JP2001078212A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hold high image performance and to make a device small-sized by providing a 1st and a 2nd image formation system corresponding to a 1st and a 2nd image pickup area and setting them so that the focal length of the 1st image formation system to light of 1st wavelength is equal to the focal length of the 2nd image formation system to light of 2nd wavelength. SOLUTION: A stop 110 has three circular apertures 110a, 110b, and 110c. Object lights which are made incident on a light incidence surface 100e of an image pickup lens 100 from the apertures exit from three lens parts 100a, 100b, and 100c of the image pickup lens 100 to form three object images on an image pickup surface of a solid-state image pickup element 120. Then the radii of the spherical surfaces of the lens parts 100a, 100b, and 100c are optimized by representative wavelengths. Namely, designs by the wavelengths are applied to lenses. Thus, the focal lengths which are different with a single wavelength are set to nearly the same focal lengths for the respective representative wavelengths and then those image signals are put together to obtain a color image having its chromatic aberration excellently corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus such as a video camera capable of picking up moving images or still images.

[0002]

2. Description of the Related Art In a digital color camera, an object image is exposed to a solid-state imaging device such as a CCD or a CMOS sensor for a desired time in response to pressing of a release button, and an image signal obtained from the exposure is converted into a digital signal. After that, predetermined processing such as YC processing is performed to obtain an image signal of a predetermined format. This digital image signal is recorded in the semiconductor memory. Then, it is possible to read out the recorded image signal at any time, reproduce the signal as a displayable or printable signal, and output the signal to a monitor or the like to visualize the recorded image.

In an exposure mode of an object image, for example, an RGB color filter including a set of 2 × 2 pixels is formed on a solid-state image sensor to give wavelength selectivity to each pixel, thereby providing an object image. A method that separates the image into RGB images, a method that does not have wavelength selectivity in the solid-state image sensor, inserts an optical filter with wavelength selectivity into the shooting optical system, and switches this in time series, Further, there is known a method in which a color separation optical system is added to the rear of the imaging optical system, and an image is captured using different imaging elements for each wavelength range.

A general digital color camera employs many of the above-described methods. Japanese Patent Application Laid-Open No. Hei 9-72649 discloses an example of the above-mentioned method, and Japanese Patent Application Laid-Open Nos. 7-84177 and 7-124418 disclose the above methods. It is an example of disclosure of a system.

[0005]

However, in any of the above methods, since the imaging optical system is commonly used for each wavelength range, good optical performance is obtained over the entire visible range. Need to have In general, a photographing optical system uses the refraction of light with an optical glass or an optical transparent resin for its imaging principle, so that a change in the refractive index depending on the wavelength occurs. An optical design technique called erasure is used. As a result, it is difficult to configure a high-performance photographing optical system with a single lens, and this has been an obstacle to downsizing the imaging optical system.

An object of the present invention is to provide a small-sized imaging device having high image performance.

[0007]

In order to achieve the above object, the present invention provides an image pickup device having at least first and second image pickup regions, and a photographing optical system for forming an object image on the image pickup device. And the imaging optical system comprises at least first and second imaging systems corresponding to the first and second imaging regions, the first optical system for the first wavelength light The focal length of the imaging system and the focal length of the second imaging system with respect to the light of the second wavelength are set to be the same (including a range that can be regarded as the same for practical use), and Imaging in which the focal length of the first imaging system for light having a wavelength other than the wavelength of the second imaging system is different from the focal length of the second imaging system for light having a wavelength other than the second wavelength. Device.

The present invention is also directed to an image pickup apparatus having an image pickup device having a plurality of image pickup regions and a photographing optical system for forming an object image on the image pickup device. With multiple imaging systems corresponding to
The focal lengths of the plurality of imaging systems are set to be the same (including a range that can be regarded as the same for practical use) with respect to the wavelength of light having a predetermined wavelength of each imaging system. The imaging apparatus is set to be different for light having a wavelength other than the predetermined wavelength in the system.

Further, the present invention provides an image pickup device having first and second image pickup areas, a photographing optical system for forming an object image on the image pickup device, and an image processing device for processing an output signal of the image pickup device. Means, the imaging optical system includes first and second imaging systems, and the first and second imaging systems respectively convert first and second object images into the first and second object images. Formed on the first and second imaging areas, from the first and second imaging areas, a first image signal based on an object light component having a first spectral distribution, and an object light component having a second spectral distribution. A second image signal is obtained, and the focal lengths of the first and second imaging systems are made different with respect to the representative wavelength of the spectrum distribution of the first image signal. The same for the representative wavelength (the range that can be regarded as the same for practical use) It is an imaging device set including) a.

Further, the present invention provides a first imaging unit and a second imaging unit for receiving at least a first wavelength component of subject light and a second wavelength component different from the first wavelength component, respectively.
And an imaging unit for guiding the first and second wavelength components of the subject light received by the first and second imaging units to the first and second imaging units via separate optical paths. A first optical system and a second optical system, wherein the first optical system and the second optical system have a focal length for the first wavelength component of the first optical system and the second optical system. The present invention is directed to an imaging apparatus configured so that the optical system has the same focal length for the second wavelength component.

[0011]

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

FIGS. 17A, 17B, and 17C are views showing the overall configuration of a digital color camera according to the present invention. 17A is a front view, FIG. 17C is a rear view, and FIG.
FIG. 18B is a cross-sectional view at the position of arrow A shown in the back view of FIG.

In FIGS. 17 (a), 17 (b) and 17 (c), reference numeral 1 denotes a camera body, and 2 denotes an illumination light take-in window which is located behind the color liquid crystal monitor 4 and is formed of a white diffuser. 5 is a main switch, 6 is a release button, 7, 8, and 9 are switches for the user to set the state of the camera. In particular, 9 is a playback button, and 13 is a display of the remaining number of images that can be taken. Reference numeral 11 denotes a finder eyepiece window, from which object light incident on the prism 12 from the finder front frame 3 exits. Reference numeral 10 denotes an imaging system, and 14 denotes a connection terminal for connecting to an external computer or the like to transmit and receive data.

