JP2009139697A - Imaging system, and imaging apparatus, portable terminal apparatus, in-vehicle apparatus and medical apparatus with imaging system, and method for manufacturing imaging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily enhance the quality of image data obtained by imaging an optical image projected on a light receiving face in an imaging system. <P>SOLUTION: When the maximum diameter of the effective area of a point image P1 projected onto the light receiving face 21 exceeds three pixels or more, a recovery coefficient K corresponding to the state of the point image P1 indicated by the first image data G1 is stored in a coefficient storage section 30. For first image data G1, such a recovering process F for creating second image data G2 equivalent to the first image data output from an imaging element 20 when the resolution of an imaging lens 10 is high is performed using the recovery coefficient K. The imaging lens includes, in order from the object side: a first lens group having positive power and composed of at least one lens; a second lens group having negative power and composed of at least one lens; and a third lens group composed of at least one lens, in which a lens located furthest on the image side has positive power. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging system capable of enhancing the quality of image data obtained by capturing an optical image of a subject, an imaging device including the imaging system, a portable terminal device, an in-vehicle device, a medical device, and an imaging system. It relates to a manufacturing method.

  An imaging system that takes an optical image of a subject formed on a light receiving surface through an imaging lens using an image pickup device such as a CCD element or a CMOS element having a light receiving surface in which a large number of light receiving pixels are arranged two-dimensionally. 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 to increase the depth of field is directly mounted on a circuit board is put into practical use. (See Patent Document 1). In addition, high-performance in-vehicle cameras and mobile phone cameras that are equipped with an imaging system in which the number of light receiving pixels of the imaging element is increased and the resolution of the imaging lens is increased are also known. Among high-performance in-vehicle cameras and mobile phone cameras capable of obtaining such high-resolution images, there are also known cameras in which the resolution of the imaging lens is close to the diffraction limit.
Special table 2007-147951

  By the way, in manufacturing an imaging system including an imaging lens capable of forming an image with such a high resolution, it is difficult to increase the yield due to difficulty in manufacturing. In other words, since image data capable of forming an image having a predetermined resolution cannot be generated, there is a possibility that many imaging systems are removed from the production line and readjusted or reassembled. The imaging system removed from the production line is reproduced so that the cause can be identified and corrected to generate image data that can form an image with a predetermined resolution.

  However, there are various causes for reducing the resolution of the image represented by the image data output from the imaging system. For example, the shape error (lens surface shape error, thickness error, eccentricity error) of each lens constituting the imaging lens. ), An assembling / adjusting error of the imaging lens (lens shift error, tilt error, air gap error between lenses), an imaging element positioning error with respect to the imaging lens, and the like. For this reason, it is necessary to identify the cause of the decrease in resolution, perform readjustment and reassembly, and generate a high-quality image data capable of forming an image with a predetermined resolution. There's a problem.

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

  The first 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 two-dimensionally arranged, and picks up an optical image of a subject projected on the light receiving surface through the imaging lens. The maximum diameter of the effective area of the point image projected onto the light receiving surface through the image pickup lens and the image sensor that outputs the first image data representing the subject extends over three or more pixels of the light receiving pixels on the light receiving surface. Coefficient storage means for storing a restoration coefficient corresponding to the state of the point image represented by the first image data output from the image sensor when the size is large, and a first image output from the image sensor For the data, the restoration coefficient stored in the coefficient storage means is used to perform restoration processing for generating second image data equivalent to the first image data output from the imaging device when the resolution of the imaging lens is high. Signal processing A signal processing means for performing restoration processing with a pixel region 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; In order from the object side, a first lens group having a positive power consisting of at least one lens, a second lens group having a negative power consisting of at least one lens, and at least one lens The lens located closest to the image side has a third lens group having a positive power.

  The coefficient storage means can store a restoration coefficient individually obtained for each imaging system for each imaging system.

  Further, the coefficient storage means includes a restoration coefficient selected according to the state of the point image represented by the first image data among the candidates for the restoration coefficients corresponding to the state of the point images classified into a plurality of types. It can also be stored.

  Further, the coefficient storage means is a restoration selected according to the state of the point image represented by the first image data from among a plurality of types of restoration coefficient candidates corresponding to the state of the point image classified into a plurality of types. It is also possible to store a corrected restoration coefficient obtained by further correcting the coefficient according to the state of the point image.

  The imaging system may include a restoration coefficient acquisition unit that acquires a restoration coefficient and stores the restoration coefficient in a coefficient storage unit.

  The signal processing means may perform the restoration process using a minimum pixel area including all effective areas of the point image projected on the light receiving surface as a minimum unit.

  The signal processing means 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. It is desirable to execute the restoration process.

  The lens surface located closest to the image side in the third lens group has an off-axis bending point, or has a concave surface on the image side at the center of the lens surface and a convex surface on the image side in the peripheral portion. Or the following conditional expression (1) can be satisfied.

0.5H <h <H (1)
However,
H: effective radius of the lens surface located closest to the image side in the second lens group,
h: Distance from the off-axis curvature point of the lens surface located closest to the image side in the second lens group to the optical axis.

  Here, the inflection point is a point on the lens surface, and when the tangent plane at this point is orthogonal to the optical axis C (Z axis), the point is referred to as a inflection point. Further, the inflection points other than the points intersecting the optical axis on the lens surface are called off-axis inflection points.

  The lens surface on the object side of the lens located closest to the image side in the third lens group may be convex on the object side at the center of the lens surface and concave on the object side in the periphery. .

  The imaging lens may be composed of three 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 image side. it can.

  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 second 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. When the maximum diameter of the effective area of the point image projected onto the light receiving surface through the imaging lens is larger than 3 pixels, the imaging element that outputs the first image data representing the lever object, and the imaging element Coefficient storage means for storing a restoration coefficient corresponding to the state of the point image represented by the first image data output from the image pickup element, and when the resolving power of the imaging lens is high with respect to the first image data Signal processing means for performing restoration processing using the restoration coefficient so as to generate second image data equivalent to the first image data output from the image processing apparatus, and the signal processing means is arranged in the vertical direction on the light receiving surface. 3 pixels or more and horizontal direction A first lens group having a positive power composed of at least one lens in order from the object side, in which restoration processing is performed with a pixel area of a total of 9 or more pixels including at least pixels as a minimum unit. And a second lens group having negative power composed of at least one lens, and a third lens group composed of at least one lens, the lens located closest to the image side having positive power. It is characterized by being.

  The manufacturing method of the imaging system of the present invention is represented by first image data output from the imaging device by projecting a point image onto the light receiving surface of the imaging device through the imaging lens in the manufacturing of the second imaging system. The restoration coefficient corresponding to the state of the point image is stored in the coefficient storage means.

  The restoration coefficient may be obtained individually for each imaging system for each imaging system.

  The restoration coefficient may be selected according to the state of the point image represented by the first image data from among candidates for the restoration coefficient corresponding to each of the state of the point images classified into a plurality of types.

  The restoration coefficient may be a restoration coefficient selected according to the state of the point image represented by the first image data from among a plurality of types of restoration coefficient candidates corresponding to the state of the point image classified into the plurality of types. Further, it can be corrected according to the state of the point image.

  Further, the restoration coefficient may be obtained individually for each imaging system for each 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. "When the maximum diameter of the effective area of the point image projected onto the light receiving surface is a size of 3 pixels or more", "the effective area of the point image projected onto the light receiving surface is the most light-receiving “When the effective area has a size covering three or more pixels of the light receiving pixels in the direction including the pixels”.

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.

  The first image pickup system of the present invention provides a first image output from the image pickup device when the maximum diameter of the effective area of the point image projected onto the light receiving surface through the image pickup lens is a size of 3 pixels or more. Coefficient storage means for storing a restoration coefficient corresponding to the state of a point image represented by data (hereinafter also referred to as a blurred state of a point image), and when the resolving power of the imaging lens is high with respect to the first image data Signal processing means for performing restoration processing using the restoration coefficient so as to generate second image data equivalent to the first image data output from the image sensor, the signal processing means on the light receiving surface In this case, the restoration process is performed with a pixel area including a total of 9 pixels or more including 3 pixels or more in the vertical direction and 3 pixels or more in the horizontal direction as a minimum unit. A first lens group having power, a second lens group having negative power composed of at least one lens, and a lens located on the most image side composed of at least one lens have positive power. Since the third lens group is included, if the restoration coefficient is stored in the coefficient storage means, the restoration process using the restoration coefficient can be performed, and thereby the optical image projected onto the light receiving surface. It is possible to easily improve the quality of image data obtained by capturing an image.

  That is, as in the prior art, when the resolution of the image represented by the first image data output from the imaging system does not reach a predetermined level, it is necessary to identify the cause and readjust or reassemble the imaging lens. Rather than simply storing the restoration coefficient corresponding to the blurring state of the point image captured by the imaging system in the coefficient storage means, and performing the restoration process (image processing) on the first image data, the predetermined resolution can be obtained. Since the second image data representing the image having the above can be obtained, the quality of the image data obtained by capturing the optical image projected on the light receiving surface can be easily improved.

  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 this 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.

  Further, if the coefficient storage means stores the restoration coefficient individually obtained for each imaging system for each imaging system, the restoration coefficient can be obtained more accurately and the restoration process can be performed more accurately. Since it can be executed, the quality of the image data obtained by capturing the optical image projected on the light receiving surface can be improved more reliably.

  It should be noted that the coefficient storage means is a restoration coefficient 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 respective blurring states of the point image classified into a plurality of types. Is stored, it is possible to determine the restoration coefficient more easily than when the restoration coefficient is obtained for each imaging system individually.

  Here, the coefficient storage means is selected according to the blurring state of the point image represented by the first image data from among the plurality of types of restoration coefficient candidates corresponding to the blurring states of the point image classified into the plurality of types. If the restored restoration coefficient obtained by further correcting the restoration coefficient according to the blurring state of the point image is stored, as compared with the case where the restoration coefficient is individually obtained for each imaging system, This restoration coefficient can be acquired more easily while suppressing a decrease in accuracy when obtaining the restoration coefficient.

  Furthermore, if the imaging system includes a restoration coefficient acquisition unit that acquires a restoration coefficient and stores it in the coefficient storage unit, the restoration coefficient can be more reliably obtained.

  Further, if the signal processing means executes the restoration process using the minimum pixel area including all the effective areas of the point image projected on the light receiving surface as the minimum unit, the amount of calculation for executing the restoration process Increase, and the restoration process can be performed efficiently.

  Further, the size of the effective area of the point image in the image represented by the second image data is made smaller than the size of the effective area of the point image in the image represented by the first image data. If the restoration process is executed as described above, the quality of image data obtained by capturing an optical image projected on the light receiving surface can be improved more reliably.

  Further, the lens surface located closest to the image side in the third lens group has an off-axis bending point, or has a concave surface on the image side in the central portion and a convex surface on the image side in the peripheral portion, If the expression 0.5H <h <H, which is the conditional expression (1), is satisfied, the telecentricity of the imaging lens can be improved more reliably, so the quality of the first image data representing the subject Can be increased more reliably.

  Further, if the lens surface on the object side of the lens located closest to the image side in the third lens group is a convex surface on the object side in the central portion of the lens surface and a concave surface on the object side in the peripheral portion, The telecentricity of the imaging lens can be improved more reliably.

  The imaging lens is composed of only three 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 image side. The telecentricity of the imaging lens can be improved more reliably by forming a meniscus shape with a convex surface facing the surface.

  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.

  In the second imaging system of the present invention, when the maximum diameter of the effective area of the point image projected onto the light receiving surface through the imaging lens is a size over 3 pixels or more, the first imaging system outputs the first imaging system. Coefficient storage means for storing a restoration coefficient corresponding to the state of a point image represented by image data, and a first output from the image sensor when the resolving power of the imaging lens is high with respect to the first image data. And a signal processing means for performing a restoration process for generating second image data equivalent to the image data using the restoration coefficient, and the signal processing means includes at least three pixels in the vertical direction on the light receiving surface and the horizontal direction. The restoration process is performed with a pixel area including a total of 9 pixels or more consisting of 3 or more directions as a minimum unit, and the imaging lens is a first lens having at least one lens in order from the object side and having a positive power. And a second lens group having negative power composed of at least one lens, and a third lens group composed of at least one lens, the lens located closest to the image side having positive power. As in the first imaging system, the restoration process using the restoration coefficient can easily improve the quality of the image data obtained by imaging the optical image projected on the light receiving surface. it can.

  The manufacturing method of the imaging system according to the present invention is represented by first image data output from the imaging device by projecting a point image onto the light receiving surface of the imaging device through the imaging lens in the manufacturing of the second imaging system. Since the restoration coefficient corresponding to the state of the point image is stored in the coefficient storage means, the second imaging system can be manufactured efficiently.

  For example, even when the resolution of the image represented by the image data output from the imaging system does not reach a predetermined level due to manufacturing reasons, etc., the reproduction processing of the imaging system that enhances the resolution of the image compared to the conventional case. It can be easily implemented. In other words, the image capturing system in which the restoration coefficient is stored in the coefficient storage means can easily perform restoration processing for improving the quality of the image data output from the imaging system, so that the resolution of the image does not reach a predetermined level. The imaging system can be easily reproduced so that a predetermined level of image resolving power can be obtained, whereby the imaging system can be efficiently manufactured.

  Furthermore, if the imaging system is mass-produced, it is possible to enjoy a greater effect of efficiently manufacturing the imaging system.

  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 and a method for manufacturing the 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 sensor 20 that captures an optical image P1 of a subject projected onto the image and outputs first image data G1 representing the subject, and a maximum effective area of a point image projected onto the light receiving surface 21 through the imaging lens 10 A coefficient storage unit for storing a restoration coefficient K corresponding to the blurring state of the point image P1 represented by the first image data G1 output from the image sensor 20 when the diameter is a size of 3 pixels or more. 30 and restoration processing for generating second image data G2 equivalent to the first image data G1 output from the image sensor 20 when the resolution of the imaging lens 10 is high with respect to the first image data G1. And a signal processing unit 40 which is carried out by using a restoration coefficient K is caused to store in the coefficient storage unit 30.

  The signal processing unit 40 executes the restoration process F with a pixel area over 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 21 as a minimum unit.

  The imaging lens 10 includes, in order from the subject side (object side), a first lens group having a positive power consisting of at least one lens and a second lens group having a negative power consisting of at least one lens. And a third lens group, which is composed of at least one lens and is located closest to the image side and has a positive power.

  Here, the maximum diameter of the effective area of the point image P1 projected onto the light receiving surface 21 is the effective area of this effective area 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 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.

  Here, the restoration coefficient acquisition device 70A provided outside the imaging system 100 acquires the 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. Then, the restoration coefficient K is stored in the coefficient storage unit 30.

  The restoration coefficient acquisition device 70A receives data Dr that is either design data relating to a point image when there is no error in the optical system including the imaging lens 10 or ideal point image state data relating to an ideal point image state exceeding that. The ideal point image storage unit 72 stored in advance and the point image state data Db indicating the analysis result obtained by analyzing the blur state of the point image represented by the first image data G1 output from the image sensor 20. Obtained by the image blur state obtaining unit 73, the point image diameter obtaining unit 74 for obtaining the maximum diameter of the effective area of the point image P1 projected onto the light receiving surface 21 through the imaging lens 10, and the point image diameter obtaining unit 74. A determination unit 76 for determining whether or not the maximum diameter is a size over three pixels or more on the light receiving surface 21; and the determination unit 76 determines that the maximum diameter is over three pixels or more on the light receiving surface 21. It is When this is done, the blurred point image state data Db output from the point image blur state acquisition unit 73 and the design data or data Dr which is ideal point image state data stored in the ideal point image storage unit 72 are input. Is used to obtain the coefficient data Dk representing the restoration coefficient K corresponding to the blurring state of the point image P1 represented by the first image data G1, and the restoration coefficient K represented by the coefficient data Dk is stored in the coefficient storage unit 30. A restoration coefficient acquisition unit 78A for storing is provided.

  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, as described above, the blurred point image state data Db mainly indicating the deterioration state of the resolution of the point image includes, for example, the size of the effective area of the point image P1 and the luminance distribution on the light receiving surface of the point image P1 (in the image). Density distribution) and the like.

<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 a 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 G1 representing the subject output from the image pickup device 20 is converted into a point image blur state acquisition unit 73 and Input to the point image diameter acquisition unit 74.

  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.

