JPH0693057B2 - Autofocus device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus device that detects an image suitable for an 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 which forms a projection image of a microphotographic original image on an image projection surface such as a screen or a photoconductor. For example, a part of the projected image is guided to a line sensor, the contrast of the image is obtained based on the output signal of the line sensor, and the position of the projection lens is controlled so as to maximize the contrast, thereby performing autofocus.

However, such an autofocus operation is premised on that an image suitable for this operation is incident on the line sensor. For example, when an image with a small difference in lightness, a base portion of the original image, or a portion in which a clear image line does not appear is incident, accurate autofocus operation cannot be performed. Therefore, it is conceivable to move the line sensor until the appropriate image is incident.

However, the image displayed on the screen may include an image unsuitable for autofocus. For example, if there is dust or scratches on the non-image side of the original film, the dust or scratches will be in focus, and the focus will deviate by the thickness of the film. Further, when the shadow of the microfish carrier, the blip mark, or the background portion between a plurality of frames appears on the screen, the number of times of black and white reversal of the image is insufficient, and a highly accurate autofocus operation cannot be performed. Further, when a vertically long original image and a horizontally long original image are mixed, the image may not be detected depending on the moving range of the line sensor. Further, although an image may be detected in the peripheral portion of the screen, even if the autofocus operation is accurately performed in this peripheral portion, it is possible that the central portion of the screen is out of focus due to the aberration of the lens.

(Object of the Invention) The present invention has been made in view of such circumstances, and when moving the line sensor to detect an image, it is less susceptible to dust and scratches and has a high probability of being suitable for autofocusing. It is an object of the present invention to provide an autofocus device that can be detected by.

(Constitution of the invention) According to the present invention, the object is to guide a projected image to a rectangular image projection plane, while moving a line sensor on which a part of this projected image is incident, while detecting an image suitable for autofocus operation. In the autofocus device, the image detection is performed by using the output signal of the line sensor with respect to a region distant from the peripheral edge of the image projection surface by a certain distance or more.

In general, dust and scratches tend to adhere to the edge of the image in the case of a film, especially a roll film, and the shadow of the carrier, blip marks, or the base portion between frames tends to appear near the edge of the image on a normal screen. When the image is long in the vertical or horizontal direction, blank areas without the image still appear near the upper and lower edges of the image.

The present invention focuses on the point that an image unsuitable for autofocus is likely to appear near the edge of the screen, and does not use the output of the line sensor based on the image near the edge of the screen, but the image near the center of the screen. Only the output is used.

Further, according to the present invention, the operator is not affected by the aberration of the optical system by performing the autofocus operation by using the image near the center of the image desired by the operator.

(Embodiment) FIG. 1 is an overall schematic view of a reader printer which is an embodiment of the present invention, FIG. 2 is a front view of a screen showing a moving range of the line sensor, FIG. 3 is a block diagram of a control system, Fourth
5 and 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 an output waveform chart of each part in the process of obtaining the contrast, and FIG. 7 is a flow chart of the image detecting operation.

In FIG. 1, reference numeral 10 is an original image of a microphotograph such as a microfish or a roll-shaped microfilm.
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 (projected image) of the original image 10 is guided by the projection lens 20 and the reflecting mirrors 22, 24, and 26 to the transmissive screen 28 as an image projection surface, and the original image 10 is enlarged and projected on the screen 28. Form an image. In the printer mode, the reflecting mirror 24 is rotated to the imaginary line position in FIG. 1, and the projection light is guided by the reflecting mirrors 22, 30 and 32 to the slit exposure type printer 34 of the PPC system. 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 CCD line sensor, and the line sensor 40 is attached to a rotating end of a rotating arm 42 that rotates about the outside of the upper left corner of the screen 28 as a fulcrum. This rotating arm
The motor 42 is rotated by the motor 44 within the shaded area in FIG.
The rotation angle θ of the motor 44, that is, the rotation arm 42 is detected by the rotary encoder 46.

Reference numeral 50 is a control means that 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 with this, determines the presence or absence of an appropriate image. The image detecting operation is performed. Further, the control means 50 performs focus determination based on the output signal of the line sensor 48, and an autofocus operation for moving the projection lens 20 to a focus position by a motor 51 (FIG. 1),
The printer 34 is controlled and the reflecting mirrors 22, 24, 30 are moved.