The schematic configuration of the signal processing system will be described. FIG.
FIG. 2 is a block diagram of a signal processing system. This camera uses a CCD
Alternatively, it is a single-chip digital color camera using a solid-state image sensor 120 such as a CMOS sensor.
Is driven continuously or sporadically to obtain an image signal representing a moving image or a still image. Here, the solid-state imaging device 120
Is an imaging device of a type that converts exposed light into an electric signal for each pixel, accumulates charges corresponding to the amount of light, and reads out the charges.

FIG. 14 shows only parts directly related to the present invention, and illustrations and descriptions of parts not directly related to the present invention are omitted.

As shown in FIG. 14, the image pickup apparatus has an image pickup system.
10, an image processing system 20, which is an image processing means, a recording / reproducing system 30, and a control system 40. Furthermore, the imaging system 10
Includes a photographing lens 100, an aperture 110, and a solid-state imaging device 120, the image processing system 20 includes an A / D converter 500, an RGB image processing circuit 210, and a YC processing circuit 230, and the recording / reproducing system 30 includes:
The control system 40 includes a recording processing circuit 300 and a reproduction processing circuit 310. The control system 40 includes a system control unit 400, an operation detection unit 410, and a drive circuit 420 for the solid-state imaging device.

The imaging system 10 is an optical processing system that forms an image of light from an object on the imaging surface of the solid-state imaging device 120 via the stop 110 and the imaging lens 100, and adjusts the light transmittance of the imaging lens 100. Then, the solid-state imaging device 120 is exposed to a subject image having an appropriate amount of light. As described above, the solid-state imaging device 120 is a CCD or C
An imaging device such as a MOS sensor is applied, and by controlling the exposure time and exposure interval of the solid-state imaging device 120, an image signal representing a continuous moving image or an image signal representing a still image by one exposure is obtained. Can be.

FIG. 1 is a detailed view of the image pickup system 10. First, the stop 110 has three circular openings 110a, 110b, 11 as shown in FIG.
0c, from each of which the light incident surface 100e of the taking lens 100
The object light that has entered the three lens units 10 of the taking lens 100
The three object images are formed on the imaging surface of the solid-state imaging device 120 by emitting light from 0a, 100b, and 100c. The stop 110, the light incident surface 100e, and the imaging surface of the solid-state imaging device 120 are arranged in parallel. As described above, the curvature of the image plane can be reduced by weakening the power on the incidence side, increasing the power on the emission side, and providing the stop on the incidence side. Note that, here, the light incident surface 100e of the photographing lens 100 is a plane, but it may be constituted by three spherical surfaces or three rotationally symmetric aspheric surfaces.

Each of the three lens portions 100a, 100b, and 100c has a spherical portion having a circular diameter as shown in FIG. 5 when the photographing lens 100 is viewed from the light exit side. Infrared cut filter with transmittance
Further, a light-shielding film is formed on the flat portion 100d indicated by hatching. That is, the photographing optical system includes a photographing lens 100 and an aperture 110, and includes three lens units 100a, 100b, 1
Each of 00c is an imaging system.

In this embodiment, the first imaging region of the present invention is an imaging region 120a, and the second imaging region is an imaging region 120b.
Alternatively, the imaging area 120c corresponds. The first imaging system is the lens unit 100a, and the second imaging system is the lens unit 100b or the lens unit.
100c corresponds. Further, the first object image corresponds to an object image formed inside the image circle 51a, and the second object image corresponds to an object image formed inside the image circle 51b or 51c. Also, the first image signal is
The G image signal and the second image signal correspond to the R image signal or the B image signal.

When the photographic lens 100 is made of glass, a glass mold manufacturing method is used, and when the photographic lens 100 is made of a resin, injection molding is used.

FIG. 2 is a front view of the solid-state image pickup device 120. The three image pickup areas 120a and 120a correspond to three object images to be formed.
0b and 120c. Each of the imaging areas 120a, 120b, 120c is a 2.24 mm x 1.68 mm area in which 800 × 600 pixels having a vertical and horizontal pitch of 2.8 μm are arranged, and the entire imaging area has a size of 2.24 mm x 5.04 mm , And the diagonal dimension of each imaging area is
It becomes 2.80mm. In the figure, 51a, 51b, 51c are image circles in which an object image is formed. The image circles 51a, 51b, and 51c are circular shapes determined by the aperture of the stop and the size of the exit-side spherical portion of the photographing lens 100. The image circles 51a and 51b, and the image circles 51b and 51c
Have overlapping portions.

In FIG. 1, portions 52a, 52b, and 52c indicated by hatching in a region between the diaphragm 110 and the photographing lens 100.
Denotes an optical filter formed on the light incident surface 100e of the taking lens 100. The optical filters 52a, 52b, 52c are formed in a range completely including the aperture openings 110a, 110b, 110c as shown in FIG. 4 when the photographing lens 100 is viewed from the light incident side.

The optical filter 52a has a spectral transmittance characteristic for transmitting mainly green light shown by G in FIG.
52b has a spectral transmittance characteristic indicated by R that mainly transmits red, and the optical filter 52c has a spectral transmittance characteristic indicated by B that mainly transmits blue. That is, these are primary color filters. Lens parts 100a, 100b, 100c
As the product of the characteristics of the infrared cut filter formed on the image circle 51a, the object image formed on the image circle 51a is formed with a green light component, the object image formed on the image circle 51b is formed with a red light component, and formed on the image circle 51c. The object image is a blue light component.

On the other hand, the three imaging regions 12 of the solid-state imaging device 120
Optical filters 53a, 53b, 53 also on 0a, 120b, 120c
c are formed, and their spectral transmittance characteristics are also the same as those shown in FIG. That is, the imaging region 120a is for green light (G), the imaging region 120b is for red light (R),
The imaging region 120c has sensitivity to blue light (B).

