JPS63172114A - Auto-focusing device - Google Patents

Abstract

PURPOSE:To detect an image suitable for auto-focusing with a high probability by using the output signal of a line sensor for an area a certain length or longer distant from the peripheral edge of an image projection face to detect the image and making it difficult that dust and flaws have an influence when the line sensor is moved to detect the image. CONSTITUTION:The slice level for image detection is changed on the basis of the output of a specified picture element of a line sensor 40 while moving the line sensor 40, and the image detecting operation to discriminate the presence or the absence of a proper image is performed in parallel with this slice level change. A control means 50 discriminates the in-focus state on the basis of the output signal of the line sensor, and the auto-focusing operation to move a projection lens 20 to the in-focus position by a motor 51, the control of a printer 34, movement of reflection mirrors 22, 24, and 30, etc., are performed. A CPU 52 sends a signal (a), which commands a proper frequency, to a clock generator 54, and a driving pulse (b) having this commanded frequency is sent to the line sensor 40 to successively send an output signal (c) of respective picture elements to an amplifier 56. Thus, the image suitable for auto-focusing is detected with a high probability to reduce the malfunction.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an autofocus device that detects an image suitable for autofocus operation while moving a line sensor.

(Technical Background of the Invention) It has been considered to provide an autofocus device in an optical device such as a reader printer that forms a projected image of a microphotographic original onto an image projection surface such as a screen or a photoreceptor. For example, a part of the projected image is guided to a line sensor, the contrast of the image is determined based on the output signal of the line sensor, and the position of the projection lens is controlled so that this contrast is maximized to perform autofocus.

However, such an autofocus operation requires that an image suitable for this operation be incident on the line sensor. For example, if an image with a small brightness difference, a base portion of the original image, or a portion where no clear image line appears is incident, accurate autofocus operation cannot be performed. For this reason, it is conceivable to move the line sensor until it comes to a position where an appropriate image is incident.

However, the images appearing on the screen may include images unsuitable for autofocus. For example, if there is dust or scratches on the side of the original film that does not have an image, the dust or scratches will be brought into focus, resulting in a focus shift corresponding to the thickness of the film. Furthermore, if the shadow of the microfiche carrier, blip marks, or the underlying portion between a plurality of frames appears on the screen, the number of black and white inversions of the image will be insufficient, making it impossible to perform highly accurate autofocus operation. Furthermore, if a vertically long original image and a horizontally long original image coexist, the image may not be detected depending on the movement range of the line sensor.

It is also possible that an image is detected at the periphery of the screen, but even if autofocusing is performed accurately at this periphery, the center of the screen may not be in focus due to lens aberrations.

(Objective of the Invention) The present invention was made in view of the above circumstances, and it is possible to detect images by moving a line sensor, which is less susceptible to dust and scratches, and which is suitable for autofocus with a high probability. The purpose of the present invention is to provide an autofocus device that can detect

(Structure of the Invention) According to the present invention, the object is to detect an image suitable for autofocus operation while guiding a projected image to a rectangular image projection surface and moving a line sensor into which a part of this projected image is incident. This is achieved by an autofocus device characterized in that image detection is performed using the output signal of the line sensor for an area that is a certain distance or more away from the periphery of the image projection surface.

In general, dust and scratches tend to appear near the edges of images on film, especially roll films, and carrier shadows, blip marks, and the underlying areas between frames tend to appear near the edges of images on ordinary screens.

Furthermore, if the image is long vertically or horizontally, blank areas with no image will appear near the top, bottom, left and right edges of the image.

The present invention focuses on the fact that images unsuitable for autofocus tend to appear near the edges of the screen, and does not use the line sensor output based on images near the periphery of the screen, but uses images near the center of the screen. It is designed to use only the output.

Furthermore, the present invention performs an autofocus operation using an image near the center of the image that the operator wants to see, thereby avoiding the effects of aberrations in the optical system. Figure 1 is an overall schematic diagram of a league printer that is an embodiment of the present invention, Figure 2 is a front view of the screen showing the movement range of the line sensor, Figure 3 is a block diagram of the control system, and Figure 4 is a block diagram of the control system.
The figure and FIG. 5 show the original image and the output waveform of a specific pixel when the line sensor is moved. FIG. 4 is for a negative original image, and FIG. 5 is for a positive original image. Further, FIG. 6 is a diagram of output waveforms of various parts in the process of determining contrast, and FIG. 7 is a flowchart of the image detection operation.

