JPH0782145B2 - Auto focus device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus device for performing focus determination using an image sensor such as a CCD line sensor.

(Technical background of the invention) Various types of autofocus devices have been proposed using an image sensor such as a CCD line sensor.
For example, in the phase difference detection method, projection light is incident on two positions on a line sensor using two optical path splitting lenses, prisms, etc., and the deviation from the in-focus position is detected from the difference in each projection position. . However, this has a problem that the optical system is complicated and miniaturization is difficult.

Therefore, a method has been considered in which the contrast of the image is obtained from the time-series pulse voltage of each pixel of the image sensor, and the position where this contrast is the maximum is the in-focus position. In this case, conventionally, the time-series pulse voltage is differentiated to obtain the sharpness of the pulse voltage (see, for example, JP-A-56-132313). However, in this case, there is a problem that the operation is apt to be unstable due to noise due to the inherent property of the differentiating circuit. Further, the output pulse from the first pixel of the line sensor is excessively detected by the differentiation, and there is a problem that the reliability is poor.

Especially for manuscripts containing many intermediate frequency band components such as photographs,
There is also a problem that the high frequency components are reduced and the reliability of the operation is deteriorated.

(Object of the Invention) The present invention has been made in view of the above circumstances, and it is not necessary to use a complicated optical system such as a phase difference detection method. An object of the present invention is to provide an autofocus device that is highly reliable.

(Structure of the Invention) According to the present invention, the object is to combine a projection lens by using a pulse voltage within one scanning period of an image sensor, which is obtained by scanning projection light of an image recorded on a film with the image sensor. In an autofocus device for controlling the focus position, a bandpass filter that selectively passes a band near the middle of the frequency bandwidth included in the time-series pulse voltage output by the image sensor, and the output of this bandpass filter is rectified Autofocus, which includes: a rectifying circuit for controlling the output of the rectifying circuit, an integrating circuit for integrating an output of the rectifying circuit within one scanning period to obtain an integrated value, and a discriminating circuit for determining a projection lens position where the integrated value is maximum Device.

(Principle) When the intensity distribution of the spatial frequency component of the time series pulse voltage when an image is read by the image sensor is obtained, the low frequency component is strong as shown in FIG. 7 and gradually weakens as the frequency increases. Here, the higher the degree of out-of-focus of the image, in other words, the smaller the contrast, the weaker the intensity of the high frequency component becomes. On the contrary, the closer to the focal point, the higher the intensity of the high frequency component. The amount of change in intensity with respect to the degree of out-of-focus (the degree of out-of-focus) is large in the frequency band A near the middle as is clear from this figure. In the present invention, the frequency band A in which the rate of change of the intensity is large is selected, and the position of the projection lens at which the intensity of the band A is maximum is set as the in-focus position.

(Operation) By extracting a band near the middle of the frequency bandwidth included in the pulse voltage output from the image sensor with a bandpass filter, rectifying the intensity change of the extracted output and integrating it for one scanning period, The sum of intensities within the frequency band is determined. This integral value is obtained each time the projection lens position is changed, and the projection lens position where this integral value is maximum is set as the in-focus position.

(Embodiment) FIG. 1 is an overall schematic view of a reader printer which is an embodiment of the present invention, FIG. 2 is a block diagram of its autofocus control device, FIG. 3 is a characteristic diagram of a bandpass filter, and FIG. Shows output waveforms of various parts, FIG. 5 shows changes in integrated value with respect to the position of the projection lens, FIG. 6 shows a flow chart of operation, and FIG. 7 shows intensity distribution of frequency components of the image sensor output for explaining the principle. It is a figure.

In FIGS. 1 and 2, reference numeral 10 is an original image of a micro photograph such as a micro fish or a micro roll film.
Reference numeral 12 denotes a light source, and the light from the light source 12 is guided to the lower surface of the original image 10 via a condenser lens 14, a heat insulating filter 16, and a reflecting mirror 18. In the reader mode, the transmitted light (image projection light) of the original image 10 is guided to the transmissive screen 28 by the projection lens 20 and the reflecting mirrors 22, 24 and 26, and the original image 10 is displayed on the screen 28.
To form an enlarged projection image of. In printer mode,
The reflecting mirror 24 is rotated to the position shown by the phantom line in FIG.
22、30、32 by PPC type slit exposure type printer 3
Guided by 4. The reflecting mirrors 22 and 30 move in synchronization with the rotation of the photosensitive drum 36 of the printer 34, and a latent image is formed on the photosensitive drum 36. This latent image is visualized with toner charged to a predetermined polarity, and this toner image is transferred to the transfer paper 38.