Since the light receiving spectrum distribution of each imaging region is given as the product of the pupil and the spectral transmittance of the imaging region, the combination of the pupil and the imaging region is selected according to the wavelength range. That is, the object light that has passed through the aperture 110a of the diaphragm is mainly
The object light photoelectrically converted at 0a and passed through the aperture 110b of the aperture is photoelectrically converted mainly at the imaging region 120b, and
The object light that has passed through 110c is mainly subjected to photoelectric conversion in the imaging region 120c. That is, the imaging area 120a stores the G image and the imaging area 120a.
b outputs an R image, and the imaging area 120c outputs a B image. As described above, by using multiple optical filters for color separation in the pupil of the imaging optical system and the imaging device, the color purity can be increased. This means that two optical filters of the same type
This is because, when the light is passed, the transmission characteristic sharply rises and the overlap between red (R) and blue (B) is eliminated. It should be noted that the optical filters 52a, 52a,
It is preferable to set the transmittance of b, 52c or the optical filters 53a, 53b, 53c.

In the image processing system 20, a plurality of imaging regions of the solid-state imaging device 120 form a color image based on a selective photoelectric conversion output obtained from one of the plurality of images. At this time, since the peak wavelength of the relative luminous efficiency is 555 nm, signal processing is performed using a G image signal including this wavelength as a reference image signal.

Considering that the pixel pitch of the solid-state imaging device is fixed, for example, an RG having a set of 2 × 2 pixels on the solid-state imaging device
Compared to the method used in general digital color cameras, which form a B color filter to give wavelength selectivity to each pixel and separate the object image into RGB images, The size of the image becomes 1 / √3, and accordingly, the focal length of the taking lens becomes about 1 / √3.
Therefore, it is extremely advantageous for reducing the thickness of the camera.

Incidentally, the optical filters 52a, 52b, 52c,
The spectral transmittance characteristics of the optical filters 53a, 53b, and 53c are as shown in FIG. 6, although R and B are almost separated from each other.
R and G and G and B overlap each other.

Therefore, the red light image circle 51
Even if b is over the imaging region 120c for photoelectrically converting blue light, or conversely, even if the image circle 51c of blue light is over the imaging region 120b for photoelectrically converting red light, these images are output from the imaging region. Will not be. However, the portion where the red light image circle 51b covers the imaging region 120a for photoelectrically converting green light and the portion where the green light image circle 51a covers the imaging region 120b for photoelectrically converting red light are originally blocked. The images of different wavelengths to be superimposed are small but superimposed. That is, the selectivity of the object image is given by the product of the spectral transmittance characteristics of the optical filter 52a and the optical filter 53b and the product of the spectral transmittance characteristics of the optical filter 52b and the optical filter 53a. Crosstalk is small but not completely zero.

Therefore, the photographing lens 100 is further provided with a characteristic of lowering the transmittance in the wavelength range of the overlapping portion of R and G. For this, an optical filter technique called a color purity correction filter may be used.

This color purity correction filter is an optical filter in which a predetermined amount of rare earth metal ions is contained in a base material made of a transparent synthetic resin or glass.

The rare earth metal ion includes one or more of neodymium ion, praseodymium ion, erbium ion, holmium ion and the like, and it is preferable to use at least neodymium ion as an essential ion. Incidentally, these ions are usually 3
Valent ions are used. The content of the metal ion is usually 0.01 part with respect to 100 parts by mass of the base material of the photographing lens 100.
To 40 parts by mass, preferably from 0.04 to 30 parts by mass.

As shown in FIG. 7, the color purity correction filter has a characteristic of selectively absorbing light in a predetermined wavelength range between peak wavelengths of each of the RGB color components to reduce the amount of transmission. By this action, red light image circle 51
b is applied to the imaging region 120a for photoelectrically converting green light,
Then, crosstalk due to the image circle 51a of the green light covering the imaging region 120b for photoelectrically converting the red light hardly occurs.

Further, the photographic lens 100 is provided with a photochromic property, which is a phenomenon of reversibly returning to a colorless state when the light is darkened and light irradiation is stopped. this is,
This is because, since the storage time control range of the solid-state imaging device 120 is limited, the amount of light reaching the solid-state imaging device when the field is extremely bright is suppressed, and the luminance range in which photography can be performed is expanded.

As the photochromic glass, for example, a phosphate-based photochromic glass (trade name: Reactolite Rapide) manufactured by Chance-Pilkinton, which has been put to practical use for eyeglasses, may be used.

FIG. 8 is a diagram showing the spectral transmittance characteristics of the photochromic glass used for the photographing lens 100.
, The solid line shows the characteristics after irradiating sunlight for 20 minutes, and the dashed line shows the characteristics when no irradiation was performed. When the camera is carried around outdoors in fine weather or the like, the luminous flux incident on the photographic lens 100 from the aperture 110 darkens the photographic lens 100 itself, and the amount of light incident on the solid-state imaging device 120 can be reduced to about half. As a result, the accumulation time can be doubled, and the control limit on the high luminance side is raised.

The screen size of each of the imaging areas 120a, 120b, and 120c is 2.24 mm × 1.68 mm from the pixel pitch of 2.8 μm and 800 × 600 pixels as described above, and the diagonal size of the screen is 2.80 mm.
Becomes Generally, the angle of view θ of a small camera is set diagonally.
It is easiest to use about 70 °. If the shooting angle of view is 70 °, the focal length is determined from the diagonal size of the screen, and in this case, it is 2.0 mm.

When a person or the like is to be photographed, the virtual subject distance D [m] is determined based on the fact that the height of a human is around 170 cm and that one to three persons are often photographed together. Equation (1) can be defined as a function of the angle θ [°].

[0040]

[Outside 2] Substituting 70 ° for θ in equation (1) gives D = 2.0 m. Therefore, if the imaging system 10 is configured to achieve the best focus when the subject distance is 2 m, the lens extension from the infinity position is 0.002 mm, and the lens extension mechanism is determined from the relationship with the allowable confusion circle diameter described later. There is no practical problem at all even with a fixed-focus imaging optical system having no lens.

The focal length f of a plano-convex lens placed in the air is given by n being the refractive index and r being the radius of the spherical surface.

[0042]

[Outside 3] Can be represented by Therefore, if the taking lens 10
Assuming that the refractive index n of 0 is 1.5, r that gives a focal length of 2.0 mm is
1.0mm.

If the size of each of the red, green, and blue object images is made uniform, it is not necessary to perform image magnification correction in subsequent signal processing, so that the processing time is not extended, which is convenient. For this reason, the lens units 100a, 100n, and 530nm, 620nm, and 450nm of the peak wavelength of the transmitted light of the RGB optical filter
Optimize b and 100c and set each image magnification constant. This can be realized paraxially by making the distance from the principal point position of each lens unit to the solid-state imaging device uniform.

In the case of glass having a _d -line (587.6 nm) refractive index n _d = 1.5 and Abbe number ν _d = 60, wavelengths of 530 nm, 620 nm and 450 nm
Are about 1.503, 1.499, and 1.509, respectively. Suppose the radius of the spherical surface of the lens parts 100a, 100b, 100c
Assuming that r is uniformly -1.0 mm, the focal lengths at these wavelengths are as follows from equation (2).

Lens section 100a Representative wavelength 530 nm: 1.988 mm Lens section 100b Representative wavelength 620 nm: 2.004 mm Lens section 100c Typical wavelength 450 nm: 1.965 mm From the pixel pitch, the allowable confusion circle diameter is 3.0 μm, and the F-number of the photographing lens is Assuming F5.6, the focal depth expressed by the product of these is 16.8 μm, and it can be seen that the difference between the focal lengths of 620 nm and 450 nm of 0.039 mm has already exceeded this. That is, although only the paraxial image magnification is uniform, it is not focused depending on the color of the subject. Usually, the spectral reflectance of an object spans a wide wavelength range,
Generally, it is extremely rare that a sharp focus is obtained.

Therefore, the radius r of the spherical surface of the lens units 100a, 100b, 100c is optimized for each representative wavelength. That is, here, achromatic design for removing chromatic aberration in the entire visible range is not performed, and a design for each wavelength is applied to each lens. First, equation (2) is transformed to obtain equation (3).

R = (1-n) f (3) f = 2.0 and n = 1.503, n = 1.499, n = 1.509 in the equation (3).
Is calculated and each radius is calculated as follows.

Lens unit 100a Representative wavelength 530 nm: r = 1.006 mm Lens unit 100b Representative wavelength 620 nm: r = −0.998 mm Lens unit 100c Representative wavelength 450 nm: r = −1.018 mm Difference in image magnification at a high image height position In order to balance
If the vertex heights of the lens units 100a, 100b, 100c are slightly adjusted, an ideal form can be obtained with respect to both sharpness and image magnification. Furthermore, an aspherical surface is used for each lens unit to satisfactorily correct field curvature. The image distortion may be corrected in the subsequent signal processing.

As described above, the green color having the highest visibility 555 nm
The reference G image signal by the object light including the wavelength of the light and the image signal by the red and blue object light are respectively obtained, and a single wavelength (for example, the wavelength of the green color having the highest visibility of 555 nm) is formed in the imaging system. Different focal lengths (for each lens part 100a ~ 10
0c is set to a different focal length for light other than the spectral distribution having each of the above representative wavelengths), and by setting substantially the same focal length for the representative wavelength of each spectral distribution, these image signals are combined. By doing so, it is possible to obtain a color image in which chromatic aberration is corrected favorably.
Since each imaging system has a single configuration, there is also an effect of reducing the thickness of the imaging system. Usually, achromatism requires a combination of two lenses having different dispersions, but the use of a single lens has an effect of reducing costs.

The imaging lens 100 is required to have a high-contrast resolution up to a high spatial frequency band up to the same level as the pixel pitch. Since the imaging system 10 captures three object images for each wavelength range, when compared with an imaging system having the same number of pixels with a mosaic optical filter such as a Bayer array, the focus of about 1 / √3 is obtained as described above. The same angle of view is obtained at different distances. Therefore, high-contrast resolution of higher spatial frequency components must be realized. The wavelength-specific optimization of each lens unit described above is a chromatic aberration suppressing technique for this purpose.

In general, methods for improving the aberration characteristics of the photographing optical system so that false resolution is less likely to occur and reducing the problem include increasing the number of constituent lenses, making the lens aspherical, using anomalous dispersion glass, There are two ways: increasing the degree of freedom in design by using several techniques, such as using an optical element in combination, and reducing the imaging light flux.

The above-described directionality of increasing the degree of freedom of design complicates the configuration of the photographing optical system even though the focal length is reduced to 1 / √3, and goes against the thinning of the photographing apparatus. That is not appropriate. On the other hand, the directionality using the above-mentioned thin luminous flux has good compatibility with a thin imaging device.

When the imaging light beam is narrowed, the response function called OTF gradually decreases monotonously in the low frequency component as shown by the solid line (b) in FIG. 10, then takes a slightly negative value and then slightly again. The characteristic has a positive value. On the other hand, in the case where a thick light beam is used without narrowing the imaging light beam, as shown by a dashed line (a) in FIG. Becomes

A state in which the OTF takes a negative value indicates the occurrence of false resolution. In an actual image, a white portion becomes black and a black portion becomes white, which corresponds to a negative-positive inversion phenomenon. Therefore, it can be seen that a natural image can be obtained by narrowing the imaging light flux.

However, when the luminous flux is narrowed down extremely, the contrast of the high-frequency range is reduced by the influence of light diffraction. In such a situation, the point image is composed of a central bright spot and diffraction fringes surrounding the central bright spot several times. The reason for this is, as is well known, that the intensity of diffraction fringes due to peripheral waves emitted from the edge of the aperture opening relatively increases.

In order to reduce diffraction fringes, a filter may be added to the photographic lens so that the center is transparent and the density increases as going to the periphery. This technique is called apodization and is an augmented version of the Optical Technology Handbook (1975,
(Asakura Shoten) on pages 172 to 174.

FIG. 9 is a view showing the transmittance distribution of the transmittance distribution type filter provided on the light incident surface 100e of the photographing lens 100 and opposed to the aperture openings 110a, 110b and 110c. The transmittance distribution type filters are indicated by 54a, 54b and 54c in FIG. 1, and the positions where the transmittance is highest are the aperture openings 110a, 110b,
The position corresponding to the center of 110c and having the transmittance of zero is matched to the edges of the aperture openings 110a, 110b, 110c. That is,
The transmittance distribution is highest at the center of the stop, and monotonically decreases as the distance from the center increases.

