JP2009065721A - Signal processing method and apparatus - Google Patents

Abstract

Kind Code: A1 To prevent jagged noise from occurring in a luminance contour of a subject image due to chromatic aberration of a lens.
In a signal processing method for processing an image signal obtained by imaging a subject image that has passed through a photographic lens by an imaging device in which pixels for detecting different colors are alternately arranged, pixels on the contour line of the subject image The luminance value A of the target pixel (hereinafter referred to as the target pixel) is obtained by filtering the luminance signals B and C of the adjacent pixels on the contour line of the target pixel with an arithmetic expression of A = (B + C) / 2. .
[Selection] Figure 6

Description

  The present invention relates to a signal processing method and apparatus for a digital camera, and more particularly to a signal processing method and apparatus that do not cause jagged edges in an image contour due to chromatic aberration of a lens.

  If a solid-state image sensor such as a single-plate CCD or CMOS mounted on a digital camera is a primary color system, R (red), G (green), and B (blue) pixels are arranged according to a predetermined rule. . FIG. 8 is a pixel arrangement diagram of a solid-state imaging device described in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 10-136391), and real pixels R, G, and B are arranged in a so-called checkered pattern, Rows in which R pixels and B pixels are alternately arranged and rows in which only G pixels are arranged in a row are alternately arranged with a ½ pitch shift.

  FIG. 9 is a pixel arrangement diagram of a Bayer CCD. In the Bayer method, rows in which B pixels and G pixels are alternately arranged and rows in which G pixels and R pixels are alternately arranged are alternately arranged.

JP-A-10-136391

  With such a solid-state imaging device, for example, as shown in FIG. 10, when an image in which a white region and a black region are partitioned by a vertical line is captured, the vertical line is not a straight line but is captured in a jagged shape. End up.

  As shown in FIG. 11, this is caused by chromatic aberration in which the refraction angles of the light beams of R, G, and B are refracted when passing through the lens with respect to the change position of the luminance Y that divides light and dark. This is because the luminance signal obtained from, G and B is not a straight line.

  An object of the present invention is to provide a signal processing method and apparatus for avoiding deterioration of an image contour portion caused by chromatic aberration of a lens.

  The signal processing method and apparatus thereof according to the present invention provide signal processing for processing an image signal obtained by capturing a subject image through a photographing lens by an imaging element in which pixels for detecting different colors are alternately arranged. The luminance value A of a pixel on the contour line of the image (hereinafter referred to as a target pixel) is calculated from the luminance signals B and C of adjacent pixels on the contour line of the target pixel by A = (B + C) / 2. It is obtained by filtering with

  With this configuration, the direction of the alternate color arrangement and the luminance contour of the subject image are orthogonal to each other, and due to chromatic aberration of the photographing lens, the color signal of the luminance contour portion shifts from the luminance contour depending on the color, and the luminance contour has a jagged noise. Even if this occurs, this noise can be reduced.

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

  FIG. 1 is a configuration diagram of a digital still camera to which a signal processing method according to an embodiment of the present invention is applied. The digital still camera includes a photographic lens 10, a solid-state image sensor 11, a diaphragm 12 provided between the two, an infrared cut filter 13, and an optical low-pass filter 14. The CPU 15 that controls the entire digital still camera controls the light emitting unit 16 and the light receiving unit 17 for flash, controls the lens driving unit 18 to adjust the position of the photographing lens 10 to the focus position, and stops the aperture driving unit. The opening amount of the diaphragm 12 is controlled via 19 to adjust the exposure amount to an appropriate exposure amount.

  Further, the CPU 15 drives the solid-state image sensor 11 via the image sensor driving unit 20 and outputs the subject image captured through the photographing lens 10 as a color signal. In addition, a user instruction signal is input to the CPU 15 through the operation unit 21, and the CPU 15 performs various controls according to the instruction. The solid-state imaging device 11 is a CCD in which pixels are arranged in a checkered pattern, a Bayer CCD, or a CMOS sensor.

  The electric control system of the digital still camera includes an analog signal processing unit 22 connected to the output of the solid-state imaging device 11, and an A / D conversion that converts RGB color signals output from the analog signal processing unit 22 into digital signals. The circuit 23 is provided and these are controlled by the CPU 15.

  Further, the electric control system of this digital still camera includes a memory control unit 25 connected to the main memory 24, a digital signal processing unit 26 described later in detail, and compresses the captured image into a JPEG image and decompresses the compressed image. A compression / decompression processing unit 27, an integration unit 28 that integrates image data output from the solid-state imaging device 11 and converted into digital data for each of R, G, and B to obtain a white balance gain and the like, and a removable recording An external memory control unit 30 to which a medium 29 is connected and a display control unit 32 to which a liquid crystal display unit 31 mounted on the back of the camera or the like is connected are connected to each other by a control bus 33 and a data bus 34. And is controlled by a command from the CPU 15.

  The digital signal processing unit 26, the analog signal processing unit 22, the A / D conversion circuit 23, and the like shown in FIG. 1 can be mounted on the digital still camera as separate circuits. It is preferable to manufacture on the same semiconductor substrate using LSI manufacturing technology to form one solid-state imaging device.

  FIG. 2 is a detailed configuration diagram of the digital signal processing unit 26 shown in FIG. The digital signal processing unit 26 can be configured by a hardware circuit or software.

  The digital signal processing unit 26 in the example shown in the figure includes an offset correction circuit 41 that takes in image signals of R, G, and B colors output from the A / D conversion circuit 23 and performs an offset process, and an output of the offset correction circuit 41. A gain correction circuit 42 that takes in a signal and performs white balance adjustment, and a gamma correction circuit 43 that performs gamma correction on a signal output from the gain correction circuit 42 using a predetermined γ value.

  The digital signal processor 26 further interpolates the RGB color signals output from the gamma correction circuit 43 to obtain RGB three color signals at each pixel position, and the RGB signals after the RGB interpolation calculations. An RGB / YC conversion circuit 45 for obtaining the luminance signal Y and the color difference signals Cr and Cb, a noise filter 46 for reducing noise from the luminance signal Y and the color difference signals Cr and Cb, and a contour for the luminance signal Y after noise reduction. A contour correction circuit 47 that performs correction, and a color difference matrix circuit 48 that performs color tone correction by multiplying the color difference signals Cr and Cb after noise reduction by a color difference matrix.

  The RGB interpolation calculation unit 44 is not required if the solid-state image sensor 11 is a three-plate image sensor, but the solid-state image sensor 11 used in the present embodiment is a single-plate solid-state image sensor. Since only one color signal of R, G, and B is output, in a pixel that does not output, that is, a pixel that outputs R, how much the G and B color signals are at this pixel position is determined by surrounding pixels. Is obtained by interpolation calculation from the G and B signals.

  Signal processing, that is, luminance signal noise reduction processing, which is a feature of the present embodiment, is executed by the noise filter 46. The noise filter 46 performs the following processing to reduce image contour noise caused by the chromatic aberration of the lens 10.

  FIG. 3 is a schematic diagram illustrating an example of an image signal obtained by a solid-state imaging device in which pixels are arranged in a checkered pattern. In the example shown in the figure, when the pattern having the outline of the black region and the white region in the direction perpendicular to the row in which the R pixel and the B pixel are alternately arranged is captured in the R pixel 5 due to the chromatic aberration of the lens 10. The red light does not hit, the blue light hits the B pixel 6 in the direction k1, and the red light does not hit the R pixel 7 in the direction k1, so the black-and-white boundary in the B pixel 6 is k2. The black and white boundary at the R pixels 5 and 7 is the k1 position, and the luminance signal obtained from the R, G, and B signals appears as jagged noise at the boundary k1, as shown in FIG. .

  Therefore, in the present embodiment, filter processing is performed on the luminance signal Y obtained from the R, G, and B signals so that the response of the alternately arranged color pixel intervals becomes “0”. For example, the luminance value of a pixel on a contour line that is a pixel of m rows and n columns is obtained by an arithmetic expression of Y′mn = (Y (m−2) n + 2 · Ymn + Y (m + 2) n) / 4. . In the example of FIG. 4, Yb '= (Yr13 + 2 · Yb33 + Yr53) / 4 is used, and this is used instead of Yb33. As described above, by calculating the luminance value of the pixel existing at the position of the contour line k1 by the above-described arithmetic expression, the jagged noise at the position of the contour line k1 disappears as shown in FIG.

  In the above-described embodiment, the luminance signal is obtained from the color signal obtained from the actual pixels arranged in the checkered pattern, and the jagged noise in the luminance signal is erased. However, no pixel is present between the actual pixels arranged in the checkered pattern. When the position R, G, B signals are obtained and the image signal is converted into a square array, Y23 which should be between Y22 and Y24 in FIG. 4 and Y43 which should be between Y42 and Y44 are obtained. Even if the luminance signal is obtained as Y′33 = (Y23 + Y43) / 2, that is, the luminance signal is obtained as Y′mn = (Y (m−1) n + Y (m + 1) n) / 2, Jagged noise can be similarly eliminated.

  The present embodiment can also be applied to a Bayer pixel arrangement. In the pixel arrangement shown in FIG. 9, it is assumed that the state of the luminance signal is as shown in FIG. 6 due to the chromatic aberration of the lens 10. Also in this case, the jagged noise on the contour line can be eliminated by performing the calculation process of Y′mn = (Y (m−1) n + 2 · Ymn + Y (m + 1) n) / 4. Specifically, in the case of FIG. 6, the calculation is performed as Yb'33 = (Yg23 + 2 · Yb33 + Yg43) / 4, and this is used instead of Yb33. Thereby, as shown in FIG. 7, the jaggedness of the luminance value on the outline is eliminated.

  The signal processing of the present invention is useful when applied to a digital camera because it can reduce jagged noise in a luminance signal caused by chromatic aberration of a lens and suppress image quality deterioration.

1 is a block configuration diagram of a digital still camera to which a signal processing method according to an embodiment of the present invention is applied. It is a detailed block diagram of the digital signal processing unit shown in FIG. It is a schematic diagram of a color signal due to lens chromatic aberration when pixels are arranged in a checkered pattern. FIG. 4 is a schematic diagram of a luminance signal obtained from the color signal shown in FIG. 3. It is a figure which shows the example which erased the jagged noise of the luminance signal shown in FIG. It is a schematic diagram of a luminance signal due to lens chromatic aberration in a Bayer pixel arrangement. It is a figure which shows the example which erased the jagged noise of the luminance signal shown in FIG. It is a figure which shows the example which arranged the pixel in the checkered pattern. It is a figure which shows the pixel arrangement | positioning of a Bayer system. It is a figure which shows the pattern in which the white area | region and the black area | region were partitioned off with the straight line. It is a figure explaining generation | occurrence | production of the jagged noise by the chromatic aberration of a lens.

Explanation of symbols

R, G, B Pixel arrangement position 10 Shooting lens 11 Solid-state imaging device 26 Digital signal processing unit 46 Noise filter

Claims (2)

  In a signal processing method for processing an image signal obtained by imaging a subject image that has passed through a photographic lens by an imaging element in which pixels that detect different colors are alternately arranged, pixels on the contour line of the subject image (hereinafter referred to as a target) The luminance value A of the pixel) is obtained by filtering the luminance signals B and C of adjacent pixels on the contour line of the target pixel with an arithmetic expression of A = (B + C) / 2. Signal processing method.   In a signal processing apparatus that processes an image signal obtained by imaging a subject image that has passed through a photographic lens with an imaging element in which pixels that detect different colors are alternately arranged, pixels on the contour line of the subject image (hereinafter referred to as a target) A noise filter that obtains the luminance value A of the pixel) from the luminance signals B and C of adjacent pixels on the contour line of the target pixel by an arithmetic expression of A = (B + C) / 2. A signal processing apparatus.

Images