JP2006094112A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an imaging device which makes imaging of high sensitivity possible without necessity of a means to move an optical filter from an optical path, or a means (mechanism) for switching the optical filter, moreover, makes imaging possible, which agrees with human's color vision property, and has good color reproduction nature. <P>SOLUTION: The imaging device has a long wave length optical filter which attenuates a long wave length region in a visible region out of an input light, and makes a light of an infrared region pass through; and color filters of at least 3 colors or more, and is provided with an imaging element which outputs at least 3 kinds or more color signals corresponding to an outputted light from the long wave length optical filter. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an imaging apparatus, and more particularly to an imaging apparatus that enables imaging with high sensitivity and color imaging with good color reproducibility.

  A conventional imaging apparatus includes a lens, an imaging element that converts an optical image formed by the lens into an electrical signal, and a signal processing unit that obtains a predetermined image signal by performing signal processing on the electrical signal obtained from the imaging element. have. When a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor used as a normal image sensor is equipped with only one sheet (hereinafter referred to as a single-plate sensor) in an image pickup device, the color filter for color separation differs for each pixel. Color is configured on a single plate sensor.

  When obtaining R, G, and B color signals, R (red), G (green), and B (blue) primary color filters that transmit light bands corresponding to R, G, and B; In some cases, Mg (magenta), Cy (cyan), Ye (yellow), and G complementary color filters. Each of the color filters has a spectral transmission characteristic designed to transmit a target color using a dye or pigment, but the infrared region has a certain transmittance.

  Further, since the photoelectric conversion portion of the image sensor is mainly composed of a semiconductor such as Si (silicon), the spectral sensitivity characteristic of the photoelectric conversion portion is sensitive to infrared light having a long wavelength. Therefore, the signal obtained from the image sensor provided with the color filter also reacts to light in the infrared region. On the other hand, the color vision characteristic, which is a sensitivity characteristic for human colors, and the relative visual sensitivity characteristic, which is a sensitivity characteristic for brightness, are sensitivity characteristics from 380 nm to 780 nm, which are referred to as the visible region, and are almost in the wavelength region longer than 700 nm. Does not have.

  Therefore, in order to improve the color reproducibility of the image pickup apparatus in accordance with human color vision characteristics, an infrared removal filter for correcting visibility (hereinafter referred to as IRCF: Infrared Cut) that does not allow light in the infrared region to pass through the image pickup device. (Referred to as Filter).

  On the other hand, since IRCF diminishes light in the infrared region, when the sensitivity is more important than color reproducibility, such as a surveillance camera, it is necessary to remove the IRCF.

  Accordingly, in view of the above-described problems, a certain imaging apparatus includes an optical filter unit for correcting visibility that moves in conjunction with a diaphragm unit that adjusts the amount of incident light. Good color reproduction is obtained by correcting the visibility. On the other hand, when the illuminance is darker than a certain illuminance, the optical filter moves out of the optical path in conjunction with the aperture means, thereby performing high-sensitivity imaging using near-infrared light. Note that an infrared filter (hereinafter referred to as IRCF (Infrared Cut Filter)) is used as the optical filter means for correcting the visibility. When the visibility correction is performed, light having a predetermined wavelength or more (specifically, approximately 650 nm or more) is attenuated (for example, Patent Document 1).

  Other imaging devices use an infrared removal filter that attenuates infrared rays during high-sensitivity imaging, and combine the infrared removal filter and a band attenuation filter that attenuates yellowish green during imaging that achieves both high sensitivity and color reproduction. Then, the video signal is obtained by adjusting the mixing ratio of the R, G, and B signals by switching the filter according to the target imaging (for example, Patent Document 2).

  Furthermore, other imaging devices output a predetermined color video signal when imaged under a light source mainly including a predetermined incident light amount or visible light, and mainly include a predetermined incident light amount or less or near infrared light. In the case of imaging under a light source, there is provided means for outputting a predetermined monochrome video signal. When outputting the predetermined color video signal, white balance is corrected by setting the R, G, and B signals to a predetermined color mixture ratio (for example, Patent Document 3).

Japanese Patent Laid-Open No. 2001-36807 (page 3-6, FIG. 1-5) JP 2003-134522 A (page 3-4, FIG. 1) JP 2003-264843 A (page 5-6, FIG. 1)

  However, the image pickup apparatus described in Patent Document 1 requires a means (mechanism) for moving the IRCF in conjunction with the aperture means, and it is difficult to realize downsizing around the image pickup element. In general, a simple image pickup device (for example, a PC camera, a mobile phone camera, a TOY camera, or a consumer monitoring camera) that performs light amount adjustment using an electronic shutter of an image pickup element does not have an aperture mechanism. Therefore, when the imaging apparatus described in Patent Document 1 is applied to the simple imaging apparatus, a means (mechanism) for attaching / detaching the IRCF must be newly provided.

  Further, when a color video signal is obtained in the imaging device described in Patent Literature 2 or Patent Literature 3, the imaging device does not correct the color signal and generates a luminance signal only by adjusting the white balance. In addition, the color mixture ratio of the R, G, and B signals used for generating the luminance signal is determined without considering the human specific visual sensitivity characteristic. For this reason, the R, G, and B values corresponding to the color video signal are different from the R, G, and B values obtained by the spectral sensitivity characteristics corresponding to the human color vision characteristics. Therefore, the color video signal is a signal having a large color difference ΔE * ab (JIS Z8730). That is, in the imaging device described in Patent Document 2 or Patent Document 3, it is difficult to obtain color reproducibility that matches human color vision characteristics.

  Further, in the imaging apparatus described in Patent Document 2, as in Patent Document 1, means for switching the filter according to the target imaging is required. Further, in the imaging device described in Patent Document 3, since the R, G, and B signals are changed in predetermined color mixture ratios by switching filters, the imaging device described in Patent Document 3 is also similar to Patent Document 1. Means for switching the filter. Therefore, it is difficult to reduce the size of the imaging device described in Patent Document 2 or Patent Document 3.

  In addition, since the imaging device described in Patent Document 2 is equipped with a filter that removes infrared rays of 700 nm or more even when realizing high sensitivity, it cannot capture light in a region that is invisible to human eyes. .

  The present invention has been made to solve the above-described problems, and does not require means for moving the optical filter from the optical path or means (mechanism) for switching the optical filter. It is an object of the present invention to obtain an imaging device that enables imaging with high sensitivity and also enables imaging with good color reproducibility that matches human color vision characteristics.

  The imaging apparatus according to the present invention has a long wavelength optical filter that attenuates a long wavelength region in the visible region and transmits light in an infrared region out of incident light, and a color filter of at least three colors, An image pickup device that outputs at least three or more color signals corresponding to light emitted from the long wavelength optical filter.

