JP2006039230A - Image scanner and its focusing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the region, in which focus is diverged, even though distortion of a reading surface of a manuscript is large. <P>SOLUTION: A plurality of focusing object regions being the reference of focusing adjustment, are provided in a reading object area. In the focus adjustment, a partial focusing position, which is the position of an image forming lens that respectively focuses to each focusing object region, is detected. Then, the depth of the field to be photographed corresponding to a maximum value (a maximum distance) of the mutual distance difference between partial focusing positions, i.e., the depth of the field to be photographed (a correct depth of the field to be photographed), that can focus all of the focusing object regions and has a width having an approximately equal distortion width of a photograph film, is obtained. Then, the diameter of a diaphragm opening is adjusted to obtain the correct depth of the field to be photographed and the depth of the field to be photographed is set. Then, the image forming lens is moved to complete the focusing adjustment so that all of the focusing object regions are to be included within the depth of the field to be photographed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention includes an imaging optical system in which an imaging lens and a diaphragm aperture are arranged on the optical axis, and an image for reading an image by forming light from a document on a light receiving surface of a photoelectric conversion means by the imaging lens. The present invention relates to a reading apparatus and a focus adjustment method thereof.

  2. Description of the Related Art An image reading apparatus is known that includes an optical system having an imaging lens and an aperture, and images an image recorded on a document by the optical system on a light receiving surface of a photoelectric conversion unit such as a CCD image sensor. It has been. An image reading apparatus (hereinafter referred to as a film scanner) using a photographic film as a document forms an image on a light-receiving surface of the CCD image sensor through the optical system by irradiating the photographic film from a light source and transmitting the photographic film.

  The photographic film is set on the film carrier, and one frame is fed to the reading position and inserted on the optical axis of the optical system. When the frame is fed to the reading position, focusing is performed by moving the imaging lens in the optical axis direction. Since the photo film pulled out from the cartridge has a curl hook, a crimping mechanism is provided at the reading position, for example, to press the periphery of the fed frame and flatten the entire reading surface of the frame. It has been. By ensuring the flatness of the frame in this way, for example, by focusing on the center of the frame, the entire surface of the frame can be focused.

  Of course, even if such a crimping mechanism is used, some distortion may remain on the reading surface, and the distance between the light receiving surface and the reading surface may change within the reading surface. In such a case, for example, even if the focus is adjusted to the center in the reading surface, the focus is not achieved around the center and the image becomes out of focus. In view of this, a film scanner that employs a multi-point AF method in which a plurality of focus target areas are set in a reading surface and focus is adjusted for each focus target area has been developed (for example, see Patent Document 1 below). ).

  In this film scanner, focus adjustment is performed on each focus target area, and the final focus position is determined so that most of each focus target area is included in the depth of field of the optical system. is doing. Here, as is well known, the depth of field refers to a range in which a lens forms a practically clear image (a range that can be regarded as being in focus), and before and after the one point on the basis of the focus. Say range. In the film scanner, the final in-focus position is determined so that many of the in-focus target areas centering on the main subject portion are included within a predetermined depth of field given in advance. Even in the case where some distortion remains on the reading surface, it is possible to reduce the focus area.

JP 2000-89374 A

  The film scanner uses a pressure-bonding mechanism to ensure a certain degree of flatness of the reading surface, and absorbs the focus shift caused by the distortion of the reading surface that cannot be wiped still by using the depth of field of the optical system. However, since the above-mentioned crimping mechanism increases the cost and leads to a delay in processing speed, in order to avoid these problems, the present applicant considers development of a film scanner that omits the above-described crimping mechanism. is doing. In that case, since the distortion of the reading surface is expected to be larger than that of the current film carrier, even if the in-focus position is determined by the above method, a large area in the reading surface becomes a defocused area. There was concern and a countermeasure was requested.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image reading apparatus and a focus adjustment method thereof that can reduce a defocus area even when a document reading surface has a large distortion.

