JP2008178047A - Image processing apparatus, image processing method, and image processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image processing apparatus capable of performing highly accurate conversion to the color of a color image output device in which a color reproduction range (gamut) is restricted, without increasing the scale of a color conversion table. <P>SOLUTION: A color converting unit 41 color-converts RGB image data to which linear masking processing is applied, into CMYK image data using a three-dimensional lookup table, the value gamut of the color-converted CMYK image data is virtually expanded to a color gamut greater than a color gamut that the image output device can reproduce, the expanded value gamut of the CMYK image data is then clipped to a value gamut that the image output device which outputs output image data can reproduce, and the clipped image data are output as output image data. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus as a digital multi-function peripheral that combines functions of a copying machine, a facsimile, a printer, a scanner, and the like, and in particular, performs color space conversion processing according to an output device and outputs image data. The present invention relates to an image processing apparatus.

  Since copiers have become digital copiers that make copies with digitized image data, they are combined with facsimile functions, printer functions, scanner functions, etc., and are called digital multi-function printers (MPFs). Became. Along with the evolution of technology, the functions and functions used in digital multifunction peripherals are becoming more diverse. However, in a digital multi-function peripheral, when a color image captured by a scanner is output to different output devices such as a facsimile, a printer, and a personal computer, a problem relating to color matching occurs.

  In digital multi-function peripherals, linear or higher-order polynomials are used for color conversion for color matching, but recently, table reference type methods using interpolation are often used. As the interpolated table reference type color conversion, there are a method using tetrahedral interpolation (see Patent Document 1), a method using prism interpolation (see Non-Patent Document 1), a method using cube interpolation, and the like. In addition, in the ICC Profile Format by ICC (International Color Consortium), a color conversion system is standardized in a form including color conversion of an interpolation combined table reference type.

  In the interpolation combination table reference type color conversion, the range or range of the color signal is determined in advance in order to handle the image data quantized in this way. For example, in an image format called TIFF (Tagged Image File Format), the type and range of a color signal are embedded in part of image data. In the ICC Profile Format, a color signal range is fixed in advance, and parameters such as table values are created based on the agreement, and color conversion is executed. That is, the range of the color signal is determined in some way.

  However, if the table value of the color conversion table of the interpolation combined type is created based on these rules, an area where a correct color conversion result cannot be obtained due to an interpolation error occurs regardless of how the table value is correctly created. A region where a correct color conversion result cannot be obtained due to an interpolation error will be described with reference to FIGS. First, with reference to FIG. 11, a case where a color signal dependent on an image input device is converted into a color signal independent of the device will be described. In FIG. 11, in order to simplify the explanation, the L * a * b * color system (hereinafter sometimes simply referred to as L * a * b *) from RGB G (green) data from the scanner. However, even in the case of multi-dimensional input such as conversion from RGB data to L * a * b * values, there is essentially no change.

  In the color conversion table in the case of FIG. 11, the input G data values are “0”, “32”, “64”, “96”, “128”, “160”, “192”, “224”, “255”. The L * values corresponding to the nine representative points are respectively plotted, and the L * values are plotted in correspondence with the representative points. For input G data values other than the representative points, an output L * value is obtained by approximating a polygonal line as shown in FIG. 11 by interpolation. The L * value is determined in the range of “0 to 100”, but as the L * data, the range of “0 to 100” of the L * value is quantized into 8 bits of “0 to 255”. It becomes.

  What should be noted here is a section in which the input G data value is “224 to 255”. Although there is no actual document read by the scanner of “L * = 100 (reflectance is 1)”, as indicated by a point Pa1, the maximum value “255” of input G data is “L * ==”. 100 ”is associated. This is to cope with paper with high whiteness such as coated paper, paper coated with a phosphor, and the like.

  However, in this case, the input G data value is “224” from the point Pa0 where the input G data value “224” is plotted as a line approximated by interpolation of the section where the input G data value is “224 to 255”. A line passing through the point Pa2 having an L * value of “100” between “255” and “255” has a smaller interpolation error and is natural and preferable.

  Next, with reference to FIG. 12 and FIG. 13, a case where a color signal independent of the device is converted into a color signal dependent on the image output device will be described. In FIG. 12, for the sake of simplicity, the L * data of L * a * b * is converted into a one-dimensional conversion from the CMYK K (black) dot area ratio of the area modulation type printer. However, there is essentially no change even in the case of multi-dimensional input such as conversion from L * a * b * data to the dot area ratio of each color of CMYK.

  In the color conversion table in FIG. 12, the input L * data values are “0”, “32”, “64”, “96”, “128”, “160”, “192”, “224”, “255”. The K halftone dot area ratios corresponding to the representative points are plotted as the table values corresponding to the nine representative points. For input L * data values other than the representative points, a polygonal line approximation as shown in FIG. 12 is performed by interpolation to obtain an output K halftone dot area ratio. The K halftone dot area ratio is limited to the range of “0 to 100%”, but as K data, the range of “0 to 100%” of the K halftone dot area ratio is “0 to 255”. Quantized to bits.

  The point to be noted here is a section where the input L * data value is “0 to 32” and “224 to 225”. As shown in FIG. 12, when converting a color signal independent of a device into a color signal depending on an image output device, the reproduction start point of TRC (Tone Reproduction Curve) and the point that should be 100% gradation are When the point Sa1 having the maximum value “255” and the point Ta1 having the minimum value “0” are set to the input L * data, the interpolation error becomes large.

  FIG. 13 is an enlarged view of the section of FIG. 12 where the input L * data value is “224 to 225”. In FIG. 13, positive / negative is shown as the K halftone dot area ratio, but the theoretical and actual K halftone dot area ratio is in a positive “0 to 100%” range. Further, the lines A1 and A2 in FIG. 13 are correct values based on the actual measurement values, and the line A3 corresponds to the maximum value “255” of the input L * data with the K halftone dot area ratio “0%”. Shows the case. Therefore, the interpolation error in this case is represented by the length of the arrow E. The same applies to the section in which the input L * data value is “0 to 32” in FIG. 13 and the section in which the input G data value is “224 to 255” in FIG.

  In order to reduce such an interpolation error, the interval between grid points in the color conversion table may be reduced, and the polygonal line may be brought closer to an ideal curve. However, this method has a problem that the scale of the color conversion table is remarkably increased. For example, in the case of three-dimensional input such as conversion from RGB data to L * value, when the number of grid points is “9 × 9 × 9 = 729” and the output L * data is 8 bits, for example, a color of 729 bytes When the grid point interval is halved in each axis direction and the number of grid points is “17 × 17 × 17 = 4913”, for example, when the output L * data is 8 bits, it is 4913 bytes. It becomes a color conversion table.

  Patent Documents 2 and 3 are conventional techniques for improving such a problem. In the prior art described in Patent Document 2, when a plurality of table values corresponding to input color signal values in a predetermined range are converted into output color signals by interpolation, the preset output color signal value range is exceeded. The output color signal is calculated using the table value.

  In the prior art described in Patent Document 3, a color image output value for an image forming apparatus corresponding to input color image data in an arbitrary three-dimensional input color space is used, and the three-dimensional input color space is converted into a plurality of three-dimensional figures. Input color image data including at least two types of colors outside the color gamut of the image forming apparatus in a color conversion apparatus obtained by interpolation using vertex output values for each output color set at the vertices when divided into segments A color space compression unit that compresses the image into the color gamut of the image forming apparatus, a color space compression unit selection unit that selects one color space compression unit, and a vertex that is compressed by the color space compression unit among the vertices And at least two types of output values corresponding to the color space compression means are stored for each output color for the vertices selected by the vertex selection means. And a selection unit that selects one output value from the output values stored in the storage unit, and the selection unit corresponds to the color space compression unit selected by the color space compression unit selection unit. The output value is selected.