The transmittance distribution type filter is a photographic lens 100
Is formed by vapor deposition or sputtering of a thin film of Inconel, chromel, chrome, or the like on the light incident side of. The characteristics shown in FIG. 9 can be obtained by making the thickness of the thin film the thinnest in the central part and the thickest in the peripheral part. In the formation of such a thin film, the position of the shield in the vapor deposition or sputtering process is continuously controlled.

Here, the transmittance distribution type filters 54a, 54a
Although 4b and 54c are formed on the taking lens, they may be formed on a glass plate and arranged on the light incident side or light emitting side of the taking lens 100.

FIG. 11 is a diagram showing a luminance distribution of a point image.
In the figure, the dashed line (a) shows the case where the transmittance of the aperture opening is constant, and the solid line (b) shows the case where the transmittance of the aperture opening decreases from the center to the periphery. In contrast to the characteristic of (a), the characteristic of (b) has no rebound at the foot of the point image, indicating that the image is clearly good. This is a manifestation of the effect of reducing diffraction fringes by reducing peripheral light beams by apodization.

Next, the positional relationship between the taking lens and the image pickup area will be described. Since the imaging system has three lens units, the positions of the three object images relatively change according to the subject distance. As described above, each imaging area has a size of 2.24 mm × 1.68 mm, and they are arranged adjacent to each other such that their long sides are in contact. Therefore, the center distance between adjacent imaging regions is 1.
68 mm. The YC processing circuit 230 described later performs signal processing on the assumption that the center of the object image matches the center of the imaging region. Assuming that an object image at a virtual object distance of 2 m is formed on the image pickup unit at the same interval as this, the distance between the lens units 100a, 100b, and 100c of the photographing lens 100 is set to 1.6 as shown in FIG.
It will be set to 783mm. In the figure, arrows 55a, 55
b, 55c are three lens parts 100a, 100b,
Symbol representing an imaging system with positive power by 100c, rectangle
Reference numerals 56a, 56b, and 56c denote symbols representing ranges of the imaging regions 120a, 120b, and 120c, and L1, L2, and L3 are optical axes of the imaging systems 55a, 55b, and 55c. Since the light incident surface of the photographing lens 100 is a flat surface and the lens portions 100a, 100b, and 100c, which are light exit surfaces, are spherical, a straight line passing through each spherical center and perpendicular to the light incident surface 100e is the optical axis.

At this time, since the image of the object at infinity is formed at the same interval as the lens units 100a, 100b, and 100c as shown in FIG. 13, the interval between the G object image and the R object image and the R object image The distance between the object image and the object B is 1.6783 mm. Therefore, the center interval of the imaging region is slightly narrower than 1.68 mm, and the difference ΔY is 0.0
017 mm or 1.7 μm. Also, the highest visibility
Considering the movement of the B object image with reference to the G object image, the difference ΔY
Is twice as large as 3.4 μm. Near objects such as people are often located in the center of the shooting screen, and distant objects are often located around the screen.Furthermore, near the screen, the aberration of the shooting lens increases and image performance deteriorates. From doing
If the maximum image interval change is smaller than twice the pixel pitch,
It can be said that there is no practical problem. As described above, since the pixel pitch P of the solid-state imaging device 120 is 2.8 μm, ΔY <2 × P, and this degree of color shift of the infinite image is at an acceptable level.

Further, the image interval also fluctuates due to a temperature change of the image pickup system 10. The linear expansion coefficient of the solid-state imaging device 120 is α _S ,
Assuming that the linear expansion coefficient of the taking lens 100 is α _L and the temperature change is ΔT, since the imaging system 10 has an extremely small imaging magnification, the image interval change amount ΔZ is the difference between the elongation of the taking lens and the elongation of the solid-state image sensor. , Equation (4).

ΔZ = 1.68 × (α _L −α _S ) × ΔT (4) Here, α _S = 0.26 × 10 ⁻⁵ , ΔT = 20 [°], and the photographing lens 100 is Α _L = 1.2 assuming that it is made of low melting glass
Assuming × 10 ⁻⁵ , ΔZ is calculated to be 0.00032 [mm]. This is the amount of change in the distance between the G object image and the R object image, and the amount of change in the distance between the R object image and the B object image.

When the B object image is considered as a change with respect to the G object image as the reference image signal, since the image interval is 1.68 × 2, the image interval change amount is ΔZ × 2 = 0.00063 [mm]. If the operating temperature range of the camera is 0 to 40 °, the deviation ΔT from the reference temperature of 20 ° is 20 °. At this time, if ΔZ × 2 is smaller than 1/2 of the pixel pitch, there is a practical problem. There is no. In general, the linear expansion coefficient α _S of the solid-state imaging device 120 takes a small value of about 0.26 × 10 ^−5, so that it is necessary to select the linear expansion coefficient α _L of the imaging lens 100 so as to satisfy Expression (5).

[0066]

[Outside 4] Note that A is the interval between any two of the R, G, and B images, and P is the pixel pitch.

Since the linear expansion coefficient α _L = 1.2 × 10 ⁻⁵ of the photographic lens 100 used earlier satisfies the relationship of the equation (5),
It can be said that this material is suitable for this camera.

Further, separately from the fluctuation of the image interval due to the change in the object distance and the temperature, the image pickup areas 120a, 120b, 12
A method is used in which the resolution is increased by a small number of pixels by shifting 0c mutually by half a pixel. The 1/2 pixel shift amount is set for a virtual subject distance of 2 m.

As shown in FIG. 15, the imaging area 120b for R pixel output and the imaging area 120c for B pixel output are shifted by 1/2 pixel in the horizontal and vertical directions with respect to the G image signal imaging area 120a. It is arranged.

This pixel shift can be realized by slightly decentering the lens portions 100b and 100c of the photographing lens 100 with respect to the lens portion 100a.
And 120c may be realized by slightly decentering the imaging region 120a.

In an optical filter array such as a Bayer array, for example, a pixel having a red optical filter or a pixel having a blue optical filter enters between pixels having a green optical filter, thereby causing aliasing distortion. An optical low-pass filter to suppress is needed. However, if such a configuration is adopted in which images having different spectral distributions are captured for each imaging region, pixels having respective optical filters can be densely arranged, and as a result, the influence of aliasing is small and an optical low-pass filter can be used. A high-definition image can be obtained without the need. Therefore, it is possible to reduce the size of the imaging system and to significantly reduce the cost.

