JP2001189941A - Solid-state image pickup device and optical filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state image pickup device and an optical filter, that applies hue reproduction and highly saturated reproduction to an image with fidelity and can enhance S/N and the sensitivity of an image more than those of a conventional image pickup device. SOLUTION: A prescribed gradient with respect to spectral transmission characteristic is provided to a color filter G in a color filter section 104a in a digital still camera 10, so as to make the gradient of a shorter wavelength steep with respect to the peak wavelength of a curve denoting the spectral sensitivity characteristic. As a result, the spectral sensitivity lower than a wavelength of 470 nm is 20 or smaller, and then the hue and saturation reproduction is enhanced with more fidelity than that in the conventional image pickup device, and images with superior color reproducibility are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device and an optical filter, and more particularly to an image input device and an image processing device having excellent color reproducibility. It is suitable for application to digital still cameras, movie cameras, and the like.

[0002]

2. Description of the Related Art When obtaining a color image, there is a strong demand from users for improving the resolution and expressing the image in a faithful color (especially, a faithful hue). There is. It is known that in order to obtain an image with such good color reproducibility, it is better to set the spectral sensitivity in the same form as the color matching function, which is determined depending on the type of the original stimulus and its relative intensity. .

Further, as well known, when the original stimulus is selected from existing colors, its color matching function includes negative sensitivity. Negative sensitivity is sensitivity that cannot be realized by actual spectral sensitivity.

On the other hand, in recent years, CCD (Charge Coupled Device)
In a digital camera using a solid-state imaging device represented by e), the number of mounted pixels, that is, the number of pixels is dramatically increased. With the increase in the number of pixels, the resolution (or resolution) of the obtained image has been significantly improved. In addition to the improvement in resolution, digital cameras are also required to improve color reproducibility, which is another major item of image quality evaluation. In addition, digital cameras have the ability to achieve, in principle, more accurate color reproducibility than silver halide photography with respect to this color reproducibility.

[0005]

By the way, at present, first, when the spectral sensitivity of the color G used for color reproduction described above is examined, the spectral sensitivity of the color G is considered to be the ideal spectral sensitivity so far. Was not designed to provide
In the conventional design, of the spectral sensitivity characteristics of the color G, the tailing that lowers the sensitivity with a gentle slope on the short wavelength side, so-called broadening, has an adverse effect on color reproducibility. It is known that a linear matrix may be introduced to subtract the color G and the color B of the spectral sensitivity to improve this effect. However, such signal processing is
The S / N ratio is deteriorated, and furthermore, for example, the calculation processing of a color which is not originally indicated by the value obtained by the interpolation processing is performed, so that a problem such as deterioration of the false color occurs.

Second, as described above, the potential of color reproducibility in a digital camera is clear from the principle, but has not yet been sufficiently studied. As a result, the image obtained from the digital camera remains at an image quality level that is inferior to silver halide photography.

[0007] These problems will be briefly described with specific examples. For example, the International Telecommunication Union recommendation
709 (International Telecommunications Union Recomm
endation 709: Standard CR specified by ITU-R709)
In the color matching function corresponding to T (Cathode Ray Tube), since the negative spectral sensitivity described above exists in all of the colors R, G, and B, faithful color reproduction has been described so far. Can not be realized as. As a countermeasure for this, color R,
By performing arithmetic processing (for example, application of linear matrix processing (linear conversion)) between G and B, a negative region of spectral sensitivity can be generated.

However, in the case of a single-panel digital camera using a mosaic-type microfilter, if arithmetic processing is performed using coefficients of a linear matrix that emphasizes faithful color reproduction, false colors are generated in an image, and image quality is reduced. Worsen. In order to prevent this false color, as a result, the processing of subtracting the signal of the color R or the color B from the signal of the color G is prohibited.

On the other hand, in the case of a three-panel digital camera,
(GR) and (GB) are allowed. However, these colors R,
The subtraction process between G and B degrades the S / N ratio of the signal. For this reason, the obtained image has a so-called rough pattern.

The present invention solves the above-mentioned drawbacks of the prior art, and can reproduce a hue and a high chroma faithfully with respect to an image, and can further improve the S / N ratio and sensitivity of the image more than ever. It is an object to provide a solid-state imaging device and an optical filter.

[0011]

According to the present invention, in order to solve the above-mentioned problems, incident light is separated by color separation means, and the separated incident light is converted into an electric signal by an image pickup means for photoelectrically converting the light. In a solid-state imaging device that performs signal processing on the converted signal, the color separation unit separates the incident light into colors, and when expressing the relative sensitivity with the peak of the spectral sensitivity of the color G being 100, the color separation means Also, it has a spectral sensitivity characteristic in which the gradient of the spectral sensitivity characteristic of the color G between the relative sensitivity 80 and the relative sensitivity 20 on the short wavelength side is a value of 2.0 or more.

