JP2007043312A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus which can reduce a false color and color bleeding generated in a photographed image. <P>SOLUTION: A system controller 11 acquires spectral sensitivity data (Qr, Qb) showing spectral sensitivity characteristics of a CCD image sensor 14 from a ROM 11a. The system controller 11 selects a filter with the most suitable strength for preventing the false color and the color bleeding based on spectral sensitivity Qr, and similarly selects a filter with the most suitable strength based on the spectral strength Qb. The system controller 11 controls an LPF 35 for Cr, and carries out filter operation processing corresponding to the selected filter for the color-difference signal Cr, similarly controls an LPF 36 for Cb, and carries out filter operation processing corresponding to the selected filter for the color-difference signal Cb. Consequently, it is possible to reduce the false color and the color bleeding generated in the photographed image. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photographing apparatus that prevents false colors and color bleeding that occur in a photographed image.

  In recent years, digital cameras that record image data acquired by an image sensor such as a CCD image sensor have been widely used as photographing apparatuses. Such a digital camera converts an image signal picked up by a CCD image sensor into image data of a digital signal, and then performs a YC conversion process on the image data to obtain a luminance signal Y and two color difference signals Cr, The image data is recorded after being converted into Cb and subjected to compression processing.

Further, in the digital camera as described above, in order to improve the S / N ratio of the color difference signals Cr and Cb, or to reduce the false color that is the saturation noise displayed as the color spot in the photographed image, Low frequency filter processing is performed on the color difference signals Cr and Cb, that is, the high frequency components of the color difference signals Cr and Cb are removed to control the frequency band. As described above, for example, an image processing device described in Patent Document 1 and an endoscope television system described in Patent Document 2 are known as devices that control the frequency bands of the color difference signals Cr and Cb of image data.
JP 2004-194121 A JP-A-5-103758

  However, when the strength of the low-pass filter is increased, the S / N ratio can be improved and the false color can be reduced, but there is a problem that a color blur occurs in the captured image. For example, although the S / N ratio of the chrominance signal Cr is good, the false color due to the chrominance signal Cb is large. Therefore, if the low-pass filter processing with the same intensity is performed, the frequency band of the chrominance signal Cr is limited more than necessary. As a result, color blur occurs in the captured image. In the image processing apparatus and the endoscope television system described in Patent Documents 1 and 2 described above, the frequency bands of the color difference signals Cr and Cb are not separately controlled by the low-pass filter. I can't.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a photographing apparatus capable of reducing false color and color blur that occur in a photographed image.

  In order to solve the above-described problems, the imaging apparatus of the present invention performs YC conversion processing on image data obtained by converting an imaging signal output from an imaging element into a digital signal, and then the image data. A low-pass filter for Cr that limits the frequency band by removing the high-frequency component of the color difference signal Cr from the image data after the YC conversion process, and the color difference signal Cb of the image data. And a control means for controlling each of the Cr low-pass filter and the Cb low-pass filter. .

  Further, it is preferable that the control unit controls the Cr low-pass filter and the Cb low-pass filter based on a spectral sensitivity characteristic of the imaging element.

  Furthermore, it comprises white balance detection means for detecting an evaluation value of white balance, and the control means calculates a correction gain for correcting the white balance based on the evaluation value detected by the white balance detection means, The Cr low-pass filter and the Cb low-pass filter may be controlled based on the correction gain.

  Further, the control means may control the Cr low-pass filter and the Cb low-pass filter based on a photographing mode set at the time of photographing.

  Further, the control means calculates the magnitude of chromatic aberration based on the zoom lens position, the aperture value, and the focal length, and determines the Cr low-pass filter and the Cb low-pass filter based on the chromatic aberration magnitude. You may control.

  According to the photographing apparatus of the present invention, the Cr low-pass filter that limits the frequency band by removing the high frequency component of the color difference signal Cr, and the Cb low pass filter that limits the frequency band by removing the high frequency component of the color difference signal Cb. Since the filter and the low-pass filter for Cr and Cb are separately controlled by the control means, it is possible to perform low-pass filter processing with optimum intensity on each of the color difference signals Cr and Cb. The occurrence of color blur can be suppressed.