Next, the signal processing will be described.

As described above, as the solid-state image pickup device 120, an image pickup device having a total of 1.44 million pixels of 1,800 pixels in the long side direction and 800 pixels in the short side direction is effectively applied. Optical filters of three primary colors of (R), green (G) and blue (B) are arranged for each predetermined area.

As shown in FIG. 14, the image signals read from the solid-state imaging device 120 are supplied to the A / A of the image processing system 20 respectively.
It is supplied to the D converter 500. The A / D converter 500 has, for example, a 10-bit signal corresponding to the amplitude of the signal of each exposed pixel.
This is a signal conversion circuit that converts the signal into a digital signal of bits and outputs the converted signal. The subsequent image signal processing is executed by digital processing.

The image processing system 20 has a signal processing circuit for obtaining an image signal of a desired format from the R, G, B digital signals.
G and B color signals are converted to luminance signal Y and color difference signals (RY) and (BY)
To a YC signal represented by

The RGB image processing circuit 210 is a signal processing circuit for processing an image signal of 1800 × 800 pixels received from the solid-state imaging device 120 via the A / D converter 500, and includes a white balance circuit, a gamma correction circuit, It has an interpolation operation circuit that performs high resolution by interpolation operation.

The YC processing circuit 230 is a signal processing circuit for generating a luminance signal Y and color difference signals RY, BY. High-frequency luminance signal generation circuit that generates high-frequency luminance signal YH, low-frequency luminance signal
Low-frequency luminance signal generation circuit for generating YL, and color difference signal
It is composed of a color difference signal generation circuit that generates RY and BY. The luminance signal Y is formed by combining the high-frequency luminance signal YH and the low-frequency luminance signal YL.

The details of the RGB image processing circuit 210 will be described.

The RGB signals output for each of the R, G, and B regions via the A / D converter 500 are first subjected to a predetermined white balance adjustment in a white balance circuit in the RGB image processing circuit 210. Further, a predetermined gamma correction is performed by a gamma correction circuit.

The interpolation operation circuit in the RGB image processing circuit 210 generates an image signal having a resolution four times as high as 600 × 800 pixels by interpolation processing, and converts the image signal from the solid-state imaging device 120 into a high-definition image quality signal. Then, the signal is supplied to the subsequent high-frequency luminance signal generation circuit, low-frequency luminance signal generation circuit, and color difference signal generation circuit.

Since the size of each of the RGB object images is already the same depending on the setting of the photographing lens 100, first, a calculation process for correcting the distortion of the photographing optical system is performed on each image signal by a known method. Subsequent interpolation processing, luminance signal processing, and color difference signal processing conform to the processing in a normal digital color camera. The interpolation process is as follows.

First, the G image signal from the image pickup area 120a, which is the reference image signal, is interpolated by the following equations (6) to (9).

G2i2j = Gij (6) G2i (2j + 1) = Gij · 1/2 + Gi (j + 1) · 1/2 (7) G (2i + 1) 2j = Gij · 1/2 + G (i + 1) j · 1/2 ………… (8) G (2i + 1) (2j + 1) = Gij · 1/4 + Gi (j + 1) · 1/4 + G (i + 1) j · 1/4 + G (i + 1) (j + 1) · 1/4... (9) As a result, as shown in FIG. 16 G pixels are generated from the G pixels of FIG.
The G image signal of 0 × 800 pixels is converted into 1200 × 1600 pixels.

Next, the R signal from the image pickup area 120b corresponding to each position of the G image signal obtained by the above equations (6) to (9) is obtained.
The pixel output is interpolated by the following equations (10) to (13).

R2i2j = R (i−1) (j−1) · 1/4 + R (i−1) j · 1/4 + Ri (j−1) · 1/4 + Rij · 1/4 ... ……… (10) R2i (2j + 1) = R (i−1) j · 1/2 + Rij · 1/2 ………… (11) R (2i + 1) 2j = Ri (j-1 ) · 1/2 + Rij · 1/2 (12) R (2i + 1) (2j + 1) = Rij (13) As described above, the imaging area of the R object image and B The imaging area of the object image is
Since the arrangement is shifted by 1/2 pixel with respect to the imaging area of the G object image, the original output of the address ij is changed to (2
i + 1) (2j + 1).

Similarly, similarly to the R pixel, the B pixel from the image pickup area 120c corresponds to the respective positions of the G image signal obtained by the above equations (6) to (9), and the following equations (14) to (14) Perform the interpolation calculation in step 17).

B2i2j = B (i−1) (j−1) · 1/4 + B (i−1) j · 1/4 + Bi (j−1) · 1/4 + Bij · 1/4 ... ……… (14) B2i (2j + 1) = B (i-1) j · 1/2 + Bij · 1/2 ………… (15) B (2i + 1) 2j = Bi (j-1 ) ・ 1/2 + Bij ・ 1/2 (16) B (2i + 1) (2j + 1) = Bij (17) By the above processing, the imaging regions 120a, 120b, and 120c are obtained. Each from
RGB signals of 600 × 800 pixels are converted to 1200 × 1600 pixel RGB signals of high definition image quality.

The high-frequency luminance signal generation circuit in the YC processing circuit 230 is a known signal forming circuit for forming a high-frequency luminance signal YH from a color signal having the highest spatial frequency component among the color component signals. The low-frequency luminance signal generation circuit is a known signal forming circuit that forms a low-frequency luminance signal YL from a signal including all the R, G, and B color components. The color difference signal generation circuit is a known arithmetic circuit that calculates a color difference signal RY, BY from a high-definition RGB signal.

The recording / reproducing system 30 is a processing system for outputting an image signal to the memory and outputting an image signal to the liquid crystal monitor 4, and is a recording processing circuit for performing a process of writing and reading the image signal to and from the memory. 300 and a reproduction processing circuit that reproduces the image signal read from the memory and outputs it to the monitor output
310. More specifically, the recording processing circuit 300 includes a compression / expansion circuit that compresses a YC signal representing a still image and a moving image in a predetermined compression format, and expands the compressed data when it is read. The compression / expansion circuit includes a frame memory or the like for signal processing. The YC signal from the image processing system 20 is stored in the frame memory for each frame, and read out for each of a plurality of blocks and compression-encoded. The compression encoding is performed, for example, by performing two-dimensional orthogonal transformation, normalization, and Huffman encoding on an image signal for each block.

