Imaging device

Abstract

Provided are wide dynamic range, multi-plate and single-plate color imaging devices capable of performing flexible dimming control for each color by means of minimally configured filters. The multi-plate imaging device comprises: a movable polarizing filter that polarizes incident light; a rotation mechanism that rotates the movable polarizing filter with respect to an optical axis; and fixed polarizing filters respectively mounted at a predetermined angle at the front surfaces of imaging elements for receiving red light and blue light. The imaging device dims the red light and the blue light by means of the angle of rotation of the movable polarizing filter. The single-plate imaging device comprises: a movable polarizing filter that polarizes incident light; a rotation mechanism that rotates the movable polarizing filter with respect to an optical axis; and an imaging element having a color Bayer array in which a polarizing filter is mounted at a predetermined angle on red and blue color filters. The imaging device dims the red light and the blue light by means of the angle of rotation of the movable polarizing filter.

Description

[Technical Field]

[0001] The present invention relates to an imaging device. [Background technology]

[0002] Image pickup devices for capturing color images include multi-chip image pickup devices that use a color separation optical system and multiple monochrome image pickup elements, and single-chip image pickup devices that use one color Bayer array image pickup element.

[0003] In these imaging devices, when the color temperature of the light source in the imaging environment is low (for example, sunlight at sunset or halogen lamps) or when the color temperature is high (for example, sunlight during the day or blue LED (Light Emitting Diode) lighting), the amount of red or blue light is high, resulting in an image with saturated color components.

[0004] If the incident light is reduced using a lens aperture or other means, the dynamic range can be secured without saturating the color components with a large amount of light, but the amount of light from other color components is also reduced, and when the insufficient light is compensated for by a downstream amplifier circuit, the noise of those color components increases. Therefore, in order to suppress the increase in noise, a means is required to reduce the amount of light for each color.

[0005] One way to reduce the amount of light for each color is to use a CC (Color Compensating) filter, which is made of colored glass. By using a CC filter with a color appropriate to the imaging environment, it is possible to reduce specific color components from the incident light, thereby obtaining the most natural image.

[0006] Another method is to use an ND (Neutral Density) filter, which is installed between the color separation optical system and the image sensor in multi-chip imagers, or for each color filter in single-chip imagers, to accurately attenuate specific color components that have a high amount of light.

[0007] Another method is to use a liquid crystal filter, a type of ND filter, which can obtain a transmittance that corresponds to the applied voltage, and by installing a liquid crystal filter for each color, flexible dimming control can be achieved to suit any imaging environment.

[0008] Another method is to use an electronic shutter function that controls the exposure time of the image sensor. The electronic shutter is advantageous in terms of cost and space because it allows light reduction control without the need for additional devices such as filters.

[0009] Patent Document 1 describes a multi-plate imaging device that uses a liquid crystal filter.

[0010] Furthermore, Patent Document 2 describes a multi-plate imaging device that uses a liquid crystal filter and an amplifier.

[0011] Furthermore, Patent Document 3 describes a four-chip imaging device in which the amount of red light is reduced by an ND filter to make the amount of light incident on each imaging element approximately equal. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Utility Model Application Publication No. 6-70386 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-209674 [Patent Document 3] Japanese Patent Application Publication No. 7-250332 Summary of the Invention [Problem to be solved by the invention]

[0013] In the case of using CC filters, a number of CC filters according to the expected imaging environment and a mechanism for switching between them are required, which increases costs and necessitates installation space. In addition, since the colors of the CC filters are fixed, seamless dimming control is not possible, and flexibility is poor.

[0014] In the case of using ND filters, it is difficult to install a mechanism for switching ND filters for each image sensor in a multi-chip image sensor due to space limitations, and it is also impossible to switch ND filters on a pixel-by-pixel basis in a single-chip image sensor. As a result, the amount of light reduction for each color is fixed, resulting in a lack of flexibility.

[0015] When using a liquid crystal filter, a liquid crystal filter is required for each image sensor in a multi-plate image sensor, which increases costs. Furthermore, because liquid crystal filters are susceptible to heat and ultraviolet light, there is also the problem that the liquid crystal filter quickly deteriorates when installed inside an image sensor used outdoors. Furthermore, a single-plate image sensor requires a matrix-shaped liquid crystal filter that matches the pixel size (a few microns) of the image sensor, but this is difficult to manufacture with current technology.

[0016] In the case of a method using an electronic shutter, if the exposure time differs for each color, the amount of afterimage generated will differ, resulting in an unnatural image with colored afterimages. Also, since a general image sensor cannot control the electronic shutter on a pixel-by-pixel basis, a method using an electronic shutter cannot be implemented in a single-chip image sensor.

[0017] An object of the present invention is to provide a multi-chip or single-chip color imaging device with a wide dynamic range that allows flexible light reduction control for each color using a minimum number of filters. [Means for solving the problem]

[0018] To solve the above problem, one representative multi-plate color imaging device of the present invention has a movable polarizing filter that polarizes incident light, a rotation mechanism that rotates the movable polarizing filter about the optical axis, and a fixed polarizing filter mounted at a predetermined angle in front of an imaging element that receives red and blue light, and attenuates the red and blue light depending on the rotation angle of the movable polarizing filter.

[0019] Furthermore, one typical single-chip color imaging device of the present invention has a movable polarizing filter that polarizes incident light, a rotation mechanism that rotates the movable polarizing filter about the optical axis, and a color Bayer array imaging element equipped with polarizing filters with red and blue color filters at a predetermined angle, and reduces red and blue light depending on the rotation angle of the movable polarizing filter. [Effects of the Invention]

[0020] According to the present invention, it is possible to flexibly control the dimming of each color using a minimum number of filters, and it is possible to realize a multi-chip and single-chip color image pickup device with a wide dynamic range.

[0021] Problems, configurations, and effects other than those described above will become apparent from the following description of the preferred embodiment of the invention. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a block diagram illustrating an example of the configuration of a multi-chip imaging device according to a first embodiment. [Figure 2A] FIG. 2A is a diagram showing an example of a filter rotation mechanism (φ=−45°). [Figure 2B] FIG. 2B is a diagram showing an example of a filter rotation mechanism (φ=0°). [Figure 2C] FIG. 2C is a diagram showing an example of a filter rotation mechanism (φ=+45°). [Figure 3A] FIG. 3A is a diagram showing another example of a filter rotation mechanism (φ=−45°). [Figure 3B] FIG. 3B is a diagram showing another example of the filter rotation mechanism (φ=0°). [Figure 3C] FIG. 3C is a diagram showing another example of the filter rotation mechanism (φ=+45°). [Figure 4] FIG. 4 is a diagram illustrating an example of reflected light in the color separation optical system according to the first embodiment. [Figure 5] FIG. 5 is a diagram illustrating an example of polarized light at the movable polarizing filter and reflected light at the color separation optical system according to the first embodiment. [Figure 6] FIG. 6 is a diagram showing the relationship between the rotation angle of the movable polarizing filter when θ=45° and the amount of attenuation of red light and blue light. [Figure 7] FIG. 7 is a diagram showing the relationship between the rotation angle of the movable polarizing filter when θ=30° and the amount of attenuation of red light and blue light. [Figure 8] FIG. 8 is a block diagram illustrating an example of the configuration of a single-chip imaging device according to the second embodiment. [Figure 9] FIG. 9 is a diagram illustrating a color filter and a fixed polarization filter of an image sensor according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, in the description of the drawings, the same parts are designated by the same reference numerals.

[0024] [Example 1] FIG. 1 is a block diagram showing an example of the configuration of a multi-chip imaging device according to a first embodiment.

[0025] 1, the imaging device 1 is made up of a lens 2, a movable polarizing filter 3, a filter rotation mechanism 4, a color separation optical system 5, a fixed polarizing filter 6R, a fixed polarizing filter 6B, an image sensor 7R, an image sensor 7G, an image sensor 7B, a video signal processing unit 8, and a CPU (Central Processing Unit) 9. The image sensor 7R, the image sensor 7G, and the image sensor 7B are all monochrome image sensors.

[0026] Incident light from the subject is focused by lens 2, passes through movable polarizing filter 3, and is then separated into red, green, and blue light by color separation optical system 5. The separated red light is received by image sensor 7R via fixed polarizing filter 6R, the green light is received by image sensor 7G without passing through a fixed polarizing filter, and the blue light is received by image sensor 7B via fixed polarizing filter 6B, and each is photoelectrically converted into an electrical signal. Video signal processing unit 8 performs various signal processes on the photoelectrically converted video signal, and the video signal output unit outputs a video signal such as HD-SDI (High Definition Serial Digital Interface). CPU unit 9 can control each unit of imaging device 1.

