JP4813451B2 - IMAGING SYSTEM, IMAGING DEVICE EQUIPPED WITH THIS IMAGING SYSTEM, PORTABLE TERMINAL DEVICE, IN-VEHICLE DEVICE, AND MEDICAL DEVICE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve quality of image data obtained by picking up an optical image projected on a photo-detection plane in an imaging system. <P>SOLUTION: As for a point image P1 projected from any position through an imaging lens 10 onto a photo-detection plane 21, an imaging system is also prepared which is constituted of the imaging lens 10 and an imaging device 20 configured in such a way that a maximum diameter of an effective area of a point image P1 is sized over three or more pixels of photo-detecting pixels. A signal processing unit 40 applies restoration processing to first image data output from the imaging device 20 in such a way as to produce second image data, equal to the first image data, which are output from the imaging device 20 when a resolution of the imaging lens 10 is high. The imaging lens includes, in order from an object side, a first lens group constituted of at least one lens and having positive power and a second lens group constituted of at least one lens and having positive power. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an imaging system that improves the quality of image data obtained by capturing an optical image of a subject using a restoration process, and an imaging device, a portable terminal device, an in-vehicle device, and a medical device including the imaging system It is about.

  An imaging system for imaging an optical image of a subject formed on a light receiving surface through an imaging lens using an image sensor such as a CCD element or a CMOS element having a light receiving surface in which a large number of light receiving pixels are two-dimensionally arranged. Are known.

  As an example of such an imaging system, an in-vehicle camera or a mobile phone camera in which an imaging system having an imaging lens designed so as to increase the depth of field is directly mounted on a circuit board is known. (See Patent Document 1). Such an imaging system that is directly attached to the circuit board is designed to reduce the size of the apparatus because the size is limited.

Furthermore, there are known imaging systems mounted on high-performance in-vehicle cameras and mobile phone cameras, in which the resolution of the imaging lens is close to the diffraction limit.
JP 2007-147951 A

  Incidentally, there is a demand for further improvement in resolution of an image obtained using such an imaging system.

  In order to improve the resolution of an image obtained by the imaging system, it is necessary to increase the number of light receiving pixels and increase the resolution of the imaging lens. That is, for example, the pixel density of the light receiving pixels arranged on the light receiving surface of the image sensor is increased, and the point image projected on the light receiving surface through the imaging lens is within the range of one light receiving pixel. By increasing the resolving power of the imaging lens, the resolution of an image obtained using the imaging system can be improved.

  Here, increasing the pixel density of the light-receiving pixels constituting the image sensor without increasing the device size can be realized relatively easily by recent technological improvements.

  On the other hand, it is extremely difficult to improve the resolution of the imaging lens. That is, in order to improve the resolution of the imaging lens without increasing the size of the imaging lens or reducing the depth of field, it is necessary to suppress the shape error and assembly error of each lens constituting the imaging lens. . However, the resolution of such imaging lenses has already been increased to a point close to the diffraction limit, and it is very difficult to improve the resolution by further increasing the manufacturing accuracy (processing, assembly, adjustment accuracy, etc.). There's a problem.

  The present invention has been made in view of the above circumstances, an imaging system capable of improving the quality of image data obtained by capturing an optical image projected on a light receiving surface, and an imaging including the imaging system. An object of the present invention is to provide a device, a portable terminal device, an in-vehicle device, and a medical device.

  The imaging system of the present invention has an imaging lens and a light receiving surface in which a large number of light receiving pixels are arranged two-dimensionally, and picks up an optical image of a subject projected on the light receiving surface through the imaging lens. An image sensor that outputs first image data representing the second image data equivalent to the first image data output from the image sensor when the resolution of the imaging lens is high with respect to the first image data. Signal processing means for performing restoration processing as generated, and the imaging lens, in order from the object side, includes a first lens group having a positive power composed of at least one lens and at least one lens. A point image in which the imaging lens and the imaging element are projected onto the light-receiving surface through the imaging lens from any position in the X, Y, and Z directions. Moso It is characterized in that the maximum diameter of the effective region of the point image is one that is configured to be sized for over three pixels of the light receiving pixels.

  The imaging lens is an MTF related to an optical image of an object projected on the light receiving surface through the imaging lens from any position in the X, Y, and Z directions separated by 10 times or more of the focal length of the imaging lens. The characteristic value may be configured to be positive.

  The signal processing means performs a restoration process with a pixel area extending over a total of 9 pixels or more consisting of 3 pixels or more in the vertical direction and 3 pixels or more in the horizontal direction on the light receiving surface, or projected on the light receiving surface. For example, the restoration process may be executed with a minimum pixel area including all the effective areas of the point image as a minimum unit.

  The signal processing means determines the size representing the effective area of the point image in the image represented by the second image data rather than the size representing the effective area of the point image in the image represented by the first image data. The restoration process can be executed so as to reduce the size.

  The signal processing means may execute the restoration process using a restoration coefficient corresponding to the state of the point image represented by the first image data.

  The restoration coefficient is obtained for each imaging system individually for each imaging system, or the first of the restoration coefficient candidates corresponding to the state of the point images classified into a plurality of types. It is selected according to the state of the point image represented by the image data, or among the plurality of types of restoration coefficient candidates corresponding to the state of the point image classified into the plurality of types, the first image data The restoration coefficient selected according to the state of the point image to be represented can be further corrected according to the state of the point image.

  The imaging system may further include restoration coefficient acquisition means for acquiring a restoration coefficient.

  The imaging lens may be composed of two single lenses.

  A single lens corresponding to the first lens group having a meniscus shape with a convex surface facing the object side, and a single lens corresponding to the second lens group having a meniscus shape having a convex surface facing the object side It can be.

  A single lens corresponding to the first lens group has a convex shape on both surfaces of the single lens, and a single lens corresponding to the second lens group has a meniscus shape with the convex surface facing the image side. can do.

  An image pickup apparatus according to the present invention includes the image pickup system.

  A portable terminal device according to the present invention includes the imaging system.

  An in-vehicle device according to the present invention includes the imaging system.

  A medical device according to the present invention includes the imaging system.

  The maximum diameter of the effective area of the point image projected onto the light receiving surface can be the diameter of this effective area in the direction in which the effective area of the point image projected onto the light receiving surface includes the most light receiving pixels. The above-mentioned “configuration in which the maximum diameter of the effective area of the point image has a size of 3 pixels or more” means that “the effective area of the point image includes the most light receiving pixels. It can be set as the structure which becomes a magnitude | size covering 3 pixels or more. "

The “effective area of the point image” means an area having a light intensity equal to or higher than 1 / e ² (about 13.5%) of the peak intensity in the light intensity distribution representing the point image.

  For the “restoration process”, an image restoration process or the like introduced in Japanese Patent Laid-Open No. 2000-123168, paragraphs 0002 to 0016 can be employed. In the implementation of the restoration process, the non-patent literature described later (Kaichi Serizawa, Yukihiko Yamashita, title “Kernel Wiener Filter”, 2003 Workshop on Information-Based Induction Sciences, (IBIS2003), Kyoto, Japan, Nov 11- 12, 2003] can be applied.

  Further, the “position that is at least 10 times the focal length of the imaging lens” refers to a position where the most object side (object side) surface of the lens surfaces constituting the imaging lens intersects with the optical axis of the imaging lens. The reference position means a position away from the reference position along the optical axis direction (Z-axis direction) of the imaging lens toward the subject by 10 times the focal length.

  The imaging system of the present invention includes a first lens group having at least one lens and a positive power, and a second lens having at least one lens and having a positive power in order from the object side. The maximum diameter of the effective area of this point image is 3 pixels or more of the light receiving pixels for the point image projected from any position through the imaging lens onto the light receiving surface. The first image data output from the image sensor is equivalent to the first image data output from the image sensor when the resolving power of the image pickup lens is high with respect to the first image data output from the image sensor. Since the restoration process for generating the second image data is performed, the quality of the image data obtained by capturing the optical image projected on the light receiving surface can be easily improved.

  That is, in the imaging system of the present invention, it is possible to obtain an image equivalent to an image obtained by imaging an optical image projected through an imaging lens having a higher resolution than the imaging lens using an imaging lens having a lower resolution. it can. For example, it is assumed that the effective area of the point image projected through the imaging lens covers a total of 9 pixels, 3 pixels in the vertical direction and 3 pixels in the horizontal direction on the light receiving surface. Then, for example, when the effective area of the point image falls within the area of one pixel on the light receiving surface with respect to the first image data output from the image pickup device by capturing a point image covering a total of nine pixels. Restoration processing for generating second image data equivalent to the first image data output from the image sensor (that is, first image data output from the image sensor when the resolving power of the imaging lens is high) is performed. Since it applied, the 2nd image data showing the same image with the resolution higher than the resolution of the image which 1st image data represents can be obtained.

  Further, in this imaging system, since the restoration process can be performed on an optical image projected from any position through the imaging lens onto the light receiving surface, the resolution of the entire image represented by the first image data is improved. be able to. That is, the resolution of any region in the image represented by the second image data can be made higher than the resolution of the image represented by the first image data.

  As a result, the quality of image data can be improved more easily than in the case of improving the resolving power of the imaging lens by increasing the manufacturing accuracy (processing, assembly, adjustment accuracy, etc.) of the imaging system as in the past. be able to.

  Further, the optical image of the subject projected on the light receiving surface through the imaging lens from any position in the X, Y, and Z directions separated from the focal length of the imaging lens by 10 times or more is also related to this optical image. If the configuration is such that the value of the MTF characteristic is positive, the quality of the first image data representing the subject at a position 10 times or more the focal length of the imaging lens can be improved more reliably. it can.

  Further, if the signal processing means performs the restoration process with a pixel area extending over a total of 9 pixels or more consisting of 3 pixels or more in the vertical direction and 3 pixels or more in the horizontal direction on the light receiving surface as a minimum unit, the restoration process is further performed. It can be implemented reliably.

  Further, if the signal processing means executes the restoration process with the smallest pixel area including all the effective areas of the point image projected on the light receiving surface as the minimum unit, an increase in the amount of calculation in the restoration process is suppressed. The restoration process can be performed efficiently.

  In addition, the signal processing means has a size representing the effective area of the point image in the image represented by the second image data rather than a size representing the effective area of the point image in the image represented by the first image data. If the restoration process is executed so as to reduce the image quality, the quality of the image data can be improved more reliably.

  Here, if the signal processing means executes the restoration process using a restoration coefficient corresponding to the state of the point image in the image represented by the first image data (hereinafter also referred to as the blurred state of the point image), Since the second image data obtained by more accurately correcting the blurred state of the point image can be obtained, the quality of the image data can be improved more reliably.

  The reason why the “point image state” is also referred to as the “point image blur state” is that the point image projected on the light receiving surface through the imaging lens and the first image data obtained by imaging the point image are as follows. This is because the image of the point image to be represented has deteriorated somewhat due to the influence of lens aberration or the like as compared with the subject that is an object point corresponding to the point image. That is, for example, if the subject is a resolution chart, an image of the resolution chart projected on the light receiving surface through the imaging lens and an image of the resolution chart represented by the first image data obtained by imaging the image of the resolution chart. Is lower than the resolution of the resolution chart as the subject. The “point image state” or “point image blur state” mainly indicates a degradation state of the resolution of the point image.

  If the restoration coefficient is obtained for each imaging system individually for each imaging system, the restoration coefficient that can improve the quality of the image data can be obtained more accurately.

  Further, the restoration coefficient is assumed to be selected according to the blurring state of the point image represented by the first image data, from among the respective restoration coefficient candidates corresponding to the blurring states of the point images classified into a plurality of types. For example, it is possible to obtain the restoration coefficient more easily than in the case where the restoration coefficient is obtained individually for each imaging system.

  The restoration coefficient is selected according to the blurring state of the point image represented by the first image data from among a plurality of types of restoration coefficient candidates corresponding to the blurring states of the point images classified into the plurality of types. If the coefficient is further corrected in accordance with the blurring state of the point image, a reduction in accuracy when obtaining the restoration coefficient is suppressed compared to the case where the restoration coefficient is obtained individually for each imaging system. However, the restoration coefficient can be acquired more easily.

  Further, if the imaging system is provided with a restoration coefficient acquisition unit that acquires a restoration coefficient, the restoration coefficient can be more reliably obtained.

  Note that the imaging lens is composed of only two single lenses, the single lens of the first lens group has a meniscus shape with the convex surface facing the object side, and the single lens of the second lens group is the object side. If it has a meniscus shape with a convex surface facing the surface, the quality of the first image data representing the subject can be improved more reliably.

  Further, if the single lens of the first lens group has a convex shape on both surfaces of the single lens, and the single lens of the second lens group has a meniscus shape with the convex surface facing the image side, The telecentricity of the imaging lens can be improved more reliably.

  Since each of the imaging device, portable terminal device, in-vehicle device, and medical device of the present invention includes the imaging system, as described above, the quality of the image data obtained by capturing the optical image projected on the light receiving surface. Can be easily increased.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an imaging system of the present invention.

<About the configuration of the imaging system>
Hereinafter, the configuration of the imaging system will be described.

  An imaging system 100 of the present invention shown in FIG. 1 is an imaging element 20 having an imaging lens 10 and a light receiving surface 21 in which a large number of light receiving pixels are two-dimensionally arranged. An image pickup device 20 that picks up an optical image P1 of a subject projected onto the image and outputs first image data G1 representing the subject, and when the resolving power of the imaging lens 10 is high with respect to the first image data G1. And a signal processing unit 40 that performs a restoration process to generate second image data G2 equivalent to the first image data G1 output from the element 20.

  The imaging lens 10 includes, in order from the subject side (object side), a first lens group having a positive power composed of at least one lens, and a second lens group having a positive power composed of at least one lens. It has.

  The imaging lens 10 and the imaging device 20 are effective areas of the point image (P1) for the point image (P1) projected onto the light receiving surface 21 through the imaging lens 10 from any position in the X, Y, and Z directions. The maximum diameter is configured to be a size over three pixels or more of the light receiving pixels.

  Here, the maximum diameter of the effective area of the point image projected onto the light receiving surface 21 is that of the point image P1 in the direction in which the effective area of the point image P1 projected onto the light receiving surface 21 includes the most light receiving pixels. The effective area diameter.

  1 is the optical axis direction of the imaging lens 10, and the directions indicated by the arrows X and Y are directions parallel to the light receiving surface 21.

  Outside the imaging system 100, a restoration coefficient acquisition device 70A that acquires a restoration coefficient K corresponding to the blurring state of the point image P1 represented by the first image data G1 output from the imaging element 20 is provided. . The signal processing unit 40 performs the restoration process F using the restoration coefficient K acquired by the restoration coefficient acquisition device 70A.

  Here, it is assumed that the imaging system 100 includes a coefficient storage unit 30 in which the restoration coefficient K acquired by the restoration coefficient acquisition device 70A is stored. This coefficient storage unit 30 is built in the signal processing unit 40. It may be. Furthermore, the coefficient storage unit 30 is not necessarily provided in the imaging system 100.

  The restoration coefficient acquisition device 70A receives data Dr that is either design data related to a point image when there is no error in the optical system including the imaging lens 10 or ideal point image state data related to an ideal point image state that exceeds the design data. The point image for acquiring the ideal point image storage unit 72 stored in advance and the blurred point image state data Db indicating the blurred state of the point image P1 represented by the first image data G1 output from the image sensor 20. The blur state acquisition unit 73, the blur point image state data Db representing the blur state of the point image P1 obtained by the point image blur state acquisition unit 73, and the design data or ideal stored in the ideal point image storage unit 72 Coefficient data Dk indicating the restoration coefficient K corresponding to the blurring state of the point image P1 represented by the first image data G1 is obtained by inputting the data Dr which is point image state data and calculating using both. , And a restoration coefficient acquisition unit 78A for storing the restored coefficient K represented by the coefficient data Dk to the coefficient storage unit 30.

  The imaging lens used in the imaging system of the present invention is not necessarily limited to the one in which the optical image is correctly “formed” on the light receiving surface through the imaging lens, but the optical image is correctly displayed on the light receiving surface through the imaging lens. In the present invention, it is assumed that the optical image is “projected” on the light receiving surface through the imaging lens. The “not imaged” state is interpreted as a so-called blurred image. For example, a state in which a point image that is wider than the original point image is generated due to a manufacturing error or a design constraint condition (optical This includes a situation where the design value itself can provide only a point image larger than the point image originally desired due to the size and cost of the system.

  Further, the blurred point image state data Db mainly indicating the degradation state of the resolution of the point image includes, for example, the size of the effective region of the point image P1, the luminance distribution (density distribution in the image) on the light receiving surface of the point image P1, and the like. Can be represented.

<Operation of imaging system>
Next, the operation of the imaging system will be described.

  First, an example in which the restoration coefficient is obtained by the restoration coefficient acquisition apparatus and the restoration coefficient is stored in the coefficient storage unit will be described.

  An optical image of the subject projected onto the light receiving surface 21 through the imaging lens 10 is picked up by the image pickup device 20, and the first image data G 1 representing the subject output from the image pickup device 20 is sent to the point image blur state acquisition unit 73. Entered.

  The point image blur state acquisition unit 73 to which the first image data G1 is input analyzes the blur state of the point image represented by the first image data G1, and outputs the blur point image state data Db indicating the analysis result.

  The restoration coefficient acquisition unit 78A includes the blur point image state data Db output from the point image blur state acquisition unit 73 and the data Dr that is the design data or the ideal point image state data stored in the ideal point image storage unit 72 in advance. Is input, a restoration coefficient K corresponding to the blurred state of the point image P1 is obtained by calculation using both, and coefficient data Dk indicating the restoration coefficient K is output.

  The coefficient data Dk indicating the restoration coefficient K output from the restoration coefficient acquisition unit 78A is input to the coefficient storage unit 30, and the restoration coefficient K represented by the coefficient data Dk is stored in the coefficient storage unit 30.

  An example of realizing the function of the point image blur state acquisition unit 73 is a DxO analyzer manufactured by DxO Labs (France) described later. According to the DxO analyzer, the blur state of the point image P1 projected onto the light receiving surface 21 can be obtained by analyzing the first image data G1 output from the imaging device 20.

<About restoration processing>
Next, using the restoration coefficient K stored in the coefficient storage unit 30, the restoration process F is performed on the first image data output from the image sensor 20, and the resolution is higher than the image represented by the first image data. A case in which the second image data representing a high image is acquired will be described. In the following description, a case where the restoration process F is performed on first image data representing a point image will be mainly described.

  FIG. 2A is a diagram showing the light intensity distribution of a point image on the coordinates indicating the light intensity E on the vertical axis and the position in the X direction on the light receiving surface on the horizontal axis. FIG. 2B shows each pixel region of the light receiving pixels constituting the light receiving surface on the coordinates where the vertical axis indicates the position in the Y direction on the light receiving surface and the horizontal axis indicates the position in the X direction on the light receiving surface. FIG. 3A shows a point image projected on the light receiving surface, and FIG. 3A shows a point image displayed in the image represented by the first image data. b) is a diagram showing a point image displayed in the image represented by the second image data. Note that the sizes of the pixel regions (indicated by reference symbol Rg ′ in the figure) in the images shown in FIGS. 3A and 3B are the same. Note that each pixel region Rg of the light-receiving pixels constituting the light-receiving surface 21 and a pixel region Rg ′ in the image represented by the first image data G1 and the second image data G2 correspond to each other.

  4A is projected on the light receiving surface 21 when the resolving power of the imaging lens 10 is high on the coordinates indicating the light intensity E on the vertical axis and the position in the X direction on the light receiving surface on the horizontal axis. It is a figure which shows the light intensity distribution of the point image which will be. This may be considered to represent an ideal point image state regardless of the optical system. FIG. 4B shows each pixel region of the light receiving pixels constituting the light receiving surface on the coordinates indicating the position in the Y direction on the light receiving surface on the vertical axis and the position in the X direction on the light receiving surface on the horizontal axis. And a point image P2 that will be projected on the light receiving surface 21 when the resolving power of the imaging lens 10 is high.

  The maximum diameter M1 of the effective region R1 of the point image P1, which is an optical image projected onto the light receiving surface 21 through the imaging lens 10, is continuous with the light receiving pixels constituting the light receiving surface 21, as shown in FIG. The size is over 3 pixels. In addition, the effective area R1 is an area covering a total of nine pixels on the light receiving surface 21 including three pixels in the vertical direction and three pixels in the horizontal direction. That is, the effective area R1 is an area that occupies nine pixels (3 pixels × 3 pixels) of the light receiving pixels constituting the light receiving surface 21.

As shown in FIG. 2A, the effective region R1 of the point image P1 is a region having a light intensity equal to or greater than 1 / e ² of the peak intensity Ep1 in the light intensity distribution H1 representing the point image P1.

  The point image P1 projected on the light receiving surface 21 is picked up by the image pickup device 20, and first image data G1 representing the point image P1 is output from the image pickup device 20.

  As shown in FIG. 3A, the image P1 ′ corresponding to the point image P1 displayed in the image Zg1 represented by the first image data G1 still has an effective area R1 ′ of 9 pixels in the image. It is displayed as covering a minute (3 pixels × 3 pixels).

  Next, the signal processing unit 40 to which the image data G1 is input performs a restoration process F using the restoration coefficient K1 on the first image data G1 to obtain second image data G2.

  As shown in FIGS. 3A and 3B, the point image P2 ′ in the image Zg2 represented by the second image data G2 corresponding to the point image P1 ′ represented by the first image data G1. Is smaller than the effective area R1 ′ of the point image P1 ′ in the image Zg1 represented by the first image data G1. Accordingly, the maximum diameter M2 ′ of the point image P2 ′ represented in the image Zg2 (region corresponding to three pixels of the pixel region Rg ′) is also the maximum diameter M1 of the point image P1 ′ represented in the image Zg1. '(Area corresponding to one pixel of the pixel area Rg').

  That is, the point image P2 ′ represented by the second image data G2 shown in FIG. 3B and the point image P2 (which will be projected on the light receiving surface 21 when the imaging lens 10 has high resolving power). The image of the point image represented by the first image data output from the image sensor 20 that captured the image of FIG. 4 is equivalent to the image.

  More specifically, the effective area R1 projected on the light receiving surface 21 through the imaging lens 10 is output from the imaging element 20 that has captured a point image P1 (see FIGS. 2A and 2B) covering nine pixels. A point image P2 ′ (see FIG. 3B) represented by the second image data G2 obtained by performing the restoration process F using the restoration coefficient K on the first image data G1 to be performed; A point image P2 that is expected to be projected onto the light receiving surface 21 when the resolution of the imaging lens 10 is increased (the maximum diameter M2 of the effective region R2 is included in one pixel region Rg, FIG. The image of the point image represented by the first image data G1 output from the imaging device 20 that has imaged (b) is equivalent to the image.

In addition, the effective area | region R2 of the point image P2 contained in one pixel area | region Rg on the light-receiving surface 21 shown to Fig.4 (a), (b) represents the point image P2 similarly to the case of the said point image P1. This is a region having a light intensity of 1 / e ² or more of the peak intensity Ep2 in the light intensity distribution H2. Here, the effective area R2 of the point image P2 is a size included in one pixel area Rg.

  Thus, the resolution of the image represented by the second image data obtained by performing the restoration process on the first image data can be made higher than the resolution of the image represented by the first image data.

  In addition, since the restoration process F can obtain an image similar to the image obtained when the depth of field of the imaging lens 10 is enlarged, the restoration process substantially performs the field of the imaging lens 10. It can also be said to expand the depth.

  In the restoration process F using the restoration coefficient K according to the state of the point image P1 represented by the first image data G1 by the signal processing unit 40, the above-mentioned JP-A-2000-123168, paragraphs 0002 to 0016 are used. The image restoration process introduced in the above can be adopted.

  In the above description, the point image is captured. However, since the optical image of the subject projected on the light receiving surface 21 through the imaging lens 10 is considered to be a collection of point images representing the subject, In any case, the first image data can be restored to generate second image data representing an image at a higher resolution than the image represented by the first image data.

<About imaging system performance>
Next, the performance of the imaging system composed of the imaging lens 10 and the imaging device 20 used in the imaging system 100 will be described.

  In FIG. 5, the horizontal axis indicates the distance U in the optical axis direction from the imaging lens to the object point in logarithmic scale (m), and the vertical axis corresponds to the number (N) of pixel regions continuously arranged on the light receiving surface. The figure which shows typically the change of the maximum diameter of the effective area | region of the point image corresponding to this object point projected on the light-receiving surface when an object point is moved to the optical axis direction on the coordinate which shows the length. It is.

  Here, the object point is moved from the position of the near point that is substantially in contact with the imaging lens (position that is close to about 0.01 m) to the position of a far point that is about infinity away from the imaging lens (position that is about 10 m away). I let you.

  Three types of curves (solid lines) indicated by the series A-1, A-2, and A-3 in FIG. 5 are different specific regions on the light receiving surface 21 through the imaging lens 10 of the imaging system of the present invention ( The change of the maximum diameter of the effective area | region of each point image projected on the specific area | region on the light-receiving surface from which image height mutually differs is shown typically. Further, the curve (broken line) indicated by the series Aw in FIG. 5 is projected on the light receiving surface through an imaging lens used in a conventional imaging system (for example, an in-vehicle camera, a mobile phone camera, a medical device camera, etc.). The general change in the maximum diameter of the effective area of the point image is shown.

  As can be seen from FIG. 5, in the conventional imaging system, the maximum diameter of the effective area of the point image formed by projecting the object point on the light receiving surface 21 is one pixel as the object point moves in the optical axis direction. The size greatly changes from 30 to 30 pixels.

  On the other hand, the maximum diameter of the effective area of the point image formed by projecting an object point on the light receiving surface 21 through the imaging lens 10 included in the imaging system 100 of the present invention is any of the series A-1, A-2, and A-3. Is also a size ranging from 3 pixels to 10 pixels. That is, regardless of the distance from the imaging lens 10 to the object point, and regardless of the position of the projected point image on the light receiving surface (for example, the image height on the light receiving surface), There is little variation in the size of the effective area. Further, for any point image projected on the light receiving surface through the imaging lens 10 from any position in the X, Y, and Z directions, that is, from any position in the three-dimensional space, the variation in the size of the effective area of this point image is It can be said that there are few.

  In FIG. 6, the horizontal axis indicates the distance U in the optical axis direction from the imaging lens to the object point in logarithmic scale (m), and the vertical axis indicates the MTF characteristic value (%) on the coordinates where the object point is expressed as light. It is a figure which shows typically the change of the value (%) of the MTF characteristic regarding the optical image of the said object point projected on the light-receiving surface when it moves to an axial direction.

  Here, the object point is moved from the position of the near point that is substantially in contact with the imaging lens (position that is close to about 0.01 m) to the position of a far point that is about infinity away from the imaging lens (position that is about 10 m away). I let you.

  Three types of curves (solid lines) relating to the imaging system of the present invention indicated by the series B1, B2, and B3 in FIG. 6 are different specific areas on the light receiving surface through the imaging lens 10 (specific specifications having different image heights). 4 schematically shows a change in MTF characteristic value (%) related to the optical image projected onto the area (1). Further, the curve (broken line) indicated by the series Bw in FIG. 6 shows a general change in the value (%) of the MTF characteristic regarding the optical image projected on the light receiving surface in the conventional imaging system.

  As can be seen from FIG. 6, in the conventional imaging system, the value (%) of the MTF characteristic relating to the optical image projected onto the light receiving surface 21 varies greatly from 0% to a value exceeding 80%. An object located in a region closer to the imaging lens 10 (a region where the MTF characteristic value is turned back from 0%) than the position where the MTF characteristic value is 0% at a near point where the imaging lens 10 and the object point are close to each other. There is a false resolution of points. Further, an object located in a region farther from the imaging lens 10 (a region where the MTF characteristic value is turned back from 0%) than a position where the MTF characteristic value is 0% at a far point where the imaging lens 10 is away from the object point. There is also a false resolution of points.

  On the other hand, the value (%) of the MTF characteristic regarding the optical image projected on the light receiving surface 21 through the imaging lens 10 included in the imaging system 100 of the present invention is 10% or more and 60% for any of the series B1, B2, and B3. The size is as follows and no false resolution occurs. In other words, regardless of the distance from the imaging lens 10 to the object point, and regardless of the position of the projected optical image on the light receiving surface (for example, the image height on the light receiving surface), the optical projected on the light receiving surface. There is little fluctuation in the value of the MTF characteristic relating to the image, and false resolution does not occur. Further, it can be said that there is little variation in the value of the MTF characteristic regarding the optical image projected onto the light receiving surface through the imaging lens 10 from any position in the X, Y, and Z directions.

  The imaging lens 10 is projected onto the light receiving surface 21 through the imaging lens 10 from any position in the X, Y, and Z directions separated by 10 times or more of the focal length (for example, 4 to 5 mm) of the imaging lens 10. The optical image of the subject is also configured so that the value of the MTF characteristic regarding this optical image is positive.

  In addition, the imaging system 10 is configured such that the imaging lens and the imaging element are limited to 10f or more in the Z direction, for example, and the X and Y in the object space within a range limited to a certain object height in the X and Y directions. For the point image projected on the light receiving surface from any position in the Z and Z directions, the maximum diameter of the effective area of this point image is such that the size of the light receiving pixels forming the light receiving surface of the image sensor extends over three or more pixels. It is good also as what was comprised.

  However, the imaging lens 10 is not limited to satisfying this condition, and the imaging lens 10 and the imaging device 20 project onto the light receiving surface 21 through the imaging lens 10 from any position in the X, Y, and Z directions. If the maximum diameter of the effective area of this point image is such that the maximum diameter of the light receiving pixels on the light receiving surface is 3 pixels or more, the image data output from the image sensor 20 is not affected. An effect of improving quality can be obtained.

  As described above, according to the imaging system of the present invention, as in the prior art, the lack of resolution of the image represented by the first image data output from the imaging system is simply restored to the first image data. It can be compensated only by applying (image processing). That is, since the second image data representing an image having a desired resolution can be obtained by the restoration process for the first image data, the quality of the image data obtained by capturing the optical image projected on the light receiving surface is reduced. It can be improved easily.

<About the operation of the restoration coefficient acquisition device>
Hereinafter, the operation of the restoration coefficient acquisition device 70A will be described in detail. As a function of the restoration coefficient acquisition device 70A,
(1) Point image measurement, in-screen uniformity judgment,
(2) Derivation of coefficient group (restoration coefficient) that gives optimal restoration processing,
(3) It is necessary to record the optimum coefficient group. Each function is explained in more detail.

  (1) is a function for actually measuring and determining the imaging performance (resolving power) in the combination of each imaging lens and imaging device. As a means for measuring an optical point image based on an electrical signal (first image data) obtained from an image sensor, a DxO analyzer manufactured by France DxO is commercially available. This uses the concept of blurring called BxU proposed by DxO, and it is possible to obtain point images (both optical point images and post-image processing point images) from the output signals from the image sensor. .

  Specifically, this DxO analyzer analyzes image data (first image data) obtained by photographing a specified chart (a chart in which countless black circles are arrayed on a white background), thereby obtaining an image sensor. The point image size at an arbitrary point on the light receiving surface is calculated (http://www.dxo.com/jp/image_quality/dxo_analyzer).

  The means for measuring the optical point image may be in any form as long as it is a measuring means that can calculate the point image from the output signal from the image sensor (ie, sensor).

  On the other hand, the size of the point image in the case of the optical design value can be calculated by the tool that designed the optical system, so the “design value point image” obtained by this calculation and a measuring instrument such as a DxO analyzer can be used. By comparing the sizes of the measured “measurement point images”, it is possible to determine how much the measurement point images deviate from the design values. For example, in most cases, the size of the measurement point image when there is an assembly error in the optical component is larger than the design value point image. In addition, the shape and luminance distribution of the effective area of the point image projected onto the light receiving surface of the image sensor is essentially a point-symmetric shape or distribution. However, if the imaging lens is tilted or its axis is deviated, As a result, front blur and rear blur occur, and a so-called “one-sided blur state” occurs. Such a deviation from the design value can be obtained by comparing the “design value point image” and the “measurement point image”, and it can be further determined whether or not the design value can be said. Further, it is also possible to arbitrarily define an ideal state and compare the ideal state (“ideal point image”) with a “measurement point image” to determine the difference without being particular about the design value point image.

  (2) is a stage where the restoration process based on the kernel Wiener filter is executed, and the coefficient group (restoration coefficient) that brings the “measurement point image” closer to the “design value point image” or “ideal point image” is calculated. is there. The kernel Wiener filter is shown in the literature (Keiichi Serizawa, Yukihiko Yamashita, title “Kernel Wiener Filter”, 2003 Workshop on Information-Based Induction Sciences, (IBIS2003), Kyoto, Japan, Nov 11-12, 2003). Similarly, when the original signal is observed together with noise through some filtering, it is widely used as a method for estimating the original signal from the observed signal including noise. Here, the original signal is “imaged object”, the filtering is “imaging lens + imaging device”, the observation signal is “image signal (first image data)”, and the noise is “design value point image (or ideal point). Image) and measurement point image ", the kernel Wiener filter can be applied to estimate the" photographed object ".

  If there is no error factor in the actual "imaging lens + image sensor", the object to be photographed should be an image signal, and after this restoration process, in principle, the ideal "image signal (Second image data) "is obtained. Actually, there are also measurement errors due to the original (1), and some of the noise components remain without being removed, but it is certain that the measurement point image will approach the design value point image or the ideal point image. Yes, the quality of the final image is improved.

  Specifically, even if the optical point image is larger than the design value due to some error factor, or even if it is not uniform within the imaging plane, the point image is corrected to be small or even within the imaging plane by restoration processing. Thus, performance that can withstand practical use can be secured. Even if the optical system is forced to have low performance in design (optical point image is larger than the element pitch) as well as error factors due to manufacturing, optical performance is apparent by correcting the point image. Can be improved. Pursuing this apparent improvement in optical performance makes it possible to exceed the limit resolution theoretically shown, so it is very useful in view of the recent trend toward smaller pixel sizes.

Here, the limit resolution is given by the size of the Airy disk, the radius Re of the effective area (peak intensity × (1 / e ² )) of the point image intensity of the non-aberration lens, and the radius Rc at which the intensity becomes zero are as follows: It is defined by the formula. The pixel pitch of recent CMOS elements used as image pickup elements is 2.2 microns and 1.75 microns, and it is expected that 1.4 microns and 1.0 microns will become mainstream in the future. As an example, calculating Re and Rc at F2.8, wavelength 550 nm, respectively,
Re (radius of effective area of point image intensity) = 0.82λF = 0.82 × 2.8 × 550 × 0.001 = 1.26 microns (diameter of effective area of point image intensity 2.52 microns)
Rc (radius at which point image intensity is zero) = 1.22λF = 1.22 × 2.8 × 550 × 0.001 = 1.88 microns (diameter at which point image intensity is zero 3.76 microns)
The pixel pitch has already exceeded the diffraction limit.

  The diffraction limit is based on the assumption that there is no aberration, but the actual optical system is not aberration-free, and in particular, in view of the demand for miniaturization and cost reduction, the aberration remains rather, and compromising performance is unavoidable. Has been. Even in such a situation, the restoration process using the kernel Wiener filter can improve the quality of the final image to a practical level.

  It is assumed that the above restoration processing is executed on a specific image plane or in the vicinity thereof (the range of blurring before and after blur), but an infinite number of image plane groups in the defocus direction corresponding to fluctuations in shooting distance If a restoration process that eliminates the difference between the measurement point image and the design value point image is taken into consideration, the depth of focus can be increased.

  In executing the restoration process, the noise component to be canceled varies depending on each “imaging lens + imaging element”, and it is desirable to perform an optimum restoration process for each combination of “imaging lens + imaging element”. However, the algorithm of the restoration process itself may be the same, and the “coefficient group” referenced there may be optimal.

  (3) is the stage where the “optimum coefficient group” is actually combined with the “imaging lens + imaging device” group. For this purpose, a coefficient group for executing an optimal restoration process for some recording medium must be stored and added to the set of “imaging lens + imaging element”. Therefore, a recording process is necessary.

  In this way, the image pickup system is used as a set of “image pickup lens + image pickup element + recording medium”, so that the optical point image is corrected in a form suitable for the application, and finally an image of good quality is obtained. Can be obtained. Specifically, even if the resolving power is unsatisfactory for some reason (manufacturing tolerance / original design value is low), a means for achieving a satisfactory resolving power as a processed image is provided. Further, it is possible to provide a depth-of-focus expansion means that matches the characteristics of each imaging lens and imaging element pair.

<Variation of Restoration Coefficient Acquisition Device>
Hereinafter, modified examples of the restoration coefficient acquisition apparatus will be described.

  The restoration coefficient acquisition apparatus that stores the restoration coefficient K1 corresponding to the blurring state of the point image represented by the first image data output from the image sensor in the coefficient storage unit 30 is the restoration coefficient acquisition apparatus 70A of the first example. It may be configured like a restoration coefficient acquisition device 70B of the second example and a restoration coefficient acquisition device 70C of the third example, which will be described below.

  FIG. 7 shows the coefficient of the restoration coefficient selected according to the blurring state of the point image represented by the first image data among the restoration coefficient candidates corresponding to the blurring states of the point images classified into a plurality of types. It is a figure which shows the restoration coefficient acquisition apparatus 70B of the 2nd example memorize | stored in a part.

  As shown in FIG. 7, the restoration coefficient acquisition device 70 </ b> B stores candidate coefficient storage units each storing restoration coefficient candidates K <b> 1, K <b> 2,. 79, the point image blur state acquisition unit 73 that acquires the blur state of the point image P1 projected onto the light receiving surface 21 through the imaging lens 10, and the first of the restoration coefficient candidates K1, K2,. A restoration coefficient acquisition unit 78B that selects a restoration coefficient (for example, K1) corresponding to the blurring state of the point image P1 represented by the image data G1 and stores the restoration coefficient K1 in the coefficient storage unit 30 is provided.

  This restoration coefficient acquisition device 70B obtains the blurred point image state data Db indicating the blurred state of the point image by the point image blur state acquisition unit 73, and the restoration coefficient acquisition unit 78B stores the restoration coefficient stored in the candidate coefficient storage unit 79. Among the candidates K1, K2,..., A restoration coefficient (for example, K1) corresponding to the blur state of the point image P1 represented by the blur point image state data Db is selected, and the coefficient data Dk indicating the restoration coefficient K1 is stored in the coefficient storage unit. Output to 30 and store.

  That is, the coefficient storage unit 30 stores the blur of the point image represented by the first image data G1 from among the restoration coefficient candidates K1, K2,... Corresponding to the blur states of the point images classified into a plurality of types. The restoration coefficient selected according to the state is stored.

  FIG. 8 shows the restoration coefficients selected according to the blurring state of the point image represented by the first image data among the plural types of restoration coefficient candidates corresponding to the blurring states of the point images classified into the plurality of types. This is a third example restoration coefficient acquisition device 70C for storing a corrected restoration coefficient, which is further corrected according to the blurring state of the point image, in a coefficient storage unit.

  As shown in FIG. 8, the restoration coefficient acquisition device 70 </ b> C has a candidate coefficient storage unit that stores the restoration coefficient candidates K <b> 1, K <b> 2,. 79, when the imaging lens 10 has a high resolving power, design data or data Dr that is ideal point image state data for the ideal point image P1 projected onto the light receiving surface 21 through the imaging lens having a high resolving power is stored in advance. The stored ideal point image storage unit 72, the point image blur state acquisition unit 73 that acquires the blur state of the point image P1 projected onto the light receiving surface 21 through the imaging lens 10, and the restoration coefficient candidates K1, K2,. A restoration coefficient (for example, K1) corresponding to the blurring state of the point image P1 is selected from the above, and the restoration coefficient K1 is a blurring state of the point image P1 and a point stored in the ideal point image storage unit 72 in advance. image Coefficient data Dk (K1 ′) indicating a corrected restoration coefficient K1 ′ corrected by calculation using design data or data Dr which is ideal point image state data is obtained, and this coefficient data Dk (K1 ′) Is provided with a restoration coefficient acquisition unit 78C that stores the corrected restoration coefficient K1 ′ represented by

  The restoration coefficient acquisition device 70 </ b> C acquires blur state data indicating the blur state of the point image P <b> 1 projected on the light receiving surface 21 through the imaging lens 10 by the point image blur state acquisition unit 73. The restoration coefficient acquisition unit 78B selects a restoration coefficient (for example, K1) according to the blurring state of the point image P1 from among the restoration coefficient candidates K1, K2,... Stored in the candidate coefficient storage unit 79. Further, the restoration coefficient K1 is corrected by a calculation using the blur state of the point image P1 and the point Dr. design data or the data Dr which is the ideal point image state data stored in the ideal point image storage unit 72 in advance. The corrected restoration coefficient K1 ′ is acquired, and the corrected restoration coefficient K1 ′ is stored in the coefficient storage unit 30.

  In other words, the coefficient storage unit 30 corresponds to the blur state of the point image P1 represented by the first image data G1 among the plurality of types of restoration coefficient candidates corresponding to the blur states of the point images classified into the plurality of types. Then, a corrected restoration coefficient K1 ′ obtained by further correcting the restoration coefficient (for example, K1) selected in accordance with the blurring state is stored.

  As shown in FIG. 9, the imaging system of the present invention includes a restoration coefficient acquisition device 70 and a coefficient storage unit 30 having functions similar to those of the restoration coefficient acquisition devices 70A, 70B, 70C, etc. in the casing of the imaging system. It may be an imaging system 100 ′ provided in the above.

  Furthermore, as shown in FIG. 10, the imaging system of the present invention may be an imaging system 100 ″ including a signal processing unit 40 ′ incorporating the restoration coefficient acquisition device 70 and the coefficient storage unit 30. The signal processing unit 40 ′ may also serve as the restoration coefficient acquisition device 70.

<Modification of each component>
Hereinafter, modified examples of the components in the imaging system will be described.

  The signal processing means is not limited to the case where the restoration process is performed with a pixel unit extending over a total of 9 pixels or more consisting of 3 pixels or more in the vertical direction and 3 pixels or more in the horizontal direction on the light receiving surface as a minimum unit. The restoration process may be performed with a pixel area that is less than or less than 9 pixels in total and less than 3 pixels in the horizontal direction as a minimum unit.

  In addition, the signal processing unit is not limited to obtaining the restoration coefficient by calculation using the first image data representing the blurred state of the point image, but may obtain the restoration coefficient by another method.

  In addition, the signal processing unit is not limited to the case where the restoration process is executed with the minimum pixel area including all of the effective areas of the point image projected on the light receiving surface as the minimum unit, but includes all of the effective areas. The restoration process may be executed with a non-pixel area as a minimum unit.

  Further, the signal processing unit makes the size of the effective area of the point image in the image represented by the second image data smaller than the size of the effective area of the point image in the image represented by the first image data. As described above, the size of the effective area of the point image in the image represented by the first image data is set to the size of the effective area of the point image in the image represented by the second image data. The restoration process may be executed as described above.

  Devices that require a deep depth of field, such as the imaging device of the present invention including the imaging system, portable terminal device, in-vehicle device, and medical device, are provided on the light-receiving surface of the imaging system provided in each device. The quality of the image data obtained by capturing the projected optical image can be easily improved as described above.

  Note that the imaging system of the present invention may be configured such that an optical image of a subject is projected onto the light receiving surface only through an optical member having an axially symmetric shape, or has an axisymmetric shape. An optical image of the subject may be projected onto the light receiving surface through the optical member. Furthermore, it is desirable that the imaging lens has a deep depth of field. That is, even if a change in the state in which the optical image of the subject is projected on the light receiving surface due to the movement of the subject or the focus adjustment of the imaging lens, the change in the blurring state of the point image projected on the light receiving surface is changed. It is desirable to configure the imaging lens and the imaging element so as to reduce the number. More specifically, it is desirable to configure the imaging lens and the imaging element so as to reduce the size of the effective area of the point image projected on the light receiving surface and the change in contrast. However, the imaging system is not limited to including an imaging lens having a deep depth of field, and may include an imaging lens having a shallow depth of field.

  In addition, the image sensor used in the imaging system can be a CCD element or a CMOS element.

