JP5033741B2 - Color characteristic conversion coefficient determination method, prism set, and imaging apparatus - Google Patents

Description

  The present invention relates to a method of determining a color characteristic conversion coefficient for reproducing a reproduction system ideal characteristic in which a spectral characteristic of a desired color reproduction system is taken into account in a color imaging system incorporating a color separation prism, a prism set, and The present invention relates to an imaging apparatus.

  In general, an imaging apparatus such as a television camera or a video camera is provided with a color separation optical system. FIG. 15 shows a configuration example of a conventional color separation optical system. The color separation optical system 101 separates incident light L incident through the photographing lens 102 into three color light components of blue light LB, red light LR, and green light LG. Image pickup devices 4B, 4R, and 4G for each color light such as a CCD (Charge Coupled Device) are arranged at positions corresponding to the respective color lights separated by the color separation optical system 101. The color separation optical system 101 is called a Philips type color separation optical system, and the first prism 110, the second prism 120, and the third prism 130 are sequentially arranged from the light incident side along the optical axis Z1. The first prism 110 extracts blue light LB, the second prism 120 extracts red light LR, and the third prism 130 extracts green light LG.

  A blue light reflecting dichroic film DB1 is formed on the reflection / transmission surface 111 of the first prism 110. On the reflection / transmission surface 121 of the second prism 120, a red light reflection dichroic film DR1 is formed. In the first prism 110 and the second prism 120, the surface 111 of the first prism 110 on which the blue light reflecting dichroic film DB1 is formed and the light incident surface of the second prism 120 are separated from each other by an air gap 110AG. It arrange | positions so that it may mutually oppose. A trimming filter 151 is provided on the light exit surface of the first prism 110. A dichroic film 151 </ b> A is formed on the light exit surface of the trimming filter 151. Similarly, a trimming filter 152 formed with a dichroic film 152A is provided on the light exit surface of the second prism 120, and a trimming filter 153 formed with a dichroic film 153A is formed on the light exit surface of the third prism 130. Is provided. The trimming filters 151, 152, and 153 are provided to bring the spectral characteristics closer to the ideal characteristics, and spectral components of wavelength components that cannot be sufficiently shaped by the blue light reflecting dichroic film DB1 and the red light reflecting dichroic film DR1. Has the role of adjusting characteristics.

  FIG. 17 shows spectral characteristics that are generally ideal in a color imaging system for three colors of a red (R) component, a blue (B) component, and a green (G) component. Note that the ideal characteristics in FIG. 17 are normalized so that the maximum value of each color light component is 1, and the vertical axis indicates the transmittance intensity. This “ideal characteristic” is a characteristic that takes into account the spectral characteristics of the color reproduction system. Here, the “spectral characteristic of the color reproduction system” is a characteristic that takes into account the spectral characteristic of the desired color reproduction medium. For example, it is converted from the chromaticity coordinates of the three primary colors of the color reproduction medium, and the color matching functions x (λ), y (λ), XYZ color system (XYZ color system introduced by the International Lighting Commission in 1931), It can be obtained by a primary transformation of z (λ). Here, the “color reproduction medium” reproduces (displays) an image taken by the imaging device, and is a display device such as a liquid crystal monitor or a projector. FIG. 16 shows an example of chromaticity coordinates of the three primary colors R, G, and B for obtaining ideal characteristics. The three primary colors R, G, and B determine the color range that can be reproduced by the color reproduction medium.

  If the same characteristic as the ideal characteristic shown in FIG. 17 is obtained using the color separation optical system 101 shown in FIG. 15, ideal color reproduction can be performed. However, in practice, it is difficult to achieve the same characteristic as the ideal characteristic, and the design is such that the characteristic approximates the ideal characteristic. In the conventional color separation optical system 101, ideal characteristics are obtained by appropriately adjusting the dichroic films DB1 and DR1 formed on each prism and the dichroic films 151A, 152A, and 153A formed on the trimming filters 151, 152, and 153. It was designed to have approximate characteristics. FIG. 18 shows spectral transmission characteristics of a conventional general color separation optical system obtained by performing such a design.

  FIG. 19 shows a design example of the dichroic films DB1 and DR1 used in the conventional color separation optical system 101. As shown in FIG. 19, conventionally, as the dichroic films DB1 and DR1, the characteristic curve of the wavelength vs. transmittance shows a sharp rise or fall compared to the ideal characteristic curve shown in FIG. Something with was used. Further, unnecessary wavelength components of light emitted from the exit surface of each prism are blocked using trimming filters 151, 152, 153 provided with dichroic films 151A, 152A, 153A.

Patent Document 1 includes a photoelectric sensor having a spectral response approximate to a color matching function and a correction sensor that maximizes the spectral response near the transmission limit wavelength of the color matching function. An invention of a color measuring device is disclosed in which a reduction in accuracy of chromaticity measurement due to a deviation between the spectral response of the photoelectric sensor and the color matching function is prevented by adding an appropriate coefficient to the output value of .
JP-A-9-49765

By the way, in the ideal characteristic shown in FIG. 17, there is a region where the negative spectral sensitivity is obtained, and in particular, there are many regions (region 100 in FIG. 17) where the red spectral property is negative. This negative region is theoretically obtained, and it is impossible to directly reproduce this negative portion with an actual optical system. In the conventional color separation optical system, the negative region cannot be reproduced as shown in FIG. On the other hand, it is conceivable that negative characteristics that cannot be directly reproduced by the optical system are reproduced by calculation of signal processing on the imaging apparatus side. For example, with respect to the ideal characteristics shown in FIG. 17, a reversible conversion characteristic that eliminates the negative region is obtained, and the conversion characteristic is set as an ideal characteristic that is reproduced by the color separation optical system. The output from the color separation optical system is inversely transformed by signal processing on the imaging device side to theoretically reproduce the negative region and simulate the original ideal characteristics. Can do.
More specifically, it is possible to reversely convert the signal value of each color output from the image sensor of each color by a color characteristic conversion coefficient called a matrix coefficient to reproduce the ideal characteristic in a pseudo manner. .

  If the entire color imaging system including the color separation optical system is ideally designed and manufactured, the desired ideal characteristics can be theoretically reproduced by the method described above. However, since there are actually manufacturing errors and design errors, it is difficult to manufacture the entire imaging system with ideal characteristics. In addition, the spectral characteristics at the time of actual shooting also affect the spectral characteristics of the light source. However, in the shooting scene, a light source different from the light source assumed at the time of design may be used, and the ideal characteristics cannot be reproduced depending on the shooting environment. There is a case. For this reason, in an actually manufactured imaging apparatus, it is difficult to completely reproduce ideal characteristics even if inverse conversion is performed on the signal values of each color by the above-described method. This is because the conversion coefficients (matrix coefficients) used for the inverse conversion are determined on the assumption that the imaging system is ideally designed. In order to reproduce an ideal characteristic by the above-described method in an actually manufactured imaging apparatus, it is necessary to make a conversion coefficient used for inverse conversion take into account a manufacturing error, a design error, and the like. In this case, in particular, in the color imaging system, it is the spectral characteristic of the color separation prism that greatly affects the spectral characteristic. For this reason, it is particularly important to consider manufacturing errors and design errors of the color separation prism.