Reference numeral 40 denotes a zone setting means, which includes a mark 42 indicating a focus zone and a manual knob 44 for moving the mark 42 on the screen 28. The position a of the zone is detected by the position detector 46 and sent to the control means 48.

A focus control optical system 50 includes a semi-transparent mirror 52 arranged on the optical axis of the image projection light, a projection lens 54, a CCD line sensor 56 as an image sensor, and a servo motor 58.
With. A part of the projection light that has passed through the projection lens 20 is guided to the line sensor 56 through the projection lens 54 by the semitransparent mirror 52. The line sensor 56 is movable by a motor 58 in a direction orthogonal to the optical axis. The projection lens 54
When the projection lens 20 is placed at a position where the projection light is focused on the projection surface of the screen 28 or the photosensitive drum 36, its focal length is determined so that it is accurately focused on the light receiving surface of the line sensor 56. ing.

The autofocus mechanism includes a servomotor 60 that moves the projection lens 20 back and forth in the optical axis direction, and the projection light is projected on the screen 28.
Alternatively, the focus is controlled by the control means 48 so that an image is correctly formed on the projection surface of the photosensitive drum 36.

The control means 48 is constructed as shown in FIG. That is, the CCD driver 64 drives the line sensor 56 in synchronization with the clock pulse output from the clock 62. The line sensor 56 outputs a pulse voltage b (see FIG. 4) that changes in voltage corresponding to the incident light amount of each pixel for each scanning. The pulse voltage b varies from pixel to pixel even if the same amount of light is projected due to variations in the characteristics of the pixels. The signal processing circuit 66 corrects variations in the characteristics of each pixel and shapes the waveform.

The pulse train b ′ thus signal-processed is input to the band pass filter 68, and the intensity of the frequency band A near the middle of the pulse train b ′ is obtained as an analog signal. That is, as shown in FIG. 3, the characteristic of the bandpass filter 68 is such that the gain G is large in the frequency band A (FIG. 7) and becomes almost zero in the other bands. The analog output c of this filter 68 is a rectifier circuit.
It is rectified by 70 and becomes output d (Fig. 4). This rectified output d is analogically integrated by the integrating circuit 72,
The output e of 72 gradually increases during one scan. This output e
Is the integrated value S, which indicates the intensity P of the frequency component within the band A (see FIG. 7).

The integrated value S is converted into a digital signal by the A / D converter 74, and is input to the CPU 78 forming a discriminating circuit via the input interface 76.

In FIG. 2, 80 is a ROM for storing the control program of the CPU 78,
82 for RAM, 84 for output interface, 86 and 88 for D / A
Converters 90 and 92 are drivers that drive motors 58 and 60, respectively.

Next, the operation of this embodiment will be described. The control means 48 first reads the position a of the zone set by the zone setting means 40, and the projection light of the area corresponding to this zone is read by the line sensor.
The servo motor 58 is controlled so as to be incident on 56. The user selects the reader mode with the reflecting mirror 24 in the position shown by the solid line in FIG. 1 and projects the target original image on the screen 28 (step
100). A part of this projection light is guided to the line sensor 56 by the semi-transparent mirror 52.

The control means 48 then measures the exposure amount based on the output of the line sensor 56 (step 102). That is, the signal processing circuit 6
The output pulse train b ′ of 6 is sent to the CPU via the interface 76.
It is read by 78 and the exposure amount is controlled by the CPU 78. If the exposure amount is not proper (step 104), the light amount is changed (step 106), and the exposure amount is measured again. This adjustment of the exposure amount is performed by, for example, among the output voltages of the pixels of the line sensor 56,
This is performed by selecting the voltage of the pixel corresponding to the background area and adjusting the light quantity of the light source 12 so that this becomes a predetermined voltage.

