JPH0664227B2 - Autofocus system - Google Patents

Description

TECHNICAL FIELD The present invention relates to an autofocus system, and more particularly to an autofocus system suitable for reading an image on a microfilm or the like.

[Conventional technology]

A conventional device for electronically reading an image on a microfilm will be described with reference to FIG.

The film 1 is exposed by the light from the light source a that has passed through the lens b, further passes through the lens c, and is then moved by the movable optical path switching mirror d to the screen h side or the reading side
Be selectively led to. The focus is adjusted by tilting the mirror d to the screen side x and adjusting the focus of the lens group c. After this adjustment, tilting the mirror d to the reading side Y switches the optical path, and the motor g. Causes CCDf to scan in the direction of the arrow, and CCDf converts the intensity of incident light into an electric signal. e is a mirror.

Here, the image formed on the CCDf and the screen h
The correspondence of the focus with the image formed on the top is adjusted by the adapter lens AL, and this adjustment is usually performed at the time of factory assembly.

Therefore, the focus of the image on the screen h and the focus on the reading CCDf side can be determined due to vibration during transport, transportation, the mechanism (optical path length) due to temperature difference, or the contraction, and the secular change. In addition to the point that it will be lost, this adjustment requires a lot of time because the service person moves the adapter lens AL and adjusts it accordingly after the device is installed by the user. Requires advanced technology.

In addition, if the adapter lens AL itself does not clearly form a film image on the screen h, the state of whether or not the operator is in the best focus state (hereinafter referred to as the in-focus position (just focus)) Therefore, the adapter lens AL is required to have very small aberration and distortion and very high resolving power. Therefore, the processing of this adapter lens is required to have high precision and cost. Will also be very expensive.

On the other hand, as described above, even if the image on the screen h and the image on the CDf obtained via the adapter lens AL have good corresponding adjustments, an unskilled operator may move the image to the in-focus position. Very difficult to set, the operator moves the focusing lens up and down to change the focal length and adjust the image focus on the microfilm 1, either by manual knob or by electric (motor). ) Is moved by a device that decelerates the power from gears by means of gears, etc., so in this type of device, the vertical movement of the focusing lens centering on the in-focus position is in the range of several μm to several tens of μm ), And beyond that, if you go out of range,
The image becomes out of focus and the image information cannot be read accurately.

As described above, in this type of apparatus, there are many problems in setting the just focus point (focusing position) only by forming an image on the screen.

Further, in recent years, the digitization of documents has progressed, and so-called optical disc electronic file systems for electronically recording documents have come to be widely used. Needless to say, users who have recorded and filed documents for a long time have made use of the records as microfilm today, but the documents on this microfilm must be converted to optical disc electronic files. It is the microfilm electronic scanner that makes these possible.
In recent years, development of this type of product has been advanced.

However, as described above, it is very inconvenient and time-consuming to adjust the focus on the image on the microfilm by using the eyes of a person skilled in the art, one frame at a time, one frame at a time.

Therefore, in order to eliminate the above-mentioned drawbacks, a method to move and set the focus adjustment lens to the position set at the factory adjustment by adjusting the thickness of the film to be used and inputting the thickness of these films is considered. To be

However, microfilm means that the film thickness varies from manufacturer to manufacturer, and even within the same manufacturer, there are various types of film, such as silver film and diazo film. In that case, usable films are limited, which is very inconvenient. In addition, the above settings were misaligned due to aging and the like during use, and it was very inconvenient to call a service man to make a troublesome adjustment.

On the other hand, in fields such as still cameras, many autofocus mechanisms have been announced. FIG. 6 is a typical example thereof, and a part of the light passing through the lens U passes through the half mirror V, is reflected by the mirror W, and is sent to the beam splitter T. Here, it is divided into three types of optical path lengths.
The third sensors R1 to R3 each detect focus information (in this case, the amount of light is detected, and the greater the amount of light, the better the focus). Thus, when the light amount of the second sensor R2 is the largest, it is determined that the focus is just, and when the third sensor R3 is larger than the second sensor R2, it is the rear pin, and the second sensor R2 is the second. When the light intensity of the sensor R1 of No. 1 is large, it means the front focus.

For such a still camera or the like having a long depth of focus (focusing distance), it is possible to easily detect the focus state by changing the optical path length via the beam splitter as described above. However, in a model with a very short depth of focus, such as a microfilm reader, of a few microns to a dozen microns, physically,
It was impossible to interpose a beam splitter.

As described above, there are many problems in the microfilm reading device, and it is the current situation that the microfilm reading device equipped with the autofocus function cannot be commercialized.

[Problems to be solved by the invention]

The present invention focuses on the above-mentioned problems, and in order to solve the problems, prior to the autofocus operation, a binarization threshold value of an image signal that makes it easy to achieve the autofocus is found in advance. It is an object of the present invention to propose an autofocus method which has a high success rate and can improve accuracy by binarizing an image signal according to a threshold value.

[Means for solving problems]

In order to achieve such an object, the present invention provides a sensor including a plurality of light receiving elements arranged in rows or on a surface, an optical means for projecting an image on the sensor, and a binary image signal from the optical means. Means, a threshold value changing means for changing the threshold value input to the binarizing means, a means for counting binary change points from the binarized image signal, and a count value from the counting means. And a means for adjusting the focus of the optical means on the basis of the optical means. Prior to the adjustment of the focus, the threshold value is changed by the threshold value changing means and the binary change point is counted by the counting means at the initial setting position. The focus adjustment is performed by obtaining the threshold value corresponding to the maximum count value of the count values.

[Work]

In the autofocus system configured in this way,
An autofocus operation performed when an image is projected on a sensor in which a plurality of light receiving elements are arranged via an optical means and an image signal obtained from the sensor is output as a binary image signal is first performed at a predetermined lens position. The threshold value for binarization is changed to obtain the count value of the number of binary change points, and the threshold value that gives the largest value among these count values is obtained. By changing the lens position with such a threshold value, obtaining the count value at each position, and setting the lens to the lens position that is the maximum of these count values, a highly accurate and accurate It is possible to guarantee the operation.

〔Example〕

FIG. 1 shows an embodiment of the present invention. Here, 10 is a microfilm on which an image is recorded. The light projected from the light source a is condensed and transmitted by the condenser lens 11 to the microfilm 10 placed at a predetermined position, and the image converged through the focusing lens 12 for focusing is displayed. The image can be projected on the image sensor 13 composed of a CCD element array.

Thus, the image sensor 13 reads an image by, for example, main scanning and sub-scanning, converts it into an electric sensor signal, and sends it to the upper amplifier 14. Reference numeral 15 is a comparator, which compares the threshold value signal from a threshold value setting circuit 16, which will be described later in detail, with the image signal supplied from the amplifier 14, and binarizes the image signal. An image signal (binary image signal) can be supplied to a printer (not shown) or an image storage memory. An apparatus that can accurately perform an autofocus operation based on the binary image signal will be described below. I will describe the configuration of.

In this embodiment, the number of changing points of the binary image signal, that is, the number of rising or falling edges (hereinafter referred to as focus information)
In the state where the lens is moved to the vicinity of the in-focus position and the out-of-focus position based on the principle that the optimum focus adjustment position is obtained when the count value shows the maximum value in the scanning of the same line. By changing the threshold value, information that changes the count value of the focus information is obtained, and from this information, the threshold value is set so that the count value becomes the maximum value, and the autofocus operation is performed.

Still to explain the principles described above by Figures 7A and FIG. 7B, where Figure 7A shows a signal binarization stage when the lens 12 is in the focused position, l ₁ in now (I)
When scanning between -l ₂ with a sensor, an image signal as shown in (II) is obtained, and when this is binarized with a threshold value TL, an output signal as shown in (III) is obtained.