  According to the imaging device of the present invention, it is possible to perform imaging with high sensitivity without requiring a means for moving the optical filter from the optical path or a means (mechanism) for switching the optical filter, and It is also possible to perform imaging with good color reproducibility that matches human color vision characteristics. In high-sensitivity imaging, it is also possible to perform imaging corresponding to light in the near infrared region that is invisible to the human eye without removing the optical filter.

Embodiment 1 FIG.
FIG. 1 is a block diagram illustrating a configuration of the imaging apparatus according to the first embodiment. In FIG. 1, a lens 1 condenses light reflected from a subject imaged by the imaging device so as to form an image on a light receiving surface of an imaging element 3. Then, the condensed light is incident on the optical filter 2.

  The optical filter 2 is disposed between the lens 1 and the image sensor 3 and attenuates light in a predetermined wavelength range (details will be described later) among the incident light. And the light radiate | emitted from the said optical filter 2 injects into the said light-receiving surface.

  FIG. 2 is an explanatory diagram for explaining the transmittance of the optical filter 2 in the first embodiment. As shown in FIG. 2, the optical filter 2 in the first embodiment has a low transmittance for light corresponding to a wavelength range from about 700 nm to about 780 nm, and has a transmittance for light in other regions. high. In the following description, the optical filter 2 is referred to as a long wavelength optical filter 2 or a NIRBCF 2 (Near Infrared Band Cut Filter).

  The imaging device 3 outputs an R signal, a G signal, or a B signal (hereinafter, the R signal, the G signal, or the B signal is also referred to as a color signal) corresponding to the light emitted from the NIRBCF 2 to the amplification unit 4. As the image sensor 3, for example, a charge coupled device (CCD) sensor or a complementary metal oxide semiconductor (CMOS) sensor is used.

  When the image pickup apparatus includes only one CCD sensor or CMOS sensor (hereinafter referred to as a single plate sensor), a color filter that performs color separation of light incident on the single plate sensor (hereinafter referred to as a color separation filter). Is arranged on the single plate sensor. The color separation filter is configured by a plurality of color filters provided in association with each pixel in the image sensor 3.

  As the color separation filter, for example, when obtaining color signals corresponding to R, G, and B colors, R (red) and G (green) that transmit light bands corresponding to R, G, and B are transmitted. ), A primary color filter composed of B (blue) color filters can be used. A complementary color filter composed of color filters of Mg (magenta), Cy (cyan), Ye (yellow), and G can also be used. In the first embodiment, a case where a primary color filter is provided on the image sensor 3 will be described.

  More specifically, the above-described imaging device 3 such as a CCD or a CMOS is configured to include a photodiode (not shown), and the photodiode constitutes a pixel of the imaging device. The primary color filter is disposed on the image sensor 3, and an R filter that allows R light to pass through, a G filter that allows G light to pass, and a B filter that allows B light to pass over the photodiode. Is placed.

  An R signal is generated in the photodiode corresponding to the R filter, a G signal is generated in the photodiode corresponding to the G filter, and a B signal is generated in the photodiode corresponding to the B filter, and the R signal, the G signal, and the B signal are generated. Is output from the imaging device 3 to the amplifying means 4.

  The amplifying unit 4 amplifies the signal output from the image sensor 3 and outputs the amplified signal to an A / D converter 5 (hereinafter referred to as ADC 5). The ADC 5 converts the signal output from the amplifying unit 4 into a digital signal and outputs the digital signal to the DC reproducing unit 6. The DC reproducing means 6 reproduces the DC level based on the digital signal output from the ADC 5 and outputs the R signal, G signal, and B signal to the integrating means 7 and the white balance means 10.

  Normally, the DC reproduction in the DC reproduction means 6 is normally performed by DC-shifting the offset level of the video signal output from the amplification means 4 so that the black level of the input video signal becomes zero. Alternatively, it is performed by performing a clamping process on the video signal. In the following description, the R signal, G signal, and B signal output from the DC reproducing means 6 are respectively referred to as the first R signal, the first G signal, the first B signal, or R1, G1, It is called B1.

  The integrating means 7 corresponds to the integrated values ΣR1, G1 corresponding to R1 by integrating the values corresponding to each of R1, G1, B1 output from the DC reproducing means 6 for each screen of at least one screen. The integrated value ΣG1 and the integrated value ΣB1 corresponding to B1 are calculated. Then, a signal corresponding to each integrated value is output to the dividing means 8.

  The dividing means 8 divides ΣR1 or ΣB1 output from the integrating means 7 by ΣG1, and calculates the ratios ΣR1 / ΣG1 and ΣB1 / ΣG1 of the integrated values. Then, the ratios ΣR1 / ΣG1 and ΣB1 / ΣG1 of the integrated values are output to the reciprocal computing means 9. The reciprocal calculation means 9 calculates the reciprocal of the ratio of the integrated values, that is, the reciprocal of ΣR1 / ΣG1 (hereinafter also referred to as the first reciprocal) and the reciprocal of ΣB1 / ΣG1 (hereinafter also referred to as the second reciprocal). And output to the white balance means 10.

  White balance means (hereinafter also referred to as WB (White Balance) means 10) includes R 1, G 1, B 1 output from the DC reproducing means 6, and the first inverse number and the first inverse number output from the inverse number calculation means 9. White balance is performed based on the reciprocal of 2.

  More specifically, the WB means 10 has amplification means (not shown) corresponding to each of R1, G1, and B1, and the amplification means corresponding to R1 has a first inverse (ΣR1 / ΣG1). R1 is amplified using a coefficient (gain) as a coefficient. Similarly, the amplification means corresponding to B1 amplifies B1 using the second reciprocal (reciprocal of ΣB1 / ΣG1) as a coefficient (gain). The coefficient in the amplification means corresponding to G1 is “1”.

  As described above, the WB means 10 performs white balance by amplifying R1, G1, and B1 by the amplifying means corresponding to each signal, and the R signal, G signal, and B signal after the white balance are obtained. Output to the color signal correction means 11. In the following description, the R signal, G signal, and B signal output from the white balance means 10 are respectively used as the second R signal, the second G signal, the second B signal, or R2, G2, and B2. That's it.

  The color signal correcting unit 11 performs a matrix operation based on R2, G2, and B2 output from the WB unit 10 to thereby determine a target color in which the color of an image obtained by the imaging apparatus is predetermined (details will be described later). ), R2, G2, and B2 are corrected to match. Then, the R signal, G signal and B signal obtained as a result of the correction are output to the γ (gamma) correction means 12.

The matrix coefficient used for the matrix calculation performed in the color signal correcting unit 11 is set based on the target color (details will be described later). In the following description, the color signals output from the color signal correcting unit 11 are referred to as R _ideal , G _ideal , and B _ideal , respectively.

  More specifically, the color signal correcting unit 11 performs a linear matrix operation such as the following Equation 1 based on R2, G2, and B2, and R so that the color reproduced by the imaging apparatus becomes the target color. , G and B signals are corrected.

