JP4368833B2 - Image processing apparatus, image processing method, image forming apparatus, program, and recording medium - Google Patents

Description

  The present invention relates to an image processing apparatus that processes a color image, an image forming apparatus including the image processing apparatus, and an image processing method thereof.

  In recent years, digitalization of office automation equipment has rapidly progressed, and the demand for color image output has increased. As a result, electrophotographic digital color copiers, ink jet and thermal transfer color printers, etc. have become widespread. Yes. For example, image information input from an input device such as a digital camera or a scanner, or image information created on a computer is output using these output devices. In these input / output devices, it is necessary to always output an image with stable color reproduction for input image information, and color conversion (color correction) processing of digital image processing technology plays an important role. Plays.

  Some of the digital color copiers / multifunction peripherals are provided with a function of performing two-color printing in addition to a function of outputting a full-color image or a monochrome image. For example, a part of a black text manuscript is corrected with a red pen, printed with red vermilion, or an advertisement with a part highlighted in red using two colors of red and black. In two-color printing, although color reproducibility as in full color is not emphasized, color unevenness and color skipping may occur, and color reproducibility as two-color printing may be impaired. Therefore, the technique of Patent Document 1 has been proposed as a method for improving the reproducibility of a two-color original and providing an image that looks more two-color.

In Patent Document 1, a digital signal (R, G, B) obtained by reading a document with a scanner or the like is converted into three coordinate values of hue (H), saturation (S), and lightness (L) using a coordinate conversion circuit. Then, after changing the values of H, S, and L so that a two-color printing result can be obtained according to the desired processing, two-color printing is performed by performing reverse coordinate conversion and returning to the R, G, and B coordinate axes again. Is realized.
Japanese Patent Laid-Open No. 11-55539 (published on February 26, 1999) JP 2004-155015 A (published June 3, 2004 (2004))

  However, the technique of Patent Document 1 requires a coordinate conversion circuit for converting the read digital signal (R, G, B) into hue (H), saturation (S), and lightness (L). There is a problem that the scale of processing and hardware is large.

  The present invention has been made in view of the above problems, and an object thereof is an image processing apparatus capable of two-color output and having a small hardware scale, and an image forming method, an image forming apparatus, a program, and a recording medium. Is to realize.

In order to solve the above-described problem, the image processing apparatus of the present invention has a first color space represented by three-dimensional Cartesian coordinates using three color components including a first color, a second color, and a third color. In an image processing apparatus for converting color image data of a color system into color image data of a second color system composed of a plurality of color components, the color image data of the first color system is converted in the color space. By mapping on the triangular plane formed by connecting the achromatic color axis and the vertex of the first color in the color space other than on the achromatic color axis, the achromatic color and the vertex of the first color are associated with each other. Data conversion means for converting into two-color image data comprising colors, and color conversion calculation means for converting the two-color image data into color image data of the second color system, and The data conversion means outputs the first color output value as follows: When the gradation data of the first color is output as it is and the average value of the gradation data of the second color and the gradation data of the third color is larger than the gradation data of the first color, The first color gradation data is output as the output values of the second color and the third color, and the average value of the second color gradation data and the third color gradation data is the first color. If it is equal to or lower than the color gradation data, the average value is output as the output value of each of the second color and the third color, whereby the color image data of the first color system is converted to the triangle. It is characterized by mapping on a plane.
In order to solve the above problems, an image processing apparatus according to the present invention converts color image data of a first color system represented by a three-dimensional Cartesian coordinate system using three color components into a plurality of color components. In the image processing apparatus for converting to color image data of the second color system comprising the color image data of the first color system other than on the achromatic color axis and the achromatic color axis in the color space A data conversion means for converting into two-color image data comprising an achromatic color and a color associated with the vertex by mapping on a triangular plane formed by connecting one vertex of the color space; and the two colors And color conversion calculation means for converting the image data into color image data of the second color system.

  According to the above invention, the data conversion means is on a triangular plane formed by connecting the color image data of the first color system with the achromatic color axis and one vertex of the color space other than the achromatic color axis. Since the image data is converted into two-color image data by mapping to the first color system, the direct color data is composed of only the adder, shifter (power multiplication), and comparator for the color image data of the first color system. Conversion can be performed. Therefore, the hardware scale for performing data conversion is reduced.

  Further, since the color image data of the first color system is all mapped on the triangular plane connecting the achromatic color axis and one vertex (one main color) of the color space as described above, the triangular color image data is mapped. In the plane, image data of only two colors of black and one main color are represented. Accordingly, the color correction table or coefficient parameter (masking coefficient or weighting coefficient in the neural network) in the full color mode can be shared for the color image data processed by the data conversion means, and the color correction table dedicated to two-color printing, Coefficient parameters are not required. As a result, memory can be reduced. Further, by using the same color correction table or coefficient parameter as in the full color mode, it is possible to realize visually good image quality.

  As described above, there is an effect that an image processing apparatus capable of two-color output and having a small hardware scale can be realized.

In the image processing apparatus of the present invention, in order to solve the above-described problem, the data conversion means includes all six colors composed of primary colors and secondary colors predetermined for the first color system. Selecting a vertex of the first color from the vertices of the color space based on a designated input color setting signal for designating any one of the colors for the color image data of the first color system. It is characterized by.
In the image processing apparatus of the present invention, in order to solve the above-described problem, the data conversion means includes all six colors composed of primary colors and secondary colors predetermined for the first color system. The one vertex of the color space is selected based on a designated input color setting signal for designating any one of the colors for the color image data of the first color system.

  According to the above invention, one vertex forming the triangular plane of the mapping destination is selected from all six colors of the primary color and secondary color of the first color system predetermined by the user or the like. It can be specified by the specified input color setting signal.

  Therefore, for example, when it is desired to obtain two-color image data composed of black and red as the color image data of the second color system, the one vertex is obtained with respect to the color image data of the first color system. Corresponding colors can be extracted in accordance with the image data of the two colors.

  As described above, there is an effect that the user's favorite color can be emphasized as a color paired with the achromatic color.

  In addition, since the user's favorite color is simply set using the designated input color setting signal, the hardware configuration is simplified.

In the image processing apparatus of the present invention, in order to solve the above-described problem, the data conversion means includes all six colors composed of primary colors and secondary colors predetermined for the second color system. A color associated with the vertex of the first color is determined based on a designated output color setting signal for designating any one of the colors for the color image data of the second color system. .
In the image processing apparatus of the present invention, in order to solve the above-described problem, the data conversion means includes all six colors composed of primary colors and secondary colors predetermined for the second color system. The color associated with the vertex is determined based on a designated output color setting signal for designating any one of the colors for the color image data of the second color system.

  According to the above invention, no matter what color the color corresponding to one vertex forming the triangular plane of the mapping destination is determined, the color is determined by the second color system predetermined by the user or the like. Can be output as a color designated by a designated output color setting signal from among all six primary colors and secondary colors.

  Therefore, for example, even if the color corresponding to the one vertex is a color other than red for the color image data of the first color system, black and red are used as the color image data of the second color system. When it is desired to obtain two-color image data consisting of the above, the color corresponding to the one vertex can be converted and output in accordance with the two-color image data.

  As described above, there is an effect that the user's favorite color can be emphasized as a color paired with the achromatic color.

  Further, since the user's favorite color is only set using the designated output color setting signal, the hardware configuration is simplified.

In the image processing apparatus of the present invention, in order to solve the above-described problem, the data conversion means includes all six colors composed of primary colors and secondary colors predetermined for the first color system. Selecting a vertex of the first color from the vertices of the color space based on a designated input color setting signal for designating any one of the colors for the color image data of the first color system; One of all six colors consisting of primary colors and secondary colors predetermined for the second color system is designated for the color image data of the second color system. A color associated with the vertex of the first color is determined based on the designated output color setting signal.
In the image processing apparatus of the present invention, in order to solve the above-described problem, the data conversion means includes all six colors composed of primary colors and secondary colors predetermined for the first color system. Selecting one vertex of the color space based on a designated input color setting signal for designating any one of the colors for the color image data of the first color system, and the second color system Based on a designated output color setting signal for designating any one of all six colors consisting of predetermined primary colors and secondary colors for the color image data of the second color system. The color associated with the vertex is determined.

  According to the above invention, one vertex forming the triangular plane of the mapping destination is selected from all six colors of the primary color and secondary color of the first color system predetermined by the user or the like. It can be specified by the specified input color setting signal. Further, no matter what color the color corresponding to one vertex forming the triangular plane of the mapping destination is determined, the color is changed to the primary color of the second color system predetermined by the user or the like. The secondary colors can be output as a color designated by the designated output color setting signal from all six colors.