  In an imaging apparatus such as a TV camera or a video camera, it is necessary to reproduce the reproduction system ideal characteristic as shown in FIG. 17 in consideration of the reproduction system characteristic as described above. When this ideal characteristic is reproduced by the above-described method, it is preferable to use a conversion coefficient corresponding to a desired reproduction system characteristic. On the other hand, in the color measuring device described in Patent Document 1, a correction sensor is provided, and the output value of the photoelectric sensor and the correction sensor is multiplied by an appropriate coefficient to add the spectral response of the photoelectric sensor and the color matching function. The deviation is minimized and ideal chromaticity measurement can be performed. That is, the technique described in Patent Document 1 is an invention for realizing the characteristic of the color matching function itself, and does not attempt to realize the characteristic in consideration of the reproduction system.

  The present invention has been made in view of such problems, and its purpose is to achieve characteristics close to ideal spectral characteristics in which the characteristics of a desired color reproduction system are added in a color imaging system incorporating a color separation prism. It is an object of the present invention to provide a color characteristic conversion coefficient determination method, a prism set, and an imaging apparatus that can be obtained.

  The color characteristic conversion coefficient determination method of the present invention is output from a plurality of image sensors in an image pickup apparatus having a color separation prism in order to obtain a reproduction system ideal characteristic that takes into account a spectral characteristic of a desired color reproduction system. This is a method for determining the color characteristic conversion coefficient to be multiplied for multiple color signals, and optically converting the ideal ideal characteristic by applying reversible conversion to reduce the negative spectral range with respect to the reproduction system ideal characteristic. The step of measuring the spectral characteristics of the color separation prism used for reproduction with a measuring instrument and the entire imaging system when the color separation prism is incorporated into the imaging device based on the measured spectral characteristics of the color separation prism The difference between the spectral characteristic and the reproduction system ideal characteristic or the conversion ideal characteristic is obtained by the second arithmetic means. Reduce the step, the deviation of the spectral characteristics, in which the matrix coefficients as overall spectral characteristics closer to the reproduction system ideal characteristics and determining by the third calculating means as the color characteristic conversion coefficients.

  Here, in the method for determining the color characteristic conversion coefficient of the present invention, the “spectral characteristic of the color reproduction system” is a characteristic that takes into account the spectral characteristic of the desired color reproduction medium. The “color reproduction medium” reproduces (displays) an image taken by an imaging device, and is a display device such as a liquid crystal monitor or a projector. “Reproduction system ideal characteristics” are, for example, converted from the chromaticity coordinates of the three primary colors of the desired color reproduction medium, and the same color of the XYZ color system (XYZ color system introduced by the International Lighting Commission in 1931) This is a characteristic having a spectral region having a negative value, which is indicated by the linear transformation of the function.

The color characteristic conversion coefficient determination method according to the present invention is a color separation designed to reproduce a conversion ideal characteristic obtained by performing a reversible conversion to reduce a negative spectral region with respect to a reproduction system ideal characteristic. The spectral characteristics of the prism are measured by a measuring instrument. Based on the measured spectral characteristics of the color separation prism, the total spectral characteristics of the entire imaging system when the color separation prism is incorporated into the imaging device are determined, and the total spectral characteristics and reproduction system ideal characteristics or conversion are obtained. Deviation of spectral characteristics from ideal characteristics is required. A matrix coefficient that reduces the deviation of the spectral characteristics and brings the total spectral characteristics closer to the reproduction system ideal characteristics is obtained as the color characteristic conversion coefficient.
By using the color characteristic conversion coefficient determined in this way in the signal processing unit on the imaging device side that incorporates the color separation prism to be measured, the design error of the color separation prism that greatly affects the spectral characteristics, The manufacturing error is corrected, and a characteristic close to an ideal spectral characteristic including a desired color reproduction characteristic is obtained as a video signal.

In the method for determining the color characteristic conversion coefficient according to the present invention, in the step of obtaining the overall spectral characteristic, the spectral characteristic of the constituent elements other than the color separation prism in the imaging device is determined using a predetermined representative value. The total spectral characteristic may be obtained by the one arithmetic means based on the predetermined representative value and the spectral characteristic measured by the color separation prism.
Here, “components other than the color separation prism in the imaging device” are, for example, a photographing lens, an IR (infrared) cut filter, an imaging element, and the like.

  Here, in the method for determining the color characteristic conversion coefficient of the present invention, the color separation prism to be measured, for example, decomposes incident light into at least three color light components of blue light, red light, and green light. In order from the light incident side, the first dichroic film is provided, the first prism for extracting the first color light component reflected by the first dichroic film, and the second dichroic film are provided. A second prism for extracting the second color light component transmitted through the dichroic film and reflected by the second dichroic film, and a third prism for extracting the third color light component transmitted through the first and second dichroic films Can be used. In this case, it is preferable that the first and second dichroic films are designed so that the slope of the characteristic curve indicating the spectral characteristics is in accordance with the slope of the characteristic curve indicating the conversion ideal characteristics.

More specifically, for example, in the color separation prism, the first dichroic film is configured to reflect blue light as the first color light component, and the second dichroic film is used as the second color light component. In the wavelength range of 430 nm or more and 670 nm or less, the slope of the transmission characteristic curve is a film configuration that reflects red light, and shows the transmittance with respect to the wavelength of the first dichroic film. It is preferably designed to have a shape in which the average slope value changing from 20% to 80% in the range is 0.2 (% / nm) to 2.0 (% / nm). Further, the slope of the transmission characteristic curve indicating the transmittance with respect to the wavelength of the second dichroic film is changed from 80% to 20% of the range between the maximum transmittance and the minimum transmittance within the wavelength range of 430 nm to 670 nm. It is preferable that the average slope value to be changed is designed to have a shape of −2.0 (% / nm) or more and −0.2 (% / nm) or less.
By using a color separation prism that is designed to have an inclination corresponding to the inclination of the characteristic curve indicating such conversion ideal characteristics, the overall imaging system when the color separation prism is incorporated into an imaging device is used. It becomes easy to approximate the spectral characteristics to the ideal conversion characteristics. Further, by combining with the color characteristic conversion coefficient obtained by the color characteristic conversion coefficient determination method of the present invention, it becomes easy to obtain a characteristic close to an ideal spectral characteristic in consideration of a desired color reproduction system characteristic.

The method for determining a color characteristic conversion coefficient according to the present invention further includes a step of recording identification information in which a color characteristic conversion coefficient is associated with a color separation prism that is a spectral characteristic measurement target on a recording medium. Also good.
In this case, in the step of recording on the recording medium, the identification information may be recorded on the recording medium together with data indicating the obtained color characteristic conversion coefficient.

The prism set according to the present invention includes the color separation prism that is the object of measurement of the spectral characteristics in the method for determining the color characteristic conversion coefficient according to the present invention, and the recording medium.
By constructing an imaging device using such a prism set, the design error and manufacturing error of the color separation prism, which have a large influence on the spectral characteristics, are corrected, and the desired color reproduction system characteristics are added to the video signal. The characteristics close to the ideal spectral characteristics can be obtained.

An image pickup apparatus according to the present invention includes a color separation prism which is a spectral characteristic measurement target in the color characteristic conversion coefficient determination method of the present invention, and a color characteristic conversion obtained in the color characteristic conversion coefficient determination method of the present invention. A coefficient storage unit that stores data indicating coefficients, a plurality of imaging elements that are provided corresponding to a plurality of color lights that have been color-separated by the color separation prism, and that output color signals corresponding to each incident color light; A signal processing unit that performs an operation of multiplying a plurality of color signals output from the image sensor by a color characteristic conversion coefficient stored in a coefficient storage unit;
In the image pickup apparatus according to the present invention, the coefficient storage unit stores data indicating the color characteristic conversion coefficient obtained by the color characteristic conversion coefficient determination method of the present invention. The signal processing unit performs an operation of multiplying a plurality of color signals output from the plurality of image sensors by a color characteristic conversion coefficient stored in the coefficient storage unit. As a result, the design error and manufacturing error of the color separation prism that have a great influence on the spectral characteristics are corrected, and a characteristic close to the ideal spectral characteristic including the characteristics of the desired color reproduction system is obtained as the video signal.

  According to the method for determining the color characteristic conversion coefficient of the present invention, the spectral characteristics of the color separation prism are measured, and based on the measured spectral characteristics, the overall imaging system when the color separation prism is incorporated into the imaging apparatus is integrated. The total spectral characteristics when the color separation prism is incorporated into the image pickup device based on the difference in spectral characteristics between the total spectral characteristics and the reproduction system ideal characteristics or conversion ideal characteristics. Since the matrix coefficient that approximates the desired reproduction system ideal characteristic is obtained as the color characteristic conversion coefficient, the determined color characteristic conversion coefficient is used as a signal on the imaging device side that incorporates the color separation prism that is the measurement target. By using it in the processing unit, it is possible to correct design errors and manufacturing errors of color separation prisms that have a large influence on spectral characteristics, and the characteristics of the desired color reproduction system in color imaging systems can be corrected. It is possible to obtain a characteristic close to the taste has been ideal spectral characteristics.

  According to the prism set of the present invention, the information on the color separation prism that is the measurement target of the spectral characteristics in the color characteristic conversion coefficient determination method of the present invention and the color characteristic conversion coefficient associated with the color separation prism is obtained. Since it is provided with a recorded recording medium, it can correct design errors and manufacturing errors of color separation prisms that have a large influence on spectral characteristics by being incorporated in an imaging device, and is desired in a color imaging system. Thus, it is possible to obtain characteristics close to ideal spectral characteristics in consideration of the characteristics of the color reproduction system.

  According to the imaging device of the present invention, the coefficient storage unit stores data indicating the color characteristic conversion coefficient obtained in the color characteristic conversion coefficient determination method of the present invention, and the signal processing unit outputs the data from a plurality of imaging elements. Since the calculation is performed on the multiple color signals that are multiplied by the color characteristic conversion coefficient stored in the coefficient storage unit, the color separation prism design and manufacturing errors that have a large influence on the spectral characteristics are corrected. Therefore, in the color imaging system, it is possible to obtain characteristics close to ideal spectral characteristics in consideration of characteristics of a desired color reproduction system.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[First Embodiment]

  FIG. 1 shows a main configuration of an imaging apparatus including a color separation optical system 1 according to the first embodiment of the present invention. This imaging apparatus can be used for, for example, a television camera or a video camera. This image pickup apparatus is provided in an image pickup optical system, a plurality of image pickup elements 4B, 4R, 4G that output color signals corresponding to each color light incident through the image pickup optical system, and a plurality of image pickup apparatus main bodies 60. And an imaging system signal circuit that processes color signals from the imaging elements 4B, 4R, and 4G and outputs the processed signals as video signals Vout. The imaging optical system includes a color separation optical system 1 and a photographing lens 2. The imaging system signal circuit includes a coefficient storage unit 61 and a signal processing unit 62. The coefficient storage unit 61 is configured by a nonvolatile semiconductor memory or the like. The signal processing unit 62 has, for example, an MPU (microprocessor unit) for image processing.

  The color separation optical system 1 separates the incident light L incident through the photographing lens 2 into three color light components of blue light LB, red light LR, and green light LG. Image pickup elements 4B, 4R, and 4G for each color light such as a CCD are arranged at positions corresponding to the respective color lights separated by the color separation optical system 1.

  The color separation optical system 1 is called a Philips type color separation optical system, and sequentially from the light incident side along the optical axis Z1, an IR (infrared) cut filter 3, a first prism 10, and a second prism. And a color separation prism composed of the prism 20 and the third prism 30. The color separation optical system 1 in this embodiment is a configuration example in which the first prism 10 extracts blue light LB, the second prism 20 extracts red light LR, and the third prism 30 extracts green light LG.

  The first prism 10 has a first surface 11, a second surface 12, and a third surface 13. The third surface 13 of the first prism 10 is a light exit surface. A trimming filter 51 is provided on the exit surface. The trimming filter 51 is not provided with a dichroic film for characteristic adjustment which has been conventionally used. Instead, an antireflection film 51AR for preventing ghost and flare is provided on the light emission surface of the trimming filter 51. Is formed. Note that the antireflection film 51AR may be formed directly on the third surface 13 of the first prism 10 without providing the trimming filter 51.

  A blue light reflecting dichroic film DB as a first dichroic film is formed on the second surface 12 of the first prism 10. The blue light reflecting dichroic film DB has a film configuration that reflects the blue light LB as the first color light component and transmits the red light LR and the green light LG. As will be described later, the blue light reflecting dichroic film DB is designed with film characteristics corresponding to a predetermined predetermined spectral characteristic.

  The second prism 20 has a first surface 21, a second surface 22, and a third surface 23. The second prism 20 is disposed with a predetermined air interval 10AG with respect to the first prism 10. More specifically, the first surface 21 of the second prism 20 and the second surface 12 of the first prism 10 are arranged to face each other with an air gap 10AG so as to be substantially parallel. The third surface 23 of the second prism 20 is a light exit surface. A trimming filter 52 is provided on the exit surface. Similar to the trimming filter 51 in the first prism 10, the trimming filter 52 is not provided with a dichroic film for characteristic adjustment. Instead, the trimming filter 52 has a light exit surface for preventing ghost and flare. An antireflection film 52AR is formed. Note that the antireflection film 52AR may be formed directly on the third surface 23 of the second prism 20 without providing the trimming filter 52.

  A red light reflecting dichroic film DR as a second dichroic film is formed on the second surface 22 of the second prism 20. The red light reflecting dichroic film DR has a film configuration that reflects the red light LR as the second color light component and transmits the green light LG. As will be described later, the red light reflecting dichroic film DR is designed with film characteristics corresponding to a predetermined spectral characteristic of interest.

  The third prism 30 has a first surface 31 and a second surface 32. The third prism 30 is bonded to the second prism 20 via the red light reflecting dichroic film DR. More specifically, the second surface 22 of the second prism 20 and the first surface 31 of the third prism 30 are joined via the red light reflecting dichroic film DR. The second surface 32 of the third prism 30 is a light exit surface. A trimming filter 53 is provided on the exit surface. Similar to the trimming filter 51 in the first prism 10, the trimming filter 53 is not provided with a dichroic film for characteristic adjustment. Instead, the trimming filter 53 has a light exit surface for preventing ghost and flare. An antireflection film 53AR is formed. Note that the antireflection film 53AR may be formed directly on the second surface 32 of the third prism 30 without providing the trimming filter 53.