  In Equation 1, r11, r12, r13, g11, g12, g13, b11, b12, and b13 are matrix coefficients, which are predetermined constants (details will be described later). Hereinafter, the matrix coefficient is referred to as a correction matrix coefficient, and a matrix composed of the correction matrix coefficient is referred to as a correction coefficient matrix.

The γ correction unit 12 performs gamma correction on R _ideal , G _ideal , and B _ideal output from the color signal correction unit 11. Specifically, nonlinear tone conversion is performed on the color signal output from the color signal correction unit 11. The YCrCb conversion unit 13 converts R _ideal , G _ideal , and B _ideal output from the γ correction unit 12 into a Y signal, a Cr signal, and a Cb signal and outputs the signals. The Y signal is a luminance signal, and the Cr signal and the Cb signal are color difference signals.

Normally, conversion from a color signal (R _ideal , G _ideal , B _{ideal in the} first embodiment) into a luminance signal or a color difference signal is performed by matrix operation of the color signal and a coefficient matrix of 3 rows and 3 columns. Specifically, the linear matrix calculation shown in the following formula 2 is performed.

  Note that the matrix coefficient in the coefficient matrix of 3 rows by 3 columns in Equation 2 (hereinafter also referred to as a conversion matrix coefficient, and a matrix composed of the conversion matrix coefficient is referred to as a conversion coefficient matrix) is, for example, IEC (International Electronic). (Commission) 61966-2-1, ie, y11 = 0.2990, y12 = 0.5870, y13 = 0.1140, Cr21 = −0.1687, Cr22 = −0.3313, Cr23 = Use 0.5000, cb31 = 0.5000, cb32 = −0.4187, cb33 = −0.0813.

  The luminance signal and the color difference signal output from the YCrCb conversion unit 13 are processed according to the device or system to which the imaging device is applied. For example, when the imaging apparatus is applied to a digital camera or a mobile phone, the luminance signal and color difference signal output from the YCrCb conversion unit 13 are subjected to JPEG compression, and then a memory unit such as a semiconductor memory or a predetermined recording medium. Saved in. When the luminance signal and the color difference signal output from the YCrCb conversion unit 13 are used as a television signal, the luminance signal and the color difference signal are encoded into, for example, an NTSC signal.

  Details of color signal correction (hereinafter, color signal correction is also referred to as color correction) in the color signal correction means 11 will be described below.

  FIG. 3 is an explanatory diagram for explaining R, G, and B spectral sensitivity characteristics (also referred to as RGB color system color matching functions or simply color matching functions) representing human color vision characteristics. In FIG. 3, the horizontal axis represents wavelength, and the vertical axis represents tristimulus values.

  The characteristic shown in FIG. 3 is an average value of the color matching function of a normal color vision person, and is defined by CIE (Commission Internationale de l'E'claage) 1931.

If colors that humans perceive can be simply expressed by ignoring the adaptation function (for example, chromatic adaptation) provided by human color vision, color matching functions (corresponding to the R, G, and B colors shown in FIG. A value obtained by multiplying r ₁ (λ), g ₁ (λ), b ₁ (λ)), the spectral reflectance of the object, and the spectral radiant intensity of the illumination, and integrating the result of multiplication for each color in the visible region ( 3 integrated values integrated for each color of R, G, and B). The color matching functions are known, and the spectral reflectance of the subject and the spectral radiant intensity of the illumination are uniquely determined if the subject and the illumination are determined. Therefore, the three integrated values can be obtained by determining the subject and the illumination. In the imaging apparatus according to Embodiment 1, the color obtained from the color matching function shown in FIG. 3 is used as a color target. Also, color reproducibility is good when a color close to the color obtained from the color matching function can be reproduced.

  As shown in FIG. 3, human color vision has sensitivity only in a wavelength range from approximately 380 nm to approximately 780 nm, which is called a visible region. Even within the visible region, there is almost no sensitivity characteristic on the long wavelength side of the visible region, specifically, in the region where the wavelength is longer than about 700 nm.

  On the other hand, the imaging device 3 constitutes the imaging device 3, and a photodiode for performing photoelectric conversion is formed of a semiconductor such as Si (silicon). Therefore, the image sensor 3 has sensitivity characteristics from the visible region to the infrared region (near 1000 nm). Therefore, when an RGB color filter for color separation is provided in the image sensor 3, R, G, and B signals corresponding to the product of the spectral characteristics of the color filter and the spectral sensitivity characteristics of the photodiode are output from the image sensor 3. Is done.

FIG. 4 is an explanatory diagram for explaining the spectral sensitivity characteristics of the image sensor 3. FIG. 4 shows the spectral sensitivity characteristics of the R, G, B signals of the image sensor 3 represented by the product of the spectral characteristics of the color filter and the spectral sensitivity characteristics of the photodiodes constituting the image sensor 3. The vertical axis represents spectral sensitivity characteristics, and the horizontal axis represents wavelength. In the figure, r ₂ (λ) is a spectral sensitivity characteristic for R, g ₂ (λ) is a spectral sensitivity characteristic for G, and b ₂ (λ) is a spectral sensitivity characteristic for B.

The spectral sensitivity characteristic will be described in detail. In FIG. 4, the spectral sensitivity characteristic (b ₂ (λ)) corresponding to the B signal gradually increases when the wavelength is about 380 nm, and is about 450 nm. After the value becomes maximum, the value gradually decreases and decreases in a wavelength region larger than about 550 nm. And it has the characteristic that the value increases again when the wavelength is about 800 nm, which is the infrared region.

In addition, the spectral sensitivity characteristic (g ₂ (λ)) corresponding to the G signal gradually increases when the wavelength is about 450 nm, and gradually decreases after reaching the maximum value near about 550 nm. The value is minimum in the vicinity of about 650 nm. And it has the characteristic that the value increases again when the wavelength is about 700 nm. Further, the spectral sensitivity characteristic (r ₂ (λ)) corresponding to the R signal gradually increases as the wavelength reaches approximately 560 nm, reaches a maximum in the vicinity of approximately 600 nm, and gradually increases over the infrared region. It has the characteristic that the value becomes smaller.

  Since the R color filter has a relatively higher transmittance in the infrared region than other color filters, the image sensor 3 is sensitive to infrared rays. Similarly, the B color filter for incident B light and the G color filter for incident G light have a constant transmittance in the infrared region. This is because the R, G and B color filters are usually constructed using dyes and pigments containing the respective colors, but the spectral transmittance depends on the constituent materials, and from the long wavelength side in the visible region. This is because the transmittance increases again in the infrared region.

Here, the color matching function (human color vision characteristic) shown in FIG. 3 and the spectral sensitivity characteristics (r ₂ (λ), g ₂ (λ), b ₂ (λ)) of the image sensor 3 shown in FIG. , The image pickup device 3 is sensitive in the wavelength range from the long wavelength side of the visible region to the infrared region, but the human color vision characteristic is greatly different in that it does not have sensitivity in the wavelength range. In particular, the difference in spectral sensitivity characteristics in the infrared region (780 nm to 1100 nm) is significant.

