JP2007195122A - Imaging apparatus, image processor and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus for effectively suppressing coloring due to chromatic aberration. <P>SOLUTION: An edge of an image acquired by an imaging device is detected and a position of the edge in the image is specified. Then, generation of useless color fading is prevented since density of a color signal near the edge is reduced according to a density reduction rule depending on the position of the edge in the image. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing technique in an imaging apparatus or an image processing apparatus.

  An imaging apparatus such as a digital camera is configured such that a light image from a subject is guided to an imaging element such as a single-plate CCD (Charge Coupled Device) via a photographing optical system (photographing lens).

  In an image photographed by such an imaging device, coloring such as false color and chromatic aberration occurs in the contour (edge) portion of the subject.

  As a technique for reducing false colors, false colors are generated by pixel interpolation processing performed to obtain signals of all color components of R (red), G (green), and B (blue) at each pixel position of the image sensor. Has proposed a technique (Patent Document 1) that effectively reduces false colors by estimating signal values.

  On the other hand, chromatic aberration occurs due to an optical factor that the wavelength varies depending on the color type of light, and the degree, range, etc. of chromatic aberration appearing in an image vary depending on characteristics of the photographing lens, focal length, and the like.

  In recent years, with the increase in the number of pixels of the image sensor, lateral chromatic aberration that gradually increases as the distance from the optical axis of the image pickup lens system (hereinafter, simply referred to as “chromatic aberration” in a place where no misunderstanding occurs) is particularly noticeable. It has become to.

JP 2001-292454 A

  The chromatic aberration of magnification is different from a false color generated in units of one pixel or two pixels due to interpolation between pixels, and is generated due to an optical factor, and may occur widely in units of several pixels (for example, about 10 pixels). Accordingly, since the chromatic aberration of magnification cannot be sufficiently dealt with by correction processing using surrounding pixels, a measure for suppressing the coloring of the colored portion and making the coloring inconspicuous is effective.

  However, as described above, there is a problem that “color loss” becomes conspicuous if the color of the colored portion is unconditionally suppressed with respect to the chromatic aberration of magnification that may occur widely in units of several pixels. “Color loss” is a phenomenon in which a color is lost in a portion where the color is suppressed (a phenomenon in which color is lost).

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of effectively reducing coloring due to lateral chromatic aberration so as not to be noticeable.

  In order to solve the above-described problem, the invention of claim 1 is an imaging apparatus, wherein the imaging device, edge detection means for detecting an edge in the image acquired by the imaging device, and the edge of the image are detected. Edge position specifying means for specifying a position, and density reducing means for reducing the density of a color signal in the vicinity of the edge in accordance with a density reduction rule corresponding to the position of the edge.

  According to a second aspect of the present invention, in the imaging apparatus according to the first aspect of the invention, the density reduction means is the edge position specifying means based on the optical axis position of the imaging lens system in the image or the screen center position of the image. For an edge determined to exist within a predetermined distance, the color signal in the vicinity of the edge is not reduced.

  According to a third aspect of the present invention, in the imaging apparatus according to the first aspect of the present invention, the edge detection means is configured such that the edge is within a predetermined distance from the optical axis position of the imaging lens system in the image or the screen center position of the image. It is characterized in that no detection is performed.

  The invention of claim 4 further includes direction determination means for determining a spatial direction in which a density change occurs at the edge in the imaging apparatus according to any one of claims 1 to 3, The density reducing means selectively reduces the density of the color signal in the vicinity of the edge according to the spatial direction of density change at the edge.

  According to a fifth aspect of the present invention, in the imaging apparatus according to any one of the first to fourth aspects, the density reducing means is a distance between the optical axis position of the imaging lens system in the image and the edge. Accordingly, the reduction range of the color signal density in the vicinity of the edge is changed stepwise.

  According to a sixth aspect of the present invention, in the imaging apparatus according to any one of the first to fifth aspects, the density reduction amount of the color signal by the density reducing means is adjusted based on the photographing conditions at the time of photographing. And adjusting means.

  According to a seventh aspect of the present invention, in the imaging apparatus according to the sixth aspect of the invention, the photographing condition includes focal length information, and the adjusting means is configured to reduce the density of the color signal based on the focal length information. It is characterized by adjusting.

  According to an eighth aspect of the present invention, in the imaging apparatus according to the sixth or seventh aspect of the present invention, the photographing condition includes photographing distance information, and the adjusting means is configured to use the color signal based on the photographing distance information. The amount of density reduction is adjusted.

  According to a ninth aspect of the present invention, in the imaging apparatus according to any one of the sixth to eighth aspects, the photographing condition includes an aperture value, and the adjusting means is configured to adjust the color based on the aperture value. It is characterized by adjusting the amount of signal density reduction.

  According to a tenth aspect of the present invention, in the image pickup apparatus according to any of the sixth to ninth aspects, the density reduction amount of the color signal by the density reducing means is adjusted based on photographing lens information at the time of photographing. Adjusting means for further comprising.

  The invention according to claim 11 is an image processing apparatus that performs predetermined image processing on an image acquired by an image sensor, and includes an edge detection unit that detects an edge in the image, and a position of the edge in the image. Edge position specifying means for specifying the color density, and density reducing means for reducing the density of the color signal in the vicinity of the edge in accordance with a density reduction rule corresponding to the edge position.

  The invention according to claim 12 is an image processing method for performing predetermined image processing on an image acquired by an image sensor, wherein an edge detection step of detecting an edge in the image, and the position of the edge in the image An edge position specifying step for specifying the color density, and a density reduction step for reducing the density of the color signal in the vicinity of the edge in accordance with a density reduction rule corresponding to the position of the edge.

  According to the first to twelfth aspects of the present invention, the edge in the image acquired by the image sensor is detected, the position of the edge in the image is specified, and the density reduction rule according to the edge position is determined. Since the density of the color signal near the edge is reduced, it is possible to prevent the occurrence of useless color loss.

  In particular, according to the invention described in claim 3, since the edge detection is not performed within a predetermined distance from the optical axis position of the imaging lens system in the image or the screen center position of the image, the region for which the suppression process is not performed is performed. Useless processing can be avoided.

  In particular, according to the fourth aspect of the invention, the direction of the spatial density change of the edge is determined, and the density of the color signal in the vicinity of the edge is selectively determined according to the spatial direction of the edge density change. Therefore, it is possible to specify the coloring due to the chromatic aberration to be suppressed and execute the suppression process.