  The IR cut filter 3 is disposed on the front side of the first prism 10. The IR cut filter 3 is preferably composed of an absorptive filter having characteristics approximating to visual sensitivity in order to easily obtain characteristics close to ideal spectral characteristics. The “absorptive filter having characteristics approximating the visibility” referred to here is called a “visibility correction filter” and is a transmission that approximates the sensitivity characteristics of the human eye and attenuates from the green to the red wavelength. This is an absorptive filter that has a low transmittance and a low transmittance even in the infrared region. Note that the IR cut filter 3 may be disposed not on the front side of the first prism 10 but on the light exit surface side of a prism (second prism 20 in FIG. 1) that extracts red light. Further, the IR cut filter 3 may be disposed on both the front side of the first prism 10 and the light exit surface side of the prism that extracts red light. Further, when infrared light cannot be sufficiently removed only by the absorption filter, a coat type infrared cut filter that cuts infrared light may be further provided. FIG. 1 shows a configuration example in which a flat absorption filter is coated with a film 3R that cuts infrared light. However, in the case where the IR cut filter 3 is arranged on the light exit surface side of the prism that extracts red light, it is preferable that the IR cut coat is not applied and only the absorption filter is used. In that case, it is more preferable that the absorption filter is provided with an antireflection film.

  Although not shown, the color separation optical system 1 may further include an absorption type or coat type ultraviolet cut filter that is disposed in front of the first prism 10 and cuts ultraviolet light.

  Here, the reproduction system ideal characteristic which is to be optically reproduced by the imaging optical system in the present embodiment will be described.

  In the present embodiment, the characteristic that is finally desired to be reproduced as the output of the imaging apparatus is a reproduction system ideal characteristic as shown in FIG. This is substantially the same as the characteristics shown in FIG. This reproduction system ideal characteristic is converted from, for example, the chromaticity coordinates of the three primary colors of the desired color reproduction medium, and is subjected to the primary conversion of the color matching functions x (λ), y (λ), z (λ) of the XYZ color system. Are expressed by the functions r (λ), g (λ), and b (λ). The functions r (λ), g (λ), and b (λ) representing the reproduction system ideal characteristics may be the color matching functions themselves of the RGB color system. The functions r (λ), g (λ), b (λ) representing the reproduction system ideal characteristics may also take into account human visual characteristics. Such a reproduction system ideal characteristic has a region having negative spectral sensitivity, but the region having negative spectral sensitivity cannot be optically directly reproduced by the imaging optical system. Therefore, in the present embodiment, a reversible conversion characteristic that eliminates the negative region is obtained in advance with respect to the reproduction system ideal characteristic shown in FIG. Conversion ideal characteristics (target predetermined spectral characteristics) that are optically reproduced by the system. Then, the signal processing unit 62 performs an inverse conversion operation on the color signals (signal values Rs, Gs, Bs) output from the image pickup devices 4B, 4R, 4G via the image pickup optical system. The negative region is reproduced, and the original ideal characteristic (reproduction system ideal characteristic) is reproduced in a pseudo manner.

FIG. 2B eliminates the negative region described above with respect to the reproduction system ideal characteristics of each color represented by the functions r (λ), g (λ), and b (λ) shown in FIG. An example of transformation ideal characteristic functions r ′ (λ), g ′ (λ), and b ′ (λ) subjected to such reversible transformation is shown. Such conversion can be performed by the calculation of primary conversion as shown in the following equation (1) of [Equation 1]. M is a matrix that minimizes negative values as much as possible in the functions r ′ (λ), g ′ (λ), and b ′ (λ) representing the conversion ideal characteristics. Here, if the imaging optical system is ideally designed and manufactured, functions r ′ (λ), g ′ (λ), b ′ ( λ) is multiplied by the inverse matrix M ⁻¹ and inversely transformed to theoretically reproduce the desired functions r (λ), g (λ), and b (λ) of the original reproduction system ideal characteristics. be able to.

  In the present embodiment, in particular, the film characteristics of the blue light reflecting dichroic film DB and the red light reflecting dichroic film DR are expressed by the functions r ′ (λ), g ′ (λ), and b ′ (λ). The design is intended to reproduce the ideal conversion characteristics, and the imaging optical system has characteristics that approximate the ideal conversion characteristics represented by the functions r ′ (λ), g ′ (λ), and b ′ (λ) as much as possible. I try to get it. Here, the conversion ideal characteristics represented by the functions r ′ (λ), g ′ (λ), and b ′ (λ) are such that the negative values are as small as possible. It can be directly reproduced optically by the imaging optical system.

  FIG. 3A shows an example of a transmission characteristic curve of the blue light reflecting dichroic film DB in the present embodiment. The blue light reflecting dichroic film DB has an ideal green spectral characteristic in which the slope of the transmission characteristic curve indicating the transmittance with respect to the wavelength is represented by the ideal green spectral characteristic (the above-described linearly converted function g ′ (λ)). ) Along the characteristic curve on the short wavelength side. Specifically, the blue light reflecting dichroic film DB has a low transmittance within a wavelength range of 430 nm or more and 670 nm or less in which the slope of the transmission characteristic curve follows the characteristic curve on the short wavelength side of the ideal green spectral characteristic. It is configured to have a shape that changes from a high rate to a high transmittance. More specifically, the average slope value at which the transmission characteristic curve changes from 20% to 80% of the range between the lowest transmittance and the highest transmittance within a wavelength range of 430 nm to 670 nm is 0.2%. It is preferable to have a shape of (% / nm) or more and 2.0 (% / nm) or less.

  FIG. 3B shows an example of a transmission characteristic curve of the red light reflecting dichroic film DR in the present embodiment. The red light reflecting dichroic film DR has an ideal green spectral characteristic in which the slope of the transmission characteristic curve indicating the transmittance with respect to the wavelength is expressed by the ideal green spectral characteristic (the above-described linearly converted function g ′ (λ)). ) Along the characteristic curve on the long wavelength side. Specifically, the red light reflecting dichroic film DR has a high transmittance within a wavelength range of 430 nm or more and 670 nm or less in which the slope of the transmission characteristic curve follows the characteristic curve on the long wavelength side of the ideal green spectral characteristic. It is configured to have a shape that changes from low to low transmittance. More specifically, the average slope value at which the transmission characteristic curve changes from 80% to 20% of the range between the highest transmittance and the lowest transmittance within a wavelength range of 430 nm to 670 nm is −2. It preferably has a shape of 0 (% / nm) or more and -0.2 (% / nm) or less.

  As described above, the blue light reflecting dichroic film DB and the red light reflecting dichroic film DR in the present embodiment are designed such that the slopes of the characteristic curves thereof are in accordance with ideal spectral characteristics.

However, even if the imaging optical system is designed to reproduce the ideal conversion characteristics represented by the functions r ′ (λ), g ′ (λ), and b ′ (λ), manufacturing errors and Due to design errors and the like, it is difficult to manufacture a completely ideal product. Therefore, in order to reproduce the reproduction system ideal characteristic by the above-described method in the actually manufactured imaging apparatus, the conversion coefficient M ⁻¹ used for the inverse transformation should be considered in consideration of a manufacturing error, a design error, and the like. is required. In this case, particularly in the color imaging system, the spectral characteristics of the color separation prism in the color separation optical system 1 have a great influence on the spectral characteristics.