In the solid-state imaging device according to the present invention, the color filter of the color G of the color separation means is designed so that a predetermined slope is obtained in the spectral sensitivity characteristic, so that the curve representing the spectral sensitivity characteristic can be adjusted with respect to the peak wavelength. The slope on the short wavelength side becomes steeper, and as a result, the spectral sensitivity (relative sensitivity) at a wavelength of 470 nm or less becomes 20 or less, thereby improving the hue fidelity and the saturation.

In order to solve the above-mentioned problems, the present invention separates incident light by means of color separation and applies the separated light to an image pickup device which converts the separated incident light into an electric signal. In an optical filter that supplies light, when the incident light is subjected to color separation, when the spectral transmission density of the color G is normalized by the spectral transmission density value with respect to the wavelength of the peak transmittance of the color G, the wavelength of the color G is 470 nm. The ratio is characterized by having a ratio of 10 or more and a wavelength of 485 nm of 3 or less.

The optical filter of the present invention increases the hue fidelity and the saturation.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the solid-state imaging device according to the present invention will be described below in detail with reference to the accompanying drawings.

According to the solid-state imaging device of the present invention, the curve representing the spectral sensitivity characteristic is obtained on the short wavelength side with respect to the peak wavelength by providing the spectral sensitivity characteristic of the color G of the color separation filter with a predetermined inclination. The steepness of
As a result, the spectral sensitivity at a wavelength of 470 nm or less becomes 20 or less,
It is characterized by enhancing the hue fidelity and saturation.

A case where this solid-state imaging device is applied to a digital still camera 10 will be described. In addition, illustration and description of parts not directly related to the present invention are omitted. Here, the reference numerals of the signals are represented by the reference numbers of the connecting lines in which they appear.

As shown in FIG. 1, the digital still camera 10 includes an imaging system 10A, a signal processing system 10B, a driving signal generation unit 10C, a signal output system 10D, a mode designation unit 10E, and a system control unit 12. I have.

The image pickup system 10A includes an image pickup lens 102, an image pickup section
104, an AF adjustment unit 106 including a focus adjustment mechanism, and an AE adjustment unit 108 including an aperture mechanism. In addition, although not shown, a shutter mechanism for completely blocking the incident light on the side of the incident light of the imaging unit 104 may be included. Imaging lens 102
Is an optical system that focuses incident light from the object field so as to focus on the light receiving surface of the imaging unit 104.

The image pickup units 104 are two-dimensionally arranged in a row direction and a column direction so that a light receiving surface is formed by a light receiving element (not shown) for photoelectrically converting the supplied incident light. Also,
The array may be of a honeycomb type in which, among the light receiving elements, the pitch of the diagonally adjacent elements is shifted by 1/2 in the row direction and the column direction and arranged in a mutual positional relationship. In the imaging unit 104, a color filter 104a for color-separating the incident light on the side of the incident light from the light receiving element corresponds to each of the light receiving elements,
It is integrally formed of a single plate. By disposing the color filter 104a, incident light that has been color-separated so as to have, for example, each of the three primary colors RGB has a color attribute. This relationship is integrally formed in the imaging unit 104. In the arrangement of the color filters R, G, and B, the positional relationship of the signal charges to be read has an important meaning, for example, when reading is performed by focusing only on the color G. The imaging unit 104 converts the imaging signal 10a into a signal processing system 10B.
Output to The spectral sensitivity characteristics of the color filter unit 104a, especially the color
G will be described in detail later.

The image pickup unit 104 responds to drive signals 10b output from a drive signal generator 10C (not shown), which will be described later. Each light receiving element is a charge coupled device (Charge Coupl
ed Device: CCD). In the light receiving element, a signal read gate (transfer gate) is formed between a transfer element disposed adjacent to the light receiving element, that is, a vertical transfer element so as not to leak the signal charge converted by receiving light. The signal readout gate transfers the signal charge from the light receiving element to the vertical transfer path by opening and closing the gate in response to the presence or absence of a field shift pulse included in the vertical drive signal supplied via the electrode. The vertical transfer path sequentially transfers the read signal charges in the column direction, that is, in the vertical direction. By the vertical transfer, the signal charges are line-shifted and supplied to the transfer elements in the row direction, that is, the horizontal transfer paths. The horizontal transfer path outputs the signal charge 10a to the signal processing system 10B via the amplifier in response to the supplied horizontal drive signal as described above.

The AF adjustment unit 106 arranges the imaging lens 102 at an optimum position in accordance with information obtained by measuring the distance between the subject and the camera 10 by a focus adjustment mechanism (not specifically shown). This position adjustment is performed as follows. At this time, the calculation of the distance measurement information and the control amount based on the distance measurement information are processed by the system control unit 12. As a result, the supplied control signal 12a
The AF adjustment unit 106 controls the focus adjustment mechanism to
6a, the imaging lens 102 is moved along the optical axis in the direction of arrow A.

The AE adjustment unit 108 controls the aperture position of the aperture mechanism under the control of an exposure control unit (not shown) provided in the system control unit 12 for calculating the photometric value of the object scene including the subject. To adjust the amount of incident light flux.
The photometry uses a part of the imaging signal. Also in this case, the exposure amount is calculated by the system control unit 12 based on the photometric value, and a control signal 12a for controlling the aperture value and the shutter speed value so as to reach the exposure amount is supplied to the AE adjustment unit 108. AE adjuster 10
8 supplies a drive signal 108a to the aperture mechanism and the shutter mechanism in response to the control signal 12a, and adjusts the aperture value and the shutter speed value to predetermined values, respectively. With this adjustment, the exposure can be optimized.

The signal processing system 10B includes a pre-processing unit 110, an A / D
A conversion section 112, a signal processing section 114, a buffer section 116, and a compression / expansion processing section 118 are provided. A control signal 12b is supplied from the system control unit 12 to the signal processing system 10B so as to control each of the above-described units according to the mode, and a timing signal 10c corresponding to each operation is supplied from the drive signal generation unit 10C. Is supplied. The timing signal 10c in FIG. 1 represents a plurality of types of signal lines. The pre-processing unit 110 performs, for example, correlated double sampling (CDS) processing on the supplied signal charge 10a to reduce noise, or performs gamma correction on the signal, and performs signal gamma correction.
a is amplified and output to the A / D converter 112. These preprocessings are performed in synchronization with the timing signal 10c. The gamma correction is not limited to this position, and may be performed by the signal processing unit 114 at the subsequent stage.

The A / D converter 112 samples the analog signal 10d supplied via the preprocessor 110 using a control signal 12b and a timing signal 10c from the system controller 12 (not shown). Digital signal (or image data) 10e. Timing signal
10c may supply a clock signal for high-speed processing. The converted digital signal 10e is supplied to the signal processing unit 114.

The signal processing unit 114 includes a digital signal 10e
In addition to the configuration that performs each signal processing such as white balance adjustment to be performed on the linear matrix (Linear-MaTriX: L
-MTX) circuit 114a and color difference matrix (Color differen)
ce-MaTriX: C-MTX) circuit 114b is provided. L-MTX
The circuit 114a is a circuit that performs arithmetic processing on the digital signal 10e (or data) so that the color reproduction of the supplied digital signal 10e approaches a color matching function. The more freely the size of the coefficient set in this process can be set, the easier it is to reproduce a faithful hue. For example, the color matching function corresponding to the primary color of the standard CRT specified in ITU-R709 is the spectral sensitivity (curve 20 of color R: curve 22 of color G: curve 24 of color B) shown in FIG. . Actually, the light passes through the color filter unit 104a,
By subjecting the resulting transmitted light to L-MTX processing, the primary colors R,
The closer the shape of the spectral sensitivity of G and B is to the color matching function, the more faithful hue reproduction is performed.

The obtained digital signal 10e has three primary colors R,
In the case of G and B, a total of nine multiplication coefficients are used for the arithmetic processing corresponding to the elements of 3 rows and 3 columns. Specifically, L-MTX
Is

[0028]

(Equation 1) It is.

Here, the elements of each arithmetic processing include a + b + c = 1,
There is a relation of d + e + f = 1 and g + h + i = 1. Incidentally, among these elements, the value of the element (b, c, d, f, g, h) of the off-diagonal term is preferably as small as possible. For example,
This is because, when a mosaic filter arrangement is applied, if the coefficient is too large, the false color may deteriorate.

In order to generate a negative spectral sensitivity of the color matching function by this arithmetic processing, it is preferable to set the spectral sensitivity in the generated wavelength range to zero before performing the L-MTX processing. In particular, in the case of FIG. 2, it is important that the spectral sensitivity of the color G be zero at a wavelength of 470 nm or less and a wavelength of 610 nm or more. This is because (GR) and (GB) are prohibited from the viewpoint of preventing false colors. The relationship between the spectral sensitivities in this wavelength range is represented by the relative sensitivity in FIG. The relative sensitivities of color R and color B are indicated by broken lines (curves 20a and 24a). In addition, two relative sensitivity curves are shown as the solution for the color G. That is, a curve 22a indicated by a solid line of relative sensitivity and a curve 22b indicated by a thick broken line.
Also, as shown in FIG. 1, when the generation of false colors is a concern, the L-MTX circuit 114a stops its operation so as not to selectively perform the calculation, and supplies a signal to the C-MTX circuit 114b to perform the calculation. Processing may be performed.

The C-MTX circuit 114b is a circuit that generates the luminance data and the two chrominance data that have been conventionally performed by calculation. In the C-MTX circuit 114b, arithmetic processing is performed in accordance with the presence or absence of elements in the C-MTX, that is, a diagonal term from upper left to lower right and a non-diagonal term from upper right to lower left. The settings in these calculation processes and the hues obtained therewith will be described later.

