JP2014033272A - Image processing apparatus, digital camera, image processing program, and image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a color inside a color gamut of an output color space from being corrected on the outside of the color gamut.SOLUTION: An image processing apparatus 100 includes: inclination acquisition means for acquiring inclination of a first straight line that passes a white point and a maximum saturation point on an equal hue surface including a correction object color in a luminance color difference separation space; input value calculation means 104 for calculating an input value of a lookup table that outputs a correction value for correcting luminance and saturation of the correction object color on the basis of the luminance and saturation or color difference of the correction object color and the inclination of the first straight line; and correction means 104 for correcting at least one of the luminance and the saturation or the color difference of the correction object color on the basis of the correction value.

Description

  The present invention relates to an image processing apparatus, a digital camera, an image processing program, and an image processing method.

  An image processing method is known in which tone correction is performed on image data in a YUV space that is a luminance / color difference separation space (see Patent Document 1).

JP 2000-188768 A

  When the color space for outputting image data (output color space) is a color space represented by a plurality of primary colors such as RGB space, output is performed when luminance gradation correction is performed in the luminance color difference separation space as in the conventional technique described above. There is a possibility that a color that is in the color gamut of the color space may be out of the color gamut. Similarly, when saturation correction is performed, there is a possibility that a color that is in the color gamut of the output color space is out of the color gamut. In this way, when a color that falls within the color gamut of the output color space goes out of the color gamut, it is clipped to the color gamut boundary value when converted to the output color space, so the hue is rotated or the color is crushed (saturated) There was a problem.

(1) The image processing apparatus according to the first aspect of the present invention is an inclination for acquiring the inclination of the first straight line passing through the white point and the maximum saturation point on the equal hue plane including the correction target color in the luminance / color difference separation space. The input value of the lookup table that outputs the correction value for correcting the luminance and the saturation of the correction target color is used as the luminance and the saturation or color difference of the correction target color and the slope of the first straight line. Input value calculation means for calculating based on, correction value acquisition means for acquiring the correction value by inputting the input value to the lookup table, and at least luminance and color difference or saturation of the correction target color based on the correction value And a correcting means for correcting one of them.
(2) In the image processing device according to the seventh aspect of the present invention, the slope of the first straight line passing through the white point and the maximum saturation point on the equal hue plane including the correction target color in the luminance / color difference separation space, and the black point And an inclination acquisition means for acquiring the inclination of the second straight line passing through the maximum saturation point, and an input value of a lookup table that outputs a correction value for correcting the luminance and saturation of the correction target color, An input value calculating means for calculating based on the luminance of the color and saturation or color difference and the slope of the second straight line; a correction value acquiring means for acquiring the correction value by inputting the input value to the lookup table; And correcting means for correcting at least one of luminance and color difference or saturation of the color to be corrected based on the value and the slope of the first straight line.
(3) A digital camera according to a fourteenth aspect of the present invention includes an image pickup unit that picks up a subject image and the image processing device according to any one of the first to thirteenth aspects. A correction process is performed on the image captured by the imaging unit.
(4) An image processing program according to a fifteenth aspect of the invention causes a computer to function as the image processing apparatus according to any one of the first to thirteenth aspects.
(5) In the image processing method according to the sixteenth aspect of the present invention, an inclination for acquiring the inclination of the first straight line passing through the white point and the maximum saturation point on the equal hue plane including the correction target color in the luminance / color difference separation space. The input value of the look-up table that outputs the correction process and the correction value for correcting the luminance and saturation of the correction target color is set to the luminance and saturation or color difference of the correction target color and the slope of the first straight line. An input value calculating step to calculate based on, a correction value acquiring step to input the input value to a lookup table to acquire a correction value, and based on the correction value, at least luminance and color difference or saturation of the correction target color And a correction step of correcting one of the two.
(6) In the image processing method according to the seventeenth aspect of the present invention, the slope of the first straight line passing through the white point and the maximum saturation point on the equal hue plane including the color to be corrected in the luminance / color difference separation space, and the black point And an inclination acquisition step for acquiring the inclination of the second straight line passing through the maximum saturation point, and an input value of a lookup table that outputs a correction value for correcting the luminance and saturation of the correction target color, An input value calculating step for calculating based on the luminance of the color, saturation or color difference and the inclination of the second straight line, a correction value acquiring step for acquiring the correction value by inputting the input value to the lookup table, and correction And a correction step of correcting at least one of luminance and color difference or saturation of the correction target color based on the value and the slope of the first straight line.

  According to the present invention, it is possible to prevent a color within the color gamut of the output color space from being corrected out of the color gamut.

It is a block diagram explaining the structural example of the image processing apparatus (digital camera) by one embodiment of this invention. It is a figure explaining the color gamut shape of an output color space. It is a figure explaining the color gamut shape of an output color space. It is a figure explaining a gradation curve. It is a flowchart explaining the flow of an image process. It is a figure explaining a gradation correction axis. It is a figure explaining a saturation correction axis. It is a figure which illustrates a computer.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating the configuration of an image processing apparatus 100 according to an embodiment of the present invention. In this embodiment, an example in which a digital camera is used as the image processing apparatus 100 will be described. The digital camera 100 includes an operation member 101, an imaging lens 102, an imaging element 103, a control device 104, a memory card slot 105, and a monitor 106. The operation member 101 includes various input members operated by the user, such as a power button, a release button, a zoom button, a menu button, and the like.