In FIG. 1, reference numeral 1O indicates an original image of a microphotograph such as a microfiche or a roll-shaped microfilm. 12 is a light source, and the light from the light source 12 is transmitted to the original image 10 via a condenser lens 14, a heat shielding filter 16, and a reflecting mirror 18.
guided to the underside of

In the reader mode, the transmitted light (projected image) of the original image 1O is guided to the transmission screen 28 as an image projection surface by the projection lens 20 and the reflecting mirrors 22, 24, 26,
An enlarged projected image of the original image IO is formed on this screen 28. In the printer mode, the reflecting mirror 24 is rotated to the imaginary line position in FIG. 1, and the projected light is guided to the PPC type slit exposure type printer 34 by the reflecting mirrors 22, 30, 32. 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 made visible by toner charged to a predetermined polarity, and this toner image is transferred onto the transfer paper 38.

40 is a CCD line sensor, and this line sensor 4
0 is attached to the rotating end of a rotating arm 42 that rotates around the outside of the upper left corner of the screen 28 as a fulcrum. This rotating arm 42 is rotated by a motor 44 within a shaded area in FIG. This motor 44, that is, the rotating arm 42
The rotation angle θ is detected by the rotary encoder 46.

50 is a control means, which changes the slice level for image detection based on the output of a specific pixel of the line sensor 40 while moving the line sensor 40, and in parallel determines the presence or absence of an appropriate image. perform image detection operations. The control means 50 also performs focus determination based on the output signal of the line sensor 48, and controls the projection lens 20 by the motor 5.
1 (Fig. 1), autofocus operation to move to the focus position, control of the printer 34, and reflection mirror 22.24.
．． 30 movements, etc.

A control system including this control means 50 is constructed as shown in FIG. That is, the CPU 52 sends a signal a commanding an appropriate frequency to the clock generator 54, and the clock generator 54 sends a drive pulse b of the commanded frequency to the line sensor 40. The line sensor 40 sequentially sends out the output signal C of each pixel to the amplifier 56 by this driving pulse b. In this way, the main scanning of the line sensor 40 is performed. This output signal C is amplified by an amplifier 56 and becomes an output signal d (see FIG. 6(I)).

This output signal d is converted into a signal e shown in FIG. 6(n) by a bandpass filter 58, and then inputted into a peak hold circuit 60 to be converted into a contrast signal C shown in FIG. 6([1). The maximum value of this signal C becomes the contrast in this one main scan. Note that in FIG. 6, the horizontal axis indicates the pixel order of the line sensor 40.

The output signal d is also input to a sample and hold circuit 62, which is connected to the clock generator 5.
4 temporarily stores only the output signal d' of this specific pixel based on the synchronizing signal b' outputted in synchronization with the output signal of the specific pixel. 64 is a changeover switch, and this switch 6
4 reads the output signal d' stored in the sample hold circuit 62 during main scanning into the CPU 52 via the A/D converter 66 according to a command from the CPU 52, while reading the output signal d' stored in the peak hold circuit 60 at the end of the main scanning. The contrast C is read into the CPU 52 via the A/D converter 66.
The PU 52 determines and temporarily stores the peak value D (max) and minimum value p (mim) of the output signal d', and also temporarily stores the contrast C.

The output signal d is also input to the non-inverting input of a comparator 68 for blooming detection. A level slightly lower than the output level set by the setter 70 at which blooming occurs is input to the inverting input terminal of the comparator 68. Therefore, comparator 68 always outputs logic 111 when blooming occurs.
A blooming signal f of 11 is input to the CPU 52. At this time, the CPU 52 sends a signal a to increase the driving frequency of the line sensor 40 and shorten the accumulation time of the line sensor 40 in order to reduce the exposure amount of the line sensor 40.
change. The output signal d is further input to the non-inverting input of a comparator 72,74.

