Patent Publication Number: US-2007120984-A1

Title: Imaging device

Description:
TECHNICAL FIELD  
      The present invention relates to imaging apparatuses, and more particularly, to an imaging apparatus capable of correcting a specific color in video signals to a predetermined color, such as a memory color.  
     BACKGROUND ART  
      In related arts, apparatuses, such as digital still cameras, select a shooting mode depending on an image to be captured (e.g., sea, a nightscape, a portrait, or a landscape) to automatically perform various settings, e.g., focusing and white balance setting, thus correcting a specific color in video signals to a predetermined color suitable for the captured image.  
      The above-mentioned apparatuses capable of correcting a specific color in video signals include an image processing apparatus for correcting a specific color to a color that human beings subconsciously remember and feel as the most beautiful color, i.e., a memory color (refer to, e.g., Japanese Unexamined Patent Application Publication No. 2001-292390 (pp. 3-5, FIG. 5)).  
      For example, when a person shoots a landscape including blue sky and views a captured image, in many cases, the person imagines a more vibrant blue than the sky blue actually seen. Accordingly, the above-mentioned apparatus corrects a blue (specific color) in the actually captured image to a memory blue color and reproduces the image with an imagined color (i.e., the memory color).  
      An overview of a color correcting process of correcting a specific color in captured video signals to a memory color will now be described.  
       FIG. 7  is a block diagram of the schematic structure of an essential part for performing a color correcting process in a conventional imaging apparatus. An imaging apparatus  100 A includes an imaging lens unit  101 A, an imaging device  102 A, an S/H (Sample/Hold) circuit  103 A, an AGC (Automatic Gain Control) circuit  104 A, an A/D (Analog/Digital) conversion circuit  105 A, a specific color extraction circuit  106 A, a WB (White Balance) circuit  107 A, a gamma correction circuit  108 A, a signal processing circuit  109 A, a color difference signal correction circuit  110 A, a shooting mode selection circuit  120 A, and a color correction value setting circuit  130 A.  
      The general outlines of a color signal correcting process in the imaging apparatus  100 A with the above-mentioned structure will now be described with reference to a flowchart of  FIG. 8 .  
      First, when a user selects a desired shooting mode (for e.g., sea, a nightscape, a portrait, or a landscape) through the shooting mode selection circuit  120 A, the respective components of the apparatus automatically perform various settings, such as focusing and white balance setting, depending on the shooting mode selected through the shooting mode selection circuit  120 A (ST 10 ).  
      The color correction value setting circuit  130 A includes table data corresponding to color correction values to correct a specific color to a memory color. Color correction values for the specific color are selected from the table data depending on the selected shooting mode and the selected color correction values are set in the color difference signal correction circuit  110 A (ST 11 , ST 12 ).  
      After shooting starts, the imaging lens unit  101 A captures light reflected or generated from a subject. The imaging device  102 A converts the light into electrical signals, which are subjected to processing through the S/H circuit  103 A and the AGC circuit  104 A. The A/D conversion circuit  105 A converts the signals into digital video signals (R [red]/G [green]/B [blue]) and supplies the signals to the specific color extraction circuit  106 A and the WB (White Balance) circuit  107 A.  
      The specific color extraction circuit  106 A extracts video signals of a specific color from the video signals transmitted from the A/D conversion circuit  105 A, calculates the amounts of white balance control suitable for the extracted specific-color video signals, and supplies the white balance control amounts to the WB (White Balance) circuit  107 A (ST 13 ).  
      The WB (White Balance) circuit  107 A determines the color temperature of the video signals (R [red]/G [green]/B [blue]) supplied from the A/D conversion circuit  105 A, corrects the white balance of the video signals (R [red]/G [green]/B [blue]) on the basis of the white balance control amounts supplied from the specific color extraction circuit  106 A, and supplies the resultant signals to the gamma correction circuit  108 A. The gamma correction circuit  108 A corrects the gray scale of the video signals and transmits the resultant signals to the signal processing circuit  109 A (ST 14 , ST 15 ).  
      The signal processing circuit  109 A converts the digital video signals (R [red]/G [green]/B [blue]) supplied from the gamma correction circuit  108 A into a luminance signal Y, a color difference signal [B-Y], and a color difference signal [R-Y], outputs the luminance signal Y, and supplies the obtained color difference signals [B-Y] and [R-Y] to the color difference signal correction circuit  110 A (ST 16 ).  
      The color difference signal correction circuit  110 A corrects the specific color in the color difference signals [B-Y] and [R-Y] supplied from the signal processing circuit  109 A to a predetermined memory color on the basis of the color correction values set by the color correction value setting circuit  130 A. Then, the color difference signal correction circuit  110 A outputs color-corrected color difference signals [B-Y]″ and [R-Y]″ to the next-stage circuit (ST 17 , ST 18 ).  
