JPH0746199B2 - Autofocus method for microfilm reader printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention finds a contrast signal of an image by using an image sensor such as a CCD line sensor, and controls a projection lens to a position where the contrast becomes maximum. The present invention relates to an autofocus method for a reader printer.

(Background of the Invention) When performing focus determination using an image sensor such as a CCD line sensor, it is necessary that the exposure amount of the image sensor is within an appropriate range. This is because, for example, blooming occurs when the exposure amount is too large, and the dynamic range of the image sensor cannot be fully utilized when the exposure amount is too small.

Conventionally, since this exposure amount is detected by CdS or the like, the average exposure amount of the image is detected, and there is a disadvantage that accurate detection cannot be performed. Especially in a micro film reader printer, the fluctuation range of the brightness of the original image is large. For example, in the case of a negative original image, blooming occurs in the image portion when the exposure amount is detected by CdS, and in the case of a positive original image, on the contrary, in the image portion. There is a problem that the exposure amount becomes insufficient.

(Object of the Invention) The present invention has been made in view of the above circumstances, and always provides an appropriate exposure amount regardless of whether the original image is a screw or a positive image, and maximizes the dynamic range of the image sensor to obtain an accurate image. An object of the present invention is to provide an autofocus method for a microfilm reader printer, which can quickly perform various focusing determinations.

(Structure of the Invention) According to the present invention, an object of the present invention is to obtain a contrast signal from an output signal obtained by scanning image projection light of a microfilm by an image sensor, and to adjust the projection lens position so that the contrast signal becomes maximum. In the method of controlling, preset the maximum value and the minimum value of the output signal,
For the projection lens position where the output signal is out of the maximum / minimum value range, the exposure amount is controlled so that the output signal is in the maximum / minimum value range, and the contrast signal already obtained has the exposure amount Correction is performed by multiplying the correction coefficient corresponding to the amount of change, and similarly, for other projection lens positions as well, the exposure amount is controlled and the contrast signal that has already been obtained is corrected, if necessary, to obtain a different exposure amount. The focus signal of the projection lens is obtained using the contrast signal for
When the output signal is larger than the maximum value and smaller than the minimum value, the exposure amount is determined by giving priority to the output signal being smaller than the maximum value to determine the exposure amount. Achieved by.

That is, the exposure amount is controlled so that the output signal of the image sensor does not go out of the maximum / minimum value range, and when the exposure amount is changed, the contrast signal already obtained is corrected and the magnitude of the contrast signal for each projection lens position is compared. To do. For the position of the projection lens where the output signal is larger than the maximum value and smaller than the minimum value, priority is given not to exceed the maximum value. Of course, the exposure amount may change the light amount of the light source, but in this case, the color temperature of the light amount, that is, the ratio of the wavelength component of the light generally changes, and the sensitivity of the photoconductor of the printer is changed. Cause a change. Therefore, it is desirable to control the exposure amount by controlling the drive pulse frequency of the image sensor.

(Principle) There is the relationship shown in FIG. 5 between the position x of the projection lens 20 and the contrast signal C. In this figure, three virtual lines e ₁ ,
e ₂ and e ₃ show virtual characteristics with respect to the exposure amounts E ₁ , E ₂ and E ₃ , respectively. Here, there is a relation of E ₁ > E ₂ > E ₃ , and at e ₁ and e ₂ , the output signal exceeds the dynamic range of the image sensor in a certain range including the in-focus position x _F , so it is not actually required. Now, assume that the projection lens is moved in the in-focus position x _F direction away from the origin in FIG. 5 with the exposure amount E ₁ . When the projection lens approaches the in-focus position x _F , the image of the projection light gradually becomes sharp, and the amplitude of the output signal V of the line sensor increases. Therefore, the maximum output signal V that maintains the linearity of the image sensor
If it exceeds the minimum value range, the exposure amount E ₁ is decreased, and for example, the exposure amount is changed from E ₁ to E ₂ at the position x ₁ in FIG. If the projection lens is further moved to the in-focus position x _F direction, the output signal V again exceeds the maximum / minimum value range, so the position x ₂
The exposure amount E ₂ is reduced to E ₃ again.

As a result, the contrast signal C is shown by the solid lines a, b, c in FIG.
It is obtained as a discontinuous curve as shown in. Since the curves e ₁ , e ₂ , e ₃ are similar to each other, the solid lines a, b
When is moved downward by a predetermined amount, the curve e ₃ is almost obtained. The movement amount of each solid line a, b is the change of the exposure amount (E ₁ −E ₂ ), (E ₂ −E ₃ ).
It can be measured in advance and stored in a memory such as RAM. Also, each solid line a, b,
The movement amount may be calculated so that c is continuous at the positions x ₁ and x ₂ of the projection lens 20, respectively.

In this way, if the curve showing the contrast signal C previously obtained with different exposure amounts is corrected and moved by an appropriate method on the curve showing the contrast signal C after the exposure amount is changed, one line is obtained. It is possible to obtain a continuous curve of, and obtain a position x _{F at} which this single curve is the maximum and place the projection lens at this position x _F to achieve focusing. Since the contrast signals obtained with different exposure amounts are used after being corrected, it is not necessary to perform scanning again from the beginning every time the exposure amount is changed, and swift operation is possible.

(Embodiment) FIG. 1 is a block diagram of an autofocus device according to an embodiment of the present invention, FIG. 2 is a flow chart of its operation, FIG. 3 is a diagram showing an output waveform, and FIG. 4 is a line sensor output signal. FIG. 5 is a diagram showing the relationship between the contrast signal and the lens position, and FIG. 6 is an overall schematic diagram of the reader printer.

In FIGS. 1 and 6, 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 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 has a line sensor 56 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.

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 clock pulse output from the clock 62 is the CCD driver 64.
The CCD driver 64 drives the line sensor 56 at the drive frequency instructed by the CPU 76 described later. The line sensor 56 outputs a pulse signal that changes substantially in proportion to the incident light amount (exposure amount) of each pixel for each scanning (see FIG. 4). 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 of this characteristic of each pixel and shapes the waveform to obtain the output signal v of FIG. 3 (I).

The output signal v signal-processed in this way is passed through the bandpass filter 68.
The output w is shown in FIG. 3 (II).

70 is a peak hold circuit. The peak hold circuit 70 detects the maximum value of the output signal w, and this maximum value becomes the contrast signal C for the position x of the projection lens 20 at this time (see FIG. 3 (III)).

The contrast signal C is converted into a digital signal by the A / D converter 72 and input to the CPU 76 via the input interface 74. In FIG. 1, 78 is a ROM for storing the control program of the CPU 76, 80 is a RAM, 82 is an output interface, and 84.
And 86 are D / A converters, 88 and 90 are motors 58 and 60, respectively.
Is a driver for driving.

92 is a setting device for setting the maximum value V (M) of the output signal V, 94
Is a setter for setting the minimum value V (m). The maximum value V (M) and the minimum value V (m) are input to the negative phase input terminal of the comparator 96 and the non-negative phase input terminal of the comparator 98, respectively, and compared with the output signal V. Therefore, the output signal is the maximum value V
If it is larger than (M), the comparator 96 sends a positive signal to the CPU 76, and if it is smaller than the minimum value V (m), the comparator 98 sends a positive signal to the CPU 76. Maximum value V (M) and minimum value V (m)
Is set in a range in which blooming does not occur and in which a proportional relationship with the exposure amount E is established as shown in FIG.

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 selects the reader mode with the reflecting mirror 24 in the position shown by the solid line in FIG.
The target original image is projected on the screen 28. A part of this projection light is guided to the line sensor 56 by the semi-transparent mirror 52.

The control means 48 then outputs the second value based on the output of the line sensor 56.
The contrast is obtained while controlling the exposure amount according to the procedure shown in the figure.

First, the CPU 76 commands the drive pulse frequency f of the CCD driver 64 so that the exposure amount becomes appropriate, and the scanning of the line sensor 56 is started at this frequency f (step 100). The maximum value (M) and the minimum value (m) of the output signal V within the range where the linearity of the output signal V of the line sensor 56 at this time is obtained (see FIG. 4) are set in advance in the setters 92 and 94, respectively. Set it.
If the scanning output signal V of the line sensor 56 is larger than V (m) (step 102) and smaller than V (M) (step 104), the peak hold circuit 70 stores it when one scanning is completed (step 106). CPU7 for contrast signal C
It is read into 6 and stored in the RAM 80 as (C, x) together with the position x of the projection lens 20 at this time (step 108). The above steps 100 to 108 are repeated while sequentially moving the projection lens 20 (step 110), and the position x of the projection lens 20 where the contrast signal C becomes maximum is obtained (step 111).

When the projection lens 20 moves toward the in-focus position here, the amplitude of the output signal V increases. For example, when the output signal V appears as the alternate long and short dash line in FIG.
When 20 approaches the in-focus position x, it changes like a solid line. Therefore, at this time, the contrast signal C also increases.

When the output signal V and the amplitude increase and become smaller than the minimum value V (m) (step 102), the output of the comparator 98 changes to positive and C
PU76 determines that the exposure amount is insufficient. At this time, the CPU 76 gradually lowers the drive pulse frequency f of the CCD driver 64 (f-
Δf). As a result, the exposure time of each pixel of the line sensor 56 becomes longer and the exposure amount E increases by ΔE (step
114). Further, the CPU 76 obtains the correction coefficient α of the contrast signal C with respect to the variation ΔE of the exposure amount E, and stores C × α as the corrected contrast signal C in the RAM 80 (step 116). This correction coefficient α may be stored in advance in the RAM 80 or ROM 78 as a function of the amount of change ΔE and may be read out as appropriate, or the curves a, b and c in FIG. 5 may be placed on one curve e _3. May be calculated.

