JPH0685552B2 - Image reader equipped with autofocus mechanism - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image reading apparatus provided with an autofocus mechanism, and more particularly to an image reading apparatus provided with an autofocus mechanism suitable for image reading of a microfilm or the like. .

[Prior art]

It has been proposed to record a large amount of image information of a document or the like on a microfilm at a high density and read the recorded image of the microfilm with an image sensor such as a CCD whenever necessary.

Such a reading device guides the transmitted light of the microfilm exposed by the light source to an image sensor by an optical member such as a lens and a mirror, and the image sensor reads an image by the intensity of the transmitted light. Therefore, good image reading cannot be achieved unless the image on the microfilm is accurately focused and directed to the image sensor.

Therefore, the transmitted light of the microfilm is guided to an optical screen to display an image, and the operator adjusts the lens position and the like while monitoring the displayed image.

However, in order to ensure this manual focusing, the image focus on the screen and that on the image sensor must be perfectly matched.
However, there is a possibility that they may not correspond due to the influence of vibration during transport or temperature difference, and in such a case, accurate focusing cannot be performed. Further, even if the correspondences between them are perfect, it is difficult for an unfamiliar operator to make the focusing accurate.

Therefore, an autofocus function has been researched and developed which automatically performs this focusing operation without the need for human intervention.
This guides the transmitted light of the film image to be read to the photoelectric conversion element, and is executed based on the output of this photoelectric conversion element, but the image from the area where the image or the image with no scratches or dirt on the film is recorded If the autofocus operation is performed with transmitted light, accurate focusing may not be performed, and good image reading may not be performed.

〔Purpose〕

The present invention has been made in view of the above points, and is provided with an autofocus mechanism capable of accurately performing image focusing without bothering humans and preventing an inconvenient autofocus operation. More specifically, the present invention provides an image reading device, and more specifically, a sensor including a plurality of light receiving elements arranged in a row, an optical unit that projects an image on the sensor, and the sensor with respect to the arrangement direction of the light receiving elements. Moving means for moving vertically in the vertical direction, counting means for counting the changing point of the output signal of the sensor for each scan, and adjusting means for adjusting the focus of the optical means based on the maximum value of the changing point by the counting means. Prior to the focus adjustment by the adjusting means, the changing means is caused to count the changing points while the sensor is moved by the moving means, and the maximum number is changed by the counting means. The count value is obtained, and then the moving means re-moves the sensor to count the change points by the counting means, and the count value by the counting means becomes a predetermined value or more obtained from the maximum count value. There is provided an image reading apparatus provided with an autofocus mechanism having a control unit that positions the sensor at a position and causes the adjusting unit to perform focus adjustment at the position.

〔Example〕

 The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing a configuration example of a reading device which electronically reads an image recorded on a microfilm.

The film 1 is exposed by the light from the light source a that has passed through the lens b, and 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 3
Be selectively led to. To adjust the focus, the mirror d is tilted to the screen side X and the operator monitors the image displayed on the screen and adjusts the position of the lens group c by a lever (not shown), or an autofocus as described later. It is executed by the scrap mechanism. After this adjustment, the optical path is switched by tilting the mirror d to the reading side Y, and the image sensor f such as CCD in which a plurality of light receiving elements are arranged in the main scanning direction by the motor g is moved in the arrow direction (with respect to the main scanning direction). Then, the image sensor f converts the intensity of incident light into an electric signal. e
Is a mirror.

FIG. 2 is a circuit block diagram showing a circuit configuration example in the reading device shown in FIG. a is a lamp which is a light source for reading an image, b is a condenser lens that collects the light, 1 is a microfilm to be read, c is an imaging lens that forms an image of the microlens, and f is an image reading device. The image sensor converts the electric signal into an electric signal.

The image sensor f outputs an analog sensor signal corresponding to the image on the microfilm 1, and an image signal obtained by amplifying the analog sensor signal by an amplifier 14 is converted into a binary signal by a binarizing circuit 15 having a comparator.
It digitizes and outputs the binary image signal to a printer or an image memory.

On the other hand, the number of change points of the binary image signal, that is, the number of edges is counted by the binary change point counter 20. Film 1
If the same line above is scanned, this count value becomes a maximum value when the imaging lens c is set at the optimum focus point.

The focusing operation based on the number of change points of the image signal will be described with reference to FIG. In FIG. 5, (I) shows the image on the microfilm, (II) shows the output of the image sensor f, and (III) shows the binary image signal.

FIG. 5 (a) shows the state of just focus, and FIG. 5 (b) shows the state of out-of-focus.

When the image sensor f performs main scanning between l _{1 and} l ₂ in (I) of FIG. 5A, a waveform as shown in (II) of FIG. 5A is obtained. (The actual CCD output signal has a stepwise form, but is omitted for ease of explanation.) The binarization circuit 15 binarizes the output with a threshold value TL to obtain a fifth value.
An output signal as shown in (III) of FIG. (At the time of just focusing) Next, the time of out-of-focus will be described with reference to FIG.

Although (I) in FIG. 5B shows an image formed on the f-plane of the image sensor, actually, the main scanning (scanning) is performed between l _{1 and} l ₂ . Here, the output signal (II) from the image sensor f
The number of signals crossing the threshold value TL is reduced, and the output signal from the binarization circuit 15 rises as shown in (III) of FIG. 5 (b), and the edges are e'1, e'4 and e'4. It is clear that the number of edges is smaller than the edge number at the time of just focusing.

Therefore, the state of focus can be known by counting the rising edges e.

The system controller 17 is composed of a microcomputer, outputs an image reading instruction signal to the image sensor driving circuit 19, and moves the image sensor f by the scanning signal output from the image reading instruction signal. On the other hand, the system controller 17 outputs a lens driving signal to the lens driving device 18 and operates a pulse motor (not shown) provided in the lens driving device 18 to change the position of the imaging lens c. This allows the image at any focus point to be read.

The system controller 17 gradually takes in the count value of the binary change point counter 20 at each point while gradually changing the focus point of the image forming lens c, and forms the image forming lens c at the focus point where the cout value becomes the maximum value.
To be set.

The sub-scanning motor g is a motor for mechanically scanning the image sensor f to read an image using the image sensor f. The image sensor drive circuit 19 is a circuit for controlling the sub-scanning motor g. The image on any line above can be read.

The autofocus mode switch 21 is a switch operated by an operator to designate execution of an autofocus operation by the system controller 17, and as described above, the focusing operation can be manually performed in the reading apparatus shown in FIG. Therefore, this selects whether the focusing operation is performed manually or by using the autofocus function.

If an autofocus operation is attempted to be performed using the above-mentioned principle using this configuration, even if a line without an image is read, autofocus cannot be performed. , The accuracy is improved. For example, when an autofocus operation is performed using an image on a film as shown in FIG. 3, even if a B line having no image is used, autofocus is impossible, and a line A is larger than C. In this case, the number of image change points is large, and the certainty and accuracy of the autofocus are improved.

In other words, when trying to execute autofocus on a film having an image as shown in FIG. 3, the image is placed at the position of the line A having the largest image information amount on this film before executing the above-mentioned autofocus operation. Setting the sensor is an effective means.

In order to realize this, the system controller 17 causes the binary change point counter 20 to capture the binary change point count value of each line while moving the image sensor f little by little with the sub-scanning motor g. In this way, after taking the binary change point count values on the line at as many points as possible in a part or the whole area of the film image, the maximum value of those count values is obtained, and a predetermined coefficient, for example, 70%
Calculate the value Th multiplied by.

Next, the image sensor f is returned to the starting point again, and while moving again little by little, the binary change point count value is fetched. The movement of the sensor is stopped at a point where the count value exceeds the value Th obtained as described above, and the above-described autofocus operation is performed at that point according to the image information on the line.

In order to detect the image line on which the autofocus operation is to be performed, the value Th obtained by multiplying the maximum value of the number of change points obtained for a part or the whole area of the image by a predetermined coefficient is used. This is because the reading position of does not completely match between the first time and the next time, and the obtained count number also differs for each scan, so that the position setting is performed by compensating for the variation of the count number. In the present embodiment, Th is set to a value obtained by multiplying the maximum value obtained in the first scan by a predetermined coefficient, but in addition, Th is set to a value within a predetermined range above and below the obtained maximum value, or obtained. It is also possible to use the average value of several values from above as Th.

FIG. 4 shows a flow chart of the control means of the system controller for the above autofocus operation.

When the auto focus operation is selected by the auto focus mode switch 21, prior to image reading,
In step S1, the sub-scanning motor g starts moving the image sensor f from the starting point for the autofocus operation. At this time, the lens C is set to the empirically determined pseudo focus position, and the binarizing circuit executes the binarizing operation of the image signal by using the threshold TL for focusing.

Next, if the reading of one line is completed in step S2,
Take in the count value of the binary change point counter 20. The counter 20 counts the changing points of the image signal input for each scanning of the image sensor. Then step S3
Then, it is judged whether or not the acquisition of the count value is completed in all the measurement areas of the image of the microfilm set at the reading position. If the image sensor f has not been completely read in all the measurement regions, the reading of the image sensor f is continued, the count value is again fetched from the counter 20 in step S2, and this is repeated until all the measurement regions of the image are finished.

When the acquisition of the count value for each running in all the measurement areas is completed, the image sensor f is returned to the starting point in step S4, and the maximum value is obtained from the acquired count values in step S5. A value Th is obtained by multiplying the maximum value by a predetermined coefficient (0.7 in this embodiment).

Then, in step S6, the sub-scanning motor g starts moving the image sensor f from the starting point again. Next, when the reading of one line is completed, the count value of the binary change point counter 20 is fetched in step S7. Then, in step S8, it is determined whether or not the count value is equal to or larger than the value Th obtained in step S5. If the count value is not the value Th or more, the count value is read from the counter 20 for reading the next line in step S7, and this is repeated until the count value becomes the value Th or more. If this operation causes a line whose count value is greater than or equal to the value Th, step S9
In step S9, the sub-scanning motor is stopped at step S9, and the image sensor f is held in the read state at that position. As a result, the image sensor f can read a position suitable for autofocus detection.

Next, in step S10, the pulse motor for moving the lens C is driven to set the lens C at the starting point. And step
In S11, the main scanning of the image sensor f is performed. At this time, the sub-scanning movement of the image sensor f is not performed. The count value (the number of focus information) of the counter 20 is taken in every main scanning of one line of the image sensor f and stored in the built-in memory.
At this time, the step number of the pulse motor is also stored. Then, in step S13, it is determined whether or not the lens C is at the end point. If the end point is not reached, step S12
Then, the pulse motor for moving the lens C is operated by one step, and the lens C is operated by one step from the start point to the end point. Then, again in step S11, the image sensor f is caused to perform main scanning, and focus information is counted and stored in the memory. When this is repeated until the lens C reaches the focal point, the count value of the counter 20 in each of the plurality of main scans in each step in which the lens C moves from the start point to the end point is stored in the memory.

If the lens C reaches the end point, proceed to step S14,
The maximum value of the count value stored in the memory for each main scan is searched, and the step number of the pulse motor corresponding to the maximum value is recognized. Then, the pulse motor of the lens driving device 18 is driven to move the lens C to the position of the step number recognized in step S15. This allows
The lens C is set to the just focus position.

As described above, according to the configuration of the present embodiment, focusing measurement can always be performed on a line having stable image information regardless of the type of film and the type of image.

Although the image sensor in which the light receiving elements are arranged in a row is used as the image reading sensor in the above embodiments, other image pickup elements may be used. Further, instead of driving the imaging lens for focusing, another lens, a lamp, a microfilm or an image sensor may be driven for focusing. Further, the measurement of the binary change point may be performed while moving the sub-scanning motor or after the sub-scanning is stopped.

When the accuracy of focusing on one image line is insufficient, the focus measurement is performed on a plurality of lines whose count value is larger than the minimum possible focus count value, and the accuracy is improved by averaging them.

Needless to say, a reading operation of a 35 mm film or an X-ray film other than the micro film may be performed.

In addition, when the image sensor is moved twice to detect the optimum position of the autofocus, the maximum count value is detected when the image sensor moves forward, and the reading position setting operation of the image sensor based on the maximum value is performed when the image sensor moves backward. You may do it. This reduces the time required to move the image sensor.

〔effect〕

As described above, according to the present invention, it is possible to perform good focus adjustment at a position suitable for autofocus in an image, and to eliminate the inconvenience of erroneous focus adjustment.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a microfilm reading device to which the present invention is applied, FIG. 2 is a block diagram showing a circuit configuration example of the reading device shown in FIG. 1, and FIG. 3 is an example of an image of a microfilm. FIG. 4 is a flow chart showing the control procedure of the autofocus operation, FIG. 5 is a view showing the principle of the autofocus operation, 1 is a microfilm, 15 is a binarization circuit, 17 Is a system controller, 20 is a binary change point counter, C is a lens, and f is an image sensor.

Claims (1)

[Claims] 1. A sensor comprising a plurality of light receiving elements arranged in a row, an optical means for projecting an image on the sensor, and a moving means for moving the sensor in a direction perpendicular to the arrangement direction of the light receiving elements. , Counting means for counting the change points of the output signal of the sensor for each scan, adjusting means for adjusting the focus of the optical means based on the maximum value of the change points by the counting means, and focus adjustment by the adjusting means. In advance, while the moving means moves the sensor, the counting means counts the change points, the maximum counting value is obtained by the counting means, and then the moving means moves the sensor again while the counting means moves. The change point is counted by, and the sensor is positioned at a position where the count value by the counting means is equal to or more than a predetermined value obtained from the maximum count value, Image reading apparatus having an autofocus mechanism, characterized in that a control means for causing the focus adjustment by the adjusting means at the position of.