JP2005130274A - Image processing apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus and method capable of expressing a color area which a color image originally has or a color area closest to it by making most use of a color reproduction area unique to an image output device. <P>SOLUTION: In the image processing apparatus 2, a data input part 201 acquires the color image and holds it in an image buffer 202. In addition, a color area data holding part 207 holds information regarding a color area which can be outputted by the predetermined image output device 1. An inside/outside of color area judgment part 203 judges whether or not a predetermined pixel in the held color image is within the color area which can be outputted by the image output device 1 here. As the result, when the pixel is judged to be outside of the color area, a color processing part 202 performs color conversion and the color image after performing the color conversion is outputted from a data output part 205. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus and method for outputting a color image corresponding to a color reproduction range unique to an image output apparatus.

Conventionally, color matching using a profile has been performed in order to match the appearance of an image displayed on a monitor and an image printed out by a printer. For example, a method is known in which a profile is adjusted by highlighting pixels whose colors are shifted by a color difference designated by the user using a preview screen (see, for example, Patent Document 1). According to the method described in Patent Document 1, it is possible to perform a quantitative evaluation that is not affected by the user's experience and sensitivity when adjusting the profile.
JP 2003-87589 A

  However, the monitor and the printer may have different color reproduction ranges for the output image, and the image cannot always be output from the printer in the same color reproduction range as the image expressed on the monitor. In addition, an image output from a monitor or printer may not reproduce all the color gamuts inherent to the image itself. Therefore, there is a problem that even if the color reproduced on the monitor can be faithfully reproduced by the printer, the original color of the image may not be reproduced.

  The present invention has been made in consideration of such circumstances, and by utilizing the color reproduction range inherent to the image output apparatus to the maximum, the color gamut originally possessed by the color image or the closest to it. An object is to provide an image processing apparatus and method capable of expressing a color gamut.

In order to solve the above problems, an image processing apparatus according to the present invention provides:
Acquisition means for acquiring a color image;
Image holding means for holding the color image;
Color gamut holding means for holding information about a color gamut that can be output by a predetermined image output device;
Determination means for determining whether or not a predetermined pixel in the color image held in the image holding means is in the color gamut;
A color conversion unit that performs color conversion on the pixel when the determination unit determines that the pixel is out of the color gamut;
Output means for outputting the color image after performing color conversion on a pixel determined to be out of the color gamut.

The image processing method according to the present invention includes:
A first acquisition step of acquiring a color image;
A second acquisition step of acquiring information about a color gamut that can be output by a predetermined image output device;
A determination step of determining whether or not a predetermined pixel in the color image is in a color gamut that can be output by the image output device;
A color conversion step for performing color conversion on the pixel when the determination step determines that the pixel is out of the color gamut;
An output step of outputting the color image after performing color conversion on the pixel determined to be out of the color gamut.

  According to the present invention, a color gamut inherent to a color image or a color gamut close to the maximum can be expressed by utilizing the color reproduction range inherent to the image output apparatus to the maximum.

  In addition, for pixels outside the maximum color range unique to the image output device in a color image, adjacent pixels having substantially the same color gamut and hue can be highlighted and displayed as a single area with a simple operation. The color gamut of the area can be converted.

  Hereinafter, an image processing system including an image processing apparatus and an image output apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram showing the configuration of an image processing system according to an embodiment of the present invention. As shown in FIG. 1, the image processing system according to the present embodiment includes an image output device 1 such as a printer and an image processing device 2 capable of wired or wireless communication via a cable or a network such as a LAN. .

  Here, in the image processing apparatus 2, 201 is a data input unit that inputs image data, 202 is a color processing unit that performs color processing (color conversion) such as saturation enhancement on a selected area, and 206 is a data input unit. An image buffer that holds image data input from the unit 201, and a color gamut data holding unit 207 that stores color gamut data of the image output apparatus 1. Reference numeral 203 denotes a color gamut inside / outside determination unit that reads image data stored in the image buffer 206 pixel by pixel and determines whether the pixel is in the color gamut data stored in the color gamut data holding unit 207. Is a grouping unit that groups data determined to be within the color gamut by the color gamut inside / outside determination unit 203, and 205 is a data output unit that outputs the image data stored in the image buffer 206 to the image output apparatus 1 or the like. Further, 208 displays the image data stored in the image buffer 206, highlights the area determined to be out of the color gamut by the color gamut determination unit 203, and emphasizes the saturation for the highlighted area. This is a display / change unit for performing processing such as setting whether to perform color processing (color conversion).

