JPS6291906A - Auto focus device - Google Patents

Abstract

PURPOSE:To improve the precision and the success rate of auto-focus by changing a threshold between the position near an in-focus point and the position of an out-of-focus point to measure how the counted value is changed and obtaining such threshold that the difference between counted values in respective positions is maximum. CONSTITUTION:The position of an image forming lens 12 is changed gradually by the driving signal from a system controller 17, and a binary change point on a scanning line of the same line read in each position by an image sensor 13 is taken into a binary change point counter 20, and the counted value from this counter 20 is supplied to the system controller 17 to obtain a maximum value of the counted value. When a threshold instructing signal is supplied from the system controller 17 to a threshold setting circuit 16, the circuit 16 changes the threshold in accordance with the instructing signal, and this threshold is supplied continuously to a comparator.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an autofocus device, and particularly to an autofocus device suitable for reading images of microfilm and the like.

[Conventional technology]

A conventional system for electronically reading images from microfilm will be explained with reference to FIG.

The film l is exposed to light from a light source a that passes through a lens b, and after passing through a lens C, a movable optical path switching mirror d directs the film to the screen h side or the reading side 3.
selectively guided by. The focal point is adjusted by tilting the mirror d toward the screen side Then scan ccn r in the direction of the arrow and select CGOf.
The intensity of the incident light is converted into an electrical signal. e is a mirror.

Here, the focus correspondence between the image formed on CC:Dfl: and the image formed on screen hh is as follows.
Adjustment is made by the adapter lens AL, but this adjustment is usually performed at the time of assembling the r field.

Therefore, mechanisms due to vibrations and temperature differences during transportation and transportation (
The focus of the image on the screen h and the CG for reading may be affected by deterioration (optical path length), shrinkage, or even aging.
D This adjustment is done by the user after the device is installed by the user, and then the service person moves the adapter lens AL.
Since adjustments must be made accordingly, such work is very time consuming and requires a high level of skill.

In addition, unless the adapter lens AL itself forms a clear film image on the screen h, the operator cannot determine whether or not the best focus state (hereinafter referred to as the in-focus position (just focus)) has been achieved. Therefore, the adapter lens AL is required to have extremely small aberrations and distortions and extremely high resolving power.Therefore, a high degree of precision is also required for the weighting of this adapter lens, which reduces cost. It also becomes very high.

On the other hand, even if the image on the screen h obtained through the adapter lens AL and the image on the CCD fJ: are well adjusted as described above, an inexperienced operator may
When it is very difficult to set the image to the exact focus point on a hill, the operator moves the focusing lens up and down to change the focal length and adjust the focus of the image on the microfilm hill. Alternatively, the movement is performed by a device that decelerates the power from an electric motor (motor) using gears, etc. In this type of device, the vertical movement of the focusing lens around the focal point position ranges from several meters to several seventy-seven meters. There is only a range (depth of focus) of , and if it goes beyond this range, it will be out of focus and the image information will not be able to be read accurately.

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

In addition, in recent years, documents have become increasingly electronic, and so-called optical disk electronic file systems, which electronically record documents such as Class 17, have come into widespread use. Users who have been recording texts and filing them since b-
Needless to say, this microfilm document must be converted into an optical disk electronic file, and the i'i7 converter is a microfilm electronic scanner, and in recent years this type of product has become increasingly popular. Development has been underway.

However, as mentioned, it takes an expert eye to adjust the focus to the microfilm and image.

It would be very inconvenient and time-consuming to match the -frames, -frames manually.

Therefore, in order to eliminate the drawbacks mentioned above, we developed a method in which the focus adjustment lens is moved and set at the position set during r-field adjustment by inputting the thickness of these films according to the thickness of the film used. is possible.

However, the thickness of microfilm varies depending on the manufacturer, and even within the same manufacturer there are many different types of film, such as silver film, diazo film, etc.
According to the method described in L, the usable films are limited, which is very inconvenient. Additionally, as the device is used, the above settings tend to deviate due to changes over time, and a service person has to be called periodically to make troublesome adjustments, which is extremely inconvenient.

On the other hand, many autofocus mechanisms have been announced in fields such as still cameras. Figure 10 is a typical example, where a part of the light passing through the lens U is transferred to the half mirror V.
, is reflected by mirror W, and is sent to beam splitter T. Here, the optical path length is divided into three types, and the first
~Third sensors R1 to R3 each have focal information Wl(
In this case, the amount of light is detected, and the larger the amount of light, the better the focus. Thus: J, 2 sensors R
When the second light j4 is the largest, it is determined that there is just the right amount of light, and when the third sensor R3 is larger than the second sensor R2, it is the rear focus, and the first sensor R1 is larger than the second sensor R2. When the amount of light is large, the focus will be on the front.