  Therefore, for example, if the designated input color is cyan and the designated output color is magenta, the cyan component of the image data having the first color system is extracted, and the color component is an image having the second color system. As the magenta component of the data, various combinations of input and output are possible so that the image data can be converted into two-color image data of black and magenta.

  As described above, there is an effect that the user's favorite color can be emphasized as a color paired with the achromatic color.

  In order to solve the above problems, an image forming apparatus according to the present invention includes the above-described image processing apparatus, and performs image processing on the image data of the input image by the image processing apparatus to form an image. It is a feature.

  According to the above invention, it is possible to perform two-color printing using the image data processed by the image enlargement processing device. Accordingly, it is possible to provide an image forming apparatus capable of suppressing the scale of hardware and outputting a visually good quality image by using the same color correction processing as in the full color mode. There is an effect.

In order to solve the above-described problem, the image processing method of the present invention has a first color space represented by three-dimensional Cartesian coordinates using three color components including a first color, a second color, and a third color. An image processing method for converting color image data of a color system into color image data of a second color system comprising a plurality of color components, wherein the color image data of the first color system is converted in the color space By mapping on the triangular plane formed by connecting the achromatic color axis and the vertex of the first color in the color space other than on the achromatic color axis, the achromatic color and the vertex of the first color are associated with each other. A data conversion step for converting the image data into two-color image data comprising colors, and a color conversion operation step for converting the two-color image data into color image data of the second color system, and the data conversion In the step, the first color When the gradation data of the first color is output as it is and the average value of the gradation data of the second color and the gradation data of the third color is larger than the gradation data of the first color Outputs gradation data of the first color as output values of the second color and the third color, and an average value of the gradation data of the second color and the gradation data of the third color is When the gradation data is less than or equal to the first color gradation data, the first color system color image data is output by outputting the average value as the output value of each of the second color and the third color. Is mapped onto the triangular plane.
In order to solve the above problems, the image processing method of the present invention converts color image data of a first color system represented by a three-dimensional Cartesian coordinate system using three color components into a plurality of color components. In the image processing method for converting to color image data of the second color system comprising the color image data of the first color system other than on the achromatic color axis and the achromatic color axis in the color space A data conversion step for converting into two-color image data comprising an achromatic color and a color associated with the vertex by mapping on a triangular plane formed by connecting one vertex of the color space; and the two colors And a color conversion calculation step for converting the image data into color image data of the second color system.

  According to the above invention, in the data conversion step, the color image data of the first color system is on a triangular plane formed by connecting the achromatic color axis and one vertex of the color space other than the achromatic color axis. Since the image data is converted into two-color image data, direct data conversion is performed on the first color system color image data only by addition processing, shift processing (power multiplication), and comparison processing. It can be carried out. Therefore, data conversion can be performed with a small hardware scale.

  Further, since the color image data of the first color system is all mapped on the triangular plane connecting the achromatic color axis and one vertex (one main color) of the color space as described above, the triangular color image data is mapped. In the plane, image data of only two colors of black and one main color are represented. Therefore, the color correction table or coefficient parameter (masking coefficient or weighting coefficient in the neural network) in the full color mode can be shared for the color image data processed in the data conversion step, and the color correction table dedicated to two-color printing, Coefficient parameters are not required. As a result, memory can be reduced. Further, by using the same color correction table or coefficient parameter as in the full color mode, it is possible to realize visually good image quality.

  As described above, it is possible to realize an image processing method capable of performing data conversion with a small hardware scale for performing two-color output.

In order to solve the above problems, the image processing method of the present invention includes all six colors consisting of primary colors and secondary colors predetermined for the first color system in the data conversion step. Selecting a vertex of the first color from the vertices of the color space based on a designated input color setting signal for designating any one of the colors for the color image data of the first color system. It is characterized by.
In order to solve the above problems, the image processing method of the present invention includes all six colors consisting of primary colors and secondary colors predetermined for the first color system in the data conversion step. The one vertex of the color space is selected based on a designated input color setting signal for designating any one of the colors for the color image data of the first color system.

  According to the above invention, one vertex forming the triangular plane of the mapping destination is selected from all six colors of the primary color and secondary color of the first color system predetermined by the user or the like. It can be specified by the specified input color setting signal.

  Therefore, for example, when it is desired to obtain two-color image data composed of black and red as the color image data of the second color system, the one vertex is obtained with respect to the color image data of the first color system. Corresponding colors can be extracted in accordance with the image data of the two colors.

  As described above, there is an effect that the user's favorite color can be emphasized as a color paired with the achromatic color.

  In addition, since the user's favorite color is simply set using the designated input color setting signal, the hardware configuration is simplified.

In order to solve the above problems, the image processing method of the present invention includes all six colors consisting of primary colors and secondary colors predetermined for the second color system in the data conversion step. A color associated with the vertex of the first color is determined based on a designated output color setting signal for designating any one of the colors for the color image data of the second color system. .
In order to solve the above problems, the image processing method of the present invention includes all six colors consisting of primary colors and secondary colors predetermined for the second color system in the data conversion step. The color associated with the vertex is determined based on a designated output color setting signal for designating any one of the colors for the color image data of the second color system.

  According to the above invention, no matter what color the color corresponding to one vertex forming the triangular plane of the mapping destination is determined, the color is determined by the second color system predetermined by the user or the like. Can be output as a color designated by a designated output color setting signal from among all six primary colors and secondary colors.

  Therefore, for example, even if the color corresponding to the one vertex is a color other than red for the color image data of the first color system, black and red are used as the color image data of the second color system. When it is desired to obtain two-color image data consisting of the above, the color corresponding to the one vertex can be converted and output in accordance with the two-color image data.

  As described above, there is an effect that the user's favorite color can be emphasized as a color paired with the achromatic color.

  Further, since the user's favorite color is only set using the designated output color setting signal, the hardware configuration is simplified.

In order to solve the above problems, the image processing method of the present invention includes all six colors consisting of primary colors and secondary colors predetermined for the first color system in the data conversion step. Selecting a vertex of the first color from the vertices of the color space based on a designated input color setting signal for designating any one of the colors for the color image data of the first color system; One of all six colors consisting of primary colors and secondary colors predetermined for the second color system is designated for the color image data of the second color system. A color associated with the vertex of the first color is determined based on the designated output color setting signal.
In order to solve the above problems, the image processing method of the present invention includes all six colors consisting of primary colors and secondary colors predetermined for the first color system in the data conversion step. Selecting one vertex of the color space based on a designated input color setting signal for designating any one of the colors for the color image data of the first color system, and the second color system Based on a designated output color setting signal for designating any one of all six colors consisting of predetermined primary colors and secondary colors for the color image data of the second color system. The color associated with the vertex is determined.

  According to the above invention, one vertex forming the triangular plane of the mapping destination is selected from all six colors of the primary color and secondary color of the first color system predetermined by the user or the like. It can be specified by the specified input color setting signal. Further, no matter what color the color corresponding to one vertex forming the triangular plane of the mapping destination is determined, the color is changed to the primary color of the second color system predetermined by the user or the like. The secondary colors can be output as a color designated by the designated output color setting signal from all six colors.

  Therefore, for example, if the designated input color is cyan and the designated output color is magenta, the cyan component of the image data having the first color system is extracted, and the color component is an image having the second color system. As the magenta component of the data, various combinations of input and output are possible so that the image data can be converted into two-color image data of black and magenta.

  As described above, there is an effect that the user's favorite color can be emphasized as a color paired with the achromatic color.

  In order to solve the above-described problems, the program of the present invention is a program for operating the image processing apparatus and causing the computer to function as each of the above-described means.

  According to the above invention, it is possible to realize the image processing apparatus by realizing each unit of the image processing apparatus with a computer.

  In order to solve the above problems, a recording medium of the present invention is a computer-readable recording medium on which the above program is recorded.

  According to the above invention, there is an effect that the image processing apparatus can be realized on the computer by the program read from the recording medium.

  As described above, the image processing apparatus according to the present invention includes the data conversion unit and the color conversion calculation unit, so that an image processing apparatus capable of outputting two colors and having a small hardware scale can be realized. There is an effect.

  An embodiment of the present invention will be described below with reference to FIGS.

  FIG. 7 is a block diagram showing the configuration of a digital color copying machine including the color image processing apparatus according to the present embodiment.

  As shown in FIG. 7, the digital color copying machine 1 includes a color image input device 2, a color image processing device 3, a color image output device 4, and an operation panel 5.