<Processing Operation in Image Processing Device 2>
Next, an example of processing operation in the above-described image processing apparatus 2 will be described. FIG. 2 is a flowchart for explaining a processing operation procedure by the image processing apparatus 2 in the present embodiment.

  First, image data is acquired from the data input unit 201, read, and stored in the image buffer 206 (step S1). Next, the color gamut inside / outside determination unit 203 acquires and reads data pixel by pixel (for example, RGB value of each pixel) from the image data stored in the image buffer 206, and stores the pixel in the color gamut data holding unit 207. It is determined by acquiring information about the color gamut of the image output device 1 whether it is within the color gamut of the image output device 1 (step S2). The details of the determination operation will be described later with reference to FIGS.

  Further, the grouping unit 204 divides the pixels determined to be out of the color gamut from the result of the determination in the color gamut in step S2 into at least one group (step S3). Details of the grouping method will be described later with reference to FIG.

  The display / change unit 208 highlights the areas grouped in step S3 (step S4). In this embodiment, as will be described later, it is possible to select display / non-display of the highlight by operating a button provided in the display / change unit 208.

  Further, the area highlighted in step S4 is selected, and color processing (color conversion) such as saturation enhancement is performed so as to be within the color reproduction range of the image output apparatus 1 (step S5).

  Then, it is determined whether or not to end the image processing (step S6). When the processing is continued, the processing returns to step S2 and the above-described processing is continued. On the other hand, when the process ends, the image data is output from the data output unit 208 to the image output apparatus 1 (step S7). As a result, the image output apparatus 1 can print out the image data using the color reproduction range to the maximum.

<Color gamut inside / outside determination processing>
Next, details of the color gamut inside / outside determination method executed in step S2 will be described with reference to FIGS. The color gamut data holding unit 207 stores output Lab values for input RGB values that can be reproduced by the image output apparatus 1 as described above. Here, the input RGB values (R, G, B) are, for example, (0, 0, 0), (0, 0, 32) ... (0, 0, 255), (0, 32, 0), ( (0, 32, 32)... (255, 255, 255) are given as data on a total of 729 lattices.

  In this case, an output Lab value that can be reproduced by the image output apparatus 1 is associated with each input point. FIG. 3 is a diagram illustrating a state when output Lab data reproducible by the image output apparatus 1 is mapped on the Lab space. In FIG. 3, output Lab data that can be reproduced by the image output apparatus 1 is given by the vertices of each triangle in the figure. In FIG. 3, since each triangle is displayed in an opaque color, only the vertexes of the outermost triangle in the Lab space are visible. That is, in this embodiment, as shown in FIG. 3, after mapping on the Lab space, a tetrahedron connecting four neighboring points is formed.

  Here, whether or not a certain point is inside a tetrahedron is determined as follows. FIG. 4 is a diagram for explaining a relationship between a tetrahedron OABC having an output Lab value mapped in the Lab space as a vertex and a certain point P. FIG. As shown in FIG. 4, three vectors OA, OB, and OC are set, and the respective components are as shown below.

  At this time, if OP = (Lp, ap, bp) for the transformation (Rp, Gp, Bp) → (LP, aP, bP) at a certain point P, there exist real numbers k, m, n satisfying the following equation: To do.

  At this time, when the point P exists inside the tetrahedron OABC, the following expression is satisfied.

  Here, when equation (4) is rewritten with vector components, the following equation is obtained.

  From this result, the following equation is derived.

That is, it may be determined whether or not the result of Expression (7) satisfies the condition shown in Expression (5). And the above determination is performed about all the tetrahedrons shown in FIG. As a result, if the point P is inside any one of the tetrahedrons, it is determined to be within the color gamut, and if the point P is outside all the tetrahedrons, it is determined to be out of the color gamut.
For example, RGB → Lab conversion ((Rp, Gp, Bp) → (LP, aP, bP) conversion) may use the following equation, for example. That is, when RGB of each patch of input data is (Rp, Gp, Bp) and the color processing parameter is a matrix of 3 rows and 3 columns, conversion is performed using the following equation.

  Further, the converted RGB data (R, G, B) is converted into CIE tristimulus values XYZ using the color system conversion parameters held in the color gamut data holding unit 207. For example, if the held color system conversion parameter is a conversion matrix in the sRGB color space defined by IEC 61966-2-1, it is converted into CIE tristimulus values XYZ using the following equation.