  Further, the control means can control the low-pass filter for Cr and Cb based on the spectral sensitivity data of the image sensor, and can perform low-pass filter processing with optimum intensity on each of the color difference signals Cr and Cb. In addition, it is possible to suppress the occurrence of false color and color blur due to the spectral sensitivity characteristics of the image sensor.

  Furthermore, the control means can control the low-pass filter for Cr and Cb based on the gain for correcting the white balance, and can perform the low-pass filter process with the optimum intensity on each of the color difference signals Cr and Cb. Yes, it is possible to suppress the occurrence of false color and color blur due to the correction gain for correcting the white balance.

  Further, the control means can control the Cr and Cb low-pass filters based on the set photographing mode, and can perform the low-pass filter processing with the optimum intensity on each of the color difference signals Cr and Cb. Yes, it is possible to suppress the occurrence of false colors and color blurs caused by the currently set shooting mode.

  Further, the control means acquires information on the zoom lens position, the aperture value, and the focal length, calculates the magnitude of chromatic aberration based on the information, and uses Cr and Cb based on the magnitude of the chromatic aberration. In order to control the low-pass filter, it is possible to perform low-pass filter processing with optimum intensity on each of the color difference signals Cr and Cb. Therefore, in the case of the zoom lens position, aperture value, and focal length where chromatic aberration is conspicuous, it is possible to prevent the chromatic aberration from being promoted by reducing the strength of the filter.

  The digital camera 10 will be described. As shown in FIG. 1, the digital camera 10 includes a system controller 11 that is a control unit that controls the entire camera, and an operation unit 12 is connected to the system controller 11. The operation unit 12 includes a plurality of buttons such as a shutter button, and the system controller 11 acquires an operation signal from the operation unit 12 and executes processing corresponding to each operation signal. Further, a ROM 11a and a RAM 11b are provided inside the system controller 11. The ROM 11a stores a control program for controlling each unit in the camera, and the RAM 11b temporarily stores work data. The system controller 11 controls each unit based on the aforementioned control program.

  The photographic lens 13 includes a zoom lens, a focus lens, and a diaphragm. A CCD image sensor 14 that is an image sensor is provided behind the photographic lens 13. The CCD image sensor 14 includes a light receiving surface in which a large number of light receiving elements (photodiodes) are arranged on a matrix, and a microlens for condensing light on each light receiving element on the front surface of the light receiving surface; Color filters corresponding to each color of RGB are arranged.

  The CCD image sensor 14 captures the subject image formed on the light receiving surface by the photographing lens 13 by photoelectric conversion. A CCD driver 15 is connected to the CCD image sensor 14. The CCD driver 15 inputs the vertical drive signal and the horizontal drive signal to the CCD image sensor 14 in accordance with the clock pulse input from the timing generator 16 to drive the CCD image sensor 14. The timing generator 16 is connected to the system controller 11. The system controller 11 controls the driving of the CCD image sensor 14 by generating a clock pulse by controlling the timing generator 16. The charge accumulation time of each light receiving element is controlled by an electronic shutter drive signal given from the CCD driver 15.

  Further, an analog signal processing unit 17 is connected to the CCD image sensor 14, and an imaging signal is output to the analog signal processing circuit 17. The analog signal processing unit 17 is configured to include a correlated double sampling circuit (CDS), an AMP, and the like, noises included in the imaging signal are removed by the CDS, and the imaging signal is set by the AMP. Amplified with a gain determined according to the sensitivity.

  Further, an A / D converter 18 is connected to the analog signal processing unit 17, and an imaging signal is output to the A / D converter 18. The A / D converter 18 digitally converts an analog imaging signal to generate image data. This image data is CCD-RAW data having luminance values (tone values) of RGB colors.

  The A / D converter 18 is connected to the frame memory 20 via the data bus 19, and the image data output from the A / D converter 18 is stored in the frame memory 20. Before the actual shooting is performed, image data for a low-resolution through image is stored in the frame memory 22, and at the time of actual shooting (when the shutter button is pressed), image data for high-resolution recording is stored. Is memorized.

  In addition to the A / D converter 18 and the frame memory 20, the data bus 19 includes a system controller 11, an AWB detection unit 21, a digital signal processing unit 22, a compression / decompression processing unit 23, an LCD driver 24, and a media controller 25. These are connected so that they can transmit and receive information via the data bus 19.

