JP2006058511A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the color reproducibility of a color imaging apparatus. <P>SOLUTION: A color imaging apparatus is provided for imaging an optical image of a subject obtained through a lens 8 with an imaging means 9, wherein a color temperature conversion filter 12 is fixed and set on the light input side of the imaging means 9. The color temperature conversion filter 12 has characteristics for improving color reproducibility relative to a various types of a light source compared to the case where the color temperature conversion filter is not used. Specifically, where the spectral transmittance of a wavelength γ[nm] is defined as T(λ), the filter 12 has the characteristics in which 1.3≤T(450)/T(540)≤1.8, 1.3≤T(540)/T(640)≤1.5, and 1.7≤T(450)/T(610)≤3.0 are satisfied. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a color image capturing apparatus such as a film camera or a digital camera, and more particularly to a color image capturing apparatus that realizes high color reproducibility.

  When capturing a color image of a subject, it is necessary to correct the captured image according to the spectral characteristics of the light source that illuminates the subject. For example, in the case of a conventional digital camera, the level difference of each color of red (R), green (G), and blue (B) constituting a captured color image is detected, and the gain of each color is set so that the level difference becomes zero. Is adjusted. This adjustment is called white balance adjustment and is widely adopted. However, there is a problem that the color reproducibility of the captured image is not sufficient only by performing the white balance adjustment.

  Therefore, conventionally, for example, as described in Patent Document 1 below, in addition to white balance adjustment, a plurality of types of color temperature conversion filters are prepared, and an optimum color temperature conversion filter is selected according to the spectral characteristics of the illumination light source. A configuration is adopted in which this is inserted into the optical path of the imaging device.

JP-A-5-68257

  By using the color temperature conversion filter, the color reproducibility of the captured image can be improved. However, a conventional imaging device equipped with a color temperature conversion filter is provided with a plurality of types of color temperature conversion filters and a control system for selecting an optimum color temperature conversion filter from among them according to the shooting situation. For this reason, there is a problem that the apparatus becomes large and the manufacturing cost increases. Although it is possible for the user to select the color temperature conversion filter by manual operation, skill is required to select the color temperature conversion filter according to the spectral characteristics of the illumination light source. Have difficulty.

  An object of the present invention is to provide a small-sized and low-cost color image capturing apparatus having excellent color reproducibility.

  The color image capturing apparatus of the present invention is characterized in that a color temperature conversion filter is fixedly installed on the light input side of the image capturing means in the color image capturing apparatus that captures the subject light image obtained through the lens by the image capturing means. .

  The color temperature conversion filter of the color image pickup apparatus of the present invention is characterized in that color reproducibility is improved with respect to various light sources as compared with a state without the color temperature conversion filter.

  The color temperature conversion filter of the color image pickup device of the present invention has 1.3 ≦ T (450) / T (540) ≦ 1.8, where T (λ) is the spectral transmittance of the wavelength λ [nm]. It is characterized by having the following characteristics.

  The color temperature conversion filter of the color image pickup device of the present invention has 1.3 ≦ T (540) / T (610) ≦ 1.5, where T (λ) is the spectral transmittance of the wavelength λ [nm]. It is characterized by having the following characteristics.

  The color temperature conversion filter of the color image pickup apparatus of the present invention has 1.7 ≦ T (450) / T (610) ≦ 3.0, where T (λ) is the spectral transmittance of wavelength λ [nm]. It is characterized by having the following characteristics.

  The color image pickup apparatus of the present invention is characterized in that the image pickup means is a solid-state image pickup device.

  The color image capturing apparatus according to the present invention includes signal processing means for performing white balance adjustment on captured image data output from the solid-state image sensor.

  The color image pickup apparatus of the present invention is characterized in that the image pickup means is a film.

  In the present invention, since the color temperature conversion filter for improving the color reproducibility of the captured image with respect to various illumination light sources is fixedly installed in the optical path in the optical system, a color image capturing apparatus having excellent color reproducibility is reduced in size and cost. Can be realized.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram of a digital still camera as an example of a color image capturing apparatus according to an embodiment of the present invention. The present invention can be applied not only to a digital still camera but also to a digital video camera, a digital camera mounted on a mobile phone, and the like, and the present invention is also applied to a film camera mounted with an optical system portion shown in FIG. Applicable.