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

This output signal d is converted into the signal e shown in FIG. 6 (II) by the bandpass filter 58, and then the peak hold circuit 60.
Is input to the contrast signal C shown in FIG. 6 (III).
It is said that 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 the sample hold circuit 62,
The sample-hold circuit 62 temporarily stores only the output signal d'of the specific pixel based on the synchronizing signal b'output from the clock generator 54 in synchronization with the output signal of the specific pixel. 64 is a changeover switch, and this switch 64 is the CPU 52
Command to read the output signal d'stored in the sample hold circuit 62 into the CPU 52 via the A / D converter 66 during the main scan, and at the end of the main scan the contrast C stored in the peak hold circuit 60. Via the A / D converter 66 to the CPU52
Read in. The CPU 52 finds and temporarily stores the peak value D (max) and the minimum value D (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 terminal of the comparator 68 for detecting blooming. A slightly smaller level is input to the inverting input terminal of the comparatively 68 due to the output level of blooming set by the setter 70. Therefore, the comparator 68 inputs to the CPU 52 the blooming signal f which becomes logical "1" whenever blooming occurs. At this time, the CPU 52 uses the line sensor to reduce the exposure amount of the line sensor 40.
The signal a is changed so that the drive frequency of the line sensor 40 is increased to shorten the storage time of the line sensor 40. The output signal d is further input to the non-inverting input terminals of the comparators 72 and 74. Comparator 72
Is used to determine the slice level S _n for the negative original image, and a predetermined value α is converted to the minimum value D (min) of the output signal d'stored by the CPU 52 at its inverting input terminal (D (min)). + Α) is input via the D / A converter 76. This (D (min) + α) indicates the slice level S _n for the negative original image. The comparator 74 is used to determine the slice level S _p for the positive original image, and its inverting input terminal has the peak value D (m of the output signal d ′ stored by the CPU 52.
(D (max) −β) obtained by subtracting the predetermined value β from ax) is input via the D / A converter 78. This (D (max) -β) indicates the slice level S _p for the positive original image. Comparator 72,
The 74 sends a signal of logic "1" to the counters 80 and 82 when the output signal d becomes _{equal to} or higher than the slice levels S _n and S _p , respectively, and the counters 80 and 82 output the outputs of the comparators 72 and 74 to logic "1". Is counted and sent to the CPU 52. That is, if the above operation is repeated while moving the line sensor 40 in the sub-scanning direction orthogonal to the main scanning direction (longitudinal direction), the counters 80, 82 are generated each time the output signal d exceeds the slice levels S _n , S _p .
Is incremented by 1. If this count value exceeds a certain number, it is assumed that there is an image. It is not desirable to set this constant value of the count value to "1" or "2" in consideration of the fact that dust may be mistakenly counted on the original film image, for example, set to "4" or more. Good to do.

In FIGS. 1 and 3, reference numeral 84 is a sensor that detects the type of the projection lens 20, and the CPU 52 detects the magnification of the projection lens 20 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 the illuminance unevenness for each lens is stored in advance in the memory 86 of FIG. 3, and the CPU 52 controls the rotational position θ of the line sensor 40.
The contrast C and the output signal d'or the slice levels S _n and S _p are corrected with respect to.

Further, the memory 88 stores the drive frequency of the line sensor 40 at which the exposure amount is substantially appropriate for the magnification of the lens 20. This frequency is sufficient if a rough exposure amount of the line sensor 40 is determined. In particular, in this embodiment, the comparator 68 has a blooming prevention function of detecting blooming and reducing the exposure amount. It is desirable to store the drive frequency so that the exposure amount is likely to be blooming.

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

In this embodiment, the drive frequency is made variable in order to change the storage time, but the present invention is not limited to this, and the drive frequency may be kept constant and the number of pulses may be changed to change the storage time. . By doing so, the same spatial frequency band can always be detected even if the bandpass filter that detects the contrast has a single characteristic.

The memory 90 stores the past focus position of each lens 20 detected by the sensor 84. The CPU 52 reads from the memory 90 the past lens focus position of the lens determined based on the output of the sensor 84 each time the lens 20 is replaced, and the lens 20 is moved to the past lens focus position prior to the image detection operation and the autofocus operation. To the in-focus position. This prevents the inoperable state due to the lens 20 being significantly separated from the in-focus position and the projected image being significantly blurred.

Next, the operation of this embodiment will be described. First of all, the user is a reflector 24
Select the reader mode with the solid line position shown in FIG. 1 to project the target original image on the screen 28. The CPU 52 determines the magnification of the projection lens 20 based on the output signal of the lens sensor 84 (step 100, FIG. 7). Further, the CPU 52 reads the past focus position of the projection lens 20 from the memory 90 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 the driving frequency of the line sensor 40 corresponding to the magnification of the lens 20 from the memory 88, and outputs the signal a for instructing this frequency to the clock generator 54 (step 102). CPU52
Also, according to the magnification of the lens 20, the correction curve of the illuminance unevenness is read from the memory 86 into the memory in the CPU 52, and the preparation for the autofocus operation is completed.

If the user selects the autofocus mode by a switch (not shown) (step 104), the CPU 52 moves the line sensor 40 from the position outside the upper side of the screen 28 shown by the solid line in FIG. 2 into the screen 28. Then, the motor 44 is started (step 106). The rotation angle θ of the line sensor 40 is detected by the encoder 46, and in this embodiment, the image detection operation is started when it enters the range θ shown in FIG. 2 (step 108).

In this embodiment, the line sensor 40 is moved on the arc locus by the rotating arm 42, so that the image detection can be surely performed. That is, if the line sensor is moved along a straight line, the line sensor may move along a ruled line in the image or a straight line in the table, and at this time, image detection becomes impossible.
This is because if the line sensor is moved on an arc, such a situation will not occur.

Further, the range Θ in the present embodiment is also a range overlapping the rectangular range X in the central portion of the screen 28. The range X of this rectangle
Is, for example, when using a square screen 28 having a side of 300 mm, the range X is 50 mm from each edge of the screen 28.
It is desirable to make it an inner square. In this case, the range X is almost equivalent to the range overlapped when a magnified image of A4 size is projected vertically and horizontally at the center of the screen 28, regardless of whether the original image is portrait or landscape. It is also a range in which it is very likely that an image always exists. When using a microfiche in which a large number of original images are arranged vertically and horizontally, the microfiche is loaded into a manual carrier and the original image is moved by moving the carrier. At this time, the shadow Y of the carrier is shown in FIG. It may appear near the edge of the screen 28 as shown in A). In addition, a frame without a film may be projected in a frame located at the beginning of the film. In addition, dust and scratches are likely to occur on the edges of the film, especially on roll films, and identification marks such as blip marks are also applied to the edges of the film.
It appears near the edge of 28.

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

When the line sensor 40 enters the range of Θ, a predetermined operation is performed using its output signal d, other signals, the contents of the memory, and the like. This output signal d is compared with the set value of the output level at which blooming occurs in the comparator 68 (step 110). If blooming occurs, the output signal f becomes "1". The signal a for instructing to increase the drive frequency of (1) and decrease the exposure amount is sent to the clock generator 54 (step 112).

If blooming has not occurred, the output signal d'of one or more specific pixels of the line sensor 40 is temporarily stored in the sample hold circuit 62 by the output signal b'of the clock generator 54, while one main scan is performed. The contrast C according to is stored in the peak hold circuit 60. By switching the switch 64, the output signal d'and the contrast C are read into the CPU 52 for each main scanning.

When blooming occurs, the accumulation time of the line sensor is shortened by the above method. Since the output of the line sensor is proportional to the accumulation time, the minimum value and the peak value stored at this time are corrected by the amount by which the accumulation time is changed. By doing so, past data can be effectively used even if the accumulation time is changed.

While the licensor 40 such as the CPU 52 is moving, the change in the output signal d'of the one or more specific pixels is monitored, and the peak value D (max) and the minimum value D (min) thereof are continuously obtained (step 114). .

FIG. 4 (A) shows the movement locus of this specific pixel with respect to the negative original image, and FIG. 4 (B) shows the change of the output signal d'at that time with respect to the movement distance l. Also, FIG. 5 (A),
(B) is also for a positive original image. Note that l =
The range of l ₀ or more corresponds to the range X in FIG. 2, and CP
U52 uses the subsequent output signal d'to determine the peak value and minimum value.

The CPU 52 uses the minimum value and the peak value to determine the predetermined values α and β.
Are added or subtracted, and S _n = D (min) + α S _p = 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 the peak value. That is, in the case of a negative original image, if scratches or dust are attached to the original image, these images become darker and the minimum value becomes smaller than the correct minimum value of the base portion based on this image. 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, on the original film
If you use and hold the minimum value for 0.5mm or longer, these scratches and dust will not be adversely affected.

On the contrary, in the case of a positive original image, in general, it does not become brighter than the actual base portion, and therefore the peak value may be directly adopted and held.

When the predetermined values α and β are expressed by the optical density represented by the logarithm of the ratio F / F ₀ of the transmitted light beam F ₀ and the incident light beam F, the minimum value and the peak value are 0.1 to 0.6, preferably 0.2 to
It is desirable to set it to about 0.4.

The CPU 52 converts these slice levels S _n and S _p into D / A converters 76 and 78.
Send to. The comparators 72 and 74 output "1" when the output signal d exceeds the slice levels S _n and S _p , and the counters 80 and 82 count this number. That is, (B) of FIGS.
As shown in, the minimum value D (min), the peak value D (max), and the slice level as the line sensor 40 moves.
S _n and S _p continue to change, and if there is an image, the output signal d due to the main scanning at that time greatly changes. Therefore, the count value of the counter 80 is a negative original image and the count value of a counter 82 is a positive original image. Will increase. If these count values are equal to or greater than a predetermined value (for example, 4), the CPU 52 determines that the slice levels S _n and S _p at that time are appropriate and determines that there is an image (step 118), and stops the line sensor 40 (step 120). .
The above steps 108 to 118 are repeated within the range X (step 122). If it cannot be determined that there is an image (steps 118 and 122), it is determined that there is an abnormality and a lens movement command or the autofocus operation is stopped. Yes (Step 12
Four).

The accuracy of the slice levels S _n and S _p becomes higher as the number of movements of the line sensor 40 and the number of main scans increase, but generally the accuracy of the movement and the main scan of about 10 to 20 open is sufficient. become.

Next, the control means 50 performs autofocus control based on the output signal d of the line sensor 40. Various algorithms are possible for this control. For example, the maximum and minimum I (M) and I (m) of the brightness I obtained from the output voltage of each pixel of the line sensor 40 at a certain position of the projection lens 20 are obtained, and the following equation V = (I (M) − The "mountain climbing method" is used to detect the position of the projection lens 20 having the maximum visibility V defined by I (m)) / (I (M) + I (m)) while sequentially moving the projection lens 20. . 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 luminance change characteristic curve at that time (half-value width method), or the projection lens 20 is moved once over the entire range. , The position where the brightness I is maximum may be obtained (full scan method).

When the autofocus control is completed in this way, the control means 50 drives the motor 44 in the reverse direction to cause the line sensor 40 to exit the screen 28. Since the rotating arm 42 to which the line sensor 40 is attached is centered on the outside of each part of the screen 28, the rotating arm 42 and the line sensor 40 are located on the upper side of the screen 28 when the line sensor 40 is retracted to the outside of the screen 28. It is parallel and fits well.

When the printer mode is set after viewing the enlarged projection image appearing on the screen 28, the reflecting mirror 24 is rotated to the virtual line position in FIG. 1 and the image is transferred to the transfer paper 38 to obtain a hard copy.

In this embodiment, since the line sensor moves within the rectangular range X of the screen 28 while drawing an arc, the image can be detected almost certainly even when the image is a straight line such as a ruled line, and malfunctions are reduced. It also includes one that moves linearly within the range X.

Further, since the blip mark and the like are generally located on the upper left side or the lower side toward the screen 28, if the rotation center of the rotation arm is located at the upper left corner or the lower left corner as in the present embodiment, The line sensor is convenient because it does not overlap the blip mark or the like.

(Effects of the Invention) As described above, the present invention performs image detection using an output signal of a line sensor for an area distant from a peripheral edge of an image projection surface by a certain distance or more, and therefore appears on the peripheral edge of the image projection surface. It is less likely to be affected by dust and scratches on the film, and it is less likely that the shadow of the carrier, the blip mark, or the background portion between frames will be mistaken for the image. It is no longer necessary to move only the inner part. Therefore, an image suitable for autofocus can be detected with high probability, and malfunctions are reduced.

[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 front view of a screen showing a moving range of its line sensor, FIG. 3 is a block diagram of a control system, and FIG.
5 and 5 show the original image and the output waveform of a specific pixel when the line sensor is moved. FIG. 4 shows the negative original image and FIG. 5 shows the positive original image. Further, FIG. 6 is an output waveform chart of each part in the process of obtaining the contrast signal, and FIG. 7 is a flow chart of the image detecting operation. 10 …… Original image, 20 …… Projection lens, 28 …… Screen as image projection surface, 40 …… Line sensor, 42 …… Rotating arm, X …… A certain range for image detection.

Claims (1)

[Claims] 1. A method for guiding a projected image to a rectangular image projection plane,
In an autofocus device that detects an image suitable for an autofocus operation while moving a line sensor on which a part of the projected image is incident, an output signal of the line sensor for an area separated from a periphery of the image projection surface by a certain distance or more. An autofocus device characterized in that an image is detected by using.