  The frame memory 20 is a working memory used when the digital signal processing unit 19 performs various signal processing on the image data, and temporarily stores the image data. The digital signal processing unit 22 includes a WB correction unit 30, a γ conversion unit 31, a color interpolation unit 32, a YC conversion unit 33, a contour enhancement unit 34, a Cr low pass filter (hereinafter referred to as Cr LPF) 35, and a Cb low pass. A filter (hereinafter referred to as Cb LPF) 36 and a multiplexing unit 37 are provided.

  The AWB detection unit 21 detects an AWB evaluation value based on the image data output from the A / D converter 18. The system controller 11 acquires an AWB evaluation value from the AWB detection unit 21, and calculates a correction gain for correcting white balance based on the AWB evaluation value. The system controller 11 controls the WB correction unit 30 based on this correction gain, adjusts the gain of the image data, and adjusts the white balance.

  Thereafter, the image data is subjected to γ conversion processing (gradation conversion processing) by the γ conversion unit 31 and then subjected to color interpolation processing by the color interpolation unit 32. Furthermore, the YC conversion process is performed on the image data by the YC conversion unit 33. By this YC conversion processing, the image data is converted into a luminance signal Y and two color difference signals Cr and Cb. The contour emphasizing unit 34 performs contour emphasis processing on the luminance signal Y. The Cr LPF 35 removes the high frequency component of the color difference signal Cr to limit the frequency band, and the Cb LPF 36 removes the high frequency component of the color difference signal Cb to limit the frequency band.

  Further, spectral sensitivity data is stored in the ROM 11a. The spectral sensitivity data is a characteristic of the CCD image sensor 14 and is measured in advance. The system controller 11 reads this spectral sensitivity data from the ROM 11a, changes the filter strength of the Cr and Cb LPFs 35 and 36 based on this spectral sensitivity data, and executes filter processing.

  For example, as shown in FIG. 2, there are filters for five pixels in the vertical direction, and the filter processing for the center pixel is performed by using coefficients 0, 1, 2, 1, and 0 for each color difference signal Cr. Multiplied by the sum of the coefficients. Thereby, simple low-pass filter processing can be performed. In this way, the image can be blurred by weighting and averaging the central pixel and surrounding pixels.

  As described above, the color difference signal Cr is weighted between the center pixel and the surrounding pixels, and the sum is averaged to perform a filter operation having frequency characteristics as shown in FIG. be able to. The strength of the filter can be controlled by changing the number of taps (the number of coefficients) and the coefficients of the filter. For example, as shown in FIG. 3, the filter operation is performed using [1] [1] as the coefficients. 3 for performing filter operation using [1] [2] [1], and performing filter operation using [1] [4] [6] [4] [1]. By performing the same calculation, low-pass filter processing of three types of intensity can be performed. This low-pass filter process is performed on all pixels.

  The system controller 11 controls the Cr and Cb LPFs 35 and 36 to perform three types of low-pass filter processing with different intensities, that is, filter operation processing with a tap number of “5” and filters with a tap number of “3”. The calculation process and the filter calculation process with the tap number “2” are selectively executed. That is, when normal low-pass filter processing is performed, the filter operation of tap number “3” is executed, and when the strength of the low-pass filter is increased, filter operation of tap number “5” is executed and the strength of the low-pass filter is increased. When the value is reduced, the filter operation with the tap number “2” is executed. Hereinafter, the filter calculation process with the tap number “5” is referred to as filter A, the filter calculation process with the tap number “3” is referred to as filter B, and the filter calculation process with the tap number “2” is referred to as filter C.

  The system controller 11 controls the Cr and Cb LPFs 35 and 36 based on the spectral sensitivity data, and executes a filter process corresponding to one of the filters A to C. That is, if the R spectral sensitivity is low, the R false color becomes large. Therefore, the system controller 11 controls the Cr LPF 35 to execute the filter calculation process corresponding to the filter A, and conversely, the B spectral sensitivity is low. For example, since the B false color increases, the Cb LPF 36 is controlled to execute the filter operation corresponding to the filter A.