      For example, a case where a certain specific color α is corrected to a memory color α 1  will now be described as an example.  
      When a certain shooting mode is selected in the shooting mode selection circuit  120 A, the color correction value setting circuit  130 A selects color correction values to correct the specific color α to the memory color α 1  from the table data depending on the shooting mode and sets the selected values in the color difference signal correction circuit  110 A.  
      Specifically, as shown in  FIG. 9A , the color correction values are given as a color correction matrix composed of parameters (coefficients), i.e., the amounts of correction GainB and GainR in the gain direction of the specific color and the amounts of correction HueB and HueR in the hue direction thereof.  
      For example, when parameters “1.5, “1.0”, “−0.5”, and “0.0” are given as GainB, GainR, HueB, and HueR, serving as the correction amounts in the gain direction of the specific color and those in the hue direction thereof, the color correction values (color correction matrix) as shown in  FIG. 9B  are obtained.  
      The above-mentioned color correction values are set in the color difference signal correction circuit  110 A. As shown in  FIG. 9C , the color difference signals [B-Y] and [R-Y] supplied from the signal processing circuit  109 A are subjected to linear transformation using the color correction values (color correction matrix), thus achieving the color correcting process.  
      For example, in a color difference plane as shown in  FIG. 9D , the specific color α (b, r) included in the color difference signals [B-Y] and [R-Y] is transformed to the predetermined memory color α 1  (b″, r″), so that the color difference signals [B-Y]″ and [R-Y]″ are-output.  
      As mentioned above, a specific color in video signals is corrected to a predetermined memory color depending on a shooting mode to reproduce an image with an imagined color (i.e., the memory color).  
      In the conventional imaging apparatus, however, when any shooting mode is selected, color correction values (amounts of color correction) to correct a specific color are fixedly selected and set. Disadvantageously, the specific color is not necessarily corrected to a favorable color depending on a shooting situation or an image to be captured.  
      Therefore, it is an object of the present invention to provide an imaging apparatus capable of changing the amounts of correction to correct a specific color in video signals depending on a shooting situation or an image to be captured.  
     DISCLOSURE OF INVENTION  
      To achieve the above-mentioned object, the present invention provides the following:  
      (1) An imaging apparatus including: shooting mode selection means, in which pieces of shooting mode information each including information concerning a specific color determined depending on a predetermined shooting condition are set, for selecting desired shooting mode information from the pieces of shooting mode information; specific color extraction means for extracting video signals of a specific color from video signals on the basis of the shooting mode information selected by the shooting mode selection means; color difference detection means for detecting color difference data of the specific color from the specific-color video signals extracted by the specific color extraction means; correction reference data storage means for storing pieces of correction reference data, serving as references for correcting the specific color to a predetermined color; color correction value calculation means for selecting correction reference data corresponding to the specific color from the correction reference data storage means on the basis of the shooting mode information selected by the shooting mode selection means to calculate color correction values on the basis of the selected correction reference data and the color difference data of the specific color detected by the color difference detection means, the color correction values being used to correct the specific color to the predetermined color; and color correction means for correcting the specific color in the video signals to the predetermined color on the basis of the color correction values calculated by the color correction value calculation means.  
      (2) The imaging apparatus according to (1), wherein the specific color extraction means has a function of changing an extraction range of the specific-color video signals depending on the luminance level of the video signals.  
      (3) The imaging apparatus according to (1), wherein the correction reference data storage means has a function capable of changing the stored correction reference data.  
      (4) The imaging apparatus according to (1), wherein the shooting mode selection means has a function of automatically selecting the shooting mode information depending on a shooting environment.  
      (5) An imaging apparatus including: shooting mode selection means, in which pieces of shooting mode information each including information concerning a specific color determined depending on a predetermined shooting condition are set, for selecting desired shooting mode information from the pieces of shooting mode information; specific color extraction means for extracting video signals of a specific color from video signals on the basis of the shooting mode information selected by the shooting mode selection means; color difference detection means for detecting color difference data of the specific color from the specific-color video signals extracted by the specific color extraction means; correction reference data storage means for storing pieces of correction reference data, serving as references for correcting the specific color to a predetermined color; color correction value calculation means for selecting correction reference data corresponding to the specific color from the correction reference data storage means on the basis of the shooting mode information selected by the shooting mode selection means to calculate color correction values on the basis of the selected correction reference data and the color difference data of the specific color detected by the color difference detection means, the color correction values being used to correct the specific color to the predetermined color; color correction means for correcting the specific color of the video signals to the predetermined color on the basis of the color correction values calculated by the color correction value calculation means; and luminance correction means for correcting the luminance level of the video signals depending on the luminance level of the specific-color video signals extracted by the specific color extraction means.  
      (6) The imaging apparatus according to (5), wherein the luminance correction means has a function of calculating the ratio of the specific-color video signals to the video signals to correct the luminance level of the specific-color video signals in accordance with the calculated ratio.  
      (7) The imaging apparatus according to (5), wherein the specific color extraction means has a function of changing an extraction range of the specific-color video signals depending on the luminance level of the video signals.  
      (8) The imaging apparatus according to (5), wherein the correction reference data storage means has a function capable of changing the stored correction reference data.  
      (9) The imaging apparatus according to (5), wherein the shooting mode selection means has a function of automatically selecting the shooting mode information depending on a shooting environment.  
      (10) An imaging method including:  
      a shooting mode selection step of selecting desired shooting mode information from pieces of set shooting mode information, each of the pieces of shooting mode information including information concerning a specific color determined depending on a predetermined shooting condition;  
      a specific color extraction step of extracting video signals of a specific color from video signals on the basis of the shooting mode information selected in the shooting mode selection step;  
      a color difference detection step of detecting color difference data of the specific color from the specific-color video signals extracted in the specific color extraction step;  
      a color correction value calculation step of selecting correction reference data corresponding to the specific color from correction reference data storage means for storing pieces of correction reference data, serving as references for correcting the specific color to a predetermined color, on the basis of the shooting mode information selected in the shooting mode selection step to calculate color correction values on the basis of the selected correction reference data and the color difference data of the specific color detected in the color difference detection step, the color correction values being used to correct the specific color to the predetermined color; and  
      a color correction step of correcting the specific color of the video signals to the predetermined color on the basis of the color correction values calculated in the color correction value calculation step.  
      According to the imaging apparatus with the above-mentioned structure, video signals of a specific color are extracted from video signals on the basis of selected shooting mode information, color difference data is detected from the extracted specific-color video signals, color correction values to correct the specific color to a predetermined color are calculated on the basis of the detected color difference data and correction reference data for the specific color, and the specific color in the video signals is corrected to the predetermined color on the basis of the calculated color correction values. Advantageously, the specific color can be corrected according to the amounts of correction depending on a shooting situation or an image to be captured.  
      In addition, the luminance level of the video signals is corrected depending on the luminance level of the specific-color video signals. Alternatively, the ratio of the specific-color video signals to the video signals is calculated and the luminance level of the specific color is corrected in accordance with the calculated ratio. Advantageously, the luminance level of the specific color can be corrected depending on a shooting situation or an image to be captured. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram of the schematic structure of an essential part for performing a color correcting process in an imaging apparatus according to the present invention.  
       FIG. 2  is a flowchart showing the color correcting process by the imaging apparatus of  FIG. 1 .  
       FIG. 3  is a diagram schematically showing a state in which an extraction range of a specific color is changed depending on the luminance level of video signals in the imaging apparatus of  FIG. 1 .  
       FIG. 4  includes diagrams explaining a lookup table included in the imaging apparatus of  FIG. 1 .  
       FIG. 5  includes diagrams explaining color point correction in the imaging apparatus of  FIG. 1 .  
       FIG. 6  includes diagrams explaining hue correction in the imaging apparatus of  FIG. 1 .  
       FIG. 7  is a block diagram of the schematic structure of an essential part for performing a color correcting process in a conventional imaging apparatus.  
       FIG. 8  is a flowchart of the color correcting process by the imaging apparatus of  FIG. 7 .  
       FIGS. 9A  to  9 D are diagrams schematically showing the details of the color correcting process by the imaging apparatus of  FIG. 7 . 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      An imaging apparatus according to an embodiment of the present invention will now be described with reference to the drawings. The drawings are used only for the description and do not limit the technical scope of the present invention.  
       FIG. 1  is a block diagram of the schematic structure of an essential part of the imaging apparatus, the part for performing a color signal correcting process and including an imaging lens unit  101 , an imaging device  102 , an S/H (Sample/Hold) circuit  103 , an AGC (Automatic Gain Control) circuit  104 , an A/D (Analog/Digital) conversion circuit  105 , a specific color extraction circuit  106 , a WB (White Balance) circuit  107 , a gamma correction circuit  108 , a signal processing circuit  109 , a color difference signal correction circuit  110 , a luminance correction circuit  111 , a shooting mode selection circuit  120 , a color correction value setting circuit  130 , and a specific-color signal processing unit  140 .  
      The imaging lens unit  101  captures light reflected or generated from a subject and allows the captured light to pass therethrough to the imaging device  102 .  
      The imaging device  102  includes an array of pixels (e.g., a CCD (Charge Coupled Device)) for converting light into electrical signals. The imaging device  102  converts the light from the subject passing through the imaging lens unit  101  into electrical signals that are analog video signals using the respective pixels and supplies the analog video signals to the S/H circuit  103 .  
      The S/H circuit  103  samples the analog video signals supplied from the imaging device  102  and transmits the signals to the AGC circuit  104 . The S/H circuit  103  holds sampled values until a process by the A/D conversion circuit  105  is finished. After the process is finished, the S/H circuit  103  transmits the next sampled values to the AGC circuit  104 .  