  After that, the white point is converted to CIELAB with D65 as the converted LAB data (L *, a *, b *). This conversion formula is shown in the following formula.

here,
X, Y and Z are the tristimulus values X, Y and Z of the XYZ color system, respectively, and Xn, Yn and Zn are the values of X, Y and Z of the white point. When D65, Xn = 95.05, Yn = 100.0, and Zn = 108.91.

  In the present embodiment, the case where the image data stored in the image buffer 206 is a conversion matrix in the sRGB color space defined by IEC 61966-2-1 has been described as an example, and therefore, when converting to CIELAB The white point is D65. Needless to say, when the color system conversion parameter is in another color space, the white point corresponding to the color space is used.

<Grouping process>
Next, a process of grouping together adjacent predetermined pixels among the pixels determined to be out of the color gamut in step S2 will be described. That is, when pixels with similar hues exist in the vicinity, it is more efficient to perform color processing (color conversion) by grouping them into the same group instead of performing color processing for each pixel. The image after color processing also becomes an image without a sense of incongruity. Therefore, first, the hue H of a certain pixel P (Lp, ap, bp) is obtained by the following equation.

FIG. 5 is a diagram illustrating a relationship between a certain pixel P (Lp, ap, bp) and the hue H. Here, as neighboring pixels, for example, eight neighboring pixels of the pixel P (that is, neighboring pixels surrounding a certain pixel on the image) are searched, and the searched neighboring pixels are in the color gamut shown in FIG. When the hue difference is within a certain threshold, it is handled as the same group. Note that the RGB → Lab conversion ((Rp, Gp, Bp) → (Lp, ap, bp) conversion) is performed in accordance with the method described above.
Note that the above-described grouping process is limited to a specific hue (for example, blue or green), and the subsequent processes are performed even if other hues (for example, yellow or red) are within the color gamut. It may not be possible. In this case, when the hue H is within a specific range, the grouping process is performed, and when the hue H is out of the specific range, it is excluded from the target of the subsequent processing.

  Further, it is also possible to execute color processing for each pixel without grouping as described above.

<Color processing>
Next, details of the color processing will be described with reference to FIG. FIG. 6 is a diagram for explaining how the color processing unit 202 is operated using the display / change unit 208. In FIG. 6, 2081 is a pointer for selecting a highlighted area, 2082 is highlighted and selected, 2083 is a highlighted area, and 2084 is a color processing execution button (ie, saturation). (Enhancement processing button) 2085 is a highlight / non-display selection button.

  Here, when performing saturation emphasis processing, first, at least one region highlighted with the pointer 2081 is selected. Then, color processing (saturation enhancement processing) is executed by pressing a color processing execution button 2084. The saturation emphasis method is, for example, after RGB → Lab conversion is performed on all pixels in the region, and a and b are changed with a being a × (1 + Δ) and b being b × (1 + Δ), for example. Then, Lab → RGB conversion is performed. Here, Δ is an arbitrary numerical value for changing a and b, such as 0.1. For example, when a and b are to be increased by 10 percent, a numerical value of Δ = 0.1 is set. Use.

  In the saturation enhancement process, for the same reason, the color gamut of the pixel after enhancement may be set within the color gamut range of the image output apparatus 1 held in the color gamut data holding unit 207. desirable. For this reason, when the color gamut of the emphasized pixel becomes out of the color gamut again, for example, on the triangle on the outermost surface in the Lab space of FIG. You may perform the process set to a point.

  Further, in order to confirm how much saturation is emphasized after the saturation enhancement processing, it is easier to confirm if the highlight display is turned off. In that case, the highlight display button 2085 may be pressed so that highlight display / non-display can be switched. Note that RGB → Lab conversion may be performed using the above-described formula, and Lab → RGB conversion may be performed by inverse calculation of RGB → Lab conversion.

<Other embodiments>
In the above-described embodiment, the color-converted image is directly output from the image processing apparatus 2 to the image output apparatus 1. However, without direct output, for example, a portable recording medium such as a compact flash (registered trademark) or a hard disk An image may be recorded in the image output device 1 and output by the image output device 1 at the convenience of the user. Further, the image output apparatus 1 may be a monitor or other multifunction peripheral as well as a printer.

  In the above-described embodiment, the color processing is limited to saturation enhancement, but other processing such as contrast enhancement and gamma conversion processing may be performed in the same manner.

  Note that the present invention can be applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), but a device (for example, a copier, a facsimile machine, etc.) composed of a single device You may apply to.