  In particular, according to the fifth aspect of the present invention, the reduction range of the color signal density in the vicinity of the edge is changed stepwise in accordance with the distance between the optical axis position of the imaging lens system in the image and the edge. Therefore, it is possible to perform appropriate suppression processing in accordance with the colored width of chromatic aberration.

  In particular, according to the sixth aspect of the present invention, since the amount of color signal density reduction can be adjusted based on the shooting conditions at the time of shooting, optimum suppression processing can be performed on the acquired image. It becomes.

  In particular, according to the tenth aspect of the present invention, since the amount of color signal density reduction can be adjusted based on the photographing lens information, it is possible to perform suppression processing that matches the lens characteristics.

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

<1. First Embodiment>
<Outline of imaging device>
FIG. 1 is a diagram illustrating a main configuration of an imaging apparatus 1A according to an embodiment of the present invention. Here, FIGS. 1A to 1C correspond to a front view, a rear view, and a top view of the imaging apparatus 1A, respectively.

  The imaging device 1 </ b> A is configured as a digital camera and includes a photographing lens 10.

  The imaging apparatus 1A is provided with a shooting mode changeover switch 12, a shutter button 13, and a power button 100 on the top surface.

  The shooting mode change-over switch 12 has a still image shooting mode (REC mode) that captures an image of a subject and records the still image, and a playback mode (PLAY mode) that plays back an image recorded on the memory card 9 (see FIG. 2). It is a switch for switching between.

  The shutter button 13 is a two-stage switch that can detect a half-pressed state (S1 on) and a fully pressed state (S2 on). When the shutter button 13 is half-pressed in the REC mode, the focus motor driver 47 (see FIG. 2) is driven to perform an operation (AF operation) for moving the photographing lens 10 to the in-focus position. When S1 is turned on, exposure control by the camera control unit 40 (see FIG. 2) is also performed.

  Further, when the shutter button 13 is fully pressed in the REC mode, a main photographing operation, that is, a recording photographing operation is performed.

  The power button 100 is a button for turning on / off the power of the imaging apparatus 1A. By pressing the power button 100, the power supply of the image pickup apparatus 1A can be turned ON and OFF alternately.

  An LCD (Liquid Crystal Display) monitor 42 that displays a captured image, an electronic viewfinder (EVF) 43, and a frame advance / zoom switch 15 are provided on the back surface of the imaging apparatus 1A.

  The frame advance / zoom switch 15 is composed of four buttons, and is a switch for instructing frame advance of a recorded image in playback mode and zooming at the time of shooting. By operating the frame advance / zoom switch 15, the focus motor driver 47 is driven, and the focal length related to the photographing lens 10 can be changed.

  In the REC mode, a mode for acquiring a still image of one frame (normal shooting mode) and a mode for performing continuous shooting at a high frame rate (pressing the left / right button of the frame advance / zoom switch 15) The mode can be switched between the high-speed continuous shooting mode).

  Further, when the imaging apparatus 1A enters the REC mode, first, the imaging apparatus 1A enters a shooting standby state before shooting (main shooting) for acquiring a recorded image for recording. In this shooting standby state, on the LCD monitor 42 and the EVF 43, the shot image data (live view) for preview is visually output in a moving image manner. Therefore, in the shooting standby state in the REC mode, it can be considered that the mode is set to a live view acquisition mode (live view mode).

  That is, in the imaging apparatus 1A, the normal shooting mode and the high-speed continuous shooting mode exist in the REC mode, and the live view mode exists in the normal shooting mode and the high-speed continuous shooting mode.

<Functional configuration of imaging device>
Next, functions of the image pickup apparatus 1A will be described. FIG. 2 is a diagram illustrating functional blocks of the imaging apparatus 1A.

  As illustrated in FIG. 2, the imaging device 1A includes an imaging device 16, a signal processing unit 2 connected to the imaging device 16 so as to be able to transmit data, an image processing unit 3 connected to the signal processing unit 2, and an image processing unit. 3 is connected to the camera control unit 40.

  The image pickup device (CCD) 16 is an area sensor (Bayer array) in which R (red), G (green), and B (blue) primary color transmission filters, which are a plurality of types of color components, are arranged in a checkered pattern on a pixel basis. Image pickup device).

  When charge accumulation is completed by exposure in the image sensor 16, the photoelectrically converted charge signal is shifted to the vertical / horizontal transfer path in the image sensor 16 which is shielded from light, and is output as an image signal from here through the buffer. Is done. That is, the imaging element 16 functions as an imaging unit that acquires an image signal (image) related to the subject.

  The signal processing unit 2 includes a CDS 21, an AGC 22, and an A / D conversion unit 23, and functions as a so-called analog front end.

  The analog image signal output from the image sensor 16 is sampled by the CDS 21 and noise is removed, and then the AGC 22 multiplies the analog gain corresponding to the imaging sensitivity to perform sensitivity correction.

  The A / D conversion unit 23 is configured as a 14-bit converter, converts the analog signal normalized by the AGC 22 into a digital signal, and outputs the digital signal to the image processing unit 3.

  The image signal output to the image processing unit 3 is an image signal in which each pixel has information on any one of the RGB primary colors and includes chromatic aberration due to the photographing optical system.

  In general, the chromatic aberration of magnification that occurs in the photographing optical system due to optical factors increases as the distance from the optical axis L increases on the light receiving surface of the image sensor 16. FIG. 3 is a diagram showing the chromatic aberration of magnification under a certain photographing condition by the photographing optical system. The distance r from the center (optical axis L) in the image and the R component light with respect to the imaging position of the G component light. The relationship with the shift amount (Δr) of the imaging position is shown. As shown in FIG. 3, the chromatic aberration 101 of the R component light is obtained from an optical simulation or actual measurement as a deviation in the radial direction with respect to the center of the optical axis on the image with respect to the G component of the R component light. The chromatic aberration 101 increases as the distance from the optical axis L increases (in other words, the distance from the optical axis L increases). That is, even if the light is from the same position of the subject, the G component imaging position and the R component imaging position are not the same, and the amount of deviation increases toward the periphery of the image.

  The same applies to the B component light. In general, when the G component is used as a reference, the aberration of the B component light appears on the opposite side of the R component light aberration (that is, on the −Δr side in FIG. 3), and is separated from the optical axis L as in the R component. (In other words, the greater the distance from the optical axis L), the greater.

