JP2019029832A - Imaging apparatus - Google Patents

Abstract

To provide an imaging apparatus capable of keeping the resolution feeling well from the lens center to the lens peripheral, even when an antivibration function is applied for shake correction.SOLUTION: An imaging apparatus having a tilt mechanism, and a tilt lens driven by the tilt mechanism, a tilt lens posture detection means for detecting the posture of the tilt lens from the output results of position detection means for detecting the position of the tilt lens, tilt lens posture correction means for correcting the posture of the tilt lens, and a tilt lens correction control mechanism for deriving the tilt lens correction value to be set in the tilt lens posture correction means, from the detection results of the tilt lens posture detection means, and driving the tilt lens by setting the tilt lens correction value in the tilt lens posture correction means, is further provided with an image processing system capable of setting an edge emphasis parameter for each image height, and performs image processing by changing the edge emphasis parameter for each image height, according to the tilt lens correction value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging apparatus having an axially symmetric optical system such as a digital camera.

  In an imaging apparatus such as a digital camera, an imaging optical system such as a lens having an axisymmetric shape with respect to one optical axis is generally used. The imaging optical characteristics of such an imaging optical system basically depend on the distance (image height) in the radial direction from the center of the screen (intersection of the optical axis and the imaging surface) on the imaging surface. . The imaging optical characteristics depending on the image height include spherical aberration, astigmatism, coma aberration, field curvature, and chromatic aberration, and the image deteriorates as these aberrations increase.

  Conventionally, in order to correct an image deteriorated by these aberrations, the configuration of an imaging optical system such as a lens is optimized so that the aberration shows a minimum value. Conventionally, an image deteriorated by image processing is also corrected, and measures such as enhancement of edges are performed to prevent a reduction in contrast caused by aberrations.

  When emphasizing an edge, it is common to use an imaging device that includes an edge emphasizing unit that emphasizes a horizontal edge on the screen and an edge emphasizing unit that emphasizes an edge in the vertical direction. In such an imaging apparatus, in order to cope with the deterioration of the image due to the aberration according to the above-described image height, image processing is performed so that the intensity at the time of enhancing these two types of edges changes according to the image height. To implement.

  More specifically, the image processing is performed by calculating the intensity at the time of emphasizing an edge obtained by multiplying each image height by a predetermined gain with respect to the intensity at the time of enhancing the edge adjusted near the center of the screen. As a result, it is possible to suppress image degradation corresponding to the aberration for each image height.

  Patent Document 1 discloses an image processing apparatus having two types of edge enhancement means, an edge enhancement means for enhancing an edge perpendicular to the radial direction of an imaging optical system and an edge enhancement means for enhancing an edge perpendicular to the azimuth direction. Is disclosed.

  Two types of bandpass filters are prepared for the two edge enhancement means disclosed in Patent Document 1. Then, by changing the ratio of these two types of edge enhancement means according to the radius, azimuth, angle of view, aperture, or subject distance, image degradation caused by aberrations (particularly astigmatism) can be further reduced. It can be suppressed.

JP 2006-21112 A

  However, in the conventional method and the method described in Patent Document 1, even when edge enhancement processing (hereinafter referred to as a Radius_APC parameter) that adaptively adjusts the edge enhancement amount according to the image height is applied, it may be good depending on the pixel. There was a problem that the resolution could not be maintained. When examined in more detail, the above-mentioned inconvenience was observed when the image stabilization function for camera shake correction was applied, and in particular, there was a problem that the sense of resolution deteriorated when the camera shake greatly.

  An object of the present invention is to provide an imaging apparatus that can maintain a good resolution from the center of the lens to the periphery of the lens even when an image stabilization function for correcting camera shake is applied.

  In order to achieve the above object, an imaging apparatus according to the present invention includes a tilt mechanism that tilts a lens, a tilt lens that is driven by the tilt mechanism, and an output result of a position detection unit that detects the position of the tilt lens. The tilt lens attitude detecting means for detecting the attitude of the tilt lens, the tilt lens attitude correcting means for correcting the attitude of the tilt lens, and the detection result of the tilt lens attitude detecting means are set in the tilt lens attitude correcting means. A tilt lens correction control mechanism for deriving a power tilt lens correction value, setting the tilt lens correction value in the tilt lens attitude correction means, and driving the tilt lens; An image processing device capable of setting an edge enhancement parameter in front of the tilt lens according to the tilt lens correction value. And performing image processing by changing the edge enhancement parameters of each image height.

  According to the present invention, it is possible to provide an imaging apparatus capable of maintaining a good resolution from the lens center to the lens periphery even when the image stabilization function for correcting camera shake is applied.

1 is a block diagram illustrating a schematic configuration example of a digital camera according to an embodiment of the present invention. 1 is a block diagram showing a schematic configuration example of an optical system 101 in an embodiment of the present invention. The graph which shows the image height characteristic of resolution performance (SFR), and the setting value for every image height of Radius_APC parameter (gain). Schematic explanatory diagram showing the relationship between the Radius_APC parameter (gain) related to edge enhancement in the sagittal direction and the meridional direction, and the Radius_APC parameter (gain) related to edge enhancement in the horizontal direction and the vertical direction

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a schematic configuration example of a digital camera 100 according to the present embodiment. In FIG. 1, the optical system 101 includes at least a zoom lens, a focus lens, and a lens group including an anti-vibration lens (tilt lens) for providing an optical anti-vibration function, and an aperture device. This optical system 101 controls the magnification of the subject image reaching the image sensor 102, the suppression of blur image output due to the focus position, camera shake, or the like, or the amount of light.

  In particular, the present embodiment is characterized by the anti-vibration function of the anti-vibration lens, and will be described in more detail with reference to FIG. FIG. 2 is a block diagram illustrating a schematic configuration example of the optical system 101 in the present embodiment.

  As shown in FIG. 2, the optical system 101 of the present embodiment constitutes an optical system in the order of a zoom lens 201, an anti-vibration lens 202, a focus lens 203, and a diaphragm device 204, and subject images are in the order described above. It reaches the image sensor 102 via each lens and the diaphragm device. Further, the image stabilizing lens 202 can be moved by a tilting unit (not shown) that tilts in the tilt direction with respect to the imaging surface of the image sensor 102, and is one of the features of this embodiment.

  Further, as shown in FIG. 2, the digital camera 100 of the present embodiment incorporates a gyro sensor 205 that detects the attitude of the digital camera 100. Then, from the output result of the gyro sensor 205, it is possible to derive a correction value (hereinafter referred to as IS correction value) indicating how much the anti-vibration lens 202 should be tilted when the anti-vibration function is operated. it can.

  The tilt means (not shown) is operated according to the IS correction value derived in this way to drive the anti-vibration lens 202 and control the lens attitude in accordance with the output of the gyro sensor 205, that is, the attitude of the camera. It can be performed and enables vibration prevention due to camera shake.

  Next, referring again to FIG. 1, the image sensor 102 is a photoelectric conversion element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) sensor. Is generated. In the present embodiment, it is assumed that the image sensor 102 is composed of a CCD. The A / D converter 103 converts the analog image signal output from the image sensor 102 into a digital image signal.

  The image processing circuit 104 performs white balance processing, noise suppression processing, gradation conversion processing, edge enhancement processing, and the like on the image signal, and outputs the image signal as a luminance signal Y and color difference signals U and V. The image processing circuit 104 also calculates a brightness value of the subject and a focus value indicating the focus state of the subject from the image signal. Note that the image processing circuit 104 can perform similar image processing not only on the image signal output from the A / D converter 103 but also on the image signal read from the recording medium 108.

  The control circuit 105 controls each circuit constituting the digital camera 100 of the present embodiment, controls the operation of the digital camera 100, and also controls the drive of the optical system 101 and the image sensor 102. The control circuit 105 also performs processing for calculating a parameter for enhancing an edge, which will be described later.

  The display memory 106 is a memory that temporarily stores an image signal that is a source of an image displayed on the display device 107. The display device 107 is configured by a liquid crystal display or an organic EL (Electro Luminescence) display, and displays an image signal generated by the image sensor 102 or an image related to an image signal read from the recording medium 108. By updating and displaying continuous image signals read from the image sensor 102 as needed, it can function as an electronic viewfinder.

  The recording medium 108 may be configured to be detachable from the digital camera 100 or may be built in the digital camera 100. The operation member 109 is a member that the user operates to send an instruction to the digital camera 100. The bus 110 is used to exchange image signals among the image processing circuit 104, the control circuit 105, the display memory 106, and the recording medium 108.

  Next, an example of an operation at the time of shooting of the digital camera 100 in the present embodiment will be described. When the operation member 109 is operated by the user and an instruction to start photographing preparation is input, the control circuit 105 starts controlling the operation of each circuit.

  First, the image sensor 102 photoelectrically converts a subject image transmitted through the optical system 101 to generate an analog image signal, and the A / D converter 103 digitizes the analog image signal. The image processing circuit 104 performs white balance processing, noise suppression processing, gradation conversion processing, edge enhancement processing, and the like on the image signal output from the A / D converter 103.

  The image signal processed by the image processing circuit 104 is displayed as an image on the display device 107 via the display memory 106. As described above, the image pickup device 102 continuously generates image signals, updates the image of the subject in real time using the read continuous image signals, and displays the image on the display device 107 so that the display device 107 is electronic. Functions as a typical viewfinder.

  These processes are repeated until the user operates the shutter button included in the operation member 109. When the user operates the shutter button, the control circuit 105 re-adjusts the operation of the optical system 101 based on the luminance value and the focus value obtained by the image processing circuit 104 and shoots a still image. The image processing circuit 104 performs various image processing on the still image signal. The image signal output from the image processing circuit 104 is recorded on the recording medium 108.

  In the present embodiment, a parameter (hereinafter referred to as an edge enhancement parameter) for emphasizing an edge by the image processing circuit 104 and the control circuit 105 is calculated using a conventional image processing parameter. Here, the conventional image processing parameter is an image processing parameter related to a color such as white balance, which is a parameter other than edge enhancement, and an edge enhancement parameter used for enhancing an edge near the conventional axis (imaging center). It refers to image processing parameters such as.

  Further, the edge enhancement parameters will be described in detail below. Edge enhancement parameters include the bandpass filter setting value for which direction and the frequency band in which azimuth is emphasized, the gain setting value for adjusting the edge enhancement degree, and noise component suppression. For example, base clip setting value.

  In the present embodiment, an edge enhancement parameter corresponding to the optical imaging performance for each pixel on the imaging surface in the imaging element 102 is calculated. More specifically, a gain G is obtained for each pixel using the control circuit 105 and input to the image processing circuit 104, and the result obtained by multiplying the edge enhancement parameter on the axis described above by the gain G is a predetermined pixel. Used as an edge enhancement parameter during image processing. The gain G for each pixel can be derived by the following procedure.

  First, the resolution performance at all pixel positions on the imaging surface is obtained, and then the resolution performance at the imaging center that is the intersection of the optical axis of the imaging optical system and the imaging surface, and the resolution at each other pixel position. The gain G for each pixel can be calculated by using the difference from the performance. Here, the resolution performance uses, for example, SFR (Spatial Frequency Response) representing a spatial frequency response including image processing or MTF (Modulation Transfer Function) representing a modulation transfer function related to a single lens. These values can be obtained in advance as design values by optical design.

  Hereinafter, an example in which the resolution performance is SFR will be described. Here, each pixel position on the imaging surface is represented by polar coordinates (r, φ), and the resolution performance at the imaging center, which is the intersection of the optical axis of the imaging optical system and the imaging surface, is SFR (r = 0). Let SFRn (r, φ) be the resolution performance at each pixel position. r is the length in the radial direction from the imaging center to each pixel position, and φ is the azimuth angle φ with the imaging center as the rotation center. At this time, the above-described difference value ΔSFR (r, φ) of the resolution performance is calculated by the following equation (1).

ΔSFR (r, φ) = {SFR (r = 0) −SFRn (r, φ)} / SFR (r = 0)
... Formula (1)
Subsequently, the gain G (r, φ) at each pixel position is calculated by the following equation (2) using the calculated difference value ΔSFR of the resolution performance.

G (r, φ) = α × ΔSFR (r, φ) +1 (2)
(Α: Arbitrary proportional constant)
In this embodiment, G (r, φ) is derived with α = 1.7. In this embodiment, a linear function is used as an expression for calculating the gain G (r, φ). However, the present invention is not limited to this, and if ΔSFR (r, φ) = 0, and G = 1, A multidimensional function such as a quadratic function may be used.

  On the other hand, in this embodiment, as G (r, φ) to be obtained, a parameter to be emphasized for edges in the sagittal direction and the meridional direction is derived. Thus, if the pixel position is the same distance r from the imaging center, the same gain G (r, φ) may be set regardless of the azimuth angle φ. That is, it can be expressed as a sagittal gain G (r, φ) = G_s (r) and a meridional gain G (r, φ) = G_m (r). It will be good. That is, gains G_s (r) and G_m (r), which are functions for the image height, are obtained as Radius_APC parameters in the sagittal direction and the meridional direction in the state where there is no camera shake correction (IS correction value = 0).

  On the other hand, as shown in the upper diagram of FIG. 3, the image height characteristic of the resolution performance (SFR) varies depending on the IS correction value (θ) in the camera shake correction. Therefore, in the present embodiment, the above-described gains G_s (r) and G_m (r) are changed according to the difference in image height characteristics of the resolution performance depending on the IS correction value, as shown in the lower diagram of FIG. To set.

  That is, for each IS correction value, the radius_APC parameter in the sagittal direction and the meridional direction is stored in a storage device (not shown), and at the time of shooting, the IS correction value is detected, and the Radius_APC parameter corresponding to this is set, Using this, image processing is performed through a predetermined calculation. As described above, the Radius_APC parameter in the sagittal direction and the meridional direction for each IS correction value (θ) is hereinafter referred to as gains G_s (r, θ) and G_m (r, θ). On the other hand, the arithmetic processing using the control circuit 105 immediately before the image processing in the image processing circuit 104 will be described later.

  As shown in the upper diagram of FIG. 3, in this embodiment, the resolution performance at the imaging center is the highest regardless of the IS correction value, and the image height characteristic of the resolution performance is point-symmetric with respect to the imaging center. There is a characteristic that shows sex. This is because the anti-vibration function using the anti-vibration lens 202 by the tilt means is mounted in the optical system employed in the present embodiment.

  In an optical system equipped with a shift lens that is generally used for the image stabilization function, the position where the resolution performance is highest tends to shift from the imaging center as the IS correction value increases. When the above-mentioned Radius_APC parameter is applied to an imaging apparatus that exhibits such image height characteristics of resolution performance, it is necessary to newly provide a mechanism (such as an increase in the number of parameters) that takes into account the amount of deviation from the imaging center. There is an increase in hardware load.

  In addition, imaging performance may vary depending on the azimuth angle even at the same moving radius position due to manufacturing errors such as mounting errors of lenses and image sensors. This is a so-called “single blur” phenomenon. In this case, even if the image stabilization function using the image stabilization lens 202 by the tilt means of this embodiment is mounted, the position where the above-described resolution performance is the highest is the center of the imaging. May deviate from. Therefore, in the present embodiment, it is preferable that the amount of deviation from the above-described imaging center can be reduced by manufacturing so as to prevent “single blurring” as much as possible.

  As described above, in the present embodiment, in order to minimize the hardware load, the image stabilizing lens 202 that is movable by the tilt unit and has a relatively small amount of deviation between the position where the resolution performance is highest and the imaging center. The vibration-proof function using is adopted. In addition, “single blur” was produced so that “single blur” hardly occurred. Thus, only one pair of sagittal and meridional Radius_APC parameters needs to be derived for one IS correction value, and two types of Radius_APC parameters are stored in the storage device for each required number of IS correction values. ing.

  Specifically, in this embodiment, two types of Radius_APC parameters are derived for each IS correction value with respect to IS correction values of 5 points at regular intervals between the minimum value (= 0) and the maximum value of the IS correction value. In total, 5 × 2 = 10 types of Radius_APC parameters are stored in the storage device. When an IS correction value without Radius_APC parameter setting is detected at the time of shooting, the Radius_APC parameter in the IS correction value before and after the setting is extracted, and a predetermined approximation (interpolation process) is performed using the Radius_APC parameter. Thus, the Radius_APC parameter can be obtained.

  If the above interpolation processing is used, it is not necessary to derive Radius_APC parameters relating to all IS correction values in advance and store them in the storage device, thereby realizing further reduction in hardware load.

  The image processing circuit 104 performs image processing using the Radius_APC parameter for each IS correction value obtained as described above. Next, regarding the setting of image quality parameters (edge enhancement parameters) in the image processing circuit 104. Described below.

  The image processing circuit 104 includes edge enhancement means for enhancing horizontal edges and edge enhancement means for enhancing vertical edges of a captured image. These edge enhancement means are set with edge enhancement parameters for enhancing horizontal and vertical edges in the vicinity of the imaging center.

  By multiplying the horizontal and vertical edge enhancement parameters in the vicinity of the imaging center by the gain that is the Radius_APC parameter in the horizontal and vertical directions and setting the gain in the image processing circuit 104, the peripheral image height is set. As for the above, good resolution performance can be obtained. Since the gain here depends on the IS correction value (θ), the image height (r), and the azimuth angle (φ), the Radius_APC parameter in the horizontal direction is set to G_h (r, θ, φ) and the vertical direction is set. The Radius_APC parameter is expressed as G_v (r, θ, φ).

On the other hand, the Radius_APC parameters in the sagittal direction and the meridional direction depending on the IS correction value (θ) and the image height (r) are the gains G_s (r, θ) and G_m (r, θ) as described above. G_h (r, θ, φ) and G_v (r, θ, φ) have the following relational expressions (see FIG. 4).
G_h (r, θ, φ) = a × G_s (r, θ) × sin φ + b × G_m (r, θ) × cos φ (3)
G_v (r, θ, φ) = c × G_s (r, θ) × cos φ + d × G_m (r, θ) × sin φ Expression (4)
(A, b, c, d: any proportional constant)
Here, in this embodiment, a = b = c = 0.5 and d = −0.5, and the arithmetic processing using the control circuit 105 is performed, and the calculation result is input to the image processing circuit 104. Perform image processing. That is, after deriving G_h (r, θ, φ) and G_v (r, θ, φ) at each pixel position (r, φ) from the equations (3) and (4) using the control circuit 105, The value is multiplied by the edge enhancement parameters in the horizontal and vertical directions near the imaging center by the image processing circuit 104 and used for image processing.

  By performing image processing as described above, even when the image stabilization function for camera shake correction is applied, the Radius_APC parameter can be updated according to the camera shake correction amount, so that the image processing can always be performed from the lens center. The resolution up to the lens periphery can be kept good. Further, the number of Radius_APC parameters corresponding to the amount of camera shake correction value stored and used in the storage device of the image processing apparatus can be minimized, and hardware load (memory capacity, etc.) can be minimized. The cost increase can be kept to a minimum.

DESCRIPTION OF SYMBOLS 100 Digital camera 101 Optical system 102 Image pick-up element 103 A / D converter 104 Image processing circuit 105 Control circuit 106 Display memory 107 Display apparatus 108 Recording medium 109 Operation member 201 Zoom lens 202 Anti-vibration lens 203 Focus lens 204 Diaphragm apparatus 205 Gyro sensor

Claims (5)

A tilt mechanism for tilting the lens, and a tilt lens driven by the tilt mechanism;
A tilt lens attitude detection means for detecting an attitude of the tilt lens from an output result of the position detection means for detecting the position of the tilt lens;
Tilt lens attitude correction means for correcting the attitude of the tilt lens;
A tilt lens correction value to be set in the tilt lens attitude correction unit is derived from the detection result of the tilt lens attitude detection unit, the tilt lens correction value is set in the tilt lens attitude correction unit, and the tilt lens is set. A tilt lens correction control mechanism to be driven;
An imaging device having
An image processing apparatus capable of setting an edge enhancement parameter for each image height, and performing image processing by changing the edge enhancement parameter for each image height according to the tilt lens correction value apparatus. The difference between the resolution performance at the imaging center on the imaging surface and the resolution performance at a predetermined pixel position away from the imaging center on the imaging surface is calculated, and the predetermined pixel is calculated from the calculated difference function. First calculating means for calculating a gain at a position;
Second calculation means for calculating an edge enhancement parameter at the predetermined pixel position using the gain calculated by the first calculation means and an edge enhancement parameter at the imaging center;
The image pickup apparatus according to claim 1, wherein image processing is performed using an edge enhancement parameter for each image height. The edge enhancement parameter for each image height is an edge enhancement parameter for image edges in the sagittal direction and the meridional direction,
An auxiliary storage device that stores the edge enhancement parameter for each correction value in advance is provided,
The image processing unit
A predetermined edge enhancement parameter is selected from a plurality of edge enhancement parameters stored in the storage device according to the correction value, and an image relating to a horizontal direction and a vertical direction at an arbitrary azimuth angle using the predetermined edge enhancement parameter. The imaging according to claim 1, wherein an edge enhancement parameter for each height is calculated, and the image processing is performed using the calculated edge enhancement parameter for each image height in the horizontal direction and the vertical direction. apparatus. The image height is r, the azimuth angle is φ, the correction value is θ, the gain in the edge enhancement parameter in the sagittal direction is G_s (r, θ), the gain in the edge enhancement parameter in the meridional direction is G_m (r, θ), and the horizontal When the gain in the edge enhancement parameter in the direction is G_h (r, θ, φ) and the gain in the edge enhancement parameter in the vertical direction is G_v (r, θ, φ), the edge at the pixel at an arbitrary position (r, φ) The enhancement parameter is a product in each direction of a gain in the horizontal direction and a vertical direction expressed by the following relational expression and an edge enhancement parameter in the horizontal direction and the vertical direction at the imaging center. The imaging device described in 1.
G_h (r, θ, φ) = a × G_s (r, θ) × sin φ + b × G_m (r, θ) × cos φ
G_v (r, θ, φ) = c × G_s (r, θ) × cos φ + d × G_m (r, θ) × sin φ
(A, b, c, d: any proportional constant)
At this time, the azimuth angle φ = 0 ° is defined as the horizontal direction, and φ = 90 ° is defined as the vertical direction. An image sensor;
Regardless of the correction value, the SFR or MTF at the center of the angle of view on the image sensor is the highest, and the image height characteristic of the SFR or MTF is an optical system exhibiting point symmetry with respect to the center of the angle of view.
The imaging apparatus according to claim 1, wherein the imaging apparatus includes: