JP2007081544A - Photographing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photographing apparatus in which a degradation of resolution is efficiently suppressed and image quality is enhanced. <P>SOLUTION: A photographing optical system 1 has a liquid crystal optical low-pass filter 3, where the separation width of birefringence can be adjusted freely for each region of a field according to an application voltage. A filter adjustment section 4 adjusts the separation width of birefringence in the liquid crystal optical low-pass filter 3 so that moire is lost at a region where the moire is detected by a main CPU (Central Processing Unit) 145 and high-frequency components cannot be removed at a region other than the region where the moire is detected. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photographing apparatus that includes a photographing optical system and generates an image signal by capturing subject light that has entered through the photographing optical system with an imaging element.

  A CCD (Charge Coupled Device) is widely used as a photographing element in a digital camera which is one of photographing apparatuses. The CCD includes a large number of photoelectric conversion elements arranged two-dimensionally at a predetermined interval (referred to as a pixel pitch) and a color filter array arranged on the large number of photoelectric conversion elements. As a color arrangement method of the color filter array, a Bayer arrangement method, a G stripe arrangement method, an R / G checkered arrangement method, a GRB stripe arrangement method, and the like are known. The CCD obtains a color image signal by discretely sampling subject light incident through a photographing lens with the photoelectric conversion element and the color filter.

  Here, when subject light having a high frequency component equal to or larger than the color arrangement pitch determined in accordance with the pixel pitch of the photoelectric conversion elements provided in the CCD and the arrangement method of the color filter array, aliasing distortion occurs. When this aliasing distortion component is mixed in an image obtained by photographing a subject, a striped pattern (moire) in which the color and brightness of the photographed image periodically change occurs. Specifically, in a photographing apparatus including a CCD having a spatial sampling frequency determined by a pixel pitch and a color arrangement pitch, when photographing a subject, the subject has a frequency equal to or higher than half the spatial sampling frequency (referred to as a Nyquist frequency). Is included at the Nyquist frequency, aliasing distortion occurs, and the aliasing distortion is superimposed on the image signal as a false signal, thereby periodically changing the color and brightness of the captured image. It is visually recognized as a striped pattern (moire).

In order to reduce such moire, there is known an optical low-pass filter that is disposed between the photographing lens and the CCD and removes high-frequency components of subject light. For example, an optical low-pass filter composed of three quartz plates that are different from each other in the direction in which the light beam is shifted, and the same light beam is incident on adjacent photoelectric conversion elements constituting the CCD, thereby having a spatial frequency smaller than the pixel pitch. A technique for dulling an image and reducing moire has been proposed (see Patent Document 1).
JP-A-2-204715

  As described above, the CCD is provided with a color filter array such as a Bayer array method, a G stripe array method, an R / G checkered array method, or a GRB stripe array method on the photoelectric conversion element. Here, the optical low-pass filter proposed in Patent Document 1 is an optical low-pass filter having a birefringence separation width that is uniquely determined by the intrinsic refractive index of each of the three quartz plates. An MTF having a spatial frequency of 1 / 3d (d: pixel pitch) in a CCD provided with a color filter array employing the GRB stripe arrangement method and 1 / 2d in a CCD provided with a color filter array employing the Bayer arrangement method. Modulation Transfer Function: When an attempt is made to set the component of the resolution (the sharpness) of the image signal for each frequency band to zero, the MTF component having a lower spatial frequency is also removed, and therefore the resolution is reduced. The problem of degradation occurs.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a photographing apparatus in which a decrease in resolution is suppressed to be small and image quality is enhanced.

An imaging apparatus of the present invention that achieves the above object is an imaging apparatus that includes an imaging optical system and captures subject light incident via the imaging optical system with an imaging element to generate an image signal.
The imaging optical system includes a low-pass filter that can freely adjust the birefringence separation width.

