JP2009134023A - Imaging device and information code reading device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device and an information code reading device capable of not only simplifying an optical system, reducing cost, and obtaining a satisfactory restored image having proper quality and affected hardly by noise but also being easily manufactured, dispensing with high mounting precision, preventing these devices from being affected by reflection, and preventing contrast from differing depending on direction of image. <P>SOLUTION: This imaging device includes an optical system 210 for forming a primary image, an imaging element 220, and an image processing device 240 for forming the primary image as a highly minute final image. In this optical system 210, a light wavefront modulation element has a symmetrical shape in rotation with respect to an optical axis, and a shape of modulation surface of the light wavefront modulation element is formed to increase or decrease monotonously from a central part to a peripheral part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image pickup apparatus and an information code reading apparatus using an image pickup element and including an optical system.

In response to the digitization of information, which has been rapidly developing in recent years, the response in the video field is also remarkable.
In particular, as symbolized by a digital camera, a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensor, which is a solid-state image sensor, is used in most cases instead of a conventional film.

  As described above, an imaging lens device using a CCD or CMOS sensor as an imaging element is for taking an image of a subject optically by an optical system and extracting it as an electrical signal by the imaging element. In addition to a digital still camera, It is used in video cameras, digital video units, personal computers, mobile phones, personal digital assistants (PDAs), image inspection devices, industrial cameras for automatic control, and the like.

FIG. 27 is a diagram schematically illustrating a configuration and a light flux state of a general imaging lens device.
The imaging lens device 1 includes an optical system 2 and an imaging element 3 such as a CCD or CMOS sensor.
In the optical system, the object side lenses 21 and 22, the diaphragm 23, and the imaging lens 24 are sequentially arranged from the object side (OBJS) toward the image sensor 3 side.

In the imaging lens device 1, as shown in FIG. 27, the best focus surface is matched with the imaging device surface.
FIGS. 28A to 28C show spot images on the light receiving surface of the image sensor 3 of the imaging lens device 1.

In addition, imaging devices have been proposed in which light beams are regularly dispersed by a phase plate and restored by digital processing to enable imaging with a deep depth of field (for example, Non-Patent Documents 1 and 2 and Patent Documents). 1-5).
In addition, an automatic exposure control system for a digital camera that performs filter processing using a transfer function has been proposed (see, for example, Patent Document 6).

In addition, in an apparatus having an image input function such as a CCD or CMOS, it is often very useful to read a close still image such as a barcode together with a desired image such as a landscape.
For barcode reading, for example, as a first example, a technique for focusing by auto-focusing that extends a lens, and as a second example as a depth expansion technique, the depth of field is expanded by, for example, reducing the F value in a camera. Some have fixed focus.

“Wavefront Coding; jointly optimized optical and digital imaging systems”, Edward R. Dowski, Jr., Robert H. Cormack, Scott D. Sarama. “Wavefront Coding; A modern method of achieving high performance and / or low cost imaging systems”, Edward R. Dowski, Jr., Gregory E. Johnson. USP 6,021,005 USP 6,642,504 USP 6,525,302 USP 6,069,738 JP 2003-235794 A JP 2004-153497 A

In the imaging devices proposed in the above-mentioned documents, all of them are based on the assumption that the PSF (Point-Spread-Function) when the above-described phase plate is inserted into a normal optical system is constant, When the PSF changes, it is extremely difficult to realize an image with a deep depth of field by convolution using a subsequent kernel.
Therefore, apart from a single-focus lens, a zoom system, an AF system, or the like has a great problem in adopting due to the high accuracy of the optical design and the associated cost increase.
In other words, in the conventional imaging apparatus, proper convolution calculation cannot be performed, and astigmatism and coma that cause a shift of a spot (SPOT) image at the time of wide or tele (Tele). Therefore, an optical design that eliminates various aberrations such as zoom chromatic aberration is required.
However, the optical design that eliminates these aberrations increases the difficulty of optical design, causing problems such as an increase in design man-hours, an increase in cost, and an increase in size of the lens.

Also, with the above technique, the restored result is not good as the image after the image restoration process is out of focus.
This is a good restoration result if the OTF during out-focus is constant, but the actual problem OTF deteriorates. Even if the restoration process is performed, the restoration is not complete due to the process of being out of focus.
Therefore, it is difficult to obtain a good restored image.

Further, in the depth extension optical system, the phase modulation element is expressed by a third-order or fifth-order polynomial as disclosed in Patent Document 5 and the like, and a proposal of a rotationally asymmetric shape with respect to the optical axis has been made. .
However, the rotationally asymmetrical shape of the phase modulation element is difficult to manufacture, requires a mounting accuracy in the rotational direction with respect to the solid-state image sensor, is affected by reflection by the phase modulation element, and has a contrast depending on the image direction. There is a problem that is different.

  In addition to being able to simplify the optical system and reduce costs, the present invention is capable of obtaining a good restored image with an appropriate image quality and a small influence of noise, and is easy to manufacture. An object of the present invention is to provide an imaging apparatus and an information code reading apparatus that do not require mounting accuracy, can suppress the influence of reflection, and do not vary in contrast depending on the direction of an image.

  An imaging apparatus according to a first aspect of the present invention includes an optical system including a lens and a light wavefront modulation element, and an imaging element that captures a subject image that has passed through the optical system, and the optical system includes the light wave The phase shape, which is the difference in shape between the case where the modulation surface of the surface modulation element is rotationally symmetric with respect to the optical axis and the optical wavefront modulation element has and does not have the optical wavefront modulation function, is the optical axis center It is monotonically increasing or decreasing monotonically from the part toward the peripheral part.

