JP2005303731A - Signal processor, signal processing method and digital camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a signal processor, a signal processing method and a digital camera capable of reducing noise while preventing the partial deterioration of image quality. <P>SOLUTION: A microcomputer 40 detects a pixel located at an edge of an image displayed by an image signal outputted form a CCD 24 and controls a noise reduction processing part 29 so as not to perform noise reduction processing of pixels located at the edge and so as to perform noise reduction processing of the other pixels. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a signal processing device, a signal processing method, and a digital camera, and in particular, performs noise reduction processing on an image signal output from an imaging unit, and executes and does not execute the noise reduction processing. The present invention relates to a signal processing device configured to be switchable for each pixel, a signal processing method of the signal processing device, and a digital camera including the signal processing device.

  In recent years, the spread of digital cameras has been striking, with annual shipments exceeding that of silver halide cameras.

  By the way, in recent digital cameras, as the S / N ratio (Signal to Noise Ratio) deteriorates as the resolution and sensitivity of imaging devices such as CCD (Charge Coupled Device) and CMOS image sensor increase. Deterioration of image quality due to random noise caused by an imaging system included in an image captured by a camera has become a problem.

In order to solve this problem, conventionally, there has been a technique for reducing noise by performing analog / digital conversion on the output of a solid-state imaging device and filtering the obtained conversion data with a median filter (for example, , See Patent Document 1).
JP-A-4-235472

  However, in the technique of performing the filtering process using the median filter described above, since the filtering process is unconditionally performed on the entire area of the image indicated by the processing target data (conversion data), the image quality partially deteriorates. There was a problem that there was a case.

  That is, the image includes more or less an edge (a color boundary portion in the image), but when a filtering process such as a median filter or a low-pass filter is performed on a pixel located at the edge, The image resolution is apparently lowered (blurred state), and the noise component in the entire image area is reduced, but the image quality at the edge portion may deteriorate.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a signal processing device, a signal processing method, and a digital camera that can reduce noise while preventing partial deterioration in image quality. To do.

  In order to achieve the above object, the signal processing device according to claim 1 performs noise reduction processing on the image signal output from the imaging unit, and performs execution and non-execution of the noise reduction processing on the image signal. Noise reduction processing means configured to be switchable for each pixel, edge pixel detection means for detecting a pixel located at an edge of an image indicated by the image signal, and pixels detected by the edge pixel detection means Control means for controlling the noise reduction processing means so that the noise reduction processing is not executed and the noise reduction processing is executed for other pixels.

  According to the signal processing apparatus of claim 1, the noise reduction processing unit configured to be able to switch between execution and non-execution of the noise reduction processing for each pixel of the image signal output from the imaging unit is used for the image signal. On the other hand, noise reduction processing is executed. Note that the imaging means includes a solid-state imaging device such as a CCD or a CMOS image sensor.

  Here, in the signal processing device of the present invention, pixels located at the edge of the image indicated by the image signal (the boundary portion of the color in the image) are detected by the edge pixel detection means, and the edge pixel detection is performed by the control means. The noise reduction processing means is controlled so that the noise reduction processing is not executed for the pixels detected by the means, and the noise reduction processing is executed for the other pixels.

  Thus, according to the signal processing device of claim 1, the pixel located at the edge of the image indicated by the image signal output from the imaging unit is detected, and noise reduction processing is performed on the pixel located at the edge. Is not executed, and noise reduction processing is controlled for other pixels, so that noise can be reduced while preventing partial deterioration in image quality.

  The edge pixel detection means according to the present invention, as in the invention according to claim 2, calculates a difference in signal level between neighboring pixels having a predetermined positional relationship for each pixel in the image signal. It is preferable to derive and detect a pixel whose difference is greater than or equal to a preset threshold as a pixel located at the edge. Thereby, the pixel located at the edge can be detected by a simple process of only derivation of the difference and comparison with the threshold value.

  In particular, the invention described in claim 2 is, as in the invention described in claim 3, a shooting condition detection unit that detects a shooting condition at the time of imaging when the image signal is output by the imaging unit, and the shooting. It is preferable to further comprise threshold setting means for setting the threshold according to the photographing condition detected by the condition detecting means. This makes it possible to detect a pixel located at an edge using a suitable threshold value corresponding to the shooting condition, and improve the detection accuracy.

  Furthermore, the invention according to claim 3 is a threshold value for correcting the threshold value set by the threshold value setting means so as to decrease as the pixel level of the pixel to be processed increases, as in the invention according to claim 4. It is preferable to further include a correction unit. As a result, it is possible to cope with the fact that the higher the pixel level, that is, the brighter the pixel is, the less likely the noise component becomes noticeable and the less likely it is to be erroneously determined to be an edge. The noise reduction process can be executed effectively.