On the other hand, FIG. 7B shows the case where the lens 12 is at the non-focus position and the image signal as shown in (II) is obtained when the sensor scans between l _{1 and} l ₂ in (I). By binarizing this with the same threshold value TL as above, an output signal as shown in (III) is obtained.

Thus, comparing the waveform of (III) in FIG. 7A with the waveform of (III) in FIG. 7B, the rising edge obtained as l ₁ -l ₇ in (III) of FIG. 7A is In FIG. 7B (III), there are three edges e ₁ ′, e ₄ ′ and e ₆ ′. Therefore, if the number of edges in the binary image signal is counted, it can be determined that the lens is at the in-focus position when the number of edges is maximum in one scan.

Returning to FIG. 1 again, the explanation will be continued. In the system controller 17 including the central processing unit CPU, the driving signal is supplied to the lens driving device 18 so that the imaging lens 12
Can be moved in the direction of the arrow to change its lens position, and at the same time, an image reading instruction signal is supplied to the image sensor drive circuit 19 and an image at that lens position is given to the image sensor 13 by the scanning signal from the drive circuit 19. Can be read.

Therefore, in this example, the position of the imaging lens 12 is gradually changed by the drive signal from the system controller 17, and the binary change point on the scanning line of the same line read by the image sensor 13 is binary at each position. Change point counter 20
The maximum value of the count value is obtained by the following procedure by supplying the count value from the counter 20 to the system controller 17 so as to be taken into.

When the threshold value setting signal is supplied from the system controller 17 to the threshold value setting circuit 16, the threshold value can be changed according to the instruction signal, and such a threshold value can be continuously supplied to the comparator.

Hereinafter, the operation procedure performed by the system controller 17 will be described in principle. FIG. 3A and FIG. 3B are diagrams for explaining the relationship between the image signal and the threshold value when the focus is just in focus and when the defocusing is out of focus. If Tb, Tc, and three levels are set, the count value of the focus information obtained from the binarized image signal is set when the most appropriate threshold value Tb is set at the time of focusing in FIG. 3A. Largest and first
At the time of non-focusing in FIG. 3B, the above-mentioned count value becomes small even at this threshold value Tb.

Further, when the threshold value Ta is higher than this, the count value is small even at the time of focusing shown in FIG. 3A, and when the threshold value Tc lower than Tb is set, the count value is shown in FIG. 3A. Similarly, the count value does not change so much both at the time of focusing and at the time of non-focusing of FIG. 3B, and both are small values.

FIGS. 4A to 4C show the relationship between the lens position and the count value for each of the threshold values Ta, Tb and Tc. That is, when the threshold value is set to an appropriate threshold value Tb, the peak of the count value is large and sharp as shown in FIG. 4B, and the maximum value point of the peak is easily discriminated. Can be accurately determined. Further, in the case of the threshold value Ta, the peak is small as shown in FIG. 4A, and in the case of the threshold value Tc, the peak is gentle as shown in FIG. 4C, and in any case, it is difficult to find JP accurately. I understand.

Therefore, in the system controller 17, before executing a series of autofocus procedures, first, the threshold value setting circuit 16 is used at a preset lens position (empirically obtained near focus position). The count value is read while changing the value.

Thus, when the reading is completed, a threshold value that maximizes the count value is found, and such threshold value is set and supplied from the threshold value setting circuit 16 to the comparator. Next, while moving the image forming lens 12 via the lens driving device 18, the change point is counted by the binary change point counter 20, and the image forming lens is located at the lens position where the count value is maximum.
12 can be set.

The operation procedure will be described below with reference to FIG.

First, in step S1, the imaging lens 12 is fixed at a predetermined position, and in this state, the threshold value is changed while taking the count value through the counter 20 in steps S2 and S3, and all threshold values are changed in step S4. It is determined whether or not the count value has been captured.