  As described above, in order to prevent false color due to the difference in spectral sensitivity between the R pixel and B pixel, it is possible to optimize the filter strength to reduce false color, and for Cr and Cb By controlling the LPFs 35 and 36 independently and optimizing the filter strength of each, the occurrence of color blur can be suppressed.

  As described above, the low-pass filter processing is performed on the color difference signals Cr and Cb by the Cr and Cb LPFs 35 and 36. Thereafter, the multiplexing unit 37 performs a multiplexing process for JPEG compression.

  The system controller 11 controls the LCD driver 24 when the shutter button is not pressed in the shooting mode, and sets the image data subjected to various processes by the digital signal processing unit 22 as a through image to the LCD 38. To display. In this case, the digital signal processing unit 22 does not perform multiplexing processing on the image data. Further, the contour enhancement process and the low-pass filter process may not be performed.

  When the shutter button is pressed and a shooting instruction is given, the system controller 11 controls the compression / decompression processing unit 23 to perform compression processing on the image data subjected to various processes by the digital signal processing unit 22. In addition, the media controller 25 is controlled to record the compressed image data on the memory card 39.

  In addition, a lens detection unit 40 is connected to the system controller 11. The lens detection unit 40 detects the zoom lens position, aperture value, and focal length, and outputs these information to the system controller 11.

  Next, the low-pass filter processing of the digital camera having the above configuration will be described with reference to the flowchart of FIG. The system controller 11 obtains spectral sensitivity data of the CCD image sensor 14 from the ROM 11a. This spectral sensitivity data is composed of the spectral sensitivity Qr of the R pixel and the spectral sensitivity Qb of the B pixel.

  The system controller 11 determines whether or not the spectral sensitivity Qr of the R pixel is greater than a predetermined value a. When the spectral sensitivity Qr is larger than the predetermined value a, the filter A is selected as a filter for the color difference Cr. When the spectral sensitivity Qr is less than or equal to the predetermined value a, it is determined whether or not the spectral sensitivity Qr is greater than the predetermined value b. When it is determined that the spectral sensitivity Qr is greater than the predetermined value b, the filter B is selected as a filter for color difference Cr. When the spectral sensitivity Qr is equal to or less than the predetermined value b, the filter C is selected as a filter for the color difference Cr.

  Next, the system controller 11 determines whether or not the spectral sensitivity Qb of the B pixel is greater than a predetermined value c. When the spectral sensitivity Qb is larger than the predetermined value c, the filter A is selected as a filter for the color difference Cb. When the spectral sensitivity Qb is less than or equal to the predetermined value c, it is determined whether or not the spectral sensitivity Qb is greater than the predetermined value d. When it is determined that the spectral sensitivity Qb is greater than the predetermined value d, the filter B is selected as a filter for the color difference Cb. When the spectral sensitivity Qb is equal to or less than the predetermined value d, the filter C is selected as a filter for the color difference Cb.

  Thereafter, the system controller 11 controls the LPFs 35 and 36 for Cr and Cb, executes filter calculation processing corresponding to each filter selected for the color difference signal Cr and the color difference signal Cb, and ends the low-pass filter processing. To do.

  In the above-described low-pass filter processing, the case where the filter strength is changed based on the spectral sensitivity data has been described.Here, the case where the filter strength is changed based on the correction gain for correcting the white balance is described below. This will be described with reference to the flowchart of FIG.

  The system controller 11 acquires an AWB evaluation value from the AWB detection unit 21, and calculates a correction gain for correcting white balance based on the AWB evaluation value. This correction gain includes a gain Gr for the R pixel and a gain Gb for the B pixel.

  The system controller 11 determines whether or not the gain Gr is greater than a predetermined value e. When the gain Gr is larger than the predetermined value e, the filter A is selected as a filter for the color difference signal Cr. When the gain Gr is equal to or smaller than the predetermined value e, it is determined whether or not the gain Gr is larger than the predetermined value f. When it is determined that the gain Gr is greater than the predetermined value f, the filter B is selected as a filter for the color difference signal Cr. When the gain Gr is equal to or less than the predetermined value f, the filter C is selected as a filter for the color difference signal Cr.