  The color image processing device 2 performs image processing of color image data input from the color image input device 2 and outputs the image data after the image processing to the color image output device 4, and includes an A / D conversion unit. 31, shading correction unit 32, input tone correction unit 33, region separation processing unit 34, color correction unit 35, black generation and under color removal unit 36, spatial filter processing unit 37, output tone correction unit 38, and tone reproduction A processing unit 39 is provided. The operation panel 5 includes a display unit configured by setting buttons, numeric keys, a liquid crystal display, and the like for setting the operation mode of the digital color copying machine 1.

  The color image input device (image reading means) 2 is composed of, for example, a scanner unit equipped with a CCD (Charge Coupled Device), and the reflected light image from the original is converted into RGB (R: red, G: green, B: blue). The analog signal is read by the CCD and input to the color image processing apparatus 3.

  The analog signal read by the color image input device 2 is sequentially sent through the color image processing device 3 to the A / D conversion unit 31 to the gradation reproduction processing unit 39, and is output as a CMYK digital color signal. It is output to the device 4.

  The A / D (analog / digital) converter 31 converts RGB analog signals into digital signals, and the shading correction unit 32 applies the digital RGB signals sent from the A / D converter 31. The color image input device 2 is subjected to processing for removing various distortions generated in the illumination system, the imaging system, and the imaging system.

  The input tone correction unit 33 adjusts the color balance of the RGB signal (RGB reflectance signal) from which various distortions have been removed by the shading correction unit 32, and at the same time provides the color image processing device 3 with a density signal or the like. A process of converting the signal into an easy-to-handle signal of the employed image processing system is performed.

  The region separation processing unit 34 separates each pixel in the input image into one of a character region, a halftone dot region, and a photograph region from the RGB signal. Based on the separation result, the region separation processing unit 34 sends a region identification signal indicating to which region the pixel belongs to the black generation and under color removal unit 36, the spatial filter processing unit 37, and the gradation reproduction processing unit 39. In addition to the output, the input signal output from the input tone correction unit 33 is output to the subsequent color correction unit 35 as it is.

  The color correction unit 35 performs processing for removing color turbidity based on the spectral characteristics of CMY (C: cyan, M: magenta, Y: yellow) color materials including unnecessary absorption components in order to realize faithful color reproduction. Is.

  The black generation and under color removal unit 36 generates black (K) signals from the CMY three-color signals after color correction, and subtracts the K signals obtained by black generation from the original CMY signals to generate new CMY signals. The CMY three-color signal is converted into a CMYK four-color signal.

  As an example of the black generation process, there is a method (general method) for generating black by skeleton black. In this method, the input / output characteristic of the skeleton curve is y = f (x), the input data is C, M, Y, the output data is C ′, M ′, Y ′, K ′, UCR (Under Color Assuming that the (removal) rate is α (0 <α <1), the black generation / under color removal processing is expressed by the following equation (1).

  The spatial filter processing unit 37 performs spatial filter processing by a digital filter on the image data of the CMYK signal input from the black generation and under color removal unit 36 based on the region identification signal, and corrects the spatial frequency characteristics. The gradation reproduction processing unit 39 performs processing so as to prevent blurring of the output image and deterioration of graininess, and the tone reproduction processing unit 39, like the spatial filter processing unit 37, uses region identification signals based on the CMYK signal image data. Is subjected to predetermined processing.

  For example, the region separated into characters by the region separation processing unit 34 has a high frequency enhancement amount in the sharp enhancement processing in the spatial filter processing by the spatial filter processing unit 37 in order to improve the reproducibility of black characters or color characters in particular. Increased. At the same time, the gradation reproduction processing unit 39 selects binarization or multi-value processing on a high-resolution screen suitable for high-frequency reproduction.

  Further, with respect to the region separated into halftone dots by the region separation processing unit 34, the spatial filter processing unit 37 performs low-pass filter processing for removing the input halftone component. The output tone correction unit 38 performs output tone correction processing for converting a signal such as a density signal into a halftone dot area ratio that is a characteristic value of the color image output device 4, and then the tone reproduction processing unit 39. Then, gradation reproduction processing (halftone generation) is performed so that the image is finally separated into pixels and each gradation is reproduced. For the region separated into photographs by the region separation processing unit 34, binarization or multi-value processing is performed on the screen with an emphasis on gradation reproducibility.

  The image data subjected to the above-described processes is temporarily stored in the storage means, read out at a predetermined timing, and input to the color image output device 4. The color image output device 4 outputs image data onto a recording medium (for example, paper). Examples of the color image output device 4 include a color image forming device using an electrophotographic method or an inkjet method, but are not particularly limited. It is not something. The above processing is controlled by a CPU (Central Processing Unit) (not shown).

  Next, the configuration of the color correction unit 35 in the color image processing apparatus 3 will be described. FIG. 2 shows the configuration of the color correction unit 35.

  The color correction unit 35 uses the input RGB data as the first color system and the output CMY data as the second color system. The color correction processing performed by the color correction unit 35 is based on the premise that the color space of the first color system is represented by three-dimensional Cartesian coordinates. Here, the second color system is also expressed in three-dimensional Cartesian coordinates. In this embodiment, in the first color system and the second color system, the CMY color system is assumed in which CMY is a primary color and RGB is a secondary color. An RGB color system in which the secondary color and CMY are secondary colors may be assumed. In any case, the color obtained by mixing two of the primary colors (three colors) is a secondary color, and the color obtained by mixing two of the secondary colors (three colors) is Primary color. Further, the first color system is not limited to RGB but may be CMY. The second color system is not limited to CMY, but may be RGB. For example, the RGB output device includes pictography. Further, the second color system may generally consist of a plurality of color components.

  The color correction unit 35 includes a one-dimensional lookup table (hereinafter referred to as 1D-LUT) 51 (51r, 51g, 51b), a data conversion unit (data conversion unit) 52, and a color conversion calculation unit (color conversion calculation). Means) 53 is provided.

The 1D-LUT 51 converts an input RGB signal (hereinafter, the signal and data are used in the same meaning) into an R ₁ G ₁ B ₁ signal by using a one-dimensional lookup table (LUT: Look Up Table). To do. The 1D-LUT 51r is provided corresponding to the R signal, the 1D-LUT 51g is provided corresponding to the G signal, and the 1D-LUT 51b is provided corresponding to the B signal. When the one-dimensional LUT adjusts the contrast of the input image data or converts the input RGB signal into CMY data, which is the second color system image data, in the subsequent color conversion calculation unit 53, both By correcting the non-linearity between the color systems, it works to prevent an increase in calculation error.

  A specific process is to refer to the address of the one-dimensional LUT based on the value of the input RGB signal, acquire another RGB data stored at the address, and output it to the subsequent stage. In this case, the input deals with an 8-bit RGB signal of 0 to 255, but it may be a pseudo CMY signal obtained by inverting the RGB signal. Further, the input may be an RGB signal, and the output of the one-dimensional LUT may be a pseudo CMY signal.

  In the present embodiment, the 1D-LUT 51 is not necessarily provided in the color correction unit 35. The correction of the non-linearity of the color system may be performed by providing the 1D-LUT 51 in the preceding stage of the color correction unit 35, and the contrast adjustment can also be performed by the input tone correction unit 33.

The digital color copying machine 1 according to the present embodiment can perform two-color printing. In the two-color printing mode, the data conversion unit 52 converts the signal (R ₁ G ₁ B ₁₎ converted by the 1D-LUT 51 into a one-dimensional LUT. Signal) is converted into another signal (R ₂ G ₂ B ₂ signal) for two-color printing. In the full color mode, this conversion process is not performed.

The color conversion calculation unit 53 (three-dimensional interpolation calculation unit) performs C ₃ M ₃ by interpolation calculation on the signal (R ₂ G ₂ B ₂ signal) converted by the data conversion unit 52 while referring to the three-dimensional LUT. converted into Y ₃ signals. The color conversion calculation unit 53 may be configured to perform other color conversion calculations such as color conversion masking, neural network, and direct LUT that does not use interpolation calculation.

  Next, the configuration and operation of the data conversion unit 52 of the color correction unit 35 relating to two-color printing will be described with examples.

[Example 1]
In this embodiment, when the input image data is 8 bits (0 to 255) in RGB and the output image data is 8 bits (0 to 255) in CMYK, the red component in the input image data RGB is extracted, and red and black A case where printing is performed only will be described.

First, the input image data RGB is converted into R ₁ G ₁ B ₁ data using a one-dimensional LUT by the 1D-LUT 51 of FIG. Next, the R ₁ G ₁ B ₁ data is input to the data converter 52 in FIG. The data converter 52 performs processing as shown in the flowchart of FIG.

In the flowchart of FIG. 1, when R ₁ G ₁ B ₁ data is input to the data conversion unit 52 in S1, the R ₁ data that is the red component of the input image data R ₁ G ₁ B ₁ remains as it is in S2. R ₂ data is processed, and an average process is performed on G ₁ data (green component) and B ₁ data (blue component). When this is realized by hardware, it is sufficient to add and shift one bit to the right.

FIG. 3 shows a CMY color space (input image data is RGB data, but CMY is a primary color, so the color space of the first color system is a CMY space). By S2, all the R ₁ G ₁ B ₁ data is mapped onto the plane KRWC as shown in FIG. 3A when the surface RYWM in FIG. This means that all R ₁ G ₁ B ₁ data are mapped to the hues of R and C across the achromatic color axis (K-W). Here, FIG. 3C conceptually shows the three-dimensional LUT in the color conversion operation unit 53 of FIG. 2, and the input space is RGB.

Next, in S3 of FIG. 1, the R ₂ data and the averaged G ₂ (or B ₂ ) data are compared in size, and the RK reproduction region is determined. In the determination of the RK reproduction area,
(1) When the G ₂ data is larger than the R ₂ data, it is determined that the point (R ₂ , G ₂ , B ₂ ) is outside the triangular plane KRW region.

(2) When the G ₂ data is equal to or less than the R ₂ data, it is determined that the point (R ₂ , G ₂ , B ₂ ) is in the triangular plane KRW region.

  This triangular plane KRW is formed by connecting the achromatic color axis and the vertex of R, which is one of the vertices of the CMY color space other than the achromatic color axis. The vertex may be other than R, but in this embodiment, a case where the vertex is determined as R will be described, and other cases will be described in Embodiment 2.

As a result, when the determination is (1) in the plane KRWC of FIG. 3C, the process proceeds to S4 in FIG. 1, and outside the hatched area (outside the triangular plane KRW area as shown in FIG. 3B) ) (R ₂ , G ₂ , B ₂ ) on the achromatic axis (KW) parallel to RW (or KC) (mapped in the direction indicated by the arrow in FIG. 3B) To do.) That is, G ₂ data and B ₂ data are all the same as R ₂ data. Then proceed with 1 to _S5, and outputs the R ₂ G _{2 B 2.} Further, when the determination is (2) in the plane KRWC in FIG. 3C, the hatched area (in the triangular plane KRW area) is already within the area composed of R and K. 1. Proceed directly to S5 at 1, and output R ₂ G ₂ B ₂ data as it is. When the G ₂ data and the R ₂ data are equal, the result is the same regardless of the above conditions, and the point (R ₂ , G ₂ , B ₂ ) is on the achromatic color axis. In this example, it is included in the determination (2).

With reference to FIG. 6, why the inside / outside of the triangular plane KRW region can be determined in the plane KRWC based on the magnitude relationship between the R ₂ data and the G ₂ data (or B ₂ data) will be described. 6C is a perspective view of the RGB color space, FIG. 6A is a diagram showing the plane KRYG in FIG. 6C, and FIG. 6B is a diagram showing the plane KRMB in FIG. 6C. FIG.

First, paying attention to the plane KRYG, it is divided into a region of R> G and a region of R <G as shown in FIG. 6A depending on the size of the R data and the G data. Next, paying attention to the plane KRMB, it is divided into a region of R> B and a region of R <B as shown in FIG. 6B depending on the size of the R data and B data. Therefore, the region in the triangular plane KRW in FIG. 6C is R> G and R> B, and the region outside the triangular plane KRW (in the triangular plane KWC) is R <G and R <B. Here, since the G ₂ data and the B ₂ data are always the same value from S2 in FIG. 1, if either the G ₂ data or the B ₂ data is compared with the R ₂ data, the point (R ₂ , G ₂ , B ₂ ) can be determined whether they are in the triangular plane KRW.

Finally, all input R ₁ G ₁ B ₁ data is mapped onto the triangular plane KRW as shown in FIG. This is because the input image data is mapped to the hatched area, and all the R ₁ G ₁ B ₁ data has only a red component and a black component. When this is input to the color conversion operation unit 53 of FIG. 2, C ₃ M ₃ Y ₃ printed with the red component and the black component is obtained, and the black generation and under color removal unit 36 of FIG. 7 and FIG. It is converted into printable CMYK data by the black generation / under color removal processing in the color correction unit 71c, and is printed as a two-color print.

A specific example will be described with reference to FIGS. First, in FIG. 4, when the input image data R ₁ G ₁ B ₁ is (0, 0, 255) (blue), R ₂ = 0 and G ₂ = B ₂ = (0 + 255) / from S2 in FIG. 2 = 127.5, and the decimal part is rounded down to 127. This indicates that the point P8 (0, 0, 255) in FIG. 4 is mapped to the point P9 (0, 127, 127). Next, when S3 of FIG. 1 is executed, since G ₂ = 127 is larger than R ₂ = 0, the determination of the RK reproduction region becomes (1) described above, and R ₂ = G _{2 in} S4 of FIG. = B ₂ = 0. This indicates that the point P9 (0, 127, 127) in FIG. 4 is mapped to the point P10 (0, 0, 0). Therefore, the input image data R ₁ G ₁ B ₁ = (0, 0, 255) is mapped to the achromatic axis of (0, 0, 0). This is because the R component of the input image data R ₁ G ₁ B ₁ is smaller than the other G components and B components, so that it is not the hue of the red region, and is therefore printed as a black component (achromatic color). .

Next, another example will be described with reference to FIG. When the input image data R ₁ G ₁ B ₁ is (255, 0, 255) (magenta), R ₂ = 255 and G ₂ = B ₂ = (0 + 255) / 2≈127 in the same manner. This means that the point P11 (255, 0, 255) in FIG. 5 is mapped to the point P12 (255, 127, 127). From the magnitude relationship between R ₂ and G ₂ , the determination of the RK reproduction region is (2) described above, and finally R ₂ G ₂ B ₂ is (255, 127, 127), and R− It represents the color on W.

As described above, since all the R ₁ G ₁ B ₁ data is mapped onto the triangular plane KRW as described above, the color conversion calculation unit 53 can realize two-color printing using only the red component and the black component. become.

Further, since the three-dimensional LUT in the color conversion calculation unit 53 in FIG. 2 is a color correction table created for full color in advance, the color reproducibility is visually (for example, similar to human luminance sensitivity on the achromatic axis). Is good). Therefore, by using this full-color table and using some triangular planes in the color space (table configuration) of FIG. 3C, it is possible to generate a visually good two-color image. Become. Therefore, it is possible to share the table to be used regardless of whether it is the full color mode or the two-color printing mode. In the case of the full color mode, the data conversion unit 52 in FIG. 2 does not perform any processing (that is, outputs R ₁ G ₁ B ₁ of the input image data as R ₂ G ₂ B ₂ data as it is). In the case of two-color printing, the data converter 52 operates as described above, so that the processing in the two modes can be easily realized.

  In addition, when two-color printing is performed with another main color (any of GBCMY) and K, it can be realized by mapping all RGB data onto the triangular planes KGW, KBW, KCW, KMW, and KYW, respectively. The configuration of the data conversion unit that realizes this will be described in the second embodiment.

  Here, the configuration of the data conversion unit 52 that performs the data conversion described so far in the present embodiment will be described. FIG. 12 shows the configuration within the data converter 52 in FIG. The data converter 52 includes an averaging processor 52a, a comparator 52b, and a selector 52c.

Averaging unit 52a has an adder 61 and bit shift 62, the average value of the G ₁ signal and B ₁ signal. The adder 61 adds the _{G 1} data and _{B 1} data, and outputs the data E11 as the addition result. Bit shift 62, by shifting 1 bit data E11 to the right, it obtains and outputs the data E12 is the average value of the _{G 1} data and _{B 1} data. This corresponds to the process in S2 of FIG. As a result, all data is mapped onto the square plane formed by KWRC in FIG.

The comparator 52b compares the magnitudes of the _{R 1} data and data E12, and outputs the result by 1 bit data E13. This corresponds to S3 in FIG. 1, and the inside / outside determination of the triangular plane KRW in FIG. 3C is performed.

The selector 52c as the control signal data E13 generated by the comparator 52 b, selects one of the _{R 1} data and data E12, and outputs it as data E14. This corresponds to the determination result processing S4 of S3 in FIG. 1, and data outside the triangular plane KRW is mapped to an achromatic color, and data within the triangular plane KRW is output as it is.

Finally, the input R ₁ data becomes R ₂ data, and the data E14 output from the selector 52c is distributed to become G ₂ data and B ₂ data. As a result, the same processing as in FIG. 1 is realized.

[Example 2]
In this embodiment, the configuration of the color correction unit 35 is almost the same as that in FIG. 2 except that a user setting signal is input to the data conversion unit 52. The operations of the 1D-LUT 51 and the color conversion calculation unit 53 are the same as those in the first embodiment. Also in this embodiment, a case will be described in which the input image data is 8-bit (0-255) RGB data and the output image data is 8-bit (0-255) CMYK data.

  In the first embodiment, only the case where the R component is extracted from the input image data and the output image data is printed by RK has been described. However, actual two-color printing is not always performed by RK. Depending on the user, various combinations may be required.

  In this embodiment, the user can select a color (any one of RGBCMY) to be extracted from a document, and can select which color (any of RGBCMY) is desired to be printed when printing a designated color. explain. The color selected by the user as the color desired to be extracted from the document is designated as the designated input color, and the color selected by the user as the color desired to be printed is designated as the designated output color. By specifying these colors, for example, the R component can be printed with R, the R component can be printed with G, and the C component can be printed with R, which satisfies the user's needs. Is possible.

  FIG. 13B is a flowchart showing the processing of the second embodiment. Broadly divided into input switching processing, averaging processing, switching processing based on designated input colors and designated output colors, mapping processing to a triangular plane, and output switching processing.

When R ₁ G ₁ B ₁ data is input to the data conversion unit 52 in S201, input switching processing (S202 to S206) is first executed. In the input switching process, data is temporarily switched from R ₁ G ₁ B ₁ data to internal data D ₁ D ₂ D ₃ data based on the user's designated input color. The internal data D ₁ , D ₂ , D ₃ are data in which R ₁ data, G ₁ data, B ₁ data are assigned in the order according to the specified input color, and the subsequent arithmetic processing is internal data D ₁ , This is performed using D ₂ and D ₃ .

The reason for performing the input switching process is to allow the same process to be performed in the subsequent averaging process regardless of which color of RGBCMY is selected by the user as the designated input color. When the user designates a secondary color (refers to any one of R, G, and B. Here, CMY is (primary color), so RGB is a secondary color), the designated color is is substituted into D ₁ data as primary color. And, the other two colors as an auxiliary color are separately assigned to the D ₂ data and D ₃ data. Conversely, when the user designates a primary color (C, M, or Y), the complementary color of the designated color (for example, when the user designates C, the complementary color R of C) is used as the auxiliary color. Assigned to ₁ data. Then, two secondary colors that generate the specified color (for example, if the user specifies C, C is generated by the secondary colors G and B) are D ₂ data and D ₃ data as the main colors. Are assigned separately.

For example, when the user's designated input color is G, the G ₁ data is the primary color and is substituted for the D ₁ data, and the other colors are auxiliary colors, so the R ₁ data and the B ₁ data are D _2. They are separately assigned to the data and D ₃ data. When the user's designated input color is M, R ₁ data and B ₁ data are the primary colors, and are thus substituted for D ₂ data and D ₃ data, respectively, and G ₁ data is an auxiliary color, so D ₁ Assigned to the data. As a result, when the user's designated input color is G or M, R ₁ , G ₁ , and B ₁ data are respectively substituted for D ₂ , D ₁ , and D ₃ data (S205 described later) ). Similarly, when the user's designated input color is R or C, R ₁ , G ₁ , B ₁ data are respectively substituted for D ₁ , D ₂ , D ₃ data (S206 described later) ), When the user's designated input color is B or Y, R ₁ , G ₁ , B ₁ data is substituted for D ₂ , D ₃ , D ₁ data, respectively (S 204 described later). In this way, R ₁ G ₁ B ₁ data is switched to D ₁ D ₂ D ₃ data.

This will be described with reference to FIG. 13. In S202, it is determined whether or not the designated input color is R or C. If R or C, the process proceeds to S206, where R ₁ data is added to D ₁ data, and D _{2 is} input. the _{G 1} data to the data, if the values are the _{B 1} data _{D 3} data. If it is not R or C in S202, the process proceeds to S203, and it is determined whether the designated input color is G or M. Proceed in the S205 when is G or M, the _{G 1} data _{D 1} data, the _{R 1} data to the _{D 2} data, substitutes _{D 3} data _{B 1} data, respectively. If not G or M to proceeds to step S204 in S203, the _{B 1} data _{D 1} data, the _{R 1} data to the _{D 2} data, if the values are the _{G 1} data _{D 3} data.

Next, an averaging process (S207) is executed. In the averaging process, D ₂ data and D ₃ data are added, and D ₄ data that is the addition result is divided by 2 (or shifted to the right by 1 bit) to obtain the D ₂ data and D ₃ data. Request D ₅ data are average values. By calculating the D ₅ data, all of the RGB data is to be mapped to a plane surrounded by K and W and the specified input color and its complementary color. Here, if the user-specified input color is a secondary color is D ₁ data main color, if the specified input color is the primary color, D ₅ data are primary colors.

Next, switching processing (S208 to S214) based on the designated input color and the designated output color in FIG. 13 is executed. In this switching process, D ₁ data and D ₅ data to D ₉ are selected depending on whether the designated input color is a primary color or a secondary color, and whether the designated output color is a primary color or a secondary color. to switch data to the data and the D ₁₀ data. By doing this, it is possible to print the primary color designated as the designated input color as a secondary color and vice versa.

Incidentally, if the specified output color of the user is a secondary color, D ₉ data primary color, D ₁₀ data is supporting colors, if the user specified output color is the primary color, D ₁₀ data primary colors, D ₉ data will supporting colors. Then, by setting the primary color on the output side as the primary color on the input side, it is possible to print the designated input color of the primary color as the designated output color of the secondary color and vice versa.

For example, since the user's designated input color is a secondary color, if the specified output color is also secondary color is the input side is D ₁ data primary color, the output-side D ₉ data is primary color, _{D 1} data is assigned to D ₉ data (S211 to be described later). Because the user's designated input color is a secondary color, if the specified output color is the primary color, the input side is the main color D ₁ data, the output-side D ₁₀ data is the primary color, D _{10 D 1} data is substituted into the data (S212 to be described later). Similarly, at user-specified input color is a primary color, if the specified output color is a secondary color, the input side is the main color D ₅ data, since the output-side D ₉ data is main colors , _{D 5} data is substituted for _{D 9} data (S213 to be described later). Because the user's designated input color is a primary color, if it is also the primary color specified output color is input is the main color D ₅ data, the output-side D ₁₀ data is the primary color, D _{10 D 5} data is substituted for the data (S214 to be described later).

The above process will be described with reference to FIG. 13. In S208, it is determined whether or not the designated input color is a secondary color. If it is a secondary color, the process proceeds to S209. If not, the process proceeds to S210. Designated output color at S209 it is determined whether a secondary color, substituting D ₁ data D ₉ data proceeds to S211 if secondary color, the process proceeds to S212 if not secondary color D ₁₀ data is substituted for _{D 1} data. Specified output color step S210 determines whether the secondary color, substituting D ₅ data to D ₉ data proceeds to S213 if secondary color, the process proceeds to S214 if not secondary color D ₁₀ data substituting _{D 5} data.

Next, mapping processing to a triangular plane is executed. In this mapping process (S215 to S220), the points (D ₁ , D ₅ , D ₅ ) are represented by K, W, and the designated input color in a square plane surrounded by K, W, the designated input color, and its complementary color. It is determined whether it is inside or outside the enclosed triangular plane, and mapping to the triangular plane enclosed by K, W, and the specified output color is performed. Determination of the triangular plane and out is carried out by comparison between the input side of the primary colors (D ₁ data) and the auxiliary color (D ₅ data).

If the designated output color is a secondary color, the process proceeds from S211 or S213 to S215. Wherein the S211 and the S213, since the primary color on the output side is _{D 9} data constantly is substituted _{D 1} data to _{D 9} data if specified input color is a secondary color (S211), specify the input color There is always _{D 5} data substituted into _{D 9} data if primary color (S213). In S215, _{D 1} data determines whether greater than _{D 5} data.

Here, if the specified input color is a secondary color (if proceeds from S211 to S215), when _{D 1} data (the main color) _{D 5} data (complementary color) is smaller than, the program proceeds to a S217 , maps _{D 5} data achromatic point _{(D 1, D 5, D} 5) as the same value as the _{D 1} data. That is, the output side of the supporting colors _{(D 10} data) is substituted for _{D 1} data. Conversely, _{D 1} data (main color Division) is a _{D 5} Data (complementary color) or more, the routine proceeds to S218, using the raw values to _{D 5} data (auxiliary color). That is, the output side of the supporting colors _{(D 10} data) Substituting _{D 5} data.

