JP4229234B2 - Digital camera - Google Patents

Description

  The present invention relates to a digital camera having a function of acquiring a relatively high sensitivity image signal and a relatively low sensitivity image signal.

  The dynamic range of a solid-state imaging device such as a CCD imaging device is generally narrow, and when shooting a high-contrast subject, the amount of light received by the solid-state imaging device exceeds the dynamic range and the output of the solid-state imaging device is saturated. Subject information may be missing.

  In order to solve such a problem, a high-sensitivity image data obtained from a relatively high-sensitivity photoelectric conversion element and a low-sensitivity image data obtained from a relatively low-sensitivity photoelectric conversion element are combined. Thus, there has been proposed a digital camera with an expanded dynamic range (see, for example, Patent Document 1).

JP-A-4-298175 JP 2000-69355 A

  In the digital camera described in Patent Document 1, it is theoretically possible to use only low-sensitivity image data without performing the above-described combining process. However, when gamma correction is performed by multiplying the low-sensitivity image data by gain, noise tends to stand out in the low-luminance area for the image data obtained from the relatively low-sensitivity photoelectric conversion element. Poor utility.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a digital camera capable of obtaining a high-quality image using a relatively low-sensitivity imaging signal.

  The digital camera of the present invention is a digital camera having a function of acquiring a relatively high-sensitivity imaging signal and a relatively low-sensitivity imaging signal, and low-sensitivity captured image data based on the low-sensitivity imaging signal. A noise reduction processing means for performing noise reduction processing for reducing noise in a low luminance region of the low sensitivity photographed image data in the low sensitivity photography mode, The processing means performs the noise reduction processing using a noise reduction signal generated based on the highly sensitive imaging signal.

  With this configuration, when shooting in the low-sensitivity shooting mode, it is possible to reduce noise in the low-luminance region of the low-sensitivity captured image data based on the low-sensitivity imaging signal using the high-sensitivity imaging signal. For this reason, high-sensitivity low-sensitivity imaging can be realized.

  The digital camera according to the present invention further includes noise reduction signal generation means for generating the noise reduction signal, and the noise reduction signal generation means is adapted for the maximum subject luminance that the low-sensitivity imaging signal can take. The gain for making the ratio of the saturation value of the low-sensitivity imaging signal substantially the same as the ratio of the saturation value of the high-sensitivity imaging signal to the maximum value of subject brightness that can be taken by the high-sensitivity imaging signal The high-sensitivity imaging signal multiplied by the high-sensitivity imaging signal and multiplied by the gain is used as the noise reduction signal.

  In the digital camera of the present invention, the maximum value of the subject brightness that can be taken by the low-sensitivity imaging signal is larger than the maximum value of the subject brightness that can be taken by the high-sensitivity imaging signal multiplied by the gain.

  The digital camera of the present invention is a solid including a first photoelectric conversion element that outputs a relatively high sensitivity photoelectric conversion signal and a second photoelectric conversion element that outputs a relatively low sensitivity photoelectric conversion signal. An image sensor is provided, wherein the high-sensitivity image signal is acquired from the first photoelectric conversion element, and the low-sensitivity image signal is acquired from the second photoelectric conversion element.

  According to the present invention, it is possible to provide a digital camera capable of obtaining a high-quality image using a relatively low sensitivity imaging signal.

FIG. 1 is a diagram showing a schematic configuration of a digital camera for explaining an embodiment of the present invention.
The digital camera in FIG. 1 includes an imaging unit 1, an analog signal processing unit 2, an A / D conversion unit 3, a driving unit 4, a digital signal processing unit 6, a compression / decompression processing unit 7, and a display unit 8. A system control unit 9, an internal memory 10, a media interface 11, a recording medium 12, and an operation unit 13. The digital signal processing unit 6, compression / decompression processing unit 7, display unit 8, system control unit 9, internal memory 10, and media interface 11 are connected to a system bus 20.

  The imaging unit 1 captures a subject with an optical system such as a photographing lens and an imaging element such as a CCD image sensor, and outputs an analog imaging signal. The analog signal processing unit 2 performs predetermined analog signal processing on the analog imaging signal obtained by the imaging unit 1. The A / D converter 3 converts the analog imaging signal processed by the analog signal processor 2 into digital. The output of the A / D converter 3 is sent to the digital signal processor 6.

  At the time of shooting, the optical system is controlled via the drive unit 4. A solid-state image sensor such as a CCD image sensor used as an image sensor has a plurality of photoelectric conversion regions arranged in a row direction and a column direction orthogonal to the surface on a semiconductor substrate, and is generated in response to incident light. Then, an analog imaging signal based on the accumulated signal charge is output. The solid-state imaging device is a timing generator (not shown) included in the drive unit 4 at a predetermined timing when a release switch (not shown) is turned on by operating a release button (not shown) which is a part of the operation unit 13. 1 is written by a drive signal from TG). The drive unit 4 outputs a predetermined drive signal by the system control unit 9.

  The imaging unit 1 outputs a relatively high sensitivity analog imaging signal (hereinafter also referred to as a high sensitivity imaging signal) and a relatively low sensitivity analog imaging signal (hereinafter also referred to as a low sensitivity imaging signal). Both of these image pickup signals are converted into digital image pickup signals through the analog signal processing unit 2 and the A / D conversion unit 3 and sent to the digital signal processing unit 6.

  Imaging signals with different sensitivities may be obtained by using a solid-state imaging device having high-sensitivity pixels and low-sensitivity pixels as shown in Patent Document 1, or as disclosed in JP-A-2001-94870. You may acquire by changing exposure conditions or an analog gain, and you may acquire by using a solid-state image sensor as shown in the following FIG.

FIG. 2 is a diagram illustrating a schematic configuration of a solid-state imaging device capable of outputting a high-sensitivity imaging signal and a low-sensitivity imaging signal.
FIG. 2 is a partially enlarged plan view of a so-called honeycomb-structured solid-state imaging device. This solid-state imaging device has a row direction (direction indicated by an arrow X) on a semiconductor substrate surface and a column direction (arrow Y direction) perpendicular thereto. ), A plurality of photoelectric conversion areas 201 to 203 (only some are numbered in the figure), vertical transfer units 204 to 209, a horizontal transfer unit 210, and an output unit 211.

  Among the plurality of photoelectric conversion regions 201 to 203, the odd-numbered columns are shifted in the column direction by about 1/2 of the column-direction pitch between the photoelectric conversion regions with respect to the even-numbered columns. The photoelectric conversion regions are arranged so as to be shifted in the row direction by approximately ½ of the row direction pitch between the photoelectric conversion regions with respect to the even number of photoelectric conversion regions.

  The photoelectric conversion areas 201 to 203 generate and accumulate signal charges corresponding to the amount of incident light, and are areas where photoelectric conversion elements such as photodiodes are arranged. The photoelectric conversion regions 201 to 203 are divided into a main region m having a relatively large light receiving area and a sub region s having a relatively small light receiving area, and each generates a signal charge corresponding to light having a predetermined spectral sensitivity. ,accumulate.

  The vertical transfer units 204 to 209 read signal charges from the photoelectric conversion regions 201 to 203 and transfer them in the column direction, and are provided on the side corresponding to the columns of the photoelectric conversion regions 201 to 203. The transfer in the column direction is performed by reading the signal charges in the main region m and the signal charges in the sub region s independently to the vertical transfer units 204 to 209.

  The horizontal transfer unit 210 transfers the signal charges from the plurality of vertical transfer units 204 to 209 and transfers the transferred signal charges in the row direction. The output unit 211 outputs an analog imaging signal corresponding to the transferred signal charge amount.

  The digital signal processing unit 6 is configured by, for example, a DSP, and performs digital signal processing corresponding to the operation mode set by the operation unit 12 on the digital imaging signal from the A / D conversion unit 3. The processing performed by the digital signal processing unit 6 includes black level correction processing (OB processing), linear matrix correction processing, white balance adjustment processing, gamma correction processing, image synthesis processing, synchronization processing, Y / C conversion processing, and the like. included. The image synthesis process is a process of generating synthesized image data obtained by synthesizing high-sensitivity captured image data based on the high-sensitivity imaging signal obtained from the imaging unit 1 and low-sensitivity captured image data based on the low-sensitivity imaging signal. With this image composition processing, the dynamic range of the digital camera 100 can be expanded. The digital camera 100 has a low-sensitivity shooting mode in which only the low-sensitivity captured image data based on the low-sensitivity imaging signal can be generated and recorded without performing this image composition processing.

The digital signal processing unit 6 performs noise reduction processing for reducing noise in a low luminance region of low sensitivity photographed image data based on a low sensitivity imaging signal in the low sensitivity photographing mode. The digital signal processing unit 6 generates a noise reduction signal based on the high-sensitivity imaging signal, and performs the noise reduction process using the noise reduction signal.
The digital signal processing unit 6 has a ratio x of the saturation value of the low-sensitivity imaging signal to the maximum value of the subject luminance that can be taken by the low-sensitivity imaging signal, and The high sensitivity imaging signal is multiplied by a gain for making the saturation value ratio y substantially the same, and the high sensitivity imaging signal multiplied by the gain is used as a noise reduction signal.

  The compression / decompression processing unit 7 performs compression processing on the captured image data (YC data) after the digital processing by the digital signal processing unit 6 and performs expansion processing on the compressed image data obtained from the recording medium 12. Apply.

  The display unit 8 includes an LCD display device, for example, and displays an image based on photographed image data that has been photographed and subjected to digital signal processing. An image is also displayed based on the image data obtained by decompressing the compressed image data recorded on the recording medium. It is also possible to display a through image at the time of shooting, various states of the digital camera, information on operations, and the like.

  The internal memory 10 is, for example, a DRAM and is used as a work memory for the digital signal processing unit 6 and the system control unit 9, as well as a buffer memory and a display unit 8 for temporarily storing image data recorded on the recording medium 12. It is also used as a buffer memory for display image data. The media interface 11 inputs / outputs data to / from a recording medium 12 such as a memory card.

  The system control unit 9 is mainly configured by a processor that operates according to a predetermined program, and performs overall control of the entire digital camera including shooting operations.

  The operation unit 13 performs various operations when using the digital camera.

  Hereinafter, the operation of the digital camera 100 will be described with reference to the drawings. Hereinafter, a case where the sensitivity ratio between the high-sensitivity imaging signal and the low-sensitivity imaging signal output from the imaging unit 1 is 16: 1 will be described as an example. FIG. 3 is a diagram showing an operation flow of the digital camera for explaining the embodiment of the present invention. FIG. 4 is a diagram illustrating the high-sensitivity imaging signal and the low-sensitivity imaging signal that are output from the imaging unit 1 and subjected to A / D conversion.

  When the low sensitivity shooting mode is set by the operation of the operation unit 13 and shooting is performed (S301), an analog high sensitivity imaging signal and a low sensitivity imaging signal are output from the imaging unit 1 (S302). The analog high-sensitivity imaging signal and low-sensitivity imaging signal are converted into digital high-sensitivity imaging signal and low-sensitivity imaging signal after analog signal processing, and are temporarily stored in the internal memory 10 (S303).

  As shown in FIG. 4A, the digital high-sensitivity imaging signal stored in the internal memory 10 reaches a saturation value 4095 with subject luminance c. On the other hand, the digital low-sensitivity imaging signal stored in the internal memory 10 reaches a saturation value of 4095/4 at a subject luminance of 4 × c.

  In order to generate a noise reduction signal, the digital signal processing unit 6 quadruple the low-sensitivity imaging signal (S304) and quadruples the high-sensitivity imaging signal (S305). As a result, as shown in FIG. 4B, the high-sensitivity imaging signal reaches the saturation value 4095/4 at the subject luminance c, and the low-sensitivity imaging signal reaches the saturation value 4095 at the subject luminance 4c. For this reason, the ratio x and the ratio y are substantially the same.

  Thereafter, the digital signal processing unit 6 performs gamma conversion on the low-sensitivity imaging signal after 4 times by using a gamma curve whose slope of the low luminance region is gentler than that of the gamma curve used at the time of image composition processing (S306), Gamma conversion is also performed on the high-sensitivity image pickup signal after ¼ using the same gamma curve (S307). This gamma conversion may be omitted.

  The digital signal processing unit 6 uses the high-sensitivity imaging signal after gamma conversion as a noise reduction signal, and uses the output value up to the subject brightness c that the high-sensitivity imaging signal can take, A process of reducing noise included in a low-luminance area (for example, an area from subject luminance 0 to c) is performed (S308). Noise reduction is performed, for example, by averaging the output value of the low-luminance region of the low-sensitivity imaging signal and the output value up to the subject luminance c that can be taken by the high-sensitivity imaging signal.

  After the noise reduction processing, the digital signal processing unit 6 determines whether or not the maximum value of the subject luminance that can be taken by the low-sensitivity imaging signal is smaller than c (S309). Here, since the maximum value of the subject luminance that can be taken by the low-sensitivity imaging signal is larger than c, the digital signal processing unit 6 performs predetermined digital signal processing on the low-sensitivity imaging signal after the noise reduction processing to obtain a low-sensitivity captured image. Data is generated (S310). The generated low-sensitivity photographed image data is compressed and recorded on the recording medium 12 (S311).

  If the maximum value of the subject luminance that can be taken by the low-sensitivity imaging signal is smaller than c in the determination of S309 (S309: YES), the digital signal processing unit 6 discards the low-sensitivity imaging signal after noise reduction and performs gamma conversion. The subsequent high-sensitivity image pickup signal is subjected to predetermined digital signal processing to generate high-sensitivity captured image data (S312). Then, the process proceeds to S311. In the case of S309: YES, it is also possible to generate low-sensitivity captured image data by performing predetermined digital signal processing on the low-sensitivity imaging signal without discarding the low-sensitivity imaging signal after noise reduction. It is.

  As described above, according to the digital camera 100, when the low-sensitivity shooting mode is set, the noise in the low luminance region of the low-sensitivity captured image data based on the low-sensitivity imaging signal is reduced using the high-sensitivity imaging signal. be able to. For this reason, it is possible to photograph a subject in the highlight area with low sensitivity, and to generate high-quality low-sensitivity photographed image data with little noise even with low sensitivity.

  In the above description, the digital noise reduction signal is generated using the digital high-sensitivity imaging signal and the low-sensitivity imaging signal. However, the analog high-sensitivity imaging signal and low-sensitivity imaging output from the imaging unit 1 are used. An analog noise reduction signal may be generated using the signal. In this case, for example, the analog signal processing unit 2 generates an analog noise reduction signal. Further, the noise of the analog low-sensitivity imaging signal may be reduced in the analog signal processing unit 2 using the noise reduction signal generated in this way.

  In the above, noise reduction processing is performed on the digital low-sensitivity imaging signal. However, noise is applied to low-sensitivity captured image data obtained after predetermined digital signal processing is performed on the digital low-sensitivity imaging signal. Reduction processing may be performed.

  In the above description, the imaging signal is a pixel unit signal of the solid-state imaging device, and the captured image data is digital data obtained by performing RGB interpolation, YC separation processing, or the like on the pixel unit imaging signal. It shows that.

The figure which shows schematic structure of the digital camera for describing embodiment of this invention The figure which shows schematic structure of the solid-state image sensor which can output a high sensitivity image signal and a low sensitivity image signal The figure which shows the operation | movement flow of the digital camera for describing embodiment of this invention The figure which shows the high sensitivity image signal and low-sensitivity image signal after being output from the imaging part of the digital camera for describing embodiment of this invention, and A / D converting

Explanation of symbols

100 Digital Camera 1 Imaging Unit 6 Digital Signal Processing Unit

Claims (5)

A digital camera having a function of acquiring a relatively high-sensitivity imaging signal and a relatively low-sensitivity imaging signal,
A low-sensitivity imaging mode for generating low-sensitivity captured image data based on the low-sensitivity imaging signal;
A noise reduction processing means for performing a noise reduction process for reducing noise in a low luminance region of the low sensitivity photographed image data during the low sensitivity photography mode;
The noise reduction processing means performs the noise reduction processing using a noise reduction signal generated based on the high-sensitivity imaging signal. The digital camera according to claim 1,
Comprising noise reduction signal generation means for generating the noise reduction signal;
The noise reduction signal generation means is configured to provide a ratio of a saturation value of the low-sensitivity imaging signal to a maximum value of the subject luminance that can be taken by the low-sensitivity imaging signal and a maximum subject luminance that can be taken by the high-sensitivity imaging signal. The high-sensitivity imaging signal is multiplied by a gain for making the ratio of the saturation value of the high-sensitivity imaging signal to the value substantially the same, and the high-sensitivity imaging signal multiplied by the gain is used as the noise reduction signal. Digital cameras that are things. The digital camera according to claim 2,
The noise reduction processing means averages the low-brightness region imaging signal of the high-sensitivity imaging signal multiplied by the gain and the low-luminance region imaging signal of the low-sensitivity imaging signal, thereby reducing the noise. A digital camera that performs processing . The digital camera according to claim 2 or 3 ,
The maximum value of the subject brightness that can be taken by the low-sensitivity imaging signal is larger than the maximum value of the subject brightness that can be taken by the high-sensitivity imaging signal multiplied by the gain .   The digital camera according to any one of claims 1 to 4,
  A solid-state imaging device including a first photoelectric conversion element that outputs a relatively high sensitivity photoelectric conversion signal and a second photoelectric conversion element that outputs a relatively low sensitivity photoelectric conversion signal;
  The digital camera in which the high-sensitivity imaging signal is acquired from the first photoelectric conversion element, and the low-sensitivity imaging signal is acquired from the second photoelectric conversion element.

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