The comparator 72 is used to determine the slice level Sn for the negative original image, and the CPU 52 is connected to the inverting input terminal of the comparator 72.
The minimum value D (min) of the output signal d' stored in
The predetermined value α is converted into (D (min) + α), which is D
/A converter 76. This (D(min
)+α) indicates the slice level Sn for the negative original image. The comparator 74 is used to determine the slice level sp for the positive original image, and the CPU 5 is connected to the inverting input terminal of the comparator 74.
2 is the peak value D(max) of the output signal d' stored in
The predetermined value β is subtracted from (D(maX)-β), which is D/A
It is input via a converter 78. This (D (m a
x)-β) indicates the slice level SO for the positive original image. The comparators 72 and 74 send a logic "1" signal to the counter 80.82 when the output signal d becomes equal to or higher than the slice level Sn,52, respectively, and the counter 80.82 outputs a logic "1" signal to the counter 80.82 when the output signal d of the comparator 72.74 becomes a logic "1". I II is counted and sent to the CPU 52.In other words, if the above operation is repeated while moving the line sensor 40 in the sub-scanning direction perpendicular to the main-scanning direction (longitudinal direction), the output signal d
counter 80 each time exceeds the slice level Sn, Sp.
．． l is added to 82. If this count value exceeds a certain number, it is assumed that an image exists. This constant count value is set to rlJ, ``2'', taking into account that dust attached to the original film may cause erroneous counting.
It is undesirable to set this value to "4" or higher, for example.

In FIG. 1.3, 84 is a sensor for detecting the type of projection lens 2o, and the CPU 52 detects the magnification of the projection lens 2o based on the output of this sensor 84. Generally, the illuminance on the screen 28 decreases as the distance from the optical axis increases, and this illuminance unevenness is almost uniquely determined by the magnification of the projection lens 20.

A correction curve for illuminance unevenness for each lens is stored in advance in the memory 86 in FIG. do.

The memory 88 also stores the driving frequency of the line sensor 40 at which the exposure amount is approximately appropriate for the magnification of the lens 20. It is sufficient to determine this frequency by determining the rough exposure amount of the line sensor 40. In particular, in this embodiment, the above-mentioned comparator 68 has a blooming prevention function that detects blooming and reduces the exposure amount. It is desirable to store the driving frequency so that the exposure amount has a tendency to bloom.

This is because even if a negative film has only a small contrast, by increasing the storage time, the output amplitude of the sensor can be increased, resulting in high accuracy.

Note that in this embodiment, the driving frequency is made variable in order to change the accumulation time, but the present invention is not limited to this, and the accumulation time may be changed by keeping the driving frequency constant and changing the number of pulses. .

By doing this, even if the bandpass filter that detects the contrast has a single characteristic, it is possible to always detect the same spatial frequency band.

The memory 90 stores the past focus position of each lens 20 detected by the sensor 84. The CPU 52 uses the lens 20
Each time the lens is replaced, the past lens focus position determined based on the output of the sensor 84 is read out from this memory 90, and the lens 20 is moved to this past focus position prior to the image detection operation and autofocus operation. move it. This prevents the occurrence of an inoperable state due to the lens 20 being significantly moved away from the in-focus position and the projected image being significantly blurred.

Next, the operation of this embodiment will be explained. The user first uses reflector 2
4 is placed at the solid line position in FIG. 1, the reader mode is selected, and the target original image is projected onto the screen 28. The CPU 52 adjusts the projection lens 2o based on the output signal of the lens sensor 84.
(Step 100, FIG. 7). Also c
The PU 52 reads the past focus position of the projection lens 20 from the memory 9o based on the output signal of the lens sensor 84, and controls the motor 51 to move the lens 20 to this focus position. The CPU 52 further reads out the driving frequency of the line sensor 4° corresponding to the magnification of the lens 20 from the memory 88, and outputs a signal a instructing this frequency to the clock generator 54 (step 102). CPU5
2 also reads the correction curve for illuminance unevenness from the memory 86 into the memory in the CPU 52 according to the magnification of the lens 20, and preparations for autofocus operation are completed.

When the user selects the autofocus mode using a switch (not shown) (step 104), the CPU 52 displays the line sensor 40 on the screen 28 shown by a solid line in FIG.
The motor 44 is started to move the screen from an upper outer position into the screen 28 (step 1o6). The rotation angle θ of the line sensor 40 is detected by an encoder 46, and in this embodiment, the image detection operation is started when the rotation angle θ is within the range e shown in FIG. 2 (step 1).
08).

In this embodiment, the line sensor 40 is moved on a circular arc trajectory by the rotating arm 42, so that image detection is ensured. In other words, if the line sensor is moved along a straight line, the line sensor may move along the ruled line in the image or the straight line in the table, and in this case, image detection is impossible. This is because if you move the top, this will not happen.