  Therefore, in the conventional imaging device, in view of the difference in the infrared region between the color matching function and the spectral sensitivity characteristic of the imaging element 3, red light is excluded in order to eliminate the influence of the spectral characteristic of the imaging element 3 in the infrared region. An outer cut filter (IRCF) is disposed between the lens 1 and the image sensor 3 to remove light in the infrared region.

  The IRCF used in a conventional imaging apparatus has a light transmittance of 100% in a short wavelength region to a wavelength of approximately 650 nm, and the transmittance sharply decreases in a wavelength range of approximately 650 to 700 nm. Thereafter, the transmittance in the long wavelength region (infrared region) where the sensitivity of the imaging device is lost is approximately 0%.

  FIG. 5 is an explanatory diagram for explaining an example of the transmittance of the IRCF. The example shown in FIG. 5 has a characteristic of removing all infrared rays having a wavelength of about 750 nm or more, with about 700 nm as a half value (50% transmittance).

  The IRCF has different transmittance characteristics depending on the configuration of the IRCF and the material used. The IRCF in the example shown in FIG. 5 is an IRCF configured by stacking a plurality of thin films using light interference, and has a feature that a steep cut-off characteristic can be realized. In addition, IRCF configured by stacking a plurality of thin films has a characteristic that the transmittance value increases again on the long wavelength side in the infrared region, and the IRCF shown in FIG. 5 has a high transmittance again at approximately 1000 nm. It has become. However, since the value of the spectral sensitivity characteristic of the image sensor is approximately 0 near 1000 nm, the value of these products is approximately 0, and the color reproducibility is not affected.

  On the other hand, as an example of IRCF utilizing light absorption, IRCF called blue glass is usually used. In the case of blue glass, a steep cut-off characteristic cannot be realized, and the half value is approximately 650 nm. Regardless of which IRCF is used, the purpose of using the IRCF is to bring the spectral sensitivity characteristic of the image sensor closer to a color matching function. Therefore, the IRCF is designed to have a cut-off characteristic such that the transmittance of 700 nm or more is substantially zero.

FIG. 6 is an explanatory diagram for explaining spectral sensitivity characteristics of a conventional imaging apparatus. In FIG. 6, IRCF (λ) indicates the transmittance of the IRCF shown in FIG. 5, and r ₂ (λ), g ₂ (λ), and b ₂ (λ) indicate the spectral sensitivity characteristics described in FIG. Further, r ₃ (λ), g ₃ (λ), and b ₃ (λ) are spectral sensitivity characteristics (r ₂ (λ), g ₂ (λ), b ₂ (λ)) in FIG. 4 and in FIG. This is a spectral sensitivity characteristic obtained from the product of the IRCF transmittance (that is, the spectral sensitivity characteristic of a conventional imaging device).

As described above, the conventional imaging apparatus performs imaging with the spectral sensitivity characteristics of the imaging element 3 indicated by r ₃ (λ), g ₃ (λ), and b ₃ (λ) in FIG. The spectral sensitivity characteristic of the conventional imaging device shown in FIG. 6 is different from the color matching function shown in FIG. For this reason, the spectral sensitivity characteristics of the conventional imaging apparatus shown in FIG. 6 cannot provide the same color reproducibility as the image obtained from the color matching function shown in FIG. However, since almost the same color reproducibility can be obtained, it has been said that a sufficient performance can be obtained with this characteristic in the conventional imaging apparatus. The color reproducibility here means to roughly match the colors that can be seen by the human eye, and colors that look different to the eyes will be reproduced as different colors, and colors that appear to be the same will be reproduced as the same color. .

  As described above, the spectral sensitivity characteristic of the image pickup device 3 alone and the human sensitivity characteristic are remarkably different from each other particularly in the infrared region. Therefore, IRCF is inserted in front of the image pickup device 3 to approximate the spectral sensitivity characteristic. Had gone. Note that the color reproducibility obtained from the spectral characteristic of the human sensitivity characteristic shown in FIG. 3 is used as the color reproducibility color target in this embodiment.

  FIG. 7 is an explanatory diagram for explaining the spectral sensitivity characteristics of the imaging apparatus according to the first embodiment. As shown in FIG. 7, the spectral sensitivity characteristic of the imaging apparatus according to the first embodiment is expressed by the product of the transmittance of NIRBCF2 (FIG. 2) and the spectral sensitivity characteristic of imaging element 3 (FIG. 4). The spectral sensitivity characteristic has no sensitivity only in the wavelength region that is not transmitted. The signal output from the image sensor 3 in the image pickup apparatus according to the first embodiment is a spectral sensitivity characteristic represented by the product of the transmittance of the NIRBCF 2 (FIG. 2) and the spectral sensitivity characteristic of the image sensor 3 (FIG. 4). That is, the value is obtained through the spectral sensitivity characteristic shown in FIG.

  Next, the operation of the color signal correction unit 11 will be described. As described above, the color signal correcting unit 11 receives the signals R2, G2, and B2 output from the WB unit 7 and performs the linear matrix calculation shown in Equation 1 to set the target color as the Rideal, Gideal, Bideal is calculated.

  Here, the correction matrix coefficients of the color signal correction means 11 can be calculated as follows, for example. As an evaluation chart for evaluating color reproducibility, there is a MACBETH color checker (hereinafter, simply referred to as a color checker) having 24 types of color patches (color charts). MACBETH is a registered trademark of “Gretag-Macbeth Holding Aktiengesellschaft.

  The color checker includes many color patches (color charts) representing existing colors as subjects, and has 24 color patches that emphasize human memory colors (skin color, plant green, sky blue, etc.). It is a chart. The 24 types of color patches are: 1 dark skin color, 2 light skin color, 3 blue sky color, 4 grass color, 5 blue flower, 6 bluish green, 7 orange and 8 : Purple blue, 9: medium red, 10: purple, 11: yellow green, 12: orange yellow, 13: blue, 14: green, 15: red, 16: yellow, 17: magenta, 18 : Cyan, 19: white, 20: gray 8, 21: gray 6.5, 22: gray 5, 23: gray 3.5, 24: black.

  FIG. 8 is an example of the differential reflectance from 300 nm to 1200 nm for the color patches included in the Macbeth color checker. Specifically, 1: dark skin color, 2: bright skin color, 4: grass color, 6: bluish green, 11: yellowish green, 13: blue, 14: green are shown as examples.

  The product of the spectral sensitivity characteristic shown in FIG. 7, which is the product of the spectral sensitivity characteristic of the image sensor 3 in Embodiment 1 and the transmittance of the NIRBCF2, the spectral radiant intensity of illumination, and the spectral reflection characteristic of the color checker ( From the first product), R, G, and B values corresponding to each color patch can be calculated. On the other hand, the R, G, and B values corresponding to the color target are the color matching function shown in FIG. 3 and the spectral radiant intensity of the illumination used for calculating the R, G, and B values corresponding to each color patch. , And can be obtained in the same manner from the product (second product) with the spectral reflection characteristic of the color checker.

