JP5119075B2 - Image processing apparatus, image processing program, and image processing method - Google Patents

Description

  The present invention relates to an image processing apparatus, an image processing program, and an image processing method, and more particularly, to a method for performing color analysis and color adjustment by converting acquired RGB image data into a color space of brightness, saturation, and hue. Is.

  There are the following conventional techniques for analyzing and adjusting hue.

  There is a method of identifying a hue by dividing data into lightness, saturation, and hue and distinguishing the selected hue from a complementary hue and a hue in a gray region (see Patent Document 1).

  Using the Lab value of the color, each judgment value, such as dark and bright if it is lightness from the viewpoint of lightness, saturation, and color tint, is binarized to make a judgment, and adjustment is made according to the judgment criteria There is a method for analyzing color tint (see Patent Document 2).

  Adjust the hue and saturation using the ab plane of the Lab space, clearly display the changed parameters at the time of adjustment, and display the reference image at the time of adjustment. There is a labor-saving method (see Patent Document 3).

There is a method in which an acquired image is analyzed for hue, brightness, and saturation, and an automatic correction is performed by using an optimal parameter as a correction value from image analysis data stored in advance (see Patent Document 4).
Japanese Patent No. 2540485 Japanese Patent No. 2541479 Japanese Patent No. 2914227 Japanese Patent No. 3264273

  Conventionally, when adjusting the brightness and saturation of RGB image data, the RGB image data is converted into XYZ, XYZ is converted into Lab, and Lab is further converted into HCB or the like. The brightness, saturation, and the like have been adjusted after conversion to the color space of degrees and hues, but there is a problem that the conversion processing takes time because a plurality of these conversion processes are required. Further, the Lab space has a problem that the center of the color space axis is shifted from the hue of the achromatic color.

An image processing apparatus according to the present invention includes an image acquisition unit that acquires RGB image data, and a color space represented by the three primary colors of RGB for each color point of the RGB image data acquired by the image acquisition unit. A color space conversion unit for converting into a color space represented by the following: the color space conversion unit sets Bk (black) as one of the opposing vertices passing through the center of the cube, and W (white) as the other vertex. , With the line connecting Bk (black) and W (white) as the central axis, the six vertices therearound are R (red) and Ye (in order of counterclockwise rotation viewed from the Bk (black) direction of the central axis. Yellow, G (green), Cy (cyan), B (blue), and each color point of the RGB image data in the RGB color space as Ma (magenta), the Bk perpendicular to the central axis of the color point (Black) The distance from the plane containing the point is the brightness, and the previous The distance of the color point from the central axis is saturation, and the projected point of the color point, the central axis, and the point when the color point and the vertex of R (red) are projected onto a plane perpendicular to the central axis R no line color space conversion to a hue angle to produce the projected point (red), analysis of the distribution of the lightness and the saturation of each of the hue of the converted the color point by the color space converter, and A color analysis unit that separates the image after the color space conversion processing for each hue; and by selecting the hue of the color point and changing at least one parameter of the lightness or the saturation, An image display capable of displaying the color adjustment unit for adjusting the brightness or the saturation on a hue plane, the analysis result by the color analysis unit and the separated image, and the hue plane and the image before and after the adjustment by the color adjustment unit. Part .

In the image processing apparatus of the present invention, in addition to the above-described configuration, the color space conversion unit has R (red) values of RGB primary colors of R _in , G (green) values of G _in , and B (blue) values. Is the color represented by B _in (Equation 1)

Hue formula expressed by (Equation 2)

Chroma expression expressed by (Equation 3)

The color space conversion processing of each color point of the RGB image data may be performed using the brightness formula expressed by