In addition, although not shown, the signal processing unit 114
After performing automatic iris adjustment (AE), white balance adjustment (AWB), aperture correction, and the like, which are generally performed, signal processing is further performed according to each of the two modes. That is, the mode here refers to the mode set by the release shutter 124 of the mode designating unit 10E, which will be described later, and a still image shooting mode in which at least the obtained still image is taken into the recording / reproducing unit 122 of the signal output system 10D. Only two photometric control modes in AF of the image pickup system 10A are shown. In the present embodiment, for example, three types (all pixels, thinning out two lines, and frame reading) are set in the still image shooting mode according to the recording capacity and the image quality to be recorded by a key switch 126 described later. The light metering control mode is set to two-line thinning-out reading from a request for high-speed operation. In this configuration, the mode is not limited to the three types of modes, and 1/4 thinning may be performed. The gamma correction process may be performed here or at a later stage.

In the digital still camera 10, which mode is currently selected is controlled by the above-described control signal 10b. Under the control of the system control unit 12, in the signal processing unit 114, in addition to the above-described signal processing, signal processing associated with predetermined digital in the still image shooting mode,
For example, the band of the luminance signal is increased. On the other hand, in the signal processing unit 114, in the photometry control mode, the system control unit 12 reads out the signal from the imaging unit 104 faster than in other modes, for example, in consideration of the fact that the supplied signal 10e is digital. Control and processing are performed. The signal processing unit 114 converts the imaging signal 10a from the imaging unit 104 into a recordable video signal by performing signal processing in the still image shooting mode. Then, the signal processing unit 11
4 outputs the signal 10f of the mode in which display / recording is selected to the buffer unit 116.

The buffer unit 116 includes the signal processing unit 11 described above.
In addition to amplifying the video signal 10f supplied from 4 to a predetermined amplitude, the video signal 10f also has a function of adjusting time during recording. The buffer unit 116 controls the signal output system 10D under the control of a recording control unit (not shown) provided in the system control unit 12.
And / or outputs the image 10g to the compression / decompression processing unit 118.

When recording an image, the compression / expansion processing section 118 takes in the image signal 10g according to the control signal 12b from the system control section 12. The supplied image signal 10g includes, for example, JPEG (Joint Photographic coding Experts Gr.
oup) A compression process based on the standard is performed. When the signal 10h recorded from the recording / reproducing unit 122 is read and reproduced, the original image signal is reproduced by performing signal processing such as inverse conversion of the above-described compression processing, and is not specifically illustrated. Supplies the restored image signal to the display unit 120 for display.

The drive signal generator 10C includes a timing signal generator and a driver (not shown). The timing signal generation unit is, for example, the current broadcast system (NTSC / P
In step AL), a synchronization signal is generated based on the original oscillation clock generated to drive the digital still camera 10 and supplied to the signal processing system 10B. That is, the timing signal generation unit includes a pre-processing unit 110, an A / D conversion unit 112, a signal processing unit 114
, A timing signal is supplied to the buffer section 116 and the compression / expansion processing section 118 as a clock serving as an operation reference of a sampling signal and a write / read signal.
When the timing signal can be shared, the number of components of the timing signal generation unit can be reduced.

The timing signal generation section generates synchronization signals from the clock of the original oscillation, and outputs various timing signals generated using these signals to the driver section. The generated timing signal includes a timing signal used for reading out the signal charge obtained by the imaging unit 104, for example, a vertical timing signal for supplying a drive timing for a vertical transfer path, a horizontal timing for supplying a drive timing for a horizontal transfer path. There are signals, timing signals for field shift and line shift, and the like. The AF adjustment unit 106, AE
The drive signal generation unit 10C also controls the operation of the adjustment unit 108.
(Here, the signal lines are not explicitly shown). As described above, various signals are output to the above-described units, and the timing signal generation unit supplies a vertical timing signal and a horizontal timing signal to the driver unit. When the photometry control mode is selected, the timing signal generator selectively switches the generation of the timing signal according to the control signal 12c from the system controller 12.

The driver section generates a drive signal 10b at each supplied timing. In general, to change the speed at which a signal is read, a vertical drive signal output from a driver unit is supplied to the imaging unit 104 in accordance with the mode. For example, driving of the entire screen, selective driving of colors, and color and area are performed. The speed is changed by performing thinning-out reading such as designated driving.

In the driver section, a drive signal corresponding to the case where the mode is set to the photometric control mode is supplied to the image pickup section 104. For example, the drive for the entire screen, in this embodiment, the color arrangement will be specifically described. Although the speed is not changed, the speed is changed by performing the selective driving of the color according to the arrangement and the driving in which the color and the area are designated. The driver generates a ternary drive signal using the vertical timing signal and the transfer gate signal.

The signal output system 10D includes a display unit 120 and a recording / reproducing unit 122. The display unit 120 includes, for example, a VGA (Video Graphics
Array) standard LCD monitor etc. are provided.
The recording / reproducing unit 122 records a video signal 10h supplied to a magnetic recording medium, a semiconductor memory used for a memory card or the like, an optical recording medium, or a magneto-optical recording medium. The recording / reproducing unit 122 can also read out the recorded video signal 10h and display it on the display unit 120. If the recording / reproducing unit 122 can detachably attach a recording medium, the recording medium may be detached to reproduce and display a video signal recorded by an external device or to print an image. These are controlled by the control signal 12d.

