JPH0815646A - Optical low-pass filter and image forming system therewith - Google Patents

Abstract

PURPOSE:To detect the information of the line of sight with high accuracy by means of the positional information of the image of eyes formed on a photographing element by providing a unit pattern region composed of minute patterns whose sizes are different from each other with a prescribed repeated pitch on a substrate, diffracting a passing light beam and obtaining a low-pass effect. CONSTITUTION:A unit pattern region is composed of three minute patterns 1-3 having projected shape and recessed shape and their sizes are different from each other. Phase differences are imparted between the light beams transmitted through the minute pattern and its surrounding region among the light beams incident on these unit pattern regions, the beams are diffracted and thus a desired low-pass effect is obtained. Specially, the low-pass filter blurs the image two-dimensionally when the positional information is not detected by an image pickup element because of the small image of eyes of an observer and has the low-pass effect detecting the positional information on the surface of the image pickup element with high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical low-pass filter and an imaging system having the same, and more particularly to a video camera,
In an electronic still camera or the like, the line-of-sight information of the eyeball of the photographer is detected, and various types of image-pickup information such as focus detection and photometry are selected based on the line-of-sight information, and the eyeball image of the observer at the time of photographing is displayed by a CCD or the like. The present invention relates to an optical low pass filter suitable for forming an image on the surface of an image sensor and an image forming system having the optical low pass filter.

[0002]

2. Description of the Related Art Generally, in an image forming system using a solid-state image pickup device having a discrete pixel structure, image information is optically spatially sampled to obtain an output image. In this case, if the subject includes a high spatial frequency component equal to or higher than the sampling frequency, a false signal such as a structure or a hue that the subject does not have occurs. That is, frequency components that cannot be sampled by the imaging system (frequency components exceeding the Nyquist frequency)
Cannot be reproduced as image information, and causes so-called waveform distortion (aliasing), moire fringes, false colors, and the like. Therefore, conventionally, an optical low-pass filter is arranged in a part of the image forming system to limit the high spatial frequency component of the subject.

Various types of optical low-pass filters and image forming systems having the same have been conventionally proposed.
Among them, for example, Japanese Patent Publication No. 52-22247 proposes an optical low-pass filter using a phase grating. In this publication, phase gratings having a trapezoidal wave-shaped cross section are continuously arranged in a one-dimensional direction, and the shapes and pitches of the flat top portion and the inclined surface at that time are specified to obtain a good low-pass effect.

Further, in Japanese Patent Publication No. 56-2936, when an optical low-pass filter composed of a phase grating is provided in a part of the photographing system and used, a predetermined low-pass effect can be obtained even when the aperture diameter of the diaphragm is reduced. I am proposing a photography system that does this.

[0005]

Recently, in a photographing system such as a video camera or a 35 mm film camera, a plurality of distance measuring points are provided in a photographing range and a distance measuring device using the distance information of an arbitrary distance measuring point is used. Various types of multi-point photometric devices have been proposed, in which a plurality of photometric points are provided and the photometric information (exposure information) of an arbitrary area in the photographing range is used.

There has been proposed each of the line-of-sight input devices in which the distance measuring point and the light measuring point at this time are selected by utilizing the line-of-sight information of the observer. At this time, as for the line-of-sight information of the observer, an image of the eyeball such as a Purkinje image of the eyeball generated at this time by irradiating the eyeball with infrared light (hereinafter abbreviated as “P image”).
Is imaged on the surface of an image pickup device such as a CCD, and the position information of the P image from the image pickup device is used to obtain the image. CCD of P image
In some cases, the P image becomes smaller than the size of one pixel of the CCD when the image is formed at. Then, the position information of the P image cannot be obtained.

According to the present invention, a P image obtained when an observer's eyeball is illuminated with infrared light is formed on the surface of an image pickup device such as a CCD, and the eyeball position is determined from the position information of the P image formed on the image pickup device. An object of the present invention is to provide an optical low-pass filter capable of detecting line-of-sight information with high accuracy and an imaging system having the optical low-pass filter.

[0008]

[Means for Solving the Problems]

(1-1) The optical low-pass filter according to the present invention is provided with a plurality of unit pattern areas each having a plurality of minute patterns having different sizes of a convex portion or a concave portion on a substrate surface at a predetermined repeating pitch. It is characterized in that a low-pass effect is obtained by diffracting the light flux passing through the region.

(2-1) In the image forming system having the optical low-pass filter of the present invention, a plurality of unit pattern areas composed of a plurality of minute patterns having different sizes of convex portions or concave portions are formed at a predetermined repeating pitch. An optical low-pass filter, which is provided on the substrate surface and diffracts the light flux passing through the unit pattern area to obtain the low-pass effect, is provided at a position apart from the focal plane of the imaging lens by a predetermined amount in the optical axis direction. It is characterized by that.

[0010]

1 to 4 are plan views of the essential parts of an optical low-pass filter according to the present invention. In each of the embodiments, the unit pattern area is a fictitious regular hexagon or concentric circles (actually, such hexagonal or concentric circle lines do not exist). A plurality of the unit pattern areas are arranged at a predetermined repeating pitch T. It shows one unit pattern area when it is arranged so as to have a honeycomb shape two-dimensionally.

In this embodiment, a plurality of minute patterns 1 to n having different convex or concave sizes are formed in the unit pattern area on the transparent substrate surface so as to have random or constant regularity.

In the first and third embodiments shown in FIGS. 1 and 3, the unit pattern area is composed of three minute patterns having different convex or concave sizes. In Embodiments 2 and 4 of FIGS. 2 and 4, the unit pattern region is composed of two minute patterns having different sizes such as a convex shape and a concave shape.

The repeating pitch T of the unit pattern region of the optical low-pass filter of the present invention is 100 μm because it is mainly intended for infrared light (wavelength λ = 880 nm).
To 200 μm. This is a normal optical low-pass filter pitch of 30 μm to 40 μ for the visible range.
It is larger than m. When the wavelength used is λ, the phase difference θ between peaks and valleys due to the minute pattern is π, the substrate material is acrylic (refractive index n), and the depth between peaks and valleys is d.

[0014]

[Equation 1] It has become a degree. If the wavelength of visible light is used as the wavelength λ, it can be used in the visible range.

In this embodiment, the minute pattern is composed of a plurality of independent circular patterns each having a different size. However, the shape of the minute pattern is not limited to a circle, but may be any shape such as an ellipse or a square. May be.

In the present embodiment, the light fluxes incident on these unit pattern areas, for example, the light fluxes passing through the minute pattern and the surrounding area of the infrared light are respectively imparted with a phase difference and diffracted, whereby The low-pass effect is obtained. For example, strengthen the low-order diffracted light (low frequency component),
Higher order diffracted light (high frequency component) is weakened.

Particularly, the optical low-pass filter of the present invention is used when the image of the eyeball of the observer (Purkinje image, iris, pupil, etc.) is so small that its position information cannot be detected by an image pickup device such as CCD. It has a low-pass effect that blurs an image two-dimensionally and can detect the position information of the image on the surface of the image sensor with high accuracy.

The optical low-pass filter of the present invention obtains a desired low-pass effect by the above-mentioned constitution,
Further, it is desirable to have the following configuration.

(1-a) In the unit pattern area, minute patterns are provided respectively on the center and on the circumference of a plurality of concentric circles having the center as the origin. This allows
The blurring in the vertical direction and the blurring in the left-right direction are prevented from becoming different from each other to prevent the blurring in an elliptical shape, so that a circular blur having a good rotational symmetry is formed.

(1-b) When the phase difference between the minute pattern and the light flux passing therethrough is θ and the area ratio of the entire minute pattern to the unit pattern region is Sr, 0.25π ≦ θ ≦ 1 .25π ... (1) 0.1 ≦ Sr ≦ 0.7 (2) The condition is satisfied.