  Next, the system controller 11 determines whether or not the gain Gb is greater than a predetermined value g. When the gain Gb is larger than the predetermined value g, the filter A is selected as a filter for the color difference signal Cb. When the gain Gb is equal to or smaller than the predetermined value g, it is determined whether or not the gain Gb is larger than the predetermined value h. When it is determined that the gain Gb is larger than the predetermined value h, the filter B is selected as a filter for the color difference signal Cb. When the gain Gb is equal to or less than the predetermined value h, the filter C is selected as a filter for the color difference signal Cb.

  Thereafter, the system controller 11 controls the Cr and Cb LPFs 35 and 36 to execute filter calculation processing corresponding to each filter selected for the color difference signal Cr and the color difference signal Cb on the color difference signals Cr and Cb. Then, the low-pass filter process ends.

  Next, a case where the filter strength is changed based on the shooting mode will be described with reference to the flowchart of FIG. The system controller 11 detects the currently set shooting mode. Thereafter, the system controller 11 determines whether or not the currently set shooting mode is a mode in which a red color is emphasized.

  When it is determined that the mode is a mode in which red color is emphasized, the filter A is selected as a filter for the color difference signal Cr. If it is determined that the mode is not a mode in which the red color is emphasized, the filter B is selected as a filter for the color difference signal Cr.

  Next, the system controller 11 determines whether or not the shooting mode is a mode in which a blue color is emphasized. If it is determined that the blue color is the enhanced mode, the filter A is selected as the filter for the color difference signal Cb. Further, when it is determined that the mode is not the mode in which the blue color is emphasized, the filter B is selected as the filter for the color difference signal Cb.

  Thereafter, the system controller 11 controls the Cr and Cb LPFs 35 and 36 to execute filter calculation processing corresponding to each filter selected for the color difference signal Cr and the color difference signal Cb on the color difference signals Cr and Cb. Then, the low-pass filter process ends.

  As described above, when the filter strength is changed based on the shooting mode of the camera, it is effective in the shooting mode that increases the contrast and sharpness because false colors are easily noticeable. Note that examples of the shooting mode for increasing the contrast and sharpness include a Fujichrome (registered trademark) mode and a saturation up mode.

  Further, chromatic aberration may be noticeable depending on the zoom lens position, aperture value, and focal length. There are chromatic aberrations mainly for R, which has a long wavelength of light, and those mainly for B, which has a short wavelength of light. Which is conspicuous depends on the zoom lens position, aperture value, and focal length. In the case of the zoom position, aperture value, and focal length where the R chromatic aberration is conspicuous, it is necessary to reduce the filter strength of the Cr LPF 35 so that the R color difference is not promoted. Conversely, in the case of a zoom lens position, aperture value, and focal length where B color aberration is conspicuous, it is necessary to reduce the filter strength of the Cb LPF 36 so that the B color difference is not promoted.

  The low-pass filter process when changing the filter strength so that chromatic aberration caused by the zoom lens position, aperture value, and focal length is not promoted by the Cr and Cb LPFs 35 and 36 will be described below using the flowchart of FIG. I will explain.

  The system controller 11 acquires information on the zoom lens position, aperture value, and focal length from the lens detection unit 40. Based on these pieces of information, the system controller 11 calculates a value Dr indicating the magnitude of aberration of the R pixel and a value Db indicating the magnitude of aberration of the B pixel.

  Thereafter, the system controller 11 determines whether or not the value Dr is larger than the predetermined value m. When it is determined that the value Dr is larger than the predetermined value m, the filter C having the weakest intensity is selected as the filter for the color difference signal Cr. If it is determined that the value Dr is equal to or less than the predetermined value m, it is determined whether or not the value Dr is greater than the predetermined value n. When it is determined that the value Dr is larger than the predetermined value n, the filter B is selected as a filter for the color difference signal Cr. When it is determined that the value Dr is equal to or less than the predetermined value n, the filter A is selected as the filter for the color difference signal Cr.

  Next, the system controller 11 determines whether or not the value Db is larger than the predetermined value o. When it is determined that the value Db is larger than the predetermined value o, the filter C having the weakest intensity is selected as the filter for the color difference signal Cb. When it is determined that the value Db is equal to or smaller than the predetermined value o, it is determined whether or not the value Db is larger than the predetermined value p. When it is determined that the value Db is larger than the predetermined value p, the filter B is selected as a filter for the color difference signal Cb. When it is determined that the value Db is equal to or less than the predetermined value p, the filter A is selected as a filter for the color difference signal Cb.