The image processing program of the present invention includes an image acquisition function for acquiring RGB image data, and a color space represented by the three primary colors for each color point of the RGB image data acquired by the image acquisition function. The color space conversion function for converting to the color space represented by is realized by a computer, and the color space conversion function is such that one of the vertices passing through the center of the cube is Bk (black) and the other vertex is W (white). R (red), Ye in the order of counterclockwise rotation of the six axes around the line connecting Bk (black) and W (white) as viewed from the Bk (black) direction of the central axis. For each color point of the RGB image data in the RGB color space of (yellow), G (green), Cy (cyan), B (blue), and Ma (magenta), the color point is perpendicular to the central axis of the color point. Including Bk (black) point The color point when the distance from a surface is brightness, the distance of the color point from the central axis is saturation, and the color point and the vertex of R (red) are projected onto a plane perpendicular to the central axis of Ri functions der of the color space conversion to a hue angle of projection point produces a projection point, the central axis, the R (red), the color point that has been converted by the color space conversion function for each of the color Analyzing the distribution of brightness and saturation, and a color analysis function for separating the image after the color space conversion processing for each hue, and selecting the hue of the color point to select at least one of the brightness or the saturation The color adjustment function for adjusting the lightness or the saturation of the color point on the hue plane by changing the parameters of the color point, the analysis result by the color analysis function, the separated image, the hue plane, and the color adjustment function That can display images before and after adjustment by Characterized in that to achieve the display function on the computer.

The image processing method of the present invention includes an image acquisition unit that acquires RGB image data, and a color space represented by the three primary colors of RGB for each color point of the RGB image data acquired by the image acquisition unit. A color space conversion procedure for converting to a color space represented by the following formula, wherein one of the vertices passing through the center of the cube is Bk (black) and the other vertex is W (white). , With the line connecting Bk (black) and W (white) as the central axis, the six vertices therearound are R (red) and Ye (in order of counterclockwise rotation viewed from the Bk (black) direction of the central axis. Yellow, G (green), Cy (cyan), B (blue), and each color point of the RGB image data in the RGB color space as Ma (magenta), the Bk perpendicular to the central axis of the color point (Black) Lightness from the plane containing the point The projected point of the color point and the center when the color point and the vertex of R (red) are projected onto a plane perpendicular to the central axis, the saturation being the distance from the central axis of the color point procedure der to hue angle projection point produces axial-the R (red) is, analysis of the distribution of the lightness and the saturation of each of the hue of the converted the color point by the color space conversion function, And color analysis means for separating the image after the color space conversion processing for each hue, and selecting the hue of the color point and changing at least one parameter of the lightness or the saturation, the color point An image capable of displaying the color adjustment means for adjusting the brightness or the saturation of the image on the hue plane, the analysis result by the color analysis means and the separated image, and the hue plane and the image before and after the adjustment by the color adjustment means. and having a display means

  Since the image processing apparatus of the present invention includes the image acquisition unit and the color space conversion unit, RGB image data in the RGB color space is quickly converted into a color space of brightness, saturation, and hue by a simple conversion formula. It becomes possible to do.

Further, in the image processing apparatus of the present invention, the color space conversion unit is configured such that the R (red) value of the RGB three primary colors is R _in , the G (green) value is G _in , and the B (blue) value is B _in . The color represented by the hue (Hue) expression represented by (Equation 1), the saturation (Chroma) expression represented by (Equation 2), and the brightness represented by (Equation 3). By performing the color space conversion process using the formula, it is possible to convert the RGB image data into the color space of brightness, saturation, and hue at high speed using the formulas (Equations 1, 2, 3) described above. Become.

  Also, the image processing apparatus of the present invention either analyzes the distribution of brightness and saturation for each hue converted by the color space conversion unit, or separates an image for each hue. By further including a color analysis unit that performs at least one of them, it is possible to perform color analysis for each hue converted by the above conversion formula.

  The image processing apparatus of the present invention is a color that adjusts the lightness or the saturation by changing at least one parameter of the lightness or the saturation for each hue converted by the color space conversion unit. By further including an adjustment unit, it is possible to adjust the lightness and saturation for each hue converted by the above conversion formula.

  The image processing program of the present invention allows a computer to realize the image acquisition function and the color space conversion function, so that RGB image data in the RGB color space can be quickly converted into brightness, saturation, and hue by a simple conversion formula. It is possible to convert the color space.

  Since the image processing method of the present invention includes the image acquisition procedure and the color space conversion procedure, the RGB image data in the RGB color space is quickly converted into a color space of brightness, saturation, and hue by a simple conversion formula. It becomes possible to convert.

  In the image processing apparatus, the image processing program, and the image processing method, the problem that RGB image data cannot be converted at high speed into a color space of brightness, saturation, and hue has been solved by a method using a simple conversion formula.