      The AGC circuit  104  amplifies the analog video signals sampled by the S/H circuit  103  and transmits the resultant signals to the A/D conversion circuit  105 .  
      The A/D conversion circuit  105  converts the analog video signals amplified by the AGC circuit  104  into digital video signals (R [red]/G [green]/B [blue]) and transmits the signals to the specific color extraction circuit  106  and the WB circuit  107 .  
      On the basis of shooting mode information supplied from the shooting mode selection circuit  120 , which will be described below, the specific color extraction circuit  106  extracts video signals of a specific color (hereinafter, referred to as specific-color signals (Rs [red]/Gs [green]/Bs [blue]) to be corrected from the video signals (R [red]/G [green]/B [blue]) transmitted from the A/D conversion circuit  105 . The specific color extraction circuit  106  calculates the amounts of white balance control and transmits the amounts to the WB circuit  107 . In addition, the specific color extraction circuit  106  transmits the extracted specific-color signals (Rs [red]/Gs [green]/Bs [blue]) to a WB circuit  141  included in the specific-color signal processing unit  140 .  
      When extracting specific-color video signals, the specific color extraction circuit  106  changes a specific color extraction range depending on the luminance level of the video signals (R [red]/G [green]/B [blue]) to detect the specific-color video signals.  
      The WB circuit  107  corrects the white balance of the video signals (R [red]/G [green]/B [blue]) transmitted from the A/D conversion circuit  105  in accordance with the control amounts calculated by the specific color extraction circuit  106  and then transmits the resultant signals to the gamma correction circuit  108 .  
      The gamma correction circuit  108  corrects the gray scale of the video signals (R [red]/G [green]/B [blue]) transmitted from the WB circuit  107 , i.e., performs gamma correction to the signals and transmits the resultant signals to the signal processing circuit  109 .  
      The signal processing circuit  109  converts the video signals supplied from the gamma correction circuit  108  into a luminance signal Y, a color difference signal [B-Y], and a color difference signal [R-Y]. The signal processing circuit  109  transmits the obtained color difference signals [B-Y] and [R-Y] to the color difference signal correction circuit  110  and also transmits the obtained luminance signal Y to the luminance correction circuit  111 .  
      The color difference signal correction circuit  110  performs a color correcting process to the color difference signals [B-Y] and [R-Y] supplied from the signal processing circuit  109  on the basis of the color correction values calculated by the color correction value setting circuit  130 , which will be described below, thus obtaining corrected color difference signals [B-Y]″ and [R-Y]″. The color difference signal correction circuit  110  transmits the corrected color difference signals [B-Y]″ and [R-Y]″ to the next-stage circuit.  
      The luminance correction circuit  111  corrects the luminance level of the luminance signal Y transmitted from the signal processing circuit  109  on the basis of the shooting mode information supplied from the shooting mode selection circuit  120  and a specific-color luminance signal Ys obtained by a signal processing circuit  143  included in the specific-color signal processing unit  140  and then transmits a corrected luminance signal Y″ to the next-stage circuit.  
      In addition, the luminance correction circuit  111  calculates the ratio of the specific-color video signals to the whole captured video signals (R [red]/G [green]/B [blue]) (whole frame) and corrects the luminance level of the specific color on the basis of the calculated ratio.  
      The shooting mode selection circuit  120  has a plurality of shooting modes corresponding to shooting conditions and scenes to be shot (e.g., sea, a nightscape, a portrait, and a landscape). A desired shooting mode can be selected.  
      After the shooting mode is selected, the shooting mode selection circuit  120  transmits shooting mode information corresponding to the selected shooting mode to the respective components of the apparatus, i.e., the specific color extraction circuit  106 , the color correction value setting circuit  130 , and the luminance correction circuit  111 .  
      The shooting mode information includes information items necessary for automatic various settings, e.g., information concerning a specific color to be corrected, the specific color being predetermined depending on a shooting mode, focusing, and white balance setting.  
      The shooting mode selection circuit  120  can also automatically select a proper shooting mode depending on a shooting environment, e.g., the brightness of ambient light or the state of a light source. Automatic selection and manual selection can be switched therebetween.  
      The color correction value setting circuit  130  has a lookup table for storing pieces of correction reference data, serving as references used in calculating color correction values to correct a specific color to a predetermined color.  
      The correction reference data includes data regarding the reference amounts of correction to correct a specific color to, e.g., a color (hereinafter, referred to as a memory color) that human beings subconsciously remember and feel as the most beautiful color.  
      The color correction value setting circuit  130  determines a specific color to be corrected on the basis of the shooting mode information supplied from the shooting mode selection circuit  120  and reads out correction reference data for correcting the determined specific color from the lookup table. On the basis of the correction reference data and color difference data transmitted from the color difference signal processing circuit  144  included in the specific-color signal processing unit  140 , the color correction value setting circuit  130  calculates color correction values necessary to correct the specific color to the predetermined color (e.g., the memory color) and transmits the calculated values to the color difference signal correction circuit  110 .  
      The correction reference data in the lookup table can be changed. For example, if the apparatus is capable of acquiring data from a recording medium, such as a memory card, other correction reference data can be read from the recording medium (e.g., a memory card) and data in the lookup table can be replaced with the read data. If the apparatus is capable of connecting to a communication network, data in the lookup table can be replaced with correction reference data acquired through the communication network. Accordingly, data in the lookup table can be changed so as to reproduce user&#39;s favorable colors and hues. Correction reference data can also be customized every user.  
      The specific-color signal processing unit  140  includes the WB (White Balance) circuit  141 , a gamma correction circuit  142 , the signal processing circuit  143 , and the color difference signal processing circuit  144 .  
      In the specific-color signal processing unit  140 , the WB (White Balance) circuit  141  corrects the white balance of the specific-color signals (Rs [red]/Gs [green]/Bs [blue]) extracted by the specific color extraction circuit  106  and transmits the resultant signals to the gamma correction circuit  142 .  
      The gamma correction circuit  142  of the specific-color signal processing unit  140 .corrects the gray scale of the specific-color signals (Rs [red]/Gs [green]/Bs [blue]) supplied from the WB circuit  141 , i.e., performs gamma correction to the signals and then transmits the resultant signals to the signal processing circuit  143 .  
      The signal processing circuit  143  of the specific-color signal processing unit  140  converts the specific-color signals (Rs [red]/Gs [green]/Bs [blue]), subjected to gamma correction by the gamma correction circuit  142 , into a luminance signal Ys, a color difference signal [Bs-Ys], and a color difference signal [Rs-Ys]. The signal processing circuit  143  transmits the obtained color difference signals [Bs-Ys] and [Rs-Ys] to the color difference signal processing circuit  144  and also transmits the luminance signal Ys to the luminance correction circuit  111 .  
      The color difference signal processing circuit  144  of the specific-color signal processing unit  140  detects color difference data from the color difference signals [Bs-Ys] and [Rs-Ys] supplied from the signal processing circuit  143  and transmits the detected color difference data to the color correction value setting circuit  130 .  
      The color correcting process of the imaging apparatus  100  with the above-mentioned structure will now be described with reference to  FIG. 2 .  
      First, when a user selects a desired shooting mode through the shooting mode selection circuit  120 , or when any shooting mode is automatically selected depending on a shooting environment, shooting mode information corresponding to the selected shooting mode is transmitted to the respective components of the apparatus (i.e., the specific color extraction circuit  106 , the color correction value setting circuit  130 , and the luminance correction circuit  111 ), so that various settings, such as focusing and white balance setting, are automatically performed (ST 100 ).  
      After shooting starts, the imaging lens unit  101  captures light from a subject and allows the light to pass therethrough to the imaging device  102 . The imaging device  102  converts the light into electrical signals, which are subjected to processing through the S/H circuit  103  and the AGC circuit  104 . The A/D conversion circuit  105  converts the signals into digital video signals (R [red]/G [green]/B [blue]) and transmits the signals to the specific color extraction circuit  106  and the WB (White Balance) circuit  107 .  
      On the shooting mode information supplied from the shooting mode selection circuit  120 , the specific color extraction circuit  106  extracts specific-color signals (Rs [red]/Gs [green]/Bs [blue]) from the video signals (R [red]/G [green]/B [blue]) supplied from the A/D conversion circuit  105 . The specific color extraction circuit  106  calculates the amounts of white balance control and transmits the control amounts to the WB circuit  107 . In addition, the specific color extraction circuit  106  transmits the extracted specific-color signals (Rs [red]/Gs [green]/Bs [blue]) to the WB (White Balance) circuit  141  in the specific-color signal processing unit  140  (ST 110 , ST 120 ).  
      Steps of processing the video signals (R [red]/G [green]/B [blue]) will now be described below (part shown by a dotted line {circle around (1)} in  FIG. 2 ).  
      The WB circuit  107  determines the color temperature of the video signals (R [red]/G [green]/B [blue]) supplied from the A/D conversion circuit  105 , corrects the white balance of the video signals (R [red]/G [green]/B [blue]) on the basis of the white balance control amounts calculated by the specific color extraction circuit  106 , and transmits the resultant signals to the gamma correction circuit  108  (ST 130 ).  
      The gamma correction circuit  108  corrects the gray scale of (i.e., performs gamma correction to) the white-balanced video signals (R [red]/G [green]/B [blue]) and transmits the resultant signals to the signal processing circuit  109  (ST 131 ).  