  Preferably, the focal length of the modulation surface of the light wavefront modulation element is larger than the absolute value of the focal length of the entire optical system.

  Preferably, the focal length of the light wavefront modulation element including the modulation surface is larger than the absolute value of the focal length of the entire optical system.

  Preferably, the optical system includes a stop, and the stop is disposed in the vicinity of the light wavefront modulation element.

  Preferably, the light wavefront modulation element includes an image processing unit that forms a subject dispersion image and generates an image signal having no dispersion from the subject dispersion image signal from the imaging element.

  An information code reader according to a second aspect of the present invention is an information code reader that optically reads an information code, and includes an optical system including a lens and a light wavefront modulation element, and a subject image that has passed through the optical system. The optical system has a shape in which the modulation surface of the light wavefront modulation element is rotationally symmetric with respect to the optical axis, and the phase shape is from the central portion of the optical axis toward the peripheral portion. Monotonically increasing or decreasing.

  According to the present invention, not only can the optical system be simplified and the cost can be reduced, but also a restored image with an appropriate image quality and a small influence of noise can be obtained, and it is easy to manufacture and attach. The accuracy is not required, the influence of reflection can be suppressed, and the contrast does not differ depending on the direction of the image.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is an external view showing an example of an information code reading apparatus according to an embodiment of the present invention.
2A to 2C are diagrams illustrating examples of information codes.
FIG. 3 is a block diagram illustrating a configuration example of an imaging apparatus applicable to the information code reading apparatus of FIG.
Here, an information code reader is illustrated as an apparatus to which the imaging apparatus of the present embodiment is applicable.

As shown in FIG. 1, the information code reader 100 according to the present embodiment has a main body 110 connected to a processing device such as an electronic register (not shown) via a cable 111, for example, a reflectance printed on a reading object 120. It is a device that can read the information code 121 such as a different symbol or code.
As an information code to be read, for example, a one-dimensional bar code 122 such as a JAN code as shown in FIG. 2A, a stack-type CODE 49 as shown in FIGS. 2B and 2C, Alternatively, a two-dimensional barcode 123 such as a matrix type QR code can be used.

In the information code reading apparatus 100 according to the present embodiment, an illumination light source (not shown) and an imaging apparatus 200 as shown in FIG.
As will be described in detail later, the imaging apparatus 200 applies a light wavefront modulation element to the optical system, regularly disperses the light beam by the light wavefront modulation element, and restores the image by digital processing to capture an image with a deep depth of field. The system adopts a wavefront aberration control optical system or a depth expansion optical system (DEOS: Optical System) that makes possible a one-dimensional barcode such as a JAN code and a two-dimensional barcode such as a QR code. An information code such as a bar code can be accurately read with high accuracy.

  As shown in FIG. 3, the imaging device 200 of the information code reader 100 includes an optical system 210, an imaging device 220, an analog front end unit (AFE) 230, an image processing device 240, a camera signal processing unit 250, and an image display memory 260. , An image monitoring device 270, an operation unit 280, and a control device 290.

FIG. 4 is a diagram showing a basic configuration of the imaging lens unit forming the optical system according to the present embodiment.
The optical system 210 </ b> A supplies an image obtained by capturing the subject object OBJ to the image sensor 220. In the optical system 210A, a first lens 211, a second lens 212, a third lens 213, a diaphragm 214, a fourth lens 215, and a fifth lens 216 are arranged in this order from the object side.
In the optical system 210A of the present embodiment, a fourth lens 215 and a fifth lens 216 are connected. That is, the lens unit of the optical system 210A of the present embodiment is configured to include a cemented lens.

The optical system 210A of the present embodiment is configured as an optical system to which an optical wavefront modulation element is applied.
In the present embodiment, a depth-expanding optical system that uses a light wavefront modulation element (for example, a phase modulation element) to make the change in OTF according to the object distance smaller than that of an optical system that does not have a light wavefront modulation element. The light wavefront modulation element is optimized.

In the present embodiment, the optical wavefront modulation surface of the optical wavefront modulation element has a phase shape that is a difference between shapes with and without the optical wavefront modulation function, rotationally symmetric with respect to the optical axis, and the optical axis It is formed so as to monotonously increase or decrease monotonously from the central portion toward the peripheral portion.
By making the phase shape rotationally symmetric with respect to the optical axis, it is easy to manufacture, the mounting accuracy in the rotating direction is not strict, the influence of reflection is small, and there is no difference in contrast depending on the image direction. By making the phase shape monotonically increase or monotonously decrease from the optical axis central portion toward the peripheral portion, the change in OTF according to the object distance can be extremely small.
Hereinafter, an optical wavefront modulation surface (for example, a phase modulation surface) that makes the phase shape monotonously increase or monotonously decrease without having an inflection point from the optical axis center portion toward the peripheral portion will be described.

In this case, basically, as described above, the light wavefront modulation surface has a rotationally symmetric shape with respect to the optical axis. By generating a larger spherical aberration than in a general optical system having no light wavefront modulation element, it is possible to reduce the change in OTF according to the object distance as compared with a general optical system without a light wavefront modulation element. It becomes possible.
The phase shape of the light wavefront modulation surface (phase modulation surface) is formed so as not to have an inflection point and to monotonously increase or monotonously decrease from the central portion to the peripheral portion.
4 shows changes in spherical aberration before and after the formation of the light wavefront modulation surface, the light wavefront modulation surface is provided in the vicinity of the diaphragm 214 or the light wavefront modulation surface itself has a diaphragm function. Thus, by optimizing only the light wavefront modulation surface, it is possible to obtain a fixed-focus lens having high performance as the final output image signal of the imaging apparatus.