When the output signal becomes larger than the maximum value V (M) (step 104), the output of the comparator 96 changes positively, and the CPU 76 determines that the exposure amount is excessive. The CPU 76 raises the scanning frequency f of the CCD driver 64 to (f + Δf) to reduce the exposure amount (step 118). Further, the correction coefficient β at this time is obtained in the same manner as in step 116, and C × β is stored in the RAM 80 as the corrected contrast signal C (step 120).

Thus, when the exposure amount E is changed in steps 114 and 118, scanning is performed again with the lens position x at that time changed (step 100).

When the exposure amount is changed as described above, the CPU 76 moves the projection lens 20 while correcting the previously obtained contrast signal C (step 110), and a single curve containing the corrected contrast signal (the fifth curve). Find the lens position x _F that maximizes the curve (corresponding to curve e ₃ in the figure) and focus on it (step 12
2). Various algorithms such as a hill-climbing method, a half-value width method, and a full-scan method, which are obtained from the inclination of the curve, can be used to obtain the focus position x _F.

If the printer mode is set in this focused state (step 12
4) The reflecting mirror 24 is rotated to the imaginary line position shown in FIG. 6, and the image is transferred onto the transfer paper 38 to obtain a hard copy.

In addition, a step arranged after step 102 in step 104
104 is prioritized over 102. Therefore, the output signal V is larger than the maximum value V (M) and is the minimum value V (M).
At the position of the projection lens 20 which is smaller than (m), the maximum value V
Priority is given not to exceed (M), and blooming of the line sensor 56 can be reliably prevented.

Although the exposure amount is controlled by changing the driving pulse frequency f of the image sensor in the above embodiments, the present invention changes the illuminance of the light source 12 or the amount of light incident on the image sensor by interposing filters having different densities. It also includes one in which the exposure amount is controlled by changing.

Further, in the above embodiment, the output signal V is compared with the maximum value V (M) and the minimum value V (m) by the comparators 96 and 98, but the functions of these comparators 96 and 98 may be performed by the CPU 76. Of course.

(Effects of the Invention) As described above, the present invention controls the exposure amount so that the output signal of the image sensor falls within the range between the maximum value V and the minimum value V. The obtained contrast signal is multiplied by a correction coefficient to be corrected. Then, by using the contrast signal thus corrected and the contrast signal which does not need to be corrected, the position of the projection lens where these contrast signals are maximum is set as the in-focus position. Therefore, the focus position can be quickly obtained, and blooming of the image sensor does not occur during the autofocus operation, and the exposure amount can always be controlled to an appropriate amount regardless of whether the original image is a screw or a positive image. In addition, the dynamic range of the image sensor can be used to the maximum extent to enable highly accurate focus determination.

In general, the image printed on the microfilm often includes an image such as a background portion and characters, and the change in brightness is significantly large. In such a document, the output signal of the image sensor is often equal to or higher than the maximum value of the allowable range and is also equal to or lower than the minimum value. In such a case, priority is given to not exceeding the maximum value, so blooming, which is a great inconvenience to the image sensor, can be reliably prevented, and focus determination can be performed with high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram of an autofocus device according to an embodiment of the present invention, FIG. 2 is a flow chart of its operation, FIG. 3 is a diagram showing output waveforms, and FIG. 4 is a line sensor output signal and exposure amount. FIG. 5 is a diagram showing the change of the contrast signal with respect to the lens position, and FIG. 6 is an overall schematic diagram of the reader printer. 20 …… Projection lens, 56 …… CCD as image sensor
Line sensor, 68 ... Band filter, 70 ... Peak hold circuit, 92,94 ... Setting device, V ... Output signal, C ...
Contrast signal, E ... Exposure amount, α, β ... Correction coefficient.

Claims (2)

[Claims] 1. A method for obtaining a contrast signal from an output signal obtained by scanning an image projection light of a microfilm by an image sensor and controlling a position of a projection lens so that the contrast signal becomes maximum. The maximum value and the minimum value are set in advance, and the exposure amount is controlled so that the output signal falls within the maximum / minimum value range for the projection lens position where the output signal is outside the maximum / minimum value range, The contrast signal already obtained is corrected by multiplying it by a correction coefficient corresponding to the amount of change in the exposure amount, while the exposure amount is similarly controlled as necessary for other projection lens positions and the contrast already obtained is adjusted. The signal is corrected and the in-focus position of the projection lens is obtained using the contrast signals for different exposure amounts, and the output signal is larger than the maximum value. And when it becomes smaller than the minimum value, the exposure amount is determined by giving priority to the output signal being smaller than the maximum value, and the exposure amount is determined. 2. The autofocus method for a micro film reader printer according to claim 1, wherein the exposure amount is controlled by changing a drive pulse frequency of the image sensor.