[0027] The movable polarizing filter 3 is structured so that it can be rotated in the range of -θ to +θ (0°<θ≦45°) with respect to the optical axis by the filter rotation mechanism 4. The filter rotation mechanism 4 is controlled by the CPU unit 9. Alternatively, it may be provided with an operation unit that allows manual rotation. It may also be provided with a reading means such as a potentiometer to more precisely control the rotation angle.

[0028] An example of a filter rotation mechanism is shown in Figures 2A, 2B, and 2C. It comprises a circular movable polarizing filter 3, and a motor and support mechanism around its periphery that rotates the movable polarizing filter 3. The support mechanism can support the movable polarizing filter 3 from both sides, and may have rollers (not shown) that contact the movable polarizing filter 3. The dashed square indicates the imaging area, and the black dot indicates the rotation axis. Because the rotation axis is within the imaging area, it is not possible to provide a physical rotation axis. This method has the advantage of minimizing the size and installation space of the movable polarizing filter 3.

[0029] Another example of a filter rotation mechanism is shown in Figures 3A, 3B, and 3C. It comprises a fan-shaped movable polarizing filter 3, with a motor and support mechanism at its base that rotates the movable polarizing filter 3 like a pendulum. The dashed square indicates the imaging area, and the black dot indicates the rotation axis. This method has the advantage of simplifying the mechanism and control, as the support mechanism that rotates together with the movable polarizing filter 3 is fixed to the rotation axis. In Figures 3A, 3B, and 3C, a motor is provided on the rotation axis, but a motor can also be provided on the outer periphery of the movable polarizing filter 3.

[0030] An example of reflected light from the color separation optical system according to the first embodiment is shown in Fig. 4, and an example of polarization by the movable polarizing filter and reflected light from the color separation optical system is shown in Fig. 5. In the multi-plate imaging device 1, the P-wave component of the reflected light may be significantly attenuated due to reflection within the color separation optical system 5, as shown in Figs. 4 and 5, so it is desirable to position the movable polarizing filter 3 at a reference angle of 0° so that the light is polarized into an S-wave component with respect to the reflection direction of the color separation optical system 5. Here, the reference angle of 0° represents the reference angle for rotation of the movable polarizing filter 3.

[0031] The fixed polarizing filter 6R is mounted in front of the image sensor 7R at an angle of -θ relative to the reference angle of 0° of the movable polarizing filter 3. Similarly, the fixed polarizing filter 6B is mounted in front of the image sensor 7B at an angle of +θ relative to the reference angle of 0° of the movable polarizing filter 3.

[0032] If the rotation angle of the movable polarizing filter 3 is φ, then the red light that reaches the image sensor 7R via the movable polarizing filter 3 and the fixed polarizing filter 6R is attenuated to cos(φ+θ). Similarly, the blue light that reaches the image sensor 7B via the movable polarizing filter 3 and the fixed polarizing filter 6B is attenuated to cos(φ-θ).

[0033] That is, for red and blue light, if the angular deviation between the movable polarizing filter 3 and the fixed polarizing filters 6R and 6B is 0°, the light passes through without being attenuated, but as the deviation increases, the amount of attenuation increases, and when the deviation reaches 90°, the light is completely blocked. Green light is not affected by the angle of the movable polarizing filter 3.

[0034] As a result, in an imaging environment with a low color temperature, by controlling the filter rotation mechanism 4, the movable polarizing filter 3 can be rotated in the +θ direction, thereby reducing the amount of dimming of blue light and increasing the amount of dimming of red light; conversely, in an imaging environment with a high color temperature, the movable polarizing filter 3 can be rotated in the -θ direction, thereby reducing the amount of dimming of red light and increasing the amount of dimming of blue light.

[0035] With this method, there is a trade-off between the amount of dimming of red light and blue light, and it is not possible to achieve both, and there is no function to dim green light. However, the main light sources that require dimming control are reddish light with a low color temperature or blue light with a high color temperature, and green or purple light sources are unlikely. For this reason, it can be said that this method is suited to the actual operation of the imaging device 1.

[0036] Figures 6 and 7 show the relationship between the rotation angle of the movable polarizing filter at angle θ and the amount of attenuation of red and blue light. The maximum rotation angle of the movable polarizing filter 3 and the angle θ of the fixed polarizing filters 6R and 6B are arbitrary. For example, when θ = 45° as shown in Figure 6, if the movable polarizing filter 3 is set to its maximum angle on the blue side of +45°, blue light is not attenuated but red light is completely blocked. Although a wider dynamic range can be expected for red light, even when a rotation angle of 0° is set, which means that neither red nor blue light is attenuated, both will be attenuated by a factor of 1 / √2. Therefore, the angle θ must be determined taking into account the amount of attenuation in steady state (when the rotation angle is 0°).

[0037] Although the imaging device in FIG. 1 is a three-chip type, it may be a four-chip type in which the green light is further divided into two.

[0038] As described above, according to the first embodiment, it is possible to realize a multi-chip imaging device with a wide dynamic range that solves problems such as cost, installation space, flexibility, filter life, and color afterimage.

[0039] Furthermore, by positioning the movable polarizing filter so that its reference angle of 0° polarizes the S-wave component relative to the reflection direction of the color separation optical system, it is possible to reduce the effect of the P-wave component of the reflected light being significantly attenuated by reflection within the color separation optical system.

[0040] [Example 2] FIG. 8 is a block diagram showing an example of the configuration of a single-chip imaging device according to the second embodiment.

[0041] 8 shows the configuration of Example 1 except for removing the color separation optical system 5, and replacing the multiple fixed polarization filters 6R, 6B and monochrome image sensors 7R, 7G, 7B with a single color Bayer array image sensor 10. The image sensor 10 can output a RAW signal or a color signal obtained by converting a RAW signal into a color signal.

[0042] The color filters and fixed polarizing filters of an image sensor according to Example 2 are shown in Fig. 9. In addition to the color filters in a Bayer array as shown in Fig. 9, the image sensor 10 of this example is an image sensor equipped with a fixed polarizing filter 6R in which the red color filter is angled by -θ with respect to the reference angle of 0° of the movable polarizing filter 3, and a fixed polarizing filter 6B in which the blue color filter is angled by +θ with respect to the reference angle of 0° of the movable polarizing filter 3.

[0043] Other operation examples and principles are the same as those in the first embodiment.

[0044] As described above, according to the second embodiment, problems such as cost and mounting space in a single-chip imaging device can be solved, and a seamless, flexible, wide dynamic range imaging device can be realized, which has been difficult to implement due to technical restrictions of a liquid crystal filter and an electronic shutter.

[0045] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0046] 1: imaging device, 2: lens, 3: movable polarizing filter, 4: filter rotation mechanism, 5: color separation optical system, 6R: fixed polarizing filter, 6B: fixed polarizing filter, 7R: imaging element, 7G: imaging element, 7B: imaging element, 8: video signal processing unit, 9: CPU (Central Processing Unit), 10: color Bayer imaging element

Claims

1. a movable polarizing filter for polarizing incident light; a rotation mechanism that rotates the movable polarizing filter about an optical axis; a fixed polarizing filter mounted at a predetermined angle on the front surface of an image sensor that receives red light and blue light; and Attenuating red light and blue light according to the rotation angle of the movable polarizing filter; the movable polarizing filter can be rotated by the rotation mechanism within a range of −θ to +θ (0°<θ≦45°) with respect to the optical axis, the fixed polarizing filter mounted on the front surface of the image sensor that receives red light is mounted at an angle of −θ with respect to a reference angle of the movable polarizing filter, The fixed polarizing filter mounted on the front surface of the image sensor that receives blue light is mounted at an angle of +θ with respect to the reference angle of the movable polarizing filter. A multi-chip color imaging device.

2. 2. The multi-chip color imaging device according to claim 1, The reference angle of the movable polarizing filter is set so as to polarize the light into an S-wave component with respect to the reflection direction of the color separation optical system. A multi-chip color imaging device.

3. a movable polarizing filter for polarizing incident light; a rotation mechanism that rotates the movable polarizing filter about an optical axis; a color Bayer array image sensor equipped with a polarization filter with red and blue color filters at a predetermined angle; and Attenuating red light and blue light according to the rotation angle of the movable polarizing filter; the movable polarizing filter can be rotated by the rotation mechanism within a range of −θ to +θ (0°<θ≦45°) with respect to the optical axis, a red color filter is provided with the polarizing filter angled by −θ with respect to the reference angle of the movable polarizing filter; The polarizing filter is mounted on a blue color filter at an angle of +θ with respect to the reference angle of the movable polarizing filter. A single-chip color imaging device.

Images