JP2000275582A - Depth-of-field enlarging system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To observe a sample image on an optimum condition at the time of observing a sample by using a depth-of-field enlarging system. SOLUTION: This depth-of-field enlarging system is provided with a subject detection optical system provided with 1st to 3rd lenses 2 to 4 condensing light from a sample 9 and a CCD 22 detecting the light condensed by the lens groups 2 to 4 so as to detect the image of the sample 9, and a liquid crystal spatial phase modulator 5 arranged between the sample 9 and an imaging device 22 and modulating the passing light to phase distribution of specified shape in accordance with the enlarging amount of field, and the phase modulation amount of the modulator 5 is varied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a depth of field expanding system for expanding the depth of field of an optical system.

[0002]

2. Description of the Related Art Conventionally, techniques for expanding the depth of field of an optical system include (1) US Pat. No. 5,748,371 (University of Colorado), and (2) Edward R. Dowski, Jr., W. Thom.
as Cathey, “Extended depth of field through wave-f
ront coding ”, Appl. Opt. Vol. 39, 1859-1866 (1995),
(3) Sara Bradburn, Wade Thomas Cathey, Edward R. Do
wski, Jr., “Realization of focus invariance in opti
cal-digital systems with wave-front coding ”, Appl.
Opt. Vol 136, 9157-9166 (1997).

FIG. 6 shows a schematic configuration of a depth-of-field expanding system disclosed in US Pat. No. 5,748,371. As shown in FIG. 6, the optical system includes a lens system 6.
And a cubic phase modulation mask 60 inserted at the pupil position of the optical system composed of the CCD 2 and the CCD 63. The cubic phase modulation mask 60 imparts a phase distribution to the light reflected from the object 61 and projects the light on a CCD 63 via a lens system 62. The output from the CCD 63 is transmitted to an image processing device 64.
Image processing.

FIG. 3 shows a specific configuration of the cubic phase modulation mask 60. Cubic phase modulation mask 60
Means that one surface (upper surface) is z as shown by hatching in FIG.
= K (x ³ + y ³ ), and the other surface, that is, the bottom surface, has a planar shape. The phase of the light transmitted through the cubic phase modulation mask 60 is, for incident light, P (x, y) = exp (jα (x ³ + y ³ )), | x according to the incident position (x, y). | ≦ 1, | y | ≦ 1 (1) Here, α is a phase modulation amount, and x and y are coordinates at a pupil position standardized by a maximum value of 1.

Next, an OTF (Optical Transfer Function: OTF) obtained by using the depth of field expanding system.
The intensity distribution of the optical transfer function will be described with reference to FIGS. FIG. 7 shows an OTF through a normal optical system. In an ordinary optical system, the intensity distribution of the OTF changes from FIG. 7A to FIG. 7C as the object shifts from the in-focus position. On the other hand, in the depth of field expansion system, FIG.
(C), and the change is small. When this is processed using an inverse filter having the characteristics shown in FIG. 9, when it is out of focus (FIGS. 10B and 10C), as shown in FIGS. Even if there is, a result close to the intensity distribution of the OTF at the time of focusing (FIG. 10A) is obtained.

If the change of the OTF is described with an actual image, blurring due to defocus occurs as the focal position shifts in a normal optical system. However, when the depth of field expanding system is used, The image before the image processing when the focal position is shifted is blurred, but the blurring does not change in each image. When image processing is performed on these images by an inverse filter, an image equivalent to an image in which a normal optical system is not defocused is obtained, and it can be seen that the depth of field can be increased.

[0007]

By the way, the cubic phase modulation mask 60 described above uses the phase modulation amount, that is, α in equation (1), to increase the depth of field and the spatial filter used in image processing. And the influence of the image pickup means on the noise when the image is taken into the image processing apparatus.

That is, as α increases, the enlargement rate of the depth of field increases, while the size of the spatial filter increases, and the amount of calculation required for image processing increases.

FIG. 11 shows OT through the depth of field expansion system at the in-focus position when α is 20 and 60.
FIG. 11 shows the intensity distribution of F. As shown in FIG.
When α is 20, the OTF intensity is higher, and when O is 60, it is lower. In order to return the OTF that has passed through the depth of field expanding system to the OTF intensity distribution in a normal optical system by image processing, a spatial filter having characteristics as shown in FIG. 12 is required.