For cameras with a long depth of focus (in-focus distance fi1) such as still cameras, it is easy to change the optical path length through a beam splitter as shown in E and thereby detect the focus state. However, the depth of focus is several micrometers like a microfilm reader.
It was physically impossible to insert a beam splitter in a very short model of 7-several micrometers.

J: As mentioned above, there are many problems with microfilm reading devices, and the current situation is that it has not been possible to commercialize a microfilm reading device equipped with an autofocus mechanism.

[Problem that the invention seeks to solve]

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

[Means for solving problems]

In order to achieve such an object, the present invention provides a sensor consisting of a plurality of light receiving elements f arranged in a line or in a row, and an optical means for projecting an image onto the sensor.

A means for binarizing the image signal from the optical r stage, a threshold changing means for changing the threshold value input to the binarizing means, and a means for counting binary change points from the z-valued image signal. and a counting means to adjust the focal point of the optical means based on the count value from the counting means, and before adjusting the focal point, a threshold value is set by a threshold value changing means at a position near the focal point and at a position t of a plurality of out-of-focus points. By changing the value, the counting means counts the binary change points for the plurality of thresholds 1 at each position, and the difference between the counted value at the position t near the focal point and the counted value at the out-of-focus position becomes the maximum value. The present invention is characterized in that it includes means for determining such a threshold value A1 and adjusting the focus after setting the threshold value to this threshold value.

[For production]

In the autofocus device configured in this way,
An image is projected onto a sensor in which a plurality of light-receiving elements E are arranged through an optical means, and the image signal obtained by the sensor is
The autofocus operation performed when outputting as a value image signal is first performed near the set focus point,
The threshold value for binarization is changed at the lens position of the out-of-focus point before and after that, and the count value of the number of binary change points is calculated respectively, and from each state where these lens positions are changed, By finding threshold 1 that yields the largest value among the obtained count values and performing autofocus operation after setting such a threshold,
It becomes possible to guarantee highly accurate and accurate operation.

〔Example〕

FIG. 1 shows an embodiment of the invention. Here, 10 is a microfilm, and an image is recorded on the front or back side of the microfilm. Microfilm 10 placed in a predetermined position
On the other hand, the light emitted from the light source a is collected by a condensing lens 11 and transmitted through the condensing lens 11, and the converged image is transmitted through an imaging lens 12 for focus adjustment to an image sensor composed of a CCD element array. 13.

In this manner, the image sensor 13 reads one image by, for example, one scanning and one sub-scanning, and sends it to the amplifier 14, which converts it into an electrical sensor signal. 15 is a comparator, and the comparator 15 compares the threshold signal from the threshold setting circuit 16, which will be described in detail later, with the image signal supplied from the amplifier 14, and converts it into 2 pixels. The image signal (binary image signal) can be supplied to a printer or image storage memory (not shown), and the following describes how an autofocus operation can be precisely performed based on this binary image signal. Let me first describe the configuration of the device.

In this embodiment, the number of changing points of the binary image signal, that is, the edges of the edge (hereinafter referred to as focus information)
The lens is moved to the vicinity of the in-focus position and to the out-of-focus position based on the principle that the optimal focus adjustment position is obtained when the counted value shows the maximum value when scanning the same line. The threshold value is changed to obtain information that changes the count value of the focus information, and based on this information, the threshold value is set so that the count value becomes the maximum value, and an autofocus operation is performed.

The above-mentioned principle will be explained with reference to FIGS. 11A and 11B. Here, FIG. 11A shows the stage of signal binarization when the lens 12 is at the in-focus position, and now (
When the sensor scans between l+-12 in I), an image signal like (■) is obtained, which is used as the threshold 41
If the signal is converted into a 2-square one, an output signal like (I[I) will be obtained.

On the other hand, Fig. 1IB shows the case where the lens 12 is at the out-of-focus position, and if the senna scans between intersection 1 and observation 2 at CI), the image signal will be as shown in (n). When this is binarized using the same threshold value TL as above, an output signal like (III) is obtained.

Thus, the waveform (III) and the first
Comparing the waveform of ([[I) in Fig. 18, the first
In (III) of Figure 1A, the rising edge is 1+ -f
The result obtained as Lr is (III) in Figure 11B.
Then the edge is e'1. There are three, e', and IL. Therefore, in a binary image signal.

By counting the number of edges, it can be determined that the lens is at the in-focus position when the number of edges is maximum in one scan.

The explanation will be continued by returning to FIG. 1 again.