The mode designating section 10E includes a release shutter.
124 and a key switch 126 are provided. The release shutter 124 has a two-step pressing function in the present embodiment. That is, in the half-pressed state of the first stage, the photometric control mode is designated, and a signal indicating that this mode setting is made is supplied to the system control unit 12 as a signal. The timing is provided to the system control unit 12, and a signal that the image recording setting (still image shooting mode) has been made is supplied to the system control unit 12 by this operation. These modes are supplied to the system control unit 12 via the signal line 124a.

The key switch 126 is used to set a mode.
Items and images are selected. In particular, as described above, one of the mode settings is selected from all pixels, 2 lines thinning, and frame reading. The selected information is also sent to the system control unit 12 via the signal line 126a.

The system control unit 12 is a controller for controlling the operation of the entire camera. In the system control unit 12,
A central processing unit (CPU) is included. System control unit
Reference numeral 12 determines which mode has been selected based on the input signal (or designation signal) 124a from the release shutter 124. Further, the system control unit 12 performs control such as processing on image signals of the camera based on the selection information 126a from the key switch 126. Based on the information supplied in this way, the system control unit 12 controls the control signal 12 based on this determination result.
c to control the operation of the drive signal generator 10C. The system control unit 12 includes a recording control unit (not shown). The recording control unit receives a control signal from the system control unit 12.
12b, the input / output to the buffer unit 116 and the control signal 12
According to d, the operation of the recording / reproducing unit 122 of the signal output system 10D is controlled.

Next, in the color filter section 104a described above,
The color filter of the color G will be described. Conventional color filters for the colors R and B are used. FIG. 1 shows a specific color filter section.
The color G filter for 104a is not shown. This color G filter is used to form the above-described image pickup unit 104, so-called Pigment Yellow 150 (PY150), Pigment Green 7 (PG
7), a color resist in which three kinds of pigments, Pigment Green 36 (PG36) were mixed. In this embodiment, the mixed color resist has a peak wavelength of 530 ± 15 nm, more preferably 530 ± 10 nm.

As shown in FIG. 4, the spectral sensitivity of the color G is, for example, as shown in FIG.
The spectral sensitivity characteristic is rotated counterclockwise as indicated by arrow B around the point 30 of the sensitivity 50 on the short wavelength side described above as a fulcrum. Due to this rotation, the slope of the spectral sensitivity characteristic becomes steep. This spectral sensitivity characteristic 22G is actually dissociated from the shape of the color matching function. Nevertheless, surprisingly, the hue fidelity and saturation are higher than when using the spectral sensitivity of the previous color G. Although point 30 in FIG. 4 indicates a wavelength of 500 nm, it is preferably 495 nm or shorter on the shorter wavelength side, and further preferably 490 nm or shorter for increasing the color G sensitivity.

Further, the sensitivity is 50 or more in a wavelength region longer than 575 nm on the longer wavelength side with respect to the peak wavelength. An example of a long wavelength region is that a sensitivity of 50 or more is obtained at a wavelength of 580 nm, and a high color is obtained at a wavelength of 585 nm or more.
G sensitivity is obtained. It is preferable from the viewpoint of faithful hue reproduction to simultaneously expand the points of the sensitivity 50 on the short wavelength side and the long wavelength side to the short wave and the long wave, respectively.

There have been proposals for compensating for a negative sensitivity region in a color matching function for faithful color reproduction. One of the first proposed methods of approximation is Epstein approximation. This proposal is based on “Epstein, d. W .: Colorimetric analysis of
RCA color television system, RCA Rev., 14, pages 2
27-258 (1953) ". The basic concept of this proposal is that, as shown in FIG. 6, in the spectral sensitivity characteristic curve S _G (λ) for the color G, the shaded area 42 indicates a negative sensitivity area. This is an intuitive approximation method for obtaining a characteristic curve drawn with the same area as that of the area, so that the half width of the characteristic curve is reduced.

FIG. 7 shows the result of the Epstein approximation. In FIG. 7, the color of the subject is represented by a symbol (●), and the position of the reproduced color of the approximation result is indicated by the tip of the arrow. As can be seen from this figure, the hue shifts to greenish for high chroma blue.

On the other hand, in this embodiment, the fulcrum of FIG.
It is sharpened by rotating around 30. Therefore, the half width is not narrowed and does not cause a decrease in sensitivity.
Further, the present invention is different from the Epstein approximation in that a high-saturation blue hue is rather faithfully reproduced as described later.

In other words, as a method of forming this characteristic curve, the characteristic curve is obtained by connecting the relative sensitivity 80 and the relative sensitivity 20 on the short wavelength side to the wavelength of the peak sensitivity (relative sensitivity 100).
It can be defined by a slope per 1 nm. Although the characteristic curves 44 and 46 of the present embodiment have different peak wavelengths,
3.13 and 3.43 respectively. In the conventional characteristic curve 48, the slope is 1.14 (see FIG. 8).