  In the photographing apparatus of the present invention, since the photographing optical system includes a low-pass filter that can freely adjust the separation width of birefringence, the separation width corresponding to the pixel pitch of the image sensor and the color arrangement pitch of the color filter As described above, the direction of the light beam of the subject incident on the image sensor can be freely adjusted. Therefore, in comparison with the technique of the optical low-pass filter having a birefringence separation width uniquely determined by the intrinsic refractive index of each of the three quartz plates proposed in Patent Document 1, for example, a specific color arrangement Even when an MTF component having a desired spatial frequency is set to 0 in an image sensor in which a color filter array employing the method is arranged, an MTF component having a spatial frequency lower than the spatial frequency is not removed, The reduction in resolution is suppressed to a small level and the image quality is improved.

  Here, the low-pass filter is preferably a low-pass filter that uses liquid crystal and has a birefringence separation width that changes in accordance with an applied voltage.

  With such a low-pass filter, the separation width of the birefringence of the low-pass filter can be freely and easily adjusted by changing the direction of alignment of the liquid crystal molecules according to the applied voltage.

  In addition, the photographing optical system includes a diaphragm member whose diaphragm diameter can be freely adjusted, and the photographing apparatus includes a filter adjustment unit that adjusts the birefringence separation width of the low-pass filter according to the diaphragm diameter of the diaphragm member. It is also a preferable aspect that it is provided.

  The MTF characteristic of the photographing lens changes according to the aperture value (F value). For example, when the F value of the photographing lens is small, the MTF value at the Nyquist frequency is relatively high, and therefore, it becomes necessary to remove the high frequency. On the other hand, when the F value of the taking lens is large, the MTF value at the Nyquist frequency is almost 0, and therefore, there is no need to remove the high frequency. As described above, since the MTF characteristic of the photographing lens changes in accordance with the F value, if the separation width of the low-pass filter is changed in accordance with the MTF characteristic of the photographing lens, the resolving power with a small stop can be improved. Can do.

Further, the low-pass filter is capable of adjusting the separation width of birefringence for each region when the object scene is divided into a plurality of regions,
A moiré detection unit for detecting moiré in each region of the subject image formed on the image sensor;
It is also preferable to include a filter adjusting unit that adjusts the birefringence separation width of the low-pass filter so that moire disappears independently for the plurality of regions.

  In this way, the moiré can be eliminated in the area where the moiré is detected, and the high frequency components are not removed in the area other than the area where the moiré is detected. be able to.

  According to the present invention, it is possible to provide a photographing apparatus in which a decrease in resolution is suppressed to be small and an image quality is enhanced.

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is an external view of a camera which is an embodiment of a photographing apparatus of the present invention.

  1A is a front view, FIG. 1B is a top view, FIG. 1C is a side view, and FIG.

  A camera 100 shown in FIGS. 1A to 1C is a digital camera that includes a photographing optical system and captures subject light incident through the photographing optical system with an image sensor to generate an image signal.

  As shown in FIG. 1D, an operation unit 120 for performing various operations when the user uses the camera 100 is provided on the back surface of the camera 100 of the present embodiment.

  The operation unit 120 includes a power switch 121 for turning on the power for operating the camera 100, a shooting / playback switching lever 122 for freely switching between shooting and playback, and a shooting mode for selecting auto shooting, manual shooting, and the like. Dial 123, cross switch 124 for setting, selecting or zooming various menus, flash emission switch 125, and execution / cancel switch 126 for executing or canceling the menu selected by cross switch 124. Is provided.

  On the back of the camera 100, an image display LCD 102 for displaying a photographed image, a reproduced image, and the like, and an operation display LCD 103 for assisting the operation are provided.

  Further, as shown in FIG. 1B, a release button 104 is provided on the upper surface of the camera 100. With this release button 104, an instruction to start shooting is transmitted to a main CPU, which will be described later, provided in the camera 100. In this camera 100, shooting / playback switching lever 122 can freely switch between shooting and playback. When shooting, the user switches shooting / playback switching lever 122 to shooting side 122a, and when playback, shooting / playback is performed. The reproduction switching lever 122 is switched to the reproduction side 122b. As shown in FIG. 1A, a flash light emitting device 105 having a flash light emitting tube 105a that emits flash light is disposed on the upper surface of the camera 100.