  Thereafter, the system controller 11 controls the Cr and Cb LPFs 35 and 36 to execute filter calculation processing corresponding to each filter selected for the color difference signal Cr and the color difference signal Cb on the color difference signals Cr and Cb. Then, the low-pass filter process ends.

  In the above description of the low-pass filter process, the process of selecting the filter for the color difference signal Cr is described before the process of selecting the filter for the color difference signal Cb. However, these selection processes are performed in parallel. May be performed or the order may be reversed.

  In the above-described embodiment, the case where the spectral sensitivity data is stored in the ROM 11a in advance has been described as an example. However, the CCD image sensor can be replaced, that is, the CCD image sensor is built in the interchangeable lens unit. In the case of the digital camera, the spectral sensitivity data corresponding to the CCD image sensor in the lens unit may be downloaded and used when the lens unit is changed. In this case, according to the spectral sensitivity of the CCD image sensor, the filter strength of the Cr and Cb LPFs can be set to the optimum strength, and low-pass filter processing can be performed on the image data (color difference signals Cr and Cb). is there.

  In the above embodiment, the case where the low-pass filter processing is performed by changing the number of TAPs and the coefficients of the filter in order to change the strength of the filter has been described as an example. However, the present invention is not limited to this, and a median filter is used. Then, change the number of pixels of the filter (for example, the sum of the central pixel and the surrounding pixels is 3 × 3 = 9 pixels, 5 × 5 = 25 pixels, 7 × 7 = 49 pixels) It may be changed.

  Furthermore, in the above-described embodiment, the case of performing three types of filter arithmetic processing with different strengths has been described. However, the present invention is not limited to this. For example, two types of filter arithmetic processing with different strengths may be performed. You may perform four or more types of filter arithmetic processing from which different.

  In the above-described embodiment, the case where a CCD image sensor is used as an imaging element has been described as an example. However, the present invention is not limited to this, and a CMOS image sensor may be used, for example.

It is a block diagram which shows the electric constitution of a digital camera. It is explanatory drawing which shows filter calculation. It is a graph which shows the frequency characteristic of filters A-C. It is a flowchart explaining the low-pass filter process which changes filter intensity | strength based on spectral sensitivity data. It is a flowchart explaining the low-pass filter process which changes filter strength based on the gain which correct | amends white balance. It is a flowchart explaining the low-pass filter process which changes filter strength based on imaging | photography mode. It is a flowchart explaining the low-pass filter process which changes filter strength based on the magnitude | size of chromatic aberration.

Explanation of symbols

10 Digital Camera 11 System Controller 11a ROM
13 Imaging Lens 14 CCD Image Sensor 21 AWB Detection Unit 30 WB Correction Unit 35 LPF for Cr
36 Cb LPF
40 Lens detector

Claims (5)

In an imaging device for recording image data after performing YC conversion processing on image data obtained by converting an imaging signal output from an imaging element into a digital signal,
A low pass filter for Cr that limits the frequency band by removing the high frequency component of the color difference signal Cr from the image data after the YC conversion processing;
A low-pass filter for Cb that limits a frequency band by removing a high-frequency component of the color difference signal Cb from the image data;
An imaging apparatus comprising: a control unit that controls each of the Cr low-pass filter and the Cb low-pass filter.   The imaging apparatus according to claim 1, wherein the control unit controls the Cr low-pass filter and the Cb low-pass filter based on a spectral sensitivity characteristic of the imaging element.   White balance detection means for detecting an evaluation value of white balance, the control means calculates a correction gain for correcting the white balance based on the evaluation value detected by the white balance detection means, and this correction 2. The photographing apparatus according to claim 1, wherein the low-pass filter for Cr and the low-pass filter for Cb are controlled based on a gain.   2. The photographing apparatus according to claim 1, wherein the control unit controls the low-pass filter for Cr and the low-pass filter for Cb based on a photographing mode set at the time of photographing. The control means calculates the magnitude of chromatic aberration based on the zoom lens position, aperture value, and focal length, and controls the Cr low-pass filter and the Cb low-pass filter based on the chromatic aberration magnitude. The photographing apparatus according to claim 1.

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