JPH06100712B2 - Autofocus method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is applied to a microfilm reader printer or the like that projects a film projection image on a screen, and uses an image sensor such as a CCD line sensor to determine the focus. It relates to the focus method.

(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 based on the difference in each projection position. It is a thing. 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 a pixel is obtained based on the output signal of each pixel of the image sensor, and the position where this contrast becomes maximum is the in-focus position. In this case, conventionally, the output signal is input to a bandpass filter and the output of this bandpass filter is differentiated to obtain the sharpness of the output signal voltage (see, for example, Japanese Patent Laid-Open No. 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. In addition, the difference in the output signal between the reference level pixel and the effective pixel of the line sensor is excessively detected by the differentiation, and there is a problem that the reliability is poor.
Further, since a bandpass filter or a differentiating circuit is used, analog signal processing is required, which causes a problem that the circuit becomes complicated.

Further, in a microfilm reader printer or the like, the size of the projected image changes variously, so that an image suitable for autofocus does not always exist at a fixed position such as the center of the screen. For example, two images that are half the size of the screen are displayed side by side or vertically,
It may be projected close to one side of the screen, or a small size image may be projected close to one side of the screen.
That is, a microfilm reader often has no projected image in the center of the screen. Therefore, if the focus zone is set near the center of the screen, there are often no images suitable for autofocus in this focus zone, and in this case the accuracy of autofocus control becomes poor or uncontrollable. May be.

(Object of the Invention) The present invention has been made in view of such circumstances, and is applied to a microfilm reader printer or the like that projects a film projection image onto a screen, and uses a complicated optical system such as a phase difference detection method. It is an object of the present invention to provide an autofocus method that is unnecessary, is less likely to malfunction due to noise, has high reliability, and is suitable for digital signal processing.

(Structure of the Invention) According to the present invention, an object of the present invention is to project a film projection image on a screen and use an output signal of the image sensor obtained by scanning a part of the focus zone of the film projection image with the image sensor. In the autofocus method for controlling the projection lens to the in-focus position, the focus zone can be set and changed on the screen, the image sensor is moved to the set focus zone, and the output signal of the image sensor is output. Is input to the digital arithmetic unit, and the digital arithmetic unit outputs the difference (V _n −V _n−1 ) between the output signals of the adjacent pixels during scanning.
This is achieved by an autofocus method characterized in that the total length of the output signal is obtained by integrating the absolute values of, and the position of the projection lens at which the total length of the output signal is maximum is determined to be in focus.

Here, the total length of the output signal may be obtained by integrating the square root of the sum of squares of the interval (Δy) between the adjacent pixels and the difference (V _n −V _n−1 ) between the output signals of the adjacent pixels.

(Principle) FIGS. 4 and 5 are views for explaining the principle of the present invention, in which the output signal v for the non-focus position (FIG. 4) and the focus position (FIG. 5) of the projection lens are shown. It is a figure which shows the change of the integrated value. As is clear from these figures, the projected image by the projection lens is the clearest when the projection lens is in the in-focus position, and the bright and dark of the image is the clearest. Further, as the projection lens moves away from the in-focus position, the fine contrast of the image becomes less clear. Therefore, the output signal v of the image sensor changes most greatly when the projection lens is at the in-focus position (FIG. 5 (A)), and as the distance from the in-focus position disappears, fine changes disappear and become smooth (fourth point). (A). This means that the total length of the output signal v becomes the longest at the time of focusing (FIG. 5 (B)) and becomes shorter as the degree of defocusing becomes larger (FIG. 4 (B)).

According to the present invention, the total length of the output signal is obtained for each scanning, and the projection lens position where the total length is maximum is determined as the in-focus position. Further, the focus zone is configured such that an area including an appropriate image can be set and changed by looking at the image projected on the screen, and the image sensor is moved to a position where the focus zone is read.

(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, and FIG. 3 is a flow chart of its operation.

In FIGS. 1 and 2, reference numeral 10 is an original image of a microphotograph such as a microfiche or a microroll film. 12
Is a light source, and the light of the light source 12 is guided to the lower surface of the original image 10 via the condenser lens 14, the heat insulating filter 16, and the 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.
It is guided to a slit exposure type printer 34 of PPC system by 22, 30, 32, for example. 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 disposed on the optical axis of the image projection light, a projection lens 54, a CCD line sensor 56 as an image sensor, and a motor 58. A part of the projection light passing through the projection lens 20 is a semi-transparent mirror 52.
Is guided to the line sensor 56 through the projection lens 54. The line sensor 56 is movable by a motor 58 in a direction orthogonal to the optical axis. Further, the projection lens 54 is a line sensor 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.
The focal length is determined so that an image can be accurately formed on the light receiving surface of 56.

The autofocus mechanism includes a motor 60 for moving the projection lens 20 forward and backward in the optical axis direction, and the focus is controlled by the control means 48 so that the projection light is properly imaged on the projection surface of the screen 28 or 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 signal having a voltage change corresponding to the amount of incident light of each pixel for each scanning. This pulse signal varies from pixel to pixel even if the same amount of light is projected due to variations in the characteristics of each pixel. The signal processing circuit 66 corrects the variation in this characteristic of each pixel and shapes the waveform to obtain the output signal v.

The output signal v thus signal-processed is converted into a digital signal by the A / D converter 68 and input to the CPU 72 as a digital arithmetic unit via the input interface 70. In FIG. 2, 74 is a ROM for storing the control program of the CPU 72, 76
Is a RAM, 78 is an output interface, 80 and 82 are D / A converters, and 84 and 86 are drivers for driving 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 motor 58 is controlled so as to be incident on 56. The user first 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 10).
0). 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 signal v of 6 is read into the CPU 72 via the interface 70, and the exposure amount is controlled by the CPU 72. If the exposure amount is not appropriate (step 104), the light amount of the light source 12 is changed (step 106), and the exposure amount is measured again. The adjustment of the exposure amount is performed by, for example, selecting the output signal of the pixel corresponding to the background area from the output of each pixel of the line sensor 56 and adjusting the light amount of the light source 12 so that this becomes a predetermined value. .

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 so that the mark 42 overlaps the position where the projected image is located.
To move.

Next, the control means 48 performs autofocus control based on the output of the line sensor 56.

The CPU 72 sequentially reads the output signal v of the line sensor 56 following the scanning of the line sensor 56 (step 114), and obtains the absolute value h of the difference between the output signals V _n and V _n-1 of the adjacent pixels (step 11).
6). That is, h = | V _n −V _n−1 | is sequentially calculated during scanning. The CPU 72 also returns the absolute value h of this difference.
Are sequentially integrated during scanning to obtain an integrated value L = Σh (step 118). When the CPU 72 completes one scan, the integrated value L
Is stored in the RAM 76 as the integrated value L at the position χ of the projection lens 20 at this time (step 120).

The CPU 72 moves the projection lens 20 by a predetermined amount Δχ and repeats the same operation as described above (step 122), finds the position of the projection lens 20 at which the integrated value L becomes maximum (step 124), and sets this position as the in-focus position. Yes (step 126).

Various algorithms are possible for the control for obtaining the maximum value of the integrated value L. For example, the projection lens 20 is moved by a predetermined amount Δχ in the direction in which the integrated value L increases, and the increase rate of the integrated value L becomes 0. Therefore, the position of the projection lens 20 at which the integrated value L becomes maximum is detected. The "mountain climbing method" is used.
Further, the projection lens 20 is moved once 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 integrated value L at that time (half-value width method), or the projection lens 20 is once moved over the entire range. Alternatively, the position where the integrated value L is maximized may be obtained by moving (all-scan method).

If the printer mode is set in this focused state (step 12
8), 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 absolute value h of the difference between the output signals of the adjacent pixels of the line sensor 56 is integrated over one scanning, and this integrated value is used as the total length of the output waveform, but the present invention is not limited to this. Not a thing. For example, the sum of squares of the pixel interval Δy of the line sensor 56 and the difference (V _n −V _n−1 ) between the output signals is obtained, and its square root, that is, Alternatively, the total length may be obtained by accumulating over one scanning.

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

(Effects of the Invention) As described above, according to the present invention, the focus zone can be set and changed by viewing the projected image on the screen, and the image sensor is moved to this focus zone. Therefore, the projected image suitable for the autofocus control is provided. Can be read. Further, since the total length of the output waveform showing the change of the output signal of the image sensor is obtained and the position of the projection lens having the maximum total length is determined to be in focus, the optical system is simple. Further, since obtaining the total length of the output waveform is a kind of integral calculation, malfunction does not occur due to noise, and the reliability of the operation becomes high. Furthermore, an analog circuit such as a bandpass filter or a differentiating circuit is not required, and the entire circuit can be configured by a digital circuit, and the circuit configuration can be extremely simplified.

[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 flow chart of operation, and FIGS. 4 and 5 are projection lenses. FIG. 6 is a diagram showing changes in an output signal and an integrated value with respect to a non-focused position and a focused position. 10… Original image, 20… Projection lens, 56… Line sensor. 72 ... CPU as digital arithmetic unit, V ... output signal, h ... difference, L ... integrated value.

Claims (2)

[Claims] 1. A projection lens is brought into a focus position by projecting a film projection image on a screen and using an output signal of the image sensor obtained by scanning a part of a focus zone of the film projection image with an image sensor. In a controlled autofocus method, the focus zone can be set and changed on the screen, the image sensor is moved to the set focus zone, and an output signal of the image sensor is input to a digital arithmetic device, The digital arithmetic unit calculates the difference (V _n −
An autofocus method characterized by determining the total length of the output signal by integrating the absolute value of V _n-1 ) and determining the position of the projection lens where the total length of the output signal is maximum as the in-focus state. 2. A projection lens is brought to a focus position by projecting a film projection image on a screen and using an output signal of the image sensor obtained by scanning a part of the focus zone of the film projection image with the image sensor. In a controlled autofocus method, the focus zone can be set and changed on the screen, the image sensor is moved to the set focus zone, and an output signal of the image sensor is input to a digital arithmetic device, The digital arithmetic unit obtains the square sum of the interval (Δy) between adjacent pixels during scanning and the difference (V _n −V _n-1 ) between the output signals of adjacent pixels, and integrates the square root to calculate the total length of the output signal. And the position of the projection lens that maximizes the total length of the output signal is determined to be in focus. Autofocus method.