Then, if the specified input color is the primary color (if proceeds from S213 to S215), when _{D 5} data (primary color) is _{D 1} data (complementary color) or less, the process proceeds to S218, the D ₁ data maps achromatic point _{(D 1, D 5, D} 5) as the same value as _{D 5} data. Therefore, the output side of the supporting colors _{(D 10} data) Substituting _{D 5} data. On the contrary, when _{D 5} data (main color) is greater than _{D 1} data (auxiliary color), the program proceeds to a S217, using the raw values to _{D 1} data, the output side of the auxiliary color _{(D 10} data ) the substitutes _{D 1} data (step S217).

When the designated output color is the primary color, the same process as described above is performed. When the designated input color is the secondary color, it is determined whether or not the D ₁ data is smaller than the D ₅ data. proceed to substitutes D ₅ data on the output side of the auxiliary color (D ₉ data), if the specified input color is the primary color, the process proceeds from S216 to S219, the output side of the auxiliary color (D the ₉ data) is substituted for _{D 1} data.

Finally, output switching processing (steps S221 to S225) is executed. In this output switching process, data is switched from D ₉ and D ₁₀ data to R ₂ G ₂ B ₂ data based on the designated output color. As described above, if the specified output color of the user is a secondary color, D ₉ data in primary colors, a D ₁₀ data supporting colors, if the user specified output color is the primary color, D ₁₀ data in primary colors, _{D 9} data is supporting colors. Then, the designated output color of the user is set as the main color, so that it is converted into desired two-color data.

For example, if the user-specified output color is R (2 primary color) substitutes the D ₉ data is the primary color R ₂ data, D ₁₀ data is an auxiliary color and G ₂ data and B ₂ data When G is substituted, G ₂ data and B ₂ data are always the same value, and R ₂ data is equal to or greater than G ₂ data (or B ₂ data), so it is converted into two-color image data of K and R. (Because R ₂ = G ₂ (= B ₂ ) becomes K, and otherwise R becomes). If the user specified output color is C (1 primary colors), by substituting D ₁₀ data is the primary color and G ₂ data and B ₂ data, substitutes D ₉ data is an auxiliary color R ₂ Data Then, since the G ₂ data and the B ₂ data are always the same value, and the G ₂ data (or B ₂ data) is equal to or higher than the R ₂ data, it is converted into two-color image data of K and C ( R ₂ = G ₂ (= B ₂ ) becomes K, otherwise it becomes C). In these two examples, the designated output colors are different between R and C, but the processing contents are the same (S225 described later). The same process is performed when the user-designated output color is G or M, B or Y (S224 and S223 described later).

To explain the above processing in FIG. 14, designated output color is determined whether the R or C in S221, the process proceeds to S225 if R or C, substituting _{D 9} data into _{R 2} data, G substituting _{D 10} data into _second data, it substitutes the _{D 10} data to _{B 2} data. If it is not R or C in S221, the process proceeds to S222, and it is determined whether or not the designated output color is G or M. If G or M proceeds to S224, and assigns the _{D 10} to _{R 2} data, substitutes _{D 9} to _{G 2} data, it substitutes the _{D 10} data to _{B 2} data. S222, the processing advances to G or M unless S223 substitutes _{D 10} to _{R 2} data, substitutes _{D 10} to _{G 2} data, substitutes _{D 9} to _{B 2} data.

When the output switching process is completed, R ₂ G ₂ B ₂ data is output in S226.

  In this way, even when the user's designated input color is different from the designated output color, two-color printing is possible.

  Next, a detailed configuration of the data conversion unit that performs data conversion of the present embodiment described so far will be described. FIG. 9 shows a configuration in the data conversion unit 52 in FIG.

  The data conversion unit 52 includes a multi-input / output selector 520a, an averaging processing unit 520b, a comparator 520c, a control signal generation unit 520d, a selector 520e, a selector 520f, and a multi-input / output selector 520g.

The multi-input / output selector 520a selects the D ₁ D ₂ D ₃ data of the R ₁ G ₁ B ₁ data based on the designated input color (any of RGBCMY) designated by the user setting signal (designated input color setting signal) s1. Switch to. When the user's designated input color is R, R ₁ data, G ₁ data, and B ₁ data are output as D ₁ data, D ₂ data, and D ₃ data, respectively. When the user's designated input color is G, G ₁ data, R ₁ data, and B ₁ data are output as D ₁ data, D ₂ data, and D ₃ data, respectively. When the user's designated input color is B, B ₁ data, R ₁ data, and G ₁ data are output as D ₁ data, D ₂ data, and D ₃ data, respectively. In this case user-specified input color is a secondary color as the designated input color is to be output as D ₁ signal. When the user's designated input color is C, the same switching process as when R is the designated input color, and when the user's designated input color is M, the same switching process as when G is the designated input color, When the user's designated input color is Y, the same switching process is performed as when B is designated as the designated input color. This correspondence is shown in Table 1. This corresponds to the input switching process of FIG.

Averaging unit 520b is provided with an adder 610 and the bit shift 620, the average value of _{D 2} data and _{D 3} data. The adder 610 adds the _{D 2} data and _{D 3} data, and outputs the addition result as _{D 4} data. Then, the bit shift 620 by shifting one bit to the right D ₄ data, an average value of the D ₂ data and D ₃ data, and outputs it as data D _5. This corresponds to the averaging process of FIG. As a result, all data is mapped onto a square plane composed of K, W, a user-specified input color and its complementary color.

The comparator 520c compares the D ₁ data with the D ₅ data obtained by the averaging process, and outputs the result as D ₆ data of a 1-bit signal. For example, _{D 1} data is equal to _{D 5} data above, 1, otherwise 0, and outputs as _{D 6} data.

Control signal generating unit 520d, the comparator 520c output from the D ₆ data and user setting signal (designated input color setting signal, and the designated output color setting signal) specified type of input color indicated by s2 and the specified output color 1-bit control signal D ₇ for the selector 520e and 1-bit control signal D ₈ for the selector 520f are generated.

A more detailed view of the control signal generator 520d is shown in FIG. The control signal generation unit 520 d includes a selector 531 and a selector 532. A control signal D ₇ for the selector 520 e is output from the selector 531, and a control signal D ₈ for the selector 520 f is output from the selector 532. The selector 531 and the selector 532 of the control signal s2, based on a signal representing the type of the specified output color (specified output color setting signal) s2b, and D ₆ data of the designated input color of the control signal s2 One of the signals indicating the type (designated input color setting signal) s2a is selected. The signal s2a is a bit signal indicating whether the designated input color is a primary color or a secondary color, and is “0” if it is a secondary color and “1” if it is a primary color. And The signal s2b is a bit signal indicating whether the designated output color is a primary color or a secondary color, and is “0” if it is a secondary color and “1” if it is a primary color. Shall.

The selector 531, if the specified output color is a secondary color (signal s2b: 0), the select signals s2a as _{D 7} data. Thus, without being influenced by D ₆ data representing the comparison result in the comparator 520c in the preceding stage, the output is always fixed. Conversely if the specified output color is the primary color (signal s2b: 1) is, D ₆ data is selected as the D ₇ data, output becomes dependent on the comparison result in the preceding stage of the comparator 520c. If the selector 532, specified output color is a secondary color (signal s2b: 0) selects the _{D 6} data as _{D 8} data, if the specified output color is the primary color (signal s2b: 1) the , selects signals s2a as _{D 8} data. That is, the operation reverse to that of the selector 531 is performed. These are summarized in Table 2. The selector 520e · 520f receives the data _D 7 · _{D 8} as a control signal operates as shown in Table 3. In this way, a combination in the case where the user's designated input color is different from the designated output color can be realized. This corresponds to the switching process based on the designated input color and the designated output color in FIG. 13 and the mapping process to the triangular plane.

The selector 520e by _{D 7} data of the control signal generated by the control signal generating unit 520d, and select one of the _{D 1} data and the _{D 5} data, and outputs it as _{D 9} data. For example, the _{D 1} data if _{D 7} data 0, _{D 7} data outputs the _{D 5} data if 1.

The selector 520f by _{D 8} data of the control signal generated by the control signal generating unit 520d, and select one of the _{D 1} data and the _{D 5 data,} and outputs it as _{D 10} data. For example, the _{D 1} data if _{D 8} data 0, _{D 8} data outputs the _{D 5} data if 1.