<Lens configuration and action of imaging lens>
Next, the configuration and operation of the imaging system according to the first embodiment used in the imaging system 100 will be specifically described. An imaging lens 10A, which will be described later, used in the imaging system of Example 1 is an example of the imaging lens 10 described above.

  As will be described later, the imaging lens 10 includes, in order from the subject side (object side), a first lens group G-1 having at least one lens and having a positive power, and at least one lens. And a second lens group G-2 having a positive power.

<< Regarding the Imaging System of Example 1 >>
FIG. 11 is a cross-sectional view illustrating a schematic configuration of an imaging lens 10A configured by two single lenses according to the first embodiment, and FIGS. Defocus the light receiving surface with respect to the imaging lens on the coordinates indicating the defocus amount Ud (μm) in the optical axis direction (Z axis direction) of the projected light receiving surface and the MTF characteristic value (%) on the vertical axis. It is a figure which shows the change of the value (%) of the MTF characteristic of the optical image projected on this light-receiving surface when it makes it focus. Here, the defocus range of the light receiving surface 21A is 400 μm.

  More specifically, FIGS. 12A to 12D show MTFs related to optical images projected at various image heights when the light receiving surface 21A is defocused in a state where the position of the subject with respect to the imaging lens 10A is fixed. It is a figure which shows the change of the value (%) of a characteristic. 12A shows changes in the value of the MTF characteristic at a spatial frequency of 20 lines / mm, FIG. 12B shows a spatial frequency of 30 lines / mm, and FIG. 12C shows 40 lines / mm. FIG. 12D shows changes in the value of the MTF characteristic at a spatial frequency of 50 lines / mm.

  The horizontal axis Ud indicating the defocus amount shown in FIG. 12 indicates the direction in which the value increases (the direction in which the Ud value approaches 400 μm) indicates the direction in which the imaging lens and the light receiving surface are separated, and the direction in which the value decreases ( The direction in which the value of Ud approaches 0) indicates the direction in which the light receiving surface and the imaging lens approach each other.

  As shown in FIG. 11, the imaging lens 10A is arranged in order from the subject side (the arrow-Z direction side in the figure) along the optical axis C (Z axis) to the aperture stop Sat and the first lens group G-1. The corresponding first single lens La1, the second single lens La2 corresponding to the second lens group G-2, and the optical member GLa1 are arranged. In addition, the lens surfaces R1 and R3 shown in FIG. 11 indicate the incident-side surfaces of the single lenses La1 to La2, and the lens surfaces R2 and R4 indicate the emission-side surfaces of the single lenses La1 to La2. An optical image of the subject is projected on the light receiving surface 21A through the imaging lens 10A.

  In addition, it is preferable to arrange a cover glass, a low-pass filter, an infrared cut filter, or the like on the subject side of the light receiving surface 21A in accordance with the configuration of the imaging system. In FIG. The example which has arrange | positioned optical member GLa1 which does not have is shown. The aperture stop Sat does not indicate the shape or size but indicates the position on the optical axis Z.

  FIG. 11 also shows seven light beams Ja1, Ja2, Ja3, Ja4, Ja5, Ja6 in order from the lowest image height of the off-axis light beam Ja6 incident at the maximum angle of view from the on-axis light beam Ja1.

  Note that the six MTF curves Mta20 shown in FIG. 12 (a) indicate the change in the value of the MTF characteristic at a spatial frequency of 20 lines / mm at each position where the five light beams are projected onto the light receiving surface 21A. Is shown. The six MTF curves Mta30 described in FIG. 12B show the change in the value of the MTF characteristic at the spatial frequency of 30 lines / mm at each position similar to the above. The MTF curve Mta40 of the MTF also shows the change in the value of the MTF characteristic at a spatial frequency of 40 lines / mm at the same positions as described above, and the six MTF curves Mta50 described in FIG. The change in the value of the MTF characteristic at a spatial frequency of 50 lines / mm at each position is shown.

  In the configuration example shown in FIG. 11, the optical member GLa1 is disposed between the second single lens La2 and the light receiving surface 21A. However, a low-pass filter or a specific wavelength region is provided between the lenses. Various filters that can be cut may be arranged. Alternatively, the surface of one of the first single lens La1 to the second single lens La2 may be subjected to surface treatment (coating) having the same function as various filters.

  The imaging lens 10A includes, in order from the object side, a single lens La1 that is a first lens group G-1 having a positive power, and a single lens La2 that is a second lens group G-2 having a positive power. It is what has.

  The single lens La1 of the first lens group G-1 has a meniscus shape with a convex surface facing the object side, and the single lens of the second lens group G-2 also has a meniscus shape with a convex surface facing the object side. It is what you make.

  Hereinafter, design data of the imaging lens 10A according to the first embodiment will be described.

Table 1 shows the lens data and various data, Table 2 shows the coefficients of the aspheric formulas for each aspheric surface, and Table 3 shows the general specifications of the imaging lens 10A.

  As shown below the lens data in Table 1, the imaging lens 10A has a focal length f of 3.011 mm and an F value of 4.0.

  In the lens data of Table 1, the surface number indicates the i-th (i = 1, 2, 3,...) Surface number that sequentially increases toward the image side with the lens surface closest to the subject as the first. In Table 1, the aperture stop Sat and the optical member GLa1 are also included, and the surface number (i = 5, 6) of the optical member GLa1 is also described.

  In Table 1, Ri represents the paraxial radius of curvature of the i-th (i = 1, 2, 3,...) Surface, and Di represents the i (i = 1, 2, 3,...) -Th surface and the i + 1-th surface. And the surface interval on the optical axis Z. Note that Ri in Table 1 corresponds to the symbol Ri (i = 1, 2, 3,...) In FIG.

  Ndj in Table 1 is the refraction of the j-th (j = 1, 2, 3,...) Optical element d (wavelength: 587.6 nm) that increases sequentially toward the image side with the optical element closest to the subject as the first. Νdj represents the Abbe number for the d-line of the j-th optical element. In Table 1, the unit of paraxial radius of curvature and surface spacing is mm, and the paraxial radius of curvature is positive when convex on the object side (object side) and negative when convex on the image side.

In the lens data of Table 1, the aspherical surfaces are marked with * in the surface number. Each aspheric surface is defined by the following aspheric expression.

  Table 2 shows the values of the coefficients K, A3, A4, A5,.

  In each of the single lenses La1 to La2 constituting the imaging lens 10A, both the incident-side and exit-side lens surfaces are aspherical.

  Table 3 also shows the maximum diameter Dmax of the effective area of the point image, the number of pixels corresponding to the maximum diameter Dmax of the effective area of the point image (number of pixel areas) Ngs, and the shortest shooting distance in the imaging system of the first embodiment. The relationship between Sk and the focal depth Sd is shown.

  The number of pixels Ngs in Table 3 is the number of pixel areas corresponding to the maximum diameter of the effective area of the point image. Each pixel pitch Pg (2.2 μm, 1.85 μm, 1.4 μm) of the pixel area on the light receiving surface. ). Here, the value of the number of pixels Ngs is obtained by the equation of the number of pixels Ngs = maximum diameter Dmax / pixel pitch Pg.

  The maximum diameter Dmax of the effective area of the point image is the diameter of the effective area of the point image in the direction in which the effective area of the point image includes the most pixels, and the pixel pitch Pg is the pixel area (light receiving pixel in the above direction). ) Pitch.

  The shortest shooting distance Sk is a recommended value when the imaging lens is put to practical use, and indicates the shortest distance from the shooting lens to the subject that can project an image of the subject on the light receiving surface with a desired resolution. This shortest distance is represented by the distance (shooting distance) from the lens surface (here, the lens surface R1) closest to the subject (object side) of the photographing lens to the subject.

  This shortest shooting distance is included within the range of the shooting distance at which the effect of enhancing the quality of image data obtained by capturing the optical image projected on the light receiving surface can be obtained by the restoration process.

  In the imaging system of the first embodiment, the range of the shooting distance that can obtain the effect of improving the quality of the image data by the restoration process is a range from 0 to ∞ (infinity), and the subject can be shot. Full range.

  Depth of focus Sd indicates a defocus range in which an image of a subject can be projected on the light receiving surface with a resolution higher than a prescribed value when the light receiving surface is defocused with the position of the subject with respect to the imaging lens fixed. is there. This depth of focus Sd is a value that is considered to correspond to some extent to the range of the photographing distance that can project the subject on the light receiving surface with a predetermined resolution in a state where the position of the light receiving surface with respect to the imaging lens is fixed at a predetermined position. That is, if the value of the focal depth Sd increases, it is considered that the range of the photographing distance that can project the subject on the light receiving surface with a predetermined resolution is increased.

  As can be seen from Table 3, in the imaging system of Example 1, the effective area of the point image projected on the light receiving surface 21A is 7 μm or more, and the pixel pitch of the light receiving pixels constituting the light receiving surface 21A is 2.2 μm or less. In some cases, the maximum diameter of the effective area of the point image is configured to extend over 3 pixels (3.2 pixels).

  The value of the shortest shooting distance Sk is 15 f (about 45.2 mm) when the maximum diameter Dmax of the effective area of the point image is 7 μm.

  The value of the focal depth Sd of the imaging lens 10A is 250 μm when the maximum diameter Dmax of the effective area of the point image is 7 μm.

  Regarding the value of the MTF characteristic related to the imaging system of the first embodiment, when the light receiving surface 21A is closest to the imaging lens 10A, that is, the value of the defocus amount Ud is 0 in FIGS. In this case, all the MTF characteristic values having a spatial frequency of 20 to 50 Line / mm are positive.

  Further, when the light receiving surface 21A is moved away from the imaging lens 10A, that is, when the value of the defocus amount is 250 μm in FIGS. 12A to 12D, all the MTF characteristics having a spatial frequency of 20 to 50 Line / mm are obtained. The value is positive.

  That is, when the value of the defocus amount is in the range of 0 to 250 μm, all the MTF characteristic values at the spatial frequency of 20 to 50 Line / mm are positive.

  When the value of the defocus amount is in the range of 250 μm to 400 μm, the value of the MTF characteristic at the spatial frequency of 20 to 50 Line / mm is inverted from 0%, and false resolution occurs. A range in which false resolution occurs is indicated by an arrow Gik in the figure.

  Here, when the value of the MTF characteristic relating to the image of the subject projected on the light receiving surface is larger than 0%, it can be said that the image data obtained by capturing this image has optically meaningful information. Therefore, there is a possibility that the image data can be improved in resolution by performing a restoration process. However, when the value of the MTF characteristic relating to the image of the subject projected on the light receiving surface is folded back from 0% or 0% and false resolution occurs, the image data obtained by capturing this image is Since there is no optically meaningful information, the quality of the image data (the resolution of the image represented by the image data) cannot be improved even if restoration processing is performed on such image data.

  As described above, according to this imaging system, the subject is received when the photographing distance is changed to the range of 15 f to ∞ in a predetermined state in which the positional relationship between the light receiving surface 21A and the imaging lens 10A is fixed. The MTF characteristic of the image projected onto the surface 21A can always be set to a value larger than 0% (false resolution can be prevented).

  That is, the image of the subject projected on the light receiving surface 21A in the range of the shooting distance of 15f to ∞ can be a meaningful image.

  Further, the effective area of the point image projected on the light receiving surface 21A when the photographing distance is changed in the range of 0 to ∞ is a size extending over 3 pixels on the light receiving surface 21A. The image resolution can be increased by performing a restoration process on image data obtained by imaging an existing subject.

  That is, the image data obtained by capturing images including various subjects whose shooting distances projected on the light receiving surface 21A through the imaging system of the first embodiment are in the range of 15f to ∞ are to be restored. It can be said that the above preconditions (conditions for improving the resolution) are satisfied.

  Note that the restoration process can be executed more easily by suppressing the variation in the size of the point image projected onto the light receiving surface 21A. That is, for example, even if the image projected on the light receiving surface includes subjects that exist at various shooting distances different from each other, as long as the blurring state of the point images constituting each subject image is the same The restoration process can be executed on the image data representing the subject existing at any position without changing the parameters. As a result, the burden on the signal processing unit that performs the calculation of the restoration process can be reduced.

  On the other hand, if it is assumed that restoration processing is always performed using the same parameters, the blurring state of the point image that constitutes the image of the subject at different shooting distances projected on the light receiving surface If the same, it is possible to increase the resolution of the image representing the subject in the same manner for the image data representing the subject existing at any position by performing the restoration process. In other words, the resolution of the image can be increased uniformly over the entire image by performing the restoration process.

  As described above, the design that increases the depth of focus of the imaging lens 10A includes various subjects in which the shooting distance projected on the light receiving surface 21A through the imaging lens 10A is in the range of 15f to ∞. The resolution of the entire image represented by the image data obtained by capturing the image can be increased by the restoration process.

  Further, according to the imaging lens 10A designed as described above, the incident angle of the light incident on the light receiving surface 21A with respect to the light receiving surface 21A can be reduced, that is, an imaging lens with good telecentricity can be obtained. it can.

<< Aberration of imaging lens described in Example 1 >>
FIG. 13 is a diagram illustrating aberrations related to the imaging lens 10A. The aberration diagrams of the imaging lens described in Example 1 are shown in order from the top in FIG. 13 in the order of spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration.

  The aberration diagram shows the aberration with the e-line (wavelength 546.07 nm) as the reference wavelength. The spherical aberration diagram and the lateral chromatic aberration diagram show the F-line (wavelength 486.1 nm) and C-line (wavelength 656.3 nm). The aberration for is also shown. The distortion diagram shows the amount of deviation from the ideal image height f × tan θ using the focal length f and half angle of view θ (variable treatment, 0 ≦ θ ≦ ω) of the entire system.

<< Comparison example imaging system >>
Hereinafter, a conventional imaging lens used for a mobile phone camera or the like will be described as a comparative example.

  14 is a cross-sectional view illustrating a schematic configuration of an imaging lens including four single lenses according to a comparative example, and FIGS. 15A to 15D are horizontal axes in the optical axis direction (Z-axis direction) of the light receiving surface. The MTF of the optical image projected on the light receiving surface when the light receiving surface is defocused with respect to the imaging lens on the coordinates indicating the defocus amount Ud (μm) and the MTF characteristic value (%) on the vertical axis. It is a figure which shows the change of the value (%) of a characteristic. Here, the defocus range of the light receiving surface is 400 μm.

  15A to 15D showing the MTF characteristics correspond to FIGS. 12A to 12D showing the MTF characteristics related to the imaging lens 10A described above.

  As shown in FIG. 14, the imaging lens 10H of the comparative example includes a first single lens Lh1 and a second single lens in order from the subject side (the arrow-Z direction side in the figure) along the optical axis C (Z axis). Each of the lens Lh2, the third single lens Lh3, the fourth single lens Lh4, and the optical member GLh1 is arranged. The imaging lens 10H having these four single lenses is designed to have a deep depth of field.

  An optical image of the subject is projected on the light receiving surface 21H through the imaging lens 10H.

  Note that the optical member GLh1 is an optical member having a parallel plate and having no power.

  15A to 15D show five light beams Jh1, Jh2, Jh3, Jh4, and Jh5 in order from the lowest image height from the on-axis light beam Jh1 to the off-axis light beam Jh5 incident at the maximum field angle. It is shown.

  Note that the five MTF curves Mth20 shown in FIG. 15 (a) indicate the change in the value of the MTF characteristic at a spatial frequency of 20 lines / mm at each position where the five light beams are projected onto the light receiving surface 21H. Is shown. The five MTF curves Mth30 described in FIG. 15B show the change in the value of the MTF characteristic at the spatial frequency of 30 lines / mm at each position similar to the above. The MTF curve Mth40 of the book also shows the change in the value of the MTF characteristic at the spatial frequency of 40 lines / mm at the same positions as described above, and the five MTF curves Mth50 described in FIG. The change in the value of the MTF characteristic at a spatial frequency of 50 lines / mm at each position is shown.

  The value of the MTF characteristic related to the imaging system of the comparative example is a spatial value when the light receiving surface is brought close to the imaging lens, that is, in the range where the defocus amount is approximately 0 to 120 μm in FIGS. The value of the MTF characteristic with a frequency of 30 to 50 Line / mm is inverted from 0%, and false resolution is generated. A range in which false resolution occurs is indicated by an arrow Gik in the figure.

  Further, when the light receiving surface is moved away from the imaging lens, that is, in the range of the defocus amount in the range from 280 μm to 400 μm in FIGS. 15A to 15D, the value for the MTF characteristic having the spatial frequency of 30 to 50 Line / mm. Is inverted from 0%, and false resolution occurs. A range in which false resolution occurs is indicated by an arrow Gik in the figure.

Here, when the value of the defocus amount Ud is between 120 μm and 280 μm (focus depth range), the value of the MTF characteristic is positive, and the fluctuation range of the value of the MTF characteristic at each spatial frequency is 85% (50 Line / mm). ), 90% (40 Line / mm), 70% (30 Line / mm), and 45% (20 Line / mm).

  As described above, according to the imaging system of the comparative example, the value of the MTF characteristic becomes positive only in a relatively narrow defocus range (a range of about 160 μm), and the variation amount of the value of the MTF characteristic is large.

  In the defocus range where the MTF characteristic value is reversed from 0% (indicated by the arrow Gik in the figure), the point image is falsely resolved, and can be specified as having an effective area of 3 pixels or more. Such an optically meaningful image cannot be obtained.

  That is, the value of the MTF characteristic is positive only within a considerably limited range of the photographing distance, and the image of the subject projected on the light receiving surface can be a meaningful image. Further, the amount of variation in the size of the point image projected on the light receiving surface is large.

  Furthermore, in the imaging system of this comparative example, the effective area of the point image projected on the light receiving surface when the shooting distance is changed in the range of 0 to ∞ is a size that covers three or more pixels on this light receiving surface. Therefore, the image data obtained through such an imaging system does not satisfy the preconditions (conditions for improving the resolution) for performing the restoration process.

  Therefore, even if restoration processing is performed on the image data obtained by capturing the image of the subject projected on the light receiving surface 21H through the imaging system of the comparative example, the effect of improving the resolution of the image representing the subject is obtained. I can't get it.

  FIG. 16 is a diagram illustrating an automobile on which an in-vehicle device including an imaging system is mounted.

  As shown in FIG. 16, in-vehicle devices 502 to 504 including the imaging system of the present invention can be used by being mounted on an automobile 501 or the like. The automobile 501 includes an in-vehicle device 502 that is an out-of-vehicle camera for imaging the blind spot range on the side surface on the passenger seat side, an in-vehicle device 503 that is an out-of-vehicle camera for imaging the blind spot range on the rear side of the automobile 1, An in-vehicle device 504 that is attached to the rear surface of the mirror and is an in-vehicle camera for photographing the same field of view as the driver is provided.

  FIG. 17 is a diagram illustrating a mobile phone that is a mobile terminal device including the imaging system.

  As shown in the figure, this mobile phone 510 is one in which an imaging system 512 is arranged in a casing 511 of the mobile phone.

  FIG. 18 is a diagram illustrating an endoscope apparatus that is a medical device including the imaging system.

  As illustrated, the endoscope apparatus 520 for observing the living tissue 525 includes an imaging system 522 for imaging the living tissue 525 illuminated with the illumination light La at the distal end portion 521 of the endoscope apparatus 520. Is.

  As described above, the imaging apparatus, the portable terminal device, the in-vehicle device, and the medical device of the present invention including the imaging system as described above are conventionally known imaging devices, portable terminal devices, in-vehicle devices, and medical devices. It is easy to replace the conventional imaging system with That is, the conventional imaging system included in these devices is replaced with the imaging system of the present invention without changing the device size and shape of the conventionally known imaging devices, portable terminal devices, in-vehicle devices, and medical devices. Thus, the imaging device, portable terminal device, in-vehicle device, and medical device of the present invention can be configured.

  In the above embodiment, an example in which the imaging lens is limited under various conditions is shown. However, the imaging lens used in the imaging system of the present invention has a positive power composed of at least one lens in order from the object side. Using a first lens group having a first lens group and a second lens group having a positive power consisting of at least one lens, and the number and shape of the lenses constituting each group are limited is not. For example, each group may be composed of a plurality of lenses.

The block diagram which shows schematic structure of the imaging system of this invention 2A is a diagram showing the light intensity distribution of the point image, and FIG. 2B is a diagram showing the point image projected on the light receiving surface. 3A shows a point image displayed in the image represented by the first image data, and FIG. 3B shows a point image displayed in the image represented by the second image data. Figure showing 4A shows a light intensity distribution of a point image that will be projected on the light receiving surface when the imaging lens has a high resolving power, and FIG. 4B shows a light receiving surface when the imaging lens has a high resolving power. Of point images that will be projected on The figure which shows the change of the maximum diameter of the effective area | region of the point image which is an optical image of the object point projected on the light-receiving surface when an object point is moved to an optical axis direction The figure which shows the change of the value (%) of the MTF characteristic regarding the optical image of the object point projected on the light-receiving surface when an object point is moved to an optical axis direction The figure which shows the restoration coefficient acquisition apparatus of the 2nd example The figure which shows the restoration coefficient acquisition apparatus of the 3rd example The figure which shows the imaging system which has the restoration coefficient acquisition device inside The figure which shows the imaging system which equipped the restoration coefficient acquisition apparatus inside the signal processing part Sectional drawing which shows schematic structure of the imaging lens distribute | arranged to the imaging system of Example 1 FIG. 12A shows a change in MTF characteristic value when the light receiving surface is defocused, FIG. 12A shows a change in MTF characteristic value at a spatial frequency of 20 lines / mm, and FIG. FIG. 12C shows a change in the value of the MTF characteristic at a spatial frequency of 40 lines / mm, FIG. 12C shows a change in the value of the MTF characteristic at a spatial frequency of 40 lines / mm, and FIG. The figure which shows the change of the value of the MTF characteristic in the spatial frequency of mm FIG. 6 is a diagram illustrating aberrations related to the imaging lens of Example 1. Sectional drawing which shows schematic structure of the imaging lens distribute | arranged to the imaging system of the comparative example FIG. 21A shows a change in the MTF characteristic value when the light receiving surface is defocused, FIG. 21A shows a change in the MTF characteristic value at a spatial frequency of 20 lines / mm, and FIG. FIG. 21C shows a change in the value of the MTF characteristic at a spatial frequency of 40 lines / mm, FIG. 21C shows a change in the value of the MTF characteristic at a spatial frequency of 40 lines / mm, and FIG. The figure which shows the change of the value of the MTF characteristic in the spatial frequency of mm A figure showing an automobile equipped with an in-vehicle device equipped with an imaging system The figure which shows the mobile telephone which is a portable terminal device provided with the imaging system The figure which shows the endoscope apparatus which is a medical device provided with the imaging system

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Imaging lens 20 Imaging element 21 Light-receiving surface 30 Coefficient memory | storage part 40 Signal processing part 70A The restoration coefficient acquisition apparatus of the 1st example 70B The restoration coefficient acquisition apparatus of the 2nd example 70C The restoration coefficient acquisition apparatus of the 3rd example 72 Ideal point memory | storage part 76 Determination unit 78 Restoration coefficient acquisition unit 79 Candidate coefficient storage unit 100 Imaging system G1 First image data G2 Second image data F Restoration process P1 Point image K Restoration coefficient Dr Design data, ideal point image state data Dk coefficient data

Claims (16)

An imaging lens;
It has a light-receiving surface in which a large number of light-receiving pixels are arranged in a two-dimensional manner, picks up an optical image of a subject projected on the light-receiving surface through the imaging lens, and outputs first image data representing the subject An image sensor
Signal processing for performing restoration processing on the first image data so as to generate second image data equivalent to the first image data output from the image sensor when the resolution of the imaging lens is high Means and
The imaging lens includes, in order from the object side, a first lens group having a positive power consisting of at least one lens and a second lens group having a positive power consisting of at least one lens. And
The point image of the point image projected on the light receiving surface through the image pickup lens from either the optical axis direction of the imaging lens or the direction parallel to the light receiving surface by the image pickup lens and the image pickup element. der those maximum diameter of the effective region is configured to be sized for over three pixels of the light receiving pixels is, and the imaging lens, apart more than ten times the focal length of the imaging lens, wherein For an optical image of a subject projected on the light receiving surface through the imaging lens from either the optical axis direction of the imaging lens or a direction parallel to the light receiving surface, the value of the MTF characteristic regarding the optical image is positive. An imaging system characterized by being configured as described above . The signal processing means performs the restoration processing with a pixel area covering a total of 9 or more pixels including 3 or more pixels in the vertical direction and 3 or more pixels in the horizontal direction on the light receiving surface as a minimum unit. The imaging system according to 1 . It said signal processing means, according to claim 1 or 2, characterized in that the minimum pixel region including all of the effective region of the point image projected on the light receiving surface is to execute the restoring processing as the minimum unit The imaging system described. The signal processing means has a size representing the effective area of the point image in the image represented by the second image data, rather than the size representing the effective area of the point image in the image represented by the first image data. The imaging system according to any one of claims 1 to 3 , wherein the restoration process is executed so as to make the direction smaller. It said signal processing means, any one of claims 1 to 4, characterized in that to perform the restoration process using the restoration coefficient corresponding to the state of the point image represented by the first image data The imaging system described. The imaging system according to claim 5 , wherein the restoration coefficient is obtained individually for each imaging system for each imaging system. The restoration coefficient is selected according to the state of the point image represented by the first image data from among the candidates for the restoration coefficient corresponding to the state of the point images classified into a plurality of types. The imaging system according to claim 5, wherein: The restoration coefficient is a restoration coefficient selected according to the state of the point image represented by the first image data from among a plurality of kinds of restoration coefficient candidates corresponding to the state of the point images classified into a plurality of types. The imaging system according to claim 5, further corrected according to the state of the point image. The imaging system according to claim 5 , further comprising a restoration coefficient acquisition unit that acquires the restoration coefficient. The imaging system of any one of claims 1 9, wherein the imaging lens is made of two single lenses. The single lens of the first lens group has a meniscus shape with a convex surface facing the object side, and the single lens of the second lens group has a meniscus shape with a convex surface facing the object side. The imaging system according to claim 10 . The single lens of the first lens group has a convex shape on both surfaces of the single lens, and the single lens of the second lens group has a meniscus shape with the convex surface facing the image side. The imaging system according to claim 10 . Imaging apparatus including an imaging system according to any one of claims 1 12. Mobile terminal apparatus comprising the imaging system of any one of claims 1 12. Vehicle device including an imaging system according to any one of claims 1 12. A medical device comprising the imaging system according to any one of claims 1 to 12 .