  The imaging lens 102 is disposed so as to form a subject image on the imaging surface of the imaging element 103. The imaging lens 102 is represented by a single lens in FIG. 1 as a representative, but actually includes a plurality of optical lenses.

  The image sensor 103 is configured by, for example, a CMOS image sensor. The image sensor 103 captures a subject image formed by the imaging lens 102 and outputs the obtained image signal to the control device 104. The image sensor 103 is formed with a color filter in which R (red), G (green), and B (blue) are arranged in a Bayer array. For this reason, the color of the image acquired by the digital camera 100 is represented by a device-dependent RGB color system.

  The control device 104 includes a CPU, a memory, and other peripheral circuits, and controls a shooting operation performed by the digital camera 100. Memory constituting the control device 104 includes SDRAM and flash memory. The SDRAM is a volatile memory, and is used as a work memory for the control device 104 to expand a program when the program is executed. The SDRAM is also used as a buffer memory for temporarily storing data. On the other hand, the flash memory is a non-volatile memory, and stores a program executed by the control device 104, various parameters read when the program is executed, and the like.

  The memory card slot 105 is a slot for inserting a memory card as a storage medium. The control device 104 writes and records the image file generated by performing the photographing process on the memory card inserted in the memory card slot 105. Further, the control device 104 reads an image file recorded in a memory card inserted in the memory card slot 105.

  The monitor 106 is a liquid crystal monitor (so-called rear monitor) mounted on the back of the digital camera 100. The monitor 106 displays a reproduction image based on the image file recorded on the memory card, a setting menu for setting the digital camera 100, and the like. When the user operates the operation member 101 to set the digital camera 100 to a shooting mode using the rear liquid crystal, the control device 104 monitors image data for display of images acquired from the image sensor 103 in time series. It outputs to 106. Thereby, the through image can be displayed on the monitor 106.

  By the way, color spaces such as a YCC space that is a luminance color difference separation space and CIELAB that is a uniform color space are known as color spaces that are close to human perception of brightness. These color spaces are often used for image processing because it is easy to correct gradation and saturation while maintaining hue.

  When the color space (output color space) for outputting image data is not a luminance color difference separation space but a color space represented by a plurality of primary colors such as an RGB color system, an output color space in a YCC space or CIELAB space As shown in FIG. 2, the color gamut shape is close to a triangle connecting the black point Bp, the white point Wp, and the maximum saturation point Cp, as shown in FIG. In FIG. 2, the vertical axis represents luminance (Y), and the horizontal axis represents saturation (C). In the YCC space, the Y-axis direction represents luminance, and the angle around the origin on the CbCr plane represents hue. That is, all the colors on the plane including the Y axis and forming a certain angle with the Cb axis or the Cr axis have the same hue, and this is called an equal hue plane. On the equi-hue surface, the distance from the Y axis represents the saturation. Further, the black point Bp indicates the color with the lowest luminance that can be expressed in the output color space, and the white point Wp indicates the color with the highest luminance that can be expressed in the output color space. The maximum saturation point Cp indicates a color having the highest saturation that can be expressed in the output color space in each hue.

  Further, the color gamut shape on the equal hue plane of the output color space differs depending on the hue. This is because the luminance at the maximum saturation point Cp varies depending on the hue. For example, since red and blue are felt darker than yellow, the luminance at the maximum saturation point Cp for red and blue is lower than the maximum luminance at the maximum saturation point Cp for yellow as shown in FIG. Further, the luminance of the maximum saturation point Cp of the chromatic color is lower than the maximum luminance of the achromatic color (that is, the white point Wp).

  For example, as shown in FIG. 4, the gradation correction is performed using an S-shaped gradation curve Tc indicating the relationship between the value before gradation correction (Input) and the value after gradation correction (Output). . In the gradation curve Tc in FIG. 4, it is assumed that Input is normalized with the minimum value being 0 and the maximum value being 1. For example, when tone correction is performed using a YCC space, if a tone curve Tc adjusted for achromatic luminance is applied to a chromatic color, the luminance of a high chroma color is low in hues such as red and blue. Therefore, the luminance of the high saturation color is corrected to be lower by the gradation correction, and the high saturation color is expressed darkly.

  In addition, as a result of this gradation correction, there is a possibility that a color originally in the color gamut may go out of the color gamut. Thus, when the color that has gone out of the color gamut is clipped to the color gamut boundary value of the output color space when converted to the output color space, the hue rotates or the color is crushed (saturates). ) And other problems occur. For example, when the B component is clipped from a negative value to 0 in yellow with high saturation, problems such as the hue turning to orange or the skin color of high brightness changing to yellow occur.

  On the other hand, when correction such as saturation enhancement is performed in the YCC space, since the maximum saturation differs depending on the luminance, there is a possibility that colors near the color gamut boundary are emphasized outside the color gamut. Therefore, in this case as well, when converted to the output color space, it is clipped to the color gamut boundary value of the output color space, causing problems such as hue rotation and color collapse (saturation).

  Therefore, in the digital camera 100 of the present embodiment, gradation correction and saturation correction are performed while preventing the above-described problems. Hereinafter, such gradation correction and saturation correction will be specifically described. FIG. 5 is a flowchart for explaining the flow of image processing including gradation correction and saturation correction in the present embodiment. This image processing is processing executed by the control device 104 in accordance with an image processing program stored in the memory of the control device 104.