Next, the control means 48 determines whether the projection light input to the line sensor 56 contains an image (step 108). This judgment is made based on, for example, whether or not the number of black and white inversions of the image is a predetermined value or more. If it is the predetermined value or more, it is judged that the image exists (step 110). When it is determined that there is no image, the control means 48 issues an alarm such as a buzzer or a lamp and requests the change of the focus zone (step 112). The user operates the knob 44 while looking at the screen 28 and marks so that the mark 42 overlaps the position where the projected image is located.
Move 42.

Next, the control means 48 performs autofocus control based on the output of the line sensor 56. As described above, from the pulse train b ', the band pass filter 68, the rectifying circuit 70, the integrating circuit 72.
The integrated value S is obtained as an analog amount via (step 112), and this is digitally converted and input to the CPU 78. This integral value S is the fifth value with respect to the movement of the projection lens 20.
Change as shown. The CPU 78 finds the position of the projection lens 20 where this integral value S is maximum. That is, the first integrated value S is stored in the RAM 82, the projection lens 20 is moved by Δ by the servomotor 60 (step 114), the integrated value S'is obtained again (step 116), and this integrated value S'is the maximum value. Whether or not it is at the in-focus position is determined depending on whether or not it is present (step 118).

Various algorithms are possible for the control for obtaining the maximum value of S. For example, the projection lens 20 is moved by a predetermined amount in the direction in which the integrated value S increases, and the increase rate of this integrated value becomes 0. Therefore, the position of the projection lens 20 where the integrated value S becomes maximum is detected. Method ”is used. Further, the projection lens 20 is once moved so as to cross the in-focus point, and the in-focus point is obtained from the half-value width of the change characteristic curve of the integral value S at that time (half-value width method), or the projection lens 20 is once moved over the entire range. The position where the integrated value S is maximum may be obtained by moving (all-scan method).

If the printer mode is set in this focused state (step 12
0), the reflecting mirror 24 is rotated to the phantom line position in FIG.
The image is transferred to and a hard copy is obtained.

In this embodiment, the integrated value S is calculated in an analog manner,
Of course, it may be obtained digitally.

The image sensor is not limited to the CCD line sensor, but may be a MOS type line sensor or an area sensor.

(Effect of the invention) As described above, the present invention passes the pulse train output from the image sensor through the bandpass filter, the rectifying circuit, and the integrating circuit to determine the magnitude of the intensity of the intermediate frequency band component by the integrated value, and The optical system is simple because the position of the projection lens is controlled so as to maximize. Further, since the determination is made based on the integrated value for one scan, malfunction does not occur due to noise, and the reliability of the operation becomes high especially for a document such as a photograph.

[Brief description of drawings]

FIG. 1 is an overall schematic view of a reader printer which is an embodiment of the present invention, FIG. 2 is a block diagram of its autofocus control device, FIG. 3 is a characteristic diagram of a bandpass filter, and FIG. 4 is an output waveform of each part. 5 and 5 are diagrams showing changes in the integrated value with respect to the projection lens position, FIG. 6 is a flow chart of the operation, and FIG. 7 is an intensity distribution diagram of frequency components of the image sensor output for explaining the principle. 10 …… Original image, 56 …… One-dimensional fixed image sensor, 68 …… Band pass filter, 70 …… Rectifier circuit, 72 …… Integrator circuit, 78 …… CPU as discrimination circuit.

Claims (1)

[Claims] 1. An autofocus device for controlling a projection lens to a focus position by using a pulse voltage within one scanning period of an image sensor obtained by scanning projection light of an image recorded on a film by the image sensor. A band pass filter that selectively passes a band near the middle of the frequency bandwidth included in the time-series pulse voltage output from the image sensor, a rectifier circuit that rectifies the output of the band pass filter, and a rectifier circuit of the rectifier circuit. An autofocus device comprising: an integrating circuit that integrates an output within one scanning period to find an integrated value; and a discriminating circuit that finds a projection lens position at which the integrated value becomes maximum.