JP2011172047A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus reducing a false signal included in a high-resolution luminance signal. <P>SOLUTION: The imaging apparatus includes: an imaging element which is composed of a plurality of pixels each having a color filter; an adjustment module for performing the adjustment of white balance on an image signal output from the imaging element; a detection module for detecting an edge component around a pixel included in the image signal adjusted by the adjustment module; an extraction module for extracting a low frequency component in a direction orthogonal to the edge component for the pixel around which the edge component has been detected, in the image signal when the edge component is detected by the detection module; and a generation module for generating a luminance signal based on the signal extracted by the extraction module. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an imaging apparatus, and more particularly, to an imaging apparatus that suppresses a false signal generated in a luminance signal.

  Patent document 1 discloses a color imaging device. This color imaging apparatus includes an image sensor having a Bayer array color filter. This color imaging device generates a luminance signal by mixing a YL luminance signal and a YH luminance signal.

JP-A-11-136690

  However, in the color imaging device disclosed in Patent Document 1, a false signal is generated when a high-resolution luminance signal is obtained, and the luminance signal is obtained when a luminance signal without a false signal is obtained. The resolution will be low.

  An object of the present invention is to provide an imaging device that can reduce a false signal included in a high-resolution luminance signal.

  In order to solve the above-described problems, an imaging apparatus according to the present invention includes a plurality of pixels, each pixel having a color filter, and white balance adjustment for an image signal output from the imaging element. An adjustment unit, a detection unit that detects an edge component around a pixel included in the image signal adjusted by the adjustment unit, and an edge component is detected in the periphery of the image signal when the detection unit detects the edge component. Each pixel includes an extraction unit that extracts a low frequency component in a direction orthogonal to the edge component, and a generation unit that generates a luminance signal based on the signal extracted by the extraction unit.

  ADVANTAGE OF THE INVENTION According to this invention, the imaging device which can reduce the false signal contained in the high-resolution luminance signal can be provided.

The block diagram which shows the structure of the digital video camera 100 Schematic diagram for explaining the configuration of some pixels of the CCD image sensor 180 Block diagram of the luminance signal generation circuit 500 Schematic diagram for explaining a filter used in the edge strength detection circuit 410 The figure which shows an example of the image signal of a vertical edge The figure which shows an example of the image signal which the false signal generate | occur | produced The figure which shows an example of the image signal to which the LPF process was performed by the LPF circuit 420 Schematic diagram showing an example of a two-dimensional filter Schematic diagram showing an example of a one-dimensional filter

[1. Embodiment 1]
[1-1. Constitution〕
The electrical configuration of the digital video camera 100 according to the present embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration of the digital video camera 100. The digital video camera 100 captures a subject image formed by an optical system including a zoom lens 110 and the like with a CCD image sensor 180. The video data generated by the CCD image sensor 180 is subjected to various processes by the image processing unit 190 and stored in the memory card 240. The video data stored in the memory card 240 can be displayed on the liquid crystal monitor 270. Hereinafter, the configuration of the digital video camera 100 will be described in detail.

  The optical system of the digital video camera 100 includes a zoom lens 110, an OIS 140, and a focus lens 170. The zoom lens 110 can enlarge or reduce the subject image by moving along the optical axis of the optical system. The focus lens 170 adjusts the focus of the subject image by moving along the optical axis of the optical system.

  The OIS 140 includes a correction lens that can move in a plane perpendicular to the optical axis. The OIS 140 reduces the shake of the subject image by driving the correction lens in a direction that cancels the shake of the digital video camera 100.

  The zoom motor 130 drives the zoom lens 110. The zoom motor 130 may be realized by a pulse motor, a DC motor, a linear motor, a servo motor, or the like. The zoom motor 130 may drive the zoom lens 110 via a mechanism such as a cam mechanism or a ball screw. The detector 120 detects where the zoom lens 110 exists on the optical axis. The detector 120 outputs a signal related to the position of the zoom lens by a switch such as a brush in accordance with the movement of the zoom lens 110 in the optical axis direction.

  The OIS actuator 150 drives the correction lens in the OIS 140 in a plane perpendicular to the optical axis. The OIS actuator 150 can be realized by a planar coil or an ultrasonic motor. The detector 160 detects the amount of movement of the correction lens in the OIS 140.

  The CCD image sensor 180 captures a subject image formed by an optical system including the zoom lens 110 and generates video data. The CCD image sensor 180 performs various operations such as exposure, transfer, and electronic shutter.

  The image processing unit 190 performs various processes on the video data generated by the CCD image sensor 180. The image processing unit 190 processes the video data generated by the CCD image sensor 180 to generate video data to be displayed on the liquid crystal monitor 270 or to store video data to be re-stored in the memory card 240. Or generate. For example, the image processing unit 190 performs various processes such as gamma correction, white balance correction, and flaw correction on the video data generated by the CCD image sensor 180. Further, the image processing unit 190 applies H.264 to the video data generated by the CCD image sensor 180. The video data is compressed by a compression format compliant with the H.264 standard or the MPEG2 standard. The image processing unit 190 can be realized by a DSP or a microcomputer.

  The controller 210 is a control means for controlling the whole. The controller 210 can be realized by a semiconductor element or the like. The controller 210 may be configured only by hardware, or may be realized by combining hardware and software. The controller 210 can be realized by a microcomputer or the like.

  The memory 200 functions as a work memory for the image processing unit 190 and the controller 210. The memory 200 can be realized by, for example, a DRAM or a ferroelectric memory.

  The liquid crystal monitor 270 can display an image indicated by the video data generated by the CCD image sensor 180 and an image indicated by the video data read from the memory card 240.

  The gyro sensor 220 is composed of a vibration material such as a piezoelectric element. The gyro sensor 220 vibrates a vibration material such as a piezoelectric element at a constant frequency, converts a force generated by the Coriolis force into a voltage, and obtains angular velocity information. By obtaining angular velocity information from the gyro sensor 220 and driving a correction lens in the OIS in a direction to cancel out the shaking, the digital video camera 100 corrects camera shake by the user.

  The card slot 230 is detachable from the memory card 240. The card slot 230 can be mechanically and electrically connected to the memory card 240. The memory card 240 includes a flash memory, a ferroelectric memory, and the like, and can store data.

  The internal memory 280 is configured by a flash memory, a ferroelectric low memory, or the like. The internal memory 280 stores a control program for controlling the entire digital video camera 100 and the like.

  The operation member 250 is a member that receives an image capturing instruction from the user. The zoom lever 260 is a member that receives a zoom magnification change instruction from the user.

[1-2. Configuration of luminance signal generation circuit)
The configuration of the luminance signal generation circuit 500 in the image processing unit 190 of the digital video camera 100 according to the present embodiment will be described with reference to FIGS. FIG. 2 is a schematic diagram for explaining the configuration of some pixels of the CCD image sensor 180. FIG. 3 is a block diagram of the luminance signal generation circuit 500.

  The CCD image sensor 180 is a Bayer array image sensor as shown in FIG. In the CCD image sensor 180, the color filter is composed of R, Gr, Gb, and B pixels. The color filter is configured by arranging (R, Gr) and (Gb, B) in the vertical direction.

  The luminance signal generation circuit 500 generates a luminance signal by separating the image signal output from the CCD image sensor 180 into R, Gr, Gb, and B color signals, subjecting each color signal to image processing, and YC conversion. To do. Next, the configuration of the luminance signal generation circuit 500 will be described.

  The luminance signal generation circuit 500 includes a color separation circuit 300, an R WB circuit 310, a Gr WB circuit 320, a B WB circuit 330, a Gb WB circuit 340, an R γ circuit 350, a Gr γ circuit 360, and a B γ circuit 370, Gb γ circuit 380, low-frequency luminance signal generation circuit 390, high-frequency luminance signal generation circuit 400, low-frequency color signal generation circuit 440, edge intensity detection circuit 410, LPF circuit 420, mixing circuit 430, color difference signal A generation circuit 450, a mixture ratio calculation circuit 460, a band pass filter circuit 480, and an addition circuit 470 are configured.

  The color separation circuit 300 separates the image signal output from the CCD image sensor into R, Gr, B, and Gb color signals. The R WB circuit 310, the Gr WB circuit 320, the B WB circuit 330, and the Gb WB circuit 340 adjust the white balance of each color signal separated by the color separation circuit 300. The R γ circuit 350, the Gr γ circuit 360, the B γ circuit 370, and the Gb γ circuit 380 perform γ correction on the color signal that is white-balance adjusted by each WB circuit.

  The color signal that has undergone γ correction in each γ circuit is output to the low-frequency luminance signal generation circuit 390, the high-frequency luminance signal generation circuit 400, and the low-frequency color signal generation circuit 440. This is because the luminance signal generation circuit 500 generates the image signal generated by the low frequency luminance signal generation circuit 390 and the image signal generated by the high frequency luminance signal generation circuit 400 by the low frequency signal generation circuit 440. This is because the luminance signal is generated based on the image signal obtained by mixing at a ratio determined based on the image signal.

  The low-frequency luminance signal generation circuit 390 adds and averages signals for four pixels of R, Gr, B, and Gb that have been subjected to γ correction. Specifically, the averaging of four pixels indicated by reference numeral 501 in FIG. 2 is performed. Thereby, a luminance signal having a low spatial frequency is generated. The luminance signal having a low spatial frequency does not include a false signal. However, the luminance signal having a low inter-space frequency has a low resolution. Hereinafter, this luminance signal having a low spatial frequency is referred to as YL.