  Also, an object of the present invention is to supply a recording medium (or storage medium) on which a program code of software that realizes the functions of the above-described embodiments is recorded to a system or apparatus, and the computer (or CPU or CPU) of the system or apparatus. Needless to say, this can also be achieved when the MPU) reads and executes the program code stored in the recording medium. In this case, the program code itself read from the recording medium realizes the functions of the above-described embodiment, and the recording medium on which the program code is recorded constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) or the like running on the computer based on an instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.

  Further, after the program code read from the recording medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that the case where the CPU or the like provided in the card or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

  When the present invention is applied to the recording medium, program code corresponding to the flowchart described above is stored in the recording medium.

1 is a schematic diagram illustrating a configuration of an image processing system according to an embodiment of the present invention. It is a flowchart for demonstrating the process operation procedure by the image processing apparatus 2 in this embodiment. It is a figure which shows a mode when the output Lab data reproducible with the image output apparatus 1 are mapped on Lab space. It is a figure for demonstrating the relationship between the tetrahedron OABC which makes the output Lab value mapped by Lab space the vertex, and a certain point P. FIG. It is a figure which shows the relationship between a certain pixel P (Lp, ap, bp) and hue H. 6 is a diagram for explaining a state in which a color processing unit 202 is operated using a display / change unit 208. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image output apparatus 2 Image processing apparatus 201 Data input part 202 Image processing part 203 Color gamut inside / outside determination part 204 Grouping part 205 Data output part 206 Image buffer 207 Color gamut data holding part 208 Display / change part

Claims (10)

Acquisition means for acquiring a color image;
Image holding means for holding the color image;
Color gamut holding means for holding information about a color gamut that can be output by a predetermined image output device;
Determination means for determining whether or not a predetermined pixel in the color image held in the image holding means is in the color gamut;
A color conversion unit that performs color conversion on the pixel when the determination unit determines that the pixel is out of the color gamut;
An image processing apparatus comprising: output means for outputting the color image after performing color conversion on a pixel determined to be out of the color gamut. The color image is expressed in RGB space;
The color gamut holding means holds an output Lab value of the image output device corresponding to an input RGB value;
Forming means for forming a tetrahedron using the pixel values of the output Lab values held in the color gamut holding means as vertices, and using four points in the Lab space of each vertex;
When the pixel of the color image does not exist on or inside the surface of any tetrahedron formed by the forming unit, the determination unit determines that the pixel is out of the color gamut that can be output by the image output device. The image processing apparatus according to claim 1, wherein:   The image processing apparatus according to claim 1, wherein the color conversion unit adjusts the saturation of the pixel. Grouping means for grouping pixels that are determined to be out of the color gamut by the determination means and that are located in the vicinity of each other to form at least one area;
Selecting means for selecting a predetermined area among the areas grouped by the grouping means;
The image processing apparatus according to claim 1, wherein the color conversion unit performs color conversion on all pixels belonging to the area selected by the selection unit.   If the difference between the color gamut and the hue between the pixel determined to be out of the color gamut by the determination unit and the adjacent pixel surrounding the pixel is within a predetermined threshold, the grouping unit sets the adjacent pixel to the same region as the pixel. The image processing apparatus according to claim 4, wherein: The output means outputs the color image to a predetermined printing apparatus;
The image processing apparatus according to claim 1, wherein the color gamut holding unit holds information regarding a color gamut that can be output by the printing apparatus.   The image processing apparatus according to claim 1, wherein the output unit stores the color image in a predetermined recording medium. A first acquisition step of acquiring a color image;
A second acquisition step of acquiring information about a color gamut that can be output by a predetermined image output device;
A determination step of determining whether or not a predetermined pixel in the color image is in a color gamut that can be output by the image output device;
A color conversion step for performing color conversion on the pixel when the determination step determines that the pixel is out of the color gamut;
And an output step of outputting the color image after performing color conversion on a pixel determined to be out of the color gamut. On the computer,
A first acquisition procedure for acquiring a color image;
A second acquisition procedure for acquiring information about a color gamut that can be output by a predetermined image output device;
A determination procedure for determining whether or not a predetermined pixel in the color image is in a color gamut that can be output by the image output device;
A color conversion procedure for performing color conversion on the pixel when the determination procedure determines that the pixel is out of the color gamut;
A program for executing an output procedure for outputting the color image after performing color conversion on a pixel determined to be out of the color gamut.   A computer-readable recording medium storing the program according to claim 9.

Images