  The digital still camera shown in FIG. 1 includes a photographing lens 8, a solid-state image pickup device 9 such as a CCD or a CMOS, a diaphragm 10 and an infrared cut filter 11 provided between the two, and a color temperature described later in detail. A conversion filter 12 and an optical low-pass filter 13 are provided.

  In the present invention, only one type of color temperature conversion filter 12 is used, and a subject image incident on the photographing lens 8 is always photoelectrically converted by the solid-state image sensor 9 after passing through the color temperature conversion filter 12. The place where the color temperature conversion filter 12 is fixedly installed in the optical path is between the infrared cut filter 11 and the optical low-pass filter 13 in the illustrated example, but may be anywhere on the light input side of the solid-state imaging device 9.

  The CPU 15 that controls the entire digital still camera controls the light emitting unit 16 and the light receiving unit 17 for flash, controls the lens driving unit 18 to adjust the position of the photographing lens 8 to the focus position, and stops the aperture driving unit. The opening amount of the diaphragm 10 is controlled via 19 so that the exposure amount becomes an appropriate exposure amount.

  Further, the CPU 15 drives the solid-state image sensor 9 via the image sensor driving unit 20 and outputs the subject image captured through the photographing lens 8 and the filters 11, 12, 13 as a color signal. In addition, a user instruction signal is input to the CPU 15 through the operation unit 21, and the CPU 15 performs various controls according to the instruction.

  The operation unit 21 includes a shutter button (release button). When the shutter button is half-pressed (switch S1), focus adjustment and exposure adjustment are performed, and when the shutter button is fully pressed (switch S2), Imaging is performed.

  The electric control system of the digital still camera includes an analog signal processing unit 22 connected to the output of the solid-state imaging device 9 and A / D conversion for converting RGB color signals output from the analog signal processing unit 22 into digital signals. The circuit 23 is provided and these are controlled by the CPU 15.

  Furthermore, the electric control system of the digital still camera includes a memory control unit 25 connected to the main memory 24, a digital signal processing unit 26 that performs white balance adjustment, gamma correction, and the like, and compresses a captured image into a JPEG image. A compression / expansion processing unit 27 that expands or compresses a compressed image; an integration unit 28 that integrates photometric data to be described later to adjust the gain of white balance; and an external memory control unit 30 to which a removable recording medium 29 is connected. And a display control unit 32 to which a liquid crystal display unit 31 mounted on the rear surface of the camera is connected. These are connected to each other by a control bus 33 and a data bus 34, and are controlled by commands from the CPU 15.

  In the digital still camera having such a configuration, the digital signal processing unit 26 uses the analog signal processing unit 22 and the A / D conversion by using the image data output in a moving image state from the solid-state imaging device 9 as photometry data when the shutter button is half-pressed. The data is taken in through the circuit 23 and processed. Based on the result of this data processing, the CPU 15 adjusts the focus position of the lens 8 and opens / closes the diaphragm 10 to adjust the exposure amount.

  Further, the integrating unit 28 integrates the R component, G component, and B component in the photometric data, and passes the integration result to the digital signal processing unit 26. The digital signal processing unit 26 adds the integrated value of the R component and the G component. The gains of the R, G, and B signals are determined so that the integrated value of B and the integrated value of the B component are equal.

  When the shutter button is fully pressed, still image data is output from the solid-state imaging device 9 to the digital signal processing unit 26 via the analog signal processing unit 22 and the A / D conversion circuit 23. The digital signal processing unit 26 multiplies the R signal, B signal, and G signal constituting the image data by the R signal gain, G signal gain, and B signal gain obtained from the above-mentioned photometric data. The balance adjustment is performed, and in addition, gamma correction, RGB / YC conversion processing, and the like are performed to generate still image data including a luminance signal and a color difference signal. The compression / decompression processing unit 27 compresses the still image data into JPEG data, The external memory control unit 30 stores the JPEG data in the recording medium 29.

  Next, the color temperature conversion filter 12 mounted on the digital still camera of this embodiment will be described.

  Illumination light sources used when a subject is imaged by a color image capturing apparatus generally include an A light source, a C light source, a D50 light source, a D55 light source, a D65 light source, a D75 light source, and the like. FIG. 2 is a graph showing the relationship between the wavelength and intensity of each light source. The wavelength that human eyes perceive as blue is around 450 nm, the wavelength perceived as green is around 540 nm, and the wavelength perceived as red is around 610 nm. As can be seen from FIG. Or

  In order to image a subject with good color reproducibility, it is preferable to use a bluish color temperature conversion filter under a reddish illumination light source and a reddish color temperature conversion filter under a bluish illumination light source. However, in the present embodiment, since one color temperature conversion filter 12 is fixedly installed in the color image capturing apparatus, it is necessary to select a color temperature conversion filter suitable for all illumination light sources.

  FIG. 3 is a graph showing the relationship between the wavelength and spectral transmittance of four types of color temperature conversion filters (a filter, b filter, c filter, and d filter). All filters from the a filter to the d filter have a lower spectral transmittance as they go from the blue to the longer wavelength side, and the spectral transmittance of the a filter is the highest and becomes a b filter, a c filter, and a d filter. Spectral transmittance is small.

  The color reproducibility obtained by inserting each of these color temperature conversion filters into the optical path of the optical system and imaging the color to be evaluated is an area on the u′v ′ chromaticity diagram (hereinafter referred to as an evaluation area). The evaluated figure is FIG. In addition, as an evaluation object color, the test color chart No. 1-No. Although 8 is used, it is not limited to this.

  When the evaluation area obtained without the color temperature conversion filter under the light source A is 0.00393, the evaluation area is 0.00472 when the a filter is inserted, and the evaluation area is 0.002 when the b filter is inserted. When the c filter is inserted, the evaluation area is 0.00555, and when the d filter is inserted, the evaluation area is 0.00577. In the case of the A light source, the evaluation area increases even if any of the color temperature conversion filters a, b, c, and d is inserted, compared to the evaluation area without the filter, and the color reproducibility of each filter is increased. It can be seen that it has improved.

  In the case of the D65 light source, the evaluation area obtained without the color temperature conversion filter is 0.00719, the evaluation area becomes 0.00726 when the a filter is inserted, and the evaluation area becomes 0.00756 when the b filter is inserted. The evaluation area becomes 0.00740 by insertion, and the evaluation area becomes 0.00707 by insertion of the d filter. Therefore, in the case of the D65 light source, the evaluation area when the d filter is inserted is smaller than the evaluation area obtained without the color temperature conversion filter, and the color reproducibility is reduced by inserting the a, b, and c filters. Although it increases, it can be seen that the color reproducibility is lowered by the d filter insertion.

  In FIG. 4, when the evaluation area obtained when each filter is inserted with each light source is larger than the evaluation area without a filter, the value is enclosed by an ellipse. A portion surrounded by the ellipse is a portion where the color reproducibility is improved. According to FIG. 4, it can be seen that if the b filter is fixedly installed in the optical path of the optical system as the color temperature conversion filter 12, the color reproducibility is improved for all light sources. It can also be seen that the a filter and the c filter have improved color reproducibility with respect to light sources other than the D75 light source, and in particular, the c filter has a lower color reproducibility with the D75 light source than the a filter.

  FIG. 5 shows spectral transmittances T (450), T (540), and T (610) at wavelengths of 450 nm, 540 nm, and 610 nm in the characteristic graph of each filter shown in FIG. 3, and “450 nm / 540 nm” of each spectral transmittance. , “540 nm / 610 nm” and “450 nm / 610 nm” ratio values.

As shown in FIG. 4, it is most preferable to insert the b filter as the color temperature conversion filter 12, and the characteristic of this b filter is the value of the spectral transmittance ratio [Characteristic 1].
1.30 ≦ T (450) / T (540) ≦ 1.73
1.28 ≦ T (540) / T (610) ≦ 1.45
1.66 ≦ T (450) / T (610) ≦ 2.53
It can be expressed as.

In addition, as described above, since the color reproducibility is improved with many light sources even with the c filter, the characteristics including the b filter and the c filter are the values of the spectral transmittance ratio.
[Characteristic 2]
1.30 ≦ T (450) / T (540) ≦ 1.93
1.28 ≦ T (540) / T (610) ≦ 1.63
1.66 ≦ T (450) / T (610) ≦ 3.18
It can be expressed as.

Summarizing the above, considering that the color reproducibility is slightly reduced with the D75 light source in the c filter, and further considering the range in which the color reproducibility is reliably improved with each light source,
[Characteristic 3]
1.30 ≦ T (450) / T (540) ≦ 1.80
1.30 ≦ T (540) / T (610) ≦ 1.50
1.70 ≦ T (450) / T (610) ≦ 3.00
It is good to do.

  As described above, the color reproducibility is improved by using the color temperature conversion filter 12 having any one of the above-described characteristic 1, characteristic 2, and characteristic 3. Furthermore, the color reproducibility is further improved by using the color temperature conversion filter 12 and performing the same white balance adjustment as in the prior art.

  The characteristics of the color temperature conversion filter, trade name LB100, manufactured by Hoya Glass Co., Ltd. are close to the characteristics of the b filter, and LB120 is close to the c filter. Therefore, these existing color temperature conversion filters are used as color images. It is good also as a structure mounted in an imaging device.

  Also, in the case of a digital camera, white balance adjustment can be performed by the digital signal processing unit, but in the case of a film camera, white balance adjustment cannot be performed on the camera side. However, by installing the above-described color temperature conversion filter in the optical system, the color reproducibility is improved as compared with the case where the color temperature conversion filter is not provided.

  The color image capturing apparatus according to the present invention is useful as a digital camera, a film camera, or the like because color reproducibility is improved at low cost.

1 is a block diagram of a digital still camera according to an embodiment of the present invention. It is a graph which shows the relationship between the wavelength and intensity | strength of various light sources. It is a graph which shows the relationship between the wavelength of four types of color temperature conversion filters, and spectral transmittance. It is a figure which shows the evaluation result of color reproducibility when four types of color temperature conversion filters shown in FIG. 3 are used. It is a figure which shows the characteristic range of four types of color temperature conversion filters shown in FIG.

Explanation of symbols

8 Shooting Lens 9 Solid Image Sensor 10 Aperture 11 Infrared Cut Filter 12 Color Temperature Conversion Filter 13 Optical Low-Pass Filter 15 CPU
26 Digital Signal Processing Unit 28 Integration Unit

Claims (8)

  A color image pickup apparatus for picking up a subject light image obtained through a lens with an image pickup means, wherein a color temperature conversion filter is fixedly installed on the light input side of the image pickup means.   The color image capturing apparatus according to claim 1, wherein the color temperature conversion filter has a characteristic that color reproducibility is improved with respect to various light sources as compared with a state without the color temperature conversion filter.   The color temperature conversion filter has a characteristic of 1.3 ≦ T (450) / T (540) ≦ 1.8, where T (λ) is a spectral transmittance of a wavelength λ [nm]. The color image imaging device according to claim 1 or 2.   The color temperature conversion filter has a characteristic of 1.3 ≦ T (540) / T (610) ≦ 1.5, where T (λ) is a spectral transmittance of a wavelength λ [nm]. The color image imaging device according to any one of claims 1 to 3.   The color temperature conversion filter has a characteristic of 1.7 ≦ T (450) / T (610) ≦ 3.0, where T (λ) is a spectral transmittance of a wavelength λ [nm]. The color image capturing device according to any one of claims 1 to 4.   6. The color image pickup apparatus according to claim 1, wherein the image pickup unit is a solid-state image pickup device.   The color image capturing apparatus according to claim 6, further comprising a signal processing unit that performs white balance adjustment on captured image data output from the solid-state image sensor.   6. The color image pickup apparatus according to claim 1, wherein the image pickup unit is a film.

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