FIG. 5 is a diagram showing the phase shape of the light wavefront modulation surface of each optical system. FIG. 6 is a diagram showing the surface shape.
5 and 6, the line indicated by A has a shape without an optical wavefront modulation element, the line indicated by B has a lightwavefront modulation element and has an inflection point, and the line indicated by C indicates an optical wave. A shape is shown in the case of having a surface modulation element but no inflection point and monotonously increasing.
FIG. 6 shows the surface shape itself.
FIG. 5 shows the difference between the case with and without the light wavefront modulation element and the inflection point, that is, the state where B-A and C-A are performed in the horizontal axis direction in FIG.

  The numerical values on the vertical axis in FIG. 5 and FIG. 6 indicate the spot positions where the diagonal image height on the image plane is 1. Specifically, as shown in FIG. 7, the center spot position is (0, 0), and the vertically upper end is (0, 1). 7A shows an image sensor, and B shows an image cycle.

In this embodiment, the focal length of the optical wavefront modulation surface of the optical wavefront modulation element is larger than the focal length of the entire optical system 210.
Alternatively, the focal length of the optical wavefront modulation element including the optical wavefront modulation surface is larger than the focal length of the entire optical system.
In other words, the power at the optical wavefront modulation surface of the optical wavefront modulation element is made weaker than the overall power of the optical system 210.
Alternatively, the power provided with the light wavefront modulation surface is made weaker than the power of the entire optical system 210.
This makes it possible to obtain a uniform OTF from the center to the periphery of the image.

  Further, it is desirable that the absolute value of the focal length of the light wavefront modulation surface (phase modulation surface) has the following relationship with the focal length of the entire optical system.

(Equation 1)
| f _phase | / f _total ≧ 2
Here, f _phase represents the focal length of the light wavefront modulation surface, and f _total represents the focal length of the entire optical system.

  In the present embodiment, the absolute value of the focal length of the light wavefront modulation element means the focal length of a light wavefront modulation surface or a lens having a light wavefront modulation surface.

By changing the phase shape of the light wavefront modulation surface from the center to the periphery without increasing the inflection point and monotonously increasing or decreasing, the change in OTF according to the object distance can be made extremely small.
That is, in FIG. 6, the change in OTF can be made smaller with a surface shape like a line indicated by C than with B.
Further, by increasing the absolute value of the focal length of the light wavefront modulation surface with respect to the focal length of the entire optical system 210, it becomes possible to obtain a uniform OTF from the center portion to the peripheral portion of the image.
Further, by increasing the absolute value of the focal length of the light wavefront modulation element (lens) having the light wavefront modulation surface with respect to the focal length of the entire optical system 210, a uniform OTF from the center to the periphery of the image. It becomes possible.
In addition, since the light wavefront modulation surface of the present invention has a rotationally symmetric shape, when the light wavefront modulation element is incorporated into the lens barrel, there is no need to rotate and adjust the optical axis direction as the center. The manufacturing process can be facilitated.
In addition, it is possible to suppress the false image and extend the depth while maintaining a natural blur.

Here, the spot images according to the presence or absence of the light wavefront modulation element and the presence or absence of the inflection point of the phase shape in the optical system will be considered in association with FIGS.
In these figures, the vertical axis represents the defocus amount, and the horizontal axis represents the image height.

FIG. 8 is a diagram showing a defocus change of a spot image of a general optical system that does not have an optical wavefront modulation element.
Since this optical system does not have a light wavefront modulation element, the spot image changes greatly according to the object distance.

FIG. 9 is a diagram showing a defocus change of a spot image of an optical system including an optical wavefront modulation element having a phase shape and no inflection point.
In this optical system, the change of the spot image according to the object distance is small due to the action of the light wavefront modulation element.

FIG. 10 is a diagram illustrating a defocus change of a spot image of an optical system having a small focal length of the light wavefront modulation element.
In this optical system, since the absolute value of the focal length of the light wavefront modulation element is small, the difference in the size of the spot image between the center and the periphery of the screen is large.

FIG. 11 is a diagram illustrating a defocus change of a spot image of an optical system in which the absolute value of the focal length of the light wavefront modulation element is large.
In this optical system, since the focal length of the light wavefront modulation element is large, the difference in spot image size between the center and the periphery of the screen is small.

The characteristic configuration, function, and effect of the optical system according to the present embodiment have been described above.
Hereinafter, the configuration and functions of other components such as the image sensor and the image processing unit will be described.

For example, as shown in FIG. 4, the image pickup element 220 includes a glass parallel plane plate (cover glass) 221 and an image pickup surface 222 of an image pickup element made up of a CCD or a CMOS sensor in order from the fifth lens 216 side. Has been.
Light from the subject OBJ via the imaging optical system 210 </ b> A is imaged on the imaging surface 222 of the imaging element 220.
Note that the subject dispersion image picked up by the image pickup device 220 is an image in which the light wavefront modulation surface 213a is not focused on the image pickup device 220 and a deep light beam and a blurred portion are formed.
And in this embodiment, it is comprised so that the resolution of the distance between objects can be complemented by adding a filter process in the image processing apparatus 240. FIG.
The optical system 210A will be described in detail later.