[Conversion of color space]
In the RGB image data acquired in this embodiment, the hue is expressed by the RGB color space. The definition of the RGB color space will be described using the cube of FIG.

  As shown in FIG. 1A, each vertex of the cube has Bk (black), W (white), R (red), G (green), B (blue), Cy (cyan), Ma (magenta). , Ye (yellow) corresponding to each color, and a straight line drawn from the vertex of Bk to the vertex of W is a neutral axis with no color, and from the central axis to each vertex of R, G, B As it gets closer, RGB colors will be added.

  For example, in FIG. 1A, consider a point P of a color closer to red, in which R and G are mixed, and create a triangular plane with Bk, W and P as the vertices.

  The color space shown in FIG. 1B is obtained by taking out this plane. Here, the brightness (brightness) of the color increases as it approaches W from Bk, and the vividness (saturation) of the color increases as it approaches the apex P from the central axis of Bk-W.

  Further, when projected onto a plane perpendicular to the axis centered on the axis connecting Bk and W of the cube of FIG. 1A as a straight line, the result is as shown in the right figure of FIG. Hue can be expressed by angle.

  The color space consisting of hue, saturation, and brightness shown in FIG. 1B is called an HCB space.

  The conversion from the RGB space to the HCB space can be expressed by the following equation.

If a value of R (red) of a color point in the RGB space is R _in , a value of G (green) is G _in , and a value of B (blue) is B _in , the hue (Hue) is

Chroma is

Brightness is

It is expressed.

  The above equation is obtained as follows.

  Here, for the sake of concreteness, each RGB value will be described as a value of the maximum number 255 represented by 8 bits.

  Note that sqrt is a square root.

  In FIG. 2A, points S and T for explanation are added to what is shown in the right diagram of FIG. 1B, and coordinate values are written together with black and white points. Is.

In FIG. 2A,
PointS is obtained from the color value of PointT.

Since vector BS and BW are parallel,
t (255,255,255) = (Sr, Sg, Sb)
The relationship Sr = Sg = Sb holds.

            Since the vector BW and the vector ST are at right angles, the inner product is 0.

255 ・ (Tr-Sr) + 255 ・ (Tg-Sg) +255 ・ (Tb-Sb) = 0
Where Sr = Sg = Sb
255 ・ (Tr-Sr) + 255 ・ (Tg-Sr) +255 ・ (Tb-Sr) = 0
Tr + Tg + Tb-3Sr = 0
Sr = (Tr + Tg + Tb) / 3
Therefore, PointS is ((Tr + Tg + Tb) / 3, (Tr + Tg + Tb) / 3, (Tr + Tg + Tb) / 3).

      Thereby, the lightness / saturation can be obtained.

      The brightness is the distance of the vector BS.

Brightness' = (Tr + Tg + Tb) / sqrt (3)
Normalize and set the maximum value to 1.

Brightness = (Tr + Tg + Tb) / (sqrt (3) ・ sqrt (3) ・ 255)
Brightness = (Tr + Tg + Tb) / (3 ・ 255)
Saturation is the distance of the vector ST.

Chroma '= sqrt (power (Tr-Sr, 2) + power (Tg-Sg, 2) + power (Tb-Sb, 2))
= sqrt (power (2Tr-Tg-Tb, 2) + power (2Tg-Tb-Tr, 2) + power (2Tb-Tr-Tg, 2)) / 3
Normalize and max sqrt (3)
Chroma = sqrt (power (2Tr-Tg-Tb, 2) + power (2Tg-Tb-Tr, 2) + power (2Tb-Tr-Tg, 2)) / (3/255)
It becomes.

Next, FIG. 2B shows the relationship between Point T and the point R (red), which is the reference point of the hue, on the hue plane (the right diagram in FIG. 1B). FIG. 2C shows the three-dimensional relationship.
Here, the angle between the vector RRh and the vector TS is obtained.

cosθ = RRh ・ TS / (| RRh | ・ | TS |)
θ = acos (RRh ・ TS / (| RRh | ・ | TS |))
TS = Tr- (Tr + Tg + Tb) / 3, Tg- (Tr + Tg + Tb) / 3, Tb- (Tr + Tg + Tb) / 3)
= (1/3) (2Tr-Tg-Tb, 2Tg-Tb-Tr, 2Tb-Tr-Tg)
RRh = (510/3, -255/3, -255/3) = (255/3) (2, -1, -1)
RRh ・ TS = (255/9) {2 * (2Tr-Tg-Tb)-(2Tg-Tb-Tr)-(2Tb-Tr-Tg)}
= (255/9) {6Tr-3Tg-3Tb}
| RRh | ・ | TS | = (255/3) ・ sqrt (6) ・ | TS |
= (255/3) ・ sqrt (6) ・ Chroma '
= (255/9) ・ sqrt (power (2Tr-Tg-Tb, 2) + power (2Tg-Tb-Tr, 2) + power (2Tb-Tr-Tg, 2))
θ = acos {(6Tr-3Tg-3Tb) / (sqrt (6) * sqrt (power (2Tr-Tg-Tb, 2) + power (2Tg-Tb-Tr, 2) + power (2Tb-Tr-Tg, 2)))}
Hue '= θ ・ 180 / π
However, the direction is determined by the outer product.

outer = (Tr + Tg-2Tb) + (-Tr + 2Tg-Tb)
When outer is positive, θ is positive, and when outer is negative, θ is also negative.

  From the above, three formulas (Equation 1, 2, 3) were derived.

[Constitution]
FIG. 3 is a functional block diagram of an image forming apparatus as an embodiment of the image processing apparatus of the present invention.

  The image forming apparatus 101 includes an operation unit 111, an image display unit 113, a printing unit 115, an interface unit 117, a software function unit 121, a data reading unit 123, a color space conversion unit 125, a color analysis unit 127, a color adjustment unit 129, data Each functional block of the comparison unit 131 and the image processing unit 133 is included.

  Each functional block will be described below.

  The operation unit 111 is a functional unit that inputs operations of the image forming apparatus 101 and receives inputs for color analysis operations and color adjustment operations.

  The image display unit 113 is configured by a liquid crystal panel or the like, and displays the display of the apparatus state of the image forming apparatus, the display at the time of operation input from the operation unit 111, the display of the result of color analysis, and the image before and after color adjustment. indicate.

  The printing unit 115 is a functional unit that performs printing. As a result of color analysis, it is possible to print images before and after color adjustment.

  The interface unit 117 connects the image forming apparatus 101 to an external device such as a host computer.

  The software function unit 121 realizes each function of the image forming apparatus 101 by software.

  The data reading unit 123 is an example of the image acquisition unit of the present invention, and reads a document image as RGB image data and acquires RGB image data for each pixel.

  Specifically, a scanner that reads a paper document, and a print engine that converts print data in a page description language into RGB image data.

  The color space conversion unit 125 calculates the frequency for each RGB value for each color point of the RGB image data acquired by the data reading unit 123 based on the equations (Equation 1), (Equation 2), and (Equation 3). Count and convert the color space to a color space of HCB (Hue Hue / Saturation Chroma / Brightness Brightness).

  The color analyzing unit 127 distributes the lightness / saturation value for each hue (Hue) of the color point changed by the color space converting unit, the histogram for each hue, and the image after the color space converting process for each hue. Are displayed separately for each hue. In addition, the color analysis unit 127 can similarly perform the color analysis on the image after being adjusted by the color adjustment unit 129 described later, and can compare the evaluation before and after the adjustment.

  FIG. 4 shows the result of color analysis performed by the color analysis unit.

  FIG. 4B shows a distribution of lightness and saturation for each hue with respect to the original image shown in FIG. 4B shows the lightness / saturation distribution of the RGB image data when the hue is 0 degree, and the right part of FIG. 4B shows the lightness / saturation distribution of the RGB image data when the hue is 30 degrees. It is.

  FIG. 4C is a histogram showing the distribution of pixels for each hue of the original image in FIG.

  FIG. 4D is a part of an image showing the lightness / saturation distribution for every 24 hues of the original image in FIG.

  The color adjustment unit 129 adjusts the color of each color point by changing the brightness and saturation parameters for the selected hue (range).

  FIG. 5 shows a user interface screen for color adjustment performed by the color adjustment unit 129. The interface screen shows the original image and the image after adjusting the brightness / saturation, the hue selection button, the button for adjusting the brightness / saturation, and the diagram showing the change in hue. The change in lightness / saturation of the selected hue can be confirmed by the central hue plane and also by the adjusted image at the lower left.

  The data comparison unit 131 prints or compares images before and after color adjustment.

  The image processing unit 133 converts the image data into a data format that can be processed by the printing unit in order to print the analysis screen, the original image, and the adjusted image.

[flowchart]
The operation flow of the image forming apparatus will be described with reference to the flowchart of FIG.

  S11: The data reading unit 123 reads an original image (RGB image data).

  S13: The image display unit 113 displays the read original image.

  S15: The color space conversion unit 125 converts each color point of the read original image from the RGB color space to the HCB color space. The color analysis unit 127 performs color analysis of the original image based on the data subjected to color space conversion (displayed in FIG. 4).

  S17: The color adjustment unit 129 adjusts the original image (displayed in FIG. 5).

  S19: The image display unit 113 displays the adjusted image (FIG. 5).

  S21: The color analysis unit 127 performs color analysis on the adjusted image (performs color analysis similar to that described with reference to FIG. 4).

  S23: It is determined whether or not the adjustment is performed again by the user input. When readjustment is performed, the operation proceeds to S17. If readjustment is not performed, the operation proceeds to S25.

  S25: The data comparison unit 131 performs printing by comparing the data before and after adjustment.

  Through the series of operations described above, the RGB image data that is the original image is converted into the HCB color space, color analysis is performed, and a series of processes for performing color adjustment for lightness and saturation for each hue is completed.

[Effect of Example]
The image processing apparatus according to the embodiment of the present invention enables the following.

  The RGB color space can be converted to the HCB color space at high speed by a simple conversion formula shown in (Equations 1, 2, 3).

  RGB image data converted based on the above conversion formula can be analyzed and displayed for each hue.

  The brightness and saturation of the image converted into the HCB color space can be adjusted for each hue.

  The color analysis unit can also analyze and display the hue-adjusted image for each hue.

  As a result, the adjustment of the color image is facilitated, and the user can confirm the change in lightness / saturation performed at the time of color adjustment with a diagram.

[Others]
In this embodiment, the color analysis and color adjustment are performed using the user interface of the operation unit 111 and the image display unit 113 of the image forming apparatus. However, these operations are performed from the host computer, and the display of the host computer is performed. And a method using a user interface of an input device such as a keyboard and a mouse.

  In the present embodiment, color space conversion, color analysis, and color adjustment are performed by each component included in the image forming apparatus. However, the color space conversion, color analysis, and color adjustment are performed on a host computer. A method of realizing a function by a program may be taken.

It is explanatory drawing of RGB color space and HCB color space. It is explanatory drawing of a color space conversion type | formula. 1 is a functional block diagram of an image forming apparatus according to an embodiment of the present invention. 4 is an example of color analysis performed by a color analysis unit of the image forming apparatus according to the embodiment of the present invention. 3 is an interface screen for color adjustment performed by a color adjustment unit of the image forming apparatus according to the exemplary embodiment of the present invention. 3 is a flowchart of the image forming apparatus according to the embodiment of the present invention.

Explanation of symbols

101 Image forming apparatus (image processing apparatus)
111 Operation Unit 113 Image Display Unit 115 Printing Unit 117 Interface Unit 121 Software Function Unit 123 Data Reading Unit (Image Acquisition Unit)
125 color space conversion unit 127 color analysis unit 129 color adjustment unit 131 data comparison unit 133 image processing unit

Claims (4)

An image acquisition unit for acquiring RGB image data;
For each color point of the RGB image data acquired by the image acquisition unit, a color space conversion unit that converts a color space represented by the three primary colors of RGB into a color space represented by brightness, saturation, and hue,
The color space conversion unit sets one of the opposing vertices passing through the center of the cube as Bk (black), the other vertex as W (white), and a line connecting Bk (black) and W (white) as a central axis. R (red), Ye (yellow), G (green), Cy (cyan), B (blue) in the counterclockwise rotation order when the six vertices therearound are viewed from the Bk (black) direction of the central axis For each color point of the RGB image data in the RGB color space of Ma (magenta),
The distance from a plane perpendicular to the central axis of the color point and including the Bk (black) point is defined as brightness.
The saturation of the distance from the central axis of the color point,
The hue formed by the projection point of the color point, the central axis, and the projection point of the R (red) when the color point and the vertex of the R (red) are projected onto a plane perpendicular to the central axis is used as the hue. no line color space conversion,
An analysis of the lightness and saturation distribution for each hue of the color point converted by the color space conversion unit, and a color analysis unit that separates the image after the color space conversion process for each hue;
A color adjustment unit that adjusts the lightness or saturation of the color point on a hue plane by selecting the hue of the color point and changing at least one of the lightness or saturation parameters; and
An image display unit capable of displaying the analysis result by the color analysis unit and the separated image and the hue plane and the image before and after adjustment by the color adjustment unit;
An image processing apparatus comprising: The image processing apparatus according to claim 1,
The color space conversion unit calculates a color represented by R _in red, R in red, G in green (G _in ), and B (blue) in B _in B. Hue formula, represented by

Chroma expression expressed by (Equation 2),

Brightness formula expressed by (Equation 3)

A color space conversion process for each color point of the RGB image data is performed using the image processing apparatus. An image acquisition function for acquiring RGB image data;
For each color point of the RGB image data acquired by the image acquisition function, the computer realizes a color conversion function that converts a color space represented by the RGB three primary colors into a color space represented by lightness, saturation, and hue,
The color space conversion function is such that one of the opposing vertices passing through the center of the cube is Bk (black), the other vertex is W (white), and the line connecting Bk (black) and W (white) is the central axis. R (red), Ye (yellow), G (green), Cy (cyan), B (blue) in the counterclockwise rotation order when the six vertices therearound are viewed from the Bk (black) direction of the central axis For each color point of the RGB image data in the RGB color space of Ma (magenta),
The distance from a plane perpendicular to the central axis of the color point and including the Bk (black) point is defined as brightness.
The saturation of the distance from the central axis of the color point,
The hue formed by the projection point of the color point, the central axis, and the projection point of the R (red) when the color point and the vertex of the R (red) are projected onto a plane perpendicular to the central axis is used as the hue. Ri function der to the color space conversion,
An analysis of the lightness and saturation distribution for each hue of the color point converted by the color space conversion function, and a color analysis function for separating the image after the color space conversion processing for each hue;
A color adjustment function for adjusting the lightness or saturation of the color point on a hue plane by selecting the hue of the color point and changing at least one of the lightness or saturation parameters;
An image display function capable of displaying the analysis result by the color analysis function and the separated image and the hue plane and the image before and after adjustment by the color adjustment function;
An image processing program for causing a computer to realize the above . Image acquisition means for acquiring RGB image data;
For each color point of RGB image data acquired by the image acquisition means, a color space conversion procedure for converting a color space represented by RGB three primary colors into a color space represented by brightness, saturation, and hue,
The color space conversion procedure is such that one of the opposing vertices passing through the center of the cube is Bk (black), the other vertex is W (white), and the line connecting Bk (black) and W (white) is the central axis. R (red), Ye (yellow), G (green), Cy (cyan), B (blue) in the counterclockwise rotation order when the six vertices therearound are viewed from the Bk (black) direction of the central axis For each color point of the RGB image data in the RGB color space of Ma (magenta),
The distance from a plane perpendicular to the central axis of the color point and including the Bk (black) point is defined as brightness.
The saturation of the distance from the central axis of the color point,
The hue formed by the projection point of the color point, the central axis, and the projection point of the R (red) when the color point and the vertex of the R (red) are projected onto a plane perpendicular to the central axis is used as the hue. procedure der is,
An analysis of the brightness and saturation distribution for each hue of the color point converted by the color space conversion function, and a color analysis means for separating the image after the color space conversion processing for each hue;
Color adjustment means for adjusting the lightness or saturation of the color point on a hue plane by selecting the hue of the color point and changing at least one of the lightness or saturation parameters; and
Image display means capable of displaying the analysis result by the color analysis means and the separated image and the hue plane and the image before and after adjustment by the color adjustment means;
An image processing method comprising: