JPS6337363B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus adjustment method in image reading using a one-dimensional solid-state image sensor.

The image to be read can be read by scanning the image plane formed by the imaging optical system with a one-dimensional solid-state image sensor. Here, the one-dimensional solid-state image sensor is also called a linear image sensor, and is composed of a self-scanning photoelectric device such as a CCD or a photodiode array. In this image reading method of reading an image by scanning the image plane of the imaging optical system, the image plane of the imaging optical system tends to shift, and therefore it is necessary to automatically focus each new image.

Focusing in conventional image reading is usually performed by detecting the contrast of an image of a subject and determining the focus position. As one method of detecting the contrast of an image of a subject, a method described in Japanese Patent Publication No. 32-8346 is known. The contrast detection method described in Japanese Patent Publication No. 32-8346 is a method in which the image plane of the subject is scanned with a slit, etc., and a waveform indicating the intensity distribution of the obtained image is processed. For example, the frequency of the waveform is This method performs analysis and determines the position containing the most high-frequency components as the correct focus position. Although this contrast detection method is theoretically accurate and reliable, it has the disadvantage that the apparatus for carrying it out is large because it includes a rotating disk with a slit as a scanning means.

Therefore, we focused on the fact that the one-dimensional solid-state image sensor used as the image reading means has self-scanning properties, and we designed this one-dimensional solid-state image sensor to also serve as the above-mentioned contrast detection means, thereby achieving automatic focusing. Utility Model Application Publication No. 53-95830 describes the miniaturization and compactness of the device.

In conventional image reading methods, focusing using the one-dimensional solid-state imaging device is performed when this device is at the reading start position, prior to image reading. However, since the reading start position is located at the edge of the image to be read, there are times when there is no information to be read, and therefore contrast cannot be detected, that is, focusing may not be possible. Therefore, in such a case, it is necessary to move the element to a position where the image information is present and perform focusing, which is a cumbersome operation.

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel automatic focus adjustment method for image reading that eliminates the drawbacks of the conventional methods as described above.

In order to achieve this objective, the automatic focus adjustment method for image reading according to the present invention scans the image plane of the image to be read by the one-dimensional solid-state image sensor using the imaging optical system from the reading start position to the reading end position to read the image. Then, the image is replaced with a new image, and then the one-dimensional solid-state image sensor is moved from the reading end position to the reading start position, and during this movement, the element is moved to a focus detection position between the two positions. It is characterized in that the optical system is stopped and the output of this element is used to focus the optical system.

The focusing position may be, for example, a fixed position between the reading start position and the reading end position of the image, where information is usually considered to exist.

Since the automatic focus adjustment method according to the present invention has the above-described configuration, it is possible to always perform focusing at a position where information is available on the screen. Furthermore, since the one-dimensional solid-state image sensor is set to the focusing position when the element returns from the reading end position to the reading start position, the entire image reading process can be performed quickly.

Hereinafter, the automatic focus adjustment method of the present invention will be explained with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of an image reading device for carrying out the automatic focusing method of the present invention.

In FIG. 1, reference numeral 1 indicates an image to be read by an image reading device, and reference numeral 2 indicates this image 1.
This is an image taken by the imaging optical system 3. A one-dimensional solid-state image sensor 4 is disposed on the image plane of this image 2, and reads the image 1 by scanning this image plane from a reading start position to a reading end position. In FIG. 1, the reading start position of this one-dimensional solid-state image sensor 4 is shown by a solid line, and the reading end position is shown by a broken line.

The image sensor 4 is connected to a drive circuit 5 and driven by this drive circuit. The image sensor 4 is
The projected image 2 is read and a video signal is generated periodically with the pixel clock. This video signal is output from the output terminal 6 after being amplified. On the other hand, this video signal is also output to the contrast detection circuit 7,
Used for automatic focusing. The contrast detection circuit 7 is a circuit that obtains a signal (contrast signal) from the video signal, which increases or decreases depending on the sharpness of the video signal, that is, whether or not the image is in focus. This contrast detection circuit 7 outputs a contrast signal corresponding to each pixel of the image sensor 4. This contrast signal is input to a peak detector 8, which detects and holds a contrast signal that takes a peak value during one scan of the image sensor. The peak value of this contrast signal is converted into a digital value by the A/D converter 9, and then sent to the microcomputer 1 via an input/output interface circuit (not shown).
Incorporated into 0. This microcomputer 10 compares the value of this contrast signal with the value of the contrast signal that was similarly taken into the microcomputer 10 before this operation, and
A step motor control signal is calculated to move the lens in the direction where the peak value of the contrast signal is maximized. This step motor control signal is transmitted to the step motor controller 11 via an input/output interface circuit (not shown).
This causes the step motor 12 to rotate in the forward or reverse direction in proportion to the magnitude of the step motor control signal. The rotation of the step motor 12 moves the imaging optical system 3 along its optical axis via, for example, a rack and pinion mechanism 13 to perform focusing.

Next, the automatic focus adjustment method of the present invention will be explained step by step with reference to FIGS. 2A to 2D.

First, the one-dimensional solid-state image pickup device 4 scans the projected image 2 of the image 1 from the reading start position (FIG. 2A) to the reading end position (FIG. 2B) to read the image. The image is then replaced with a new image. The projected image of this exchanged image is denoted by 2'. After the images are exchanged, the image sensor 4 is moved from the reading end position to the reading start position and stopped at a focus detection position (FIG. 2C) between the two positions. Focusing is performed as described above using the image pickup device 4 stopped at this focus detection position. After this focusing is completed, the image sensor 4 is moved to the reading start position (Fig. 2D).
image 2' is then read as described above. The above steps are repeated to read a large number of images while focusing each image.
The focus detection position may be a predetermined fixed position that is between the reading end position and the reading end position and corresponds to a portion of the image where information is normally considered to exist. Alternatively, it is also possible to read an image with the image sensor 4 moving toward the reading start position, stop the image sensor 4 at a position where information exists, and use this stopping position as the focus detection position.

According to the automatic focusing method of the present invention described above, since information is always present in the part of the image corresponding to the focus detection position, accurate focusing can be performed using a one-dimensional solid-state image sensor. can.
In addition, since the one-dimensional solid-state image sensor is set to the focusing position when the element returns from the reading end position to the reading start position, the next one is immediately set after the element returns to the reading start position. Since it is included in the image reading process, the entire process can be carried out quickly and without waste.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus for carrying out the automatic focusing method of the present invention, and FIGS. 2A to 2D are diagrams for explaining the automatic focusing method of the present invention. DESCRIPTION OF SYMBOLS 1... Image, 2... Projection image, 3... Imaging optical system, 4... One-dimensional solid-state image sensor, 5... Drive circuit, 6... Output terminal.

Claims (1)

[Scope of Claims] 1. Scan the image plane of an image to be read by a one-dimensional solid-state image sensor using an imaging optical system from a reading start position to a reading end position to read the image, and then replace the image with a new image. Then, the one-dimensional solid-state image sensor is moved from the reading end position to the reading start position, and during this movement, the element is stopped at a focus detection position between the two positions, and the output of this element is used. An automatic focusing method characterized by focusing the optical system. 2. When the one-dimensional solid-state image sensor moves from the reading end position to the reading start position, it moves while reading the exchanged images, and stops when it detects that information is included in the image. An automatic focus adjustment method according to claim 1, characterized in that: