JPS63172147A - Auto-focusing method - Google Patents

Abstract

PURPOSE:To raise a probability that the movement range of a specific picture element includes an image and to extend the extent of its movement by discriminating the presence or the absence of image based on the output signal of the specific picture element near the far end of a line sensor when the output signal of the specific picture element of the moving line sensor is used todetect an image. CONSTITUTION:When the auto-focusing mode is selected by a switch, a CPU 52 starts a motor 44 so that a line sensor 40 is moved into a screen 28 form the outside above the screen 28. A turning angle theta of the line sensor 40 is detected by an encoder 46, and the image detecting operation is started when it enters into a range THETA. Since the line sensor 40 is moved on an arcuate locus by a turning arm 42, an image is surely detected. That is, though the line sensor may be moved along a ruled line in the image or a straight line in a table to make image detection impossible if the line sensor is moved along a straight line, impossibility of image detection is very reduced because the line sensor is moved along an arc. Thus, the image suitable for the auto-focusing operation is accurately detected.

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 I 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.

In this case, as the line sensor moves, the output signal of a specific pixel of the line sensor is monitored, and the value obtained by subtracting and adding a certain number from the peak value and minimum value of this output signal is defined as the slice level, and the main scanning of the line sensor is An image detection method has been proposed that determines that an image exists when the output signal crosses this slice level a predetermined number of times or more.

However, in this case, the movement range of a specific pixel of the line sensor is
It is desirable that the probability of including an image is particularly high and that the moving distance can be ensured as large as possible.

(Purpose of the invention) The invention has been made in view of the above circumstances, and when performing image detection using the output signal of a specific pixel of a moving line sensor, the movement range of the specific pixel is calculated based on the probability that the moving range includes the image. It is an object of the present invention to provide an autofocus method that can increase the distance of movement and the distance of movement of the autofocus.

(Structure of the Invention) According to the present invention, this purpose 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. In the autofocus device, the line sensor is provided so as to be rotatable within a range closer to the fulcrum than two adjacent parts with a fulcrum near a corner of the image projection surface, and a specific pixel near a far end of the line sensor This is achieved by an autofocus method characterized by determining the presence or absence of an image based on the output signal of.

(Example) Fig. 1 is an overall schematic diagram of a league printer that is an embodiment of the present invention, Fig. 2 is a front view of the screen showing the movement range of the line sensor, and Fig. 3 is a block diagram of the control system. 4 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 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 10 is an original image of a microphotograph such as microfiche or microroll film. 1
2 is a light source, and the light from the light source 12 is passed through a condenser lens 14.
, a heat shielding filter 16, and a reflecting mirror 18, and are guided to the lower surface of the original image 10. In the camera mode, the transmitted light (projected image) of the original image 10 is transmitted through the projection lens 20 and the reflecting mirror 22.2.
4.26, the image is guided to a transmission screen 28 as an image projection surface, and an enlarged projected image of the original image 10 is formed on this screen 28. In printer mode, reflector 2
4 is rotated to the imaginary line position in FIG. 1, and the projected light is reflected by the reflecting mirror 22.
30.32 leads to a PPC type slit exposure type printer 34.

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 the shaded area in FIG. 2, that is, within the area closer to the fulcrum than the two corners adjacent to the upper left corner. The rotation angle 0 of this motor 44, that is, the rotation arm 42, is detected by a rotary encoder 46.

Reference numeral 50 denotes a control means, which performs main scanning from the end far from the fulcrum while moving the line sensor 40, and controls the line sensor 40.
The slice level for image detection is changed based on the output of a specific pixel, and in parallel with this, an image detection operation is performed to determine the presence or absence of an appropriate image. Here, one or more pixels near the end far from the fulcrum are used as the specific pixel.

Further, this control means 50 performs focus determination based on the output signal of the line sensor 48, and controls the projection lens 20 by the motor 51.
(FIG. 1), autofocus operation to move to the in-focus position, control of the printer 34, reflector 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 is scanned from the end farthest from the fulcrum toward the fulcrum by this driving pulse b, and outputs the output signal C of each pixel to the amplifier 56 in sequence. In this way, the main scanning of the line sensor 40 is performed. This output signal C is amplified by an amplifier 56 and an output signal d
(See Figure 6 (I)).

This output signal d is converted into a signal e shown in FIG. 6(II) 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(III). 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 54.
synchronization signal b that is output in synchronization with the output signal of a specific pixel
', only the output signal d' of this specific pixel is temporarily stored. 64 is a changeover switch, and this switch 64
In response to a command from the CPU 52, the output signal d' stored in the sample hold circuit 62 during main scanning is read into the CPU 52 via the A/D converter 66, while the output signal d' stored in the peak hold circuit 60 is read in at the end of the main scanning. contrast C
is read into the CPU 52 via the A/D converter 66. C.P.
U52 determines and temporarily stores the peak value D (max) and 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 of a comparator 68 for blooming detection. A voltage 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, the comparator 68 inputs to the CPU 52 the blooming signal f which becomes logic "l" when blooming occurs. CPU
52 changes the signal a so as 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 at this time. The output signal d is further input to the non-inverting input of a comparator 72,74. A comparator 72 determines the slice level S for the negative original image. The minimum value D (min) of the output signal d' stored in the CPU 52 is added to the predetermined value α (D (min)).
)+α) is input via the 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 its inverting input terminal has a predetermined value β subtracted from the peak value D (max) of the output signal d' stored in the CPU 52 (D ( ma
x)-β) is input via the D/A converter 78.

This (D(max)-β) indicates the slice level Sp for the positive original image. The comparators 72 and 74 send a logic '''l II signal to the counters 80 and 82 when the output signals d exceed slice levels Sn and Sp, respectively.
The output of the comparator 72.74 is logic + for the counter 80.82.
The number of times the number reaches 1111 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 perpendicular to the main-scanning direction (longitudinal direction), the output signal d will change to the slice level Sn, Sp.
1 is added to the counters 80 and 82 each time the value exceeds .

If this count value exceeds a certain number, it is assumed that an image exists. Considering that the fixed number of this count value may be incorrectly counted due to dust attached to the original film, it is not desirable to set it to "1" or "2"; for example, set it to "4" or more. It is better to do so.

In FIG. 1.3, 84 is a sensor that detects the magnification and type of the projection lens 20.
The magnification of the projection lens 20 is detected based on the output. 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 type of the projection lens 20. A correction curve for illuminance unevenness for each lens is stored in advance in the memory 86 in FIG.
are the contrast C and the output signal d' or the slice levels Sn and S with respect to the rotational position θ of the line sensor 40.
Correct p.

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 detects blooming and reduces the exposure amount by shortening the accumulation time based on the blooming signal. This memory 8 has an anti-blooming function that reduces
8, it is desirable to store the driving frequency so that the exposure amount is slightly blooming. This is to increase the accumulation time and obtain a large output amplitude from the line sensor even for images with low contrast.

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 controls the projection lens 20 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 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 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 4o on the screen 28 shown in solid line in FIG.
The motor 44 is started to move the screen 28 from an upper outer position into the screen 28 (step 106). 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.
08).

Since the line sensor 40 is moved along an arcuate trajectory by the rotating arm 42, 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, such things will be extremely rare.

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.

For example, this rectangular range X corresponds to the range that overlaps when A4 size enlarged images are projected vertically and horizontally onto the center of the screen 28, and there is a possibility that the image will always exist regardless of whether the original image is vertically or horizontally oriented. is also in a very high range.

When using a microfiche with a large number of original images arranged vertically and horizontally, the microfiche is loaded into a driving shaft, and the original image is moved by the movement of this carrier. At this time, the shadow Y of the carrier is shown in Figure 4. As shown in (A), it may appear near the edge of the screen 28. Also, frames located at the edge of the film may be projected onto parts of the film where there is no film. Furthermore, for roll films, identification marks such as blip marks are placed on the screen 28.
It may appear near the edge of. In this embodiment, even if such a shadow Y of the carrier, a non-image area of the film, or a blip mark appears on the screen 28, the image detection operation is performed using an image within a certain range X near the center of the screen 28. Malfunctions are further reduced.

