JP4867204B2 - Imaging device - Google Patents

Description

  In the imaging apparatus, for example, when a single-plate imaging element is used, color moiré caused by high-frequency return is effectively reduced by preventing resolution deterioration and S / N deterioration. The present invention relates to a signal processing method for an imaging apparatus.

  Conventionally, in order to “provide an imaging device that eliminates a vertical phase shift between a color signal and a luminance signal and suppresses an increase in circuit scale” (problem of the summary of Patent Document 1), An RGB signal and a luminance signal are generated from the adjacent 3H output signals using the circuits 8 and 8 ', and the γ correction circuit 7a converts the RGB signals into dot-sequential signals and performs γ correction ”(Patent Document 1) (Summary Solution).

Japanese Patent Laid-Open No. 10-108210

  By the way, in an imaging apparatus using an imaging device generally called a single plate in which a plurality of color filters are arranged in a mosaic pattern, the spatial sampling frequency of each color signal is lower than the sampling frequency of the pixels of the imaging device. Color moire, which is aliasing noise of high-frequency signals, is likely to occur.

  For example, in the example of FIG. 5, R, G, and B color filters are arranged, and the sampling frequency of each RGB color signal is half the sampling frequency of the pixel in both the horizontal and vertical directions. An optical crystal filter is used to reduce this color moire. This optical crystal filter removes a high-frequency component that causes color moiré from light incident on the image sensor.

  FIG. 4 is a diagram of frequency characteristics of the optical system unit in the imaging apparatus. The horizontal axis is frequency and the vertical axis is gain. If the pixel sampling frequency is fs / 2, the color sampling frequency is fs / 4 in the example of FIG. The optical crystal filter lowers the gain near the limit frequency fs / 2, which causes color aliasing noise, and suppresses the occurrence of color moire. However, the limit frequency in the luminance signal is fs / 2 which is the sampling frequency of the pixel, and on the contrary, the luminance resolution is deteriorated by weakening the high frequency gain.

  In an imaging apparatus using an optical crystal filter, enhancement processing is performed in a digital signal processing unit provided at a later stage in order to suppress resolution degradation due to the optical crystal. However, analog noise is superimposed on the pixel signal that has passed through the image sensor and the A / D conversion circuit, and the enhancement processing amplifies the analog noise, resulting in a problem of deteriorating S / N. Therefore, in the conventional imaging device, there is a trade-off between the reduction of color moire, the resolution, and the S / N ratio.

  The present invention solves the above problems by effectively reducing color moire while preventing resolution degradation and S / N degradation.

  The above problems are solved by the invention described in the claims.

  According to the present invention, an imaging apparatus with improved usability can be provided.

  Embodiments will be described below with reference to the drawings.

FIG. 1 shows a conceptual diagram of Embodiment 1 of the present invention.
Light from the subject that has passed through the lens 101 enters the image sensor 102. The imaging element 102 has a plurality of cells, and each cell photoelectrically converts light from the subject and converts it into an electrical signal, thereby generating a pixel signal. The pixel signal generated by the image sensor 102 is converted into digital data by the A / D conversion unit 103. The preprocessing unit 104 performs preprocessing such as signal level gain adjustment on the digital data from the A / D conversion unit 103.

  The pixel signal whose gain has been adjusted by the preprocessing unit 104 is input to the line memory 105, and the pixel delay signal for nH (n is a constant) from the line memory is input to the luminance signal generation unit 109, and the luminance signal Is generated.

  Further, the nH pixel delay signal from the line memory 105 is input to the broadband luminance signal generation unit 106. The broadband luminance signal generation unit performs low-pass filter processing that prevents gain reduction of high-frequency components and removes color carrier components. The luminance signal generated by the broadband luminance signal generation unit 106 is input to the band pass filter 110, and a high-frequency AC component signal of the luminance signal is generated.

The high frequency attenuation gain calculation unit 111 performs a process of calculating a gain for attenuating the high frequency gain for each pixel signal based on the output signal from the bandpass filter. The high frequency signal gain attenuating unit 107 multiplies the gain obtained from the high frequency gain attenuation gain calculating unit 111 by the pixel delay signal of nH that is an output signal from the line memory 105, thereby obtaining a high frequency gain for the pixel signal. Attenuate. The pixel signal that is the output from the high-frequency signal gain attenuating unit is input to the color difference signal generation unit, and a color difference signal is generated.
According to the present embodiment, a broadband luminance signal is generated, a pixel correction gain is calculated from the luminance signal, and the pixel correction gain is multiplied by the pixel signal to reduce the gain of the high frequency component and perform the band limitation signal. A signal for generating a color difference signal that can be generated can be used to suppress the occurrence of color moiré, which is a high-frequency component aliasing noise, by using the band-limited signal.

  Further, when generating a luminance signal, a signal is output from the line memory 105 to the luminance signal generation unit 109, and processing for suppressing the utterance of color moiré when generating a color difference signal (broadband luminance signal generation unit 106). (The processing of the high-frequency signal gain attenuation unit 107) is not performed. Therefore, the signal for generating the luminance signal is a broadband signal as compared with the case where the optical crystal filter is used, thereby preventing the resolution from being deteriorated.

  In this embodiment, a single-plate image pickup device is used. However, the present invention is not limited to this, and output pixel signals from a plurality of image pickup devices that have optically shifted the pixel center of gravity are rearranged to obtain a high-pixel single-plate image pickup device. Needless to say, the present embodiment can also be applied to an imaging apparatus that performs signal processing as the pixel signal.

FIG. 2 shows a conceptual diagram of Embodiment 2 of the present invention.
Light from the subject that has passed through the lens 101 enters the image sensor 102. The image sensor 102 has a plurality of cells, and each cell photoelectrically converts light from the subject and converts it into an electrical signal, thereby generating a pixel signal. The pixel signal generated by the image sensor 102 is converted into digital data by the A / D conversion unit 103. The preprocessing unit 104 performs preprocessing such as signal level gain adjustment on the digital data from the A / D conversion unit 103.

  The pixel signal whose gain has been adjusted by the pre-processing unit 104 is input to the line memory 105, and the pixel delay signal for nH (n is a constant) from the line memory 105 is input to the luminance signal generation unit 109. Is generated.

  The nH pixel delay signal from the line memory 105 is input to the wideband G interpolation signal generation unit 201. The broadband G interpolation signal generation unit 201 performs processing for complementing the G signal in the case where a single-plate image sensor with a primary color Bayer array is used. This G signal has twice as many pixels as the R signal and B signal, and it is easy to generate a broadband signal. The luminance signal generated by the broadband G interpolation signal generation unit 201 is input to the band pass filter 110, and a high frequency component signal of the pixel signal is generated.

  The high frequency attenuation gain calculation unit 111 performs a process of calculating a gain for attenuating the high frequency gain for each pixel signal based on the output signal from the band pass filter 110. The high frequency signal gain attenuating unit 107 multiplies the gain obtained from the high frequency gain attenuation gain calculating unit 111 by the pixel delay signal of nH that is an output signal from the line memory 105, thereby obtaining a high frequency gain for the pixel signal. Attenuate. The pixel signal that is the output from the high-frequency signal gain attenuating unit 107 is input to the color difference signal generation unit, and a color difference signal is generated.

  According to the present embodiment, in an imaging apparatus using a primary color Bayer array single-plate imaging device, a broadband G interpolation signal is generated, a pixel correction gain is calculated from the G interpolation signal, and the pixel correction gain is converted into a pixel signal. By multiplying, it is possible to generate a signal in which the gain of the high-frequency component is reduced and the band is limited, and the signal for generating the color difference signal is the aliasing noise of the high-frequency component by using this band-limited signal. Generation of color moire can be suppressed.

  Also, when generating a luminance signal, a signal is output from the line memory 105 to the luminance signal generation unit 109, and processing for suppressing the utterance of color moiré when generating a color difference signal (broadband G interpolation signal generation unit) 201 to high-frequency signal gain attenuator 107). Therefore, the signal for generating the luminance signal is a broadband signal as compared with the case where the optical crystal filter is used, thereby preventing the resolution from being deteriorated.

  In this embodiment, a single-plate image sensor having a primary color Bayer array is used. However, the present invention is not limited to this. Needless to say, this embodiment can be applied to an image pickup apparatus that performs signal processing as a pixel signal of a single-plate image pickup element, particularly when pixel rearrangement is performed so as to be equivalent to the primary color Bayer arrangement.

FIG. 3 shows a conceptual diagram of Embodiment 3 of the present invention.
The light from the subject that has passed through the lens 101 first enters the prism 301. The prism splits the light from the lens in two directions, and one of the lights is incident on the optical crystal filter 302, is subjected to frequency band limitation, and is incident on the image sensor 102. The other light split by the prism enters the image sensor 303. According to this configuration, it is possible to simultaneously generate both a pixel signal with a frequency band restriction and a pixel signal without a frequency band restriction. The image sensor 102 is an image sensor in which a plurality of color filters are arranged. The image sensor 303 may be a color filter different from the image sensor, or may be a single-plate image sensor in which single color filters are arranged.

  The analog pixel signal from the image sensor 102 subjected to the band limitation is converted into digital data by the A / D conversion unit 103, and gain adjustment or the like is performed by the preprocessing unit 104. The digital pixel signal after gain adjustment is input to the line memory 105, and a pixel delay signal corresponding to nH (n is a constant) from the line memory is input to the color difference signal generation unit 108 to generate a color difference signal. .

  An analog pixel signal from the image sensor 303 not subjected to the band limitation is converted into digital data by the A / D conversion unit 103, and gain adjustment or the like is performed by the preprocessing unit 104. The gain-adjusted digital pixel signal is input to the line memory 105, and the pixel delay signal for nH (n is a constant) from the line memory 105 is input to the luminance signal generation unit 109 to generate a luminance signal. .

  According to the present embodiment, in an imaging apparatus using a single-plate imaging device, light from a subject is split in two directions by a prism, and the split one light passes through an optical crystal filter and is converted into a pixel signal by the imaging device. Thus, a signal with reduced bandwidth can be generated by reducing the gain of the high-frequency component, and the signal for generating the color difference signal can be generated with the aliasing noise of the high-frequency component by using this band-limited signal. Occurrence of a certain color moire can be suppressed. The other split light is a wideband signal that is converted into a pixel signal by the image sensor as it is, thereby preventing resolution degradation.

  In the present embodiment, the light is split by the prism 301. However, the present invention is not limited to this, and it goes without saying that the present embodiment can be applied if the luminance signal can be separated before being input to the optical crystal filter 302.

  According to the above embodiment, it is possible to effectively suppress color moire, which is high-frequency aliasing noise, without causing resolution degradation or S / N degradation.

  The present invention aims to effectively reduce color moiré that occurs due to high-frequency return in an imaging apparatus, particularly when a single-plate imaging element is used, by preventing resolution degradation and S / N degradation. The present invention relates to a signal processing method for an imaging apparatus.

The conceptual diagram of Example 1 by this invention Conceptual diagram of Embodiment 2 according to the present invention Conceptual diagram of Embodiment 3 according to the present invention Frequency characteristics diagram of input signal to signal processing circuit Image sensor color filter array example

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Lens 102 Image pick-up element 103 A / D conversion part 104 Pre-processing part 105 Line memory 106 Broadband luminance signal generation part 107 High frequency signal gain attenuation part 108 Color difference signal generation part 109 Luminance signal generation part 110 Band pass filter 111 High frequency attenuation gain calculation part 201 Broadband G interpolation signal generation unit 301 Prism 302 Optical crystal filter 303 Image sensor 501 Image sensor

Claims (6)

A single-plate image sensor in which a plurality of color filters are arranged, a pixel signal frequency band limiting unit that attenuates a high frequency component by performing gain control for each pixel on the pixel signal from the image sensor, and the pixel signal frequency band An image pickup apparatus comprising: a color difference signal generation unit configured to generate a color difference signal from an output signal from the limiting unit. The imaging device according to claim 1,
The pixel signal frequency band limiting means includes a broadband luminance signal generation unit that generates a broadband luminance signal from the pixel signal, a bandpass filter that extracts a high frequency component from the luminance signal from the broadband luminance signal generation unit, and the pixel signal And a high-frequency attenuation gain calculation unit that calculates a gain for attenuating high-frequency components from the output of the bandpass filter. In the imaging device according to claim 1,
The pixel signal frequency band limiting unit includes a pixel interpolating unit that generates an interpolated pixel signal by interpolating the pixel signal from the image sensor, a bandpass filter that extracts a high frequency component of the interpolated pixel signal, and a An imaging apparatus, comprising: a high-frequency attenuation gain calculation unit that calculates a gain for attenuating a high-frequency component with respect to a pixel signal from an output of the bandpass filter. The imaging apparatus according to claim 2,
A single-plate image sensor in which a plurality of color filters are arranged, an A / D converter that converts pixel signals from the image sensor into digital data, and the pixel signals converted into digital data are delayed by a plurality of horizontal scanning periods A line memory that generates a signal, and a luminance signal generation unit that generates a luminance signal from pixel signals delayed by a plurality of horizontal scanning periods by the line memory;
A broadband luminance signal generating unit that generates a broadband luminance signal from a plurality of pixel signals delayed by a horizontal scanning period by the line memory; and a bandpass filter that extracts a high-frequency component from the luminance signal from the broadband luminance signal generating unit; A high-frequency attenuation gain calculation unit for calculating a gain for attenuating a high-frequency component from the output of the bandpass filter with respect to an output pixel signal from the line memory; and a gain calculated by the high-frequency attenuation gain calculation unit for the line memory A high-frequency signal gain attenuator that attenuates the high-frequency signal by multiplying the output pixel signal from
The color difference signal generation unit generates a color difference signal using an output pixel signal from the high-frequency signal gain attenuation unit;
An imaging apparatus characterized by the above. The imaging apparatus according to claim 3,
A single-plate image sensor with a primary color Bayer array, an A / D converter that converts pixel signals from the image sensor into digital data, and a signal obtained by delaying the pixel signals converted into digital data by a plurality of horizontal scanning periods A line memory, a color difference signal generating unit that generates a color difference signal from a pixel signal delayed by a plurality of horizontal scanning periods by the line memory, and a luminance signal that generates a luminance signal from the pixel signal delayed by a plurality of horizontal scanning periods by the line memory An imaging device having a generation unit;
A wideband G interpolation signal generation unit that generates a G signal by interpolation from a plurality of pixel signals delayed by a horizontal scanning period by the line memory, and a band that extracts a high frequency component from the G signal from the wideband G interpolation signal generation unit A pass filter, a high-frequency attenuation gain calculation unit that calculates a gain for attenuating a high-frequency component with respect to an output pixel signal from the line memory, and a gain calculated by the high-frequency attenuation gain calculation unit. A high frequency signal gain attenuating unit for attenuating the high frequency signal by multiplying the output pixel signal from the line memory;
The color difference signal generation unit generates a color difference signal using an output pixel signal from the high-frequency signal gain attenuation unit;
An imaging apparatus characterized by the above. 6. The image pickup apparatus according to claim 1, wherein a plurality of image pickup elements comprising a single color filter optically shifted from the center of gravity of the pixel and an output pixel signal from the plurality of image pickup elements are interpolated. Pixel signal double sampling means having the same color arrangement as the output signal from the single-plate image sensor,
Realization using the pixel signal generated by the pixel signal double sampling means instead of the pixel signal output from the single-plate image sensor;
An imaging apparatus characterized by the above.

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