The reproduction processing circuit 310 is a circuit that converts the luminance signal Y and the color difference signals RY, BY into a matrix, for example, into an RGB signal. The signal converted by the reproduction processing circuit 310 is output to the liquid crystal monitor 4, and a visible image is displayed and reproduced.

On the other hand, the control system 40 includes control circuits of respective units for controlling the imaging system 10, the image processing system 20, and the recording / reproduction system 30, respectively, in response to an external operation. Driving the solid-state imaging device 120, RGB image processing circuit 210
, The compression processing of the recording processing circuit 300, and the like.
Specifically, an operation detection circuit 410 that detects the operation of the release button 6, and controls each unit in response to the detection signal,
A system control unit 400 that generates and outputs a timing signal and the like at the time of imaging, and a drive circuit 420 of the solid-state imaging device that generates a drive signal for driving the solid-state imaging device 120 under the control of the system control unit 400. Including.

Next, the operation of the imaging apparatus according to the present embodiment will be described with reference to FIGS. First, when the main switch 5 is turned on, a power supply voltage is supplied to each unit, and the respective units enter an operable state. Next, it is determined whether or not an image signal can be recorded in the memory. At this time, the number of recordable images that can be taken is displayed on the remaining number display 13 of the liquid crystal monitor 4 according to the remaining capacity. When the operator sees the display,
Point the camera at the object scene and press the release button 6.

When the release button 6 is pressed halfway down,
Exposure time is calculated. When all shooting preparation processing is completed, shooting becomes possible, and the display is reported to the photographer. As a result, when the release button 6 is pressed down to the end, the operation detection circuit 410 sends a detection signal to the system control circuit 400. At this time, the elapsed time of the exposure time calculated in advance is counted, and when the predetermined exposure time has elapsed, a timing signal is supplied to the drive circuit 420. As a result, the drive circuit 420 generates horizontal and vertical drive signals and sequentially reads out each of the exposed 1600 × 800 pixels in the horizontal and vertical directions.

Each pixel read out is converted into a digital signal of a predetermined bit value by the A / D converter 500 and is sequentially supplied to the RGB image processing circuit 210 of the image processing system 20. The RGB image processing circuit 210 performs an interpolation process to quadruple the pixel resolution in a state where these have been subjected to white balance and gamma correction, respectively.
To supply.

In the YC processing circuit 230, the high-frequency luminance signal generation circuit generates a high-frequency luminance signal YH for each of the RGB pixels, and similarly, the low-frequency luminance signal generation circuit generates the low-frequency luminance signal YH.
Calculate YL respectively. High-frequency luminance signal YH resulting from the calculation
Is output to the adder via the low-pass filter.
Similarly, the low-frequency luminance signal YL is output to the adder through a low-pass filter after the high-frequency luminance signal YH is subtracted. As a result, the difference YL between the high-frequency luminance signal YH and its low-frequency luminance signal
The luminance signal Y is obtained by adding -YH. Similarly, the color difference signal generation circuit obtains and outputs the color difference signals RY and BY. The output color difference signals RY and BY are each passed through a low-pass filter and supplied to the recording processing circuit 300.

Next, the recording processing circuit 300 receiving the YC signal
Compresses each of the luminance signal Y and the color difference signals RY, BY by a predetermined still image compression method, and sequentially records them in a memory.

When each image is reproduced from an image signal representing a still image or a moving image recorded in the memory, when the reproduction button 9 is pressed, the operation is detected by the operation detection circuit 410, and the system control unit Supply detection signal to 400. Thereby, the recording processing circuit 300 is driven. The driven recording processing circuit 300 reads the recorded content from the memory and displays an image on the liquid crystal monitor 4. The operator
A desired image is selected by pressing a selection button or the like.

The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the configurations of the embodiments, and the functions described in the claims or the embodiments are not limited thereto. Any configuration that can achieve the function of the above configuration can be applied.

For example, in the above-described embodiment, the primary color filters of red, green, and blue are used as the optical filters for color separation. However, the present invention replaces these with the complementary colors of cyan, magenta, and yellow. The present invention is applicable even when a filter is used.

In the above-described embodiment, a description will be given of a change in an interval due to a change in an object distance from an object image having other visibility (color) with reference to an object image having the highest visibility (green). However, this is applicable to the present invention even when the reference is not based on the most visible (green) object image.

Further, the present invention is directed to a system in which all or a part of the configuration of the claims or the embodiment is combined with another device even if the device forms one device. However, it may be an element constituting the device.

[0102]

As described above, according to the present invention,
It is possible to provide a small-sized imaging device having high image performance.

[Brief description of the drawings]

FIG. 1 is a sectional view of an imaging system of a digital color camera according to an embodiment of the present invention.

FIG. 2 is a front view of the solid-state imaging device of the imaging system in FIG. 1;

FIG. 3 is a plan view of a diaphragm of the imaging system in FIG. 1;

FIG. 4 is a diagram illustrating a formation range of an optical filter of the imaging system in FIG. 1;

FIG. 5 is a diagram of a photographing lens of the imaging system in FIG. 1 as viewed from a light exit side.

FIG. 6 is a diagram illustrating a spectral transmittance characteristic of an optical filter of the imaging system in FIG. 1;

FIG. 7 is a diagram illustrating a spectral transmittance characteristic of a color purity correction filter of the imaging system in FIG. 1;

8 is a diagram illustrating a spectral transmittance characteristic of the photochromic glass of the imaging system in FIG.

FIG. 9 is a diagram illustrating a transmittance distribution of a transmittance distribution type filter of the imaging system of FIG. 1;

10 is a diagram illustrating OTF characteristics of a photographing lens of the imaging system in FIG.

11 is a diagram illustrating a luminance distribution of a point image of the imaging system in FIG. 1;

FIG. 12 is a diagram for explaining setting of an interval between lens units of the imaging system in FIG. 1;

13 is a diagram for explaining a position of an image of an object at infinity of the imaging system in FIG. 1;

FIG. 14 is a block diagram of a signal processing system of the digital color camera of FIG. 1;

15 is a diagram illustrating a positional relationship between an imaging region for R pixels and an imaging region for B pixels with respect to an imaging region for a G image of the imaging system in FIG. 1;

FIG. 16 is an explanatory diagram of an interpolation process of the digital color camera of FIG. 1;

FIG. 17 is a diagram illustrating an entire configuration of the digital color camera in FIG. 1;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Camera main body 2 Illumination light capturing window 3 Front viewfinder frame 4 Color LCD monitor 5 Main switch 6 Release button 7, 8, 9 switch 10 Imaging system 11 Viewfinder eyepiece window 12 Prism 13 Display of remaining number of images that can be photographed 51b, 51c Image circles 52a, 52b, 52c Optical filters 53a, 53b, 53c formed on photographing lens Optical filters 54a, 54b, 54c formed on solid-state imaging device Transmittance distribution type filter 100 Photographing lenses 100a, 100b , 100c Lens portion of photographing lens 110 Aperture 120 Solid-state image sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03B 11/00 G03B 11/00 19/07 19/07 H04N 5/238 H04N 5/238 Z 9/097 9 / 097

Claims (22)

[Claims] 1. An imaging apparatus comprising: an imaging device having at least first and second imaging regions; and an imaging optical system for forming an object image on the imaging device, wherein the imaging optical system is at least the first imaging device. And a first and second imaging system corresponding to a second imaging region, wherein the first imaging system has a focal length for light of a first wavelength and the second imaging system for light of a second wavelength. The focal length of the second imaging system is set to be the same, and the focal length of the first imaging system and light of a wavelength other than the second wavelength for light having a wavelength other than the first wavelength. An imaging apparatus characterized in that the focal length of the second imaging system is set to be different from the focal length of the second imaging system. 2. The imaging device according to claim 1, wherein the light having the first wavelength is a representative wavelength of light having a first spectral distribution, and the light having the second wavelength is a light having a second spectrum. An image pickup apparatus, wherein the light has a representative wavelength of light having a distribution. 3. An imaging apparatus comprising: an imaging device having a plurality of imaging regions; and an imaging optical system for forming an object image on the imaging device, wherein the imaging optical system has a plurality of imaging regions corresponding to the plurality of imaging regions. The focal lengths of the plurality of imaging systems are set to be the same with respect to the wavelength of light of a predetermined wavelength of each imaging system, and the predetermined An imaging apparatus characterized in that it is set to be different for light having a wavelength other than the above wavelength. 4. The imaging apparatus according to claim 3, wherein the light having the predetermined wavelength is a representative wavelength of light having a predetermined spectrum different from each other. 5. An image pickup device having first and second image pickup regions, a photographing optical system for forming an object image on the image pickup device,
In an imaging apparatus having an image processing unit that processes an output signal of the imaging element, the imaging optical system includes first and second imaging systems,
The first and second imaging systems form first and second object images on the first and second imaging regions, respectively, and provide a first spectrum from the first and second imaging regions. A first image signal based on the object light component of the distribution and a second image signal based on the object light component of the second spectral distribution are obtained, and for the representative wavelength of the spectral distribution of the first image signal, An imaging apparatus, wherein the first and second imaging systems have different focal lengths and are set to be the same for the representative wavelength of the spectral distribution of each image signal. 6. The imaging apparatus according to claim 2, wherein the object light having the first spectral distribution is an object light having a spectral distribution including a peak wavelength of visibility. Imaging device. 7. A first imaging unit and a second imaging unit for receiving at least a first wavelength component of subject light and a second wavelength component different from the first wavelength component, respectively, 1, the first of the subject light received by the second imaging unit;
A first optical system and a second optical system for guiding the second wavelength component to the first and second imaging units via different optical paths, respectively, and the first optical system and the second optical system Of the first optical system
An imaging apparatus, wherein the focal length of the optical system for the first wavelength component is the same as the focal length of the second optical system for the second wavelength component. 8. The imaging apparatus according to claim 7, wherein the first wavelength component is a representative wavelength of light having a first spectral distribution, and the second wavelength component is a light having a first spectral distribution. An imaging device characterized in that the wavelength is a representative wavelength of light having a second spectral distribution different from the representative wavelength. 9. The imaging apparatus according to claim 7, wherein the first wavelength component is included in a spectral distribution including a peak wavelength of luminosity. 10. The imaging device according to claim 7, wherein the first and second wavelength components are red,
An image pickup apparatus characterized by two or more color components of green and blue. 11. The image pickup apparatus according to claim 7, wherein said first and second optical systems include said first and second optical systems.
An image pickup apparatus having a filter for extracting each of the wavelength components. 12. The imaging apparatus according to claim 7, wherein each of the first and second optical systems has a single lens. 13. The imaging device according to claim 12, wherein the single lens is integrally formed of a glass material or a resin material. 14. The imaging device according to claim 13, further comprising a light-shielding film between the integrally formed single lenses. 15. The imaging apparatus according to claim 7, wherein each of the first and second optical systems has a single lens having an infrared cut filter. 16. The imaging apparatus according to claim 7, wherein each of the first and second optical systems has photochromic glass. 17. The image pickup apparatus according to claim 7, wherein each of said first and second optical systems has a color purity correction filter. 18. The imaging apparatus according to claim 7, wherein each of the first and second optical systems has a filter whose transmittance decreases as the distance from the optical axis increases. Characteristic imaging device. 19. The imaging apparatus according to claim 7, wherein a virtual subject distance D [m] is a function of an imaging angle of view θ [°] of the first and second optical systems. When the subject is at the virtual subject distance and when the subject is at infinity, the subject image of the first wavelength component received by the first imaging unit and the second imaging unit receive light. The change in the distance between the second wavelength component and the subject image is smaller than twice the pixel pitch of the imaging unit,
An imaging apparatus, wherein an interval between optical axes of the plurality of optical systems is set. 20. The imaging apparatus according to claim 7, wherein said first and second imaging units are integrally formed. 21. The imaging apparatus according to claim 7, wherein the first and second imaging units are configured in a planar shape. 22. The imaging apparatus according to claim 7, wherein said first and second optical systems each have a plurality of apertures for taking in external light.