Conditional expressions (1) and (2) are for obtaining a good low-pass effect by appropriately setting the phase difference between the minute pattern and the light flux passing through it and the area ratio in the unit pattern area. is there.

If the lower limit of conditional expression (1) is exceeded, the zero-order light (straight component) becomes too strong, blurring is reduced, and the low-pass effect is diminished. On the other hand, if the upper limit is exceeded, on the contrary, the 0th-order light becomes too weak and the blur becomes large, which is not good.

If the lower limit of conditional expression (2) is exceeded, the low-order diffracted light will be small, blurring will be small, and the low-pass effect will be weakened. On the other hand, if the upper limit is exceeded, it becomes difficult to independently arrange minute patterns on the substrate surface, which is not preferable.

In order to obtain a better low-pass effect in the present invention, it is preferable to set the numerical ranges of conditional expressions (1) and (2) as follows.

0.5π ≦ θ ≦ 1.1π (1a) 0.35 ≦ Sr ≦ 0.6 (2a) (1-c) The repeating pitch of the unit pattern area is T
Then, the condition that 0.1 mm ≦ T (3) is satisfied. If the repeating pitch T is below the lower limit of conditional expression (3), the high-order diffracted light becomes too strong and the blur becomes large, which is not good.

In the present invention, it is more preferable to set the numerical range of conditional expression (3) as follows.

0.1 mm ≦ T ≦ 2.0 mm (3a) Generally, when a low-pass filter is provided in the imaging system, a unit pattern area of at least two cycles exists in the diameter of the diaphragm (pupil). Good to do. Conditional expression (3a) is set in consideration of this, and by satisfying conditional expression (3a), a good low-pass effect is obtained.

Next, Example 1 of the optical low-pass filter
Numerical examples of 4 are shown. In the numerical data, No. Is the fine pattern number, X and Y are the center coordinates of the fine pattern when the center of the unit pattern area (within the hexagon) is the origin (0, 0), d is the depth of the peaks and valleys, and R is the fine The radius of the pattern is shown.

<Numerical Example 1> No. Xmm Ymm dmm Rmm 1 0.000 0.000 0.00094 0.077 2 0.095 0.000 0.00094 0.012 3 -0.095 0.000 0.00094 0.012 4 -0.142 0.082 0.00094 0.043 5 -0.142 -0.082 0.00094 0.043 6 0.000 -0.165 0.00094 0.043 7 0.142 -0.082 0.00094 0.043 8 0.142 0.082 0.00094 0.043 9 0.000 0.165 0.00094 0.043 Unit pattern regular hexagonal side 0.165 mm θ = 1.0π (λ = 880 nm) Sr = 44.5%
T = 0.286mm <Numerical example 2> No. Xmm Ymm dmm Rmm 1 0.000 0.000 0.0008 0.070 2 -0.066 0.116 0.0008 0.030 3 -0.134 0.000 0.0008 0.030 4 -0.067 -0.115 0.0008 0.030 5 0.067 -0.116 0.0008 0.030 6 0.133 0.000 0.0008 0.030 7 0.066 0.116 0.0008 0.030 Unit pattern regular hexagonal side 0.154 mm θ = 0.88π (λ = 880 nm) Sr = 38.8%
T = 0.267 mm <Numerical example 3> No. Xmm Ymm dmm Rmm 1 0.000 0.256 0.0007 0.050 2 -0.222 0.128 0.0007 0.050 3 -0.222 -0.127 0.0007 0.050 4 0.000 -0.256 0.0007 0.050 5 0.223 -0.127 0.0007 0.050 6 0.221 0.128 0.0007 0.050 7 0.000 0.000 0.0007 0.040 8 0.000 0.134 0.0007 0.062 9 -0.115 0.066 0.0007 0.062 10 -0.116 -0.066 0.0007 0.062 11 0.000 -0.136 0.0007 0.062 12 0.119 -0.067 0.0007 0.062 13 0.117 0.067 0.0007 0.062 14 -0.111 0.191 0.0007 0.040 15 -0.222 0.000 0.0007 0.040 16 -0.111 -0.192 0.0007 0.040 17 0.111 -0.192 0.0007 0.040 18 0.222 0.000 0.0007 0.040 19 0.111 0.191 0.0007 0.040 Unit pattern regular hexagonal side 0.256 mm θ = 0.77π (λ = 880 nm) Sr = 63. 6%
T = 0.443 mm <Numerical example 4> No. Xmm Ymm dmm Rmm 1 0.000 0.421 0.0006 0.101 2 -0.362 0.211 0.0006 0.101 3 -0.362 -0.209 0.0006 0.101 4 0.001 -0.417 0.0006 0.101 5 0.363 -0.211 0.0006 0.101 6 0.363 0.208 0.0006 0.101 7 -0.001 0.007 0.0006 0.101 8 0.000 0.161 0.0006 0.043 9 -0.139 0.077 0.0006 0.043 10 -0.134 -0.077 0.0006 0.043 11 0.001 -0.152 0.0006 0.043 12 0.138 -0.079 0.0006 0.043 13 0.140 0.080 0.0006 0.043 14 0.000 0.264 0.0006 0.043 15 -0.118 0.205 0.0006 0.043 16 -0.225 0.129 0.0006 0.043 17 -0.225 -0.001 0.0006 0.043 18 -0.222 -0.128 0.0006 0.043 19 -0.115 -0.203 0.0006 0.043 20 0.001 -0.256 0.0006 0.043 21 0.120 -0.206 0.0006 0.043 22 0.227 -0.133 0.0006 0.043 23 0.229 -0.001 0.0006 0.043 24 0.227 0.130 0.0006 0.043 25 0.118 0.208 0.0006 0.043 26 -0.134 0.340 0.0006 0.043 27 -0.228 0.289 0.0006 0.043 28 -0.364 0.051 0.0006 0.043 29 -0.366 -0.055 0.0006 0.043 30 -0.230 -0.288 0.0006 0.043 31 -0.136- 0.342 0.0006 0.043 32 0.135 -0.344 0.0006 0.043 33 0.226 -0.2 90 0.0006 0.043 34 0.363 -0.052 0.0006 0.043 35 0.362 0.054 0.0006 0.043 36 0.230 0.284 0.0006 0.043 37 0.134 0.341 0.0006 0.043 Unit pattern regular hexagonal side 0.420 mm θ = 0.66π (λ = 880 nm) Sr = 52.5%
T = 0.727 mm FIGS. 5A and 5B are a schematic view of a main part of an optical system of an image forming system having an optical low-pass filter of the present invention and an explanatory diagram of output signals from a photoelectric element array. 5A and 5B mainly show the optical system of the detection principle when obtaining the line-of-sight information of the eyeball of the observer. FIG. 6 is a schematic view of a main part when an image forming system having an optical low-pass filter according to the present invention is applied to a part of a viewfinder system of a single-lens reflex camera.

In this embodiment, a parallel light beam from a light source is projected onto the anterior segment of the eyeball of an observer, and the visual axis is obtained by utilizing the corneal reflection image by the reflected light from the cornea and the imaging position of the pupil. .

In FIGS. 5 and 6, LF is an optical low-pass filter, and 5 is a light source such as a light emitting diode that emits infrared light insensitive to the observer, and is arranged on the focal plane of the light projecting lens 3. There is.