  In view of the above background, the image reading apparatus of the present invention performs focus adjustment for each focus target area for a plurality of focus target areas set as reference points for focus adjustment in the read target area of the document. Based on the difference between the partial focus positions and the partial focus position detection means for detecting the partial focus position, which is the position of the imaging lens when the focal position and the light receiving surface of each focus target area coincide. A depth-of-field setting unit that obtains a depth of field that can focus on each of the focusing target areas, and sets the depth of field by adjusting the size of the aperture, and an imaging lens And a lens position adjusting unit that adjusts the position to an overall focusing position in which all the focusing target areas are included within the depth of field.

  The plurality of focus target areas are set to at least three points of a central portion of the reading target area and a pair of end portions that are located symmetrically with respect to the central portion and located near the diagonal of the reading target area. It is preferred that Further, it is preferable that the plurality of focus target areas are set according to the position and size of the reading target area or an effective area set in the reading target area.

  Also, the focus adjustment method of the present invention is a focus adjustment of an image reading apparatus that reads an image by forming light from a document on a light receiving surface of a photoelectric conversion means through an imaging lens and an aperture opening disposed on an optical axis. In the method, with respect to a plurality of focus target areas set as reference points for focus adjustment in the read target area of the document, focus adjustment is performed for each focus target area, and the focus position for each focus target area The partial focusing position, which is the position of the imaging lens when the light receiving surface coincides with the light receiving surface, can be detected, and all the focusing target areas can be focused based on the difference between the partial focusing positions. A depth of field is set, and the depth of field is set by adjusting the size of the aperture, and the position of the imaging lens is set within the depth of field. Adjust to the in-focus position that includes everything. It is characterized in.

  The present invention detects a partial focusing position, which is the position of an imaging lens that focuses on each of a plurality of focusing target areas, and adjusts the size of the aperture opening based on the partial focusing position, thereby adjusting each focusing position. Since the depth of field is set so that all of the focus target areas are in focus, an appropriate depth of field according to the distortion of the document is set. Then, the focusing lens is adjusted by moving the imaging lens so that all of the focus target areas are included in the depth of field. As a result, even if the document is distorted, it is possible to focus on the entire area to be read.

  A digital print system 2 shown in FIG. 1 includes an area CCD scanner 3, an image processing device 4, a display 5, a laser printer 6, and a processor 7. The digital print system 2 displays an image of each frame of a photographic film 21 (see FIG. 2). The image is read by the area CCD scanner 3 and printed by the laser printer 6. The area CCD scanner 3, the image processing device 4, and the display 5 are integrated as an input device 8, and the laser printer 6 and the processor 7 are integrated as an output device 9.

  The area CCD scanner 3 is an image reading device that reads a photographic image of each frame from a photographic film 21 that is a read original. This read signal is converted into digital data by an A / D converter 64 (see FIG. 2), and this photographic image data is taken into the image processing apparatus 4. The image processing device 4 performs various image processing such as density correction, color correction, and sharpness processing on the photographic image data. The photographic image data that has been subjected to image processing is converted into image data for recording and sent to the laser printer 6.

  As is well known, the laser printer 6 includes a laser exposure unit including R, G, and B laser light sources, a polygon mirror, an Fθ lens, a reflection mirror, and the like. Record the latent image. The processor 7 performs development processing on the printed color paper.

  FIG. 2 is a block diagram showing the configuration of the area CCD scanner 3. The photographic film 21 is set on the film carrier 22. The film carrier 22 is provided with a conveyance path 23 and a conveyance roller 24. The conveyance path 23 of the photographic film 21 has a U-shaped cross section at both sides in the width direction (see FIG. 6). These both side portions are in contact with both side end portions of the photographic film 21 to control distortion caused by curl of the photographic film 21.

  The film carrier 22 does not include a pressure-bonding mechanism that ensures the flatness of the frame at the reading position, and the photographic film 21 is sent to the reading position in a posture guided only by the transport path 23. For this reason, the photographic film 21 is read with the distortion remaining on the reading surface. The transport roller 24 includes a pair of rollers disposed on the upper side and the lower side of the photographic film 21, and is provided on the upstream side and the downstream side of the transport path 23, respectively. The conveying roller 24 nips and conveys the photographic film 21 from above and below.