  As described above, the lateral chromatic aberration generated in the photographing optical system is generated symmetrically with respect to the optical axis L, and the colored width increases as the distance from the optical axis L increases. FIG. 4 is a diagram illustrating the coloring of chromatic aberration in the image acquired by the imaging apparatus 1A. For example, in the imaging apparatus 1A, assuming that the R component light is shifted in the direction of the optical axis L (image center CP), in the edge pattern image as shown in FIG. A magenta colored Ma is generated at the center, and a cyan colored Cy is generated in a direction away from the center. Depending on the design of the lens, the magenta colored Ma and the cyan colored Cy may be interchanged.

  The image processing unit 3 is configured to effectively reduce (suppress) chromatic aberration having such characteristics. However, as will be described later, the image processing unit 3 is configured to perform not only chromatic aberration reduction processing but also various other image processing.

  The image processing unit 3 includes a digital processing unit 3a, an image compression unit 36, a chroma suppress unit 37, a memory card driver 38, and a video encoder 39.

  The digital processing unit 3 a includes a pixel interpolation unit 31, a resolution conversion unit 32, a white balance control unit 33, and a gamma correction unit 34.

  The image data input to the image processing unit 3 is written in the image memory 41 configured by, for example, SDRAM in synchronization with the reading of the image sensor 16. Thereafter, the image data stored in the image memory 41 is accessed, and various processes are performed by the digital processing unit 3a.

  In the image data in the image memory 41, first, the white balance control unit 33 performs gain correction of RGB pixels independently, and RGB white balance correction is performed. In this white balance correction, a portion that is originally white from a photographic subject is estimated from brightness, saturation data, and the like, and an average value, a G / R ratio, and a G / B ratio for each of R, G, and B are obtained. Based on these pieces of information, the R and B correction gains are controlled.

  Next, the pixel interpolating unit 31 masks each RGB pixel with a respective filter pattern, and for G pixels having pixel values up to a high band, for example, based on the contrast pattern of 12 pixels surrounding the pixel of interest, A spatial change is estimated, and an optimal pixel value is calculated and assigned to the subject pattern based on the data of the surrounding four pixels. On the other hand, the R pixel and the B pixel are interpolated based on the same color pixel values of the surrounding eight pixels.

  The pixel-interpolated image data is subjected to non-linear conversion suitable for each output device by the gamma correction unit 34, and then a color space having RGB primary color components by a matrix calculation is converted into a luminance component (Y) (hereinafter, luminance signal). Y) and color difference components (Cr, Cb) (hereinafter also referred to as color difference signals Cr, Cb).

  The chroma suppression unit 37 generates a chromatic aberration reduction signal (hereinafter also referred to as “chroma suppression signal”) using the luminance signal Y, and performs chromatic aberration reduction processing on the color difference signals Cr and Cb. Details will be described later.

  An image signal composed of the luminance signal Y and the color difference signals Cr and Cb subjected to the chromatic aberration reduction process is stored in the image memory 41.

  Then, the image data stored in the image memory 41 is horizontally or vertically reduced or thinned to the number of pixels set by the resolution conversion unit 32, and after compression processing by the image compression unit 36, the memory card driver 38. Is recorded in the memory card 9 set in At the time of this image recording, a photographed image having a designated resolution is recorded. The resolution conversion unit 32 also performs pixel thinning during image display (preview), and creates a low-resolution image to be displayed on the LCD monitor 42 or the EVF 43. At the time of preview, a low resolution image of 640 × 240 pixels read out from the image memory 41 is encoded into NTSC / PAL by the video encoder 38, and this is reproduced as a field image on the LCD monitor 42 or the EVF 43.

  The camera control unit 40 includes a CPU, a ROM, a RAM, and the like, and is a part that comprehensively controls each unit of the imaging apparatus 1A. Various controls and functions by the camera control unit 40 are realized by reading and executing a predetermined program stored in the ROM into the CPU.

  Specifically, an operation input performed by the photographer is processed with respect to the camera operation unit 50 having the mode switch 12, the shutter button 13, the frame advance / zoom switch 15, and the like. In addition, the camera control unit 40 switches between a still image shooting mode for capturing an image of a subject and recording the image data and a playback mode for reproducing the captured image data by operating the shooting mode switching switch 12 by the photographer. . Furthermore, in the still image shooting mode, one of the normal shooting mode and the high-speed continuous shooting mode is selectively set in response to the operation of the frame advance / zoom switch 15 by the photographer. Further, in the shooting standby state, the live view mode is set under the control of the camera control unit 40.

  In the imaging apparatus 1 </ b> A, the optical aperture of the aperture 44 is fixed open by the aperture driver 45 during preview display (live view display) in which the subject is displayed on the LCD monitor 42 in a moving image mode in the imaging standby state before the actual imaging. As for the charge accumulation time (exposure time) of the image sensor 16 corresponding to the shutter speed (SS), the camera control unit 40 calculates the exposure control data based on the live view acquired by the image sensor 16. Then, feedback control is performed on the timing generator sensor driver 46 so that the exposure time of the image sensor 16 is appropriate based on a program diagram set in advance based on the calculated exposure control data.

  At the time of actual shooting, the aperture driver 45 and the timing generator sensor driver are set according to a program diagram set in advance based on the light amount data measured using the live view acquired by the image sensor 16 by the function of the camera control unit 40. 46, the AE control for controlling the exposure amount to the image sensor 16 is executed.

  As for the autofocus (AF) operation by the photographing lens 10, so-called contrast AF control is performed using the live view acquired by the image sensor 16 by the function of the camera control unit 40. Specifically, in the camera control unit 40, based on the live view, the position of the photographing lens 10 having the highest contrast in the main subject (main subject) is determined as the lens position (focusing lens position) that focuses on the main subject. ). The focus motor driver 47 moves the focus lens in the photographing lens 10 to the focus lens position.

<Generation of chroma suppression signal>
Next, the process executed by the chroma suppress unit 37 will be described in detail.

  In the chroma sub-respons part 37, a chromatic aberration reduction signal (hereinafter also referred to as “chroma suppression signal”) is generated using the luminance signal Y, and a chroma suppression degree is determined based on the generated chromatic aberration reduction signal (chroma suppression signal). . Then, chromatic aberration reduction processing is executed by executing suppression processing of color difference signals (color signals) Cr and Cb (also referred to as “color signal density (tone value) reduction processing)” according to the degree of chroma suppression.

  First, the chroma suppression degree determination process will be described. FIG. 5 is a diagram illustrating an image PI on which chromatic aberration reduction processing is executed. FIG. 6 is a functional block diagram of the chroma suppression degree determination circuit. FIG. 7 is a diagram illustrating a signal that has passed through each processing unit.

  The luminance signal Y of each pixel calculated by matrix calculation from the image data of the image PI shown in FIG. 5 is input to an HPF (High Pass Filter) 51a (see FIG. 6).

  In the HPF 51a shown in FIG. 6, edge extraction processing is performed by performing filtering processing on the input luminance signal Y (generally a gray component signal) of each pixel. Specifically, assuming that the HPF 51a in the present embodiment is expressed in a matrix form of 3 rows and 3 columns as shown in Expression (1), the luminance signal Y of the target pixel (target pixel) and the target pixel are adjacent to each other. Edge extraction processing is performed using the luminance signals Y of the eight pixels.

  The output value from the HPF 51a represents how much high-frequency components are included in each pixel position, that is, the content of high-frequency components (in other words, the detection level of edge components). The output value from the HPF 51a can also be expressed as representing the magnitude of contrast.

  For example, an image expressed using the luminance value (pixel value) of each pixel constituting the image PI is regarded as a space in which the pixel at coordinates (h, v) has the height of the luminance value f (h, v). Consider a case where a one-dimensional function f (h) corresponding to a cross section in the h direction is input as the luminance signal Y in this space (see the signal SY in FIG. 7). However, h and v correspond to the horizontal direction and the vertical direction in the CCD cell array, respectively.

  In this case, the signal output from the HPF 51a is a signal SA as shown in FIG. 7, and signals AX1 and AX2 in which pulses in both positive and negative directions are adjacent at positions X1 and X2 are detected.

  Next, the output signal from the HPF 51 a is input to the negative signal clip 52. The negative signal clip 52 removes the negative component signal from the input signal.

  For example, when the signal SA in FIG. 7 is input to the negative signal clip 52, the negative component signal is removed, and the signal SB including only the positive component signal is output.

  Here, the HPF 51a outputs a positive component signal for a region having a large luminance value (hereinafter also referred to as “bright region” or “region having a large gradation value”) with reference to the center position of the edge, and A region having a small luminance value (hereinafter also referred to as “dark region” or “region having a small gradation value”) has a characteristic of outputting a negative component signal.

  Therefore, by inputting the signal output from the HPF 51a to the negative signal clip 52 and removing the negative component signal, it is possible to specify a region having a large luminance value in the vicinity of the edge.

  The signal output from the negative signal clip 52 is input to the amplifier 56a after only a high frequency component equal to or greater than a predetermined value is detected in the base clip 53.

  In the amplifier 56a, output control of the chroma suppression signal is performed based on the position of the pixel of interest currently being processed in the image. FIG. 8 is a diagram illustrating a state of suppression control according to the target image position.

  Specifically, the position information (pixel coordinate value) in the image of the pixel of interest currently being processed is acquired by the pixel counter 54, and the area determination unit 55 stores the position information and the control area table 81 (see FIG. 8). Based on this, an amplifier control signal is generated. More specifically, when the target pixel is present in a substantially circular region (range) CR1 at a predetermined distance L1 from the screen center CP of the image, an amplifier control signal indicating that chroma suppression is not executed is output. On the other hand, if the pixel of interest is outside the region (range) CR1 of the predetermined distance L1 from the center CP of the image, an amplifier control signal for executing chroma suppression is output. In the amplifier 56a, the output control of the chroma control signal is performed using the amplifier control signal output from the area determination unit 55 as a gate signal.

  For example, when the position X1 in FIG. 7 is outside the region CR1, and the position X2 is in the region CR1, the chroma suppression signal output from the amplifier 56a is as a signal SC in FIG. That is, the chroma suppression signal is output at position X1, and the chroma suppression signal is not output at position X2.

  Next, the suppression degree determination unit 57 determines the suppression degrees of the color difference signals Cr and Cb based on the signal output from the amplifier 56a. Specifically, the suppression degree of the color difference signals Cr and Cb is determined with reference to the suppression degree setting LUT (Lookup Table) based on the edge signal amplitude of the signal output from the amplifier 56a. The suppression degree setting LUT is created in advance and stored in the ROM.

  FIG. 9 is a graph showing the setting contents of the suppression degree setting LUT as a suppression degree curve LC. In the figure, the horizontal axis indicates the edge signal amplitude, and the vertical axis indicates the degree of suppression. That is, suppression control is performed such that a higher suppression is applied to a pixel having a higher edge signal amplitude.

  For example, when the edge signal amplitude at the pixel n is An, the color difference component near the pixel n is suppressed by about 20%. When the edge signal amplitude at the pixel m is Am, the color difference component in the vicinity of the pixel m is suppressed by about 60%. As described above, the vicinity of the pixel m having a relatively high edge signal amplitude is suppressed more than the vicinity of the pixel n having a relatively low edge signal amplitude. According to this, since the degree of suppression of the signal value of the color component of the pixel (that is, the degree of suppression control) is changed according to the edge signal amplitude, the suppression process that does not leave unnaturalness in the output image. Is possible.

  However, in order to remove noise components, it is preferable to set the degree of suppression to a lower value when the edge signal amplitude is small so that the degree of suppression does not become excessively large. For example, as shown in FIG. 9, when the edge signal amplitude is smaller than An, it is preferable that the suppression curve LC is an S-shaped curve that exists below the virtual direct proportional line LL.

  Then, suppression processing of the color difference signals Cr and Cb as color signals is executed according to the chroma suppression degree determined as described above.

  Through the above processing, the chroma suppression unit 37 according to the present embodiment outputs the color difference signals Cr and Cb subjected to the suppression processing. The output color difference signals Cr and Cb are recorded in the image memory 41 together with the luminance signal Y.

  As described above, in the present embodiment, since the suppression process can be executed only for pixels extracted as bright areas among the areas on both sides of the edge, the pixels on both sides near the edge are suppressed. Problems caused by executing processing uniformly can be solved.

  Conventionally, since the color difference signals Cr and Cb of the pixels on both sides near the edge are suppressed, it is effective for suppressing coloring due to chromatic aberration, but color loss occurs on the dark region side. There was a problem. According to the present embodiment, it is possible to identify a bright region in which coloring is conspicuous and suppress coloring due to chromatic aberration. Therefore, it is possible to acquire a natural image without noticeable color loss.

  Further, in the present embodiment, by using the density reduction rule as described above, it is possible to determine whether or not to execute the suppression process according to the position of the target pixel currently being processed in the image. Thus, it is possible to solve the problem caused by executing the suppression process on the pixels in which coloring due to chromatic aberration has not occurred.

  Specifically, as shown in FIG. 4, the chromatic aberration generated in the photographing optical system is generated symmetrically with respect to the optical axis L, and the colored width increases as the distance from the optical axis L increases. Becomes larger. On the other hand, in the vicinity of the center of the image within a predetermined distance from the optical axis L, there is a characteristic that coloring due to chromatic aberration is not so noticeable.

  Therefore, as in the chroma suppression unit 37 according to the present embodiment, the position of the pixel of interest currently being processed is specified in the image, and the pixel of interest exists within the region (range) CR1 at a predetermined distance L1 from the center CP of the image. In this case, by preventing the suppression process from being performed, it is possible to prevent the occurrence of useless color loss. In other words, the position of the detected edge in the image is specified, and the density (tone value) of the color signal in the vicinity of the edge is reduced based on the position, thereby preventing the occurrence of useless color loss. Suppression processing is possible.

<2. Second Embodiment>
Next, a second embodiment will be described. The configuration of the imaging apparatus 1B in the second embodiment is the same as that described in the first embodiment except for the following points, and elements having the same functions as those in the first embodiment are denoted by the same reference numerals. The description is omitted.

<Generation of chroma suppression signal>
In the chroma suppress unit 37 according to the present embodiment, the color type to be subjected to the suppression process is specified and the suppression process is executed.

  As described above, the lateral chromatic aberration generated in the photographing optical system is generated symmetrically with respect to the optical axis L. When the G component (edge) is used as a reference, the B component light aberration occurs on the opposite side of the R component light aberration.

  In the present embodiment, the case where the imaging device 1B also specifies and suppresses magenta colored Ma is assumed on the assumption that coloring due to chromatic aberration as shown in FIG. 4 occurs.

  Hereinafter, the process performed in the chroma suppress part 37 in this embodiment is explained in full detail. FIG. 10 is a functional block diagram of the chroma suppression degree determination circuit according to the present embodiment. FIG. 11 is a diagram illustrating a signal that has passed through each processing unit.

  First, as shown in FIG. 10, the luminance signal Y of each pixel calculated by matrix calculation from the image data of the image PI (see FIG. 5) is an HPF (high-pass filter) 51a in the H direction (horizontal direction). It is input to the differential filter 51b and the primary differential filter 51c in the V direction (vertical direction).

  The HPF 51a performs edge extraction processing by performing filtering processing on the input luminance signal Y of each pixel.

  In a primary differential filter (hereinafter also referred to as “H differential filter”) 51b in the horizontal direction (H direction), a spatial change amount (“density change amount”) of the luminance signal Y in the H direction in the vicinity of the target pixel (target pixel). Is also detected). For example, if the H differential filter 51b in the present embodiment is expressed in a matrix form of 3 rows and 3 columns as shown in Expression (2), it is adjacent to the luminance signal Y of the target pixel (target pixel) and the target pixel. The process of detecting the amount of change in the luminance signal Y in the H direction at the target pixel is performed using the luminance signals Y of the eight pixels. Here, it is expressed that the luminance value is large when the density is high.

  The output value of the H differential filter 51b indicates the directionality of the density change (luminance change) with respect to the H direction of the corresponding edge (output signal of the HPF 51a). Specifically, when the output signal of the H differential filter 51b is a positive component signal, the edge detected by the HPF 51a is a rising edge that changes from a dark region to a bright region with respect to the H direction. Can be expressed. Conversely, when the output signal of the H differential filter 51b is a negative component signal, the edge detected by the HPF 51a is a falling edge that changes from a bright region to a dark region with respect to the H direction. Can express.

  Further, in the primary differential filter (hereinafter also referred to as “V differential filter”) 51c in the vertical direction (V direction), the spatial change amount (density change) of the luminance signal Y in the V direction in the vicinity of the target pixel (target pixel). Amount) is detected. For example, if the V differential filter 51c in the present embodiment is expressed in a matrix form of 3 rows and 3 columns as shown in Expression (3), it is adjacent to the luminance signal Y of the target pixel (target pixel) and the target pixel. The process of detecting the amount of change in the luminance signal Y in the V direction at the target pixel is performed using the luminance signals Y of the eight pixels.

  The output value of the V differential filter 51c indicates the directionality of the density change with respect to the V direction of the corresponding edge (output signal of the HPF 51a). Specifically, when the output signal of the V differential filter 51c is a positive component signal, the edge detected by the HPF 51a is a rising edge that changes from a dark region to a bright region in the V direction. Can be expressed. Conversely, when the output signal of the V differential filter 51c is a negative component signal, the edge detected by the HPF 51a is a falling edge that changes from a bright region to a dark region with respect to the V direction. Can express.

  As described above, the directionality of the edge detected by the HPF 51a with respect to the H direction can be specified by the output value of the H differential filter 51b, and the directionality of the edge detected by the HPF 51a with respect to the V direction is determined by the V differential. It can be specified by the output value of the filter 51c.

  For example, consider a case where the same signal SY as in the first embodiment is input to the chroma suppression degree determination circuit as the luminance signal Y. In this case, in order to simplify the explanation, the signal SF output from the V differential filter 51c is not considered.

  When the signal SY is input, the signal output from the HPF 51a is a signal SD as shown in FIG. 11, and signals DX1 and DX2 in both positive and negative directions are detected at the positions X1 and X2, respectively.

The signal output from the H differential filter 51b is a signal SE as shown in FIG. 11, and a positive component signal EX1 and a negative component signal EX2 are detected at positions X1 and X2, respectively.

  The signal EX1 is a signal corresponding to the output signal DX1 of the HPF 51a. Since the signal EX1 is a positive component signal, the corresponding output signal DX1 of the HPF 51a detects a rising edge in the H direction. It can be seen that it was output. On the other hand, the signal EX2 is a signal corresponding to the output signal DX2 of the HPF 51a, and since the signal EX2 is a negative component signal, the corresponding output signal DX2 of the HPF 51a falls on the falling edge in the H direction. Is detected and output.

  Next, signals output from the filters are input to the polarity determination unit 61. In the polarity determination unit 61, a process for specifying a pixel to be subjected to the suppression process is executed. FIG. 12 is a diagram illustrating the directionality of the edge to be suppressed according to the target pixel position.

  Specifically, the position information (pixel coordinate value) in the image of the pixel of interest currently being processed is acquired by the pixel counter 54, and the area determination unit 55 stores the position information and the control area table 81 (see FIG. 8). Based on this, a process for specifying a pixel to be subjected to the suppression process is performed. More specifically, when the target pixel is present in a substantially circular area (range) CR1 at a predetermined distance L1 from the center CP of the image, a signal indicating that chroma suppression is not performed is output to the target pixel. On the other hand, if the pixel of interest exists outside the region (range) CR1 at a predetermined distance L1 from the center CP of the image, a signal indicating that the pixel of interest is subjected to chroma suppression and position information of the pixel of interest are output. .

  Then, the polarity determination unit 61 determines whether or not to perform the suppression process on the pixel of interest currently being processed based on the signal from the area determination unit 55 and the signal output from each filter. Specifically, when the signal from the area determination unit 55 is a signal indicating that chroma suppression is not performed, no suppression signal is output for the target pixel currently being processed.

  On the other hand, when the signal from the area determination unit 55 is a signal to execute chroma suppression, the output signal of the H differential filter 51b and the direction determination table 82 conceptually shown in FIG. The output signal from the HPF 51a is controlled based on the polarity (positive / negative) of the output signal of the V differential filter 51c. Here, the directionality determination table 82 is a condition for executing suppression processing in four quadrants, that is, density reduction when the center (optical axis) of the image is the origin O, the H direction is the x axis, and the -V direction is the y axis. Shows the rules.

  Specifically, when the position of the target pixel is in the first quadrant R1, the output signal of the H differential filter 51b corresponding to the output signal of the HPF 51a in the target pixel is a negative component signal, and the V differential When the output signal of the filter 51c is a positive component signal, the output signal of the HPF 51a at the target pixel is output as it is. In other words, in the first quadrant R1, a process is performed in which an edge having a falling direction with respect to the H direction and a rising direction with respect to the V direction is regarded as a target of the suppression process. The

  If the position of the target pixel is in the second quadrant R2, the output signal of the H differential filter 51b corresponding to the output signal of the HPF 51a in the target pixel is a positive component signal, and the V differential filter 51c. The output signal of the HPF 51a at the target pixel is output as it is. In other words, in the second quadrant R2, a process is executed in which an edge having a rising direction with respect to the H direction and a rising direction with respect to the V direction is regarded as a target of the suppression process. .

  When the position of the target pixel is in the third quadrant R3, the output signal of the H differential filter 51b corresponding to the output signal of the HPF 51a in the target pixel is a positive component signal, and the V differential filter 51c. Output signal of the HPF 51a in the target pixel is output as it is. In other words, in the third quadrant R3, processing is performed in which an edge having a rising direction with respect to the H direction and a falling direction with respect to the V direction is regarded as a target of the suppression process. The

  When the position of the target pixel is in the fourth quadrant R4, the output signal of the H differential filter 51b corresponding to the output signal of the HPF 51a in the target pixel is a negative component signal, and the V differential filter 51c. Output signal of the HPF 51a in the target pixel is output as it is. In other words, in the fourth quadrant R4, processing is performed in which an edge having a falling directionality with respect to the H direction and a falling directionality with respect to the V direction is regarded as a target of the suppression process. Is done.

  For example, when both the positions X1 and X2 are in the second quadrant R2 in FIG. 11, an edge having a rising directionality with respect to the H direction (that is, a positive component in the output signal SE of the H differential filter 51b) is detected. It is determined that it is the target of suppression processing. Therefore, as shown in FIG. 11, the signal SG output from the polarity determination unit 61 is a signal including the signal DX1 at the position X1 and removing the signal DX2 at the position X2. In this example, the output signal SF of the V differential filter 51c is not taken into consideration for the sake of simplicity.

  In this manner, the polarity determination unit 61 specifies an edge where a magenta colored Ma is generated in a bright area by excluding signals other than edges having directionality suitable for the directionality determination table 82. can do.

  As described above, the directionality of the density change with respect to the H direction, the directionality of the density change with respect to the V direction, and the position information (pixel coordinate value) in the image of the target pixel are obtained, and the directionality determination table 82 is referred to. It is possible to specify an edge to be subjected to suppression processing.

  Further, the suppression target edge specifying process executed in the polarity determination unit 61 determines the spatial directionality of the density change (luminance change) with respect to the center (optical axis) direction in the image, and is predetermined for the optical axis direction. It can be generalized to be a process for specifying an edge having a directivity (here, a rising directivity).

  Next, the output signal of the polarity determination unit 61 is input to the negative signal clip 52. The negative signal clip 52 removes the negative component signal from the input signal.

  For example, when the signal SG of FIG. 11 is input to the negative signal clip 52, the negative component signal is removed, and the signal SH including only the positive component signal is output.

  This makes it possible to specify a bright area among the areas on both sides of the edge.

  In the signal output from the negative signal clip 52, only a high frequency component equal to or higher than a predetermined value is detected in the base clip 53, amplified by the amplifier 56b, and then output as a chroma suppression signal.

  Next, the suppression degree determination unit 57 determines the suppression degrees of the color difference signals Cr and Cb based on the signal output from the amplifier 56b. Specifically, the degree of suppression of the color difference signals Cr and Cb is determined with reference to the degree-of-suppression setting LUT (Lookup Table) (see FIG. 9) based on the edge signal amplitude of the signal output from the amplifier 56b.

  Then, the color difference signals Cr and Cb are suppressed according to the degree of chroma suppression.

  Through the above processing, the chroma suppression unit 37 according to the present embodiment outputs the color difference signals Cr and Cb subjected to the suppression processing. The output color difference signals Cr and Cb are recorded in the image memory 41 together with the luminance signal Y.

  As described above, in this embodiment, the combination of the suppression target edge specifying process by the polarity determination unit 61 and the suppression target area limiting process by the negative signal clip 52 combines the magenta colored Ma in the bright area. Can be selected (specified) and suppressed.

  Specifically, the polarity determination unit 61 identifies an edge where a magenta colored Ma occurs in a bright region by a density reduction rule according to the position of the edge and the spatial directionality of the edge density change. In addition, by preventing the negative signal clip 52 from performing the suppression process on the dark area, the suppression process can be performed only on the bright area where the magenta colored Ma is generated.

  As a result, it is possible to suppress the noticeable coloring of the magenta system, and it is possible to acquire a natural image that does not cause noticeable color loss.

<3. Modification>
Although the embodiments of the present invention have been described above, the present invention is not limited to the contents described above.

  For example, the filter coefficients of the HPF 51a, the H differential filter 51b, and the V differential filter 51c used in the above embodiments are not limited to this. For example, the suppression level of the color signal can be changed by multiplying each coefficient of the HPF 51a as shown in Expression (1) by a constant.

  In each of the above embodiments, the scale parameter corresponding to the number of pixels to be processed by the HPF 51a is always constant. However, the present invention is not limited to this. For example, the scale parameter of the HPF 51a may be changed using the following elements (PT1 to PT3) as parameters.

◎ PT1: Distance from the center CP (pixel position corresponding to the optical axis L) As described above, the lateral chromatic aberration occurs symmetrically with respect to the optical axis L, and the distance from the optical axis L increases. Therefore, since the colored width becomes large, the scale parameter of the HPF 51a may be changed stepwise in accordance with the distance from the image center of the target pixel currently being processed. FIG. 13 is a diagram illustrating the change of the scale parameter of the HPF 51a in accordance with the target pixel position.

  For example, as shown in FIG. 13, in the region CR2 where the target pixel is located at a predetermined distance L2 from the center CP, the HPF 51a represented in a matrix form of 3 rows and 3 columns is located within the predetermined distance L3 from the center CP and the region CR2. In the region CR3 not including the HPF 51a expressed in a matrix format of 5 rows and 5 columns, and in the region CR4 not included in the region within the predetermined distance L3 from the center CP, expressed in a matrix format of 7 rows and 7 columns. The HPF 51a may be used. However, L2 <L3.

  In this way, by changing the scale parameter of the HPF 51a stepwise according to the distance between the optical axis position in the image and the position of the target pixel, the suppression target execution region (density reduction range) is changed stepwise. Therefore, it is possible to perform appropriate suppression processing according to the colored width of chromatic aberration.

◎ PT2: Shooting condition Since the colored width due to chromatic aberration of magnification is affected by shooting conditions such as the focal length, shooting distance, and aperture, the scale parameter of the HPF 51a may be changed based on such information.

  For example, in close-up shooting, the colored width of chromatic aberration increases, so the shooting distance may be reduced and the scale parameter of the HPF 51a may be increased. Further, since the colored width of the chromatic aberration increases as the focal length increases, the focal length may be increased and the scale parameter of the HPF 51a may be increased. In addition, since the full aperture of the chromatic aberration is increased in the open aperture, the aperture value (F value) may be decreased and the scale parameter of the HPF 51a may be increased.

  According to this, since the scale parameter of the HPF 51a can be appropriately changed based on the imaging condition PT2, it is possible to perform an optimal suppression process on the acquired image.

FIG. 14 is a conceptual diagram showing a cross section when the imaging system 200 is cut along a plane including the optical axis LX.

  Since the chromatic aberration of magnification varies depending on the characteristics of the photographing lens, for example, in an imaging system 200 with interchangeable lenses as shown in FIG. 14, the camera control unit is configured to acquire lens information of the photographing lens to be mounted. The scale parameter of the HPF 51a may be changed based on the chromatic aberration characteristic table of the taking lens stored in the ROM or the like in the 40.

  Further, the scale parameters of the HPF 51a may be changed by using the elements (PT1 to PT3) in combination.

  According to this, since the scale parameter of the HPF 51a can be appropriately changed based on the characteristic PT3 of the photographing lens, it is possible to perform a suppression process that matches the characteristic of the lens.

  An imaging system 200 in FIG. 14 includes a single-lens reflex digital still camera (digital single-lens reflex camera) including a camera body (camera body) 201 and an interchangeable lens 202 that is detachably mounted at the front center of the camera body 201. Camera).

  Further, as shown in FIG. 14, the mount portion Mt is provided with a connector EC for electrical connection with the CPU 211 in the attached interchangeable lens 202 and a coupler MC for mechanical connection. ing.

  The connector EC sends lens information such as a model and model number regarding the lens from the lens ROM (read only memory) 213 built in the interchangeable lens 202 to the camera control unit 40 in the camera body 201 via the CPU 211, For example, the position of the focus lens 203 or the like detected by the position detection unit 212 is sent to the camera control unit 40.

  The coupler MC transmits the driving force of the focus lens driving motor M1 provided in the camera body 201 to the lens driving mechanism 204 in the interchangeable lens 202. The lens driving mechanism 204 causes the focus lens 203 to move in the optical axis direction. It will move to LX.

  Alternatively, a plurality of candidates for the control area table 81 may be prepared, and the control area table 81 shown in FIG. 8 may be selected according to the above elements (shooting condition PT2, shooting lens characteristic PT3).

  For example, in close-up photography, since the colored width of chromatic aberration increases, the photographing distance becomes small, and even if the region (range) CR1 in which the suppression process is not performed is narrowed by reducing the predetermined distance L1 from the center CP of the image. Good. Further, since the colored width of chromatic aberration increases as the focal length increases, the focal length increases and the region (range) CR1 in which the suppression process is not performed is reduced by reducing the predetermined distance L1 from the center CP of the image. Good. . In addition, since the coloration width of the chromatic aberration is increased in the open aperture, the aperture value (F value) is decreased, and the region (range) CR1 in which the suppression process is not performed by decreasing the predetermined distance L1 from the center CP of the image. It may be narrowed. According to this, the density reduction amount of the color signal can be appropriately adjusted according to the photographing condition PT2, and thus it is possible to perform an optimal suppression process for the acquired image.

  Further, for example, in the imaging system 200, the lens information of the photographic lens to be mounted is acquired, and the center of the image is obtained based on the chromatic aberration characteristic table of the photographic lens stored in the ROM or the like in the camera control unit 40. The region (range) CR1 where the suppression process is not performed may be narrowed by reducing the predetermined distance L1 from the CP.

  According to this, since the density reduction amount of the color signal can be appropriately adjusted based on the characteristic PT3 of the photographing lens, it is possible to perform a suppression process that matches the characteristic of the lens.

  Further, the directionality determination table 82 (FIG. 12) used in the second embodiment may be changed according to a colored position to be a suppression processing target.

  For example, in order to suppress the magenta colored Ma in the case where the magenta colored Ma and the cyan colored Cy shown in FIG. A directionality determination table 83 as shown in FIG. 15 may be used.

  According to this, it is possible to specify the coloring due to the chromatic aberration to be suppressed and execute the suppression process.

  In each of the above embodiments, the edge extraction processing by the HPF 51a is executed for all pixels, but the present invention is not limited to this. Specifically, as shown in FIG. 16, the luminance signal Y is input to the HPF 51a, and the position of the target pixel to be processed is specified in advance in the area determination unit 55, so that the position of the target pixel is determined. When it is within the region (range) CR1 of the predetermined distance L1 from the center CP (see FIG. 8), the edge extraction process by the HPF 51a may not be executed.

  According to this, it is possible to avoid useless processing for an area where no suppression processing is performed.

  In the second embodiment, the edge to be subjected to the suppression process is specified using the direction of density change with respect to the H direction and the direction of density change with respect to the V direction. However, the present invention is not limited to this. For example, the directionality of the density change (luminance change) with respect to the center (optical axis) direction in the image is detected to have a predetermined directionality (for example, rising directionality) with respect to the optical axis direction. The edge may be specified as the target edge of the suppression process.

  In each of the above embodiments, the density reduction rule is set based on the image center CP. However, it is more accurate to set the rule based on the optical axis L. Further, variation due to lens assembly errors may be taken into consideration in advance.

It is a figure which shows the principal part structure of 1 A of imaging devices which concern on 1st Embodiment of this invention. It is a figure which shows the functional block of 1 A of imaging devices. FIG. 6 is a diagram illustrating chromatic aberration of magnification under a certain shooting condition by the shooting optical system. It is a figure which shows the mode of coloring of the chromatic aberration in the image acquired by 1 A of imaging devices. It is a chromatic aberration diagram of magnification of a photographing optical system under a certain imaging condition. It is a functional block diagram of a chroma suppression degree determination circuit. It is a figure which shows the signal which passed each process part. It is a figure which shows the mode of the suppression control according to an attention image position. It is the figure which showed the setting content of the suppression degree setting LUT as a graph as the suppression degree curve LC. It is a functional block diagram of a chroma suppression degree determination circuit according to the second embodiment. It is a figure which shows the signal which passed each process part. It is a figure which shows the directionality of the edge used as the suppression object according to an attention pixel position. It is a figure which shows the change of the scale parameter of HPF51a according to an attention pixel position. It is a conceptual diagram which shows a cross section when the imaging system 200 is cut | disconnected by the plane containing the optical axis LX. It is a figure which shows the directionality of the edge used as the suppression object according to an attention pixel position. It is a functional block diagram of a chroma suppression degree determination circuit.

Explanation of symbols

101 Chromatic aberration of R component light Ma Magenta coloring Cy Cyan coloring LC Suppression curve LL Direct proportional line R1 First quadrant R2 Second quadrant R3 Third quadrant R4 Fourth quadrant

Claims (12)

An imaging device,
An image sensor;
Edge detection means for detecting an edge in an image acquired by the image sensor;
Edge position specifying means for specifying the position of the edge in the image;
Density reducing means for reducing the density of the color signal in the vicinity of the edge according to a density reduction rule corresponding to the position of the edge;
An imaging apparatus comprising: The imaging device according to claim 1,
The density reducing means, for the edge determined by the edge position specifying means to be within a predetermined distance from the optical axis position of the imaging lens system in the image or the screen center position of the image, outputs a color signal in the vicinity of the edge An imaging device characterized by not being reduced. The imaging device according to claim 1,
The imaging apparatus according to claim 1, wherein the edge detection means does not detect the edge within a predetermined distance from an optical axis position of an imaging lens system in the image or a screen center position of the image. In the imaging device in any one of Claims 1-3,
Direction determination means for determining a spatial direction in which a density change occurs at the edge;
Further comprising
The imaging apparatus according to claim 1, wherein the density reducing unit selectively reduces the density of a color signal in the vicinity of the edge according to a spatial direction of density change at the edge. In the imaging device according to any one of claims 1 to 4,
The density reduction means changes the density reduction range of the color signal in the vicinity of the edge stepwise in accordance with the distance between the optical axis position of the imaging lens system in the image and the edge. apparatus. In the imaging device in any one of Claims 1-5,
Adjusting means for adjusting the density reduction amount of the color signal by the density reducing means based on the shooting conditions at the time of shooting;
An image pickup apparatus further comprising: The imaging device according to claim 6,
The shooting conditions include focal length information,
The image pickup apparatus, wherein the adjustment unit adjusts a density reduction amount of the color signal based on the focal length information. In the imaging device according to claim 6 or 7,
The shooting condition includes shooting distance information,
The image pickup apparatus, wherein the adjustment unit adjusts a density reduction amount of the color signal based on the shooting distance information. In the imaging device in any one of Claims 6-8,
The shooting conditions include an aperture value,
The image pickup apparatus, wherein the adjustment unit adjusts a density reduction amount of the color signal based on the aperture value. In the imaging device in any one of Claims 6-9,
Adjusting means for adjusting the density reduction amount of the color signal by the density reducing means based on photographing lens information at the time of photographing;
An image pickup apparatus further comprising: An image processing apparatus that performs predetermined image processing on an image acquired by an imaging element,
Edge detection means for detecting edges in the image;
Edge position specifying means for specifying the position of the edge in the image;
Density reducing means for reducing the density of the color signal in the vicinity of the edge according to a density reduction rule according to the position of the edge;
An image processing apparatus comprising: An image processing method for performing predetermined image processing on an image acquired by an image sensor,
An edge detection step of detecting edges in the image;
An edge position specifying step for specifying the position of the edge in the image;
A density reduction step of reducing the density of the color signal in the vicinity of the edge according to a density reduction rule according to the position of the edge;
An image processing method comprising:

Images