  Furthermore, as shown in FIG. 1C, a video output terminal 106 to which a cable for outputting an image signal of a subject photographed by the camera 100 to a television or a projector is connected to the side surface of the camera 100. A cable for outputting an image signal of a subject photographed by the camera 100 to a personal computer or the like provided with a Universal Serial Bus (USB) terminal, and inputting an image signal from the personal computer or the like to the camera 100 Are connected to a USB terminal 107, and a DC voltage input terminal 108 to which a DC voltage from an AC adapter is input.

  FIG. 2 is a block diagram showing a circuit configuration of the camera shown in FIG.

  The camera 100 includes a photographing optical system 1. The photographing optical system 1 includes a photographing lens 101, a diaphragm member 2, and a liquid crystal optical low-pass filter 3 (corresponding to an example of a low-pass filter according to the present invention). The taking lens 101 includes a zoom lens 101_1 and a focus lens 101_2.

  The liquid crystal optical low-pass filter 3 is a low-pass filter whose birefringence separation width can be freely adjusted. Specifically, the liquid crystal optical low-pass filter 3 uses liquid crystal, and the birefringence separation width changes according to the applied voltage. This is a low-pass filter. Further, the liquid crystal optical low-pass filter 3 is capable of adjusting the separation width of birefringence for each region when the object field is divided into a plurality of regions.

  The diaphragm member 2 is a member whose diaphragm diameter can be freely adjusted, and the camera 100 has a filter adjustment for adjusting the birefringence separation width of the liquid crystal optical low-pass filter 3 in accordance with the diaphragm diameter of the diaphragm member 2. Part 4 is provided.

  Further, in this camera 100, the zoom drive unit 5 that drives the zoom lens 101_1, the focus drive unit 6 that drives the focus lens 101_2, the aperture drive unit 7 that drives the aperture member 2, and the positions of the zoom lens 101_1 are set. A zoom position detection unit 8 for detection is provided.

  Further, the camera 100 is provided with a CCD 132 that is an image pickup element that forms an image of subject light incident via the photographing optical system 1 and converts it into an analog image signal.

  The camera 100 also includes an A / D unit 133 that A / D converts an analog image signal from the CCD 132 into digital image data, and a white balance of a subject image represented by the digital image data from the A / D unit 133. And a white balance / γ processing unit 134 that adjusts the slope (γ) of the straight line in the gradation characteristics of the subject image and further amplifies the digital image signal.

  Furthermore, the camera 100 is provided with a buffer memory 135 that stores image data from the white balance / γ processing unit 134.

  The camera 100 also includes a CG (clock generator) unit 136, a photometry / ranging CPU 137, a charge / light emission control unit 138, a communication control unit 139, a YC processing unit 140, and a power source 141. ing.

  The CG unit 136 outputs a drive signal for driving the CCD 132, a control signal for controlling the A / D unit 133, the white balance / γ processing unit 134, and a control signal for controlling the communication control unit 139. Further, a shutter control signal from a main CPU 145 described later and a control signal from a photometry / ranging CPU 137 are input to the CG unit 136.

  The photometry / ranging CPU 137 drives the photographing lens 101 and the aperture member 2 with the zoom drive unit 5, the focus drive unit 6 and the aperture drive unit 7 and detects them with the zoom position detection unit 8, thereby performing photometry and distance measurement. The CG unit 136 and the charge / light emission control unit 138 are controlled. Further, the photometry / ranging CPU 137 performs data communication with a main CPU described later.

  The charging / light emission control unit 138 is supplied with electric power from the power source 141 to emit light from the flash light emission tube 105a, charges a flash light emission capacitor (not shown), and controls light emission from the flash light emission tube 105a.

  The communication control unit 139 is provided with a USB terminal 107 shown in FIG. 1C. The communication control unit 139 is a personal computer or the like provided with a USB terminal for image signals of a subject photographed by the camera 100. The data communication with the external device is performed by outputting the image signal to the external device and inputting an image signal to the camera 100 from such an external device.

  Further, the camera 100 is provided with the video output terminal 106 shown in FIG. 1C, and the YC processing unit 140 reads out the image data stored in the buffer memory 135 via the bus line 142, and luminance A color video signal YC separated into a signal (Y) and a color signal (C) is generated. The generated color video signal YC is output from the video output terminal 106.

  A power supply 141 supplies power to each part of the camera 100.

  Further, the camera 100 includes a compression / decompression & ID extraction unit 143 and an I / F unit 144. The compression / decompression & ID extraction unit 143 reads and compresses the image data stored in the buffer memory 135 via the bus line 142 and stores the image data in the memory card 200 via the I / F unit 144. In addition, the compression / decompression & ID extraction unit 143 extracts an identification number (ID) unique to the memory card 200 and reads the image data stored in the memory card 200 when reading the image data stored in the memory card 200. Are decompressed and stored in the buffer memory 135.

  The camera 100 also includes a main CPU 145, an EEPROM 146, a YC / RGB conversion unit 147, and a display driver 148.

  The main CPU 145 controls the entire camera 100. The main CPU 145 serves as a moire detection unit according to the present invention, and detects the moire of each area of the image representing the subject image formed on the CCD 132. Here, as described above, the liquid crystal optical low-pass filter 3 is capable of adjusting the separation width of birefringence for each region when the object field is divided into a plurality of regions. The unit 4 also adjusts the birefringence separation width of the liquid crystal optical low-pass filter 3 so that moire disappears independently for a plurality of regions. Details will be described later.

  The EEPROM 146 stores solid data unique to the camera 100 and the like.

  The YC / RGB conversion unit 147 converts the color video signal YC generated by the YC processing unit 140 into RGB signals of three colors, and outputs them to the image display LCD 102 via the display driver 148.

  FIG. 3 is a cross-sectional view of the liquid crystal optical low-pass filter shown in FIG.

  The liquid crystal optical low-pass filter 3 shown in FIG. 3 includes a spacer 31, flat plate-like transparent substrates 32 and 33 arranged to face each other with the spacer 31 interposed therebetween, and a transparent disposed on the inner surfaces of the transparent substrates 32 and 33. Electrodes 34, 35, light distribution films 36, 37 disposed on the inner surfaces of the transparent electrodes 34, 35, and a liquid crystal 38 sealed in a space formed by the spacer 31 and the light distribution films 36, 37 are provided. The liquid crystal 38 has liquid crystal molecules 38a. The transparent electrodes 34 and 35 are applied with a voltage V for adjusting the alignment direction of the liquid crystal molecules 38a.

  The transparent substrates 32 and 33 are formed of a material having a high transmittance with respect to the wavelength band of incident light, and glass, polymer film, or the like can be used.

  The transparent electrodes 34 and 35 have an electrode pattern to which the voltage V is applied. Although the structure of the electrode pattern will be described later, the alignment direction of the liquid crystal molecules 38a can be freely adjusted according to the structure of the electrode pattern and the magnitude of the voltage V applied to the electrode pattern.

  The light distribution films 36 and 37 are for keeping the liquid crystal molecules 38 a in a predetermined alignment direction when the voltage V is not applied to the transparent electrodes 34 and 35.

  FIG. 4 is a diagram for explaining how to adjust the alignment direction of the liquid crystal molecules of the liquid crystal optical low-pass filter shown in FIG.

  FIG. 4 shows the transparent electrodes 34 and 35, the light distribution films 36 and 37, and the liquid crystal 38 having the liquid crystal molecules 38a constituting the liquid crystal optical low-pass filter 3. The liquid crystal molecules 38a have an optical axis in the major axis direction. A voltage V for adjusting the alignment direction of the liquid crystal molecules 38a is applied to the transparent electrodes 34 and 35, whereby the alignment direction of the liquid crystal molecules 38a is changed by an angle (tilt angle) β with respect to the optical axis. Has been.

  FIG. 5 is a diagram showing the birefringence separation width of the liquid crystal molecules shown in FIG. 4 that changes according to the applied voltage.

  The alignment direction of the liquid crystal molecules 38a is changed by the tilt angle β with respect to the optical axis P. The liquid crystal molecules 38a in such a state have an optical path length L. Incident light A is incident on the liquid crystal molecules 217a having such an optical path length L. The incident light A is birefringent by the liquid crystal molecules 38a, separated into ordinary light A1 and extraordinary light A2, and emitted. The separation width B between the ordinary light A1 and the extraordinary light A2 is determined according to the tilt angle βn. In this way, the incident light A is birefringent by the liquid crystal molecules 38a to be separated into the ordinary light A1 and the extraordinary light A2, and the same light beam is incident on the adjacent photoelectric conversion elements constituting the CCD 132. A subject image having a fine spatial frequency is dulled to reduce moire.

  Assuming the refractive index of normal liquid crystal molecules, it is possible to change the separation width up to 10 μm.

  Here, an embodiment of the liquid crystal optical low-pass filter 3 will be described. In this example, indium tin oxide (ITO) was applied as a transparent electrode 34, 35 on a glass substrate by sputtering. On top of that, a polyimide film (Nissan Chemical) was applied as the light distribution films 36 and 37, fired, and then rubbed. Liquid crystal ZLI-1132 (manufactured by Merck) was injected and sealed in an element sandwiched between 40 μm spacers 31 (manufactured by Sekisui Chemical).

  The tilt angle when no voltage V was applied was 30 degrees, and the separation width of the liquid crystal optical low-pass filter 3 was observed with a polarizing microscope and found to be 7 μm. When the voltage V is applied to this element (liquid crystal optical low-pass filter 3) and the tilt angle is 45 degrees, the separation width is 5 μm, and when the voltage V is applied to this element and the tilt angle is 60 degrees The separation width was 4 μm. That is, the separation width of the liquid crystal optical low-pass filter 3 can be reversibly changed by the voltage Vn.

  In the camera 100 according to the present embodiment, the photographing optical system 1 includes the liquid crystal optical low-pass filter 3 in which the separation width of birefringence can be freely adjusted. The direction of the light beam of the subject incident on the CCD 132 can be freely adjusted so that the separation width is the same. Therefore, the MTF component of the desired spatial frequency is set to 0 compared with the technique proposed in Patent Document 1 that has a birefringence separation width that is uniquely determined by the intrinsic refractive index of each of the three quartz plates. Even in such a case, it is possible to prevent the removal of the MTF component having a lower spatial frequency than that spatial frequency, and it is possible to suppress a decrease in resolution and improve the image quality.

  FIG. 6 is a diagram showing a cross-sectional shape of the liquid crystal optical low-pass filter of this embodiment together with the structure of the electrodes.

  FIG. 6 shows the light distribution films 36 and 37 constituting the liquid crystal optical low-pass filter 3 and the transparent electrodes 34 and 35 disposed on the outer surfaces of the light distribution films 36 and 37. The transparent electrode 34 has a striped electrode pattern 34a formed in the horizontal direction. Similarly to the transparent electrode 34, the transparent electrode 35 also has a striped electrode pattern 35a formed in the horizontal direction. In the liquid crystal optical low-pass filter 3, since the electrode patterns 34a and 35a of the transparent electrodes 34 and 35 are symmetrical, for example, the value gradually decreases (or increases) from the upper part to the lower part of the electrode patterns 34a and 35a. By applying the voltage V, the alignment direction of the liquid crystal molecules 38a can be adjusted to be gradually reduced (or increased). By doing so, the separation width of birefringence in the vertical direction of the liquid crystal optical low-pass filter 3 can be adjusted. In addition, for example, by applying a voltage V having an arbitrary magnitude to each part of the electrode patterns 34a and 35a, the direction of alignment of the liquid crystal molecules 38a can be freely adjusted. By doing so, the separation width of the birefringence of the liquid crystal optical low-pass filter 3 can be freely adjusted.