  In step S <b> 1 of FIG. 5, the control device 104 acquires RGB image data read from the image sensor 103. Then, the control device 104 performs processing such as interpolation, white balance, and noise removal on the RGB image data, and proceeds to step S2.

In step S2, the control device 104 converts the RGB image data processed in step S1 from the RGB space unique to the image sensor 103 to a YCC space that is a color space for performing gradation correction and saturation correction. Then, the process proceeds to step S3. This conversion is performed by the following formulas (1) to (3) when, for example, an sRGB space is used as a color space (output color space) for outputting an image. In the following formulas (1) to (3), (R, G, B) are input values (the above RGB image data) of formula (1). (R ₁ , G ₁ , B ₁ ) are the output value of Equation (1) and the input value of Equation (2). (R ₂ , G ₂ , B ₂ ) are the output value of Expression (2) and the input value of Expression (3). (Y, Cb, Cr) is the output value of equation (3). M _RGB2XYZ is a conversion matrix for converting an RGB space unique to the image sensor 103 to an XYZ space (for example, CIE 1964 XYZ), and is determined based on the spectral sensitivity characteristics of the image sensor 103, illumination conditions at the time of shooting, and the like. Is done. M _XYZ2sRGB is a conversion matrix for converting from the XYZ space to the sRGB space. LUT1 is a lookup table for performing γ conversion in a standard sRGB space. M _sRGB2YCC is a conversion matrix for converting from the sRGB space to the YCC space.

  In step S3, the control device 104 calculates a hue for each pixel in the YCbCr image data converted in step S2, and proceeds to step S4. The hue is calculated based on, for example, a ratio between Cb and Cr, or a ratio between Cr or Cb and a saturation approximation value using absolute values of Cr and Cb.

  In step S4, the control device 104 calculates the color gamut shape of the output color space (sRGB space) on the equal hue plane of the hue calculated in step S3 for each pixel of the YCbCr image data.

  As described above, when the color gamut of the output color space (sRGB space) is represented on the equal hue plane in the YCC space, the black point Bp, the white point Wp, and the maximum saturation point Cp are connected as shown in FIG. It can be approximated by a triangle. In FIG. 6, the vertical axis represents luminance (Y), and the horizontal axis represents saturation (C). In FIG. 6, the luminance and saturation of the black point Bp are (0, 0), and the luminance and saturation of the white point Wp are (1, 0), and the luminance and saturation of each pixel are normalized. And In step S4, for the hue of each pixel, the slope of the first straight line L1 passing through the white point Wp and the maximum saturation point Cp on the luminance and chromaticity coordinates on the equal hue plane (hereinafter referred to as the first slope). pdy1 and the slope (hereinafter referred to as the second slope) pdy2 of the second straight line L2 passing through the black point Bp and the maximum saturation point Cp are calculated as the gamut shape of the output color space in the hue of the target pixel. To do. Note that pdy1 and pdy2 are absolute values.

  Here, the first slope pdy1 for red, yellow, and green is equal to the second slope pdy2 for cyan, blue, and magenta, which are opposite colors, respectively. On the other hand, the second slopes pdy2 for red, yellow, and green are equal to the first slopes pdy1 for cyan, blue, and magenta, which are opposite colors, respectively. Therefore, in the memory (not shown) in the control device 104, the first inclination pdy1 and the second inclination pdy2 are recorded in advance for at least three colors (for example, red, yellow, and green). Based on the first gradient pdy1 and the second gradient pdy2 for red, yellow, and green recorded in the memory, the control device 104 determines the first gradient pdy1 and the second gradient pdy2 for cyan, blue, and magenta. Can also be sought.

  In step S4, among the six colors (red, yellow, green, cyan, blue, magenta), by interpolation from the first gradient pdy1 and the second gradient pdy2 in two hues adjacent to the hue of the target pixel, A first gradient pdy1 and a second gradient pdy2 in the hue of the target pixel are calculated. For example, when the hue of the target pixel is between green and cyan, the first slope pdy1 and the second slope pdy1 and the second slope pdy2 in red recorded in the memory are used. Find the slope pdy2. Then, the first slope pdy1 and the second slope pdy2 in cyan, the first slope pdy1 and the second slope pdy2 in green recorded in the memory, and the difference between the hue of the target pixel and green and cyan The first gradient pdy1 and the second gradient pdy2 in the hue of the target pixel are calculated in consideration.

  In this way, the control device 104 calculates the first gradient pdy1 and the second gradient pdy2 in the hue of each pixel of the YCbCr image data, and proceeds to step S5.

  In step S5, the control device 104 performs tone correction on the YCbCr image data. In this gradation correction, correction is not performed along the luminance (Y) axis, but as shown in FIG. 6, the luminance of the correction target color and the color of the correction target color on the equal hue plane of the color of the pixel to be corrected (correction target color). Correction is performed so that the luminance and saturation change along a third straight line L3 connecting the point (color point to be corrected) Tp indicating the saturation and the black point Bp.