Multi-input multi-output selector 520g is the user setting signal (designated output color setting signal) s3 is designated to direct output color (either RGBCMY), for switching the _{D 9} data and two _{D 10} data. When the user's designated output color is R, D ₉ data, D ₁₀ data, and D ₁₀ data are output as R ₂ data, G ₂ data, and B ₂ data, respectively. Also, if the user-specified output color is G, _{D 9 data, D 10 data, D 10} data each _{G 2} data, _{R 2} data is output as _{B 2} data. When the user's designated output color is B, D ₉ data, D ₁₀ data, and D ₁₀ data are output as B ₂ data, R ₂ data, and G ₂ data, respectively. When the user's designated output color is C, the same processing as when R is designated as the designated output color. When the user's designated output color is M, the same processing as when G is designated as the designated output color. When the color is Y, the same processing is performed as when B is the designated output color (see Table 4). This corresponds to the output switching process of FIG.

  Eventually, the triangular plane surrounded by the user's designated input color and K and W is mapped to the triangular plane surrounded by the user's designated output color and K and W. With this configuration, all combinations of the user's designated input color and designated output color in RGBCMY can be realized.

Here, an example using numerical values is shown. The user-specified input color and user-specified output color can be selected from RGBCMY, and there are 36 combinations. Since RGBCMY can be classified into primary colors or secondary colors, the 36 combinations can be divided into the following combinations 1) to 4). And in each case of 1) to 4), Table 5 shows a summary of specific examples.
1) The designated input color is a secondary color and the designated output is also a secondary color.
2) The designated input color is the primary color and the designated output is also the primary color.
3) The designated input color is a secondary color and the designated output is a primary color.
4) The designated input color is a primary color and the designated output is a secondary color.

1) will be described in detail. When the designated input color is R (secondary color) and the designated output color is R (secondary color), the input image data RGB is (255, 0, 0). That is, (R ₁ , G ₁ , B ₁ ) = (255, 0, 0). In this case, D ₁ data is 255, D ₂ data, and D ₃ data are each 0, D ₂ data and D ₃ data are averaged, and D ₅ data is 0. Then treated with a comparator 520c and _{D 1} data and the _{D 5 data,} the case of D 1 _{<D 5} and 0 to _{D 6} data, but otherwise outputs a 1, this case, _{D 6} The data becomes 1. Since the specified input color and the specified output color is both secondary color, D ₇ data becomes 0, the D ₉ data D ₁ data, i.e. 255 is R is selected. Then, the _{D 8} data _{D 6} data is selected, since _{D 6} data is _1, the _{D 10} data _{D 5} data (= 0) is selected. Since the designated output color is now R, (255, 0, 0) is output as the output RGB data (R ₂ , G ₂ , B ₂ ). This means that the input itself is output because the R component is larger than the other components and exists in the KWR triangular plane.

Next, another example will be described. When the designated input color is B (secondary color) and the designated output color is M (primary color), the input image data RGB is (255, 255, 0). That is, (R ₁ , G ₁ , B ₁ ) = (255, 255, 0). In this case, the D ₁ data is 0, the D ₂ data, and the D ₃ data are 255, respectively, and the D ₂ data and the D ₃ data are averaged to be D ₅ = 255. Next, because of the magnitude relationship between the D ₁ data and the D ₅ data, the D ₆ data becomes 0 (when D ₁ <D ₅ , the D ₆ data is set to 0, and the other is set to 1). In specifying the input color is a secondary color, because the specified output color is the primary color, D ₆ data is selected to D ₇ data, D ₈ data becomes 0. Since the D ₆ data and the _{D 8} data are both 0, _{D 9} data also _{D 10} data also becomes _{D 1} data, output RGB signals _{(R 2, G 2, B} 2) to (0,0,0) Become. This means that all are mapped to an achromatic color because there is no B component.

  The embodiment of the configuration and operation of the data conversion unit 52 of the color correction unit 35 has been described above.

Next, a method for selecting the two-color printing mode will be described.
1) First, a method for selecting the two-color printing mode will be described.

1-A) Example of automatically selecting the two-color printing mode (see, for example, Patent Document 2)
An explanation will be given of the case where the two-color printing mode is selected and the automatic selection is made without bothering the user. The user selects a two-color printing mode in advance and selects an automatic determination (input from the operation panel of the image forming apparatus). In this case, it is assumed that an ACS (Auto Color Select) determination unit is provided in the input tone correction unit 33 of FIG. The ACS determination unit calculates the ratio of each RGBCMY color component in the document in advance and determines the most color components. In the document, the most common color component is set as the main color (any of RGBCMY), the color to be extracted is designated, and the color is printed. The two-color printing can be realized by printing the components other than the most color components in monochrome. This saves the user from specifying which color he wants to print in which color.

  In the case of the first embodiment, only the R component is calculated by the ACS determination unit, and the R component is larger than a certain threshold value (which may be arbitrarily determined by the user or set in a register in advance) (for example, When 70% or more of the entire original is an R component), two-color printing is performed as RK.

  In the above description, an example in which the ACS determination unit is provided in the input tone correction unit 33 is shown. However, a plurality of feature amounts are extracted from the input image data before the input tone correction unit 33, and the input document is a character. An automatic document type discriminating section is provided for determining whether a document, text / print photo document, text / print paper photo document, or print photo document, etc., and one of these functions automatically determines two colors. You may make it provide the function to perform.

1-B) Manual selection example: Mode and color selection method (only applicable in Example 2)
On the operation panel 5 in FIG. 7, the user selects a two-color printing mode from among a plurality of printing modes (character mode, character printing photo mode, photographic paper photo mode, etc.). FIG. 11 is a simple display example on the operation panel 5 in the two-color printing mode. The user selects a color (any one of RGBCMY) to be extracted from the manuscript from the designated input color column on the operation panel 5 displaying FIG. 11 (for example, the operation panel is configured with a touch panel). This is the designated input color. Similarly to the above, when printing the designated color, the user selects which color (any of RGBCMY) to print from the designated output color column. By designating these, for example, the R component can be printed with R, the R component can be printed with G, and the C component can be printed with R. Since it prints in monochrome, two-color printing can be realized. The content set on the operation panel 5 is input to the color correction unit 35 in FIG. 7 as a setting signal. The color correction unit 35 performs processing of the contents of the second embodiment based on the setting signal.
2) Next, an example of a printer driver will be described.

  When a document created on a computer or edited image data is output by a printer, it is possible to specify input colors and output colors on the setting screen of the printer driver, and set whether or not two colors are automatically selected. For example, a setting screen similar to that shown in FIG. 11 may be displayed on the display, and the mouse may be used to select a color to be extracted from the original from the designated input color column and a color to be printed from the designated output color column. By designating these, for example, the R component can be printed with R, the R component can be printed with G, and the C component can be printed with R. Since it prints in monochrome, two-color printing can be realized. The contents set on the setting screen of the printer driver are input to the color correction unit (see FIG. 8) as a setting signal.

  FIG. 8 shows a configuration example of the computer 70. The computer 70 includes a printer driver 71, a communication port driver 72, and a communication port 73. Further, the printer driver 71 includes a color correction unit 71a, a gradation reproduction processing unit 71b, and a printer language translation unit 71c. Image data generated by executing various application programs in the computer 70 is supplied to the printer driver 71, color correction processing is performed by the color correction unit 71a, and then halftone generation processing is performed by the tone reproduction processing unit 71b. Is made. The color correction processing of the color correction unit 71a includes black generation / under color removal processing.

  The image data subjected to the above processing is converted into a printer language by the printer language translation unit 71c, and is input to the printer (image output device) 74 through the communication port driver 72 and the communication port (RS232C, LAN, etc.) 73 in order. . The printer 74 may be a digital complex machine having a copy function and a fax function in addition to the printer function.

  After these are selected, the two-color printing process as in Example 1 or Example 2 is performed.

  As described above, according to the present invention, it is possible to provide a good two-color image quality with a small hardware scale.

  The data converter 52 performs dichroism by mapping all data of the three-dimensional LUT into a triangle connecting the achromatic color axis and any one of the main colors (any one of RGBCMY). Furthermore, the user's designated input color (any of RGBCMY) is extracted, and all the data is mapped onto a triangular plane surrounded by the designated input color and the achromatic color axis, and the user's designated output color (any one of RGBCMY) 2), it can be converted into two colors by mapping to a triangular plane surrounded by the designated output color and the achromatic axis.

  Further, there is no need to perform coordinate transformation on the input image data RGB as in the prior art, and only an averaging processing unit composed of an adder and a shifter (power multiplication), a comparator, and a selector. By using the configured data conversion unit, the hardware scale becomes smaller than that of the conventional coordinate conversion circuit.