FIG. 8 shows a characteristic curve 62 when the half width is narrower than the characteristic curves 44 and 46 in this embodiment. The slope at this time is 4.0. This characteristic curve 62 is also used for comprehensive evaluation in a later stage.

Although the above description has been made using the spectral sensitivity characteristics of the color G, the present invention will be described with reference to the spectral transmission characteristics of the color filters. As a parameter representing this concept, a transmission density ratio (hereinafter, referred to as a transmission density ratio) in which the spectral transmission density of each wavelength is normalized by the spectral transmission density of the wavelength of the peak transmittance. Here, the transmittance is T (%), and the peak transmittance is
T _P %. The transmission density ratio is given by equation (2)

[0053]

## EQU2 ## Transmission density ratio = log ₁₀ (T / 100) / log ₁₀ ( _TP / 100) (2) (see FIG. 9). Color proposed in this embodiment
The G color filter is a thick solid line 44 in FIG. FIG. 9 also shows a characteristic curve 62 with a reduced half-value width and a characteristic curve 64 of a color G filter candidate slightly different from the present embodiment.
As is clear from the figure, the conventional characteristic curve 48 is different from the characteristic curve 44,
It can be seen that the density is increased with a gentle slope compared to 64. The characteristic curve of the color filter for color G shows that this transmission density ratio is 10% at a wavelength of 470 nm as shown by point D.
The characteristic is adopted so that the value becomes 12 or more, preferably 12 or more.
In addition to this condition, the transmission density ratio at a wavelength of 500 nm is 3 or less,
Preferably, it should be 2.5 or less.

The image pickup unit 10 passes through the color filter of color G having such spectral transmission characteristics and the color filters of other colors R and B.
The spectral sensitivity characteristic of the imaging device (CCD) of No. 4 is represented by the relative sensitivity of FIG. The spectral sensitivity characteristic of the image sensor for the color G in the present embodiment is a characteristic curve 66 reflecting the characteristics of the color filter of the color G. The characteristic curves of the colors B and R and the conventional relative sensitivity curve are denoted by reference numerals 68, 70 and 72, respectively.
Indicated by The color G spectral sensitivity of the imaging device of this embodiment is clearly 470 nm or less and the relative sensitivity is 20 or less. More preferably, the relative sensitivity is set to 10 or less.

As shown in FIG. 10, it can be seen that the color filter of the color G satisfies the conditions described above. By making the sensitivity of color G substantially zero at wavelengths below 470 nm, a linear matrix can be used that produces negative characteristics even though the color-matching function of color G is negative in this wavelength range. The result is a faithful reproduction of the hue and a reproduction that enhances the saturation even without it.

The characteristics of the color filter of the color G shown in the present embodiment are different from the conventional spectral sensitivity of the color G on the short wavelength side, but the characteristics on the long wavelength side are longer than 610 nm. In the region, the sensitivity is reduced to the same degree as the conventional characteristics. Specifically, the relative sensitivity may be set to 20 or less at a wavelength of 610 nm or more.

If it is difficult to obtain such a characteristic on the long wavelength side, an image sensor package, a digital camera or a digital movie camera, for example, an infrared ray (650 nm or more) shown in FIG. IR)
A cut deposition filter (hereinafter, referred to as an infrared filter) may be used as the infrared filter 104b (see FIG. 1). The mounting position is not limited to the position shown in FIG.

When an infrared filter having this characteristic is incorporated, there is substantially no problem even if the sensitivity is high at a wavelength of 660 nm or more. Although not shown, since the image sensor has sensitivity in the infrared region, an infrared filter that cuts incident light up to 1100 nm is preferable. The transmittance of infrared light is preferably 10% or less, more preferably 5% or less. The infrared filter used in this embodiment has a transmittance of 50% at a wavelength of 660 nm as can be seen from a characteristic curve 74 in FIG. 11, but is not limited to this characteristic. Further, the characteristic curve 76 shown by the broken line
Indicates the spectral sensitivity characteristics of the camera lens.

Although not specifically shown, it is preferable that there is no sensitivity not only at the long wavelength side but also at a short wavelength of 380 nm or less. In effect, for example,
It is known that an image pickup device such as a CCD does not have a specific sensitivity in this ultraviolet region, but a configuration in which an ultraviolet cut filter is combined may be used.

For example, even when a linear matrix can be used as in a three-panel electronic camera, the use of such a color G filter can reduce the amount of (GB) subtraction in the linear matrix processing. As a result, it is possible to prevent the S / N of the image signal obtained in the three-panel electronic camera from deteriorating.

In order to further improve the sensitivity, the characteristic curve of the color G is expanded while maintaining the shape on the short wavelength side and the long wavelength side of the peak wavelength, so that the overall shape of the characteristic is increased. By forming a characteristic curve in such a shape, faithful reproducibility of hue is maintained and sensitivity is improved. However, with this characteristic curve, the saturation decreases.

To recover this point, the C-MTX circuit 114b
It turned out that it is good to use the signal processing effectively. The off-diagonal term calculation function of this signal processing is the off-diagonal term calculation processing in linear matrix processing ((GR) and (GB) functions)
Because it is similar to That is, the function of the off-diagonal term in the C-MTX arithmetic processing is similar to the effect of subtracting the sensitivity of color R from the sensitivity of color G and the sensitivity of color B from the sensitivity of color G. When this “subtraction” is performed in the C-MTX circuit 114b, even if the sensitivity area of the color G is increased to the left and right, the sensitivity R area of the color R and the area of the sensitivity of the color B are subtracted. This is because the same effect as slightly narrowing the area of the color G can be obtained while substantially improving the sensitivity.

In view of the respective processes described above, comprehensive evaluations of the faithful hue and the high chroma reproducibility are performed based on the signal processing and the specifications of the color filter of the color G to be used. The chromaticity of the subject used here is the difference between the hue angle difference and the saturation difference from the reproduced color with respect to the original color value of the subject shown in FIG. 12 (defined by the coordinates in the L ^* a ^* b ^* color space). I asked. The color filter of color G includes a conventional filter (characteristic curve 48) and a filter having a narrow half width (characteristic curve 62).
A filter having a wide half width (characteristic curve 46) was used. Whether the signal processing unit 114 performs L-MTX processing (linear matrix: where element values or coefficients d = f = 0 in equation (1)) is used, and C-MTX processing (color difference matrix) is performed. ) Were divided into processes including only diagonal terms and processes including non-diagonal terms, and a hue angle difference and a chroma difference from a reproduced color were obtained. FIG. 13 shows the obtained results.

The hue and saturation of the linear matrix and the color difference matrix are determined so that there is no difference in the hue and the saturation between the samples.

The hue angle difference is obtained by processing the color difference matrix using only the diagonal term without performing a linear matrix in order to know the influence of the element of the color filter of color G. The value of the color filter was close to 0, indicating that the hue fidelity was excellent.

In particular, it is a surprising and unexpected result that even the color G filter of the present invention having a wide half width has the same hue fidelity as the color G filter having a narrow half width. Further, it can be seen that the presence of the off-diagonal term of C-MTX further reduces the slight difference in hue fidelity due to the difference in half width. The sensitivity of the wide color half width G of the present invention is
It was about 15% higher than G.

At the same time, the saturation difference between the subject color and the reproduced color when four types of signal processing were performed on these three color G filters was obtained. It can be seen that the color G filter of the present invention reproduces higher saturation than the conventional color G filter in any signal processing. In particular, even with the color G filter of the present invention having a wide half width, much higher saturation is realized as compared with the conventional color G filter. In addition, compared to the color G filter of the present invention having a narrow half width,
It is surprising that the MTX off-diagonal term is slightly inferior, but the off-diagonal term reproduces the same or higher saturation depending on the color. Further, in combination with the color G filter of the present invention, L-MTX processing is performed,
When the C-MTX processing including the off-diagonal terms is performed, the saturation becomes the highest level.

With the above-described configuration, it is possible to improve the color reproduction and the saturation more faithfully than in the prior art, and to provide an image having excellent color reproducibility. Further, it is possible to improve the color reproducibility of the image obtained through the color G filter according to the present embodiment without causing the image quality to be rough due to a decrease in the S / N ratio. In addition, even when applied to a single-panel solid-state imaging device, false colors generated in an obtained image can be suppressed, and faithful color reproduction is realized.

Further, the color reproducibility is maintained while increasing the sensitivity of the color G. These hue reproducibility, saturation and sensitivity are
Although it can be improved by using a G filter, by further performing signal processing by combining diagonal terms and / or non-diagonal terms of the linear matrix and / or the color difference matrix, the hue of the object can be made closer to the hue of the subject. A high-quality image can be obtained.

[0070]

As described above, according to the solid-state imaging device of the present invention, the color filter of the color G in the color separation means is designed so that a predetermined inclination can be obtained in the spectral sensitivity characteristic.
The slope of the curve representing the spectral sensitivity characteristic on the short wavelength side with respect to the peak wavelength becomes steep, and as a result, the spectral sensitivity at a wavelength of 470 nm or less becomes 20 or less, and the hue reproduction and saturation more faithful than the conventional one are achieved. Thus, it is possible to provide an image with improved color reproducibility. In addition, the color reproducibility can be improved without causing the image obtained through the color G filter of the present embodiment to have a rough image quality due to a decrease in the S / N ratio. In addition, faithful color reproduction is realized without deteriorating false colors generated in an obtained image even when applied to a single-plate solid-state imaging device. By increasing the half width of the color G filter, the color reproducibility is maintained while increasing the sensitivity of the color G. These color reproducibility, saturation and sensitivity can be improved by using this color G filter, but further, signal processing is also performed by combining diagonal and off-diagonal terms of a linear matrix and / or a color difference matrix. By applying, an image closer to the color of the subject can be obtained.