As shown in FIG. 3, the image sensor 220 forms an image captured by the optical system 210, and forms an image primary image information as a primary image signal FIM of an electrical signal via the analog front end unit 230. It consists of a CCD or CMOS sensor output to the image processing device 240.
In FIG. 3, the imaging element 220 is described as a CCD as an example.

The analog front end unit 230 includes a timing generator 231 and an analog / digital (A / D) converter 232.
The timing generator 231 generates the drive timing of the CCD of the image sensor 220, and the A / D converter 232 converts an analog signal input from the CCD into a digital signal and outputs it to the image processing device 240.

An image processing apparatus (two-dimensional convolution means) 240 constituting a part of the signal processing unit inputs a digital signal of a captured image coming from the previous AFE 230, performs two-dimensional convolution processing, and performs subsequent camera signal processing. Part (DSP) 250.
Filter processing is performed on the optical transfer function (OTF) according to the exposure information of the image processing device 240 and the control device 290. Note that aperture information is included as exposure information.
The image processing device 240 performs a filtering process so as to improve the response of the optical transfer function (OTF) to a plurality of images by the image sensor 220 and eliminate the change of the optical transfer function (OTF) according to the object distance. It has a function of performing (for example, convolution filter processing) and obtains a deep depth of field while depending on a plurality of object distances. Further, the image processing apparatus 240 has a function of performing noise reduction filtering in the first step.
The image processing device 240 has a function of performing processing for improving the contrast by performing filter processing on the optical transfer function (OTF).
The processing of the image processing device 240 will be described in further detail later.

  The camera signal processing unit (DSP) 250 performs processing such as color interpolation, white balance, YCbCr conversion processing, compression, and filing, and stores in the memory 260 and displays images on the image monitoring device 270.

  The control device 290 performs exposure control and has operation inputs from the operation unit 280 and the like, determines the operation of the entire system in accordance with those inputs, and controls the AFE 230, the image processing device 240, the DSP 250, the aperture 213, and the like. It governs mediation control for the entire system.

  Hereinafter, the configuration and function of the optical system and the image processing apparatus according to the present embodiment will be specifically described.

Next, filter processing of the image processing apparatus 240 will be described.
In the present embodiment, the light beam converged by the optical system 210 is regularly dispersed. By inserting the light wavefront modulation element in this way, an image that does not fit anywhere on the imaging element 220 is realized.
In other words, the optical system 210 forms a deep luminous flux (which plays a central role in image formation) and a flare (blurred portion).
As described above, means for restoring the regularly dispersed image to a focused image without moving the optical system 210 by digital processing is a wavefront aberration control optical system system or a depth extension optical system system (DEOS). : Depth Expansion Optical System), and this processing is performed in the image processing apparatus 240.

Here, the basic principle of DEOS will be described.
As shown in FIG. 12, when the subject image f enters the DEOS optical system H, a g image is generated.
This is expressed by the following equation.

(Equation 2)
g = H * f
However, * represents convolution.

  In order to obtain the subject from the generated image, the following processing is required.

(Equation 3)
f = H ^-1 * g

Here, the kernel size and calculation coefficient regarding H will be described.
Let the zoom positions be ZPn, ZPn-1,. In addition, each H function is defined as Hn, Hn-1,.
Since each spot image is different, each H function is as follows.

The difference in the number of rows and / or the number of columns in this matrix is the kernel size, and each number is the operation coefficient.
Here, each H function may be stored in a memory, and the PSF is set as a function of the object distance, and is calculated based on the object distance. By calculating the H function, an optimum object distance is obtained. It may be possible to set so as to create a filter. Alternatively, the H function may be directly obtained from the object distance using the H function as a function of the object distance.

  In this embodiment, as shown in FIG. 3, an image from the optical system 210 is received by the image sensor 220 and input to the image processing device 240 when the aperture is opened, and a conversion coefficient corresponding to the optical system is acquired. The image signal having no dispersion is generated from the dispersion image signal from the image sensor 220 with the acquired conversion coefficient.

  In the present embodiment, DEOS can be employed to obtain high-definition image quality, and the optical system can be simplified and the cost can be reduced.

  As described above, the image processing apparatus 240 receives the primary image FIM from the image sensor 220, and performs a process of extending the depth of field by a convolution process using a filter to form a high-definition final image FNLIM. .

The MTF correction processing of the image processing apparatus 140 is performed after edge enhancement, chroma enhancement, etc., using the MTF of the primary image, which is essentially a low value, as shown by a curve A in FIG. In the process, correction is performed so as to approach (reach) the characteristics indicated by the curve B in FIG.
A characteristic indicated by a curve B in FIG. 13 is a characteristic obtained when the wavefront is not deformed without using the wavefront forming optical element as in the present embodiment, for example.
It should be noted that all corrections in the present embodiment are based on spatial frequency parameters.

In the present embodiment, as shown in FIG. 13, in order to achieve the MTF characteristic curve B that is finally realized with respect to the MTF characteristic curve A with respect to the spatial frequency obtained optically, each spatial frequency is changed to each spatial frequency. On the other hand, as shown in FIG. 14, strength such as edge enhancement is added, and the original image (primary image) is corrected.
For example, in the case of the MTF characteristic shown in FIG. 13, the edge enhancement curve with respect to the spatial frequency is as shown in FIG.

  That is, a desired MTF characteristic curve B is virtually realized by performing correction by weakening edge enhancement on the low frequency side and high frequency side within a predetermined spatial frequency band and strengthening edge enhancement in the intermediate frequency region. To do.

As described above, the imaging apparatus 200 according to the embodiment basically includes the optical system 210 and the imaging element 220 that form a primary image, and the image processing apparatus 140 that forms the primary image into a high-definition final image. In the optical system, a wavefront shaping optical element is newly provided, or an optical element such as glass, plastic or the like is formed for wavefront shaping, thereby forming an imaging wavefront. The image is deformed (modulated), and such a wavefront is imaged on the imaging surface (light-receiving surface) of the imaging device 220 including a CCD or CMOS sensor, and a high-definition image is obtained from the imaged primary image through the image processing device 240. An image forming system.
In the present embodiment, the primary image from the image sensor 220 has a light flux condition with a very deep depth. For this reason, the MTF of the primary image is essentially a low value, and the MTF is corrected by the image processing device 240.

Here, the imaging process in the imaging apparatus 200 in the present embodiment will be considered in terms of wave optics.
A spherical wave diverging from one of the object points becomes a convergent wave after passing through the imaging optical system. At that time, aberration occurs if the imaging optical system is not an ideal optical system. The wavefront is not a spherical surface but a complicated shape. Wavefront optics lies between geometric optics and wave optics, which is convenient when dealing with wavefront phenomena.
When dealing with the wave optical MTF on the imaging plane, the wavefront information at the exit pupil position of the imaging optical system is important.
The MTF is calculated by Fourier transform of the wave optical intensity distribution at the imaging point. The wave optical intensity distribution is obtained by squaring the wave optical amplitude distribution, and the wave optical amplitude distribution is obtained from the Fourier transform of the pupil function in the exit pupil.
Further, since the pupil function is exactly from the wavefront information (wavefront aberration) at the exit pupil position itself, if the wavefront aberration can be strictly numerically calculated through the optical system 210, the MTF can be calculated.

Accordingly, if the wavefront information at the exit pupil position is modified by a predetermined method, the MTF value on the imaging plane can be arbitrarily changed.
In this embodiment, the wavefront shape is mainly changed by the wavefront forming optical element, but the target wavefront is formed by increasing or decreasing the phase (phase, optical path length along the light beam). .
Then, if the target wavefront is formed, the exiting light flux from the exit pupil is formed from a dense portion and a sparse portion of the light, as can be seen from the geometric optical spot image.
The MTF in the luminous flux state shows a low value at a low spatial frequency and a characteristic that the resolving power is managed up to a high spatial frequency.
That is, if this MTF value is low (or such a spot image state in terms of geometrical optics), the phenomenon of aliasing will not occur.
That is, a low-pass filter is not necessary.
Then, the flare-like image that causes the MTF value to be lowered by the image processing device 240 may be removed. Thereby, the MTF value is significantly improved.

  Next, the response of the MTF of this embodiment and the conventional optical system will be considered.

FIG. 15 is a diagram illustrating the MTF response when the object is at the focal position and when the object is out of the focal position in the case of the conventional optical system.
FIG. 16 is a diagram showing the response of the MTF when the object is at the focal position and when the object is out of the focal position in the optical system of the present embodiment having the light wavefront modulation element.
FIG. 17 is a diagram illustrating a response of the MTF after data restoration of the imaging apparatus according to the present embodiment.

As can be seen from the figure, in the case of an optical system having a light wavefront modulation element, the change in the response of the MTF is less than that in an optical system in which no light wavefront modulation element is inserted even when the object deviates from the focal position.
The response of the MTF is improved by processing the image formed by this optical system using a convolution filter.

The absolute value (MTF) of the OTF of the optical system having the light wavefront modulation element shown in FIG. 16 is preferably 0.1 or more at the Nyquist frequency.
This is because, in order to achieve the OTF after restoration shown in FIG. 17, the gain is increased by the restoration filter, but the noise of the sensor is also raised at the same time. For this reason, it is preferable to perform restoration without increasing the gain as much as possible at high frequencies near the Nyquist frequency.
In the case of a normal optical system, resolution is achieved if the MTF at the Nyquist frequency is 0.1 or more.
Therefore, if the MTF before restoration is 0.1 or more, the restoration filter does not need to increase the gain at the Nyquist frequency. If the MTF before restoration is less than 0.1, the restored image becomes an image greatly affected by noise, which is not preferable.

  The configuration and processing of the image processing apparatus 240 will be described.

  As shown in FIG. 3, the image processing apparatus 240 includes a raw (RAW) buffer memory 241, a two-dimensional convolution operation unit 242, a kernel data storage ROM 243 as a storage unit, and a convolution control unit 244.

  The convolution control unit 244 controls the convolution process on / off, the screen size, the replacement of kernel data, and the like, and is controlled by the control device 290.

The kernel data storage ROM 243 stores kernel data for convolution calculated from the point image intensity distribution (PSF) of each optical system prepared in advance as shown in FIG. 18, FIG. 19, or FIG. The exposure information determined at the time of setting the exposure is acquired by the control device 290, and the kernel data is selected and controlled through the convolution control unit 244.
The exposure information includes aperture information.

  In the example of FIG. 18, the kernel data A is data corresponding to the optical magnification (× 1.5), the kernel data B is data corresponding to the optical magnification (× 5), and the kernel data C is data corresponding to the optical magnification (× 10).

  In the example of FIG. 19, kernel data A is data corresponding to F number (2.8) as aperture information, and kernel data B is data corresponding to F number (4).

  In the example of FIG. 20, the kernel data A is data corresponding to an object distance information of 100 mm, the kernel data B is data corresponding to an object distance of 500 mm, and the kernel data C is data corresponding to an object distance of 4 m.

FIG. 21 is a flowchart of a switching process based on exposure information (including aperture information) of the control device 290.
First, exposure information (RP) is detected and supplied to the convolution control unit 244 (ST101).
In the convolution control unit 244, the kernel size and numerical performance coefficient are set in the register from the exposure information RP (ST102).
The image data captured by the image sensor 220 and input to the two-dimensional convolution operation unit 242 via the AFE 230 is subjected to a convolution operation based on the data stored in the register, and is calculated and converted. The transferred data is transferred to the camera signal processing unit 250 (ST103).

  A more specific example of the signal processing unit and kernel data storage ROM of the image processing apparatus 240 will be described below.

FIG. 22 is a diagram illustrating a first configuration example of the signal processing unit and the kernel data storage ROM. For simplification, AFE and the like are omitted.
The example of FIG. 22 is a block diagram when a filter kernel corresponding to the exposure information is prepared in advance.

  The image processing apparatus 240 acquires exposure information determined at the time of setting the exposure from the exposure information detection unit 253, and selects and controls kernel data through the convolution control unit 244. The two-dimensional convolution operation unit 242 performs convolution processing using kernel data.

FIG. 23 is a diagram illustrating a second configuration example of the signal processing unit and the kernel data storage ROM. For simplification, AFE and the like are omitted.
The example of FIG. 23 is a block diagram in the case where the image processing device 240 has a noise reduction filter processing step at the beginning, and noise reduction filter processing ST1 corresponding to exposure information is prepared in advance as filter kernel data.

Exposure information determined at the time of exposure setting is acquired from the exposure information detection unit 253, and kernel data is selected and controlled through the convolution control unit 244.
In the two-dimensional convolution operation unit 242, after performing the noise reduction filter processing 1ST1, the color space is converted by the color conversion processing ST2, and then the convolution processing (OTF restoration filter processing) ST3 is performed using the kernel data.
The noise reduction filter process 2ST4 is performed again, and the original color space is restored by the color conversion process ST5. The color conversion process includes, for example, YCbCr conversion, but other conversions may be used.
Note that the second noise processing ST4 can be omitted.

FIG. 24 is a diagram illustrating a third configuration example of the signal processing unit and the kernel data storage ROM. For simplification, AFE and the like are omitted.
The example of FIG. 24 is a block diagram when an OTF restoration filter corresponding to exposure information is prepared in advance.

Exposure information determined at the time of exposure setting is acquired from the exposure information detection unit 253, and kernel data is selected and controlled through the convolution control unit 244.
The two-dimensional convolution calculation unit 242 performs the convolution process ST13 using the OTF restoration filter after the noise reduction filter process 1ST11 and the color conversion process ST12.
The noise reduction filter process 2ST14 is performed again, and the original color space is restored by the color conversion process ST15. The color conversion process includes, for example, YCbCr conversion, but other conversions may be used.
Note that only one of the noise reduction filter processes ST11 and ST14 may be used.

FIG. 25 is a diagram illustrating a fourth configuration example of the signal processing unit and the kernel data storage ROM. For simplification, AFE and the like are omitted.
The example of FIG. 25 is a block diagram in the case where a noise reduction filter processing step is included and a noise reduction filter corresponding to exposure information is prepared in advance as filter kernel data.
Note that the second noise processing ST4 can be omitted.
Exposure information determined at the time of exposure setting is acquired from the exposure information detection unit 253, and kernel data is selected and controlled through the convolution control unit 244.
In the two-dimensional convolution operation unit 242, after performing the noise reduction filter processing 1ST21, the color space is converted by the color conversion processing ST22, and then the convolution processing ST23 is performed using the kernel data.
The noise reduction filter process 2ST24 corresponding to the exposure information is performed again, and the original color space is restored by the color conversion process ST25. The color conversion process includes, for example, YCbCr conversion, but other conversions may be used.
The noise reduction filter process ST21 can be omitted.

  The example in which the filter processing is performed in the two-dimensional convolution calculation unit 242 according to only the exposure information has been described above. However, for example, subject distance information, zoom information, or a calculation coefficient suitable by combining shooting mode information and exposure information Can be extracted or calculated.

  FIG. 26 is a diagram illustrating a configuration example of an image processing apparatus that combines subject distance information and exposure information.

  As illustrated in FIG. 26, the imaging device 200 </ b> A includes a convolution device 401, a kernel / numerical operation coefficient storage register 402, and an image processing operation processor 403.

In this imaging apparatus 200A, the image processing arithmetic processor 403 that has obtained the information about the approximate object distance of the subject and the exposure information read from the object approximate distance information detection apparatus 500 performs an appropriate calculation on the object separation position. The kernel size to be used and its calculation coefficient are stored in the kernel / numerical calculation coefficient storage register 402, and an appropriate calculation is performed by the convolution device 401 that calculates using the value, thereby restoring the image.
In this example, the distance to the main subject is detected by the object approximate distance information detection device 500 including the distance detection sensor, and different image correction processing is performed according to the detected distance.

The above image processing is performed by convolution calculation. To realize this, for example, one type of convolution calculation coefficient is stored in common, and a correction coefficient is stored in advance according to the focal length, The correction coefficient is used to correct the calculation coefficient, and an appropriate convolution calculation can be performed using the corrected calculation coefficient.
In addition to this configuration, the following configuration can be employed.

  The kernel size and the convolution calculation coefficient itself are stored in advance according to the focal length, the convolution calculation is performed using the stored kernel size and calculation coefficient, and the calculation coefficient according to the focal length is stored in advance as a function. In addition, it is possible to employ a configuration in which a calculation coefficient is obtained from this function based on the focal length and a convolution calculation is performed using the calculated calculation coefficient.

  Corresponding to the configuration of FIG. 26, the following configuration can be taken.

At least two or more conversion coefficients corresponding to the aberration caused by the resin lens corresponding to the phase plate are stored in advance in the kernel / numerical calculation coefficient storage register 402 serving as the conversion coefficient storage unit according to the subject distance. The image processing arithmetic processor 403 selects a conversion coefficient according to the distance from the kernel / numerical calculation coefficient storage register 402 to the subject based on the information generated by the object approximate distance information detection device 500 as the subject distance information generating means. It functions as a coefficient selection means.
Then, the convolution device 401 as the conversion unit converts the image signal using the conversion coefficient selected by the image processing arithmetic processor 403 as the coefficient selection unit.

Alternatively, as described above, the image processing arithmetic processor 403 as the conversion coefficient calculation unit calculates the conversion coefficient based on the information generated by the object approximate distance information detection device 500 as the subject distance information generation unit, and the kernel / numerical value Stored in the arithmetic coefficient storage register 402.
Then, the convolution device 401 serving as a conversion unit converts the image signal using the conversion coefficient obtained by the image processing calculation processor 403 serving as the conversion coefficient calculation unit and stored in the kernel / numerical calculation coefficient storage register 402.

Alternatively, at least one correction value corresponding to the zoom position or zoom amount of the zoom optical system 210 is stored in advance in the kernel / numerical calculation coefficient storage register 402 serving as a correction value storage unit. This correction value includes the kernel size of the subject aberration image.
Then, based on the distance information generated by the object approximate distance information detection device 500 as the subject distance information generation unit, the image processing calculation processor 403 as the correction value selection unit stores the kernel and numerical calculation coefficient as the correction value storage unit. A correction value corresponding to the distance from the register 402 to the subject is selected.
The convolution apparatus 401 serving as the conversion means performs the conversion coefficient obtained from the kernel / numerical calculation coefficient storage register 402 serving as the second conversion coefficient storage means and the correction selected by the image processing arithmetic processor 403 serving as the correction value selection means. The image signal is converted based on the value.

As described above, according to the present embodiment, the optical system 210 and the image sensor 220 that form a primary image, and the image processing device 240 that forms the primary image into a high-definition final image, include the optical system. 210, since the light wavefront modulation surface of the light wavefront modulation element has a rotationally symmetric shape with respect to the optical axis, and the phase shape is formed so as to monotonously increase or monotonically decrease from the center to the periphery. The following effects can be obtained.
A general optical system that does not have a light wavefront modulation element by making the light wavefront modulation surface rotationally symmetric with respect to the optical axis and generating a larger spherical aberration than a general optical system that does not have a light wavefront modulation element. It becomes possible to make the change of OTF according to the object distance much smaller than that of the system.

In addition, by forming the phase shape so as to monotonously increase or decrease monotonously from the central portion to the peripheral portion, it is possible to reduce the spot image while having the effect of reducing the change in OTF according to the object distance. Become.
Further, in the present embodiment, it is possible to obtain a uniform OTF from the center portion to the peripheral portion of the image by increasing the focal length of the light wavefront modulation surface with respect to the focal length of the entire optical system 210. .
Further, by increasing the focal length of the light wavefront modulation element (lens) having the light wavefront modulation surface with respect to the focal length of the entire optical system 210, a uniform OTF can be obtained from the center portion to the peripheral portion of the image. Is possible.
In addition to simplifying the optical system and reducing costs, it is possible to obtain a good restored image with appropriate image quality and low noise, as well as easy manufacturing and mounting accuracy. Therefore, it is possible to suppress the influence of reflection and to realize an imaging device in which the contrast does not vary depending on the image direction.

In addition, the kernel size used in the convolution calculation and the coefficient used in the numerical calculation are made variable, know by the input of the operation unit 280 shown in FIG. There is an advantage that the lens can be designed without worrying about the defocus range and that the image can be restored by convolution with high accuracy.
Further, there is an advantage that a natural image can be obtained without requiring an optical lens that is difficult, expensive, and large in size, and without driving the lens.
The imaging apparatus 200 according to the present embodiment can be used in a DEOS optical system in consideration of the small size, light weight, and cost of consumer devices such as digital cameras and camcorders.
Further, the configuration of the optical system 210 can be simplified, manufacturing becomes easy, and cost reduction can be achieved.

By the way, when a CCD or CMOS sensor is used as an image sensor, there is a resolution limit determined by the pixel pitch, and if the resolution of the optical system exceeds the limit resolution, a phenomenon such as aliasing occurs, which adversely affects the final image. It is a well-known fact that
In order to improve image quality, it is desirable to increase the contrast as much as possible, but this requires a high-performance lens system.

However, as described above, aliasing occurs when a CCD or CMOS sensor is used as an image sensor.
Currently, in order to avoid the occurrence of aliasing, the imaging lens apparatus uses a low-pass filter made of a uniaxial crystal system to avoid the occurrence of aliasing.
The use of a low-pass filter in this way is correct in principle, but the low-pass filter itself is made of crystal, so it is expensive and difficult to manage. Moreover, there is a disadvantage that the use of the optical system makes the optical system more complicated.

As described above, in order to form a high-definition image, the optical system must be complicated in the conventional imaging lens apparatus in spite of the demand for higher-definition image due to the trend of the times. . If it is complicated, manufacturing becomes difficult, and if an expensive low-pass filter is used, the cost increases.
However, according to this embodiment, the occurrence of aliasing can be avoided without using a low-pass filter, and high-definition image quality can be obtained.

  Also, the kernel data storage ROMs of FIGS. 18, 19, and 20 are not necessarily used for the values of optical magnification, F number, size of each kernel, and object distance. Also, the number of kernel data to be prepared is not limited to three.

1 is an external view showing an example of an information code reading device according to an embodiment of the present invention. It is a figure which shows an example of an information code. It is a block which shows the structural example of the imaging device applied to the information code reader of FIG. It is a figure which shows the basic structural example of the imaging lens unit which forms the optical system which concerns on this embodiment, Comprising: In the optical system which concerns on this embodiment, the light wavefront in the surface adjacent to the lens provided with the light wavefront modulation element and a diaphragm It is a figure which shows the structural example which implement | achieves modulation. It is a figure which shows the phase shape of the light wavefront modulation surface of each optical system. It is a figure for demonstrating a phase shape. It is a figure for demonstrating about the vertical axis | shaft of FIG. 5 and FIG. It is a figure which shows the defocus change of the spot image of the general optical system which does not have an optical wavefront modulation element. It is a figure which shows the defocus change of the spot image of an optical system provided with the optical wavefront modulation element which does not have an inflection point. It is a figure which shows the defocus change of the spot image of an optical system with a small focal distance of an optical wavefront modulation element. It is a figure which shows the defocus change of the spot image of an optical system with a large focal distance of a light wavefront modulation element. It is a figure for demonstrating the principle of DEOS. It is a figure for demonstrating the MTF correction process in the image processing apparatus which concerns on this embodiment. It is a figure for demonstrating concretely the MTF correction process in the image processing apparatus which concerns on this embodiment. It is a figure which shows the response (response) of MTF when an object exists in a focus position in the case of the conventional optical system, and when it remove | deviated from the focus position. It is a figure which shows the response of MTF when an object exists in a focus position in the case of the optical system of this embodiment which has a light wavefront modulation element, and remove | deviates from a focus position. It is a figure which shows the response of MTF after the data restoration of the imaging device which concerns on this embodiment. It is a figure which shows an example (optical magnification) of the storage data of a kernel data storage ROM. It is a figure which shows the other example (F number) of the storage data of a kernel data storage ROM. It is a figure which shows the other example (F number) of the storage data of a kernel data storage ROM. It is a flowchart which shows the outline | summary of the optical system setting process of an exposure control apparatus. It is a figure which shows the 1st structural example about a signal processing part and a kernel data storage ROM. It is a figure which shows the 2nd structural example about a signal processing part and a kernel data storage ROM. It is a figure which shows the 3rd structural example about a signal processing part and kernel data storage ROM. It is a figure which shows the 4th structural example about a signal processing part and kernel data storage ROM. It is a figure which shows the structural example of the image processing apparatus which combines subject distance information and exposure information. It is a figure which shows typically the structure and light beam state of a general imaging lens apparatus. FIG. 28A is a diagram showing a spot image on the light receiving surface of the image sensor of the imaging lens device of FIG. 27, where FIG. 27A shows a case where the focal point is shifted by 0.2 mm (Defocus = 0.2 mm), and FIG. In the case (Best focus), (C) is a diagram showing each spot image when the focal point is shifted by -0.2 mm (Defocus = -0.2 mm).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 200 ... Imaging device, 210 ... Optical system, 211 ... 1st lens, 212 ... 2nd lens, 213 ... 3rd lens, 214 ... Aperture, 215 ... 4th Lens ... 220 ... Image sensor 230 ... Analog front end unit (AFE) 240 ... Image processing device 250 ... Camera signal processing unit 280 ... Operation unit 290 ... Control Device, 242... Two-dimensional convolution operation unit, 243... Kernel data storage ROM, 244.

Claims (6)

An optical system including a lens and a light wavefront modulation element;
An image sensor that images a subject image that has passed through the optical system,
The optical system is
The phase shape, which is the difference in shape between the case where the light wavefront modulation element has a light wavefront modulation function and the case where the light wavefront modulation element does not have a light wavefront modulation function, is a light wave shape. An imaging device that monotonously increases or decreases monotonously from the axial center toward the peripheral. The imaging device according to claim 1, wherein a focal length of a modulation surface of the light wavefront modulation element is larger than an absolute value of a focal length of the entire optical system. The imaging apparatus according to claim 1, wherein a focal length of the light wavefront modulation element including the modulation surface is larger than an absolute value of a focal length of the entire optical system. The imaging apparatus according to claim 1, wherein the optical system includes a diaphragm, and the diaphragm is disposed in the vicinity of the light wavefront modulation element. A subject dispersion image is formed by the light wavefront modulation element,
The imaging apparatus according to claim 1, further comprising: an image processing unit that generates an image signal having no dispersion from a subject dispersion image signal from the imaging element. An information code reader for optically reading an information code,
An optical system including a lens and a light wavefront modulation element;
An image sensor that images a subject image that has passed through the optical system,
The optical system is
The information code reading device, wherein the modulation surface of the light wavefront modulation element has a rotationally symmetric shape with respect to the optical axis, and the phase shape monotonously increases or decreases monotonously from the optical axis central portion toward the peripheral portion.

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