JP2000066141A - Optical low-pass filter, optical low-pass filter correction method, ccd solid-state image pickup element, color image pickup device and camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical low-pass filter which is capable of executing optical low-pass filter correction suitable for pixel arrays of the same colors in image regions of an RGB type and an optical low-pass filter correction method which does not form moire images, etc., even in any of the horizontal direction, perpendicular direction and diagonal direction of the image regions of the RGB type. SOLUTION: The optical low-pass filter is the optical low-pass filter for an image pickup element having the image regions of the RGB type and is formed with phase gratings extending in the diagonal direction in such a manner that the cut-off characteristics corresponding to the Nyquist space frequency of the diagonal direction when the MTF characteristics in the diagonal direction of the image regions are measured. This optical low-pass filter correction method is the optical low-pass filter correction method for the image pickup element having the image regions of the RGB type arrayed with the pixels in the matrix form and executes the correction in the diagonal direction by arranging the optical low-pass filter in such a manner that the phase gratings extend in the diagonal direction of the image regions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical low-pass filter, an optical low-pass correction method, a CCD solid-state imaging device, a color imaging device, and a camera.

[0002]

2. Description of the Related Art In recent years, as the sensitivity of a CCD or C-MOS image sensor has been improved, an image sensor having an RGB type image area (image area) has been widely used. In the RGB type image area, red (R)
Each of green (G) and blue (B) pixels (color filters) is arranged in a matrix. Here, as an array of pixels (color filters) in an RGB type image area, an array called a Bayer in which green pixels (G) are arranged in a checkered pattern as shown in FIG.
It is referred to as an "r array." ) Is known, and according to the Bayer arrangement, it is possible to obtain many green signals that have the highest human visibility and most affect the image quality of an image.

On the other hand, in a CCD or a C-MOS image sensor for discretely obtaining color image information as described above, a high spatial frequency component of subject light is limited, and light generated by a subject due to generation of a pseudo signal is reduced. In order to remove different color light components, it is necessary to perform correction by an optical low-pass filter. Here, an optical low-pass filter using a phase type diffraction grating (phase grating) is known.

Conventionally, correction using a phase grating type optical low-pass filter has been performed in the pixel arrangement direction (horizontal direction / vertical direction). That is, when the MTF characteristic is measured, the grid height is set so that the cutoff characteristic corresponding to the Nyquist spatial frequency in the horizontal direction and the vertical direction (the Nyquist spatial frequency obtained by the pixel pitch in the horizontal direction and the vertical direction) is obtained. The length and grating period were designed.

[0005]

However, as an array of pixels (color filters) in an image area, Baye is used.
In the case where the r array is employed, even if the optical low-pass correction is performed in the pixel array direction (horizontal direction / vertical direction), even in the direction (oblique direction) connecting the green pixels (G) with high visibility, Since the correction is not performed, there is a problem that an image defect due to the generation of the pseudo signal in the oblique direction cannot be sufficiently prevented.

FIG. 2 shows an image area (Bayer arrangement) in which green pixels (G) are arranged in a checkered pattern. In the figure, (R) shows a red pixel and (B) shows a blue pixel. The pitch of the pixels arranged in this image area is 5.1 μm in both the horizontal and vertical directions. In FIG. 2, a dotted line (a) extending in the horizontal direction and a dotted line (b) extending in the vertical direction indicate directions in which correction is performed by the optical low-pass filter.

Here, in order to perform the optical low-pass correction in the direction indicated by the dotted line (a) in FIG. 2 (horizontal direction of the image area), the optical element is formed so as to extend in the horizontal direction when it is arranged in the image pickup system. When the MTF characteristic in the horizontal direction is measured, a cutoff characteristic corresponding to the Nyquist spatial frequency in the horizontal direction (98 mm ^{−1 of the} Nyquist spatial frequency obtained from the pixel pitch of 5.1 μm) is obtained. It is necessary to use an optical low-pass filter in which the grating height and grating period are designed to be adjusted.

Further, in order to perform optical low-pass correction in the direction indicated by the dotted line (b) in FIG. 2 (vertical direction of the image area), it is formed so as to extend in the vertical direction when it is arranged in the imaging system. When the MTF characteristic in the vertical direction is measured with a phase grating, a cutoff characteristic corresponding to the Nyquist spatial frequency in the vertical direction (98 mm ^{−1 of the} Nyquist spatial frequency obtained from the pixel pitch of 5.1 μm) can be obtained. Thus, it is necessary to use an optical low-pass filter in which the grating height and the grating period are designed.

Therefore, a grating height 440 is used as a phase grating for performing optical low-pass correction in the horizontal direction of the image area.
A phase grating having a grating height of 440 nm and a grating period of 3 is formed as a phase grating for forming an optical low-pass correction in the vertical direction of the image region while forming a phase grating having a grating period of 540 μm.
An optical low-pass filter is manufactured by forming a 50 μm phase grating, and the obtained optical low-pass filter is converted into an air-equivalent distance between the phase grating and the image region for correcting the image region in the horizontal direction. Is 3 mm,
When the air-equivalent distance between the phase grating for performing correction in the vertical direction of the image area and the image area is 2 mm,
When the MTF characteristic (wavelength: 550 nm) of the optical low-pass filter is measured in each of the horizontal direction of the image area, the vertical direction of the image area, and the oblique direction of the image area, as shown in FIGS. Become.

As shown in FIGS. 3A and 3B, an optical low-pass filter is arranged so that the phase grating extends in the horizontal and vertical directions, and performs optical low-pass correction in the horizontal and vertical directions of the image area. This makes it possible to obtain cutoff characteristics that match the Nyquist spatial frequency (98 mm ⁻¹ ) in each of the horizontal direction of the image area and the vertical direction of the image area. However, as shown in FIG. 3C, the cutoff frequency in the oblique direction of the image area is 1
40 mm ^−1, which is significantly different from the Nyquist spatial frequency in the oblique direction (the Nyquist spatial frequency 69 mm ⁻¹ obtained from the green pixel pitch of 7.2 μm). As a result, depending on the optical low-pass filter (optical low-pass correction), an image defect (such as a moire image) due to the generation of a pseudo signal occurs in the oblique direction of the obtained image, and the image quality of the image is impaired. I will.

The present invention has been made based on the above circumstances. A first object of the present invention is to perform an optical low-pass correction suitable for an arrangement of pixels of the same color in an RGB type image area, and in any of a horizontal direction, a vertical direction, and an oblique direction of the image area, An object of the present invention is to provide an optical low-pass filter that does not cause an image defect due to generation of a pseudo signal. A second object of the present invention is to provide a pixel (color filter) in an image area of an image sensor.
In the case where the Bayer array is adopted as the array, the correction can be performed in a direction (oblique direction) connecting the green pixels (G), and in the oblique direction, an image defect due to the generation of a pseudo signal can be generated. It is to provide an optical low-pass filter free of noise. A third object of the present invention is to provide an optical low-pass filter that also has a visibility correction function and can configure a small-sized imaging system. A fourth object of the present invention is to provide an optical low-pass filter that also has a color purity correction function and can form a small-sized imaging system. A fifth object of the present invention is to reliably remove, in the horizontal, vertical, and oblique directions of an RGB type image area, a color light component different from light from a subject caused by generation of a pseudo signal. It is an object of the present invention to provide an optical low-pass correction method capable of reliably preventing an image defect from occurring due to the occurrence of the image defect. A sixth object of the present invention is to provide a CCD solid-state imaging device capable of obtaining an image of good quality without image defects due to generation of a pseudo signal. A seventh object of the present invention is to provide a color imaging device capable of obtaining an image of good image quality without image defects due to generation of a pseudo signal. An eighth object of the present invention is to provide a board camera capable of obtaining an image of good image quality without image defects due to generation of a pseudo signal. A ninth object of the present invention is to provide a digital still camera capable of obtaining an image of good image quality without image defects due to generation of a pseudo signal.

[0012]

An optical low-pass filter according to the present invention comprises an RG having pixels arranged in a matrix.
An optical low-pass filter for an image sensor having a B-type image area, wherein an MT of the image area in an oblique direction is
When the F characteristic is measured, a phase grating extending in the oblique direction is formed so that a cutoff characteristic corresponding to the Nyquist spatial frequency in the oblique direction is obtained.

