Variable optical low-pass filter, camera module including the variable optical low-pass filter, imaging system including the camera module, smart phone including the imaging system, and method for controlling the imaging system

Abstract

The present invention provides a variable optical low pass filter (vOLPF) (10) with reduced thickness. The vOLPF (10) comprises: two opposite transparent substrates (110, 120); two opposite transparent electrodes (130, 140); two opposite liquid crystal orientation layers (150, 160); a liquid crystal layer (170) sandwiched between the two opposite transparent substrates (110, 120), each transparent substrate (110, 120) having the transparent electrodes (130, 140) and the liquid crystal orientation layer (150, 160), wherein the birefringence of the liquid crystal layer (170) can be adjustable.

Description

Technical Field

[0001] The present invention relates to an optical low pass filter (OLPF) used in a digital camera or the like. Background Art

[0002] Digital cameras have an image processing mode called pixel overlay mode. The pixel overlay mode combines several pixels and treats them as one pixel, which can improve detection sensitivity. For example, when using the 2×2 pixel overlay mode, in which 4 pixels in total, 2 pixels in the vertical direction and 2 pixels in the horizontal direction, are combined into one pixel, the sampling frequency is reduced by half compared to the case where the 2×2 pixel overlay mode is not used. Therefore, with the 2×2 pixel overlay mode, more moiré patterns appear when shooting a subject with a periodic pattern such as a stripe pattern.

[0003] The generation of moiré patterns can be reduced by using an optical low pass filter (OLPF) including one or more birefringent plates.

[0004] However, since the optical axis of each birefringent plate used in a conventional OLPF is fixed, multiple birefringent plates are required to separate light into multiple directions, which increases the thickness of the OLPF. The increase in the thickness of the OLPF limits the use of the OLPF on smartphones where the space between the imaging lens and the image sensor is limited.

[0005] In addition, since smartphones have a short back focal length and a wide CRA, when incident light is separated by the OLPF, the difference between the separation distance at the center and the separation distance at the periphery is large. As a result, there is a problem of a difference in the moiré suppression effect between the center and the periphery, as well as a difference in resolution between the center and the periphery.

[0006] Therefore, the problem solved by this embodiment is to provide an OLPF that is thin and suitable for smartphones. Summary of the invention

[0007] The present inventors propose an OLPF in which the overall thickness of the OLPF is reduced and which is suitable for use in smartphones by using a liquid crystal layer in which birefringence can be tuned.

[0008] According to one embodiment, a variable optical low pass filter (vOLPF) includes: two opposite transparent substrates; two opposite transparent electrodes; two opposite liquid crystal orientation layers; a liquid crystal layer sandwiched between the two opposite transparent substrates, each transparent substrate having the transparent electrode and the liquid crystal orientation layer, wherein the birefringence of the liquid crystal layer can be adjustable.

[0009] The vOLPF according to the above configuration can make the thickness of the vOLPF small because the liquid crystal layer includes a birefringence function, and thus the vOLPF is suitable for a smartphone having a limited space between the imaging lens and the image sensor.

[0010] In the above configuration, the liquid crystal layer may include nematic liquid crystals, and an alignment pattern of one of the two opposing liquid crystal alignment layers may be the same as an alignment pattern of the other of the two opposing liquid crystal alignment layers.

[0011] In the above configuration, the two opposing liquid crystal alignment layers may have one or more alignment directions.

[0012] In the above configuration, the two opposing liquid crystal alignment layers may have alignment directions extending radially from the center of the vOLPF.

[0013] In the above configuration, at least one of the two opposing transparent electrodes may include a central electrode disposed at the center of the vOLPF and one or more concentric electrodes surrounding the central electrode.

[0014] In the above configuration, the transparent substrate may be non-birefringent.

[0015] In the above configuration, the thickness of the vOLPF may range from 200 μm to 3000 μm.

[0016] In the above configuration, the transparent substrate may have a thickness ranging from 100 μm to 1500 μm.

[0017] In the above configuration, the thickness of the liquid crystal layer may range from 5 μm to 150 μm.

[0018] According to another embodiment, a camera module includes: an imaging lens; an image sensor; and the above-mentioned vOLPF arranged between the imaging lens and the image sensor.

[0019] According to another embodiment, an imaging system includes: the above-mentioned camera module; an optical low pass filter (OLPF) driver connected to the vOLPF; an image signal processor connected to the image sensor; a display; and a controller unit connected to the OLPF driver, the image sensor, the image signal processor and the display.

[0020] The camera module and imaging system according to the above configuration have a reduced vOLPF thickness, so they can be suitable for smartphones with limited space between the imaging lens and the image sensor.

[0021] A smartphone according to yet another embodiment includes the above-described imaging system.

[0022] The smartphone according to the above configuration has a reduced vOLPF thickness, thereby making it possible to realize a thinner smartphone.

[0023] A method for controlling an imaging system according to yet another embodiment includes transmitting an electrical signal from the OLPF driver to the two opposing transparent electrodes of the vOLPF, thereby controlling the birefringence of a liquid crystal layer.

[0024] The method for controlling the imaging system according to the above aspect can easily control the birefringence function because only the liquid crystal layer has the birefringence function and therefore there is no need to consider the relationship with any birefringence plate.

[0025] In the above aspects, the imaging system may include an automatic mode or a manual mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic cross-sectional view of a camera module including a variable optical low pass filter (vOLPF) provided by the present invention.

[0027] Figure 2 (a) is a top view of the vOLPF provided by the present invention, viewed from the side where the incident light enters. Figure 2 (b) along Figure 2 Cross-sectional view taken along line AA in (a).

[0028] Figure 3 A plan view of an exemplary pattern of a transparent electrode used in a vOLPF provided by the present invention.

[0029] Figure 4 A perspective view of an exemplary pattern of alignment grooves formed in a liquid crystal alignment layer used in a vOLPF provided by the present invention.

[0030] Figure 5 When using vOLPF Figure 4 The illustrated liquid crystal alignment layer is an exploded perspective view of an exemplary alignment condition of liquid crystal molecules in the liquid crystal layer.

[0031] Figure 6 When using vOLPF Figure 4 The liquid crystal alignment layer is shown as an exploded perspective view of an exemplary separation condition of incident light.

[0032] Figure 7 A block diagram of an imaging system including a vOLPF is provided for the present invention.

[0033] Figure 8 An exploded perspective view of a traditional optical low pass filter (OLPF). DETAILED DESCRIPTION

[0034] Figure 8 An exemplary configuration of a conventional OLPF is shown as a first embodiment. Figure 8 The OLPF shown is composed of two birefringent plates 1, 4 and a wave plate 2 and an infrared cut filter 3 sandwiched therebetween.

[0035] The incident light L1 is separated into two beams by the front birefringent plate 1, and the two beams are separated into four beams by the rear birefringent plate 4, and the four beams enter the image sensor 5. The four separated beams can reduce the spatial frequency, thereby reducing the generation of moiré.

[0036] However, since the OLPF according to the first embodiment uses two birefringent plates, the thickness of the OLPF in the optical axis direction is relatively thick. Therefore, the above OLPF is not suitable for use in a smartphone where the space between the imaging lens and the image sensor is limited.

[0037] Since a digital single-lens reflex (DSLR) camera has a long back focal length and a narrow chief ray angle (CRA) (e.g., within about 15°), the difference between the separation distance at the center position and the separation distance at the peripheral position is not significant with respect to the light separation distance separated by the OLPF. On the other hand, since a smartphone has a short back focal length and a wide CRA (e.g., within about 40°), the difference between the separation distance at the center position and the separation distance at the peripheral position is large. Therefore, there is a problem of a difference in the moiré suppression effect between the center position and the peripheral position and a difference in resolution between the center position and the peripheral position.

[0038] In addition, since the optical axis of each birefringence plate in the OLPF according to the first embodiment is fixed, a plurality of birefringence plates are required in order to separate light into a plurality of directions.

[0039] As a second embodiment, there is another conventional OLPF, which can make the cutoff frequency in the oblique direction lower than the cutoff frequency in the longitudinal and transverse directions, so as to solve the problem that the moiré generated in the oblique direction of the image sensor is more distinguishable than the moiré generated in the longitudinal and transverse directions. Specifically, the OLPF according to the second embodiment includes: a first birefringent plate having a transverse optical axis; a second birefringent plate having a longitudinal optical axis; a third birefringent plate having an optical axis at an angle of 45° relative to the transverse direction; and a fourth birefringent plate having an optical axis at an angle of 90° relative to the optical axis of the third birefringent plate. In addition, in the OLPF according to the second embodiment, when the separation width of the incident light in the longitudinal and transverse directions of the first birefringent plate and the second birefringent plate is "a", and the separation width of the incident light in the oblique direction of the third birefringent plate and the fourth birefringent plate is "b", the width "b" is set to be greater than the width "a" (for example, 1.15<b / a<3). Based on the above configuration, the OLPF according to the second embodiment can reduce the occurrence of moiré in the oblique direction while maintaining the resolution in the longitudinal and transverse directions.

[0040] However, since the OLPF according to the second embodiment uses four birefringent plates, the thickness of the OLPF in the optical axis direction is very thick. Therefore, the above OLPF is not suitable for use in a smartphone where the space between the imaging lens and the image sensor is limited.

[0041] Furthermore, the OLPF according to the second embodiment cannot solve the problem that the difference between the separation distance at the center position and the separation distance at the peripheral position is large due to the short back focus and wide CRA of the smartphone.

[0042] In addition, since the optical axis of each birefringence plate in the OLPF according to the second embodiment is fixed, a plurality of birefringence plates are required in order to separate light into a plurality of directions.

[0043] There is another conventional OLPF as a third embodiment, which can change the low-pass characteristic. Specifically, the OLPF according to the third embodiment includes: a first birefringent plate; a first electrode; a liquid crystal layer; a second electrode; a second birefringent plate, which are laminated in this order. The liquid crystal layer uses TN (twisted nematic) liquid crystal, and the low-pass characteristic can be controlled according to the intensity of the electric field applied through the first and second electrodes. Specifically, when the applied voltage is 0V, the low-pass characteristic can be 0. However, when a large voltage is applied, the low-pass characteristic can be maximum. On the other hand, when an intermediate voltage is applied, the incident light can be separated into three beams with an intermediate separation distance, so that an intermediate low-pass characteristic can be obtained.

[0044] However, since the OLPF according to the third embodiment cannot control the low-pass characteristics according to the position in the field of view, the OLPF according to the third embodiment cannot solve the problem of a large difference between the separation distance at the center position and the separation distance at the peripheral position due to the short back focal length and wide CRA of the smartphone.

[0045] In addition, since the OLPF according to the third embodiment separates light in only one direction, resolution adjustment is performed in only one direction. In order to separate incident light into multiple directions, it is necessary to add multiple OLPFs described above, which causes the total thickness of the OLPF to become thicker.

[0046] Figure 1 4 is a cross-sectional view of a camera module 40 according to a fifth embodiment. The camera module 40 according to the fifth embodiment includes the variable optical low pass filter (vOLPF) 10 according to the fourth embodiment. The vOLPF 10 is disposed on the light receiving surface side of the image sensor 30. Therefore, light passing through the imaging lens 20 reaches the light receiving surface of the image sensor 30 through the vOLPF 10. Figure 1 The camera module 40 shown can be integrated into a digital camera, a smart phone, a laptop computer, a tablet computer or a wearable device.

[0047] The imaging lens 20 has at least one lens and can form an image on a light receiving surface of the image sensor 30. The image sensor 30 may be a charge-coupled device (CCD) sensor or a complementary metal oxide semiconductor (CMOS) sensor and may have a plurality of pixels. Each pixel of the image sensor 30 may photoelectrically convert light to generate image data.

[0048] Figure 2 A vOLPF 10 according to a fourth embodiment is shown. Figure 2 (a) Top view from the side where the incident light enters, Figure 2 (b) along Figure 2 (a) is a cross-sectional view taken along line AA of FIG. The vOLPF 10 includes: two opposing substrates, namely a first transparent substrate 110 and a second transparent substrate 120; two opposing transparent electrodes, namely a first transparent electrode 130 and a second transparent electrode 140; two opposing liquid crystal alignment layers, namely a first liquid crystal alignment layer 150 and a second liquid crystal alignment layer 160; and a liquid crystal layer 170 sandwiched between the first transparent substrate 110 and the second transparent substrate 120, each transparent substrate 120 having a transparent electrode and a liquid crystal alignment layer.

[0049] The first transparent substrate 110 and the second transparent substrate 120 may be provided to support the transparent electrode and the liquid crystal alignment layer, and may be transparent so as to transmit incident light. The materials of the first transparent substrate 110 and the second transparent substrate 120 are not particularly limited, for example, the first transparent substrate 110 and the second transparent substrate 120 may be glass substrates.

[0050] The first transparent substrate 110 and / or the second transparent substrate 120 may have a function of blocking infrared light. In this case, the first transparent substrate 110 and / or the second transparent substrate 120 may be an IR cut-off filter. By adopting the IR cut-off filter, light having a desired wavelength range may be selectively transmitted. For example, the selectively transmitted light is visible light.

[0051] The vOLPF 10 according to the fourth embodiment does not require a birefringent plate used in a conventional OLPF because the liquid crystal layer 170 can tune the birefringence as described below. That is, it is preferred that the first transparent substrate 110 and / or the second transparent substrate 120 are non-birefringent. More preferably, the first transparent substrate 110 and the second transparent substrate 120 are non-birefringent.

[0052] The vOLPF 10 according to the fourth embodiment can make the thickness of the first transparent substrate 110 and the second transparent substrate 120 thinner because there is no need to separate the incident light in the first transparent substrate 110 and the second transparent substrate 120. The thickness of the first transparent substrate 110 and the second transparent substrate 120 can occupy the thickness of the vOLPF 10 in the optical axis direction ( Figure 2 Therefore, reducing the thickness of the first transparent substrate 110 and the second transparent substrate 120 can significantly reduce the thickness of the vOLPF in the optical axis direction. In addition, since the vOLPF 10 according to the fourth embodiment does not need to provide any substrate other than the first transparent substrate 110 and the second transparent substrate 120, such as a birefringent plate, the thickness of the vOLPF 10 can be thinner.

[0053] The thickness D1 of the vOLPF 10 in the optical axis direction is preferably 200 μm to 3000 μm. For example, the thickness D1 of the vOLPF in the optical axis direction may be 250 μm to 1000 μm, or may be 300 μm to 500 μm. When the thickness D1 of the vOLPF 10 in the optical axis direction is 200 μm or more, the substrate may have appropriate strength. When the thickness D1 of the vOLPF 10 in the optical axis direction is 3000 μm or less, it may be appropriately applied to smartphones.

[0054] The thickness D2 of the first transparent substrate 110 and / or the second transparent substrate 120 in the optical axis direction preferably ranges from 100 μm to 1500 μm. For example, the thickness D2 of the first transparent substrate 110 and / or the second transparent substrate 120 in the optical axis direction may be from 150 μm to 500 μm, and may be from 200 μm to 300 μm. When the thickness D2 of the first transparent substrate 110 and / or the second transparent substrate 120 in the optical axis direction is 100 μm or more, the transparent substrate may have appropriate strength. When the thickness D2 of the first transparent substrate 110 and / or the second transparent substrate 120 in the optical axis direction is 1500 μm or less, light transmission may be highly maintained.

[0055] The first transparent electrode 130 and the second transparent electrode 140 change the arrangement of liquid crystal molecules in the liquid crystal layer 170 by applying an electric field in the liquid crystal layer 170. When the arrangement of the liquid crystal molecules changes, the birefringence of the liquid crystal layer 170 can change. The first transparent electrode 130 and the second transparent electrode 140 can be transparent so as to transmit incident light. The first transparent electrode 130 and the second transparent electrode 140 are made of a transparent conductive material. For example, the first transparent electrode 130 and the second transparent electrode 140 are made of indium tin oxide (ITO) or indium zinc oxide (IZO).

[0056] Figure 3 An exemplary electrode pattern of the first transparent electrode 130 is shown. Preferably, the first transparent electrode 130 includes a central electrode 131 located at the center of the vOLPF and one or more concentric electrodes 132 surrounding the central electrode 131. In the present invention, the center of the vOLPF is defined as the point in the vOLPF through which the optical axis of the imaging lens 20 passes. The geometric shape of the central electrode 131 is not particularly limited, but is preferably circular.

[0057] The central electrode 131 and the one or more concentric electrodes 132 are electrically isolated from each other and are electrically connected to a voltage source through wires (not shown). Therefore, the size of the electrical signal applied to each electrode can be controlled separately. The electrode pattern of the second transparent electrode 140 can be the same as the electrode pattern of the first transparent electrode 130.

[0058] The electrical signals applied to the central electrode 131 and the one or more concentric electrodes 132 can be adjusted separately to concentrically control the birefringence of the liquid crystal layer 170. For example, the birefringence effect can be made relatively large near the center of the vOLPF and gradually reduce the birefringence effect toward the outside of the vOLPF. Therefore, the separation distance of the separation of the incident light at any position in the field of view can be uniform. That is, since the vOLPF according to the fourth embodiment can adjust the separation distance at the central position and the separation distance at the peripheral position respectively, it is suitable for use in smartphones with short back focus and wide CRA.

[0059] The first liquid crystal orientation layer 150 and the second liquid crystal orientation layer 160 are used to define the orientation direction of the liquid crystal molecules. The first liquid crystal orientation layer 150 and the second liquid crystal orientation layer 160 preferably have one or more orientation directions. Specifically, the orientation grooves in the first liquid crystal orientation layer 150 and the second liquid crystal orientation layer 160 can be formed to have one or more orientation directions. The orientation direction of the liquid crystal orientation layer defines the orientation direction of the liquid crystal molecules in the liquid crystal layer 170. That is, when the first liquid crystal orientation layer 150 and the second liquid crystal orientation layer 160 have one or more orientation directions, the liquid crystal molecules in the liquid crystal layer 170 can be oriented in a predetermined orientation direction accordingly. The material of the liquid crystal orientation layer can be selected considering heat resistance, solvent resistance and hygroscopicity. For example, the liquid crystal orientation layer is made of polyimide.

[0060] The liquid crystal layer 170 includes liquid crystal molecules, which can tune the birefringence according to the intensity of the electric field applied by the first transparent electrode 130 and the second transparent electrode 140. The liquid crystal layer 170 preferably includes nematic liquid crystals. When the liquid crystal layer 170 includes nematic liquid crystals, it becomes easy to control the birefringence. The thickness D3 of the liquid crystal layer 170 in the optical axis direction preferably ranges from 5 μm to 150 μm. For example, the thickness D3 of the liquid crystal layer 170 in the optical axis direction may be 10 μm to 100 μm, or may be 20 μm to 50 μm. When the thickness D3 of the liquid crystal layer 170 in the optical axis direction is 5 μm or more, the liquid crystal layer 170 can fully separate the incident light. When the thickness D3 of the liquid crystal layer 170 in the optical axis direction is 150 μm or less, it is easy to control the orientation direction of the liquid crystal molecules of the liquid crystal layer 170.

[0061] Figure 4 FIG. 2 shows an exemplary pattern of the alignment grooves formed in the first liquid crystal alignment layer 150. Figure 4 As shown, the alignment groove 151 of the first liquid crystal alignment layer 150 preferably extends radially from the center of the vOLPF.

[0062] See also Figure 4 , the orientation grooves in the central region 152 located near the center of the vOLPF can be oriented in the longitudinal direction ( Figure 4The orientation grooves in the central region 152 are formed in the longitudinal direction, the orientation of the liquid crystal molecules in the central region 152 can be controlled. However, it is desired that the central region 152 is as small as possible. The direction of the orientation grooves in the central region 152 is not limited to the longitudinal direction, and can be a transverse direction (x-axis direction) or an inclined direction (a direction having a predetermined angle with the x-axis). The pattern of the orientation grooves in the second liquid crystal orientation layer 160 is preferably the same as the pattern of the orientation grooves in the first liquid crystal orientation layer 150. When the pattern of the orientation grooves in the first liquid crystal orientation layer 150 is the same as the pattern of the orientation grooves in the second liquid crystal orientation layer 160, it is easy to control the orientation direction of the liquid crystal molecules in the liquid crystal layer 170.

[0063] The patterns of the alignment grooves in the first and second liquid crystal alignment layers 150 and 160 may be formed such that the alignment direction of the liquid crystal molecules adjacent to the first liquid crystal alignment layer 150 is parallel to the alignment direction of the liquid crystal molecules adjacent to the second liquid crystal alignment layer 160. Therefore, the pattern of the alignment grooves in the first liquid crystal alignment layer 150 is preferably the same as the pattern of the alignment grooves in the second liquid crystal alignment layer 160. Figure 4 The pattern of the alignment grooves shown in FIG. 1 is merely one example, and various patterns may be provided as desired.

[0064] Figure 5 Shows the use of Figure 4 1. Example orientation states of liquid crystal molecules in the liquid crystal layer 170 in the case of the first liquid crystal orientation layer 150 and the second liquid crystal orientation layer 160 of the orientation groove pattern shown. The first liquid crystal orientation layer 150 and the second liquid crystal orientation layer 160 preferably have an orientation direction extending radially from the center of the vOLPF. When the orientation grooves of the first liquid crystal orientation layer 150 and the second liquid crystal orientation layer 160 are formed to extend radially from the center of the vOLPF, the liquid crystal molecules in the liquid crystal layer 170 may also be radially oriented from the center of the vOLPF. For example, in the longitudinal region 171 where the direction of the orientation groove is parallel to the y-axis direction, the liquid crystal molecules may be oriented parallel to the y-axis direction. In the transverse region 173 where the direction of the orientation groove is parallel to the x-axis direction, the liquid crystal molecules may be oriented parallel to the x-axis direction. In the inclined region 172 where the direction of the orientation groove is at an angle of about 45° to the x-axis, the liquid crystal molecules may be oriented at an angle of about 45° to the x-axis direction. When the liquid crystal molecules in the liquid crystal layer 170 are also radially oriented from the center of the vOLPF, since the incident light is radially separated from the center of the vOLPF, the moiré can be effectively suppressed by only one liquid crystal layer.

[0065] Figure 6 Shown in the use of Figure 4In the case of the first liquid crystal orientation layer 150 and the second liquid crystal orientation layer 160 of the orientation groove pattern shown, the incident light is subjected to the birefringence effect and is thereby separated into a state of two light beams. As described above, since the liquid crystal molecules in the liquid crystal layer are radially oriented from the center of the vOLPF, the incident light is also radially separated from the center of the vOLPF. For example, in the longitudinal region 171 where the direction of the orientation groove is parallel to the y-axis direction, the incident light can be separated along the y-axis direction. In the transverse region 173 where the direction of the orientation groove is parallel to the x-axis direction, the incident light can be separated along the x-axis direction. In the inclined region 172 where the direction of the orientation groove is at an angle of about 45° to the x-axis, the incident light can be separated along a direction at an angle of about 45° to the x-axis direction.

[0066] In a conventional OLPF, since one birefringent plate separates light in one direction, multiple birefringent plates must be used to separate light in multiple directions. However, in the vOLPF according to the fourth embodiment, the alignment grooves in the liquid crystal alignment layer can have multiple directions, so that one liquid crystal layer can separate light in multiple directions.

[0067] Figure 7 An imaging system 200 including a vOLPF 10 according to a sixth embodiment is shown. The imaging system 200 according to the sixth embodiment can be integrated into a digital camera, a smartphone, a laptop, a tablet computer, or a wearable device. The imaging system 200 according to the sixth embodiment is particularly suitable for integration into a smartphone. That is, the smartphone according to the seventh embodiment includes the imaging system 200 according to the sixth embodiment. The imaging system 200 includes a camera module 40 according to the fifth embodiment. The camera module 40 includes: the vOLPF 10 according to the fourth embodiment, an imaging lens 20, and an image sensor 30.

[0068] The imaging lens 20 may collect light from a photographic subject and may form an image of the photographic subject on a light receiving surface of the image sensor 30. For example, when the imaging lens 20 is used for a digital single-lens reflex (DSLR) camera, its CRA may be from 0 degrees (on-axis) to 18 degrees (1.0 field image height of some DSLR lenses). For example, when the imaging lens 20 is used for a smartphone, its CRA may be from 0 degrees (on-axis) to 38 degrees (1.0 field image height of some smartphone lenses).

[0069] Each pixel of the image sensor 30 can photoelectrically convert light to generate raw image data. The image sensor 30 outputs image data in a single pixel mode, in which each pixel of the image sensor 30 is used as it is, or in a 2×2 pixel overlay mode, a 3×3 pixel overlay mode, a 4×4 pixel overlay mode, or other pixel overlay modes, in which several adjacent pixels of the image sensor 30 are combined.

[0070] See again Figure 7 The imaging system 200 includes: an optical low pass filter (OLPF) driver 50 connected to the vOLPF 10; an image signal processor 60 connected to the image sensor 30; a display 70; and a controller unit 80. The controller unit 80 is connected to the OLPF driver 50, the image sensor 30, the image signal processor 60, and the display 70.

[0071] In the process of controlling the imaging system 200 according to the sixth embodiment, the OLPF driver 50 transmits an electrical signal to the first transparent electrode 130 and the second transparent electrode 140 to control the birefringence of the liquid crystal layer 170. When the first transparent electrode 130 and / or the second transparent electrode 140 include the following: Figure 3 When there is a central electrode 131 and one or more concentric electrodes 132 as shown, electrical signals with different voltages or different frequencies can be transmitted to the central electrode 131 and the one or more concentric electrodes 132. For example, electrical signals with different voltages or different frequencies are transmitted to the central electrode 131 and the one or more concentric electrodes 132 so that the birefringence effect is relatively large near the center of the vOLPF and gradually decreases toward the outside of the vOLPF. Therefore, the separation distance of the incident light at any position in the field of view can be uniform. That is, the separation distance of the incident light at the central position and the peripheral position of the image sensor 30 can be appropriately adjusted. The voltage range of the electrical signal is 0 to 10V, and the frequency range of the electrical signal is 0 to 10kHz.

[0072] The image signal processor 60 may perform image processing such as white balance, grayscale conversion, color conversion, and noise reduction on the image data obtained from the image sensor 30 to create an image file, and transmit the image file to the controller unit 80 .

[0073] For example, the display 70 may be composed of a liquid crystal panel and may be used as a display unit for displaying a live view image according to an image file obtained from the controller unit 80. The display 70 may also display a setting menu of the device and an operation status of a user.

[0074] The controller unit 80 may control the OLPF driver 50, the image sensor 30, the image signal processor 60, and the display 70. The controller unit 80 may control the OLPF driver 50 to switch between enabling or disabling the birefringence function of the vOLPF 10. In addition, the controller unit 80 may control the OLPF driver 50 to output different electrical signals to the central electrode 131 and the one or more concentric electrodes 132. In addition, the controller unit 80 may control the image sensor 30 to determine whether to acquire raw image data in a single pixel mode or any one of a 2×2 pixel overlay mode, a 3×3 pixel overlay mode, a 4×4 pixel overlay mode, and other pixel overlay modes.

[0075] The eighth embodiment includes a method for controlling the imaging system 200. The method for controlling the imaging system 200 includes transmitting an electrical signal from the OLPF driver 50 to two opposing transparent electrodes, namely the first transparent electrode 130 and the second transparent electrode 140 of the vOLPF 10, thereby controlling the birefringence of the liquid crystal layer 170.

[0076] The imaging system 200 preferably includes an automatic mode or a manual mode for using the vOLPF 10, and the user can select the automatic mode and the manual mode. When the user selects the automatic mode and selects any one of the single pixel mode, the 2×2 pixel superposition mode, the 3×3 pixel superposition mode, the 4×4 pixel superposition mode, and the other pixel superposition modes, the controller unit 80 obtains an image file according to each mode of the image sensor 30, and automatically estimates the occurrence of moire from the obtained image file. Then, the controller unit 80 considers the trade-off relationship between resolution and moire suppression, and can control the OLPF driver 50 to perform moire suppression as much as possible without reducing the resolution as much as possible.

[0077] When the user selects the manual mode, the user can manually switch between using or not using the vOLPF. When photographing a subject having a periodic pattern, moiré may occur. That is, when there is no periodic pattern in the subject, moiré is rarely produced. In addition, there is a trade-off between resolution and moiré suppression, so using the OLPF reduces resolution. Therefore, for example, when the user confirms that there is no periodic pattern in the subject or the user wants to obtain a high-resolution image without caring about slight moiré, the user can manually disable the birefringence function of the vOLPF 10. Specifically, the user selects an item not to use the vOLPF through the user interface of the display, and the controller unit 80 that receives the instruction controls the OLPF driver 50 to disable the birefringence function of the vOLPF 10.

[0078] On the other hand, when the user confirms that there are some periodic patterns in the photographed object or the user finds the occurrence of critical moiré when confirming the live view image displayed on the display, the user can manually enable the birefringence function of the vOLPF 10. Specifically, the user selects an item for using the vOLPF through the user interface of the display, and the controller unit 80 receiving the instruction controls the OLPF driver 50 to enable the birefringence function of the vOLPF 10.

[0079] As described above, the method according to the eighth embodiment can easily control the birefringence function because only the liquid crystal layer has the birefringence function and therefore there is no need to consider the relationship with any birefringence plate.

[0080] Description of Reference Numerals

[0081] 1: Double refraction plate

[0082] 2: Wave plate

[0083] 3: Infrared cut filter

[0084] 4: Double refraction plate

[0085] 5: Image sensor

[0086] 10: Variable optical low-pass filter

[0087] 20: Imaging lens

[0088] 30: Image sensor

[0089] 40: Camera module

[0090] 50: Optical Low Pass Filter (OLPF) Driver

[0091] 60: Image Signal Processor

[0092] 70: Display

[0093] 80: Control unit

[0094] 110: first transparent substrate

[0095] 120: Second transparent substrate

[0096] 130: First transparent electrode

[0097] 131: Center electrode

[0098] 132: Concentric Electrode

[0099] 140: Second transparent electrode

[0100] 150: first liquid crystal alignment layer

[0101] 151: Orientation groove

[0102] 152: Central area

[0103] 160: second liquid crystal alignment layer

[0104] 170: Liquid crystal layer

[0105] 171: Vertical area

[0106] 172: Sloped area

[0107] 173: Horizontal area

[0108] 200: Imaging System

Claims

1. A variable optical low-pass filter, characterized in that: include: two opposing transparent substrates; two opposing transparent electrodes; two opposing liquid crystal alignment layers; A liquid crystal layer is sandwiched between the two relative transparent substrates, each of which has the transparent electrode and the liquid crystal orientation layer, wherein the birefringence of the liquid crystal layer is adjustable, and the two relative liquid crystal orientation layers have an orientation direction radially extending from the center of the variable optical low-pass filter.

2. The variable optical low-pass filter according to claim 1, characterized in that: The liquid crystal layer includes nematic liquid crystal, An alignment pattern of one of the two opposing liquid crystal alignment layers is the same as an alignment pattern of the other of the two opposing liquid crystal alignment layers.

3. The variable optical low-pass filter according to claim 1, characterized in that: The two opposite liquid crystal alignment layers have multiple alignment directions.

4. The variable optical low-pass filter according to claim 1, characterized in that: At least one of the two opposing transparent electrodes includes a central electrode disposed at the center of the variable optical low-pass filter and one or more concentric electrodes surrounding the central electrode.

5. The variable optical low-pass filter according to any one of claims 1 to 4, characterized in that: The transparent substrate is non-birefringent.

6. The variable optical low-pass filter according to any one of claims 1 to 4, characterized in that: The variable optical low-pass filter has a thickness ranging from 200 μm to 3000 μm.

7. The variable optical low-pass filter according to any one of claims 1 to 5, characterized in that: The transparent substrate has a thickness ranging from 100 μm to 1500 μm.

8. The variable optical low-pass filter according to any one of claims 1 to 4, characterized in that: The thickness of the liquid crystal layer is in a range of 5 μm to 150 μm.

9. A camera module, characterized in that: include: Imaging lens; Image sensor; The variable optical low-pass filter according to any one of claims 1 to 8, wherein the variable optical low-pass filter is arranged between the imaging lens and the image sensor.

10. An imaging system, characterized in that: include: The camera module according to claim 9; an optical low-pass filter driver connected to the variable optical low-pass filter; an image signal processor connected to the image sensor; monitor; A controller unit is connected to the optical low-pass filter driver, the image sensor, the image signal processor, and the display.

11. A smart phone, characterized in that: Comprising the imaging system according to claim 10.

12. A method for controlling the imaging system according to claim 10, characterized in that: include: An electrical signal is transmitted from the optical low pass filter driver to the two opposing transparent electrodes of the variable optical low pass filter, thereby controlling the birefringence of the liquid crystal layer.

13. The method according to claim 12, characterized in that The imaging system includes an automatic mode or a manual mode.

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