  Further, according to the third or fourth aspect of the present invention, as in the fifth aspect of the present invention, the image in the case where the image capturing unit outputs a color image signal is set as the image capturing condition. It can be a light source type for white balance adjustment processing between the colors indicated by the signal. Accordingly, it is possible to detect a pixel located at an edge using a suitable threshold value corresponding to a light source type for white balance adjustment processing, and it is possible to further improve the detection accuracy.

  On the other hand, according to the present invention, as in the invention described in claim 6, the imaging means is provided corresponding to each pixel so that a plurality of color filters are arranged in a predetermined arrangement for capturing a color image. The edge pixel detecting means detects a pixel located at an edge of the image indicated by the image signal for each color of the color filter, and the control means reduces the noise for each color of the color filter. It is preferable to control the processing means. As a result, the pixel located at the edge can be detected with high accuracy, and noise reduction processing can be performed with high accuracy without color mixing.

  Particularly, the invention according to claim 6 is obtained by the array type acquisition means for acquiring the array type information indicating the array type of the color filter and the array type acquisition means, as in the invention according to claim 7. It is preferable to further comprise switching means for switching the processing content of the noise reduction processing according to the arranged type information. Thereby, a suitable noise reduction process according to the arrangement type of the color filter can be executed, and the noise reduction process can be executed effectively.

  Furthermore, according to the present invention, it is preferable that the noise reduction processing unit executes the noise reduction processing using a non-linear filter. The non-linear filter is more effective in removing one-shot noise than the linear filter and does not cause a decrease in spatial frequency, so that the noise reduction process can be executed effectively.

  On the other hand, in order to achieve the above object, the signal processing method according to claim 9 performs the noise reduction process on the image signal output from the imaging unit, and performs the execution and non-execution of the noise reduction process. A signal processing method of a signal processing device configured to be switchable for each pixel of an image signal, wherein a pixel located at an edge of an image indicated by the image signal is detected, and the noise reduction processing is performed on the detected pixel. The non-execution is performed, and the other pixels are controlled to execute the noise reduction process.

  Therefore, since the signal processing method according to the ninth aspect operates in the same manner as the invention according to the first aspect, the noise can be reduced while preventing partial deterioration of the image quality, similarly to the first aspect. Can do.

  On the other hand, in order to achieve the above object, a digital camera according to a tenth aspect includes the signal processing device according to any one of the first to eighth aspects and the imaging means.

  Therefore, since the digital camera according to claim 10 operates in the same manner as the invention according to claim 1, it is possible to reduce noise while preventing partial deterioration of the image quality, similarly to the invention according to claim 1. it can.

  According to the present invention, the pixel located at the edge of the image indicated by the image signal output from the imaging means is detected, the noise reduction processing is not executed for the pixel located at the edge, and the noise is detected for the other pixels. Since the control is performed so as to execute the reduction process, it is possible to reduce noise while preventing partial deterioration in image quality.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings. Here, the case where the signal processing apparatus and the signal processing method according to the present invention are applied to a digital camera will be described.

  First, an external configuration of the digital camera 10 according to the present embodiment will be described with reference to FIG.

  In front of the digital camera 10, a lens 21 for forming a subject image, a strobe 44 that emits light to irradiate the subject when necessary, and a viewfinder used to determine the composition of the subject to be photographed. 20 is provided. Further, on the upper surface of the digital camera 10, a release button (so-called shutter) 56A that is pressed when performing shooting and a power switch 56B are provided.

  Note that the release button 56A of the digital camera 10 according to the present embodiment is pressed down to an intermediate position (hereinafter referred to as “half-pressed state”) and to a final pressed position beyond the intermediate position. A two-stage pressing operation of a state (hereinafter referred to as a “fully pressed state”) can be detected.

  In the digital camera 10, the release button 56A is pressed halfway to activate the AE (Automatic Exposure) function to set the exposure state (shutter speed, aperture state), and then AF (Auto Focus). , Automatic focusing) function is performed to control focusing, and then exposure (photographing) is performed when the button is fully pressed.

  On the other hand, on the back surface of the digital camera 10, an eyepiece of the finder 20 described above and a liquid crystal display (hereinafter referred to as “LCD”) 38 for displaying a photographed subject image, a menu screen, and the like are provided. It has been.

  Also, on the back of the digital camera 10, a mode changeover switch 56C that is slid to be set to any one of a photographing mode that is a photographing mode and a reproduction mode that is a mode for reproducing a subject image by the LCD 38, Further, a cross cursor button 56D and a forced light emission switch 56E that is pressed when setting the forced light emission mode, which is a mode for forcibly causing the flash 44 to emit light at the time of shooting, are further provided.

  The cross-cursor button 56D includes four arrow keys that indicate four moving directions of up, down, left, and right in the display area of the LCD 38.

  Next, the main configuration of the electrical system of the digital camera 10 according to the present embodiment will be described with reference to FIG.

  The digital camera 10 includes an optical unit 22 including the lens 21 described above, a charge coupled device (hereinafter referred to as “CCD”) 24 disposed behind the optical axis of the lens 21, and an input analog. And an analog signal processing unit 26 that performs various analog signal processing on the signal.

  The CCD 24 is provided with color filters of R (red), G (green), and B (blue) according to a predetermined arrangement on the light receiving surface of each light receiving element. Here, examples of the predetermined array include a Bayer array illustrated in FIG. 3A and a honeycomb array illustrated in FIG.

  In each of these color filter arrays, the number of G color filters is doubled with respect to R and B, and even if any color filter array is applied, the CCD 24 , R and B analog signals are output in time series and intermittently. Accordingly, in any color filter array, signal processing (so-called synchronization processing) is performed in which intermittent R and B pixel signals are generated by interpolation with pixel signals of surrounding pixels.

  In any color filter array, one pixel in the subject image is represented by pixel signals obtained by the four light receiving element groups adjacent to each other in the CCD 24. In the digital camera 10 according to the present embodiment, a CCD whose color filter array is a Bayer array or a honeycomb array is applicable as the CCD 24.

  On the other hand, as shown in FIG. 2, the digital camera 10 includes an analog / digital converter (hereinafter referred to as “ADC”) 28 that converts an input analog signal into digital data, and an input digital data. A noise reduction processing unit 29 that performs noise reduction processing and a digital signal processing unit 30 that performs various types of digital signal processing on input digital data are included.

  In the noise reduction processing unit 29, digital image data (pixel data) for each pixel is converted into a color filter having the same color as that of the pixel (hereinafter referred to as “target pixel”) and the color filter of the target pixel. And a plurality (four in this case) of peripheral pixels (hereinafter referred to as “peripheral pixels of the same color”) that have a predetermined positional relationship with respect to the pixel of interest according to the arrangement state of the color filter. The noise reduction process is performed by a filter process using a so-called median filter that uses the median value of the pixel data of each pixel.

  In the digital camera 10 according to the present embodiment, when the arrangement of the color filters provided in the CCD 24 is the Bayer array shown in FIG. 3A, the pixel of interest (center of FIG. And the median value of a total of five pieces of pixel data of four neighboring pixels of the same color (pixels of the same filter color closest to the top, bottom, left, and right of the target pixel) are applied as the pixel data of the target pixel. . On the other hand, when the arrangement of the color filters provided in the CCD 24 is the honeycomb arrangement shown in FIG. 3B, the pixel of interest (pixel in the center of the figure) indicated by the diagonal lines in FIG. A median value of a total of five pixel data of pixels (pixels of the same filter color closest to the upper left, lower left, upper right, and lower right of the target pixel) is applied as the pixel data of the target pixel. In FIG. 3, among the R, G, and B colors, the target pixel of the noise reduction process for the R pixel is illustrated, but the positional relationship between the pixel of interest and the same color peripheral pixel for G and B also Are the same, and noise reduction processing similar to R is performed.

  In addition, the noise reduction processing unit 29 is configured to be switchable for each pixel of digital data that has been input to execute or not execute the noise reduction processing in accordance with an external instruction input.

  On the other hand, the digital signal processing unit 30 incorporates a line buffer having a predetermined capacity, and also performs control to directly store the input digital data in a predetermined area of the memory 48 described later.

  The output end of the CCD 24 is the input end of the analog signal processing unit 26, the output end of the analog signal processing unit 26 is the input end of the ADC 28, the output end of the ADC 28 is the input end of the noise reduction processing unit 29, and the noise reduction processing unit 29 Are connected to input terminals of the digital signal processing unit 30, respectively. Therefore, the analog signal indicating the subject image output from the CCD 24 is subjected to predetermined analog signal processing by the analog signal processing unit 26, converted into digital image data by the ADC 28, and then subjected to noise reduction processing by the noise reduction processing unit 29. And then input to the digital signal processing unit 30.

  On the other hand, the digital camera 10 includes a microcomputer 40 that controls the operation of the entire digital camera 10 and a memory 48 that temporarily stores digital image data obtained by photographing. The microcomputer 40 incorporates a nonvolatile memory 40A in which various programs, parameters, and the like are stored in advance.

  Further, the digital camera 10 is configured such that a portable recording medium 52 is detachable, and the recording medium 52 can be accessed by the digital signal processing unit 30 with the recording medium 52 mounted.

  In the digital camera 10 according to the present embodiment, a VRAM (Video RAM) is used as the memory 48 and a smart media (Smart Media®) is used as the recording medium 52.

  Further, the digital camera 10 includes a compression / decompression processing unit 54 that performs compression processing and decompression processing on digital image data.

  Further, the digital camera 10 is provided with a digital / analog converter (hereinafter referred to as “DAC”) 60 that converts input digital data into an analog signal, and cooperates with the digital signal processing unit 30. A video signal indicating an image to be displayed on the LCD 38 (in this embodiment, an NTSC signal) can be generated and output as a video output from a video output terminal (not shown).

  On the other hand, the digital camera 10 includes a timing generator 32 that mainly generates a timing signal for driving the CCD 24 and supplies the timing signal to the CCD 24, and the driving of the CCD 24 is controlled by the microcomputer 40 via the timing generator 32. The

  The microcomputer 40 is connected to the input end of the motor drive unit 62, and the output end of the motor drive unit 62 is connected to the focus adjustment motor, zoom motor, and aperture drive motor provided in the optical unit 22.

  The lens 21 according to the present embodiment has a plurality of lenses, is configured as a zoom lens that can change (magnify) the focal length, and includes a lens driving mechanism (not shown). The lens drive mechanism includes the focus adjustment motor, the zoom motor, and the aperture drive motor. The focus adjustment motor, the zoom motor, and the aperture drive motor are supplied from the motor drive unit 62 under the control of the microcomputer 40, respectively. Driven by a drive signal.

  When changing the optical zoom magnification, the microcomputer 40 controls the zoom motor to change the focal length of the lens 21 included in the optical unit 22.

  Further, the microcomputer 40 performs focus control by driving and controlling the focus adjustment motor so that the contrast of an image obtained by imaging by the CCD 24 is maximized. In other words, the digital camera 10 according to the present embodiment employs a so-called TTL (Through The Lens) method in which the lens position is set so that the contrast of the read image is maximized as the focus control. .

  The microcomputer 40 is also connected to the noise reduction processing unit 29, the digital signal processing unit 30, the strobe 44, and the compression / decompression processing unit 54, and can control the operation of each of these parts. The noise reduction processing unit 29 also has a role of outputting digital image data input from the ADC 28 to the microcomputer 40.

  Further, the release button 56A, the power switch 56B, the mode changeover switch 56C, the cross cursor button 56D, and the forced light emission switch 56E (generically referred to as “operation unit 56” in the figure) are connected to the microcomputer 40. The microcomputer 40 can always grasp the operation state of the operation unit 56.

  In the digital camera 10 according to the present embodiment, as the CCD 24 to be applied, a plurality of types of different color filter arrays (here, the Bayer array shown in FIG. 3A and the honeycomb shown in FIG. 3B) are used. Two types of arrangements) can be selectively applied. For this reason, the digital camera 10 is provided with an array changeover switch 56 </ b> F for setting the type of color filter array in the applied CCD as a part of the operation unit 56. The arrangement changeover switch 56F is set by the manufacturer of the digital camera 10 at the time of product assembly, and is provided inside the housing of the digital camera 10.

  In the digital camera 10 according to the present embodiment, for white balance adjustment processing, suitable gain values for white balance adjustment processing corresponding to preset light source types are set for each of R, G, and B. And it is memorize | stored beforehand in the predetermined area | region of memory 40A for every predetermined several light source types (for example, fluorescent lamp, a light bulb, sunlight, shade light, etc.).

  Next, the overall operation of the digital camera 10 according to the present embodiment in the shooting mode will be briefly described.

  First, a subject image is picked up by the CCD 24, and analog signals for R, G, and B indicating the subject image are sequentially output to the analog signal processing unit 26. The analog signal processing unit 26 performs analog signal processing such as correlated double sampling processing on the analog signal input from the CCD 24 and sequentially outputs the analog signal to the ADC 28.

  The ADC 28 converts the R, G, and B analog signals input from the analog signal processing unit 26 into 12-bit R, G, and B signals (digital image data) and sequentially outputs them to the noise reduction processing unit 29. To do.

  The noise reduction processing unit 29 subjects the digital image data sequentially input from the ADC 28 to filter processing using a built-in noise reduction filter (median filter), and sequentially outputs the digital image data to the digital signal processing unit 30. The digital signal processing unit 30 accumulates digital image data sequentially input from the noise reduction processing unit 29 in a built-in line buffer and temporarily stores the digital image data directly in a predetermined area of the memory 48.

  Digital image data stored in a predetermined area of the memory 48 is read out by the digital signal processing unit 30 in accordance with control by the microcomputer 40, and a digital gain corresponding to a predetermined physical quantity is applied to each of R, G, and B. The white balance adjustment process and sharpness process are performed to generate 8-bit digital image data.

  Then, the digital signal processing unit 30 performs YC signal processing on the generated 8-bit digital image data to perform luminance signal Y and color difference signals Cr (= R−Y), Cb (= B−Y) (hereinafter, “ YC signal ") is generated, and the YC signal is stored in an area different from the predetermined area of the memory 48.

  The LCD 38 is configured to display a moving image (through image) obtained by continuous imaging by the CCD 24 and can be used as a finder. When the LCD 38 is used as a finder, the LCD 38 is generated. The YC signals thus obtained are sequentially supplied to the LCD 38 as image signals. As a result, a through image is displayed on the LCD 38.

  Here, when the release button 56A is half-pressed by the user, after the AE function is activated and the exposure state is set as described above, the AF function is activated and focus control is performed, and then the fully-pressed state is continued. In this case, the YC signal stored in the memory 48 at this time is compressed in a predetermined compression format (in this embodiment, JPEG format) by the compression / expansion processing unit 54 and then recorded on the recording medium 52. .

  By the way, in the digital camera 10, noise reduction control processing for controlling the noise reduction processing by the noise reduction processing unit 29 is executed during imaging by the CCD 24. Hereinafter, the noise reduction control process will be described with reference to FIG. FIG. 4 is a flowchart showing a processing flow of a noise reduction control processing program executed in the microcomputer 40 every predetermined period (in this embodiment, an imaging period per image) during imaging by the CCD 24. The program is stored in advance in the memory 40A.

  In step 100 of the figure, information indicating a predetermined shooting condition (here, the light source type for white balance adjustment processing) set in the digital camera 10 at this time is acquired, and acquired in the next step 102. A gain value for each of R, G, and B for white balance adjustment processing corresponding to the light source type is read out from the memory 40A, and the gain value is derived for each of the derived R, G, and B in the next step 104. A threshold value for each of R, G, and B for edge detection described later is derived according to the gain value.

  In the present embodiment, in the present step 104, the threshold value is derived so as to increase as the gain value of the corresponding color increases. The reason for deriving the threshold in this way is to cope with this because the higher the gain value, the higher the degree of noise enhancement, and the higher the possibility that it will be erroneously determined to be an edge. is there.

  The processing from the next step 106 to step 120 is executed for each color (R, G, B) of the color filter provided in the CCD 24 for the digital image data to be processed. Here, the filter color that is the execution target of the process is hereinafter referred to as a “process target color”.

  First, in step 106, whether or not the type of the color filter array of the CCD 24 is a predetermined type (here, the Bayer array (see also FIG. 3A)) according to the setting state of the array switch 56F. If the determination is affirmative, the process proceeds to step 108.

  In step 108, for the rectangular image area of a predetermined number of horizontal pixels × a predetermined number of vertical pixels (here, 5 pixels × 5 pixels) in the image indicated by the digital image data to be processed, the predetermined type of color Digital image data (pixel data) of a predetermined number (here, 5) of pixels (hereinafter referred to as “application target pixels”) positioned at predetermined positions corresponding to the filter array (Bayer array). Based on this, an evaluation value for edge detection, which will be described later, of the pixel located at the center of the image region is calculated, and then the process proceeds to step 112.

  On the other hand, if a negative determination is made in the process of step 106, the process proceeds to step 110, where the predetermined number of horizontal pixels × the predetermined number of vertical pixels in the image indicated by the digital image data to be processed (here, 5 Application of a predetermined number (here, 5) of rectangular image areas (pixels × 5 pixels) positioned in a predetermined position corresponding to the color filter array (honeycomb array) on the non-predetermined type side Based on the pixel data of the target pixel, an evaluation value for edge detection, which will be described later, of the pixel located at the center of the image region is calculated, and then the process proceeds to step 112. The step 108 and the step 110 are for calculating an evaluation value of a pixel located at the center of the rectangular image area having the predetermined number of horizontal pixels × the predetermined number of vertical pixels. Then, it is called “processing target pixel”.

  In the digital camera 10 according to the present embodiment, the application target pixels when the color filter of the CCD 24 is a Bayer array are pixels indicated by hatching in FIG. 3A, that is, the processing target pixels and the processing target. There are five pixels, four pixels of the same filter color that are closest to the top, bottom, left, and right of the pixel.

  Then, in step 108, as shown in FIG. 5A, the difference value (absolute value) of pixel data between the processing target pixel in the application target pixel and the remaining application target pixels is used as the evaluation value. To derive. Specifically, as shown in FIG. 5B, when the pixel data of the processing target pixel is D3, and the pixel data of the remaining four application target pixels are D1, D2, D4, and D5, the above steps In 108, the difference value is calculated by the following equations (1) to (4).

SUB1 = abs (D1-D3) (1)
SUB2 = abs (D2-D3) (2)
SUB3 = abs (D4-D3) (3)
SUB4 = abs (D5-D3) (4)
Note that abs (X) in each of the above arithmetic expressions represents taking the absolute value of X.

  Further, in the digital camera 10 according to the present embodiment, the pixel to be applied when the color filter of the CCD 24 has a honeycomb arrangement is the pixel indicated by the oblique lines in FIG. 3B, that is, the pixel to be processed and the pixel to be processed. There are five pixels, four pixels of the same filter color that are closest to the upper left, lower left, upper right, and lower right of the pixel.

  In step 110, as shown in FIG. 6A, the difference value (absolute value) of pixel data between the processing target pixel in the application target pixel and the remaining application target pixels is used as the evaluation value. To derive. Specifically, as shown in FIG. 6B, when the pixel data of the processing target pixel is E3 and the pixel data of the remaining four application target pixels are E1, E2, E4, and E5, respectively, At 110, the difference value is calculated by the following equations (5) to (8).

SUB1 = abs (E1-E3) (5)
SUB2 = abs (E2-E3) (6)
SUB3 = abs (E4-E3) (7)
SUB4 = abs (E5-E3) (8)
In step 112, the threshold value of the processing target color derived by the processing in step 104 is corrected according to the pixel data of the processing target pixel used in step 108 or step 110, and then the process proceeds to step 114.

  In the present embodiment, in the above step 112, the threshold value of the processing target color is corrected so that the smaller the pixel data value of the processing target pixel, the smaller the value. The reason for correcting the threshold in this way is that as the pixel data value increases, that is, the brightness of the pixel becomes brighter, the noise component becomes less conspicuous and the possibility of erroneous determination as an edge is low. This is to cope with this.

  In step 114, it is determined whether or not the evaluation values SUB1 to SUB4 derived by the processing in step 108 or step 110 are equal to or greater than the threshold value of the processing target color. Assuming that the pixel is not located at the edge, the process proceeds to step 116, where an instruction is input to the noise reduction processing unit 29 so as to execute the noise reduction process on the processing target pixel, and then the process proceeds to step 120.

  On the other hand, if the determination in step 114 is affirmative, it is assumed that the processing target pixel is located at the edge, and the process proceeds to step 118 to instruct the noise reduction processing unit 29 not to perform the noise reduction processing on the processing target pixel. After inputting, the process proceeds to step 120.

  In step 120, it is determined whether or not the processing of step 106 to step 118 has been completed for all pixels of the processing target color. If the determination is negative, the process returns to step 106, and the step is performed when the determination is affirmative. 122. Note that, when the processes of Step 106 to Step 120 are repeatedly executed, pixels of the processing target color that have not been set as processing target pixels are set as processing target pixels.

  In step 122, it is determined whether or not the processing of step 106 to step 120 has been completed for all the R, G, and B filter colors. If a negative determination is made, the process returns to step 106 to make an affirmative determination. At this point, the noise reduction control processing program ends. Note that, when the processes of Step 106 to Step 122 are repeatedly executed, filter colors that have not been set as processing target colors so far are set as processing target colors.

  With this noise reduction control processing program, the noise reduction processing is not executed for the pixels located at the edge and the noise reduction processing is executed for the other pixels with respect to the digital image data that is the target of the noise reduction processing. As a result, the digital image data output from the noise reduction processing unit 29 to the digital signal processing unit 30 is not subjected to the noise reduction processing for the pixels located at the edges. It is assumed that noise reduction processing has been performed for the pixels.

  As described above in detail, according to the present embodiment, the pixel located at the edge of the image indicated by the image signal output from the CCD 24 is detected, and noise reduction processing is not performed on the pixel located at the edge. Since execution is controlled so that noise reduction processing is executed for other pixels, noise can be reduced while preventing partial deterioration in image quality.

  Further, according to the present embodiment, a signal level difference (in this case, the evaluation values SUB1 to SUB4) between neighboring pixels having a predetermined positional relationship for each pixel in the image signal is derived, Since a pixel whose difference is equal to or greater than a preset threshold value is detected as a pixel located at the edge, a pixel located at the edge can be detected by simple processing of only derivation of the difference and comparison with the threshold value. .

  In addition, according to the present embodiment, the photographing condition at the time of imaging when the image signal is output by the CCD 24 is detected, and the threshold value is set according to the detected photographing condition. A pixel located at the edge can be detected using a suitable threshold value, and the accuracy of the detection can be improved.

  Further, according to the present embodiment, since the set threshold value is corrected so as to decrease as the pixel level of the pixel to be processed increases, the higher the pixel level, that is, the brightness of the pixel. As the brightness becomes brighter, the noise component becomes less conspicuous and the possibility of erroneous determination as an edge can be reduced. As a result, the noise reduction processing can be effectively executed.

  Further, according to the present embodiment, since the photographing condition is the light source type for white balance adjustment processing between the colors indicated by the image signal when the CCD 24 outputs a color image signal. The pixel located at the edge can be detected using a suitable threshold value corresponding to the light source type for white balance adjustment processing, and the accuracy of the detection can be further improved.

  Further, according to the present embodiment, the CCD 24 is provided corresponding to each pixel so that a plurality of color filters are arranged in a predetermined arrangement in order to capture a color image, and for each color of the color filter. In addition, the pixel located at the edge of the image indicated by the image signal is detected and the noise reduction processing unit 29 is controlled for each color of the color filter, so that the pixel located at the edge can be detected with high accuracy. In addition, it is possible to perform noise reduction processing with high accuracy without color mixing.

  Further, according to the present embodiment, information indicating the type of the color filter array is acquired, and the processing content of the noise reduction processing is switched according to the acquired array type. Therefore, the preferred noise reduction process can be executed, and the noise reduction process can be executed effectively.

  Furthermore, according to the present embodiment, since the noise reduction processing is executed by a non-linear filter (here, a median filter), the non-linear filter has an effect of removing one-shot noise as compared with the linear filter. Therefore, noise reduction processing can be effectively executed.

  It should be noted that the flow of processing of the noise reduction control processing program described in the present embodiment (see FIG. 4) is an example, and it goes without saying that it can be changed as appropriate without departing from the gist of the present invention.

  For example, in step 108 of the noise reduction control processing program, the case where the evaluation values SUB1 to SUB4 are calculated using the application target pixels as the five pixels indicated by the oblique lines in FIG. 3A has been described, but the present invention is not limited to this. For example, as shown in FIG. 7, in addition to these pixels, pixels of the same color that are closest to the upper left, lower left, upper right, and lower right of the processing target pixel are set as application target pixels. The difference value (absolute value) between the pixel data of the pixel and the pixel data of the processing target pixel can be included in the evaluation value. In this case, although the calculation load of the evaluation value increases, edge determination can be performed with higher accuracy.

  In the noise reduction control processing program, the case where the light source type for white balance adjustment processing is applied as the photographing condition of the present invention has been described. However, the present invention is not limited to this, for example, ISO 100, Sensitivity setting values such as ISO 200, exposure time setting values, and the like can also be applied. When a sensitivity setting value is applied as a shooting condition, a threshold value for each of R, G, and B is derived so as to increase as the sensitivity increases, and when an exposure time setting value is applied as a shooting condition, the exposure time. The threshold value for each of R, G, and B is derived so as to increase as the value of becomes longer. In these cases, the same effects as in the present embodiment can be obtained.

  Furthermore, in the noise reduction control processing program, the case where the arrangement position of pixels (application target pixels) used for edge determination is switched as switching of noise reduction processing according to the type of color filter array provided in the CCD 24 has been described. The present invention is not limited to this. For example, the threshold deriving method by the process of step 104 of the noise reduction control processing program is switched, or the threshold correction method by the process of step 112 is switched. You can also. Also in this case, the same effects as in the present embodiment can be obtained.

  The configuration of the digital camera 10 described in this embodiment (see FIGS. 1 to 3) is also an example, and it is needless to say that the configuration can be appropriately changed without departing from the gist of the present invention.

  For example, in the present embodiment, the case where the microcomputer 40 performs the edge determination and the noise reduction processing setting for the noise reduction processing unit 29 has been described. However, the present invention is not limited to this, for example, The noise reduction processing unit 29 itself may be configured.

  In this case, the noise reduction processing unit 29 has a built-in microcomputer that executes the noise reduction control processing program according to the present embodiment, or has a built-in hardware that executes processing similar to the processing by the program. become.

  Also in this case, the same effects as in the present embodiment can be obtained.

  Further, in the present embodiment, the case where the median filter is applied as the nonlinear filter of the present invention has been described. However, the present invention is not limited to this, and other examples such as a Wiener filter are used. It is also possible to apply a non-linear filter. Also in this case, the same effects as in the present embodiment can be obtained.

  In this embodiment, the case where the signal processing apparatus and the signal processing method according to the present invention are applied to a digital camera has been described. However, the present invention is not limited to this, and for example, a CCD, a CMOS image, Applicable to various information processing devices such as PDAs (Personal Digital Assistants, personal digital assistants), mobile phones, computers, etc. that have built-in imaging means such as sensors or that can input image signals acquired by the imaging means You can also Also in this case, the same effects as in the present embodiment can be obtained.

It is an external view which shows the external appearance of the digital camera which concerns on embodiment. It is a block diagram which shows the main structures of the electric system of the digital camera which concerns on embodiment. FIG. 4 is a schematic diagram illustrating an example of an arrangement of color filters for R, G, and B colors provided on a light receiving surface of a light receiving element of a CCD according to an embodiment, and an arrangement state of pixels applied in noise reduction processing and edge determination. FIG. 4A is a schematic diagram illustrating an example of a Bayer array, and FIG. It is a flowchart which shows the flow of a process of the noise reduction control processing program which concerns on embodiment. It is the schematic where it uses for description of the arithmetic expression of the evaluation value applied in the edge determination which concerns on embodiment when the arrangement | sequence of a color filter is a Bayer arrangement. FIG. 6 is a schematic diagram for explaining an arithmetic expression of evaluation values applied in edge determination according to the embodiment when the arrangement of color filters is a honeycomb arrangement. It is the schematic which shows the other example of the arrangement | positioning state of the pixel applied to edge determination in case the arrangement | sequence of a color filter is a Bayer arrangement.

Explanation of symbols

10 Digital camera 24 CCD (Imaging means)
29 Noise reduction processing section (noise reduction processing means)
40 Microcomputer (edge pixel detection means, control means, photographing condition detection means, threshold setting means, threshold correction means, switching means)
56F array changeover switch (array type acquisition means)

Claims (10)

Noise reduction processing means configured to perform noise reduction processing on the image signal output from the imaging means, and to switch execution and non-execution of the noise reduction processing for each pixel of the image signal;
Edge pixel detection means for detecting a pixel located at an edge of the image indicated by the image signal;
Control means for controlling the noise reduction processing means so as not to execute the noise reduction processing for the pixels detected by the edge pixel detection means, and to execute the noise reduction processing for other pixels;
A signal processing apparatus comprising: The edge pixel detection means derives a signal level difference from neighboring pixels having a predetermined positional relationship for each pixel in the image signal, and determines a pixel whose difference is equal to or greater than a preset threshold value. The signal processing device according to claim 1, wherein the signal processing device is detected as a pixel located at the edge. Shooting condition detection means for detecting shooting conditions at the time of imaging when outputting the image signal by the imaging means;
Threshold setting means for setting the threshold according to the shooting conditions detected by the shooting condition detection means;
The signal processing apparatus according to claim 2, further comprising: The signal processing device according to claim 3, further comprising: a threshold correction unit that corrects the threshold set by the threshold setting unit so that the threshold level of the pixel to be processed increases as the pixel level increases. The light source type for white balance adjustment processing between each color indicated by the image signal when the imaging unit outputs an image signal of a color image is used as the photographing condition. Signal processing device. The imaging means is provided corresponding to each pixel so that a plurality of color filters are arranged in a predetermined arrangement in order to capture a color image,
The edge pixel detecting means detects a pixel located at an edge of an image indicated by the image signal for each color of the color filter;
The signal processing apparatus according to claim 1, wherein the control unit controls the noise reduction processing unit for each color of the color filter. Array type acquisition means for acquiring array type information indicating an array type of the color filter;
Switching means for switching the processing content of the noise reduction processing according to the array type information acquired by the array type acquisition means;
The signal processing device according to claim 6, further comprising: The signal processing device according to claim 1, wherein the noise reduction processing unit performs the noise reduction processing using a nonlinear filter. A signal processing method of a signal processing apparatus configured to perform noise reduction processing on an image signal output from an imaging unit and to switch execution and non-execution of the noise reduction processing for each pixel of the image signal. There,
Detecting pixels located at the edge of the image indicated by the image signal;
The noise reduction processing is not executed for the detected pixels, and the other pixels are controlled to execute the noise reduction processing.
Signal processing method. A signal processing device according to any one of claims 1 to 8,
The imaging means;
Digital camera equipped with.

Images