FIG. 12 shows how many times the information of the corresponding spatial frequency of the sample under observation is multiplied by the image processing. FIG. 15 shows that when α = 20, the maximum is about five times. On the other hand, when α = 60, it becomes about 8 times. When image processing is performed using such a spatial filter, if noise of the imaging unit is present in the image before image processing, the noise is also enhanced together. 60, the degree of noise emphasis is greater, and the influence of the imaging means on noise is greater. The influence on the noise also differs depending on the structure of the sample to be observed.

As described above, when observing a sample, the necessary depth of field, the amount of calculation that can be spent on image processing, the structure of the sample, and the like are not fixed conditions, but there are optimal conditions. In addition, it is necessary to change the phase modulation amount α.

However, in a cubic phase modulation mask or the like used in a conventional depth-of-field expansion system, the amount of phase modulation α is uniquely determined, and any noise caused by a change in the structure of the sample. Could not be reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to observe a sample image under optimum conditions when observing the sample using a depth-of-field expanding system. It is an object of the present invention to provide a depth-of-field expansion system capable of performing the following.

[0014]

According to a first aspect of the present invention, there is provided a lens system for condensing light from a subject, and a method for detecting light condensed by the lens system and detecting the light. A subject detection optical system having an imaging unit that detects an image of the object, and disposed between the subject and the imaging unit;
A wavefront conversion element capable of modulating the phase distribution of light from the subject, and image conversion means for image-converting an image detection signal output from the imaging means using a spatial filter, wherein the phase is modulated by the wavefront conversion element A depth-of-field expansion system that generates an image with an expanded depth of field by subjecting a subject image to image processing by image conversion means, wherein the wavefront conversion element arbitrarily adjusts a phase modulation amount of light from the subject. The depth of field expanding system is provided, wherein the spatial filter of the image converting means can be set according to the phase modulation amount of the light set by the wavefront converting element.

According to such a configuration, the amount of phase modulation for obtaining the depth of field can be arbitrarily controlled by the wavefront conversion element according to the state of noise in the image obtained by the imaging means. The degree of freedom of the system is improved as compared with the case where the conventional cubic phase modulation mask is used, and the sample can be observed more favorably.

Further, since the spatial filter of the image conversion means can be changed according to the amount of phase modulation of light set by the wavefront conversion element, the control of the depth-of-field expansion system can be performed better.

The wavefront conversion element is preferably a matrix liquid crystal spatial phase modulator, and preferably has a liquid crystal controller that causes the matrix liquid crystal spatial phase modulator to function as a cubic phase modulation mask.

The wavefront conversion element functions as a cubic phase modulation mask that deforms the optical transfer function of the object detection optical system almost uniformly regardless of the position of the object in the observation optical axis direction. A phase modulation amount setting for arbitrarily setting a phase modulation amount of a wavefront conversion element as a cubic phase modulation mask by image-converting an image detection signal from an imaging unit using a spatial filter so as to restore an optical transfer function. And a spatial filter control unit that changes a spatial filter in accordance with the phase modulation amount set by the phase modulation amount setting unit.

It is more desirable to provide image display means for displaying an image output by the image pickup means and subjected to image processing by the image conversion means, and to set the amount of phase modulation while checking the display image.

Preferably, the image conversion means has a control unit for controlling the spatial filter.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows the overall configuration of a video microscope apparatus to which the present invention is applied. The video microscope is roughly classified into an objective lens unit 1, a video microscope head 21 to which the objective lens unit 1 is attached, and a control system for controlling the apparatus.

The optical system of the objective lens unit 1 has first to first
It comprises three lens groups including third lenses 2 to 4 and one liquid crystal spatial phase modulator 5 which is a main part of the present invention. The objective lens unit 1 has a cylindrical tube 6 that holds the lens groups 2 to 4 and the liquid crystal spatial phase modulator 5,
The cylinder 6 is covered by a cylindrical cover 7. A gap surrounding the periphery of the cylinder 6 is provided between the cylinder 6 and the cover 7, and an optical fiber 8 for guiding illumination light is inserted through the gap from the head 21 side. The optical fiber 8 guides the illumination light introduced from the light source device 32 and can irradiate the sample indicated by 9 in FIG. The optical fiber 8 is connected to a light source device 32 provided outside the video microscope head 21. An illumination head 15 is attached to a tip portion of the cover 7 so that light from the optical fiber 8 is reflected to efficiently irradiate the sample 9 to be observed.

The first to third lenses 2 to 4 and the liquid crystal spatial phase modulator 5 provided in the cylinder 6 are held via holding members 10 to 13, respectively. Each lens 2-4
The liquid crystal spatial light modulator 5 is inserted into the cylinder 6 in the order shown in the drawing while being held by the holding members 10 to 13 and fixed at a fixed position. Thereby, the liquid crystal spatial phase modulator 5
Is disposed at or near the pupil position of the optical system including the lens groups 2 to 4.

On the other hand, the liquid crystal spatial phase modulator 5 is a wavefront conversion element capable of arbitrarily modulating the phase of transmitted light, and is composed of, for example, a homogeneous alignment liquid crystal panel. FIG. 2 is a schematic diagram of the liquid crystal spatial phase modulator 5. The liquid crystal spatial phase modulator 5 sandwiches liquid crystal molecules between matrix-like electrodes as shown in FIG. 2A, and the liquid crystal molecules are in a homogeneous alignment.

In the homogeneous alignment, the liquid crystal molecules 5b are parallel to the glass surface when the voltage is 0 V shown in FIG. 2B, that is, when the voltages of the electrodes 5a and 5a 'are the same.
Unlike the panel, the liquid crystal molecules are not twisted, so the director, that is, the major axis direction of the liquid crystal molecules is constant in the liquid crystal layer. As shown in FIG. 2C, when the applied voltage becomes larger than the threshold voltage, the director becomes perpendicular to the glass surface from the liquid crystal molecules 5b in the middle of the liquid crystal layer. Since the liquid crystal molecules 5b are not twisted, they have no light-emitting property and cannot be used as a light intensity modulation element. However, the optical path length, that is, the phase can be changed by the applied voltage from the birefringence of the liquid crystal molecules 5b.

According to such a liquid crystal spatial phase modulator 5, an arbitrary phase distribution can be given by the voltage distribution applied to the matrix electrodes of the liquid crystal panel. FIG. 3 is a schematic diagram showing a phase difference distribution to be provided by the modulator 5. That is, the phase of the light transmitted through the phase modulator 5 is shifted as follows: P (x, y) = exp (jα (x ³ + y ³ )), | x | ≦ 1, | y | ≦ 1 (2) Is generated. α represents a phase modulation amount, and x and y represent coordinates at a pupil position standardized by a maximum value of 1. The phase difference given to the transmitted light differs depending on the value of α in the equation (2), and α = 20
The maximum phase difference is 80 rad at the time of α, and 240 rad at α = 60.

However, in the present embodiment, the liquid crystal spatial phase modulator 5 can only provide a phase shift of 2πrad at the maximum. Therefore, in this embodiment, a voltage that gives a phase distribution that is the remainder of dividing the phase P (x, y) by 2π is applied to the electrode 5a of the panel, thereby giving a phase distribution equivalent to the equation (2). Like that.

For the sake of simplicity, in the phase distribution shown in FIG. 3, a sectional view at y = 0 when α = 20 is shown in FIG.
Shown in The horizontal axis represents the coordinates at the pupil position standardized by the maximum value 1, and the vertical axis represents the phase. In order to realize the phase distribution shown in FIG. 4 by the liquid crystal spatial phase modulator 5, a phase distribution as shown in FIG. The horizontal axis represents the coordinates at the pupil position standardized by the maximum value 1, and the vertical axis represents the phase. Therefore, by giving an appropriate voltage distribution to the liquid crystal spatial phase modulator 5, the phase difference which is the maximum when α is 20 or 60 is 8
A phase distribution equivalent to 0 rad and 240 rad can be given.

The objective lens unit 1 configured as described above is attached to a video microscope head 21. This video microscope head 21
While holding the base end of the optical fiber 23 for guiding the illumination light to the optical fiber 8 irradiating the sample 9, the CCD 22 is held and the light reflected by the sample 9 is reflected by the lenses 2 to 4 and the liquid crystal spatial light modulator 5. The light is received by the CCD 22 through the.

Next, a control system for controlling the microscope will be described. This system applies a voltage to the matrix electrode 5a of the liquid crystal spatial phase modulator 5,
A liquid crystal controller 36 for forming an arbitrary phase distribution, a setting unit 39 for a phase modulation amount (α), a central control unit 35 for operating the liquid crystal controller 36 in accordance with α to generate a desired depth of field, and the CCD 22 A CCD controller 31 for detecting the intensity of light passing through the liquid crystal spatial phase modulator 5, a spatial filter 40, and a filter control unit for setting a filter coefficient of the spatial filter 40 according to α. And a monitor 34 for displaying an image output from the image processing means 33. Here, α through the phase modulation amount (α) setting unit 39
May be set while the operator looks at the monitor 34, or may be set in advance according to the subject.

Next, the operation of the video microscope configured as described above will be described.

The light from the light source device 32 is
8, is reflected by the illumination head 15 and irradiates the sample 9 to be observed. The light reflected by the sample 9 passes through the optical system of the first lens 2, the liquid crystal spatial phase modulator 5, the second lens 3, and the third lens 4, and then forms an image on the CCD 22. At this time, the liquid crystal controller 36
The voltage distribution (FIG. 5) that gives the phase distribution (FIGS. 3 and 4) of the corresponding cubic phase modulation mask is given to the liquid crystal spatial phase modulator 5 based on the arbitrary α set by 5. Thus, the depth of field can be increased.

The image picked up by the CCD 22 through the liquid crystal spatial phase modulator 5 having the same phase modulation function as the cubic phase modulation mask is taken into the image processing device 33 via the CCD controller 31. The image processing device 33 sets the spatial filter 40 so as to correspond to α set by the central control unit 35, and performs image processing using the spatial filter.

According to such an operation, a desired depth of field can be obtained by controlling the liquid crystal spatial phase modulator 5 according to the phase modulator α, and the spatial filter 40 corresponding to the α can be obtained. By performing image processing using, it is possible to obtain an image with an increased depth of field.

Next, the setting of the phase modulation amount will be described.

The operator sets α to an arbitrary initial value and starts observing the sample 9 using the monitor 34. That is, the operator observes the image of the sample 9 on the monitor 34 while shifting the image near the in-focus position, and confirms the depth of field and the amount of noise through the monitor 34. Then, if the depth of field is not enough or the noise on the image is large with the set α, the setting of α is changed by adjusting the phase modulation amount (α) setting unit 39. That is, α is increased when the depth of field is insufficient, and α is decreased when the noise is large. As described above, the observer determines the optimal α while observing the monitor 34 and performs observation.

According to the above configuration, operation, and observation method, when observing the sample 9, the necessary depth of field, the amount of calculation that can be spent on image processing, the structure of the sample, and the like are optimized. Observation can be performed using the phase modulation amount α as a condition.

In this embodiment, an example in which the present invention is applied to a video microscope has been described. However, the present invention is not limited to the video microscope but can be applied to various optical systems such as a microscope, a camera, and an endoscope. The liquid crystal spatial phase modulator 5 is not particularly limited as long as it is a wavefront conversion element (for example, a phase modulation element made of an electro-optical material or a magneto-optical material) capable of giving an arbitrary phase distribution to transmitted light.
Further, in the present embodiment, a transmission type configuration is adopted, but a reflection type wavefront conversion element can be used, and in this case, a myroc mirror device or the like can be used. Although the case where the value of α is set by controlling the central control unit 35 manually by the observer has been described, a predetermined phase modulation amount control unit is provided, and the value of α is automatically set based on a captured image. A function for setting can also be added.

It is confirmed that the present specification includes the following inventions.

(1) a subject detection optical system having a lens system for condensing light from a subject and an image pickup means for detecting light condensed by the lens system and detecting an image of the subject;
A wavefront conversion element disposed between the subject and the imaging unit and capable of modulating the phase distribution of light from the subject; and an image conversion unit for performing image conversion of an image detection signal output from the imaging unit using a spatial filter. A depth-of-field expanding system that has a depth-of-field expanded image by subjecting the subject image phase-modulated by the wavefront converting element to image processing by image conversion means. The amount of phase modulation of light from the subject can be set arbitrarily, the spatial filter of the image conversion means can be changed according to the amount of phase modulation of light set by the wavefront conversion element, and the wavefront conversion element is The optical transfer function of the subject detection optical system is deformed almost uniformly regardless of the position of the subject in the observation optical axis direction, and the image conversion means uses a spatial filter to restore the optical transfer function. A phase modulation amount setting unit for arbitrarily setting the phase modulation amount of the wavefront conversion element, and a phase modulation amount corresponding to the phase modulation amount set in the phase modulation amount setting unit. And a spatial filter control unit for changing a spatial filter.

(2) The wavefront conversion element is a matrix-shaped liquid crystal spatial phase modulator, and includes a liquid crystal controller that functions as a cubic phase modulation mask using the matrix liquid crystal spatial phase modulator. Depth of field expansion system.

(3) A system for expanding the depth of field, wherein the wavefront conversion element is a liquid crystal spatial phase modulator having a homogeneous alignment.

(4) A depth-of-field expansion system characterized by comprising image display means for displaying an image output by the image pickup means and subjected to image processing by the image conversion means.