Central processing bag 21 The system controller 17 equipped with the GPU can move the imaging lens 12 in the direction of the arrow and change the lens position by supplying a drive signal to the lens drive device 18. At the same time, the image sensor drive circuit By supplying an image reading instruction signal to the drive circuit 19, it is possible to cause the image sensor 13 to read an image at the lens position using a scanning signal from the drive circuit 19.

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 in the scanning line ball of the same line read by the image sensor 13 at each position t is calculated. The maximum value of the counted value is determined by the following procedure by inputting the counted value into the 2-4 change point counter 20 and supplying the counted value from this counter 20 to the system controller 17.

When the threshold setting circuit 16 is supplied with a threshold instruction signal from the system controller 17, it can change the threshold according to the instruction signal and continue to supply such a threshold to the comparator.

Below, the operational procedure performed by the system controller 17 will be explained in principle. FIGS. 3A and 3B are diagrams for explaining the relationship between image signals and threshold values when in just focus (focus point) and when defocus (out of focus point); ,Tb,
If Tc is set in three stages, at the in-focus point in Figure 3A, if the threshold value is set at the most appropriate level,
The count value of the focus information obtained from the binarized image signal is the largest, and when the focus is out of focus in the fS3B diagram, the count value described above becomes small even at this threshold Tb.

In addition, when the threshold value Ta is higher than this, the count value is small even at the time of focus shown in the third factor A, and furthermore, when the threshold value Tc is set lower than Tb, the count value I1 is the third factor.
Similarly, the count value does not change much at the time of the in-focus point shown in FIG. 3A and at the time of the out-of-focus point shown in FIG. 3B, and both become small values.

FIGS. 4A to 4C show the relationship between the lens position and the L count value for threshold values Ta, Tb, and Tc, respectively. That is, when the appropriate threshold value Tb is set, the peak of the count value is large and sharp as shown in FIG. 4B, and the maximum value point of the peak is also easy to determine, and therefore the most appropriate lens position JP is set. can be determined with high accuracy. In addition, in the case of the threshold value Ta, the peak is small as shown in Fig. 4A, and the threshold value (4
In the case of jc, the peak is gentle as shown in FIG. 4C, and it can be seen that it is difficult to accurately find JP in either case.

Therefore, before executing a series of autofocus procedures, the system controller 17 first sets a preset lens position (an empirically obtained focusing design position 2).
In 1), the count value is read while changing the threshold value via the threshold setting circuit 16. This lens position is indicated by X in FIG. The data string of the count value for the threshold value obtained by scanning this poem is assumed to be X as shown in FIG. 6A.

Next, the lens position is moved from X by a constant value a1 to defocus the image. Then, it is assumed that the data of the count value is taken in in the same manner while changing the threshold value again, and a data string Yl as shown in FIG. 6B is obtained.

Next, in Fig. 5, move in the opposite direction from X by a fixed value d2 to defocus, and in this state, take in the data of the count value while changing the threshold value in the same way as before. Assume that a data string Y2 as shown in FIG. 6C is obtained. Next, data string Y is converted from data string X by calculation.
2 subtracted from the count value data and data column X to data column Y
By adding the count value data obtained by subtracting 2, a data string l as shown in FIG. 7347 is obtained. If you look at the graph of this data string Z now, the threshold value for the large count value is SL, that is, the peak of the count value is extremely high when the focus is in focus, so the count value when the focus is out of focus is SL. Even if we calculate the difference between the calculated value and the graph, we can see that the peak between the calculated value and the graph becomes sharper. Note that FIG. 8 shows a graph of the count value with respect to the lens position.

That is, the threshold value at which the count value is maximum in the f57 diagram is set as SL, and the values before and after it are SLI and S, respectively.
When L2 is set, the threshold values are SL and SLI.

FIG. 8 shows the counted values for the lens position t when the lens is set to SL. As is clear from this figure, the peak of the graph when the threshold value is set to SL is the sharpest, and therefore, when such a threshold value is set, the highest in-focus position WIJP can be obtained and it is easiest to do so. can be determined with high accuracy.

The following operation of the system controller 17 regarding autofocus will be further explained in sequence with reference to FIG. First, in step S1, the imaging lens 12 is set at a predetermined position, and in this state, the counter 2 is set in steps S2 and S3.
The threshold setting circuit 16 takes in the count value through 0.
The threshold value is changed through step S4, and it is determined whether or not the count values have been taken in for all the threshold values.If the count values for all the threshold values have been obtained, the process is performed in step S5.
Then, the imaging lens 12 is defocused in the positive direction by a predetermined value al.

Thus, in this state, in steps 86 to S8, the steps performed in steps S2 to S4 are repeated, and if the count values for all thresholds are obtained, the process proceeds to step S9, and this time the defocus is performed in the negative direction. let

Then, steps SIO to S12 perform steps S8 to S.
8 is repeated, and the data strings X, Ml, and Y2 of the count values obtained by each procedure up to steps S4, S8, and S12 are processed in step S13.
i, : calculate 7=(X-Yl)+(X-Y2), find the threshold value at which Z is maximum in step S14, and set the threshold value to SL in step S15.

Next, the process proceeds to step 81B, where the binary change points are counted and captured again by the counter 20 with the threshold value set to SL, and the process further proceeds to step S17, where the imaging lens 12 is moved this time. Step 2 S1B until the count value is obtained at the lens position of
After repeating S17 and obtaining count values at all lens positions, proceed to step S19 and select lens position 2, which has the largest count value from the results obtained in step S1B.
(JP is found, and the lens is moved to this lens position JP in step S20, thereby ending the autofocus operation.

Note that the sensor described as an image sensor in the above explanation may be a solid sensor or an image pickup tube, and even if it is a one-dimensional sensor or a two-dimensional sensor, the same effect can be obtained by the same procedure as described above. be able to. Also, instead of driving the imaging lens, other lenses, lamps,
It goes without saying that focusing may be performed by driving a microfilm or an image sensor, and instead of using a CPU, the system controller can be constructed using only hardware that can execute the above operations. In addition to microfilm, it can also be applied to reading 351-layer films, X-ray films, etc.17.

〔Effect of the invention〕

As explained above, first, we measure how the count value changes by changing the threshold value at a position near the in-focus point and at an out-of-focus position, and the difference in count A1 at each position is the maximum value. By finding the threshold value, the optimum threshold value for performing the ten-to-focus operation can be obtained using this threshold value, so that the lens can be reliably set at the in-focus position by the autofocus operation. It is possible,
The accuracy and success rate of autofocus can be significantly improved compared to conventional methods.

Furthermore, according to the present invention, not only is the feature that autofocus can be performed without setting a threshold value in advance, but also the most appropriate threshold value is set, which improves the accuracy and success rate of focusing. It is also possible to apply this device as it is to an automatic concentration adjustment device due to its high value.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of the configuration of the autofocus device of the present invention, Fig. 2 is a flowchart showing its operating procedure, and Figs. 3A and 3B show how the binarization of the image signal changes depending on the threshold value. 1F: In order to explain the state in which the number of rising or falling edges of the z-value changes, waveform diagrams each showing the form of an image signal at the time of an in-focus point and at the time of an out-of-focus point. FIGS. 4A, 4B, and 4C are characteristic curve diagrams showing the relationship between the lens position and the count value when threshold 1 is the value of Ta, Tb, and Tc in FIG. 3A. FIG. 5 is a schematic diagram of the optical part for explaining the state in which the imaging lens is moved in the present invention, and FIGS. 6A to 6
Figure C is a data diagram of the three aspects of threshold value and count value determined during the operating procedure of the present invention, and Figure 7 is the threshold value determined from the results of Figures 6A to 6C during the operating procedure of the present invention. Figure 8 is a characteristic curve diagram showing, as an example, the relationship between the lens position and the count value obtained based on Figure 7. Figure 9 shows an example of the configuration of a conventional autofocus device. The perspective view and the first θ diagram are explanatory diagrams showing an example of the configuration of a conventional camera autofocus device. FIGS. 11A and 11B are explanatory diagrams showing the process of converting the image signal into 2-1 when the lens is in the in-focus position and in the out-of-focus position, respectively. a...Light source, lO...Microfilm. DESCRIPTION OF SYMBOLS 11... Condensing 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. Figure 6A Figure 7 Figure 6C t? -*-'= Fun--fu λ-11 no.

Claims (1)

[Claims] A sensor consisting of a plurality of light receiving elements arranged in a row or on a surface, an optical means for projecting an image onto the sensor, a means for binarizing an image signal from the optical means, and a means for binarizing the image signal from the optical means. Threshold changing means for changing a threshold value to be input; means for counting binary change points from the binarized image signal; and adjusting the focus of the optical means based on the counted value from the counting means. prior to adjusting the focus, the threshold value changing means changes the threshold value at a position near the focal point and a plurality of out-of-focus points, and the counting means changes the threshold value at each position. The threshold value is calculated by counting the binary change points with respect to the threshold value, and determining the threshold value such that the difference between the count value at the position near the focal point and the count value at the out-of-focus position becomes the maximum value. An autofocus device characterized by comprising means for adjusting the focus after the setting is made.