Thus, if the count values have been taken in for all the threshold values, the process proceeds to step S5, the threshold value T at which the maximum count value is obtained is found, and the threshold value is set to T in step S6.
In subsequent steps S7 and S8, the position of the lens 12 is moved while fetching the count value via the counter 20, and in step S9, it is determined whether or not the count value is fetched at all the lens positions.

Then, if the count values at all the lens positions are captured, the process proceeds to step S10 to find the lens position JP that is the maximum among the captured count values, and at step S11 select this lens position JP. The lens is set and the focus operation ends. Then, image reading is started.

Note that the sensor described as an image sensor in the above description may be a solid-state sensor or an image pickup tube, and may be a one-dimensional sensor or a two-dimensional sensor to obtain the same effect by the same procedure as described above. You can Further, instead of driving the imaging lens, other lens, lamp, microfilm or image sensor may be driven for focusing, and the above operation is performed instead of using the CPU for the system controller. It is also possible to configure using only executable hardware. Needless to say, the present invention can be applied to reading of 35 mm film and X-ray film as well as reading of mask film.

〔The invention's effect〕

As described above, according to the present invention, the threshold value for binarizing the image signal is changed while the lens is fixed at a predetermined position before the focusing, so that the rising edge or the falling edge of the binary image signal is changed. The change point is counted, and the threshold value that maximizes the count value is calculated.Next, while setting this threshold value, the focal length of the lens is changed and the count value is calculated again. The lens position where the numerical value becomes the maximum value is found, and the focus is adjusted so that the lens comes to this lens position.Therefore, by obtaining the threshold value that maximizes the count value, the focus position of the focus position becomes the sharpest. A state that is easy to find can be obtained, and by fixing the threshold value and moving the lens in this state, the sharp peak of the count value, which is the in-focus position, can be accurately specified. S and thickness, or in comparison with the conventional device accurate focus has been difficult due to aging or deviation during movement of the apparatus, it can be carried out very easily and precisely autofocus.

Furthermore, according to the present invention, not only is there a feature that auto-focusing can be executed without setting a threshold value in advance, but since the threshold value is set to the most appropriate value, the precision of focusing and the success rate are improved. However, this method can be applied to an automatic density adjusting device as it is.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of the configuration of an apparatus to which the autofocus system of the present invention is applied, FIG. 2 is a flow chart showing the operation procedure, and FIGS. 3A and 3B show thresholding of image signals. FIG. 4A and FIG. 4B are waveform charts showing the forms of the image signal at the in-focus and out-of-focus points, respectively, for explaining the state in which the number of rising or falling of the binarization changes depending on the value. And FIG. 4C is a characteristic curve diagram showing the relationship between the lens position and the count value when the threshold values are the values of Ta, Tb and Tc in FIG. 3A, and FIG. 5 is the configuration of the conventional autofocus device. FIG. 6 is an explanatory view showing an example of a conventional autofocus system for a camera, FIG. 7A is when the lens is at the in-focus position, and FIG. 7B is when the lens is out of focus. Signal binarization state when It is an explanatory view stepwise showing. a: light source, 10: micro film, 11: condenser lens, 12: imaging lens, 13: image sensor, 14: amplifier, 15 ... comparator, 16 ... threshold setting circuit, 17 …… System controller, 18 …… Lens drive device, 19 …… Image sensor drive circuit, 20 …… Binary change point counter.

Claims (1)

[Claims] 1. A sensor comprising a plurality of light receiving elements arranged in rows or on a plane, an optical means for projecting an image on the sensor, and a means for binarizing an image signal from the optical means.
Threshold value changing means for changing the threshold value input to the binarizing means, means for counting binary change points from the binarized image signal, and the optical means based on the count value from the counting means. Means for adjusting the focus of the means, and prior to the adjustment of the focus, the threshold value is changed by the threshold value changing means and the binary change point is counted by the counting means at an initial setting position. Then, the autofocus method is characterized in that the focus adjustment is performed by obtaining a threshold value corresponding to the maximum count value of the count values.