Here, the "diagonal direction of the image area" means a direction oblique to the pixel arrangement direction (horizontal direction / vertical direction) in the image area (downward diagonal direction / downward diagonal direction). . Further, “a phase grating that extends in an oblique direction” refers to a phase grating that extends in an oblique direction in an image region of an image sensor when an optical low-pass filter is arranged in an imaging system.

The optical low-pass filter of the present invention preferably has a cutoff characteristic corresponding to the Nyquist spatial frequency obtained from the pitch of the green pixels (G) arranged in a checkered pattern. Here, the “pitch of green pixels (G) arranged in a checkered pattern” refers to a pitch in an oblique direction connecting the green pixels (G).

The optical low-pass filter of the present invention preferably has a visibility correction function. Specifically, it is preferable to have a visibility correction function by containing divalent copper ions or by forming a vapor-deposited film that reflects near-infrared light.

The optical low-pass filter of the present invention preferably has a color purity correcting function. Specifically, by containing at least one metal ion selected from neodymium ions, praseodymium ions, erbium ions and holmium ions,
It preferably has a color purity correction function.

An optical low-pass correction method according to the present invention is an optical low-pass correction method for an image sensor having an RGB type image area in which pixels are arranged in a matrix, wherein the phase of the image area is oblique in the oblique direction. An optical low-pass filter is arranged so that the grating extends, and correction is performed in the oblique direction.

A CCD solid-state imaging device according to the present invention is characterized in that it comprises a cover member comprising the optical low-pass filter according to the present invention. A color imaging device according to the present invention includes the optical low-pass filter according to the present invention. A board camera according to the present invention includes the optical low-pass filter according to the present invention. Also,
A board camera according to the present invention includes the CCD solid-state imaging device according to the present invention. A digital still camera according to the present invention includes the optical low-pass filter according to the present invention. A digital still camera according to the present invention includes the CCD solid-state imaging device according to the present invention.

[0019]

By performing optical low-pass correction in the oblique direction of the image area (in the direction oblique to the pixel arrangement direction),
In the MTF characteristics in the oblique direction, a cut-off characteristic corresponding to the Nyquist spatial frequency in the oblique direction of the image area, for example, the Nyquist spatial frequency determined by the pitch of the green (G) pixel in the Bayer array can be exhibited. As a result, an image defect such as a moiré image does not occur in an oblique direction in the obtained image.
Further, as is clear from the results of the embodiments described later, by performing optical low-pass correction in the oblique direction of the image area, the MTF characteristics in the pixel arrangement direction (horizontal / vertical direction) can be improved. The cut-off characteristic corresponding to the Nyquist spatial frequency can be exhibited, and thereby, an image defect such as a moire image does not occur in the obtained image in the horizontal and vertical directions. As a result, it is possible to reliably prevent an image defect due to the generation of a pseudo signal, and to obtain a high-quality image faithful to a subject.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. FIG. 4 shows an image area (Bayer arrangement) in which green pixels (G) are arranged in a checkered pattern. The pitch of the green pixels (G) arranged in this image area is about 7.2.
(5.1 × √2) μm. In FIG. 4, a dotted line (c) extending in an oblique direction (downward to the right) and a dotted line (d) extending in an oblique direction (downward to the left) indicate directions in which correction is performed by an optical low-pass filter.

Here, in order to perform optical low-pass correction in an oblique direction (downward to the right) indicated by a dotted line (c) in FIG. 4, it is formed so as to extend in an oblique direction of an image area when arranged in an imaging system. MTF with tilted phase grating
When the characteristics are measured, the grid height is set so as to obtain a cutoff characteristic corresponding to the Nyquist spatial frequency in the oblique direction (a Nyquist spatial frequency of 69 mm ⁻¹ obtained from a pitch of 7.2 μm of the green pixel (G)). It is necessary to use an optical low-pass filter with a designed grating period.

In order to perform optical low-pass correction in an oblique direction (downward left) indicated by a dotted line (d) in FIG.
It has a phase grating formed so as to extend in the oblique direction of the image area when placed in the imaging system, and when measuring the MTF characteristics in the oblique direction, the Nyquist spatial frequency in the oblique direction (green pixel (G) It is necessary to use an optical low-pass filter whose grating height and grating period are designed so as to obtain a cutoff characteristic corresponding to the Nyquist spatial frequency 69 mm ^-1 ) obtained from the pitch of 7.2 μm.

Therefore, the oblique direction of the image area (downward right)
As a phase grating for optical low-pass correction,
Form a phase grating with a height of 440 nm and a grating period of 370 μm.
Light in the diagonal direction (downward to the left) of the image area.
The grating height is used as a phase grating for performing
To form a phase grating having a length of 440 nm and a grating period of 250 μm.
The optical low-pass filter (light of the present invention)
Optical low-pass filter).
-About the pass filter, the diagonal direction of the image area (lower right
Between the phase grating and the image area for correcting
The air-equivalent distance is 3 mm, and the oblique direction of the image area (lower left is
The space between the phase grating and the image area for correcting
Horizontal of image area when Qi conversion distance is 2mm
Direction (pixel pitch = 5.1 μm, Nyquist frequency = 9
8mm^-1), The vertical direction of the image area (pixel pitch =
5.1 μm, Nyquist frequency = 98 mm^-1), Picture
Oblique direction of image area (green pixel pitch = 7.2 μm,
Exist spatial frequency = 69mm ^-1) For each
The MTF characteristics (wavelength) of the optical low-pass filter
(Length: 550 nm) was measured.
Become like

As shown in FIGS. 5A to 5C, the optical low-pass filter of the present invention is arranged so that the phase grating extends in an oblique direction, and performs optical low-pass correction in an oblique direction of an image area. This makes it possible to obtain cutoff characteristics that match the Nyquist spatial frequency in each of the horizontal direction of the image region, the vertical direction of the image region, and the oblique direction of the image region. As a result, according to the optical low-pass filter (optical low-pass correction) of the present invention, in the obtained image, in any of the horizontal direction, the vertical direction, and the oblique direction, an image defect due to the generation of the pseudo signal is generated. There is no.

The optical low-pass filter according to the present invention is provided with a phase grating formed so as to extend in an oblique direction of the image area in the image pickup device (in a direction oblique to the arrangement direction of the pixels) when the filter is arranged in the image pickup system. Is a required component. The lattice shape of the phase grating constituting the optical low-pass filter of the present invention is not particularly limited, such as a triangular shape, a rectangular shape, a trapezoidal shape, and a sine wave shape.

The combination of (grating height / grating period) in the phase grating constituting the optical low-pass filter of the present invention has an expected cutoff characteristic (cutoff characteristic corresponding to the Nyquist spatial frequency in the oblique direction). As described above, the design can be made in consideration of the setting conditions and the lattice shape.

The optical low-pass filter of the present invention can be manufactured by forming a phase grating on the surface of a transparent substrate made of glass or resin. Although the resin constituting the transparent substrate is not particularly limited, it is preferable to use a resin material that absorbs near-infrared light.
Resin materials described in JP-A-118228 can be exemplified.

By using a resin material containing divalent copper ions, an optical low-pass filter having a visibility correction function can be manufactured. Further, by using a resin material containing at least one metal ion selected from neodymium ions, praseodymium ions, erbium ions and holmium ions, an optical low-pass filter having a color purity correction function is manufactured. can do.

As a method of forming a phase grating on the surface of a transparent substrate made of glass, a mask member in which wires are arranged at a predetermined pitch is mounted on the surface of the transparent substrate, and then the mask is applied via the mask member. A method of depositing a thin film material (Japanese Patent Application Laid-Open No. 9-263933, Japanese Patent Application No. 9-3331)
24, a lift-off method, an etching method, and the like.

As a method of forming a phase grating on the surface of a transparent substrate made of a resin, the following method can be used. A method in which a monomer composition for obtaining a resin is cast-polymerized in a mold in which a negative pattern of a phase grating is formed on a molding surface. Here, the negative pattern on the molding surface of the mold can be formed on the surface of glass by a method described in, for example, Japanese Patent Application Laid-Open No. 9-263932 and Japanese Patent Application No. 9-333124. A method in which a heating plate having a negative pattern of a phase grating formed on the surface is pressure-bonded to the surface of a transparent substrate. A method in which a photosensitive resin is applied to the surface of a transparent substrate, and the formed coating film is exposed through a photomask and then developed. A method of injection molding using a mold having a negative pattern of a phase grating formed on a molding surface. On the surface of the transparent substrate, a monomer composition for obtaining a resin was applied by spin coating, and a negative pattern of a phase grating was formed on the surface of the formed coating film of the monomer composition. A method in which the molding surface is pressed and the monomer composition is polymerized in this state. Here, by using a photosensitive composition as the monomer composition, a curing (polymerization) treatment can be performed using ultraviolet rays.

The optical low-pass filter of the present invention may have a phase grating formed on one surface and a vapor-deposited film for reflecting near-infrared light provided on the other surface. According to the low-pass filter, the near-infrared light can be cut with high efficiency, and the visibility correction function can be exhibited. An example of such a deposited film is an optical multilayer film having a function of reflecting near-infrared rays. Specifically, a silica (SiO ₂ ) layer and titania (T
iO ₂₎ layers such as alternating laminated films of can be exemplified,
The thickness of each layer, the number of layers, and the like can also be appropriately selected.

The optical low-pass filter of the present invention has a C
It can be suitably used as a cover material of a CD solid-state imaging device. Further, the optical low-pass filter of the present invention,
It can be mounted on an imaging system such as a color imaging device, a board camera, a digital still camera, and the like. Images obtained by such a color imaging device and a camera have moiré in any of horizontal, vertical, and oblique directions. No image defects such as images occur.

[0033]

Hereinafter, embodiments of the present invention will be described.
The present invention is not limited to these examples. In the following examples, “parts” means “parts by mass”. In the following, a color image pickup apparatus having an RGB type image area in which pixels are arranged in a matrix (Bayer arrangement) is used. In the image area of the color imaging device, the pixel pitch in the horizontal direction and the pixel pitch in the vertical direction are each 5.6 μm.
(Nyquist spatial frequency = 89 mm ⁻¹ ), the pixel pitch in the oblique direction [the pitch of green pixels (G) arranged in a checkered pattern] is 7.9 μm (Nyquist spatial frequency = 63 m)
m ^-1 ).

<Example 1> (1) Production of a glass mold: As shown in FIG. 6, a stainless wire 20 (diameter) was formed on a surface of a transparent substrate 10 made of borosilicate glass at a constant pitch p (p = 340 μm). : 170 μm) is mounted, and a vacuum deposition process of a thin film material (SiO ₂ ) is performed through the mask member to obtain a height of 420 nm and a period of 3
A 40 μm projection 30 (a negative pattern of a phase grating) was formed on the surface of the transparent substrate 10.

On the other hand, the diameter of the stainless wire is 210 μm.
And a height of 420 n in the same manner as described above except that the arrangement pitch of the stainless steel wires was changed to 420 μm.
m, protrusions with a period of 420 μm (negative pattern of phase grating)
Was formed on the surface of the transparent substrate.

The two transparent substrates on which the convex portions are formed as described above are placed in such a manner that the vapor deposition surfaces (convex portion forming surfaces) face each other, and the directions in which the convex portions formed on the vapor deposition surfaces extend. A glass mold was produced by disposing them so as to be orthogonal to each other with a gap (1 mm) therebetween and sealing the outer end of the transparent substrate.

(2) Preparation of a monomer composition: 10 parts of a specific phosphate group-containing monomer represented by the following structural formula [1]:
10 parts of a specific phosphoric acid group-containing monomer represented by the following structural formula [2], 58.5 parts of methyl methacrylate, 20 parts of diethylene glycol dimethacrylate, and 1.5 parts of α-methylstyrene are well mixed. Thus, a mixed monomer was prepared. To this mixed monomer, 14 parts of anhydrous copper benzoate (the content of copper metal with respect to 100 parts of the mixed monomer is 2.9 parts) was added, and the mixture was sufficiently dissolved by stirring and mixing at 60 ° C. A monomer composition in which copper benzoate was dissolved in the mixed monomer was obtained.

[0038]

Embedded image

[0039]

Embedded image

(3) Production of an optical low-pass filter (cast polymerization): 2.0 parts of t-butyl peroxypivalate was added to the monomer composition prepared in the above (2). The monomer composition was charged into the glass mold prepared according to the above (1), and was placed at 45 ° C. for 16 hours for 60 hours.
C. for 8 hours and 90.degree. C. for 3 hours to perform cast polymerization, thereby forming a crosslinked copolymer containing copper ions, having a lattice height of 420 nm and a lattice period of 34.
A phase grating of 0 μm is formed on one surface, and the grating height is 420 n
m, an optical low-pass filter (1 mm thick) of the present invention in which a phase grating having a grating period of 420 μm is formed on the other surface.
Was manufactured. About this optical low-pass filter,
When a spectral transmittance curve was measured using a spectrophotometer,
It was confirmed that it was excellent in the function of absorbing near infrared light (700 to 1000 nm).

(4) Evaluation of optical low-pass filter:
With respect to the optical low-pass filter of the present invention obtained as described above, MTF characteristics in a horizontal direction, a vertical direction, and an oblique direction were measured using an MTF measuring device (manufactured by Image Science). A cut-off characteristic was observed in the vicinity of 89 mm ^{-1 in} the MTF characteristic of
Cutoff characteristics were observed near ^-1 . Here, the measurement of the MTF characteristic in the optical low-pass filter of the present invention was performed by arranging the optical low-pass filter at a predetermined position (air-equivalent distance from the imaging plane = 3.2 mm).

Also, this optical low-pass filter is
One surface thereof (the surface on which the phase grating having a grating period of 340 μm is formed) faces the image area, and the other surface (the surface on which the phase grating having a grating period of 420 μm is formed) is opposed to the lens system. It was arranged in the image pickup system of the color image pickup apparatus so as to have a diagonal direction of −45 ° (direction connecting green pixels (G)). Here, the phase grating (grating period 3
The air equivalent distance between the 40 μm phase grating) and the image area was 3.2 mm. When an image obtained by the color imaging device corrected by the optical low-pass filter was observed in this way, the obtained image showed a moire image in any of the horizontal, vertical, and oblique directions. It was not recognized and the image was of high quality.

Comparative Example 1 A stainless steel wire having a diameter of 24
Except that the arrangement pitch was changed to 0 μm and the arrangement pitch was changed to 480 μm, a protrusion (a negative pattern of a phase grating) having a height of 420 nm and a period of 480 μm was formed on the surface of the transparent substrate in the same manner as in Example 1 (1). Furthermore, a height of 420 n was set in the same manner as in Example 1 (1) except that the diameter of the stainless wire was changed to 290 μm and the arrangement pitch was changed to 580 μm.
m, protrusions with a period of 580 μm (negative pattern of phase grating)
Was formed on the surface of the transparent substrate. A glass mold was produced in the same manner as in Example 1 (1) except that the two transparent substrates thus obtained were used.

Next, casting polymerization was carried out in the same manner as in Example 1 (3) except that the obtained glass mold was used to obtain a grating height of 420 nm and a grating period of 480 μm.
Was formed on one surface, and a phase grating having a grating height of 420 nm and a grating period of 580 μm was formed on the other surface to produce an optical low-pass filter for comparison (1 mm thick).

With respect to the optical low-pass filter for comparison obtained as described above, the MTF characteristics in the horizontal, vertical and oblique directions were measured using an MTF measuring device (manufactured by Image Science). The cut-off characteristic was observed near 89 mm ^-1 in the MTF characteristics in the vertical direction, and the cut-off characteristic was observed in the vicinity of 120 mm ^{-1 in} the MTF characteristics in the oblique direction.
Here, M in the optical low-pass filter for comparison
The measurement of the TF characteristic was performed by arranging the optical low-pass filter at a predetermined position (the air-equivalent distance from the image plane = 3.2 mm).

Also, this optical low-pass filter is
One surface thereof (the surface on which the phase grating having a grating period of 480 μm is formed) faces the image area, and the other surface (the surface on which the phase grating having a grating period of 580 μm is formed) is opposed to the lens system. It was arranged in the imaging system of the color imaging device so as to be in the vertical direction. Here, the air-equivalent distance between the phase grating (phase grating having a grating period of 480 μm) and the image area was set to 3.2 mm. Observation of the image obtained by the color image pickup device corrected by the optical low-pass filter in this way showed that although the obtained image did not show a moire image in the horizontal and vertical directions, In addition, a moire image was remarkably observed in the oblique direction.

[0047]

According to the optical low-pass filter of the present invention, it is possible to perform an optical low-pass correction suitable for an arrangement of pixels of the same color in an RGB type image area of an image sensor, and to perform a horizontal In both the vertical direction and the oblique direction, no image defect is caused due to the generation of the pseudo signal. According to the optical low-pass filter of the present invention, when the Bayer array is used as the array of pixels (color filters) in the image area of the image sensor, the direction connecting the green pixels (G) (oblique direction). Can be corrected.

According to the optical low-pass correction method of the present invention, in the horizontal, vertical, and oblique directions of the RGB type image area, a color light component different from the light from the subject due to the generation of the pseudo signal is reliably removed. Therefore, it is possible to reliably prevent the occurrence of image defects due to the generation of the pseudo signal.

According to the CCD solid-state image pickup device, the color image pickup device, the board camera and the digital still camera of the present invention, it is possible to obtain an image of good image quality without any image defects due to the generation of a pseudo signal.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of an array of pixels (Bayer array) in an RGB type image area.

FIG. 2 is an explanatory diagram illustrating directions (horizontal and vertical directions) in which correction is performed on a Bayer array image area by a conventional optical low-pass filter.

FIG. 3 shows a horizontal and vertical view using a conventional optical low-pass filter.
FIG. 4 is a curve diagram illustrating MTF characteristics in vertical and oblique directions.

FIG. 4 is an explanatory diagram showing a direction (oblique direction) in which correction is performed on an image area of the Bayer array by the optical low-pass filter of the present invention.

FIG. 5 is a curve diagram showing MTF characteristics in horizontal, vertical, and oblique directions by the optical low-pass filter of the present invention.

FIG. 6 is an explanatory view illustrating an example of a manufacturing process of a glass mold.

[Explanation of symbols]

Reference Signs List 10 transparent substrate 20 stainless wire 30 protrusion R red pixel G green pixel B blue pixel a direction in which optical low-pass correction is performed (horizontal direction) b direction in which optical low-pass correction is performed (vertical direction) c optical Direction in which low-pass correction is performed (downward diagonal direction) d Direction in which optical low-pass correction is performed (downward diagonal direction)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 BA06 BA45 BC22 4M118 AA10 AB01 BA10 BA14 FA06 GC08 GC14 GC20 5C065 BB13 DD02 DD17 EE05 EE06 EE14 EE20

Claims (14)

[Claims] An RG in which pixels are arranged in a matrix
An optical low-pass filter for an image sensor having a B-type image region, wherein a cut-off characteristic corresponding to the Nyquist spatial frequency in the oblique direction is obtained when MTF characteristics in the oblique direction of the image region are measured. Thus, an optical low-pass filter characterized in that the phase grating extending in the oblique direction is formed. 2. An optical low-pass filter according to claim 1, wherein the optical low-pass filter has a cutoff characteristic corresponding to a Nyquist spatial frequency determined from a pitch of green pixels (G) arranged in a checkered pattern. Optical low-pass filter. 3. The optical low-pass filter according to claim 1, having a visibility correction function. 4. The optical low-pass filter according to claim 3, wherein the optical low-pass filter contains divalent copper ions. 5. The optical low-pass filter according to claim 3, wherein a deposited film reflecting near-infrared light is formed. 6. The optical low-pass filter according to claim 1, having a color purity correction function. 7. Neodymium ions, praseodymium ions,
The optical low-pass filter according to claim 6, comprising at least one metal ion selected from erbium ions and holmium ions. 8. An RG in which pixels are arranged in a matrix
An optical low-pass correction method for an image sensor having a B-type image region, wherein an optical low-pass filter is arranged so that a phase grating extends in a diagonal direction of the image region, and correction is performed in the diagonal direction. An optical low-pass correction method comprising: 9. A CCD solid-state imaging device comprising a cover member comprising the optical low-pass filter according to claim 1. 10. A color imaging device comprising the optical low-pass filter according to claim 1. 11. A board camera comprising the optical low-pass filter according to claim 1. 12. A board camera comprising the CCD solid-state imaging device according to claim 9. 13. A digital still camera comprising the optical low-pass filter according to claim 1. 14. A digital still camera comprising the CCD solid-state imaging device according to claim 9.