Further, the range e in this embodiment is also a range that overlaps with the rectangular range X at the center of the screen 28.

The range X of this rectangle is 1. For example, when using a square screen 28 with sides of 300 mm, this range This area roughly corresponds to the area that overlaps when A4 size enlarged images are projected vertically and horizontally at the center, and is also a range where there is a very high possibility that the image will always exist regardless of whether the original image is oriented vertically or horizontally. When using microfiche with a large number of original images arranged vertically and horizontally, the microfiche is loaded into a manual carrier and the original images are moved by moving the carrier. At this time, the shadow Y of the carrier is shown in Figure 4 ( It may appear near the edge of the screen 28 as shown in A).

Also, frames located at the edge of the film may be projected onto parts of the film where there is no film. Furthermore, since roll films and the like are particularly susceptible to dust and scratches at the edges of the film, and identification marks such as blip marks are similarly placed on the edges of the film, these images appear near the edges of the screen 28.

In the present invention, even if an image such as a shadow Y of the carrier, a non-image area of the film, dust, scratches, or blip marks appears on the screen 28, the image within a certain range X near the center of the screen 28 is used to display the image. Since the detection operation is performed, there are very few malfunctions, and an appropriate image can be detected with a high probability.

When the line sensor 40 enters the range of θ, a predetermined operation is performed using the output signal d, other signals, the contents of the memory, etc.

This output signal d is compared with a set value of the output level at which blooming occurs in the comparator 68 (step 110).
), if blooming occurs, the output signal f becomes pulse l', so the CPU 52 outputs a signal a that instructs the line sensor 40 to increase the driving frequency and decrease the exposure amount.
is sent to the clock generator 54 (step 112).

If no blooming occurs, the line sensor 40
The output signal d' of one or more specific pixels is temporarily stored in the sample hold circuit 62 by the output signal b' of the clock generator 54, while the contrast signal (d') from - times of main scanning is stored in the peak hold circuit 60. I can do it. By switching the switch 64, the output signal d' and the contrast C are read into the CPU 52 for each main scan.

Furthermore, when blooming occurs, the storage time of the line sensor is shortened by the method described above.

Since the output of the line sensor is proportional to its accumulation time, the minimum value and peak value stored at this time are corrected by the change in accumulation time. By doing this, past data can be used effectively even if the storage time is changed.

While the line sensor 40 such as the CPU 52 is moving, this l
or monitor changes in the output signal d' of a plurality of specific pixels,
The peak value D (max) and minimum value D (min) are continuously determined (step 114).

FIG. 4(A) shows the locus of movement of this particular pixel with respect to the negative original image, and FIG. 4(B) shows the change in the output signal d' at that time with respect to the moving distance. Also, Fig. 5 (A), (B
) is also for positive original pictures. Note that 1=lo
The above range corresponds to range X in FIG. 2, and CP
U52 uses the subsequent output signal d' to find the peak value and minimum value.

The CPU 52 calculates a predetermined value α from these minimum values and peak values.
, β are respectively added and subtracted, and S, = D (min) + a Sp = D (max) - β are set as slice levels for the negative and positive original images, respectively (step 116).

In this case, it is desirable to consider the following points when detecting the minimum value and peak value. That is, in the case of a negative original image, if there are scratches or dust on the original image, these will result in an even darker image, and based on this image, the minimum value will be smaller than the correct minimum value for the base portion. Therefore, the minimum value is adopted as the correct minimum value only when the line sensor 40 continues to move for a predetermined distance. For example, if the minimum value is adopted and held when the original film continues for 0.5 mm or more, it will not be adversely affected by these scratches and dust.

On the other hand, in the case of a positive original image, it is generally not brighter than the actual base part, so the peak value can be adopted and held as is.The predetermined values α and β are the transmitted luminous flux Fo and the incident luminous flux. 0.1-0.6 of the minimum and peak values, preferably 0.2-0.
．． It is desirable to set the slice levels to about 4, and the CPU 52 sets these slice levels Sn and S to D/A.
Transducer 76.78. The comparators 72 and 74 output 111 signals each time the output signal d exceeds the slice level S, , Sp.
11, and counters 80 and 82 count this number. That is, as shown in FIG. 4.5 (B), as the line sensor 40 moves, the minimum value D (min)
, peak value p(max) and slice level Sn, S
If there is an image, the output signal d from the main scanning at that time changes greatly, so that the count value of the counter 80 increases if the image is a negative original, and the count value of the counter 82 increases if the image is a positive original. The CPU 52 determines the current slice level S when these count values exceed a predetermined value (for example, 4). +SP is appropriate and it is determined that there is an image (step 118), and the line sensor 40 is stopped (step 120). Repeating the operations of steps 108 to 118 above (step 122), if it cannot be determined that there is an image (steps 118, 122),
It is determined that there is an abnormality and a command is given to move the lens or the focus operation is stopped (step 124).

Slice level S. , S, is the accuracy of line sensor 40
The accuracy increases as the number of times the line sensor 40 moves and the number of main scans increases, but in general, if the line sensor 40 is moved about 10 to 20 times and the main scan is performed, sufficient accuracy is obtained.

Next, the control means 50 outputs the output signal d of this line sensor 40.
Performs autofocus control based on

Various algorithms are possible for this control.

For example, the line sensor 40 is located at the position where the projection lens 20 is located.
The maximum and minimum I of the luminance factor obtained from the output voltage of each pixel in
(M), I (m) are determined, and the position of the projection lens 20 where the visibility V defined by the following formula % ()) is maximized is detected while sequentially moving the projection lens 20.
The mountain climbing method is used. Alternatively, the projection lens 20 is moved once across the focused point, and the focused point is determined from the half-width of the luminance change characteristic curve at that time (half-width method).
Once the projection lens 20 is moved over the entire range, the brightness I
You may also find the position where the value is maximum (full scan method).

When the autofocus control is completed in this manner, the control means 50 drives the motor 44 in the opposite direction to move the line sensor 40 out of the screen 28. The rotating arm 42 to which the line sensor 40 is attached is attached to the screen 28
Since each part is centered on the outside of the screen 28, if the line sensor 40 is moved out of the screen 28, the rotating arm 42 and the line sensor 40 will be parallel to the upper side of the screen 28, so that they fit well.

After viewing the enlarged projected image appearing on the screen 28, if the printer mode is selected, the reflecting mirror 24 is rotated to the position shown by the imaginary line in FIG. 1, and the image is transferred onto the transfer paper 38 to obtain a hard copy.

In this embodiment, the line sensor moves in a circular arc within the rectangular range X of the screen 28, so even if the image consists of straight lines such as ruled lines, the image can be almost certainly detected and malfunctions will be reduced. This includes those that move linearly within range X.

Furthermore, since blip marks and the like are generally located above or below the left side when facing the screen 28, if the center of rotation of the rotating arm is located at the upper left corner or lower left corner as in this embodiment, The line sensor is convenient because it does not overlap with blip marks.

(Effects of the Invention) As described above, the present invention detects an image using the output signal of a line sensor for an area that is more than a certain distance away from the periphery of the image projection surface. The line sensor is less susceptible to the effects of film dust and scratches, and there is less risk of mistaking carrier shadows, blip marks, or the underlying areas between frames for images. There is no need to keep moving only the internal parts.

Therefore, images suitable for autofocus can be detected with a high probability, and malfunctions are reduced.

[Brief explanation of the drawing]

Fig. 1 is an overall schematic diagram of a reader printer that is an embodiment of the present invention, Fig. 2 is a front view of the screen showing the moving range of the line sensor, Fig. 3 is a block diagram of the control system, and Fig. 4 is a block diagram of the control system.
The figure and FIG. 5 show the original image and the output waveform of a specific pixel when the line sensor is moved. FIG. 4 shows the waveform for the negative original image, and FIG. 5 shows the waveform for the positive original image. Further, FIG. 6 is a diagram of output waveforms of various parts in the process of obtaining a contrast signal, and FIG. 7 is a flowchart of the image detection operation. DESCRIPTION OF SYMBOLS 10... Original picture, 20... Projection lens, 28... Screen as an image projection surface, 40...
Line sensor, 42... Rotating arm, X... Fixed range for image detection.

Claims (1)

[Scope of Claims] An autofocus device that detects an image suitable for an autofocus operation while guiding a projected image to a rectangular image projection surface and moving a line sensor into which a part of the projected image is incident, comprising the steps of: An autofocus device characterized in that image detection is performed using an output signal of the line sensor for an area that is a certain distance or more away from a periphery of a projection surface.