JP2011040839A - Optical device and digital camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device capable of sufficiently eliminating reflection light. <P>SOLUTION: First, three images are acquired with an image pickup element by rotating a transmission polarization axis by 60°. Then, two images except the image having the highest image level in the three images are selected. After that, images are further acquired by an intermediate transmission polarization axis of the transmission polarization axis 21a of the two images is acquired, and of the images, an image having the largest number of dark pixels is selected. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical device and a digital camera.

  Conventionally, a liquid crystal unit and a polarizing film are provided. The liquid crystal unit rotates a transmission polarization axis of reflected light of incident light by a predetermined angle, and the polarizing film reflects reflected light (for example, reflected light of window glass). ) Is known (see the following publication).

JP 2000-266931 A

  However, when the transmission polarization axis of the reflected light is rotated by a predetermined angle, the deviation from the optimum value (the angle of the transmission polarization axis at which the reflected light is weakest) becomes large depending on the rotation angle, and the reflected light is sufficiently removed. There is a risk that it will not be possible. In addition, when there are a plurality of polarized reflectors or the polarized reflectors are widely distributed on the light receiving surface of the image sensor, the liquid crystal unit is set to a specific transmitted polarization axis when the transmitted polarization axis differs depending on the reflected light. There is a possibility that only specific reflected light can be removed only by setting.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an optical device and a digital camera that can sufficiently remove reflected light.

  In order to solve the above problem, an invention according to claim 1 is an optical element comprising a liquid crystal element that rotates a transmission polarization axis of image light of a subject incident on a photographing optical system and a polarization filter that transmits only polarized light in a specific direction. An imaging element that converts image light of the subject that has passed through the imaging optical system and the optical element into an electrical signal, and a control unit that controls a voltage applied to the liquid crystal element based on an output of the imaging element. The control means first rotates the transmission polarization axis by 60 ° to acquire three images by the imaging device, and then removes two images excluding the image having the highest image level from the three images. And then further acquiring an image with a transmission polarization axis that is intermediate between the transmission polarization axes of the two images, and selecting an image with the largest number of dark pixels among these images.

  According to a second aspect of the present invention, in the optical device according to the first aspect, the control means includes two images excluding an image having the highest image level among the three images and transmission polarization axes of the two images. Compare the images acquired with the intermediate transmission polarization axis, and acquire further images with the intermediate transmission polarization axis of the two images excluding the transmission polarization axis that acquired the image with the brightest pixel among those images, Of these images, the image having the most dark pixels is selected.

  According to a third aspect of the present invention, there is provided an optical element comprising a liquid crystal element that rotates a transmission polarization axis of image light of a subject incident on a photographing optical system, and a polarizing filter that transmits only polarized light in a specific direction, and the photographing optical system. And an imaging element that converts image light of the subject that has passed through the optical element into an electrical signal, and a control unit that controls driving of the liquid crystal element based on an output of the imaging element. A plurality of images are acquired by the imaging element by rotating the transmission polarization axis in a range of at least 90 ° or more, and then the pixels at the same position between the acquired images are compared to determine the pixel with the lowest pixel level. The plurality of images are selected and combined into a single image.

  According to a fourth aspect of the present invention, in the optical device according to any one of the first to third aspects, an exposure control value is fixed when the transmission polarization axis is rotated and the image is acquired by the imaging device. It is characterized by that.

  The optical device according to any one of claims 1 to 4 is a digital camera.

  According to the present invention, the reflected light can be sufficiently removed.

FIG. 1 is a block diagram showing the configuration of the optical apparatus according to the first embodiment of the present invention. FIG. 2A shows a transmission polarization axis where the reflected light is the strongest among the image light of the subject incident on the objective lens, and FIG. 2B shows a transmission polarization axis where the reflected light is the weakest. It is a figure for demonstrating the method to remove reflected light using the optical apparatus of. FIG. 3 is a view for explaining a method of removing reflected light using the optical device according to the second embodiment of the present invention.

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

  FIG. 1 is a block diagram showing the configuration of a digital camera (optical apparatus) 100 according to the first embodiment of the present invention.

  The digital camera 100 includes a liquid crystal rotator (liquid crystal element) 21 that rotates a transmission polarization axis 21a (refer to FIG. 2) of reflected light of image light of a subject incident on an objective lens (imaging optical system) 10 and a specific direction. An optical element 20 including a polarizing filter 22 that transmits only the polarized light, an imaging element 30 such as a CCD that converts image light of an object that has passed through the objective lens 10 and the optical element 20 into an image signal (electrical signal), and imaging A camera system control unit (control means) 40 that controls the voltage applied to the liquid crystal optical rotator 21 based on the output of the element 30 is provided.

  The optical element 20 is an element that can realize the same function as rotating the polarizing filter 22 by rotating the transmission polarization axis 21 a by the liquid crystal rotator 21.

  The camera system control unit 40 is configured by a microcomputer or the like.

  The camera system control unit 40 includes an image processing unit 41, a camera control unit 42, and a buffer memory 43.

  The image processing unit 41 performs predetermined signal processing on the image signal output from the image sensor 30, and the image signal subjected to the signal processing is stored in the buffer memory 43. Further, the image signal temporarily stored in the buffer memory 43 is output to the camera control unit 42.

  The camera control unit 42 compares and calculates the image signal output from the image processing unit 41 to detect the transmission polarization axis 21a where reflected light is the least (lowest image level), or an image acquired by the image sensor 30. Or synthesize. When the operation member 60 such as a shutter button is operated, the camera control unit 42 controls the voltage applied to the liquid crystal optical rotator 21 and rotates the transmission polarization axis 21a (see FIG. 2) of the reflected light. The camera control unit 42 changes the direction (polarization angle) of the transmission polarization axis 21a of the reflected light by 60 °, for example.

  The digital camera 100 also has a memory 50 for storing images. The memory 50 is, for example, a memory card or a hard disk.

  Next, a method for removing reflected light when the reflected light of one polarized reflector (not shown) is within the screen 35 (the light receiving surface of the image sensor 30) will be described.

  FIG. 2A is a diagram showing a transmission polarization axis where the reflected light is the strongest among the image light of the subject incident on the objective lens 10 and a transmission polarization axis where the reflected light is the weakest, and FIG. It is a figure for demonstrating the method to remove light.

  2A and 2B, the solid line 21b indicates the direction of the transmission polarization axis 21a where the reflected light is the strongest, and the chain line 21c indicates the direction of the transmission polarization axis 21a where the reflected light is the weakest. 2A and 2B, the circle surrounding the transmission polarization axis 21a indicates the light beam lf incident on the objective lens 10.

  In this embodiment, the direction 21b of the transmission polarization axis 21a in which the reflected light is the strongest is set to a 50 ° direction (a direction rotated 50 ° clockwise from the vertical direction (12 o'clock position)). Therefore, the direction 21c of the transmission polarization axis 21a in which the reflected light is the weakest is a direction of 140 ° (a direction rotated 90 ° clockwise from the polarization direction in which the reflected light is the strongest).

  Since the reflected light in the screen 35 can be weakened by adjusting the transmission polarization axis 21a to the direction of 140 °, the camera system control unit 40 controls the voltage applied to the liquid crystal optical rotator 21 so as to do so.

  Hereinafter, a method for removing the reflected light will be described in detail.

  First, three cuts are taken while changing the polarization angle (direction of the transmission polarization axis 21a) from 0 ° by 60 ° per step, and an image is acquired.

  Next, the dark pixels of the three images are compared to detect the polarization angle (60 ° in FIG. 2) closest to the angle at which the reflected light cannot be removed. The direction of the transmission polarization axis 21a with the least amount of reflected light (polarization angle 140 °) is a direction rotated 90 ° clockwise from the polarization angle with the most reflection, so the polarization angle with the least amount of reflected light is the remaining image. Exists between polarization angles (120 ° and 180 °).

  Therefore, if the polarization angle is set to an intermediate angle (150 °) between the remaining polarization angles (120 ° and 180 °), and further photographing is performed at this polarization angle, ± 15 with respect to the polarization angle with the least reflected light. An image can be obtained with an accuracy of °.

  Thereafter, the three-cut images of the image acquired at the polarization angle of 150 °, the image acquired at the polarization angle of 0 °, and the image acquired at the polarization angle of 120 ° are compared, and the image with the most dark pixels (polarized light) If an image acquired at an angle of 150 ° is selected, an image with the least amount of reflected light (see the bottom screen 35 in FIG. 2) can be obtained. This image is stored in the memory 42.

  Polarization intermediate between the polarization angle of 150 ° and the polarization angle of 120 ° (the polarization angle of the darker image (with less reflected light) in the remaining images (0 ° and 120 °)). If an image is acquired at an angle of 135 ° and the darkest image is selected from three cut images acquired at polarization angles of 120 °, 135 °, and 150 °, ± 7. An image can be obtained with an accuracy of 5 ° or less.

  At the time of polarization detection, the image may be taken with all pixels or with coarse pixels.

  Further, when acquiring an image, the exposure control value is fixed to a constant value. As a result, calculation / control time related to exposure control can be omitted, light and dark can be easily determined, and an optimum transmission polarization axis can be quickly obtained.