  In addition, the point image diameter acquisition unit 74 to which the first image data G1 is input calculates the maximum diameter of the effective area of the point image P1 projected onto the light receiving surface 21, and outputs the diameter data Dm indicating the maximum diameter. . The determination unit 76 to which the diameter data Dm indicating the maximum diameter is input determines whether or not the maximum diameter of the effective region of the point image P1 is a size extending over three pixels on the light receiving surface 21, and the maximum diameter is determined. When it is determined that the size is over 3 pixels, the signal Te is output.

  The restoration coefficient acquisition unit 78A to which the signal Te is input has the blur point image state data Db output from the point image blur state acquisition unit 73 and the design data or ideal point image previously stored in the ideal point image storage unit 72. Data Dr, which is state data, 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 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.

  In addition, as an example which implement | achieves the function of the point image blur state acquisition part 73 and the point image diameter acquisition part 74, the DxO analyzer made from DxO Labs (France) mentioned later is mentioned. According to this DxO analyzer, the first image data G1 output from the image sensor 20 is analyzed, and the point image P1 projected onto the light receiving surface 21 is blurred (resolution degradation state) or the maximum effective area. The diameter can be determined.

  As described above, the restoration coefficient K is stored in the coefficient storage unit 30, and the imaging system 100 is ready to execute the restoration process.

<About restoration processing>
Next, using the restoration coefficient K stored in the coefficient storage unit 30, the restoration process F is executed on the first image data output from the image sensor 20, and the resolution is higher than that of 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. It can also be considered that this represents 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 subjecting the first image data G1 to the restoration process F using the restoration coefficient K, and an imaging lens The point image P2 expected to be projected onto the light receiving surface 21 when the resolving power of 10 is increased (the maximum diameter M2 of the effective region R2 is included in one pixel region Rg, FIGS. 4A and 4B). The image of the point image represented by the first image data G1 output from the imaging device 20 that has captured (see) is an image 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.

<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. 5 is a diagram showing a restoration coefficient acquisition device 70B of the second example, and FIG. 6 is a diagram showing a restoration coefficient acquisition device 70C of the third example. FIG. 7 is a diagram illustrating an imaging system provided with a restoration coefficient acquisition device, and FIG. 8 is a diagram illustrating an imaging system including a restoration coefficient acquisition device and a coefficient storage unit in a signal processing unit. 5 to 8, components having the same functions as those of the restoration coefficient acquisition apparatus 70A of the first example are denoted by the same reference numerals as those of the restoration coefficient acquisition apparatus 70A of the first example.

  As shown in FIG. 5, the restoration coefficient acquisition apparatus 70B of the second example stores candidates for restoration coefficient candidates K1, K2,... Corresponding to the blur states of point images previously classified into a plurality of types. The blur state of the point image represented by the coefficient storage unit 79 and the first image data G1 output from the image sensor 20 is analyzed, blur point image state data Db indicating the analysis result is obtained, and a restoration coefficient acquisition unit 78B described later is obtained. Point image blur state acquisition unit 73 that outputs to the image sensor, point image diameter acquisition unit 74 for acquiring the maximum diameter of the effective area of the point image P1 projected on the light receiving surface 21 through the imaging lens 10, and point image diameter acquisition A determination unit 76 for determining whether or not the maximum diameter obtained by the unit 74 is a size over three pixels or more on the light receiving surface 21; and the determination unit 76 determines that the maximum diameter is three pixels on the light receiving surface 21. When it is determined that the size is over the above, A restoration coefficient (for example, K1) corresponding to the blurring state of the point image P1 represented by the blur point image state data Db is selected from the restoration coefficient candidates K1, K2,. And a restoration coefficient acquisition unit 78B to be stored.

  The restoration coefficient acquisition device 70B acquires the maximum diameter of the effective area of the point image P1 projected onto the light receiving surface 21 through the imaging lens 10 by the point image diameter acquisition unit 74, and determines the diameter data Dm indicating the maximum diameter. To the unit 76. The determination unit 76 to which the diameter data Dm is input determines whether or not the maximum diameter is a size over 3 pixels or more on the light receiving surface 21, and determines that the maximum diameter is over 3 pixels. In addition, a signal Te indicating this is output to the restoration coefficient acquisition unit 78B. The restoration coefficient acquisition unit 78B, to which the signal Te is input, is in a blurred state of the point image P1 represented by the blurred point image state data Db among the restoration coefficient candidates K1, K2,... Stored in the candidate coefficient storage unit 79. A corresponding restoration coefficient (for example, K1) is selected, and coefficient data Dk indicating the restoration coefficient K1 is output and stored in the coefficient storage unit 30.

  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. A restoration coefficient (for example, K1) selected according to the state is stored.

  On the other hand, as shown in FIG. 6, the restoration coefficient acquisition device 70C of the third example stores the restoration coefficient candidates K1, K2,... Corresponding to the blur states of the point images previously classified into a plurality of types. In addition, when the resolving power of the candidate coefficient storage unit 79 and the imaging lens 10 is high, design data or ideal point image state data about an ideal point image projected onto the light receiving surface 21 through the imaging lens having a high resolving power. An ideal point image storage unit 72 that stores data Dr in advance, and a blur point image state data Db that analyzes the blur state of the point image represented by the first image data G1 output from the image sensor 20 and indicates the analysis result. A point image blur state acquisition unit 73 that is acquired and output to a restoration coefficient acquisition unit 78C described later, and a point image diameter for acquiring the maximum diameter of the effective area of the point image P1 projected on the light receiving surface 21 through the imaging lens 10 Take And parts 74, the maximum diameter obtained by the Tenzo径 acquisition unit 74 and a determination unit 76 whether a size for over three pixels on the light receiving surface 21.

  Furthermore, when the determination unit 76 determines that the maximum diameter is a size that extends over three pixels or more on the light receiving surface 21, the recovery coefficient acquisition device 70C has the recovery coefficient candidates K1, K2,. The restoration coefficient (for example, K1) corresponding to the blur state of the point image P1 represented by the blur point image state data Db output from the point image blur state acquisition unit 73 is selected, and the restoration coefficient K1 is selected as the blur point image. The coefficient indicating the corrected restoration coefficient K1 ′ corrected by calculation using the state data Db and the point image design data or the data Dr which is ideal point image state data stored in the ideal point image storage unit 72 in advance. A restoration coefficient acquisition unit 78C that acquires data Dk (K1 ′) and stores the corrected restoration coefficient K1 ′ represented by the coefficient data Dk (K1 ′) in the coefficient storage unit 30 is provided.

  The restoration coefficient acquisition device 70C acquires the maximum diameter of the effective area of the point image P1 projected onto the light receiving surface 21 through the imaging lens 10 by the point image diameter acquisition unit 74, and determines the diameter data Dm indicating the maximum diameter. To the unit 76. The determination unit 76 to which the diameter data Dm is input determines whether or not the maximum diameter is a size over 3 pixels or more on the light receiving surface 21, and determines that the maximum diameter is over 3 pixels. In addition, a signal Te indicating this is output to the restoration coefficient acquisition unit 78B. The restoration coefficient acquisition unit 78B, to which the signal Te is input, is in a blurred state of the point image P1 represented by the blurred point image state data Db among the restoration coefficient candidates K1, K2,... Stored in the candidate coefficient storage unit 79. A corresponding restoration coefficient (for example, K1) is selected, and the restoration coefficient K1 is the above-described blurred point image state data Db and point image design data or ideal point image state data stored in the ideal point image storage unit 72 in advance. A corrected restoration coefficient K1 ′ further corrected by an operation using the data Dr 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. The corrected restoration coefficient K1 ′ obtained by further correcting the restoration coefficient (for example, K1) selected in this manner according to the blurring state of the point image is stored.

  Note that the imaging system 100 may include the restoration coefficient acquisition devices 70A, 70B, or 70C as a part thereof, or may not include any of the restoration coefficient acquisition devices 70A, 70B, and 70C. Good.

  In addition, an imaging system 100 ′ illustrated in FIG. 7 includes a restoration coefficient acquisition device 70 having a function similar to that of the restoration coefficient acquisition devices 70A, 70B, 70C, and the like in a housing of the imaging system. The imaging system may be configured as described above.

  8 includes the restoration coefficient acquisition device 70 and the coefficient storage unit 30 as described above built in the signal processing unit 40 ′. The imaging system is configured as described above. Also good.

<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. 9, 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. 9 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. 9 is projected on the light receiving surface through an imaging lens used in a conventional imaging system (for example, a 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. 9, 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. Furthermore, it can be said that the variation of the size of the effective area of the point image is small for the point image projected on the light receiving surface through the imaging lens 10 from any position in the X, Y, and Z directions.

  In FIG. 10, 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 B-1, B-2, and B-3 in FIG. 10 are different specific regions (mutually different) on the light receiving surface through the imaging lens 10. 6 schematically shows a change in the value (%) of the MTF characteristic relating to the optical image projected on a specific region having a different image height. Further, the curve (broken line) indicated by the series Bw in FIG. 10 indicates 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. 10, in the conventional imaging system, the value (%) of the MTF characteristic relating to the optical image projected on 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 point located in a region farther than a position where the MTF characteristic value is 0% at a far point where the imaging lens 10 is separated from the object point (a region where the MTF characteristic value is turned back from 0%) is also false. Resolution has occurred.

  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 any of the series B-1, B-2, and B-3. The size is 10% or more and 60% or less, and false resolution does not occur. That is, regardless of the distance from the imaging lens 10 to the object point, and regardless of the position (image height) of the projected optical image on the light receiving surface, the value of the MTF characteristic related to the optical image projected on the light receiving surface. There are few fluctuations 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, that is, from any position in the three-dimensional space.

  As described above, according to the imaging system of the present invention, when the resolution of the image represented by the first image data output from the imaging system does not reach a predetermined level, the cause is identified and imaged. Without re-adjusting or reassembling the lens, the restoration coefficient corresponding to the blurring state of the point image is simply stored in the coefficient storage unit, and the restoration process is performed on the first image data. Since the second image data representing the image having the resolution can be obtained, the quality of the image data obtained by capturing the optical image projected on the light receiving surface can be easily improved. It can also be said that the lack of resolving power in the imaging system can be easily recovered.

<About manufacturing method of imaging system>
Hereinafter, a method for manufacturing an imaging system of the present invention, that is, a method for manufacturing an imaging system in which a predetermined restoration coefficient is stored by storing a predetermined restoration coefficient in an imaging system in which the predetermined restoration coefficient is not stored is shown in FIG. This will be described with reference to 5, 6 and the like.

  This imaging system manufacturing method is to manufacture the imaging systems 100A, 100B,... Having the restoration coefficients stored therein, by storing the restoration coefficients in the coefficient storage unit 30, and performing restoration processing.

  The imaging systems 100A, 100B,... Are equivalent to the imaging system 100 already described with reference to FIGS.

  The manufacturing method of the imaging system includes an imaging lens 10 and a light receiving surface 21 in which a large number of light receiving pixels are arranged two-dimensionally. An optical image of a subject projected on the light receiving surface 21 through the imaging lens 10 is obtained. An image pickup device 20 that picks up an image and outputs first image data G1 representing the subject, and a first image output from the image pickup device 20 when the image pickup lens 10 has a high resolving power with respect to the first image data G1. The restoration process F that generates the second image data G2 equivalent to the data G1 is performed on the light receiving surface 21 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 as a minimum unit. The signal processing unit 40 to be implemented and the coefficient storage unit 30 in which the restoration coefficient K used for the restoration process is stored are stored, and the restoration process is executed using the restoration coefficient K stored in the coefficient storage unit 30. Imaging system 100A that is a method of manufacturing 100B · · ·.

  In this manufacturing method, the point image P1 is projected onto the light receiving surface 21 through the imaging lens 10, and the restoration coefficient K corresponding to the state of the point image P1 represented by the first image data G1 output from the imaging element 20 is obtained. The coefficient is stored in the coefficient storage unit 30.

  In this method of manufacturing an imaging system, the restoration coefficient is obtained using the restoration coefficient acquisition device 70A of the first example, the restoration coefficient acquisition device 70B of the second example, or the restoration coefficient acquisition device 70C of the third example. Can be stored in the coefficient storage unit of each imaging system 100A, 100B.

  Hereinafter, a method for manufacturing an imaging system using the restoration coefficient acquisition apparatus 70A of the first example, the restoration coefficient acquisition apparatus 70B of the second example, and the restoration coefficient acquisition apparatus 70C of the third example will be specifically described. The configuration and operation of the imaging systems 100A, 100B,..., The restoration coefficient acquisition device 70A of the first example, the restoration coefficient acquisition device 70B of the second example, and the restoration coefficient acquisition device C of the third example are described above. Since the description is the same as the content related to the imaging system 100, overlapping description is omitted, and the content of the imaging system manufacturing method that does not overlap with the description of the imaging system 100 described above will be described.

<< About the manufacturing method of the imaging system corresponding to 70 A of restoration coefficient acquisition apparatuses of a 1st example >>
In the manufacturing process corresponding to “one-to-one” in which the restoration coefficient obtained individually for each imaging system is stored in each imaging system,
(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 a point image (both optical point image and post-image point image) from the output signal from the digital camera. .

  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 is not limited as long as it is a measuring means that can calculate the point image from the output signal from the digital camera (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 the measured point image is close to the design value point image or the ideal point image. It is certain and 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 the 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.

<< About the manufacturing method of the imaging system corresponding to the restoration coefficient acquisition device 70B of the second example >>
A second preferred method for manufacturing the above point image correcting optical system comprising an imaging lens, an imaging device, and a signal processing circuit will be described, but the positioning is assumed to be a case where a large number of digital cameras are produced at low cost. is there. In its manufacturing process,
(1) Construction of a library of coefficients (restoration coefficients) used for restoration processing
(2) Point image measurement and in-screen uniformity judgment
(3) Extraction from the library of coefficient groups that gives optimal restoration processing for each group
(4) It is necessary to record the optimum coefficient group for each group. Each function is explained in more detail.

  In (1), the number of imaging lenses (for example, 1/10 of all lots) that can cover the entire trend is measured in advance, and the resolution tendency (problem tendency) is grouped. An optimal restoration process is calculated for each group, and an optimum coefficient group for each group is obtained to construct a library. Ideally, it is ideal if the coefficient group is applied in a “one-to-one” correspondence as in the first example, but it is not suitable for mass production or when the cost is to be suppressed. Therefore, as in the present embodiment, a library is created in which the whole is divided into groups to some extent and an optimum solution is obtained for each group.

  (2) is the same as (1) in the first example, but it is determined from the measurement point image where it belongs to the group obtained in (1) of the second example. Actually, those other than those measured in advance when the above grouping is applied to the group (for example, 9/10 of all lots).

  (3) is a stage in which the optimum coefficient group of the group determined in (2) is extracted from the library, and the selected coefficient group is applied to the set of “imaging lens + imaging element”. At this time, the optimum coefficient group for each “imaging lens + imaging device” group is not obtained one by one. Thereby, the calculation time required in the first example can be shortened, and mass production can be made inexpensively.

  (4) is the same as (3) of the first example.

<< About the manufacturing method of the imaging system corresponding to the restoration coefficient acquisition apparatus 70C of the third example >>
A third preferred method for manufacturing the above point image correcting optical system comprising an imaging lens, an imaging device, and a signal processing circuit will be described. However, the positioning is assumed to be a case where a large number of digital cameras are produced at low cost. is there. In its manufacturing process,
(1) Construction of a library of coefficients (restoration coefficients) used for restoration processing
(2) Point image measurement and in-screen uniformity judgment
(3) Extraction of coefficient group that gives optimal restoration processing from library
(4) Partially modify the coefficient group
(5) It is necessary to record the modified coefficient group. Each function is explained in more detail.

  (1) (2) (3) is the same as (1) (2) (3) in the second example.

  (4) is a process of partially correcting the extracted coefficient group. Although the coefficient group is an array of certain numerical values, a necessary correction is added to “imaging lens + imaging device” in which only a part thereof is corrected. Unlike the first example in which all the coefficient groups are optimized, the coefficients are only partially corrected, so that the time can be shortened.

  (5) is a stage in which the corrected corrected coefficient group is recorded, and a set of “imaging lens + imaging element + recording medium” is configured by this.

  As described above, the imaging system manufactured by the imaging system manufacturing method of the present invention can easily improve the quality of image data obtained by capturing an optical image projected on the light receiving surface.

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

  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.

  In addition, the imaging device of the present invention provided with the imaging system described above, a portable terminal device, an in-vehicle device, a medical device, or the like that is required to have a deep depth of field is a light receiving device of the imaging system provided in each device. The quality of the image data obtained by capturing the optical image projected on the surface can be easily improved as described above.

  In the imaging system of the present invention, the imaging lens and the imaging element are limited to, for example, 10f or more in the Z direction, and limited to the object height in the X and Y directions. For the point image projected on the light receiving surface from any position in the Y and Z directions, the maximum diameter of the effective area of this point image is the size of three or more light receiving pixels forming the light receiving surface of the image sensor. It may be configured as described above.

  In addition, the imaging lens also relates to 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 by 10 times or more of the focal length of the imaging lens. It is desirable that the value of the MTF characteristic is configured to be positive. Note that “a position that is at least 10 times the focal length of the imaging lens” refers to a position where the most object side surface of the lens surfaces constituting the imaging lens intersects with the optical axis of the imaging lens, It means “a position away from the reference position toward the subject side by 10 times or more of the focal length along the optical axis direction (Z-axis direction) of the imaging lens”.

  In this imaging system, only this point image is projected on the light receiving surface through the imaging lens from the position where the imaging lens and the imaging device are limited in at least one of the X, Y, and Z directions. It may be configured such that the maximum diameter of the effective area of the image has a size extending over three or more of the light receiving pixels forming the light receiving surface. In such a case, the restoration process is performed only on the first image data representing an area in which the maximum diameter of the effective area of the point image projected onto the light receiving surface is a size extending over 3 pixels of the light receiving pixels. Thus, the second image data can be obtained.

  The imaging system 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 an optical member having an axisymmetric shape. The optical image of the subject may be projected onto the light receiving surface through the light receiving surface. 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 negative power and a third lens group G-3 having at least one lens and the lens located closest to the image side having a positive power. is there.

<< Regarding the Imaging System of Example 1 >>
FIG. 11 is a cross-sectional view illustrating a schematic configuration of an imaging lens 10A including three 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, the third single lens La3 corresponding to the third lens group G-3, and the optical member GLa1 respectively. It is arranged. In addition, lens surfaces R1, R3, and R5 shown in FIG. 11 are incident-side surfaces of the single lenses La1 to La3, and lens surfaces R2, R4, and R6 are emission-side surfaces of the single lenses La1 to La3. Show. 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 shows seven light beams Ja1, Ja2, Ja3, Ja4, Ja5, Ja6, Ja7 in order from the lowest image height from the on-axis light beam Ja1 to the off-axis light beam Ja7 incident at the maximum angle of view. .

  The seven 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 seven 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 seven MTF curves Mta50 described in FIG. The change of the value of the MTF characteristic at the spatial frequency of 50 lines / mm at each position is shown.

  In the configuration example shown in FIG. 11, an example in which the optical member GLa1 is disposed between the third single lens La3 and the light receiving surface 21A is shown. 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 lens surface of any one of the first single lens La1 to the third single lens La3 may be subjected to surface treatment (coating) having the same action 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 negative power. The lens surface R6 located on the image side of the single lens La3 corresponding to the third lens group G-3 has a single lens La3 that is the third lens group G-3 having positive power. It has an off-axis curvature point Qa.

  As described above, the inflection point is a point on the lens surface, and when the tangent plane at this point is orthogonal to the optical axis C (Z axis), the point is referred to as a inflection point. Further, the inflection points other than the points intersecting the optical axis on the lens surface are called off-axis inflection points.

  In the imaging lens 10A, the lens surface R6 located closest to the image side in the third lens group has a concave surface on the image side at the center of the lens surface R6 and a convex surface on the image side in the peripheral portion. Furthermore, this lens surface R6 satisfies the following conditional expression (1).

0.5H <h <H (1)
However,
H: effective radius of lens surface R6,
h: Distance from the off-axis curvature point Qa of the lens surface R6 to the optical axis.

  The distance h from the off-axis bending point Qa of the lens surface R6 to the optical axis is the light on the point on the aspheric surface where the inclination of the tangential plane with respect to the tangential plane of the aspherical vertex (plane perpendicular to the optical axis) is zero It can be said that it is the height from the axis.

  Regarding the single lens La3 that is the lens located closest to the image side in the third lens group G-3 of the imaging lens 10A, the object-side lens surface R5 has a convex surface on the object side at the center of the lens surface R5. A concave surface is formed on the object side in the peripheral portion.

  Further, the single lens La1 constituting the first lens group G-1 has a meniscus shape with a convex surface facing the object side, and the single lens La2 constituting the second lens group G-2 is the image side. It has a meniscus shape with a convex surface facing the surface.

  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 3.847 mm and an F value of 3.5.

  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 = 7, 8) 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 La3 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.

  In the column of “h: H / 2” in Table 3, “h” indicates the distance from the optical axis to the off-axis bending point of the lens surface R6. In addition, “H / 2” indicates a size that is ½ of the effective radius H of the lens surface R6 (a size of 0.5H). Here, it is understood that the lens surface R6 satisfies the conditional expression (1) of “0.5H <h <H”.

  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 onto the light receiving surface 21A is 9 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 extends over 3 pixels (4.1 pixels).

  The value of the shortest shooting distance Sk is 16 f (about 61.5 mm) when the maximum diameter Dmax of the effective area of the point image is 9 μm.

  The value of the focal depth Sd of the imaging lens 10A is 300 μm when the maximum diameter Dmax of the effective area of the point image is 9 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 300 μm in FIGS. 12A to 12D, all 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 300 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 300 μm to 400 μm, the value of the MTF characteristic at 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 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 shooting distance is changed to the range of 16f 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 16f 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 16f to ∞ are to perform restoration processing. 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, by designing the imaging lens 10A so as to increase the depth of focus, the imaging distance projected onto the light receiving surface 21A through the imaging lens 10A includes various subjects in the range of 16f 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.

  FIG. 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. 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 a 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, and a room. 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. A first lens group having at least one lens, a second lens group having negative power, and a third lens having at least one lens located closest to the image side has positive power. And the number of lenses constituting each group, the shape, and the like are not limited. For example, each group may be composed of a plurality of lenses.

1 is a block diagram showing a schematic configuration of an imaging system of the present invention and a manufacturing method of the imaging system. 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 FIG. 4A is a diagram showing 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 is a diagram showing each pixel of the light receiving pixels constituting the light receiving surface. The figure which shows the point image which will be projected on a light-receiving surface when the resolving power of a field and an imaging lens is high 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 provided with the restoration coefficient acquisition apparatus The figure which shows the imaging system which provided the restoration coefficient acquisition apparatus and the coefficient memory | storage part in the signal processor 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 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 70B of the 1st example The restoration coefficient acquisition apparatus of the 2nd example 70C The restoration coefficient acquisition apparatus of the 3rd example 72 Ideal point image storage part 74 Point image diameter acquisition unit 76 Judgment 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 Db Blurred point image state data Dk coefficient data

Claims (22)

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
When the maximum diameter of the effective area of the point image projected onto the light receiving surface through the imaging lens is a size over 3 pixels or more, the first image data represented by the first image data output from the imaging element is used. Coefficient storage means for storing a restoration coefficient according to the state of the point image;
With respect to the first image data, a restoration process for generating second image data equivalent to the first image data output from the imaging element when the resolving power of the imaging lens is high is performed using the restoration coefficient. Signal processing means implemented using,
The signal processing means performs the restoration processing 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 imaging lens includes, in order from the object side, a first lens group having a positive power consisting of at least one lens, a second lens group having a negative power consisting of at least one lens, and at least one. An imaging system comprising: a third lens group having a positive power, wherein the lens located closest to the image side is composed of a single lens.   2. The imaging system according to claim 1, wherein the coefficient storage means stores a restoration coefficient individually obtained for each imaging system for each imaging system.   The coefficient storage means stores a restoration coefficient selected according to the state of the point image represented by the first image data among the candidates of the restoration coefficients corresponding to the state of the point images classified into a plurality of types. The imaging system according to claim 1, wherein:   The restoration coefficient selected by the coefficient storage unit according to the state of the point image represented by the first image data from among a plurality of types of restoration coefficient candidates corresponding to the state of the point image classified into a plurality of types. The imaging system according to claim 1, wherein a corrected restoration coefficient obtained by further correcting the image according to the state of the point image is stored.   The imaging system according to any one of claims 1 to 4, further comprising a restoration coefficient acquisition unit that acquires the restoration coefficient and stores the restoration coefficient in the coefficient storage unit.   6. The signal processing means executes the restoration processing with a minimum pixel area including all effective areas of a point image projected on the light receiving surface as a minimum unit. The imaging system according to any one of the above.   The signal processing means determines the effective area of the point image in the image represented by the second image data rather than 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 6, wherein the restoration process is executed so as to reduce the size.   The imaging system according to claim 1, wherein a lens surface located closest to the image side in the third lens group has an off-axis bending point.   2. The lens surface located closest to the image side in the third lens group is a concave surface on the image side at the central portion of the lens surface and a convex surface on the image side in the peripheral portion. 9. The imaging system according to any one of 1 to 8. 10. The imaging system according to claim 8, wherein a lens surface of a lens located closest to the image side in the third lens group satisfies the following conditional expression (1).
0.5H <h <H (1)
However,
H: effective radius of the lens surface located closest to the image side in the third lens group,
h: Distance from the off-axis curvature point of the lens surface located closest to the image side in the third lens group to the optical axis.   The lens surface on the object side of the lens located closest to the image side in the third lens group has a convex surface on the object side at the center of the lens surface and a concave surface on the object side in the peripheral portion. The imaging system according to any one of claims 1 to 10.   The imaging system according to any one of claims 1 to 11, wherein the imaging lens includes three 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 image side. The imaging system according to claim 12.   An imaging apparatus comprising the imaging system according to claim 1.   A mobile terminal device comprising the imaging system according to claim 1.   An in-vehicle device provided with the imaging system according to claim 1.   A medical device comprising the imaging system according to any one of claims 1 to 13. 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
When the maximum diameter of the effective area of the point image projected onto the light receiving surface through the imaging lens is a size over 3 pixels or more, the first image data represented by the first image data output from the imaging element is used. Coefficient storage means for storing a restoration coefficient corresponding to the state of the point image;
With respect to the first image data, a restoration process for generating second image data equivalent to the first image data output from the imaging element when the resolving power of the imaging lens is high is performed using the restoration coefficient. Signal processing means implemented using,
The signal processing means performs the restoration processing 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 imaging lens includes, in order from the object side, a first lens group having a positive power consisting of at least one lens, a second lens group having a negative power consisting of at least one lens, and at least one. An imaging system comprising: a third lens group having a positive power, wherein the lens located closest to the image side is composed of a single lens.   A point image is projected onto the light receiving surface of the image sensor through the imaging lens, and a restoration coefficient corresponding to the state of the point image represented by the first image data output from the image sensor is stored in the coefficient storage unit. 19. The method of manufacturing an imaging system according to claim 18, wherein the imaging system is stored.   20. The method of manufacturing an imaging system according to claim 19, wherein the restoration coefficient is obtained individually 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 candidates for the restoration coefficient corresponding to each state of the point images classified into a plurality of types. The method of manufacturing an imaging system according to claim 19.   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 types of restoration coefficient candidates corresponding to the state of the point images classified into a plurality of types. 20. The method of manufacturing an imaging system according to claim 19, wherein the correction is further made according to the state of the point image.