  Then, the R, G, and B values corresponding to the 24 types of color patches calculated by the first product and the R, G, and B values corresponding to the 24 types of color patches calculated by the second product are used. Nine correction matrix coefficients in the correction coefficient matrix shown in Equation 1 can be calculated using the least square error method so that the difference from the value (color target) is minimized. In the imaging apparatus of Embodiment 1, the correction matrix coefficient is calculated using the spectral radiation intensity corresponding to the illumination of 5000K.

  As described above, by calculating the correction matrix coefficient and setting it in the color signal correction means 11, the color signal can be corrected and good color reproducibility can be obtained.

  Hereinafter, setting of the wavelength range to be attenuated in the NIRBCF 2 will be described. Usually, in designing color reproducibility, a Macbeth color checker is a typical example used as an evaluation chart.

  On the other hand, the correction matrix coefficient is a coefficient calculated using only the color patch included in the color checker with the subject as a color checker. The color checker is created to cover as much as possible the characteristic colors existing in nature, but the spectral reflectance of the color checker is created taking into consideration only the visible region. That is, the spectral reflectance in the infrared region is not considered. Therefore, when the correction matrix coefficient calculated by the color checker is used, the color of the subject is good due to the influence of the infrared region of the spectral reflectance corresponding to the color of the subject imaged by the imaging device. There are cases where reproduction cannot be realized. In the following description, a subject color for which good color reproducibility cannot be realized by the imaging apparatus is referred to as an exceptional color.

  Here, for example, in the visible region, the influence of the infrared region has a tendency that the spectral reflectance of the subject and the spectral reflectance of the color patch are similar (that is, the same color for human eyes). This is a case where the color reproduced by the imaging device is different from the actual color due to the large value of the spectral reflectance of the subject in the infrared region.

  Exceptional colors include, for example, foliage and synthetic clothing. For example, the green color of the paint and the leaves of the leaves appear to be the same color to the human eye (that is, the tendency of the spectral reflectance of both in the visible region is the same), but the spectral reflectance and the paint in the infrared region of the leaves of the tree are the same. Due to the difference in the spectral reflectance in the green infrared region, the color of the leaves of the tree reproduced in the imaging device and the color of the paint are different.

  FIG. 8 is an explanatory diagram for explaining the spectral reflectance corresponding to a leaf of a tree which is an example of an exceptional color. In FIG. 8, examples of green color in the color checker include grass color (foliage), blue green (green), yellow green (yellow green, green), and leaves of trees naturally occurring in nature (leaves (1), The spectral reflectance of the leaves (2)) of the tree was shown.

  For example, when reproducing the color of a leaf, the color patch of the grass color shown in FIG. 8 is used. The spectral reflectance corresponding to the color of the grass and the spectral reflectance corresponding to the leaf (1) or the leaf (2) of the tree have the same tendency in the visible light region in that it has a peak at 500 nm to 600 nm. . The same applies to other green colors. However, for the leaf (1) or the leaf (2) of the tree, the spectral reflectance value suddenly increases from around 700 nm, unlike other colors.

  As described above, the human eye has little sensitivity on the long wavelength side from around 700 nm. Therefore, human eyes recognize colors having similar spectral reflectances in the visible region as substantially the same color as shown in FIG. However, as shown in FIG. 4, the spectral sensitivity characteristic of the image sensor 3 has sensitivity even in the infrared region, so that it is sensitive to light in the infrared region that cannot be recognized by human eyes. . For this reason, when the imaging device 3 that is sensitive to light in the infrared region is used, the color reproduction obtained by the imaging device is greatly different. Specifically, when the ratio of the R signal becomes larger than necessary with respect to the G signal or the B signal, the color of the leaves of the tree, which should be green, is reproduced brownish.

  FIG. 9 is an explanatory diagram for explaining the spectral reflectance corresponding to the clothes of synthetic fibers, which is another example of the exceptional color. FIG. 9 shows the spectral reflectance corresponding to blue clothing (hereinafter referred to as blue clothing), which is an example of a synthetic fiber clothing, and the spectral reflectance corresponding to blue in the color checker.

  The spectral reflectance corresponding to blue clothes and the spectral reflectance corresponding to blue tend to be similar in the visible light region in that they have a peak in the vicinity of 450 nm. However, for blue clothing, the value of spectral reflectance rapidly increases from around 650 nm. Therefore, as in the case of the leaves (1) and leaves (2) of the tree, in the case of human eyes that do not respond to the infrared region, the blue color of the blue clothes and the blue color of the color checker appear to be the same blue, In the case of an imaging device that is sensitive to the outside region, the blue color of the blue clothes and the blue color of the color checker are reproduced as different colors. Specifically, when the ratio of the R signal becomes larger than necessary with respect to the G signal or the B signal, the blue clothes that should originally be blue are reproduced in purple.

  Therefore, the wavelength range attenuated by the NIRBCF2 is such that the color reproduced by the imaging device and the color recognized by the human eye are suppressed by suppressing the R signal from becoming larger than necessary for the exceptional colors. It is set so that color reproducibility so as to obtain substantially the same color can be obtained and light having a long wavelength is transmitted to such an extent that imaging with high sensitivity is possible. For the above reasons, in the NIRBCF2 used in the first embodiment, it is possible to suppress the R signal from becoming larger than necessary by attenuating the wavelength range of 700 nm to 780 nm and to be longer than 780 nm that transmits the NIRBCF2. High-sensitivity imaging using wavelength light is possible.

  FIG. 11 is an explanatory diagram for describing signal levels (hereinafter referred to as signal levels) corresponding to R, G, and B output from the image sensor 3 according to the first embodiment. In FIG. 11, the horizontal axis represents the name of the subject, and the vertical axis represents the signal level. In addition, R, G, and B shown in the bar graph indicate R signal, G signal, and B signal, respectively, and the numbers given on each bar graph indicate the values of signal levels corresponding to the respective color signals.

  11A shows the spectral sensitivity characteristic shown in FIG. 4 (that is, the product of the spectral sensitivity characteristic of the color filter and the spectral sensitivity characteristic of the photodiode constituting the image sensor 3), the spectral radiant intensity of illumination, And the signal level calculated from the product of the spectral reflectance of the subject.

  On the other hand, FIG. 11B shows the spectral sensitivity characteristic shown in FIG. 7 (that is, the product of the transmittance of NIRBCF2, the spectral sensitivity characteristic of the color filter, and the spectral sensitivity characteristic of the photodiode constituting the imaging device 3), It is a signal level obtained by calculating from the product of the spectral radiation intensity of illumination and the spectral reflectance of the subject.