[0046]

As described above in detail, according to the present invention, an observation can be made by giving an arbitrary phase distribution with an optimum phase modulation amount to the structure of a sample, and thus a sufficient enlarged depth of field can be ensured. Under such conditions, it is possible to observe a sample with less noise.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a video microscope to which a depth-of-field expanding system according to a first embodiment of the present invention is applied.

FIG. 2 is a schematic diagram of a liquid crystal spatial light modulator according to the same embodiment.

FIG. 3 is a diagram showing a phase difference distribution provided by a liquid crystal spatial phase modulator.

FIG. 4 is a cross-sectional view at y = 0 when a phase modulation amount α = 20 of a phase difference distribution provided by a liquid crystal spatial phase modulator.

FIG. 5 is a view showing a phase distribution of the liquid crystal spatial light modulator according to the embodiment.

FIG. 6 is a diagram showing a schematic configuration of a conventional depth of field expanding system.

FIG. 7 is a diagram showing a light intensity distribution of a normal optical system.

FIG. 8 is a diagram showing a light intensity distribution of the depth of field expanding system.

FIG. 9 is a diagram showing a characteristic curve of an inverse filter for returning the light intensity distribution of the sample deformed by the depth of field expansion system to the state before the deformation.

FIG. 10 is a diagram showing a light intensity distribution passed through an inverse filter.

FIG. 11 is a diagram showing an intensity distribution of OTF through a depth of field expansion system at a focus position.

FIG. 12 is a diagram showing a characteristic curve of a spatial filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Objective lens 2 ... 1st lens 3 ... 2nd lens 4 ... 3rd lens 5 ... Liquid crystal spatial phase modulator 6 ... Cylinder 7 ... Cover 8 ... Optical fiber 9 ... Sample 10, 11, 12, 13 ... Holding member 14 Fixed frame 15 Illumination head 21 Video microscope head 22 CCD 23 Optical fiber 31 CCD controller 32 Light source device 33 Image processing device 34 Monitor 35 Central control unit 36 Liquid crystal controller 39 Phase modulation amount (α) setting unit 40: spatial filter

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 5/225 H04N 5/335 V 5C024 7/18 M 5C054 5/335 G06F 15/64 320D 7/18 15 / 68 400A F term (reference) 2H088 EA47 HA10 MA02 MA03 4C061 AA00 BB02 CC06 DD00 LL01 NN01 NN05 PP01 SS13 SS30 5B047 AA17 BB01 BC07 CA17 CB16 DA10 5B057 AA07 BA02 BA15 BA23 CE06 5C022 AA51 AC01 AB15 AC15 CA00 CA02 EA08 FA01 GA11 HA27 5C054 AA01 CA04 CC03 CD01 CE06 DA08 EA01 EJ00 FA01 FC00 FC03 HA01 HA12

Claims (3)

[Claims] 1. An object detection optical system comprising: a lens system for condensing light from an object; and image pickup means for detecting light condensed by the lens system and detecting an image of the object; A wavefront conversion element that is arranged between the imaging means and a light source and modulates a phase distribution of light from the subject; and an image conversion means that converts an image detection signal output from the imaging means using a spatial filter. A depth-of-field expanding system that generates an image having an expanded depth-of-field by subjecting the subject image phase-modulated by the wavefront converting element to image processing by the image converting means; The element can arbitrarily set the amount of phase modulation of light from the subject, and the spatial filter of the image conversion means changes the amount of phase modulation according to the amount of light phase modulation set by the wavefront conversion element. Possible depth of field expansion system characterized in that a. 2. The image processing apparatus according to claim 1, wherein the wavefront conversion element functions as a cubic phase modulation mask that deforms an optical transfer function of the object detection optical system to be substantially constant regardless of the position of the object in the observation optical axis direction. The conversion unit converts the image detection signal from the imaging unit to an image using the spatial filter so as to restore the optical transfer function. The phase modulation amount of the wavefront conversion element as the cubic phase modulation mask 2. A phase modulation amount setting unit that arbitrarily sets the spatial modulation amount, and a spatial filter control unit that changes the spatial filter in accordance with the phase modulation amount set by the phase modulation amount setting unit. 3. The depth of field expansion system according to 1. 3. The liquid crystal device according to claim 2, wherein the wavefront converting element is a matrix liquid crystal spatial phase modulator, and further includes a liquid crystal controller that causes the matrix liquid crystal spatial phase modulator to function as the cubic phase modulation mask. The depth of field expansion system according to claim 1.