  FIG. 7 is a diagram showing a cross-sectional shape of a liquid crystal optical low-pass filter different from the liquid crystal optical low-pass filter shown in FIG. 6 together with the electrode structure.

  The liquid crystal optical low-pass filter 3_1 shown in FIG. 7 is formed in the vertical direction instead of the transparent electrode 35 having the striped electrode pattern 35a formed in the horizontal direction, as compared with the liquid crystal optical low-pass filter 3 shown in FIG. The difference is that a transparent electrode 3_11 having a striped electrode pattern 3_11a is provided. Here, for example, the upper and lower birefringence separation width of the liquid crystal optical low-pass filter 3_1 is adjusted by the electrode pattern 34a, and the left and right birefringence separation width of the liquid crystal optical low-pass filter 3_1 is adjusted by the electrode pattern 3_11a. The separation width of birefringence in the vertical direction and the horizontal direction of the optical low-pass filter 3_1 can be adjusted. Further, for example, by applying a voltage V having an arbitrary magnitude to each part of the electrode patterns 34a and 3_11a, the separation width of the birefringence of the liquid crystal optical low-pass filter 3_1 can be freely adjusted.

  FIG. 8 is a diagram showing a cross-sectional shape of a liquid crystal optical low-pass filter different from the liquid crystal optical low-pass filter shown in FIGS. 6 and 7 together with the structure of the electrodes.

  Compared with the liquid crystal optical low-pass filter 3 shown in FIG. 6, the liquid crystal optical low-pass filter 3_2 shown in FIG. 8 replaces the transparent electrode 35 having the stripe-like electrode pattern 35a formed in the horizontal direction with a plurality of concentric circular shapes. The difference is that a transparent electrode 3_21 having an electrode pattern 3_21a is arranged. Here, birefringence is applied from the peripheral part to the central part of the liquid crystal optical low-pass filter 3_2 by applying a voltage V whose value gradually decreases (or increases) from the peripheral part to the central part of the concentric electrode pattern 3_21a. The separation width can be adjusted.

  FIG. 9 is a diagram showing a cross-sectional shape of a liquid crystal optical low-pass filter different from the liquid crystal optical low-pass filters shown in FIGS. 6, 7, and 8 together with the structure of the electrodes.

  Compared with the liquid crystal optical low-pass filter 3 shown in FIG. 6, the liquid crystal optical low-pass filter 3_3 shown in FIG. 9 replaces the transparent electrode 35 having the stripe-like electrode pattern 35a formed in the horizontal direction and has a matrix-like electrode pattern. The difference is that a transparent electrode 3_31 having 3_31a is arranged. Here, by applying a voltage V having a different value to each of the matrix-like electrode patterns 3_31a, the separation width of birefringence with respect to an arbitrary position of the liquid crystal optical low-pass filter 3_3 can be adjusted.

  Further, in the camera 100 of the present embodiment, the resolution of a small aperture is improved by adjusting the birefringence separation width of the liquid crystal optical low-pass filter 3 by the filter adjustment unit 4 according to the aperture diameter of the aperture member 2. be able to. Hereinafter, a description will be given with reference to FIG.

  FIG. 10 is a diagram illustrating the relationship between the F value of the photographic lens and the resolving power.

  The horizontal axis in FIG. 10 indicates the spatial frequency, and the vertical axis indicates the MTF. Note that 1 / d (d: pixel pitch) on the horizontal axis indicates the position of the spatial sampling frequency, and 1 / 2d indicates the position of the Nyquist frequency.

  The MTF characteristic of the photographing lens changes according to the aperture value (F value). For example, as shown in FIG. 10, when the F value of the photographic lens is small (F2.8), the MTF value at the Nyquist frequency is relatively high, and therefore it is necessary to remove the high frequency.

  On the other hand, when the F value of the photographic lens increases (F11), the MTF value at the Nyquist frequency becomes almost zero, and therefore the necessity for removing the high frequency is reduced. Thus, the MTF characteristic of the taking lens changes according to the F value. Therefore, in the camera 100 of this embodiment, the separation width of the liquid crystal optical low-pass filter 3 is adjusted by the filter adjustment unit 4 according to the MTF characteristics of the photographing lens 101 of the camera 100, that is, according to the aperture diameter of the aperture member 2. This improves the resolving power with a small aperture. Next, moire will be described.

  FIG. 11 is a diagram showing the relationship between the image signal representing the subject light and the aliasing component.

  In FIG. 11, the horizontal axis represents frequency, and the vertical axis represents MTF. In addition, fs indicated by a solid line indicates the frequency of an image signal representing subject light, fc indicates a spatial sampling frequency determined by the pixel pitch, and fn indicates a Nyquist frequency that is a half of the spatial sampling frequency.

  In the CCD, pixels are discretely arranged two-dimensionally, and an optical image of a subject that has entered through a photographing lens is formed thereon. Therefore, although the optical image is a continuous image, sampling is performed at the spatial sampling frequency fc when photoelectric conversion is performed. Here, when subject light having a high frequency component equal to or greater than the pixel pitch is incident, as shown by a dotted line in FIG. 11, the return is made up of a difference (fc−fs) between the spatial sampling frequency fc and the frequency fs of the image signal. Distortion occurs. When this aliasing distortion component is mixed in the component of the image signal fs, a striped pattern (moire) in which the color and brightness of the photographed image periodically fluctuate occurs and the image quality deteriorates.

  FIG. 12 is a diagram for explaining moire.

  FIG. 12A shows a CZP (Circular Zone Plate) chart A for determining the presence or absence of aliasing distortion components. FIG. 12B shows an image B of the CZP chart A shown in FIG. In the image B shown in FIG. 12B, a CZP chart image C (a component of aliasing distortion) appears in a portion where no signal originally exists, and moiré is generated. Since this moire occurs at the time of photoelectric conversion, it is necessary to remove an optical low-pass filter provided between the photographing lens and the CCD.

  FIG. 13 is a diagram illustrating an example of a captured image displayed on an image display LCD provided in the camera of the present embodiment.

  The image display LCD 102 displays a captured image 1000 having an image area 1001 representing a tree and an image area 1002 representing a person wearing striped clothes. Here, the image region 1001 representing the tree does not include a component having a frequency equal to or higher than the Nyquist frequency, while the image region portion 1002a representing the striped clothes in the image region 1002 representing the person is equal to or higher than the Nyquist frequency. The frequency component is included.

  Here, as described above, the liquid crystal optical low-pass filter 3 provided in the camera 100 of the present embodiment can adjust the separation width of birefringence for each region when the object field is divided into a plurality of regions. Is something. The main CPU 145 serving as a moiré detection unit according to the present invention detects moiré in each area of an image representing a subject image formed on the CCD 132. As a technique for detecting moire, paying attention to the fact that moire does not occur in an out-of-focus state, a technique for obtaining a moire signal by subtracting an image signal in an out-of-focus state from an image signal in the in-focus state, A technique for determining the presence / absence of moire and the frequency of moire based on the correlation between the change of the peak value of the power spectrum in the region and the change of the peak value of the power spectrum in the low frequency region is known. Moire in each area of the image is detected using a known technique. Furthermore, the filter adjustment unit 4 adjusts the birefringence separation width of the liquid crystal optical low-pass filter 3 so that moire disappears independently for a plurality of regions. Specifically, the main CPU 145 detects the moiré of the image area portion 1002a, and the filter adjustment unit 4 eliminates the moiré in the image area portion 1002a, and the image area 1002 includes the image area portion 1002a in which the moiré is detected. In the other image region 1001, the separation width of the birefringence of the liquid crystal optical low-pass filter 3 is adjusted so that high frequency components are not removed. By adjusting in this way, the image quality of the entire captured image 1000 can be improved.

1 is an external view of a camera which is an embodiment of a photographing apparatus of the present invention. It is a block diagram which shows the circuit structure of the camera shown in FIG. It is sectional drawing of the liquid crystal optical low-pass filter shown in FIG. It is a figure for demonstrating a mode that the orientation direction of the liquid crystal molecule of the liquid crystal optical low-pass filter shown in FIG. 3 is adjusted. It is a figure which shows the separation width of the birefringence which changes according to the applied voltage of the liquid crystal molecule shown in FIG. It is a figure which shows the cross-sectional shape of the liquid crystal optical low-pass filter of this embodiment with the structure of an electrode. It is a figure which shows the cross-sectional shape of the liquid crystal optical low-pass filter different from the liquid crystal optical low-pass filter shown in FIG. 6 with the structure of an electrode. It is a figure which shows the cross-sectional shape of the liquid-crystal optical low-pass filter different from the liquid-crystal optical low-pass filter shown in FIG. 6, FIG. 7 with the structure of an electrode. It is a figure which shows the cross-sectional shape of the liquid crystal optical low-pass filter different from the liquid crystal optical low-pass filter shown in FIG.6, FIG.7, FIG.8 with the structure of an electrode. It is a figure which shows the relationship between F value of a taking lens, and resolving power. It is a figure which shows the relationship between the image signal showing to-be-photographed light, and a folding component. It is a figure for demonstrating a moire. It is a figure which shows an example of the picked-up image displayed on the image display LCD with which the camera of this embodiment was equipped.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shooting optical system 2 Aperture member 3, 3_1, 3_2, 3_3 Liquid crystal optical low-pass filter 3_11, 3_21, 3_31, 34, 35 Transparent electrode 4 Filter adjustment part 5 Zoom drive part 6 Focus drive part 7 Aperture drive part 8 Zoom position detection part 31 spacer 32, 33 transparent substrate 34a, 35a, 3_11a, 3_21a, 3_31a electrode pattern 36, 37 light distribution film 38 liquid crystal 38a liquid crystal molecule 100 camera 101 photographing lens 101_1 zoom lens 101_2 focus lens 102 image display LCD
103 Operation display LCD
104 Release Button 105 Flash Light Emitting Device 105a Flash Light Emitting Tube 106 Video Output Terminal 107 USB Terminal 108 DC Voltage Input Terminal 120 Operation Unit 121 Power Switch 122 Shooting / Playback Switch Lever 123 Shooting Mode Dial 124 Cross Switch 125 Flash Light Emitting Switch 126 Execution / Cancel switch 132 CCD
133 A / D unit 134 White balance / γ processing unit 135 Buffer memory 136 CG unit 137 Metering / ranging CPU
138 Charging / light emission control unit 139 Communication control unit 140 YC processing unit 141 Power supply 142 Bus line 143 Compression / decompression & ID extraction unit 144 I / F unit 145 Main CPU
146 EEPROM
147 YC / RGB conversion unit 148 Driver 200 Memory card 1000 Captured image 1001, 1002 Image area 1002a Image area part

Claims (4)

In an imaging apparatus that includes an imaging optical system and captures subject light that has entered via the imaging optical system with an imaging device and generates an image signal,
An imaging apparatus, wherein the imaging optical system includes a low-pass filter that can freely adjust a separation width of birefringence.   The imaging apparatus according to claim 1, wherein the low-pass filter is a low-pass filter that uses liquid crystal and changes a separation width of birefringence according to an applied voltage. The photographing optical system includes a diaphragm member whose diaphragm diameter can be freely adjusted,
The imaging apparatus according to claim 1, further comprising a filter adjustment unit that adjusts a birefringence separation width of the low-pass filter in accordance with a diaphragm diameter of the diaphragm member. The low-pass filter is capable of adjusting the separation width of birefringence for each region when the object scene is divided into a plurality of regions,
A moiré detection unit that detects moiré in each region of the subject image formed on the image sensor;
The imaging apparatus according to claim 1, further comprising: a filter adjusting unit that adjusts the birefringence separation width of the low-pass filter so that moire disappears independently for the plurality of regions.

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