  Therefore, in the present embodiment, in consideration of manufacturing errors and design errors of the color separation prism in particular, the spectral characteristics of the color separation prism are measured in advance in the manufacturing stage before the color separation optical system 1 is incorporated into the imaging apparatus. It is made to measure with the instrument 71. Based on the measured spectral characteristics, the coefficient calculation unit 72 obtains the total spectral characteristics of the entire imaging system when the color separation prism is incorporated in the color imaging system.

Here, in order to obtain the overall spectral characteristics of the entire imaging system, the spectral characteristics of components other than the color separation prism in the imaging apparatus are required. For example, the spectral characteristics of the light source, the photographing lens 2, the IR cut filter 3, and the image sensors 4B, 4R, and 4G are necessary. In the present embodiment, predetermined representative values determined in advance are used for the spectral characteristics of the components other than the color separation prism. The coefficient calculation unit 72 obtains a total spectral characteristic based on the predetermined representative value and the spectral characteristic measured by the color separation prism. Further, the coefficient calculation unit 72 obtains a shift of the spectral characteristic between the total spectral characteristic and the ideal characteristic of the desired reproduction system, and based on the deviation of the characteristic, the total spectral characteristic is converted into the ideal characteristic of the reproduction system. A matrix coefficient that approaches is obtained as a color characteristic conversion coefficient. The color characteristic conversion coefficient is stored in the coefficient storage unit 61 of the imaging apparatus as the conversion coefficient M ⁻¹ used for the inverse conversion described above.
Hereinafter, in the present embodiment, instead of the above-described theoretical conversion coefficient M ⁻¹ , the color characteristic conversion coefficient used for the actual inverse conversion operation is
Indicated as (M ⁻¹ ) ′.
The signal processing unit 62 performs an operation of multiplying each color signal output from the image pickup devices 4R, 4G, and 4B by the color characteristic conversion coefficient (M ⁻¹ ) ′ stored in the coefficient storage unit 61 to obtain a video signal. Output as Vout.

Here, the overall spectral characteristics of the entire imaging system taking into account manufacturing errors, design errors, and the like are expressed by functions r ₀ ′ (λ), g ₀ ′ (λ), and b ₀ ′ (λ). Then, as shown in the following equation (3) of [Equation 3], a color characteristic conversion coefficient (M ⁻¹ ) ′ is ^added to the functions r ₀ ′ (λ), g ₀ ′ (λ), b ₀ ′ (λ). By performing inverse transformation by multiplying by, the characteristics represented by the functions r ″ (λ), g ″ (λ), b ″ (λ) are obtained. By determining a value that minimizes the deviation from the reproduction system ideal characteristic as the color characteristic conversion coefficient (M ⁻¹ ) ′, functions r ″ (λ), g ″ (λ), b ″ ( λ) can be a characteristic approximated to a desired function r (λ), g (λ), b (λ) of the original reproduction system ideal characteristic. That is, as the color characteristic conversion coefficient (M ⁻¹ ) ′, the functions r (λ), g (λ), b (λ) of the theoretical formula represented by the above formula (2) and the above formula (3) are used. What is necessary is just to obtain | require the coefficient which makes the difference with the function r '' ((lambda)), g '' ((lambda)), b '' ((lambda)) based on the actual measurement value which considered the manufacturing error etc. represented. For example, a coefficient that minimizes the square difference may be obtained by the least square method.

  The measuring instrument 71 that measures the spectral characteristics of the color separation prism includes, for example, a spectroscope 81 and optical sensors 82R, 82G, and 82B such as photomultipliers, as shown in FIG. The measuring device 71 is incident on the color separation prism as light L from the spectroscope 81 and detects output light from the color separation prism by the optical sensors 82R, 82G, and 82B.

The coefficient calculation unit 72 is configured to include, for example, an MPU (microprocessor unit). The coefficient calculation unit 72 obtains a total spectral characteristic of the entire imaging system calculated based on the spectral characteristic of the color separation prism measured by the measuring device 71, and the color in the present embodiment is calculated by, for example, the above least square method. The characteristic conversion coefficient (M ⁻¹ ) ′ is calculated. Data indicating the color characteristic conversion coefficient (M ⁻¹ ) ′ obtained by the coefficient calculation unit 72 is stored in the coefficient storage unit 61 via the recording medium 73 or the communication unit 74, for example. The communication unit 74 is a communication interface that conforms to an external interface standard (not shown) provided in the imaging apparatus, for example. As the recording medium 73, a semiconductor memory, various optical disks, or the like can be used.
In the present embodiment, the coefficient calculation unit 72 corresponds to a specific example of “first calculation means”, “second calculation means”, and “third calculation means” in the present invention.

The recording medium 73 includes identification information (ID, serial number, etc.) in which the color characteristic conversion coefficient (M ⁻¹ ) ′ obtained by the coefficient calculation unit 72 is associated with the color separation prism that is a spectral characteristic measurement target. May be recorded. This identification information may be recorded on the recording medium 73 together with data indicating the obtained color characteristic conversion coefficient (M ⁻¹ ) ′. A recording medium 73 on which such information is recorded and a color separation prism that is a spectral characteristic measurement target are prepared as a “prism set”, and the built-in color separation prism is supported when the entire imaging apparatus is assembled. Data of the color characteristic conversion coefficient (M ⁻¹ ) ′ to be read may be read from the recording medium 73 and stored in the coefficient storage unit 61.

  Next, the operation of the imaging device in this embodiment will be described.

  In the imaging apparatus shown in FIG. 1, subject light from a subject (not shown) irradiated by a light source (not shown) enters the color separation optical system 1 via the photographing lens 2. In the color separation optical system 1, the incident light L is decomposed into three color light components of blue light LB, red light LR, and green light LG. More specifically, first, the blue light LB of the incident light L is reflected by the blue light reflecting dichroic film DB and extracted from the first prism 10 as the first color light component. Further, the red light LR that has passed through the blue light reflecting dichroic film DB is reflected by the red light reflecting dichroic film DR and is extracted from the second prism 20 as the second color light component. Further, the green light LG transmitted through the blue light reflecting dichroic film DB and the red light reflecting dichroic film DR is extracted from the third prism 30 as a third color light component. Each color light separated by the color separation optical system 1 enters the image pickup devices 4B, 4R, 4G provided corresponding to each color light. The imaging elements 4B, 4R, and 4G output an electrical signal corresponding to each incident color light as an imaging signal.

  Here, spectral characteristics obtained by the imaging optical system in the present embodiment will be shown by an actual design example. FIG. 4 shows the characteristics of a specific design example of the blue light reflecting dichroic film DB and the red light reflecting dichroic film DR used in the color separation optical system 1. The characteristics shown in FIG. 4 can be obtained by, for example, the film design specifically shown as numerical data in FIGS. However, the film substance, the number of layers, and the film thickness of each layer are not limited to the examples of FIGS. FIG. 7 shows the spectral transmission characteristics of the entire prism portion (the first, second, and third prisms 10, 20, and 30) on which the film design shown in FIG. 4 is applied.