Further, according to the optical filter of the present invention, the spectral sensitivity can be set to this characteristic curve, and the hue fidelity and the saturation can be improved. As with the solid-state imaging device described above, even when applied to a single-chip solid-state imaging device, while suppressing false colors that occur in an image, faithful hue reproduction and high-saturation reproduction are realized, and the color G sensitivity is increased while increasing the sensitivity. Reproducibility can be maintained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration when a solid-state imaging device according to the present invention is applied to a digital still camera.

FIG. 2 is a diagram showing a characteristic curve of a color matching function corresponding to a primary color of a standard CRT defined by ITU-R709.

FIG. 3 is a diagram showing a characteristic curve of spectral sensitivities of colors R, G, and B including a conventionally used characteristic curve of color G spectral sensitivity in terms of relative sensitivity.

FIG. 4 is a schematic diagram showing how it is preferable to change the spectral sensitivity on the short wavelength side with respect to the peak wavelength in the spectral sensitivity of a color G.

FIG. 5 is a diagram illustrating the characteristics of the spectral transmission characteristics of an actual color G filter that provides the preferred color G spectral sensitivity after the modification of FIG. 4;

FIG. 6 is a schematic diagram illustrating the concept of Epstein approximation.

FIG. 7 is a chromaticity diagram showing a positional relationship between a subject color and a reproduced color of an Epstein approximation result.

FIG. 8 is a diagram illustrating a spectral sensitivity characteristic of a CCD using a color G filter having a different half-value width applied to the present embodiment and a conventional color G filter.

FIG. 9 is a diagram illustrating transmission density ratios of a color G filter applied to the present embodiment and a conventional color filter.

FIG. 10 is a diagram illustrating relative sensitivity characteristics of an image sensor of the image pickup unit used in FIG. 1;

FIG. 11 is a diagram illustrating spectral transmission characteristics of a lens and an infrared filter mounted on a digital still camera.

FIG. 12 is a diagram illustrating the chromaticity of a subject color used for comprehensive evaluation.

FIG. 13 is a diagram classifying and expressing a hue angle difference and a saturation difference between a subject color and a reproduced color obtained according to a difference in a color G filter used in each signal processing.

[Explanation of symbols]

 10 Digital still camera 12 System control unit 104 Imaging unit 114 Signal processing unit 104a Color filter unit 104b Infrared filter 114a L-MTX circuit 114b C-MTX circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H048 AA12 AA18 BB02 BB46 5C065 AA03 BB08 BB11 BB12 BB14 CC01 CC04 CC05 DD02 EE03 EE12 EE16 FF02 GG12 GG18 GG27 GG32

Claims (11)

[Claims] 1. A solid-state imaging device that separates incident light by a color separation unit, converts the separated incident light into an electric signal by an imaging unit that performs photoelectric conversion, and performs signal processing on the converted signal. Means for separating the incident light into colors G
When the relative sensitivity is expressed as a relative sensitivity where the peak of the spectral sensitivity is 100, the slope of the spectral sensitivity characteristic of the color G between the relative sensitivity 80 and the relative sensitivity 20 on the shorter wavelength side than the wavelength of the peak is expressed as A solid-state imaging device having a spectral sensitivity characteristic of substantially 2.0 or more. 2. The apparatus according to claim 1, wherein said color separation means has a spectral sensitivity characteristic of said color G of 470 nm to 400 n.
a solid-state imaging device having a relative sensitivity of 20 or less in a wavelength range of m 2. 3. The apparatus according to claim 1, wherein the color separation means has a spectral sensitivity characteristic of the color G having a characteristic of the relative sensitivity 50 at a wavelength of 500 nm or less on the short wavelength side. Characteristic solid-state imaging device. 4. The apparatus according to claim 1, wherein said color separation means has a spectral sensitivity characteristic of said color G of 575 nm or more on said longer wavelength side. A solid-state imaging device having characteristics. 5. The solid-state imaging device according to claim 1, wherein the color separation unit includes a single-plate type filter. 6. The solid-state imaging device according to claim 5, wherein the single-plate type filter is a primary color filter. 7. The solid-state imaging device according to claim 1, wherein the color separation unit uses a combination of a filter unit that blocks light of an infrared wavelength. 8. The solid-state imaging device according to claim 1, wherein the peak wavelength is in a range of a wavelength of 530 ± 15 nm. 9. The apparatus according to claim 1, wherein the signal processing includes performing a linear conversion on the supplied converted signal, and / or the calculation processing unit. A solid-state imaging device including a color-difference calculating unit that generates a color-difference signal from the signal processed in (1). 10. An optical filter that splits incident light by means of color separation and supplies the split light as incident light to an image pickup device that converts the split incident light into an electric signal. When the incident light is subjected to color separation, when the spectral transmission density of the color G is normalized by the spectral transmission density value with respect to the wavelength of the peak transmittance of the color G, the ratio normalized by the wavelength of the color G at 470 nm An optical filter characterized by having a characteristic of not less than 10 and not more than 3 at a wavelength of 500 nm. 11. The filter according to claim 10, wherein
An optical filter, wherein the peak wavelength is in a range of 530 ± 15 nm.