  Note that the spectral radiant intensity of the illumination used for the calculation of the signal level in FIGS. 11A and 11B is a spectral reflection intensity corresponding to an illumination of 5000K. Among the spectral reflectances of the subject, dark skin color and light skin color are spectral reflectances of Macbeth color checker (FIG. 7), and leaves (1) and leaves (2) of leaves are the leaves (1) and leaves shown in FIG. It is a spectral reflectance of a leaf (2) of a tree.

  Since “dark skin color” and “light skin color” in FIGS. 11A and 11B are not exceptional colors, the imaging apparatus can reproduce colors close to a color target. However, since “leaves (1)” and “leaves (2)” are exceptional colors, in the conventional imaging device, as shown in FIG. The level of the R signal becomes larger than that of the signal or the B signal. As a result, the ratio of the R signal to the G signal or B signal corresponding to “leaves (1)” or “leaves (2)” is similar to “dark skin color” and “light skin color”.

  Then, when reproducing the green color of “leaves (1)” and “leaves (2)”, if the signal level of the R signal is too large relative to the signal level of the G signal, the WB in the subsequent stage of the imaging device 3 Even if white balance or color correction is performed in the means 10 or the color signal correction means 11, the R signal cannot be corrected accurately. Therefore, the green color of the leaves cannot be accurately reproduced. As a result, the leaf color reproduced by the imaging device is reproduced as a skin color or brown color in the target color of the first embodiment.

  On the other hand, when NIRBCF2 is used, the signal level of the R signal is suppressed as shown in FIG. This is because light of 700 nm to 780 nm is attenuated by the NIRBCF2. In particular, for “leaves (1)” and “leaves (2)”, the range in which the spectral reflectance value suddenly increases (near 700 nm in FIG. 9) can be removed. The magnitude (ratio) of the signal level of the R signal can be adjusted effectively. That is, unlike the case of FIG. 11A, the ratio of the R signal to the G signal or the B signal can be reduced.

  As described above, according to the imaging apparatus in the first embodiment, it is possible to achieve high sensitivity without requiring a means for moving the optical filter from the optical path or a means for switching the optical filter. Color imaging with good imaging and color reproducibility can be made possible.

  Further, by appropriately selecting the wavelength range to be attenuated by the NIRBCF 2 according to the spectral sensitivity characteristics of the image sensor used in the imaging device according to the first embodiment and the spectral emissivity of the subject, the influence of the infrared region is suppressed, Good color reproducibility can be obtained for all of the colors other than the exceptional colors and the exceptional colors.

  Furthermore, since the imaging apparatus according to Embodiment 1 also has sensitivity to the infrared region, monochrome high-sensitivity imaging can be realized only by switching the signal processing method.

  Further, since no means for moving and switching the optical filter is required, the image pickup apparatus can be easily downsized.

  In the first embodiment, leaf color and blue clothing have been described as examples of exceptional colors. However, the imaging apparatus according to the first embodiment has a sharp spectral reflectance value on the infrared region side in the visible light region. As with the leaves and blue clothes, good color reproducibility can be obtained with respect to the color of the subject that rises rapidly.

  In the first embodiment, the case where the wavelength range attenuated by NIRBCF2 is set to 700 nm to 780 nm has been described. However, as long as the wavelength in the infrared region can be transmitted to some extent for high-sensitivity imaging, A wider wavelength range may be set. Therefore, for example, the wavelength range in which light is attenuated may be 700 nm to 850 nm.

  In the first embodiment, the predetermined correction matrix coefficients are calculated using 24 colors of Macbeth color checker. However, the spectrum of evaluation colors of 24 colors or more including the leaves and the colors of the synthetic fibers described above as exceptional colors is added. The correction matrix coefficient may be calculated using the reflectance so that the color difference with respect to the color target is minimized by the least square method.

  In the first embodiment, the case where the color signal correction unit 11 sets the correction coefficient matrix of 3 rows and 3 columns has been described. For example, a first correction coefficient matrix corresponding to colors other than exceptional colors, You may set the 2nd correction coefficient matrix corresponding to exceptional colors, such as the color of a leaf or a synthetic fiber.

Further, in the first embodiment, the case where an image sensor having a primary color filter composed of R, G, and B color filters is used has been described. However, the image sensor is composed of Ye, Mg, Cy, and G color filters. An image sensor provided with a complementary color filter can also be used. When a complementary color filter is used, a correction coefficient matrix of 3 rows and 4 columns shown in the following equation 3 is set in the color signal correction unit 11 and an appropriate correction matrix coefficient is set as in the case of using a primary color filter. calculate.

Embodiment 2. FIG.
FIG. 12 is a block diagram illustrating a configuration of the imaging apparatus according to the second embodiment. In the following description, the same reference numerals are given to the configurations described in the first embodiment, and description thereof is omitted. In FIG. 12, the color signal correction means 21 includes a storage means 21a and a selection means 21b.

  The storage unit 21 a stores a plurality of correction matrix coefficients used for matrix calculation of the color signal correction unit 21. The plurality of correction matrix coefficients are set according to the color temperature of the illumination used when imaging is performed by the imaging device (details will be described later).

  The selection unit 21b specifies the color temperature of the illumination based on the ratio of the integrated values input from the division unit 8, and reads the correction matrix coefficient stored in the storage unit 21a. The color signal correcting unit 21 performs matrix calculation using the correction matrix coefficient selected by the selecting unit 21a.

  FIG. 13 shows the spectral radiation intensity corresponding to illumination with a color temperature of 3000K, and FIG. 14 shows the spectral radiation intensity corresponding to illumination with a color temperature of 6500K. Comparing FIG. 13 and FIG. 14, it can be seen that the spectral radiation intensity varies depending on the color temperature.

  For example, when the spectral sensitivity characteristic of the image pickup device and the color matching function shown in FIG. 3 are indicated by the same curve, the color reproduced by the image pickup device is obtained by performing white balance in the WB means 10. Good color reproduction can always be obtained without being affected by the change in the spectral radiation intensity of illumination.

  However, as described in Embodiment 1, the spectral sensitivity characteristic (FIG. 7) and the color matching function (FIG. 3) of the imaging apparatus are greatly different. Therefore, in the case of the correction matrix coefficient calculated under the illumination of 5000K in the first embodiment, good color reproducibility can be obtained (conditional color matching) in the imaging under the illumination of 5000K, but the color temperature is Under different illuminations, good color reproducibility is not always obtained.

  That is, for example, the correction matrix calculated in the first embodiment in imaging under illumination with different color temperatures, such as imaging under 3000K illumination shown in FIG. 13 or imaging under 6500K illumination shown in FIG. When the coefficient is used, the color reproducibility obtained by the imaging apparatus becomes different color reproducibility.

  For this reason, in the imaging apparatus according to the second embodiment, optimal correction matrix coefficients are calculated in advance under illumination with different color temperatures, and are stored in the storage unit 21a. The calculation of the correction matrix coefficient can be performed by the method described in the first embodiment. That is, the R, G, and B values corresponding to the product of the spectral radiant intensity corresponding to the illumination of the color temperature set arbitrarily, the spectral reflectance of the color checker, and the spectral sensitivity characteristic of the imaging device (FIG. 7), and the same color Calculated by the least square error method so that the difference between the function, the spectral radiant intensity corresponding to the illumination of the color temperature set arbitrarily, and the R, G, B values corresponding to the product of the spectral reflection characteristics of the color checker is minimized. can do.

  FIG. 15 is an explanatory diagram for explaining the relationship between the ratio of integrated values input from the dividing means 8 and the color temperature. In FIG. 15, the horizontal axis represents the ratio of the integrated value of R1 to the integrated value of G1 (ΣR1 / ΣG1), and the vertical axis represents the ratio of the integrated value of B1 to the integrated value of G1 (ΣB1 / ΣG1). In the figure, ◯ indicates points corresponding to each color temperature.

  As shown in FIG. 15, the relationship between ΣR1 / ΣG1 and ΣB1 / ΣG1 is uniquely determined according to the color temperature. That is, if ΣR1 / ΣG1 or ΣB1 / ΣG1 is known, the color temperature of the illumination can be specified.

  Therefore, the curve shown in FIG. 15 is set in advance in the selection means 21b. Then, the selection unit 21b selects the correction matrix coefficient stored in the storage unit 21a according to the ratio of the integrated values output from the division unit 8. That is, the correction matrix coefficient corresponding to the color temperature indicated by the integrated value ratio is selected.

  The color signal correcting unit 11 corrects the color signal by performing matrix calculation using the correction matrix coefficient selected by the selecting unit 21b. Note that the matrix calculation in the color signal correction means 21 in the second embodiment is expressed by the following formula 4.

  Note that (ΣR1 / G1 or ΣB1 / ΣG1) given to each correction matrix coefficient in Expression 4 indicates that the correction matrix coefficient is selected by the ratio (ΣR1 / G1 or ΣB1 / ΣG1) of the integrated value output from the dividing unit 8.

  As described above, according to the imaging apparatus in the second embodiment, the correction matrix coefficient is selected according to the color temperature, and the matrix calculation is performed using the selected correction matrix coefficient to perform the color correction. Thus, good color reproduction can be obtained even under illumination with different color temperatures.

  In the description of the second embodiment, the case where the curve shown in FIG. 15 is stored in the selection unit 21b has been described. However, the curve need not be stored. For example, the curve has a predetermined color temperature. Corresponding points (for example, points corresponding to 3000K, 4000K, 5s000K and 6000K in FIG. 15) are stored, and the correction corresponding to the color temperature indicated by the closest point of the integrated value input to the selection means 21b. Matrix coefficients may be selected.

Embodiment 3 FIG.
FIG. 16 is a block diagram illustrating a configuration of the imaging device according to the third embodiment. Note that the imaging apparatus is configured by each unit within the broken line in FIG. In FIG. 16, the same components as those in the first or second embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The change-over switch 34 is used to select color imaging (hereinafter also referred to as a first imaging mode) or imaging with increased sensitivity (hereinafter also referred to as a second imaging mode) in the imaging apparatus. Operated by the user. Then, the control unit 35 outputs a signal (hereinafter also referred to as a selection signal) corresponding to the imaging mode indicated by the changeover switch 34 to the color signal correction unit 31 and the YCrCb conversion unit 33.

  The color signal correction unit 31 includes a first storage unit 31a and a selection unit 31b. The first storage unit 31a and the correction matrix coefficient described in the first embodiment and the matrix coefficient (hereinafter referred to as the matrix coefficient) set so that the R, G, and B signals are output from the color signal correction unit 31 without being corrected. (Referred to as uncorrected matrix coefficients). The non-correction matrix coefficients are specifically r11 = 1, r12 = 0, r13 = 0, g21 = 0, g22 = 1, g23 = 0, b31 = 0, b32 = 0, b33 = 1. . That is, the coefficient matrix constituted by uncorrected matrix coefficients is a unit matrix.

The selection unit 31b selects either the correction matrix coefficient or the non-correction matrix coefficient stored in the storage unit 31a according to the selection signal output from the control unit 35. Specifically, when a selection signal indicating that the first imaging mode is selected is input from the second control unit 35, a correction matrix coefficient is selected, and the second imaging mode is selected. When a selection signal indicating this is input, an uncorrected matrix coefficient is selected. Then, the color signal correction unit 31 corrects the color signal using either the correction matrix coefficient or the non-correction matrix coefficient selected by the selection unit 31b, and the corrected color signal (R _ideal , G _ideal , B _ideal ) are output to the γ correction means 12.

  The YCrCb conversion unit 33 includes a second storage unit 33a and a selection unit 33b. The second storage unit 31a stores in advance the conversion matrix coefficients described in the first embodiment. Further, a matrix coefficient (hereinafter also referred to as a Y conversion matrix coefficient) that generates only the Y signal and sets the color difference signal to “0” is stored in advance. The Y conversion matrix coefficients are specifically y11 = 1, y12 = 1, y13 = 1, Cr21 = 0, Cr22 = 0, Cr23 = 0, Cb31 = 0, Cb32 = 0, and Cb33 = 0. . That is, when the color signal is converted by the Y conversion matrix coefficient, the video (image) corresponding to the signal output from the image sensor is a black and white video.

  The selection unit 33b selects either the conversion matrix coefficient or the Y conversion matrix coefficient stored in the storage unit 33a in accordance with the selection signal output from the control unit 35. Specifically, when a signal indicating that the first imaging mode is selected is input from the control unit 35, a conversion matrix coefficient is selected, and a signal indicating that the second imaging mode is selected is received. When input, a Y conversion matrix coefficient is selected. Then, the YCrCb conversion unit 33 generates and outputs a luminance signal or a color difference signal using either the conversion matrix coefficient or the Y conversion matrix coefficient selected by the selection unit 33b.

  As described above, in the imaging apparatus according to Embodiment 3, when the second imaging mode is selected, the color signal correction unit 31 selects the uncorrected matrix coefficient. Therefore, the signal levels of R2, G2, and B2 are not attenuated as in the case where the correction matrix coefficient is used. In the YCrCb conversion means 33, since the Y conversion matrix coefficient is selected, R2, G2, and B2 that are not attenuated are simply added. In other words, the color signal is corrected and selected by the correction unit 31 and the YCrCb conversion unit 33 so as to adapt to the selected imaging mode.

  Therefore, according to the imaging apparatus in Embodiment 3, it is possible to capture the subject more reliably even when the signal level of the R signal, the G signal, or the B signal is low. That is, imaging with higher sensitivity is possible.

  It should be noted that, by performing the calculation using the non-correction coefficient matrix and the matrix calculation using the Y conversion coefficient matrix by the inventors' experiments and simulations, for example, under illumination of 3000K shown in FIG. It has been confirmed that the sensitivity is improved by 1.8 times or more.

  Further, according to the imaging apparatus of the third embodiment, by providing means for selecting a matrix coefficient, no means for moving the optical filter is required, and a simple configuration with good color reproducibility can be achieved. Capable of switching between imaging and monochrome imaging with high sensitivity

  In the third embodiment, the case where the color signal correction unit 31 includes the first storage unit 31a and the first selection unit 31b has been described. For example, the imaging apparatus is configured as illustrated in FIG. Also good.

  That is, the switch means 36 is provided at the subsequent stage of the WB means 10, and a control signal from the control means 35 is input to the switch means 36. Then, when a control signal corresponding to color imaging is input to the switch means 36, the color signal correction means 31 changes R 2, G 2, and B 2 by the first switch 361, the second switch 362, and the third switch 363. To input.

  On the other hand, when a control signal corresponding to high-sensitivity imaging is input, the switch unit 36 uses the first switch 361, the second switch 362, and the third switch 363 to change R2, G2, and B2 to γ correction unit. 12 to input. In the case of the configuration as shown in FIG. 17, the matrix coefficient stored in the storage unit 31a may be only the correction matrix coefficient.

  In the third embodiment, the color signal correction unit 31 includes the first storage unit 31a and the first selection unit 31b, and the YCrCb conversion unit 33 includes the second storage unit 33a and the second selection unit 33b. For example, as illustrated in FIG. 18, the second control unit 45 includes a storage unit 45a and a selection unit 45b, and the storage unit 45a includes a correction matrix coefficient, a non-correction matrix coefficient, and a conversion matrix coefficient. Alternatively, the Y conversion matrix coefficient may be stored, and the selection means 45b may select the matrix coefficient in accordance with the imaging mode indicated by the changeover switch.

  Further, the imaging mode may be switched by the user with a changeover switch, or the imaging mode may be automatically switched according to the ambient brightness by using, for example, a photoelectric element.

  In the above description, the case where the changeover switch 34 is not provided in the imaging apparatus has been described. However, the changeover switch 34 may be provided in the imaging apparatus according to the design of the imaging apparatus.

  Further, the imaging device may be configured by combining the configuration described in Embodiment 2 and the configuration described in Embodiment 3. Therefore, for example, the imaging apparatus described in the second embodiment is provided with the changeover switch 34, the control unit 35, the unit for storing the non-correction matrix coefficient, the Y conversion matrix coefficient described in the third embodiment, and the like. It is possible to switch between high-sensitivity imaging and to enable imaging according to the color temperature of the illumination.

  In addition, the imaging apparatus described in the first to third embodiments includes a video camera that captures video or still images, a camera-integrated VTR, a digital still camera, a PC camera, a mobile phone, or a mobile terminal (for example, PDA: Personal The present invention can be applied to a digital still camera built in Digital Assistants, a surveillance camera used for night vision, an in-vehicle camera, or the like.

It is a block diagram which shows the structure of the imaging device in Embodiment 1 of this invention. 6 is an explanatory diagram for explaining the transmittance of the optical filter 2 in Embodiment 1. FIG. It is explanatory drawing for demonstrating a color matching function. It is explanatory drawing for demonstrating the spectral sensitivity characteristic of an image pick-up element. It is explanatory drawing for demonstrating an example of the transmittance | permeability of IRCF. It is explanatory drawing for demonstrating the spectral sensitivity characteristic of the conventional imaging device. 6 is an explanatory diagram for explaining spectral sensitivity characteristics of the imaging apparatus according to Embodiment 1. FIG. It is explanatory drawing for demonstrating the partial reflection factor of the color patch contained in the Macbeth color checker. It is explanatory drawing for demonstrating the spectral reflectance of a tree leaf. It is explanatory drawing for demonstrating the spectral reflectance corresponding to the clothes of a chemical fiber. 4 is an explanatory diagram for explaining signal levels corresponding to R, G, and B output from the image sensor 3 in Embodiment 1. FIG. It is a block diagram which shows the structure of the imaging device in Embodiment 2 of this invention. It is explanatory drawing for demonstrating the spectral radiation intensity | strength corresponding to illumination of 3000K. It is explanatory drawing for demonstrating the spectrum radiation intensity corresponding to 6500K illumination. It is explanatory drawing for demonstrating the relationship between ratio of an integrated value, and color temperature. It is a block diagram which shows the structure of the imaging device in Embodiment 3 of this invention. It is a block diagram which shows the 2nd example of a structure of the imaging device in Embodiment 3 of this invention. It is a block diagram which shows the 3rd example of a structure of the imaging device in Embodiment 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lens, 2 NIRBCF, 3 Image pick-up element, 4 Amplifying means, 5 AD converter, 6 DC reproducing means, 7 Accumulating means, 8 Dividing means, 9 Reciprocal means, 10 White balance means, 11, 21, 31, 41 Color signal Correction means, 12 gamma correction means, 13, 33, 43 YCrCb conversion means, 21a, 31a, 33a, 45a storage means, 21b, 31a, 33b, 45b selection means, 34 changeover switch, 35, 45 control means, 36 switch means .

Claims (6)

Of the incident light, a long wavelength optical filter that attenuates the long wavelength region in the visible region and transmits light in the infrared region;
An image pickup apparatus comprising: an image pickup device that has at least three color filters and outputs at least three kinds of color signals corresponding to light emitted from the long wavelength light filter. The imaging apparatus according to claim 1, wherein the long wavelength region in the visible region is a wavelength range of approximately 700 nm to 780 nm. The image pickup apparatus according to claim 1, wherein the three or more color filters are red (R), green (G), and blue (B) color filters. Color signal correcting means for correcting a plurality of color signals output from the image sensor;
The color signal correcting means includes
A predetermined color target obtained based on the spectral sensitivity characteristics of the imaging device and three or more types of color signals obtained from the imaging device is linearly converted into first to third types of signals. 4. The image pickup apparatus according to claim 1, wherein the correction is performed by performing a matrix operation on a correction coefficient and a plurality of color signals output from the image pickup device. The color signal correcting means includes
Storage means for storing a plurality of correction coefficients set in advance according to the color temperature of the illumination used when imaging with the imaging device;
Selecting means for specifying a color temperature of the illumination at the time of image pickup by the image pickup device based on a color signal output from the image pickup device and selecting a correction coefficient corresponding to the color temperature from the storage means; Prepared,
The imaging apparatus according to claim 4, wherein the correction is performed by performing a matrix operation on the correction coefficient selected by the selection unit and a plurality of color signals output from the imaging element. Control means for outputting a control signal corresponding to any one of the first imaging mode for performing color imaging or the second imaging mode for performing imaging with high sensitivity;
Color signal correction means for correcting and outputting the color signal output from the image sensor in accordance with the control signal;
Means for converting the signal output from the color signal correction means into either a first signal corresponding to the first imaging mode or a second signal corresponding to the second imaging mode; The imaging device according to claim 1, further comprising:

Images