This gradation correction will be specifically described. In the following description, the YCbCr image data uses values normalized by setting the minimum value of Y (minimum luminance) to 0 and the maximum value of Y (maximum luminance) to 1. First, the control device 104 calculates an approximate value of the saturation C of the target pixel from the Cb value and Cr value of the target pixel according to the following equation (4). The division (/ 4) in equation (4) may correspond using a bit shift.
C = (| Cb | + | Cr | + | Cb + Cr | + | Cb-Cr |) / 4 (4)

In order to calculate a good saturation approximation value while reducing the processing load, the equation (4) is used. However, when there is a margin in the processing load, the following equation (5) is used or the equation (4) is used. ) And (5) may be used to calculate the saturation.
C = (Cb ² + Cr ² ) ^1/2 (5)

Next, the control device 104 calculates the coordinate value of the correction target color point Tp in the coordinate system (hereinafter referred to as the gradation correction coordinate system) about the third straight line L3 as the gradation correction parameter yGainIn. The gradation correction coordinate system, the coordinate values of the black point Bp is 0, the coordinate values of the intersection point P ₃₁ of the third straight line L3 and the first straight line L1 is 1, the intersection point P ₃₁ from the black point Bp It is assumed that the coordinate system is such that the coordinate value increases in the direction toward. Specifically, the control device 104 calculates the gradation correction parameter yGainIn by the following equation (6) using the luminance Y and saturation C of the target pixel and the first gradient pdy1.
yGainIn = Y + C * pDy1 (6)

That is, the correction target color point Tp is next yGainIn = 0 If on a black point Bp, corrected color point Tp is yGainIn = 1 if on the intersection P _31. Further, when the correction target color point Tp is between the black point Bp and the intersection P ₃₁ , 0 <yGainIn <1, and as the correction target color point Tp is closer to the intersection P ₃₁ , yGainIn increases toward 1. As the correction target color point Tp becomes closer to the black point Bp, yGainIn becomes smaller toward zero. Further, when the correction target color point Tp is far from the black point Bp than the intersection point _{P 31} is a yGainIn> 1. In this case, the correction target color point Tp is located outside the color gamut of the output color space.

  Next, the control device 104 obtains a gradation correction gain yGain. The gradation correction gain yGain is the ratio (Output / Input) of the luminance (Output) after gradation correction to the luminance (Input) before gradation correction. The gradation correction gain yGain is set so that gradation correction is performed using, for example, the S-shaped gradation curve Tc of FIG. 4 described above for Input. The gradation correction gain yGain is set so that Output, which is a value obtained by multiplying Input by the gradation correction gain yGain, is 0 or more and 1 or less when Input is 0 or more and 1 or less. Are converted into the color gamut. Note that when Input is larger than 1, Output may be set to be smaller than 1, so that colors outside the color gamut may be compressed within the color gamut.

In the memory of the control device 104, when Input is input, a lookup table LUT2 that outputs the gradation correction gain yGain set in this way is recorded in advance. The control device 104 uses the lookup table LUT2 to calculate the gradation correction gain yGain by the following equation (7). That is, the gradation correction gain yGain is obtained using the gradation correction parameter yGainIn as the input value of the lookup table LUT2.
yGain = LUT2 (yGainIn) (7)

Next, the control device 104 multiplies YCbCr and saturation C of the target pixel by the tone correction gain yGain by the following equations (8) to (11), respectively, thereby correcting the tone. ₁ Cb ₁ Cr ₁ and saturation C ₁ are calculated.
Y ₁ = Y * yGain (8)
Cb ₁ = Cb * yGain (9)
Cr ₁ = Cr * yGain (10)
C ₁ = C * yGain (11)

As a result, if the correction target color point Tp is between the black point Bp and the intersection P ₃₁ is corrected along a third straight line L3 between the black point Bp and the intersection P ₃₁ is performed. Thereby, gradation correction can be performed in the color gamut for pixels in the color gamut of the output color space. Therefore, since the pixels in the color gamut of the output color space are not converted out of the color gamut, it is possible to prevent a problem that hue rotation occurs due to clipping to the color gamut boundary value of the output color space when converted to the output color space. be able to.

  In addition, the input value of the lookup table LUT2 is not set to Y, but the gradation correction parameter yGainIn normalized using the first slope pdy1 is used, so that correction for increasing the luminance of high chroma color can be performed. Therefore, it is possible to prevent correction for lowering the luminance of high-saturation colors with particularly low luminance such as red and blue. Therefore, even if the same gradation curve Tc is used for chromatic colors and achromatic colors, gradation correction can be performed without adverse effects, and simple and high-performance color processing can be performed.

  In addition, since the tone correction parameter yGainIn is calculated using the first slope pDy1 and used as the input value of the lookup table LUT2, the color gamut shape of the output color space can be obtained without performing heavy division processing. Accordingly, the input value of the lookup table LUT2 can be corrected, and gradation correction can be performed using one gradation curve Tc regardless of the hue. In equation (4), division by 4 is included, but this can be realized with a very small load by using the bit shift method.

  As described above, when the gradation correction is performed on each pixel of the YCbCr image data, the control device 104 proceeds to step S6.

In step S6, the control device 104 performs saturation correction on the image data (Y ₁ Cb ₁ Cr ₁ ) after the gradation correction in step S5. In this saturation correction, correction is not performed along the saturation (C) axis, but a fourth straight line L4 that passes through the correction target color point Tp and is parallel to the first straight line L1 as shown in FIG. So that the luminance and saturation change along the line.

This saturation correction will be specifically described. First, the control device 104 calculates the coordinate value of the correction target color point Tp in the coordinate system (hereinafter referred to as the saturation correction coordinate system) with the fourth straight line L4 as an axis as the saturation correction parameter cGainIn. This saturation correction coordinate system, the coordinate values of the intersection point P ₄₂ of the second straight line L2 and the fourth straight line L4 is 1, fourth straight line L4 and the luminance (Y) axis (i.e. black point Bp and white coordinate in a direction from the intersection P _4Y of the straight line) to the intersection point P ₄₂ which passes through the point Wp - value is assumed to be larger coordinate system. Specifically, the control unit 104 uses the luminance _{Y 1} and chroma _{C 1} of the target pixel and the second inclination pdy2, the following equation (12), calculates the saturation correction parameter CGainIn.
_{cGainIn = 1 -Y 1 + pDy2 *} C 1 ... (12)

That is, the correction target color point Tp is cGainIn = 1 if on the intersection _{P 42.} Further, when the correction target color point Tp is between the intersection point P _4Y and the intersection point P ₄₂ , cGainIn <1, and as the correction target color point Tp is closer to the intersection point P ₄₂ , cGainIn increases toward 1, and correction is performed. nearer cGainIn target color point Tp is the intersection _{P 4Y} is reduced. Further, when the correction target color point Tp is far from the intersection point _{P 4Y} than the intersection point _{P 42} is a cGainIn> 1. In this case, the correction target color point Tp is located outside the color gamut of the output color space.

  Next, the control device 104 obtains a saturation correction gain cGain. The saturation correction gain cGain is a ratio (Output / Input) of saturation (Output) after saturation correction to saturation (Input) before saturation correction. The saturation correction gain cGain is set so that saturation correction is performed using, for example, an S-shaped saturation curve similar to FIG. 5 described above for Input. The saturation correction gain cGain is set so that Output, which is a value obtained by multiplying Input by the saturation correction gain cGain, is 0 or more and 1 or less when Input is 0 or more and 1 or less. Are converted into the color gamut. Even when Input is larger than 1, by setting Output to be smaller than 1, colors outside the color gamut may be compressed into the color gamut.

In the memory of the control device 104, when Input is input, a lookup table LUT3 that outputs the saturation correction gain cGain set in this way is recorded in advance. The control device 104 uses the lookup table LUT3 to calculate the saturation correction gain cGain by the following equation (13). That is, the saturation correction gain cGain is obtained using the saturation correction parameter cGainIn as the input value of the lookup table LUT3.
cGain = LUT3 (cGainIn) (13)

Next, based on Y ₁ and C ₁ of the target pixel, the first slope pdy 1, and the saturation correction gain cGain, the control device 104 calculates Y ₂ with the saturation corrected by the following equation (14). To do. Further, the control device 104 multiplies Cb ₁ Cr ₁ of the target pixel by a saturation correction gain cGain by the following equations (15) to (16), thereby correcting Cb ₂ Cr ₂ whose saturation is corrected. Is calculated.
_{Y 2 = Y 1 - C 1} * (cGain-1) * pDy1 ... (14)
Cb ₂ = Cb ₁ * cGain (15)
Cr ₂ = Cr ₁ * cGain (16)

As a result, if the correction target color point Tp on a fourth straight line L4 is between the intersection point _{P 4Y} and the intersection _{P 42} is between the intersection point _{P 4Y} and the intersection _{P 42} along a fourth straight line L4 Correction is performed. Thereby, it is possible to perform saturation correction within the color gamut for the pixels within the color gamut of the output color space. Therefore, since the pixels in the color gamut of the output color space are not converted out of the color gamut, it is possible to prevent a problem that hue rotation occurs due to clipping to the color gamut boundary value of the output color space when converted to the output color space. be able to.

  In addition, the saturation correction parameter cGainIn is calculated using the second slope pDy2 and is used as the input value of the lookup table LUT3, so that the color gamut shape of the output color space can be obtained without performing heavy division processing. Accordingly, the input value of the lookup table LUT3 can be normalized, and the saturation correction can be performed using one saturation curve regardless of the hue.

  As described above, when the control device 104 performs the saturation correction on each pixel of the YCbCr image data, the process proceeds to step S7.

  In step S7, the control device 104 sets the level of gamut mapping (that is, the degree of color gamut compression), and proceeds to step S8. Specifically, the control device 104 creates a histogram of the tone correction parameter yGainIn and the saturation correction parameter cGainIn calculated in steps S5 and S6, and yGainIn> 1 or cGainIn> 1 from this histogram (that is, the output color space). The distribution of the number of pixels (outside the color gamut) is obtained. Then, the gamut mapping level is set according to the distribution of the number of pixels outside the color gamut of the output color space. For example, the larger the number of pixels outside the color gamut of the output color space, the larger the gamut mapping level is set. The smaller the number of pixels outside the color gamut of the output color space, the smaller the gamut mapping level is set.

  Note that the gamut mapping level may be adjusted according to a color reproduction mode (saturation emphasis mode or tone emphasis mode that emphasizes tone without emphasizing saturation) set by the user. . For example, in the saturation enhancement mode that emphasizes the overall saturation even if it is saturated and saturated rather than leaving the gradation, the gamut mapping level is set to the lowest (that is, gamut mapping is not performed) and the gradation is emphasized. In the mode, the gamut mapping level is set according to the histogram.

  In step S8, the control device 104 selects a color gamut compression curve for compressing the color gamut according to the gamut mapping level set in step S7. Note that the color gamut compression curve is a curve showing the relationship between the value before color gamut compression and the value after color gamut compression, and a plurality of color gamut compression curves are prepared according to various gamut mapping levels. Using the selected color gamut compression curve, the control device 104 compresses and converts the color gamut of the YCbCr image data after the saturation correction in step S6, and proceeds to step S9.

  In step S9, the control device 104 converts the YCbCr image data after the gamut mapping in step S8 into a value in the output color space (here, sRGB space) using a known conversion formula, and proceeds to step S10.

  In step S10, the control device 104 encodes the image data converted into the output color space in step S9 in accordance with the output file format, records it on the memory card inserted in the memory card slot 105, and performs the processing of FIG. finish.

According to the embodiment described above, the following operational effects can be obtained.
(1) The digital camera 100 controls to obtain the slope pdy1 of the first straight line L1 passing through the white point Wp and the maximum saturation point Cp on the equal hue plane including the correction target color in the luminance / color difference separation space (YCC space). The input value (tone correction parameter yGainIn) of the device 104 and the look-up table LUT2 that outputs correction values for correcting the luminance and saturation of the correction target color are set as the luminance of the correction target color and the saturation or color difference. A control device 104 that calculates based on the slope pdy1 of the first straight line L1, a control device 104 that inputs an input value to the lookup table LUT2 and obtains a correction value (tone correction gain yGain), and a correction value And a control device 104 that corrects at least one of luminance and saturation or color difference of the color to be corrected. As a result, the correction target color can be corrected according to the color gamut shape of the output color space, so that it is possible to prevent a color within the color gamut of the output color space from being corrected outside the color gamut.

(2) In the digital camera 100 of (1), the correction target color is along the third straight line L3 passing through the black point Bp and the correction target color point Tp on the equal hue plane including the correction target color by the correction. The brightness and the saturation are corrected so as to change. As a result, for example, a high-saturation color with a low luminance such as red or blue can be corrected appropriately without dark correction.

(3) In the digital camera 100 of the above (2), the control device 104 sets the third straight line L3 as an axis based on the brightness of the color to be corrected, the color difference or saturation, and the inclination pdy1 of the first straight line L1. The coordinate value (gradation correction parameter yGainIn) of the correction target color point Tp in the gradation correction coordinate system is calculated and used as the input value of the lookup table LUT2. Thereby, it can correct | amend according to the color gamut shape of output color space, without applying processing load.

(4) In the digital camera 100 of (3) above, the correction value (tone correction gain yGain) output by the lookup table LUT2 is the ratio of the luminance after correction to the luminance before correction. At least one of the luminance and the color difference or the saturation of the correction target color is corrected by multiplying at least one of the luminance and the color difference or the saturation of the correction target color by a correction value. As a result, since only one lookup table LUT2 is required, memory capacity can be saved as compared with the case of using a plurality of lookup tables that output at least one of luminance after correction and color difference or saturation. can do.

(5) in the digital camera 100 described above (4), the gradation correction coordinate system, a first straight line L1 coordinate values reference values of the intersection point _{P 31} of the third straight line L3 (1), and black coordinate value increases in the direction toward the intersection P ₃₁ from point Bp, the look-up table LUT 2, when the input value is a reference value (1) or less is multiplied by the correction value (Ygain) to the input value (input) The input value and the correction value are associated with each other so that the obtained value (Output) is equal to or less than the reference value (1). This makes it possible to correct a color within the color gamut of the output color space within the color gamut.

(6) In the digital camera 100 of the above (1) to (5), the digital camera 100 further includes a memory for storing the inclination pdy1 of the first straight line L1 in a hue of at least three hues, and the control device 104 is stored in the memory The configuration is such that the slope pdy1 of the first straight line L1 in the hue of the correction target color is obtained by interpolation from the slope pdy1 of the first straight line L1. As described above, since it is sufficient to store the slope pdy1 of the first straight line in at least three hues, the memory capacity can be saved as compared with the case of storing the slope pdy1 of the first straight line in many hues. .

(7) The digital camera 100 includes the slope pdy1 of the first straight line L1 passing through the white point Wp and the maximum saturation point Cp on the equal hue plane including the correction target color in the luminance / color difference separation space (YCC space), and the black point. Input of the control device 104 that acquires Bp and the slope pdy2 of the second straight line L2 that passes through the maximum saturation point Wp, and a lookup table LUT3 that outputs correction values for correcting the luminance and saturation of the correction target color A controller 104 that calculates a value (saturation correction parameter cGainIn) based on the brightness of the color to be corrected, the saturation or color difference, and the slope pdy2 of the second straight line L2, and the input value cGainIn to the lookup table LUT3. The brightness of the color to be corrected based on the control device 104 that receives the correction value (saturation correction gain cGain) and inputs the correction value cGain and the slope pdy1 of the first straight line. And includes a control unit 104 for correcting at least one of a chroma or color difference, the. As a result, the correction target color can be corrected according to the color gamut shape of the output color space, so that it is possible to prevent a color within the color gamut of the output color space from being corrected outside the color gamut.

(8) In the digital camera 100 of the above (7), the correction target color passes through the correction target color point Tp on the equal hue plane including the correction target color and is parallel to the first straight line L1 by the correction. The brightness and the saturation are corrected so as to change along the straight line L4. As a result, it is possible to perform saturation correction without correcting colors within the color gamut of the output color space outside the color gamut.

(9) In the digital camera 100 of the above (8), the control device 104 uses the fourth straight line L4 as an axis based on the luminance and saturation or color difference of the color to be corrected and the inclination pdy2 of the second straight line. The coordinate value of the correction target color point Tp in the saturation correction coordinate system to be calculated is calculated and used as the input value of the lookup table LUT3. Thereby, it can correct | amend according to the color gamut shape of output color space, without applying processing load.

(10) In the digital camera 100 of (9) above, the correction value (saturation correction gain cGain) output by the lookup table LUT3 is the ratio of the saturation after correction to the saturation before correction, and the control device 104 Corrects at least one of the saturation or the color difference of the correction target color by multiplying at least one of the saturation or the color difference of the correction target color by the correction value cGain, and the slope pdy1 of the correction value cGain and the first straight line. Based on the above, the luminance of the correction target color is corrected. As a result, since only one lookup table LUT3 is required, the memory capacity can be saved as compared with the case of using a plurality of lookup tables that output at least one of corrected luminance and saturation or color difference. can do.

(11) in the digital camera 100 described above (10), the saturation correction coordinate system, is the second straight line L2 coordinate values reference values of the intersection point _{P 42} of the fourth straight line L4 (1), and black from the fifth linear (brightness axis) the intersection _4Y of the fourth straight line L4 which passes through the point Bp and white point Wp, coordinate values in a direction in which the second straight line L2 toward the intersection P ₄₂ the fourth straight line L4 In the lookup table LUT3, when the input value is equal to or less than the reference value (1), a value (output) obtained by multiplying the input value (input) by the correction value cGain is equal to or less than the reference value (1). As described above, the input value and the correction value are associated with each other. This makes it possible to correct a color within the color gamut of the output color space within the color gamut.

(12) The digital camera 100 of the above (7) to (11) further includes a memory for storing the slope pdy1 of the first straight line L1 and the slope pdy2 of the second straight line L2 in a hue of at least three hues or more. The control device 104 interpolates from the slope pdy1 of the first straight line L1 and the slope pdy2 of the second straight line L2 stored in the memory, and the slope pdy1 and second slope of the first straight line L1 in the hue of the correction target color. The inclination pdy2 of the straight line L2 is acquired. In this way, since it is only necessary to store the slopes pdy1 and pdy2 of the first and second straight lines in at least three hues, as compared with the case of storing the slopes pdy1 and pdy2 of the first and second straight lines in many hues. Memory capacity can be saved.

(Modification 1)
In the above-described embodiment, the example in which the sRGB space is used as the output color space has been described. However, Adobe RGB or other multi-primary color space may be used as the output color space.

(Modification 2)
In the above-described embodiment, the example in which the YCC space is used as the color space for performing gradation correction and saturation correction has been described. However, other color-chrominance (saturation) separation spaces such as CIELAB space and HSV space may be used as the color space for gradation correction and saturation correction.

(Modification 3)
In the image processing of the above-described embodiment, an example in which both the gradation correction and the saturation correction are executed has been described. However, either the gradation correction or the saturation correction may be executed.

(Modification 4)
In the above-described embodiment, the example in which the image processing apparatus is mounted on the digital camera 100 has been described. However, the image processing apparatus may be configured by a personal computer. Further, the image processing apparatus may be configured by causing the personal computer 200 illustrated in FIG. 8 to execute a program for performing the processing illustrated in the flowchart illustrated in FIG. When the program is loaded into the personal computer 200 and used, the program is loaded into the data storage device of the personal computer 200 and then used as an image processing apparatus by executing the program.

  The loading of the program to the personal computer 200 may be performed by setting a storage medium 201 such as a CD-ROM storing the program in the personal computer 200, or to the personal computer 200 by a method via the communication line 202 such as a network. You may load. When passing through the communication line 202, the program is stored in the hard disk device 204 of the server (computer) 203 connected to the communication line 202. The program can be supplied as various forms of computer program products such as provision via the storage medium 201 or the communication line 202.

  Note that the RGB image input as a processing target by the personal computer 200 (step S1) is so-called RAW data (that is, an RGB image having a linear gradation with respect to the amount of light received by the image sensor 102).

  The above description is merely an example, and is not limited to the configuration of the above embodiment. Moreover, you may combine the structure of each modification suitably with the said embodiment.

DESCRIPTION OF SYMBOLS 100 ... Digital camera, 101 ... Operation member, 102 ... Imaging lens, 103 ... Imaging element, 104 ... Control apparatus, 105 ... Memory card slot, 106 ... Monitor

Claims (17)

Inclination acquisition means for acquiring the inclination of the first straight line passing through the white point and the maximum saturation point on the equal hue plane including the correction target color in the luminance / chrominance separation space;
The input value of the lookup table that outputs the correction value for correcting the luminance and saturation of the correction target color is based on the luminance of the correction target color, the saturation or the color difference, and the slope of the first straight line. Input value calculating means for calculating
Correction value acquisition means for inputting the input value to the lookup table and acquiring the correction value;
Correction means for correcting at least one of luminance and saturation or color difference of the correction target color based on the correction value;
An image processing apparatus comprising: The image processing apparatus according to claim 1.
The correction target color is corrected by the correction so that the luminance and the saturation change along a third straight line passing through the black point and the correction target color point on the equal hue plane including the correction target color. An image processing apparatus. The image processing apparatus according to claim 2,
The input value calculating means is configured to determine the correction target color point in a correction coordinate system having the third straight line as an axis based on the luminance and saturation or color difference of the correction target color and the slope of the first straight line. The image processing apparatus is characterized in that the coordinate value is calculated, and the coordinate value is used as an input value of the lookup table. The image processing apparatus according to claim 3.
The correction value output by the lookup table is a ratio of the luminance after correction to the luminance before correction,
The correction unit multiplies at least one of luminance and saturation or color difference of the correction target color by the correction value, thereby obtaining at least one of luminance and saturation or color difference of the correction target color. An image processing apparatus that performs correction. The image processing apparatus according to claim 4.
In the correction coordinate system, the coordinate value of the intersection of the first straight line and the third straight line is a reference value, and the coordinate value increases in the direction from the black point toward the intersection,
In the lookup table, when the input value is equal to or less than the reference value, the input value and the correction value are set such that a value obtained by multiplying the input value by the correction value is equal to or less than the reference value. An image processing apparatus characterized by being associated with each other. In the image processing device according to any one of claims 1 to 5,
Storage means for storing the slope of the first straight line in a hue of at least three or more hues;
The image processing apparatus according to claim 1, wherein the inclination acquisition unit acquires the inclination of the first straight line in the hue of the correction target color by interpolation from the inclination of the first straight line stored in the storage unit. In the equal hue plane including the color to be corrected in the luminance / chrominance separation space, the slope of the first straight line passing through the white point and the maximum saturation point and the slope of the second straight line passing through the black point and the maximum saturation point are calculated. An inclination acquisition means to acquire;
The input value of the look-up table that outputs correction values for correcting the luminance and saturation of the correction target color is based on the luminance of the correction target color and the saturation or color difference and the slope of the second straight line. Input value calculating means for calculating
Correction value acquisition means for inputting the input value to the lookup table and acquiring the correction value;
Correction means for correcting at least one of luminance and saturation or color difference of the correction target color based on the correction value and the slope of the first straight line;
An image processing apparatus comprising: The image processing apparatus according to claim 7.
The correction target color changes in luminance and saturation along a fourth straight line that passes through the correction target color point and is parallel to the first straight line on the equal hue plane including the correction target color due to the correction. An image processing apparatus which is corrected so as to perform. The image processing apparatus according to claim 8.
The input value calculating means is configured to determine the correction target color point in a correction coordinate system having the fourth straight line as an axis based on the luminance and saturation or color difference of the correction target color and the slope of the second straight line. An image processing apparatus characterized in that the coordinate value is calculated and the coordinate value is used as an input value of the lookup table. The image processing apparatus according to claim 9.
The correction value output by the lookup table is a ratio of the saturation after the correction to the saturation before the correction,
The correction unit corrects at least one of saturation or color difference of the correction target color by multiplying at least one of saturation or color difference of the correction target color by the correction value, and corrects the correction value and the first difference. An image processing apparatus that corrects the luminance of the correction target color based on the slope of one straight line. The image processing apparatus according to claim 10.
In the correction coordinate system, the coordinate value of the intersection of the second straight line and the fourth straight line is a reference value, and the fifth straight line passing through the black point and the white point and the fourth straight line The coordinate value increases in the direction from the intersection point to the intersection point of the second straight line and the fourth straight line,
In the lookup table, when the input value is equal to or less than the reference value, the input value and the correction value are set such that a value obtained by multiplying the input value by the correction value is equal to or less than the reference value. An image processing apparatus characterized by being associated with each other. The image processing apparatus according to any one of claims 7 to 11,
Storage means for storing the slope of the first straight line and the slope of the second straight line in hues of at least three hues or more;
The inclination acquisition means interpolates from the inclination of the first straight line and the inclination of the second straight line stored in the storage means, and the inclination of the first straight line and the second straight line in the hue of the correction target color. An image processing apparatus characterized by acquiring an inclination. The image processing apparatus according to any one of claims 1 to 6,
An image processing apparatus according to any one of claims 7 to 12,
An image processing apparatus comprising: Imaging means for capturing a subject image;
The image processing apparatus according to any one of claims 1 to 13,
With
The digital processing apparatus, wherein the image processing apparatus performs the correction process on an image captured by the imaging unit.   An image processing program for causing a computer to function as the image processing apparatus according to any one of claims 1 to 13. An inclination acquisition step of acquiring an inclination of a first straight line passing through the white point and the maximum saturation point in the equal hue plane including the correction target color in the luminance color difference separation space;
The input value of the lookup table that outputs the correction value for correcting the luminance and saturation of the correction target color is based on the luminance of the correction target color, the saturation or the color difference, and the slope of the first straight line. An input value calculating step for calculating
A correction value obtaining step of obtaining the correction value by inputting the input value to the lookup table;
A correction step of correcting at least one of luminance and saturation or color difference of the correction target color based on the correction value;
An image processing method comprising: In the equal hue plane including the color to be corrected in the luminance / chrominance separation space, the slope of the first straight line passing through the white point and the maximum saturation point and the slope of the second straight line passing through the black point and the maximum saturation point are calculated. An inclination acquisition step to acquire;
The input value of the look-up table that outputs correction values for correcting the luminance and saturation of the correction target color is based on the luminance of the correction target color and the saturation or color difference and the slope of the second straight line. An input value calculating step for calculating
A correction value obtaining step of obtaining the correction value by inputting the input value to the lookup table;
A correction step of correcting at least one of luminance and saturation or color difference of the correction target color based on the correction value and the slope of the first straight line;
An image processing method comprising:

Images