The infrared light emitted from the light source 5 is projected by the projection lens 3
Parallel light is reflected by the half mirror 2 and the eyeball 2
The cornea 21 of No. 01 is illuminated. At this time, the corneal reflection image d by a part of the infrared light reflected on the surface of the cornea 21 is transmitted through the half mirror 2, is condensed by the light receiving lens 4, and is positioned on the photoelectric element array 6 via the optical low pass filter LF. Z
Reimage to d '. Light fluxes from the ends a and b of the iris 23 pass through the half mirror 2, the light receiving lens 4 and the optical low pass filter LF to the positions Za ′ and Z on the photoelectric element array 6.
Images of the end portions a and b are formed on b '. When the rotation angle θ of the optical axis a of the eyeball with respect to the optical axis (optical axis a) of the light receiving lens 4 is small, assuming that the Z coordinates of the ends a and b of the iris 23 are Za and Zb, the coordinates of the center position c of the pupil 24. Zc is expressed as Zc≈ (Za + Zb) / 2.

Further, the Z coordinate of the generation position d of the corneal reflection image is Z
d, when the distance between the center O of curvature of the cornea 21 and the center C of the pupil 24 is OC, the rotation angle θ of the optical axis a of the eyeball substantially satisfies the relational expression of OC * SIN θ≈Zc−Zd (T1). . Therefore, the calculating means 9 detects the position of each singular point (corneal reflection image d and edge parts a and b of the iris) projected on the surface of the photoelectric element array 6 as shown in FIG. The rotation angle θ of the optical axis a can be obtained. At this time, the formula (T1) is

[0034]

[Equation 2] Can be rewritten as However, β is a magnification determined by the distance L1 between the corneal reflection image generation position and the light receiving lens 4 and the distance L0 between the light receiving lens 4 and the photoelectric element array 6, and is usually a substantially constant value.

By the way, the optical axis a of the eyeball of the observer does not coincide with the visual axis. Therefore, the line of sight is detected by correcting the angle between the optical axis of the eyeball of the observer and the visual axis. Now, when the horizontal rotation angle θ of the optical axis of the eyeball of the observer is calculated, the angle of sight δH between the optical axis of the eyeball and the visual axis is corrected δ so that the horizontal line of sight θH of the observer is θH = θ ±. It is calculated as δ ... (T3). Here, if the rotation angle to the right with respect to the observer is positive, the sign ± is selected as + if the observer's eye looking into the observation device is the left eye, and − if the observer's eye is the right eye.

Although FIG. 5 shows an example in which the observer's eyeball rotates in the Z-X plane (eg, horizontal plane), the observer's eyeball rotates in the XY plane (eg, vertical plane). In the case, it can be detected similarly. However, the vertical component of the line of sight of the observer is the vertical component θ ′ of the optical axis of the eyeball.
Therefore, the line of sight θV in the vertical direction is θV = θ '... (T4).

Next, an optical system when the present invention shown in FIG. 6 is applied to a part of a viewfinder system of a single-lens reflex camera will be described.

In the figure, the subject light that has passed through the taking lens 101 is reflected by the flip-up mirror 102 and forms an image near the focal plane of the focusing plate 104. Further focus plate 10
The subject light diffused at 4 is the condenser lens 105,
Through the penta roof prism 106 and the eyepiece 1 having the light splitting surface 1a, the eyepoint 201a of the photographer
Be led to.

The imaging system for detecting the line of sight is an illumination means (optical axis c) composed of a light source 5 such as an infrared light emitting diode which is insensitive to the photographer (observer) and a light projecting lens 3 and an optical low pass filter. The light receiving means (optical axis A) including the LF, the photoelectric element array 6, the half mirror 2 and the light receiving lens 4 is arranged above the eyepiece 1 having the light dividing surface 1a formed of a dichroic mirror. The infrared light emitted from the infrared light emitting diode 5 is reflected by the light dividing surface 1a and illuminates the eyeball 201 of the photographer. Further eyeball 201
A part of the infrared light reflected by is reflected again by the light splitting surface 1a, and is condensed on the photoelectric element array 6 through the light receiving lens 4, the half mirror 2, and the optical low pass filter LF. The direction of the line of sight of the photographer is calculated by the calculation means 9 from the image information of the eyeball (for example, the output signal shown in FIG. 5B) obtained on the photoelectric element array 6. That is, the focus surface 1 observed by the observer
04 I am looking for a point (attention point).

The focus plane 10 seen by the photographer from the horizontal line of sight θH and the vertical line of sight θV at this time.
The position (Zn, Yn) on 4 is

[0041]

(Equation 3) Is required. However, m is a constant determined by the finder system of the camera. In this way, when it is possible to know which position on the focus plane 104 the photographer is observing in the single-lens reflex camera, for example, the point where focus detection is possible in the automatic focus detection device of the camera is not limited to the screen center, but the screen. In the case where the photographer selects one of the points to perform automatic focus detection when it is provided at a plurality of positions, the trouble of selecting and inputting one of the points is eliminated, and the point the photographer is observing, That is, it is effective to regard the gazing point as a point for focus detection and automatically select the point for automatic focus detection.

[0042]

As described above, according to the present invention, the P image obtained when the observer's eyeball is illuminated with infrared light is formed on the surface of the photographing element such as CCD and formed on the photographing element. It is possible to achieve an optical low-pass filter capable of detecting the eye-gaze information with high accuracy based on the position information of the P image, and an imaging system having the same.

[Brief description of drawings]

FIG. 1 is a plan view of a main part of a first embodiment of an optical low-pass filter according to the present invention.

FIG. 2 is a plan view of the essential parts of Embodiment 2 of the optical low-pass filter of the present invention.

FIG. 3 is a plan view of the essential parts of Embodiment 3 of the optical low-pass filter of the present invention.

FIG. 4 is a plan view of the essential parts of Embodiment 4 of the optical low-pass filter of the present invention.

FIG. 5 is a schematic view of a main part of an image forming system having an optical low pass filter of the present invention.

FIG. 6 is a schematic diagram of a main part when an imaging system having an optical low-pass filter of the present invention is applied to a single-lens reflex camera.

[Explanation of symbols]

 LF Optical low-pass filter 5 Infrared light emitting diode 3 Light emitting lens 4 Light receiving lens 6 CCD 201 Eyeball

Claims (8)

[Claims] 1. A plurality of unit pattern areas, each of which is composed of a plurality of minute patterns having different sizes of a convex portion or a concave portion, are provided on a substrate surface at a predetermined repetition pitch, and a light beam passing through the unit pattern area is diffracted. An optical low pass filter characterized by having a low pass effect. 2. The optical low-pass filter according to claim 1, wherein the unit pattern area is provided with a minute pattern on a center thereof and on a circumference of a plurality of concentric circles having the center as an origin. 3. When a phase difference between the minute pattern and a light beam passing through the periphery thereof is θ and an area ratio of the entire minute pattern to the unit pattern area is Sr, 0.25π ≦ θ ≦ 1.25π 0 3. The optical low pass filter according to claim 2, wherein the condition of 1 ≦ Sr ≦ 0.7 is satisfied. 4. The optical low pass filter according to claim 1, wherein the condition that 0.1 mm ≦ T is satisfied, where T is the repeating pitch of the unit pattern region. 5. A plurality of unit pattern areas, each of which is composed of a plurality of minute patterns having different sizes of convex portions or concave portions, are provided on a substrate surface at a predetermined repetition pitch, and a light flux passing through the unit pattern areas is diffracted. An imaging system characterized in that an optical low-pass filter for obtaining a low-pass effect is provided at a position apart from the focal plane of the imaging lens by a predetermined amount in the optical axis direction. 6. The image forming system according to claim 5, wherein the unit pattern area is provided with a minute pattern on a center thereof and on a circumference of a plurality of concentric circles having the center as an origin. 7. When the phase difference between the minute pattern and a light beam passing around the minute pattern is θ and the area ratio of the entire minute pattern to the unit pattern region is Sr, 0.25π ≦ θ ≦ 1.25π 0 7. The image forming system according to claim 6, wherein the condition of 1 ≦ Sr ≦ 0.7 is satisfied. 8. The image forming system according to claim 5, wherein a condition of 0.1 mm ≦ T is satisfied, where T is a repeating pitch of the unit pattern area.