  On the other hand, the high-frequency luminance signal generation circuit 400 rearranges the R, Gr, B, and Gb that have been subjected to the γ correction into the Bayer array again without any particular processing. Then, the high frequency luminance signal generation circuit 400 sets the rearranged color signal as a luminance signal. This luminance signal has a higher spatial frequency than YL. This is because LPF is not applied to this luminance signal. The luminance signal having a high spatial frequency includes a high-frequency false signal. However, the luminance signal having a high spatial frequency has a high resolution.

  The edge strength detection circuit 410 detects the edge strength in the horizontal direction and the vertical direction of the luminance signal generated by the high frequency luminance signal generation circuit 400. Specifically, the edge strength detection circuit 410 detects the edge strength using a filter for calculating the edge strength described below. Here, the edge strength is the magnitude of the difference in brightness between the pixel of interest and its surrounding pixels.

  The LPF circuit 420 performs LPF processing on the luminance signal generated by the high frequency luminance signal generation circuit 400 in a direction orthogonal to the direction of the edge detected by the edge intensity detection circuit 410. That is, the LPF circuit 420 extracts a low frequency component in a direction orthogonal to the edge from the luminance signal generated by the high frequency luminance signal generation circuit 400. Thereby, when a false signal exists in a direction orthogonal to the direction of the edge among the luminance signals generated by the high frequency luminance signal generation circuit 400, the false signal is suppressed. Here, the generated luminance signal is hereinafter referred to as YH.

  The low-frequency color signal generation circuit 440 performs oversampling processing on the R, Gr, B, and Gb color signals that have been subjected to γ correction. Thereby, the low-frequency color signal generation circuit 440 interpolates pixels in which the color signal is spatially missing. The color signal generation circuit 450 generates a color difference signal based on the color signal generated by the low-frequency color signal generation circuit 440.

  The mixing circuit 430 mixes YH and YL based on Equation 1.

Ymix = (1−k) × YL + k × YH (0 ≦ k ≦ 1)
The mixing ratio calculation circuit 460 determines the coefficient k. Specifically, the mixture ratio calculation circuit 460 converts the color difference signal generated by the color difference signal generation circuit 450 into saturation, and calculates k based on this saturation. The mixing ratio calculation circuit 460 determines the coefficient k so as to approach 0 when the saturation is high, and determines the coefficient k so as to approach 1 when the saturation is low.

  The band pass filter circuit 480 applies a band pass filter to Ymix to generate a contour signal. The adder circuit 470 adds a contour signal generated by the YL and the bandpass filter circuit 480 to generate a luminance signal.

  As described above, the digital video camera 100 according to the present embodiment performs the LPF process on the luminance signal generated by the high frequency luminance signal generation circuit 400 in the direction orthogonal to the edge of the luminance signal. Thereby, it is possible to suppress the false signal without degrading the resolution with respect to the luminance signal generated by the high frequency luminance signal generation circuit 400.

[1-3. (Principle capable of suppressing false signals by applying LPF)
The reason why the false signal can be suppressed by performing LPF processing in a direction orthogonal to the edge of the luminance signal generated by the high frequency luminance signal generation circuit 400 will be described with reference to FIGS. FIG. 4 is a schematic diagram for explaining a filter used in the edge intensity detection circuit 410. FIG. 5 is a diagram illustrating an example of a vertical edge image signal. FIG. 6 is a diagram illustrating an example of an image signal in which a false signal is generated. FIG. 7 is a diagram illustrating an example of an image signal subjected to LPF processing by the LPF circuit 420.

  The LPF circuit 420 performs LPF processing on the luminance signal generated by the high frequency luminance signal in a direction orthogonal to the edge direction. This is to suppress a false signal generated when a pixel that is not originally colored is colored due to a WB shift or the like. The principle that a false signal can be suppressed by performing LPF processing will be described using a specific example.

  When a subject having a vertical edge is achromatic, no false signal is generated as shown in FIG. However, an achromatic subject may become chromatic due to a deviation in white balance adjustment. In this case, a false signal is generated in the luminance signal generated by the high frequency luminance signal generation circuit 400. FIG. 6 shows an example in which the R signal level of the achromatic subject is increased due to the white balance adjustment shift. In FIG. 6, the portion indicating “2” corresponds to R. In this portion R, a dot-like false signal is generated.

  In order to suppress this false signal, the LPF circuit 420 performs LPF processing in a direction orthogonal to the edge direction. The edge strength detection circuit 410 detects the edge direction using the two-dimensional filter shown in FIGS. FIG. 4A shows a filter for detecting an edge in the vertical direction. FIG. 4B shows a filter for detecting horizontal edges.

  When the pixel in i row and j column in FIG. 6 is a (i, j), the edge strength detection circuit 410 calculates the edge strength in the vertical direction of a (3, 2) by the following equation.

Edge strength in the vertical direction = | −1 × a (2,1) −2 × a (2,2) −1 × a (2,3) + 2 × a (3,1) + 4 × a (3,2) + 2 × a (3,3) −1 × a (4,1) −2 × a (4,2) −1 × a (4,3) |
Further, the edge strength detection circuit 410 calculates the horizontal edge strength of a (3, 2) by the following equation.

Horizontal edge strength = | −1 × a (2,1) + 2 × a (2,2) −1 × a (2,3) −2 × a (3,1) + 4 × a (3,2) −2 × a (3,3) −1 × a (4,1) + 2 × a (4,2) −1 × a (4,3) |
In this example, the edge strength in the vertical direction is “72”. Also, the edge strength in the horizontal direction is “8”. Accordingly, the edge strength detection circuit 410 detects that the vertical edge is strong because the vertical edge strength is larger than the horizontal edge strength.

  In this example, the LPF circuit 420 performs LPF processing in the horizontal direction based on the detection result of the edge strength detection circuit 410. Specifically, the LPF circuit 420 performs an average of two pixels in the horizontal direction and performs LPF processing. FIG. 7 shows the result of applying the LPF process to all the pixels in FIG. 6 in the horizontal direction. With this processing, the dot-like false signal is suppressed while the vertical edge of the subject is preserved.

With the above processing, the digital video camera 100 according to the present embodiment can suppress the false signal without sacrificing the resolution, and can generate a high-resolution luminance signal.
[2. Other Embodiments]
As described above, the first embodiment has been described as the embodiment of the present invention. However, the present invention is not limited to these. Therefore, other embodiments of the present invention will be described collectively in this section.

  The optical system and drive system of the digital camera 100 according to the present embodiment are not limited to those shown in FIG. For example, although FIG. 1 illustrates an optical system having a three-group configuration, a lens configuration having another group configuration may be used. In addition, each lens may be composed of one lens or a lens group composed of a plurality of lenses.

  In the first embodiment, the CCD image sensor 180 is exemplified as the imaging unit, but the present invention is not limited to this. For example, it may be composed of a CMOS image sensor or an NMOS image sensor.

  In Embodiment 1, the filter shown in FIG. 4 was illustrated as a filter for calculating edge strength. However, the filter for calculating the edge strength is not limited to this. A two-dimensional filter as shown in FIG. 8 or a one-dimensional filter as shown in FIG. 9 may be used as long as the orientation of horizontal and vertical edges can be determined.

  In Embodiment 1, two-pixel addition is exemplified as the filter processing in the LPF circuit 420, but the present invention is not limited to this. Any filter may be used as long as it is an LPF.

  In the first embodiment, the filtering process in the LPF circuit 420 applies LPF only in the direction orthogonal to the edge, but the present invention is not limited to this. You may apply the filter which changed the coefficient with the intensity | strength of the horizontal and vertical edge in both directions.

  The present invention can be applied to an imaging apparatus such as a digital video camera or a digital still camera.

100 Digital Camera 110 Zoom Lens 120 Detector 130 Zoom Motor 140 OIS
150 OIS Actuator 160 Detector 170 Focus Lens 180 CCD Image Sensor 190 Image Processing Unit 200 Memory 210 Controller 220 Gyro Sensor 230 Card Slot 240 Memory Card 250 Operation Member 260 Zoom Lever 270 Liquid Crystal Monitor 280 Internal Memory

Claims (3)

An image sensor comprising a plurality of pixels, each pixel having a color filter;
Adjusting means for adjusting white balance for the image signal output from the image sensor;
Detecting means for detecting edge components around pixels included in the image signal adjusted by the adjusting means;
When an edge component is detected by the detection means, an extraction means for extracting a low frequency component in a direction orthogonal to the edge component for pixels in which the edge component is detected in the periphery of the image signal;
Generating means for generating a luminance signal based on the signal extracted by the extracting means,
Imaging device. Further comprising low-frequency generation means for averaging the signal levels of adjacent four pixels of the image signal adjusted by the adjustment means to generate a low-frequency luminance signal,
The generation unit generates a luminance signal by adding the signal extracted by the extraction unit and the low-frequency luminance signal.
The imaging device according to claim 1. The generating means determines a ratio when adding the signal extracted by the extracting means and the low-frequency luminance signal based on the saturation of the image signal;
The imaging device according to claim 2.

Images