  Unlike the above-described embodiment, when 4 cuts are taken at an equal interval of 180 °, the polarization angle changes by 45 ° per step, which is optimal when trying to obtain an image with the least amount of reflected light. The error with respect to the direction of the transmission polarization axis 21a is 22.5 °.

  In addition, when 5 cuts are taken at an equal interval of 180 °, the polarization angle changes by 36 ° per step, and when trying to obtain an image with the least amount of reflected light, the optimum transmission polarization axis 21a can be obtained. The error with respect to the direction is 18 °, which is larger than the error (7.5 °) in the case where the above five cuts are taken.

  According to this embodiment, since the direction of the transmission polarization axis 21a can be accurately adjusted to 140 ° (direction indicated by the chain line 21c), the reflected light can be sufficiently removed. In addition, the transmission polarization axis can be detected with high accuracy with a smaller number of times of photographing than when a plurality of cuts are photographed at equal intervals. Furthermore, since it is not necessary to scan the entire area and the calculation / control time for exposure control can be omitted, an optimum polarization angle can be quickly searched.

  Next, a method for removing reflected light when a plurality of polarized reflectors are present in the screen 35 will be described.

  FIG. 3 is a view for explaining a method of removing reflected light using the optical device according to the second embodiment of the present invention, and the description of the parts common to the first embodiment is omitted.

  This embodiment is different from the first embodiment in that the reflected light of a plurality of polarized reflectors is in the screen 35 and the transmission polarization axis 21a of each reflected light is different.

  In this embodiment, six cuts are taken while changing the polarization angle from 0 ° by 30 ° per step, and six images are acquired in a range of 90 ° or more, and the six images are combined into one image. The reflected light is removed by doing so.

  Hereinafter, a method for removing the reflected light will be described in detail.

  First, the image positions between the images of each cut are matched.

  Next, the pixel values of the pixels at the same position are compared between the images, and a pixel having a lower (darker) pixel value is selected.

  This comparison / selection of pixel values is repeated for six images and combined into one image.

  As a result, a dark image (without reflected light) is synthesized and an image from which the reflected light is removed (see the bottom screen 35 in FIG. 3) can be obtained. This image is stored in the memory 42.

  According to this embodiment, since the dark pixel is selected and combined, the reflected light can be sufficiently removed even when the reflected light of a plurality of polarized reflectors having different polarization angles is in the screen 35. it can.

  In the above embodiment, the optical device is the digital camera 100. However, the present invention is not limited to this, and may be a mobile phone having a camera function, for example.

  10: objective lens (imaging optical system), 20: optical element, 21: liquid crystal rotator (liquid crystal element), 21a: transmission polarization axis, 22: polarization filter, 30: image sensor, 40: camera system control unit (control means) ), 100: Digital camera (optical device).

Claims (5)

An optical element composed of a liquid crystal element that rotates a transmission polarization axis of image light of a subject incident on a photographing optical system and a polarization filter that transmits only polarized light in a specific direction;
An image sensor that converts image light of the subject that has passed through the imaging optical system and the optical element into an electrical signal;
Control means for controlling the voltage applied to the liquid crystal element based on the output of the imaging element;
The control means first rotates the transmission polarization axis by 60 ° to acquire three images with the imaging device, and then selects two images excluding the image with the highest image level from the three images. Then, an image is further acquired with a transmission polarization axis intermediate between the transmission polarization axes of the two images, and an image with the largest number of dark pixels is selected from these images.   The control means compares two images excluding the image having the highest image level among the three images and an image acquired with a transmission polarization axis intermediate between the transmission polarization axes of the two images, and compares them. A further image is acquired with a transmission polarization axis intermediate between two images excluding the transmission polarization axis from which an image having the brightest pixel is acquired, and an image having the darkest pixel is selected from among the images. The optical device according to claim 1. An optical element composed of a liquid crystal element that rotates a transmission polarization axis of image light of a subject incident on a photographing optical system and a polarization filter that transmits only polarized light in a specific direction;
An image sensor that converts image light of the subject that has passed through the imaging optical system and the optical element into an electrical signal;
Control means for controlling the voltage applied to the liquid crystal element based on the output of the imaging element;
The control means first rotates the transmission polarization axis within a range of at least 90 ° to acquire a plurality of images by the imaging device, and then compares pixels at the same position between the acquired images. An optical apparatus comprising: selecting a pixel having the lowest level, and combining the plurality of images into one image.   The optical device according to claim 1, wherein an exposure control value is fixed when the transmission polarization axis is rotated and the image is acquired by the imaging device.   The optical device according to any one of claims 1 to 4 is a digital camera.

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