      The signal processing circuit  109  converts the gamma-corrected video signals (R [red]/G [green]/B [blue]) into a luminance signal Y, a color difference signal [B-Y], and a color difference signal [R-Y]. The signal processing circuit  109  transmits the luminance signal Y to the luminance correction circuit  111  and also transmits the color difference signals [B-Y] and [R-Y] to the color difference signal correction circuit  110  (ST 132 ).  
      Step of processing the specific-color signals (Rs [red]/Gs [green]/Bs [blue]) will now be described below (part shown by a dotted line {circle around (2)} in  FIG. 2 ). The steps are executed simultaneously with the above-mentioned steps of processing the video signals (R [red]/G [green]/B [blue]).  
      First, in the specific-color signal processing unit  140 , the WB circuit  141  determines the color temperature of the specific-color signals (Rs [red]/Gs [green]/Bs [blue]) extracted by the specific color extraction circuit  106 , corrects the white balance of the specific-color signals (Rs [red]/Gs [green]/Bs [blue]), and transmits the resultant signals to the gamma correction circuit  142  (ST 140 ).  
      The gamma correction circuit  142  of the specific-color signal processing unit  140  corrects the gray scale of (i.e., performs gamma correction to) the white-balanced specific-color signals (Rs [red]/Gs [green]/Bs [blue]) and transmits the resultant signals to the signal processing circuit  143  (ST 141 ).  
      Subsequently, the signal processing circuit  143  of the specific-color signal processing unit  140  converts the gamma-corrected specific-color signals (Rs [red]/Gs [green]/Bs [blue]) into a luminance signal Ys, a color difference signal [Bs-Ys], and a color difference signal [Rs-Ys]. The signal processing circuit  143  transmits the luminance signal Ys to the luminance correction circuit  111  and also transmits the color difference signals [Bs-Ys] and [Rs-Ys] to the color difference signal processing circuit  144  (ST 142 ).  
      Subsequently, the color difference signal processing circuit  144  of the specific-color signal processing unit  140  detects color difference data of the specific color from the color difference signals [Bs-Ys] and [Rs-Ys] supplied from the signal processing circuit  143  and transmits the detected color difference data to the color correction value setting circuit  130  (ST 143 ).  
      The color correction value setting circuit  130  determines a specific color to be corrected on the basis of the shooting mode information and reads out correction reference data for correcting the determined specific color from the lookup table.  
      On the basis of the correction reference data for the specific color and the color difference data detected by the color difference signal processing circuit  144 , the color correction value setting circuit  130  calculates correction values to correct the specific-color video signals to be corrected to a predetermined color (e.g., a memory color) and transmits the calculated color correction values to the color difference signal correction circuit  110  (ST 144 ).  
      Subsequent to processing of the video signals (R [red]/G [green]/B [blue]) and processing of the specific-color signals (Rs [red]/Gs [green]/Bs [blue]), the specific color is corrected by the color difference signal correction circuit  110  and the luminance correction circuit  111 .  
      On the basis of the color correction values set by the color correction value setting circuit  130 , the color difference signal correction circuit  110  performs color correction to the color difference signals [B-Y] and [R-Y] supplied from the signal processing circuit  109  and outputs corrected color difference signals [B-Y]″ and [R-Y]″ to the next-stage circuit (ST 150 , ST 160 ).  
      On the other hand, the luminance correction circuit  111  corrects the luminance level of the luminance signal Y supplied from the signal processing circuit  109  on the basis of the shooting mode information supplied from the shooting mode selection circuit  120  and the luminance signal Ys obtained by the signal processing circuit  143  in the specific-color signal processing unit  140 . The luminance correction circuit  111  outputs a corrected luminance signal Y″ to the next-stage circuit (ST 150 , ST 160 ).  
      The process of correcting a specific color in  FIG. 2  will now be described in more details.  
      On the basis of shooting mode information supplied from the shooting mode selection circuit  120 , the specific color extraction circuit  106  extracts video signals of a specific color, i.e., specific-color signals (Rs [red]/Gs [green]/Bs [blue]) from video signals (R [red]/G [green]/B [blue]).  
      In this instance, as shown in  FIG. 3 , the specific color extraction circuit  106  changes a specific-color extraction range depending on the luminance level of the video signals (R [red]/G [green]/B [blue]) and then extracts the specific-color video signals.  
      The specific-color signals (Rs [red]/Gs [green]/Bs [blue]) extracted by the specific color extraction circuit  106  are subjected to white balance correction and gray scale correction by the WB circuit  141  and the gamma correction circuit  142  in the specific-color signal processing unit  140 . The resultant signals are converted into a luminance signal Ys, a color difference signal [Bs-Ys], and a color difference signal [Rs-Ys] through the signal processing circuit  143 .  
      The color difference signal processing circuit  144  of the specific-color signal processing unit  140  detects color difference data from the color difference signals [Bs-Ys] and [Rs-Ys] supplied from the signal processing circuit  143  and transmits the detected color difference data to the color correction value setting circuit  130 .  
      Subsequently, on the basis of the shooting mode information supplied from the shooting mode selection circuit  120 , the color correction value setting circuit  130  determines a specific color to be corrected and reads out correction reference data for the specific color from the lookup table.  
      The lookup table will now be described with reference to  FIG. 4 .  
      In a color difference plane, a position (or a range) where a predetermined color (e.g., a memory color) exists is determined. A color existing in a predetermined range (hereinafter, referred to as a correction target range) relative to the position (or the range) where the predetermined color (memory color) exists is to be corrected, i.e., a specific color.  
      The correction target range is equally divided into segments each having a predetermined size. For example, in a color difference plane as shown in  FIG. 4 ( a ), the correction target range is divided into a matrix of 5×5 (0 to 4 in each of the row and column directions). Color correction reference data corresponds to color correction matrices “M 00 ” to “M 44 ”, which include reference values of the amounts of correction for colors existing in positions (“M” in the diagram) corresponding to respective intersections, i.e., reference values of the amounts of correction to correct the specific color to the memory color.  
      As shown in  FIG. 4 ( b ), four parameters (coefficients) GainB, GainR, HueB, and HueR are assigned to each of the color correction matrices “M 00 ” to “M 44 ”, serving as the color correction reference data. The parameters GainB and GainR correspond to the amounts of correction in the gain direction of the color difference signal [B-Y] and the color difference signal [R-Y], respectively. The parameters HueB and HueR correspond to the amounts of correction in the hue direction of the color difference signals [B-Y] and [R-Y], respectively.  
      For example, when the parameters GainB and GainR as the amounts of correction in the gain direction are set to “1.5” and “1.0”, respectively, and the parameters HueB and HueR as the amounts of correction in the hue direction are set to “−0.5” and “0.0”, respectively, and those parameters are given to a certain specific color, a color correction matrix is obtained as shown in  FIG. 4 ( c ).  
      As shown in  FIG. 4 ( d ), the lookup table is a data structure having pieces of correction reference data for various specific colors previously stored as pieces of table data in a memory.  
      On the basis of the correction reference data for the specific color read from the lookup table and the color difference data supplied from the color difference signal processing circuit  144 , the color correction value setting circuit  130  calculates color correction values to correct the specific color to a predetermined color (memory color).  
      Specifically, parameters of each color correction matrix in the read correction reference data are recalculated on the basis of the color difference data. The calculated parameters are set in a color correction matrix. The color correction matrix serves as data including color correction values.  
      In calculating color correction values, a correcting method varies depending on the characteristics of a specific color to be corrected.  
      First, color point correction will now be described. In the color point correction, for example, when the color of blue sky photographed is corrected to a memory blue-sky color, the color (specific color) to be corrected is converged to the memory color corresponding to a certain point (hereinafter, referred to as a color point) in the color difference plane.  
       FIG. 5  schematically shows color correction values for color point correction. For example, when correction reference data including color correction matrices “M 00 ” to “M 44 ” is assigned to a correction target range as shown in  FIG. 5 ( a ), color correction values are calculated such that the closer a position is to a color point X 0  from the outermost position of the correction target range, the more corresponding amounts of correction are increased, and the closer a position is to the color point X 0  from a position corresponding to the maximum amounts of correction, the more the corresponding amounts of correction are reduced.  
      In this case, the center of the correction target range matches the color point X 0 , i.e., a color corresponding to the center of the range is the same as that in the color point X 0 . Accordingly, parameters corresponding to the center are set so as not to perform color correction. Regarding a color corresponding to the outermost position of the correction target range, if the color is corrected, a change in color is increased, thus resulting in unnatural correction. Therefore, parameters corresponding to the outermost position are set so as not to perform color correction.  
       FIG. 5 ( b ) shows an example of a set of color correction values calculated on the basis of the correction reference data including the color correction matrices “M 00 ” to “M 44 ” and the color difference data. A so-called unit matrix (in which parameters of  FIG. 4 ( b ) are set such that GainB →“1.0”, GainR →“1.0”, HueB →“0.0”, and HueR →“0.0”) is assigned to each of the color correction matrices excluding the matrices “M 11 ” to “M 13 ”, “M 21 ”, “M 23 ”, and “M 31 ” to “M 33 ”. Consequently, colors corresponding to the center position and the outermost position of the correction target range are not corrected.  
      Hue correction will now be described. In the hue correction, e.g., when the skin color of a person who has been shot as a subject is corrected to a memory skin color, a color (specific color) to be corrected is converged to a color in a predetermined hue range in the color difference plane.  
       FIG. 6  schematically shows correction values for hue correction. For example, when correction reference data including color correction matrices “M 00 ” to “M 44 ” is assigned to a correction target range shown in  FIG. 6 ( a ), color correction values are calculated such that the closer a position is to a predetermined hue range W from the outermost position of the correction target range, the more the corresponding amounts of correction are increased, and the closer a position is to the hue range W from a predetermined position corresponding to the maximum amounts of correction, the more the corresponding amounts of correction are reduced.  
      In this case, parameters for a color corresponding to the hue range W in the correction target range are set so as not to perform color correction. Regarding a color corresponding to the outermost position of the correction target range, if the color is corrected, a change in color is increased, thus resulting in unnatural correction. Therefore, parameters corresponding to the outermost position are set so as not to perform color correction.  
       FIG. 6 ( b ) shows an example of a set of color correction values calculated on the basis of the correction reference data including the color correction matrices “M 00 ” to “M 44 ” and the color difference data. A so-called unit matrix (in which parameters of  FIG. 4 ( b ) are set such that GainB →“1.0”, GainR →“1.0”, HueB →“0.0”, and HueR →“0.0”) is assigned to each of the color correction matrices excluding the matrices “M 12 ”, “M 13 ”, “M 21 ”, “M 23 ”, “M 31 ”, and “M 32 ”. Consequently, colors corresponding to the hue range W and the outermost position of the correction target range are not corrected.  
      As mentioned above, the color correction value setting circuit  130  calculates color correction values corresponding to the characteristics of the specific color to be corrected and transmits the calculated color correction values to the color difference signal correction circuit  110 .  
      On the basis of the following Expression 1, the color difference signal correction circuit  110  linearly transforms the color difference signals [B-Y] and [R-Y] supplied from the signal processing circuit  109  using the color correction values calculated by the color correction value setting circuit  130 , thus performing color correction.  
               [             [     B   -   Y     ]     ″                 [     R   -   Y     ]     ″           ]     =       [         GainB       HueR           HueB       GainR         ]     ⁡     [           [     B   -   Y     ]               [     R   -   Y     ]           ]               Expression   ⁢           ⁢   1             
 
      In other words, the color difference signals [B-Y] and [R-Y] are subjected to color correction on the basis-of the color correction values (color correction matrix) calculated in accordance with the color difference data, so that the specific color is corrected to a predetermined color (e.g., a memory color).  
      To correct a color corresponding to a position (arranged in an area other than the intersections in the color correction target range) in which a color correction matrix is not set in the color difference plane, the amounts of correction are calculated on the basis of (parameters of) color correction matrices surrounding the position and the color is corrected on the basis of the calculated correction amounts.  
      For example, regarding a color corresponding to a position x 1  in  FIG. 5 ( a ), the amounts of correction are calculated on the basis of parameters of the color correction matrices “M 02 ”, “M 03 ”, “M 12 ”, and “M 13 ” in the color correction reference data and the color is corrected using the calculated correction amounts.  
      On the other hand, the luminance correction circuit  111  corrects the luminance level of the luminance signal Y supplied from the signal processing circuit  109  on the basis of the shooting mode information supplied from the shooting mode selection circuit  120  and the luminance signal Ys obtained by the signal processing circuit  143  in the specific-color signal processing unit  140 , and then outputs the resultant luminance signal Y″ to the next-stage circuit.  
      The luminance correction circuit  111  can also calculate the ratio of the specific-color video signals to the whole captured video signals (R [red]/G [green]/B [blue]) (whole frame) and change the amount of correction for the luminance level of the specific color in accordance with the calculated ratio.  
      For example, in the shooting mode for shooting a portrait, to correct the skin color of a subject person, the ratio of the skin color, serving as a specific color, to the whole captured image (frame) is determined. When the ratio is higher than a predetermined ratio, the amount of correction for the luminance level of the skin color is increased. If the ratio is lower than the predetermined ratio, the correction amount for the luminance level of the skin color is reduced.  
      As mentioned above, even in the same shooting mode, the amount of correction for the luminance level of a specific color is changed depending on a shooting situation, so that the corrected specific color can be further corrected to a favorable color.  
      As mentioned above, video signals of a specific color to be corrected are extracted from captured video signals, the amounts of color correction are calculated on the basis of the extracted specific-color video signals, and the specific color to be corrected is corrected on the basis of the calculated correction amounts. In addition, the luminance level of the captured video signals is corrected depending on the luminance level of the extracted specific-color video signals. Advantageously, the specific color of the captured video signals can be corrected to a favorable color (e.g., a memory color) based on the correction amounts corresponding to a shooting situation or a captured image.  
      In addition, the ratio of the specific-color video signals to the whole captured video signals (whole frame) is calculated and the amount of correction for the luminance level of the specific color is changed depending on the calculated ratio. Advantageously, the luminance level can be corrected so that the specific color of the captured video signals is corrected to a favorable color depending on a shooting situation or a captured image.  
      In addition, the extraction range of the specific color is varied depending on the luminance level of the captured video signals. Advantageously, the accuracy of extracting video signals of the specific color to be corrected can be increased.