  In addition, a color correction table or coefficient parameter (masking coefficient or weighting coefficient in a neural network) in the full color mode can be shared for the RGB data processed by the data converter 52 (a color correction table dedicated to two-color printing, (No coefficient parameter is required), leading to a reduction in memory. In addition, by using the same color correction table or coefficient parameter as in the full color mode as described above, it is possible to realize visually good image quality.

  Finally, each block of the color image processing apparatus 3, in particular, the color correction unit 35 may be configured by hardware logic, or may be realized by software using a CPU as follows.

  That is, the color image processing apparatus 3 includes a CPU (central processing unit) that executes instructions of a control program that realizes each function, a ROM (read only memory) that stores the program, and a RAM (random access memory) that expands the program. ), A storage device (recording medium) such as a memory for storing the program and various data. An object of the present invention is a recording medium on which a program code (execution format program, intermediate code program, source program) of a control program of the color image processing apparatus 3 which is software for realizing the above-described functions is recorded so as to be readable by a computer. Can also be achieved by reading the program code recorded on the recording medium and executing it by the computer (or CPU or MPU).

  Examples of the recording medium include a tape system such as a magnetic tape and a cassette tape, a magnetic disk such as a floppy (registered trademark) disk / hard disk, and an optical disk such as a CD-ROM / MO / MD / DVD / CD-R. Card system such as IC card, IC card (including memory card) / optical card, or semiconductor memory system such as mask ROM / EPROM / EEPROM / flash ROM.

The recording medium is read by a program reading device provided in a digital color image forming apparatus or a computer system, whereby the above-described image processing method is executed.
The computer system includes an image input device such as a flatbed scanner, a film scanner, and a digital camera, a computer that performs various processes such as the above image processing method by loading a predetermined program, and a CRT display that displays the processing results of the computer. An image display device such as a liquid crystal display and a printer that outputs the processing results of the computer to paper or the like.

  Further, the color image processing apparatus 3 is configured to be connectable to a communication network by including a network card, a modem, or the like as a communication means for connecting to a server or the like via a network, and the program code is transmitted via the communication network. May be supplied. The communication network is not particularly limited. For example, the Internet, intranet, extranet, LAN, ISDN, VAN, CATV communication network, virtual private network, telephone line network, mobile communication network, satellite communication. A net or the like is available. Further, the transmission medium constituting the communication network is not particularly limited. For example, even in the case of wired such as IEEE 1394, USB, power line carrier, cable TV line, telephone line, ADSL line, etc., infrared rays such as IrDA and remote control, Bluetooth ( (Registered trademark), 802.11 wireless, HDR, mobile phone network, satellite line, terrestrial digital network, and the like can also be used. The present invention can also be realized in the form of a computer data signal embedded in a carrier wave in which the program code is embodied by electronic transmission.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  The present invention can be suitably used for a digital color copying machine.

FIG. 3 is a flowchart illustrating a first example in the embodiment of the present invention and illustrating a flow of an image processing method performed by the image processing apparatus. 1 is a block diagram illustrating a configuration of a color correction unit of an image processing apparatus according to an embodiment of the present invention. (A) thru | or (c) is a figure which shows the image processing method of FIG. 1 using color space. It is a figure which shows an example of the image processing method of FIG. 1 using color space. It is a figure which shows the other example of the image processing method of FIG. 1 using color space. (A) thru | or (c) is a figure which shows that the image processing method of FIG. 1 is possible using color space. 1 is a block diagram illustrating an image processing apparatus and an image forming apparatus including the image processing apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure for implement | achieving the image processing apparatus and image processing method of this invention with a computer. FIG. 5 is a block diagram illustrating a configuration of a data conversion unit included in the color correction unit of FIG. 2, illustrating a second example of the embodiment of the present invention. It is a block diagram which shows the structure of the control signal generation part with which the data conversion part of FIG. 9 is provided. FIG. 4 is a diagram illustrating an example of display on an operation panel in a two-color printing mode according to an embodiment of the present invention. FIG. 3 is a block diagram illustrating a first example of the embodiment of the present invention and illustrating a configuration of a data conversion unit included in the color correction unit of FIG. 2. 7 illustrates a second example of the embodiment of the present invention and is a part of a flowchart illustrating a flow of an image processing method performed by the image processing apparatus. It is a figure which shows the remaining part of the flowchart of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 3 Color image processing apparatus (image processing apparatus)
52 Data converter (data converter)
53 color conversion calculation unit (color conversion calculation means)

Claims (11)

The color image data of the first color system represented by three-dimensional Cartesian coordinates using three color components of which the color space is composed of the first color, the second color and the third color is the first color image data composed of a plurality of color components. In an image processing apparatus for converting to color image data of 2 color system,
Mapping the color image data of the first color system on a triangular plane formed by connecting the achromatic color axis and the vertex of the first color of the color space other than the achromatic color axis in the color space. A data conversion means for converting into a two-color image data composed of an achromatic color and a color associated with the vertex of the first color ;
Color conversion calculation means for converting the two-color image data into color image data of the second color system ,
The data conversion means is
As the output value of the first color, the gradation data of the first color is output as it is,
When the average value of the second color gradation data and the third color gradation data is larger than the first color gradation data, the output values of the second color and the third color, respectively. If the average value of the second color gradation data and the third color gradation data is less than or equal to the first color gradation data, the first color gradation data is output as An image processing apparatus for mapping the color image data of the first color system on the triangular plane by outputting the average value as an output value of each of the second color and the third color . The data conversion means is
One of all six colors consisting of primary colors and secondary colors predetermined for the first color system is designated for the color image data of the first color system. 2. The image processing apparatus according to claim 1, wherein a vertex of the first color is selected from each vertex of the color space based on a designated input color setting signal. The data conversion means is
One of all six colors consisting of primary colors and secondary colors predetermined for the second color system is designated for the color image data of the second color system. The image processing apparatus according to claim 1, wherein a color associated with a vertex of the first color is determined based on a designated output color setting signal. The data conversion means is
One of all six colors consisting of primary colors and secondary colors predetermined for the first color system is designated for the color image data of the first color system. Based on the designated input color setting signal, the vertex of the first color is selected from the vertices of the color space,
One of all six colors consisting of primary colors and secondary colors predetermined for the second color system is designated for the color image data of the second color system. The image processing apparatus according to claim 1, wherein a color associated with a vertex of the first color is determined based on a designated output color setting signal.   An image comprising the image processing device according to claim 1, wherein the image processing device performs image processing on image data of an input image to form an image. Forming equipment. The color image data of the first color system represented by three-dimensional Cartesian coordinates using three color components of which the color space is composed of the first color, the second color, and the third color is the first color image data composed of a plurality of color components. In the image processing method for converting into color image data of 2 color system,
Mapping the color image data of the first color system on a triangular plane formed by connecting the achromatic color axis and the vertex of the first color of the color space other than the achromatic color axis in the color space. A data conversion step of converting into a two-color image data composed of an achromatic color and a color associated with the vertex of the first color ;
Performing a color conversion operation step of converting the two-color image data into color image data of the second color system;
In the data conversion step,
As the output value of the first color, the gradation data of the first color is output as it is,
When the average value of the second color gradation data and the third color gradation data is larger than the first color gradation data, the output values of the second color and the third color, respectively. If the average value of the second color gradation data and the third color gradation data is less than or equal to the first color gradation data, the first color gradation data is output as An image processing method characterized by mapping the color image data of the first color system on the triangular plane by outputting the average value as an output value of each of the second color and the third color . In the data conversion step,
One of all six colors consisting of primary colors and secondary colors predetermined for the first color system is designated for the color image data of the first color system. 7. The image processing method according to claim 6, wherein a vertex of the first color is selected from each vertex of the color space based on a designated input color setting signal. In the data conversion step,
One of all six colors consisting of primary colors and secondary colors predetermined for the second color system is designated for the color image data of the second color system. The image processing method according to claim 6, wherein a color associated with the vertex of the first color is determined based on a designated output color setting signal. In the data conversion step,
One of all six colors consisting of primary colors and secondary colors predetermined for the first color system is designated for the color image data of the first color system. Based on the designated input color setting signal, the vertex of the first color is selected from the vertices of the color space,
One of all six colors consisting of primary colors and secondary colors predetermined for the second color system is designated for the color image data of the second color system. The image processing method according to claim 6, wherein a color associated with the vertex of the first color is determined based on a designated output color setting signal.   A program for operating the image processing apparatus according to any one of claims 1 to 4, wherein the program causes a computer to function as each means described above.   The computer-readable recording medium which recorded the program of Claim 10.

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