  Below the film carrier 22, an LED unit 30 is arranged. The LED unit 30 is a light source that illuminates the photographic film 21. The LED unit 30 is provided with a plurality of LEDs that emit light of each color of R, G, B, and IR, and these LEDs emit light selectively for each color. Each color light of R, G, and B is light for obtaining image data of each color. The IR light is light for obtaining position data of dust and film scratches attached to the photographic film 21.

  Above the film carrier 22, an imaging lens 40, a diaphragm plate 50, and an area CCD 60 are arranged side by side along the reading optical axis 39. The imaging lens 40 is driven by a lens driving mechanism 42 including a stepping motor, and moves in the vertical direction in the drawing to change the focal position.

  The aperture plate 50 is driven by an aperture drive mechanism 52 including a stepping motor, and changes the diameter of the aperture opening 54. As is well known, the depth of field changes depending on the amount of light traveling from the photographic film 21 toward the light receiving surface 62 of the area CCD 60, and the F value representing the brightness of the imaging lens 40 and the diameter of the aperture 54. Determined by relationship. The F value of the imaging lens 40 is a value unique to the lens. For this reason, the depth of field changes as the diameter of the aperture 54 changes.

  The imaging lens 40 and the diaphragm plate 50 are driven, and focus adjustment is performed by changing the focal position and the depth of field. With this focus adjustment, image light for each color emitted from the LED unit 30 and transmitted through the photographic film 21 is imaged on the light receiving surface 62 of the area CCD 60. As will be described in detail later, the area CCD scanner 3 can perform high-quality image reading by setting the depth of field according to the distortion of the photographic film 21 when adjusting the focus.

  As is well known, in the area CCD 60, a large number of photoelectric conversion elements corresponding to the pixels are arranged on the light receiving surface 62, and the image light from the photographic film 21 is converted into a light source and acquired as an image signal. The area CCD 60 acquires a simple image signal with a reduced number of pixels when performing focus adjustment, and acquires a main image signal using all the pixels when outputting to the image processing device 4. The analog image signal acquired by the area CCD 60 is output to the A / D converter 64. The A / D converter 64 A / D converts the analog image signal input from the area CCD 60, generates digital image data, and outputs the digital image data to the control unit 70. In this example, an area CCD is used, but a line CCD that reads an image for each line may be used.

  The control unit 70 is provided to control the area CCD scanner 3 in an integrated manner, and is connected to each part of the area CCD scanner 3. The control unit 70 performs drive control of each connected unit based on an operation signal input from an operation unit (not shown) such as a keyboard and a mouse attached to the area CCD scanner 3.

  The control unit 70 is provided with a frame memory 72 and a focus adjustment unit 74. The frame memory 72 is a working memory and temporarily stores the image data output from the A / D converter 64. Then, the image data based on the main image signal stored in the frame memory 72 is output to the image processing device 4 as photographic image data. The image data based on the simple image signal stored in the frame memory 72 is used for focus adjustment.

  The focus adjusting unit 74 adjusts the focus by controlling the lens driving mechanism 42 and the aperture driving mechanism 52. As described above, when the photographic film 21 is distorted, the distance between the reading target area set in the photographic film 21 and the area CCD 60 becomes non-uniform in the plane of the reading target area. When focus adjustment is performed with the center of the region as a reference, other portions may be out of focus. For this reason, the area CCD scanner 3 employs the multi-point AF method, and a plurality of focus target areas serving as focus adjustment references are provided in the read target area. The focus adjustment unit 74 performs focus adjustment considering the distortion of the photographic film 21 by using a plurality of focus target areas as a reference.

  The photographic film 21 has a strong tendency to curl in both the transport direction and the width direction. For this reason, in this embodiment, as shown in FIG. 3A, five focus target areas 82a to 82e are provided in the center and near the four corners of the read target area 80 of the photographic film 21.

  For example, as shown in FIG. 3B, when three focus target regions 82f to 82h are arranged in the center in the width direction of the read target region 80, the photographic film 21 is curled in the width direction ( Although the distance between the reading target area 80 and the area CCD 60 is different in the plane of the reading target area 80, the distances from the respective focusing target areas 82f to 82h to the area CCD 60 are all equal. End up. As described above, even if an area having the same distance from the area CCD 60 is set as the focus target area, focus adjustment in consideration of distortion of the photographic film 21 cannot be performed.

  Similarly, when three focus target areas are arranged side by side in the center of the reading target area 80 in the conveyance direction, if the photographic film 21 is curled in the conveyance direction, the distance between the reading target area 80 and the area CCD 60 is read. Despite being different in the target area 80, the distances from the respective focus target areas to the area CCD 60 are all equal, and focus adjustment in consideration of the distortion of the photographic film 21 cannot be performed.

  By providing five focus target areas 82a to 82e as in the present embodiment, the reading target area 80 is closest to the area CCD 60 even if the photographic film 21 is distorted in either the transport direction or the width direction. The region and the region farthest from the area CCD 60 are included in any of the focusing target regions 82a to 82e. Focusing in consideration of distortion of the photographic film 21 can be performed by using as a reference a focusing target area having a different distance from the area CCD 60.

  The focus adjustment method will be described below with reference to the flowcharts shown in FIGS. As shown in FIG. 4, the focus adjustment unit 74 refers to the frame memory 72 while moving the imaging lens 40, and examines the contrast change in each of the focusing target regions 82a to 82e (S10). Subsequently, in each focus target area 82a to 82e, the position of the imaging lens 40 when the contrast value is the highest is set as a partial focus position in focus with respect to each focus target area 82a to 82e. Detect (S20). The partial focus positions detected in the focus target areas 82a to 82e are stored in the RAM 77 (S30).

  For example, as shown in FIG. 6A, when the photographic film 21 is curled in the width direction, the distance to the light receiving surface 62 is different between the center in the width direction and both sides in the width direction in the reading target region 80. . For this reason, as shown in FIG. 5B, the in-focus target area 82a provided in the center in the width direction of the read target area 80 and the in-focus target areas provided in both sides in the width direction of the read target area 80. The contrast is maximized at different lens positions from 82b to 82e. The two lens positions are detected as partial focusing positions, respectively.

  Thereafter, the focus adjustment unit 74 performs a depth-of-field setting process (S40). As shown in FIG. 5, the focus adjustment unit 74 refers to the RAM 77 and detects the maximum value (maximum distance) of the distance difference between the partial in-focus positions (S41). This maximum distance corresponds to the distortion width of the photographic film 21.

  Subsequently, the focus adjustment unit 74 has a depth of field corresponding to the maximum distance, that is, a width (depth) substantially equal to the distortion width of the photographic film 21, and aligns all the focusing target regions 82a to 82e. Determine the depth of field (appropriate depth of field) that enables focusing. Then, the diameter of the aperture 54 is determined so as to obtain an appropriate depth of field (S42). As is well known, the depth of field becomes shallower as the diameter of the aperture opening 54 is opened (the range that can be regarded as being in focus is narrower), and deeper as the diameter of the aperture opening 54 is reduced (in focus). The range that can be regarded as wide). For this reason, if the appropriate depth of field is determined, the diameter of the aperture 54 that can obtain the appropriate depth of field can be determined.

  The look-up table (LUT) 78 stores the relationship between the maximum distance and the diameter of the aperture 54 for obtaining an appropriate depth of field at the maximum distance in association with each other. The focus adjustment unit 74 determines the diameter of the aperture 54 by referring to a look-up table (LUT) 78. After the diameter of the aperture 54 is determined, the focus adjustment unit 74 controls the aperture drive mechanism 52 to drive the aperture plate 50 so as to form an aperture with the selected diameter (S43). Thereby, the setting process of the depth of field is completed.

  In the example shown in FIG. 6, the distance difference between the two partial focusing positions is detected as the maximum distance, and the diameter of the aperture 54 is adjusted based on this maximum distance. In this example, since the reading target area 80 does not fit within the initial depth of field with the aperture fully opened, the width of the depth of field is expanded so that the entire reading target area 80 is within the depth of field. So that the diameter of the aperture 54 is reduced.

  Subsequent to the depth-of-field setting process, the focus adjustment unit 74 determines the overall focus position, which is the position of the imaging lens 40 that can be regarded as being in focus on the entire reading area 80, as shown in FIG. (S50). The overall in-focus position is the position of the imaging lens 40 in which all of the in-focus areas 82a to 82e are included within the appropriate depth of field, and the center of the appropriate depth of field and the distortion of the photographic film 21. The position of the imaging lens 40 that coincides with the center of the width is determined as the overall focusing position. The focus adjustment unit 74 has an intermediate position between the partial focus position closest to the photographic film 21 and the partial focus position closest to the area CCD 60 among the partial focus positions detected from the focus target areas 82a to 82e. The position is determined as the overall focus position. Then, the focus adjustment is completed by moving the imaging lens 40 to the entire in-focus position (S60).

  In the example shown in FIG. 6, an intermediate position between two partial focusing positions is determined as a whole focusing position, and the imaging lens 40 is moved here. Thereby, the focus adjustment is completed, and all of the focusing target areas 82a to 82e are accommodated within the set depth of field, and it can be considered that the entire surface of the reading target area 80 is in focus.

  As described above, the area CCD scanner 3 sets the depth of field according to the distortion of the document by adjusting the size of the aperture at the time of focus adjustment. The focusing lens is adjusted by moving the imaging lens so that the entire focus target area is included. As a result, even if the document is distorted, it is possible to focus on the entire area to be read.

  As described above, the depth of field is determined by the F value representing the brightness of the imaging lens and the size of the aperture, so that the depth of field is deep in advance without adjusting the aperture. It may be possible to focus on the entire surface of the reading target area by using an imaging lens. However, a lens having a deep depth of field is a dark lens having a large F value. If this lens is used, the quality of an image to be read is generally lowered. In the present invention, since the depth of field is set by adjusting the size of the aperture, it is possible to focus on the entire area to be read using a bright lens having a small F value. Thereby, high-quality image reading can be performed.

  In the above embodiment, five focus target areas are provided in the center and near the four corners of the read target area, but the position and shape of the focus target area can be freely set. Further, the number of focusing target areas may be freely set as long as it is two or more. However, as described above, depending on the set position of the focus target area, the distance between the set focus target areas and the area CCD may be equal even if the document is distorted. For this reason, the focus target area is set to at least three points of a central portion of the read target area and a pair of end portions that are located symmetrically with respect to the central portion and located near the diagonal of the read target area. It is preferable.

  For example, when a part of a frame of a photographic film is enlarged and output, it is preferable to set a focus target area according to the position and size of the enlarged part. As a method for enlarging the frame, a part of the entire frame is read as a reading target area, and the entire surface of the scanned image data is expanded, and the entire surface of the frame is read as a reading target area. A method of extracting and enlarging a part of image data is conceivable. In the former case, it is preferable to set the focusing target area according to the position and size of the reading target area with respect to the frame. In the latter case, it is preferable to set the focusing target area in accordance with the position and size of the effective area in the reading target area to be extracted.

  A film scanner often reads from a long photographic film in which a plurality of frames are continuous. In such a photographic film, it can be considered that almost the same distortion has occurred in all the frames. For example, based on partial focus positions detected from a plurality of focus target areas only for the top image frame. Focus adjustment may be performed, and the number of focus target areas may be reduced for the remaining image frames, or the focus adjustment performed at the top frame may be applied as it is without performing focus adjustment. As described above, accurate focus adjustment is performed only on the first image frame, and simplified focus adjustment is performed on the remaining image frames, thereby shortening the time required for reading.

  In the above embodiment, the example in which the diameter of the aperture opening is automatically adjusted according to the distortion of the document has been described. However, since reducing the diameter of the aperture opening leads to a decrease in reading resolution, the diameter of the aperture opening is reduced. Before the change, the approval of the operator of the image reading apparatus may be requested. In this case, the diameter of the aperture opening is usually maximized, the distortion (maximum distance) of the document is large, and it is necessary to reduce the aperture to keep the entire area to be read within the depth of field. The operator is notified by displaying it on the screen. Then, the final selection of whether or not to change the aperture is left to the operator, and the diameter of the aperture opening may be changed when the operator approves.

  In the above embodiment, the intermediate position between the farthest partial focusing positions (the position where the film is focused on the center of the distortion width of the film) has been described as an example of the overall focusing position. It is not limited to. It is known that the depth of field has a characteristic that the back side (LED unit side) is wider than the near side (area CCD side) from the object to be focused. For this reason, the position for focusing on the area CCD side rather than the center of the distortion width of the film may be determined as the overall focusing position. In this way, the entire surface of the reading target area can be more reliably contained within the appropriate depth of field.

  In the above embodiment, a photographic film has been described as an example of a document. However, the present invention is not limited by the type of document, and the present invention can be applied to various documents of different sizes and types. it can. For example, in the above embodiment, an explanation has been given of an example of an image reading apparatus that uses a transmissive original and provides illumination from the back side of the original, but a reflective original that uses a reflective original and provides illumination from the front side of the original. The present invention may be applied to an image reading apparatus such as a scanner.

  In the above embodiment, a CCD image sensor is used and the focus is adjusted based on the contrast of the image formed on the light receiving surface. However, instead of the CCD image sensor, for example, a light emitting unit and A distance measuring sensor is provided to measure the distance from the time from when the light from the light emitting part is reflected by the irradiation target to enter the light receiving part to the irradiation target. You may make it adjust focus by measuring the distance to a focus object area | region and moving an imaging lens based on the measured distance.

1 is a schematic configuration diagram of a digital print system. It is a schematic block diagram of an area CCD scanner. It is explanatory drawing showing a focusing object area | region. It is a flowchart showing the adjustment procedure of a focus. It is a flowchart showing the setting process of a depth of field. It is explanatory drawing showing the contrast change when the state of a photographic film and the imaging lens are moved.

Explanation of symbols

2 Digital Print System 3 Area CCD Scanner 21 Photo Film 23 Transport Path 39 Reading Optical Axis 40 Imaging Lens 42 Lens Drive Mechanism 50 Diaphragm Plate 52 Diaphragm Drive Mechanism 54 Diaphragm Opening 60 Area CCD
62 Light-receiving surface 70 Control unit 74 Focus adjustment unit 80 Reading target region 82a to 82h Focusing target region

Claims (4)

In an image reading apparatus comprising an imaging optical system in which an imaging lens and an aperture opening are arranged on the optical axis, and reading an image by forming an image of light from a document on a light receiving surface of a photoelectric conversion means by the imaging lens,
Focus adjustment is performed for each focus target area for a plurality of focus target areas set as reference points for focus adjustment in the read target area of the document, and the focus position for each focus target area and the focus position A partial focusing position detecting means for detecting a partial focusing position which is a position of the imaging lens when the light receiving surface coincides with the light receiving surface;
Based on the difference between the partial focusing positions, the depth of field at which all of the focusing target areas can be focused is determined, and the depth of field is set by adjusting the size of the aperture opening. Depth-of-field setting means,
An image reading apparatus comprising: a lens position adjusting unit that adjusts a position of the imaging lens to an entire in-focus position where all of the in-focus target areas are included within the depth of field.   The plurality of focus target areas are set to at least three points of a central portion of the reading target area and a pair of end portions that are located symmetrically with respect to the central portion and located near the diagonal of the reading target area. The image reading apparatus according to claim 1, wherein:   The image reading apparatus according to claim 1, wherein the plurality of focus target areas are set according to the position and size of the reading target area or an effective area set in the reading target area. . In a focus adjustment method of an image reading device that reads an image by imaging light from a document on a light receiving surface of a photoelectric conversion unit through an imaging lens and an aperture opening disposed on an optical axis.
Focus adjustment is performed for each focus target area for a plurality of focus target areas set as reference points for focus adjustment in the read target area of the document, and the focus position for each focus target area and the focus position Detecting a partial focusing position that is the position of the imaging lens when the light receiving surface coincides,
Based on the difference between the partial focusing positions, the depth of field at which all of the focusing target areas can be focused is determined, and the depth of field is set by adjusting the size of the aperture opening. And
A focus adjustment method for an image reading apparatus, wherein the position of the imaging lens is adjusted to an overall focus position where all of the focus target areas are included within the depth of field.

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