is not limited to this example, and may be circular or the like.

In the same figure, e 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 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 optical 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).

An arrow 19 in the figure schematically indicates that a signal from the ring counter 17 is sent to each photoelectric element portion 14.

FIG. 4 is a diagram for explaining the detection principle of the object image sharpness detection method of the present invention.

Figures a and b show time-series digital values of each photoelectric output of each photoelectric element portion 14 when the object image clarity is low and high, respectively (hereinafter, these will be expressed as Pj).

However, in j-1, 2, . . . , n, n is the total number of photoelectric element portions.

), and the horizontal axis of the figure indicates time t.

Here, each data (P
Considering finding the root mean square value from j), this root mean square value (supposed to be S) is expressed as follows using the above symbols.

nj = 1 Therefore, when the sharpness of the object image is low, as shown in Figure a, the variation of individual Pj from the average value P is relatively small, and S becomes small.
On the other hand, when the sharpness of the object image is high, as shown in the figure, the individual variations in Pj from the average value P become large, and therefore S becomes large.

Figure C shows how the value of the root mean square S changes when the focusing state of the object image on the photoelectric conversion means 3 is changed by the optical system 2.

In the figure C, the vertical axis shows the value of the root mean square S, and the horizontal axis shows the position of the optical system 2.

When the object image is most clearly formed on the photoelectric conversion means 3 by the optical system 2 at the point A on the horizontal axis, the value of S becomes maximum as shown in the figure.

Incidentally, such root mean square S is calculated by program 8 in computer 7.
The computer T calculates the average value P=-ΣPj with respect to n of Pj according to the program 8.
= 1, then subtract P from Pj and the result (Pj
-P) to the power of (Pj-1,000)2, and then
An operation is performed to find the average value -(Pj -P)2.

The root mean square value S obtained in this manner is converted into an analog value according to the path described in FIG. It will look like this.

As described above, the object image sharpness detection method of the present invention includes:
This method uses the property of the root mean square to obtain information on object image clarity through calculation, and by digitally processing the illuminance at each point in the object image, the signal-to-noise ratio is greatly improved and accurate It is possible to obtain accurate image clarity information.

That is, the root mean square value is a well-known function that measures the degree of variation in individual data, but in the present invention, as the clarity of the object image improves, the illuminance of the image on each photoelectric element portion increases. In other words, if we pay attention to the fact that the fluctuation of This represents the object image clarity.

In 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 etc. can be adjusted based on the obtained image sharpness information. In particular, since much of the information processing process is performed using digital signals, as is well known in information theory, the amount of information lost due to noise during the process is extremely small compared to analog processing. It becomes possible to significantly overcome the problem of signal-to-noise ratio, which always presents a difficult technical barrier when processing the electrical output obtained from low-light object images.

Furthermore, according to the present invention, it is possible to equip the above-mentioned computer with a program suitable for extracting information on object image sharpness with the highest sensitivity, so that image sharpness can be detected with high sensitivity. As a separate 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, by extension, extraction of the video signal 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 the drawing]

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 photoelectric element portions each having a small area vertically and horizontally; b, c, and d are photoconductive elements as photoelectric element portions, respectively; It is an electrical connection diagram of each element part when a photodiode and a solar cell are used. FIG. 3 is a block diagram of an embodiment of a signal time-series means suitable for use in the present invention, and FIG. 4 is a diagram for explaining the detection principle of the method according to 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.

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 Pj ( j
is a number for distinguishing each of the above n pixels), and the sharpness of the above image on a predetermined scanning plane is determined by performing the calculation expressed by the following formula using the digital signal Pj. A method for detecting object image sharpness, the method comprising: determining the sharpness of an object image.