  FIG. 8 shows an example of spectral characteristics of optical elements other than the prism portion in the imaging apparatus. In FIG. 8, as the characteristics of the optical elements other than the prism portion, a light source having a color temperature of 3200K, a photographing lens 2, an IR cut filter 3, and a CCD as the image sensors 4R, 4G, and 4B are shown. FIG. 9 shows the overall spectral transmission characteristics of the entire imaging system, which combines the characteristics of optical elements other than the prism section shown in FIG. 8 and the characteristics of the entire prism section shown in FIG.

In the overall spectral characteristic of the entire imaging system shown in FIG. 9, the negative spectral region cannot be reproduced with respect to the reproduction system ideal characteristic shown in FIG. 2A. The signal processing unit 62 multiplies each color signal output from the image pickup devices 4R, 4G, and 4B by the color characteristic conversion coefficient (M ⁻¹ ) ′ stored in the coefficient storage unit 61 to obtain the final result. Specifically, it is possible to reproduce a characteristic approximate to the reproduction system ideal characteristic as shown in FIG.

Next, referring to FIG. 11 and FIG. 12, a process for guiding the spectral characteristics of the imaging apparatus according to the present embodiment to the final ideal state is described as a color characteristic conversion coefficient (M ^{− 1} ) Explain with the determination method.

  First, for example, the function r (λ), x (λ), y (λ), z (λ) of the XYZ color system is converted into a function, and the spectral characteristics of the desired color reproduction system are added. The reproduction system ideal characteristics represented by g (λ) and b (λ) are obtained (steps S101 and S102 in FIG. 11, FIGS. 12A and 12B). Next, with respect to the reproduction system ideal characteristics of each color represented by the functions r (λ), g (λ), and b (λ), a transformation matrix M as shown in the above equation (1) of [Equation 1] The conversion ideal characteristic represented by functions r ′ (λ), g ′ (λ), and b ′ (λ) having positive values subjected to reversible conversion to eliminate the negative region is obtained by the calculation used ( Steps S103 and S104, FIG. 12 (C)). The functions r ′ (λ), g ′ (λ), and b ′ (λ) obtained through the steps so far are theoretical values. Based on this theoretical value, an imaging optical system including a color separation prism is designed and manufactured.

  As a design stage, design values for the entire imaging system are determined (step S105, FIG. 12D). This is an overall design value of a positive value approximated to the conversion ideal characteristic represented by the functions r ′ (λ), g ′ (λ), and b ′ (λ) of positive values. The color separation prism is designed and manufactured with the goal of reproducing the total design value approximated to the ideal conversion characteristics (steps S106 and S107).

Next, the spectral characteristic of the color separation prism is measured by the measuring instrument 10, and an actual measurement value of the characteristic is obtained (step S108). Next, based on the measured spectral characteristics of the color separation prism, the coefficient calculation unit 72 obtains the overall spectral characteristics of the entire imaging system when the color separation prism is incorporated in the imaging device (step S109, FIG. E)). In the step of obtaining the total spectral characteristic, the coefficient calculation unit 72 determines a predetermined “predetermined” spectral characteristic of components (photographing lens 2, IR cut filter 3, etc.) other than the color separation prism in the imaging apparatus. The total spectral characteristics are obtained based on the predetermined representative value and the measured spectral characteristics of the color separation prism. The total spectral characteristics required here are expressed by functions r ₀ ′ (λ), g ₀ ′ (λ), b ₀ ′ (λ) in consideration of manufacturing errors, design errors, and the like regarding the color separation prism. This is a total measured value of the entire imaging system to be performed, and is a positive value.
The above-mentioned “predetermined representative value” may be, for example, a value obtained in advance by simulation for components other than the color separation prism, or may be an actual value obtained by measuring in advance with a measuring instrument. Also good. In addition, these values may be simulation values or measured values of the components themselves that are actually incorporated into the imaging apparatus together with the color separation prism that is the measurement target, or other parts that are equivalent to those that are actually incorporated. The simulation value or the measurement value may be used.

Next, the coefficient calculation unit 72 calculates the total spectral characteristics represented by the functions r ₀ ′ (λ), g ₀ ′ (λ), b ₀ ′ (λ) and the functions r (λ), g (λ). , B (λ), the deviation of the spectral characteristic from the reproduction system ideal characteristic is obtained. The coefficient calculation unit 72 obtains a matrix coefficient that reduces the deviation of the spectral characteristic and brings the total spectral characteristic close to the reproduction system ideal characteristic as the color characteristic conversion coefficient (M ⁻¹ ) ′ (step S110). Specifically, as described above, the functions r (λ), g (λ), b (λ) of the theoretical formula expressed by the above formula (2) and the manufacturing error expressed by the above formula (3). A coefficient that minimizes the difference from the actual value-based functions r ″ (λ), g ″ (λ), and b ″ (λ) in consideration of the above is obtained by an operation such as a least square method.

When the data indicating the color characteristic conversion coefficient (M ⁻¹ ) ′ obtained by the coefficient calculation unit 72 is assembled into the entire imaging apparatus, the coefficient storage unit in the imaging apparatus, for example, via the recording medium 73 or the communication unit 74. 61 is stored. Further, when assembling the entire image pickup apparatus, a color separation prism which is the measurement target of the spectral characteristics is incorporated. In the imaging device incorporating the color separation prism, the signal processing unit 62 converts the color characteristics stored in the coefficient storage unit 61 for the plurality of color signals output from the plurality of imaging elements 4R, 4G, and 4B. An operation (approximate inverse transformation) for multiplying by the coefficient (M ⁻¹ ) ′ is performed (step S111). As a result, it is possible to obtain a characteristic that approximates the reproduction system ideal characteristic that takes into account the spectral characteristics of the desired color reproduction system (step S112, FIG. 12F).

Through the process as described above, according to the method for determining the color characteristic conversion coefficient according to the present embodiment, the overall spectral characteristic when the color separation prism is incorporated into the imaging apparatus approaches the desired reproduction system ideal characteristic. Since such a matrix coefficient is obtained as a color characteristic conversion coefficient (M ⁻¹ ) ′, the determined color characteristic conversion coefficient is used as the signal processing unit on the imaging apparatus side incorporating the color separation prism to be measured. By using it in 62, it is possible to correct a design error and a manufacturing error of a color separation prism that greatly affect the spectral characteristics, and an ideal spectral characteristic in which a desired color reproduction system characteristic is added in a color imaging system. A characteristic close to can be obtained.

Further, according to the imaging apparatus according to the present embodiment, the coefficient storage unit 61 stores data indicating the color characteristic conversion coefficient (M ⁻¹ ) ′ obtained in the color characteristic conversion coefficient determination method, and performs signal processing. The unit 62 performs an operation of multiplying a plurality of color signals output from the plurality of image sensors 4R, 4G, and 4B by a color characteristic conversion coefficient (M ⁻¹ ) ′ stored in the coefficient storage unit 61. Therefore, it is possible to correct design errors and manufacturing errors of color separation prisms that have a large effect on spectral characteristics, and characteristics close to ideal spectral characteristics that take into account the characteristics of the desired color reproduction system in color imaging systems. Can be obtained.

Furthermore, according to the imaging apparatus according to the present embodiment, the slope of the characteristic curve indicating the spectral characteristic (film characteristic) of the color separation prism is converted to the ideal conversion characteristic as shown in FIGS. (See FIG. 2B and FIG. 12C.) Since it is designed to have an inclination corresponding to the inclination of the characteristic curve shown in FIG. 2, the overall imaging system when the color separation prism is incorporated in the imaging apparatus. It becomes easy to approximate the spectral characteristics to the ideal conversion characteristics. Thus, an ideal spectrum that takes into account the characteristics of a desired color reproduction system by combining with the color characteristic conversion coefficient (M ⁻¹ ) ′ obtained by the color characteristic conversion coefficient determination method according to the present embodiment. It becomes easy to obtain characteristics.

For example, the slope of the film characteristic of the color separation prism is assumed to show a steep rise as shown in FIG. 19, and the overall spectral transmission characteristic of the entire imaging system is converted as shown in FIG. Consider the case where the ideal characteristics deviate significantly. In this case, since the shape of the overall spectral transmission characteristic is rectangular for each color, the color characteristic conversion coefficient (M ⁻¹⁾ obtained by the color characteristic conversion coefficient determination method according to the present embodiment. ) 'Is difficult to obtain the ideal spectral characteristics sufficiently. The color characteristic conversion coefficient (M ⁻¹ ) ′ performs a relatively simple calculation by primary conversion as shown in Equation (3) of the above [Equation 3]. By simply performing such a relatively simple calculation, the rectangular characteristic cannot be made sufficiently close to the ideal characteristic having a gentle curve shape as shown in FIG.
[Second Embodiment]

  Next, a second embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the component substantially the same as the said 1st Embodiment, and description is abbreviate | omitted suitably.

FIG. 13 and FIG. 14 show the process for deriving the spectral characteristics of the imaging apparatus according to the present embodiment to the final ideal state, and the method for determining the color characteristic conversion coefficient (M ⁻¹ ) ′ in the present embodiment. It is shown with.

The process shown in FIGS. 13 and 14 is different from the process in the first embodiment shown in FIGS. 11 and 12 in steps S210 and S211 for obtaining the color characteristic conversion coefficient (M ⁻¹ ) ′. This is a part (part (E) → (F) in FIG. 14). In the first embodiment, the coefficient calculation unit 72 expresses the color characteristic conversion coefficient (M ⁻¹ ) ′ as functions r ₀ ′ (λ), g ₀ ′ (λ), b ₀ ′ (λ). Is calculated by an operation that minimizes the deviation of the spectral characteristic between the total spectral characteristic based on the actual measurement value and the reproduction system ideal characteristic represented by the functions r (λ), g (λ), and b (λ). I did it.

On the other hand, in the present embodiment, the coefficient calculation unit 72 first has positive values of functions r ′ (λ), g ′ (λ), which are obtained by performing reversible conversion using the conversion matrix M on the reproduction system ideal characteristics. Comparison between ideal conversion characteristics represented by b ′ (λ) and total spectral characteristics based on actual measurement values represented by functions r ₀ ′ (λ), g ₀ ′ (λ), and b ₀ ′ (λ) Then, the first color characteristic conversion coefficient N is obtained by an operation (such as the least square method) that minimizes the deviation (step S210). Then, the coefficient calculation unit 72 calculates the total spectral characteristics (FIG. 14E) based on the actual measurement values represented by the functions r ₀ ′ (λ), g ₀ ′ (λ), and b ₀ ′ (λ). On the other hand, by multiplying the first color characteristic conversion coefficient N, an approximate conversion ideal characteristic having a positive value approximated to the positive conversion ideal characteristic (FIG. 14C) is obtained (step S211, FIG. 14 (F)). Here, it is assumed that the approximate conversion ideal characteristic of a positive value is expressed by functions r ′ (λ) ⁺ , g ′ (λ) ⁺ , and b ′ (λ) ⁺ of positive values. Next, the second color characteristic is compared with the approximate approximate ideal characteristic of the positive value represented by this positive value function r ′ (λ) ⁺ , g ′ (λ) ⁺ , b ′ (λ) ^+. By performing the operation of multiplying the conversion matrix M ⁻¹ as the conversion coefficient, it is possible to obtain a characteristic that approximates the reproduction system ideal characteristic that takes into account the spectral characteristics of the desired color reproduction system (steps S111 and S112).

Note that the transformation matrix M ⁻¹ is a coefficient that is theoretically uniquely determined as described above with reference to FIGS. 2A and 2B, and is a positive value function r ′ (λ), g ′ ( This is an inverse matrix of the transformation matrix M used when obtaining the transformation ideal characteristics (FIG. 14C) represented by λ) and b ′ (λ). In the present embodiment, the color characteristic conversion coefficient (M ⁻¹ ) ′ in the first embodiment is
(M ⁻¹ ) ′ = N · M ⁻¹
Is equivalent to being given by the product of the first color characteristic conversion coefficient N and the second color characteristic conversion coefficient M ⁻¹ . Data indicating the color characteristic conversion coefficient (M ⁻¹ ) ′ represented by N · M ⁻¹ is stored in the coefficient storage unit 61 in the imaging apparatus in the same manner as in the first embodiment. Other parts are basically the same as those in the first embodiment.
[Other embodiments]

The present invention is not limited to the above embodiments, and other modifications can be made.
For example, in each of the above embodiments, the color separation optical system 1 that separates the incident light L in the order of the blue light LB, the red light LR, and the green light LG has been described as an example. However, the order of the color separation is not limited thereto. Alternatively, color separation may be performed in another order. In each of the above-described embodiments, an example in which three prisms are provided as a color separation optical system and the light is separated into three color lights has been shown. However, the present invention is provided with four or more prisms and has four or more colors. The present invention can also be applied to a color separation optical system that decomposes.

  In each of the above-described embodiments, the color imaging system using the color separation prism has been described. However, a single-plate color camera equipped with a color filter corresponding to each unit cell of the imaging element called a mosaic filter, or a surface The present invention can also be applied to all color cameras equipped with a color filter, such as a color camera equipped with a rotary color filter called a sequential method. In this case, the spectral characteristic of the filter may be measured in the same manner as the spectral characteristic of the color separation prism, and an optimum color characteristic conversion coefficient may be obtained based on the measurement result.

It is a block diagram which shows one structural example of the imaging device which concerns on the 1st Embodiment of this invention. It is explanatory drawing about the ideal characteristic applied with the color separation optical system which concerns on the 1st Embodiment of this invention, (A) shows the ideal characteristic before primary conversion, (B) is after primary conversion. Shows ideal characteristics. It is explanatory drawing about the characteristic (A) of the blue light reflection dichroic film | membrane DB in the color separation optical system which concerns on the 1st Embodiment of this invention, and the characteristic (B) of red light reflection dichroic film | membrane DR. FIG. 6 is a characteristic diagram showing a design example of a blue light reflecting dichroic film DB and a red light reflecting dichroic film DR in the color separation optical system according to the first embodiment of the present invention. It is a figure which shows the numerical example of the film | membrane design of the blue light reflection dichroic film | membrane DB in the color separation optical system which concerns on the 1st Embodiment of this invention. It is a figure which shows the numerical example of the film | membrane design of the red light reflection dichroic film | membrane DR in the color separation optical system which concerns on the 1st Embodiment of this invention. It is a characteristic view which shows an example of the spectral characteristic of the prism part in the imaging device which concerns on the 1st Embodiment of this invention. It is a characteristic view which shows an example of the spectral characteristic of optical elements other than the prism part in the imaging device which concerns on the 1st Embodiment of this invention. FIG. 6 is a characteristic diagram illustrating an example of a comprehensive spectral characteristic of the imaging optical system (before coefficient conversion) in the imaging apparatus according to the first embodiment of the present invention. It is a block diagram which shows an example of the measuring method of the spectral characteristics of a color separation prism. 3 is a flowchart showing a process for guiding spectral characteristics of the imaging apparatus according to the first embodiment of the present invention to a final ideal state. It is explanatory drawing which shows the process for guide | inducing the spectral characteristic of the imaging device which concerns on the 1st Embodiment of this invention to a final ideal state. It is a flowchart which shows the process for guide | inducing the spectral characteristic of the imaging device which concerns on the 2nd Embodiment of this invention to a final ideal state. It is explanatory drawing which shows the process for guide | inducing the spectral characteristic of the imaging device which concerns on the 2nd Embodiment of this invention to a final ideal state. It is sectional drawing which shows the structural example of the conventional color separation optical system. It is an xy chromaticity diagram showing chromaticity coordinates of three primary colors for obtaining ideal characteristics. It is a characteristic view which shows the normalized ideal characteristic. It is a characteristic view which shows the spectral characteristic of the conventional general color separation optical system. It is a characteristic view which shows an example of the characteristic of the dichroic film | membrane used with the conventional color separation optical system.

Explanation of symbols

  L ... incident light, LB ... blue light component, LR ... red light component, LG ... green light component, DB ... blue light reflecting dichroic film, DR ... red light reflecting dichroic film, DG ... green light reflecting dichroic film, 1 ... color Decomposing optical system, 2 ... photographing lens, 3 ... IR cut filter, 4R, 4G, 4B ... image sensor, 10 ... first prism, 20 ... second prism, 30 ... third prism, 51 ... first Trimming filter, 52 ... second trimming filter, 53 ... third trimming filter, 51AR ... first antireflection film, 52AR ... second antireflection film, 53AR ... third antireflection film, 60 ... imaging device Main unit 61 ... Coefficient storage unit 62 ... Signal processing unit 71 ... Measuring instrument 72 ... Coefficient calculation unit 73 ... Recording medium 74 ... Communication means 81 ... Spectroscope 82R, 82G, 82B ... Optical sensor Vout ... the video signal.

Claims (9)

Color characteristics multiplied by a plurality of color signals output from a plurality of image sensors in an imaging apparatus having a color separation prism in order to obtain a reproduction system ideal characteristic that takes into account the spectral characteristics of the desired color reproduction system. A method for determining a conversion coefficient, comprising:
The spectral characteristic of the color separation prism used for optically reproducing the ideal conversion characteristic obtained by performing a reversible conversion to reduce the negative spectral range with respect to the ideal reproduction characteristic is measured by a measuring instrument. Steps,
Based on the measured spectral characteristic of the color separation prism, a step of obtaining a total spectral characteristic of the entire imaging system when the color separation prism is incorporated in an imaging apparatus by a first arithmetic unit;
Obtaining a shift in spectral characteristics between the overall spectral characteristics and the reproduction system ideal characteristics or the conversion ideal characteristics by a second computing means;
A step of reducing the spectral characteristic deviation and obtaining a matrix coefficient by which the total spectral characteristic approaches the reproduction system ideal characteristic as the color characteristic conversion coefficient by a third calculation means. How to determine the characteristic conversion factor. In the step of obtaining the comprehensive spectral characteristics, the spectral characteristics of the constituent elements other than the color separation prism in the imaging apparatus are determined by the first calculation means using predetermined predetermined representative values. The color characteristic conversion coefficient determination method according to claim 1, wherein the total spectral characteristic is obtained based on a representative value of the color separation and the measured spectral characteristic of the color separation prism. The reproduction system ideal characteristic is a characteristic having a spectral region of a negative value converted from the chromaticity coordinates of the three primary colors of the desired color reproduction medium and indicated by the primary conversion of the color matching function of the XYZ color system. The color characteristic conversion coefficient determination method according to claim 1, wherein the color characteristic conversion coefficient is determined. The color separation prism separates incident light into at least three color light components of blue light, red light, and green light, and sequentially from the light incident side,
A first prism that has a first dichroic film and extracts a first color light component reflected by the first dichroic film;
A second prism that has a second dichroic film and extracts a second color light component transmitted through the first dichroic film and reflected by the second dichroic film;
And a third prism for extracting a third color light component that has passed through the first and second dichroic films,
The first and second dichroic films are designed such that the slope of the characteristic curve indicating the spectral characteristics is in accordance with the slope of the characteristic curve indicating the conversion ideal characteristic. Item 4. A method for determining a color characteristic conversion coefficient according to any one of Items 1 to 3. In the color separation prism, the first dichroic film has a film configuration that reflects blue light as the first color light component, and the second dichroic film has red light as the second color light component. And a film configuration that reflects
The slope of the transmission characteristic curve showing the transmittance with respect to the wavelength of the first dichroic film changes from 20% to 80% of the range between the minimum transmittance and the maximum transmittance within the wavelength range of 430 nm to 670 nm. Having an average slope value of 0.2 (% / nm) or more and 2.0 (% / nm) or less,
The slope of the transmission characteristic curve showing the transmittance with respect to the wavelength of the second dichroic film changes from 80% to 20% of the range between the maximum transmittance and the minimum transmittance within the wavelength range of 430 nm to 670 nm. The method for determining a color characteristic conversion coefficient according to claim 4, wherein the average inclination value is −2.0 (% / nm) or more and −0.2 (% / nm) or less. 6. The method according to claim 1, further comprising a step of recording on the recording medium identification information that associates the color characteristic conversion coefficient with the color separation prism that is the measurement target of the spectral characteristic. The method for determining the color characteristic conversion coefficient according to the item. The method for determining a color characteristic conversion coefficient according to claim 6, wherein in the step of recording on the recording medium, the identification information is recorded on the recording medium together with data indicating the obtained color characteristic conversion coefficient. . 8. A prism set comprising: the color characteristic conversion coefficient determination method according to claim 6; and a color separation prism which is a measurement target of the spectral characteristic, and the recording medium. A color separation prism which is a measurement target of the spectral characteristic in the method for determining a color characteristic conversion coefficient according to any one of claims 1 to 7,
A coefficient storage unit that stores data indicating the color characteristic conversion coefficient obtained in the method for determining a color characteristic conversion coefficient according to any one of claims 1 to 7,
A plurality of imaging elements provided corresponding to a plurality of color lights separated by the color separation prism, and outputting color signals corresponding to the incident color lights;
An image pickup apparatus comprising: a signal processing unit that performs an operation of multiplying a plurality of color signals output from the plurality of image pickup elements by a color characteristic conversion coefficient stored in the coefficient storage unit.

Images