When the line sensor 40 enters the range e while being main-scanned from the end far from the rotation fulcrum, a predetermined operation is performed using the 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), and if blooming occurs, the output signal f becomes 'l'', so the CPU 52 adjusts the driving frequency of the line sensor 40. A signal a instructing the clock generator 54 to increase the exposure amount 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 located on the end side far from the fulcrum is temporarily stored in the sample and hold circuit 62 by the output signal b' of the clock generator 54, while the contrast C by - times of main scanning is is stored in the peak hold circuit 60. By switching the switch 64, the output signal d' and the contrast C are changed every main scan.
It is read into PU52. The CPU 52 monitors changes in the output signal d' of one or more specific pixels while the line sensor 40 is moving, and determines the peak value D (max
) and the minimum value D (min) are continued to be found (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 pressure ra. Also, Fig. 5 (A), (
B) is also for a positive original image. Note that 1=n
The range from o to L corresponds to the range X in FIG. 2,
The CPU 52 uses the subsequent output signal d' to determine 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 Sn = D (min) + a Sp = [) (max) - β are set as slice levels for the negative and positive original images, respectively (step 116).

Further, the predetermined values α and β are the minimum value and the peak value o, i ~ 0.6 when expressed as an optical density expressed by the logarithm of the ratio F/FO of the transmitted luminous flux F and the incident luminous flux F.
, preferably set to about 0.2 to 0.4.

The CPU 52 converts these slice levels Sn and Sp into D/A
Transducer 76.78. The comparators 72 and 74 output 111 signals each time the output signal d exceeds the slice level Sn, 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 D(max) and slice level Sn, S
p continues to change, and 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 it is a negative original image, and the count value of the counter 82 increases if it is a positive original image. If these count values exceed a predetermined value (for example, 4), the CPU 52 determines that the slice levels Sn and Sp at that time are appropriate and that there is an image (step 118), and stops the line sensor 4o (step 118).
Step 120). Repeating the operations of steps 108 to 118 above (step 122), if it cannot be determined that there is an image (Stella 7'l18.122),
It is determined that there is an abnormality and a command is given to move the lens or the autofocus operation is stopped (step 124).

The accuracy of the slice levels Sn and Sp is determined by the line sensor 40.
The accuracy increases as the number of times the line sensor 40 moves and main scans increases, but in general, if the line sensor 40 moves and main scans about 10 to 20 times, sufficient accuracy can be achieved.

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 brightness I 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).
The projection lens 20 may be moved over the claw range to find the position where the brightness I 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.

Although the above embodiments apply the present invention to a reader printer, the present invention is also applicable to and includes other optical devices such as cameras, microscopes, and magnifying projectors.

In this embodiment, the output of the line sensor is valid only within the rectangular range X of the screen 28, which further reduces malfunctions as described above.
This includes those that move on an arc over the entire range of .

In addition, 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 each part of the upper left or each part of the lower left as in this embodiment, the line sensor is convenient because it does not overlap with blip marks, etc.

(Effects of the Invention) As described above, the present invention is provided with a line sensor rotatable around the outside corner of the image projection surface.
The line sensor will move along an arcuate range. For this reason, the configuration is generally simpler and cheaper than a system in which line sensors are linearly linked. That is, when the movement of the line sensor is realized by the rotational movement of a motor, there is no need for a mechanism to convert the rotational movement into linear movement. Furthermore, since the line sensor performs image detection using the output signal of a specific pixel on the end side far from the rotation fulcrum, the moving distance of this specific pixel becomes large. Therefore, even if the image contains ruled lines or straight lines in the table, the line sensor will not move on these straight lines, and the probability of image detection failure is significantly reduced, making it possible to accurately select images suitable for autofocus operation. can be detected.

[Brief explanation of the drawing]

Fig. 1 is an overall schematic diagram of a league 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.

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: The sensor has a fulcrum near the corner of the image projection plane, and is rotatable within a range closer to the fulcrum than each of the two adjacent parts. An autofocus method characterized by determining presence or absence.