Japanese Patent Publication No.58-16180 JP 2000-261679 A Japanese Patent No. 3550426 23rd Image Engineering Conference Proceedings, page 249 “RGB-Lab conversion of color images using prism interpolation”

  However, the conventional techniques described in Patent Document 2 and Patent Document 3 relate to color conversion accuracy in the memory map method, and the problem of color conversion accuracy near the color reproduction outermost contour of the image forming apparatus when the number of divisions is small. Is a solution. As shown in FIG. 14, in the uniform color space L * a * b *, when the plane of the constant brightness region is viewed, the vertexes Aa, Ba, Ca, Da in the figure are within the color gamut of the image forming apparatus. There is only the vertex Ca. If the output values of the vertices Aa, Ba, Da outside the color reproduction range are made the output values of the outermost color reproduction range by compressing the color space, the output of the input Pa outside the color reproduction range is present. Since the value is output as a color within the color gamut, that is, a color closer to the color corresponding to the vertex Ca than the actual color, there is a problem in correctly outputting the color within the color gamut.

  On the other hand, the memory capacity and cost reduction and the functions of MFPs that convert paper documents into digital image data have evolved and evolved. In recent years, digital image data is stored and stored inside the MFP, and the information is required. In such a case, it is increasingly used to re-output.

  For example, in color management, not only images acquired by a scanner but also image data stored and stored in the MFP by a user received from an external I / F device is commonly used for image processing. Even when extended RGB having a wider color reproduction range than the sRGB space assuming a standard monitor is set as the color space, color conversion with high accuracy is required.

  However, when color conversion is performed by memory mapping or the like, lattice points (parameters) per unit volume decrease as the color space becomes wider. For this reason, there is a problem that it becomes more difficult to achieve both color reproduction control of saturated colors frequently used in graphic documents created by a personal computer or the like and color reproduction accuracy at the color reproduction area boundary described above.

  The prior arts described in Patent Document 2 and Patent Document 3 both try to increase the accuracy by increasing the scale of the color conversion table of the interpolation combined system. However, in the color conversion table of color signals expressed with three or more attributes basically, there is a problem that the scale of the output color signal increases considerably even if it is expanded from 8 bits to 9 bits.

  Also, in the technique of calculating an output color signal using a table value exceeding the range of the output color signal as in the prior art described in Patent Document 2 above, a method of performing clipping processing to a predetermined range is created by a personal computer or the like. However, there is a problem that it is difficult to control the color reproduction of saturated colors frequently used in graphic documents.

  The present invention has been made in view of the above, and can perform high-accuracy conversion to a color of a color image output device with a limited color reproduction range (gamut) without increasing the scale of a color conversion table. It is an object to obtain an apparatus, an image processing method, and an image processing program.

  In order to solve the above-described problems and achieve the object, the invention according to claim 1 is connected to at least one image output device, and is a color signal expressed in a color space of n (n is a natural number) dimension. In an image processing apparatus that converts input image data into output image data of a color signal having a format different from that of the input image data, and outputs the converted output image data to an image output apparatus, the n-dimensional lookup table is used to The input image data is color-converted into the format of the output image data, the range of the color-converted image data is virtually expanded to a color gamut larger than the color gamut that can be reproduced by the image output device, and then the expanded image data Color conversion means for clipping a range into a range that can be reproduced by the image output device that outputs the output image data, and outputting the clipped image data as the output image data; Characterized in that it comprises.

  According to a second aspect of the present invention, an image reading is performed in which an original is read to generate input image data of color signals expressed in an n-dimensional color space (n is a natural number) and incidental information indicating attributes of the input image data. A first image data processing device for generating unified image data in which input image data generated by the image reading device is unified with predetermined characteristics, and a unified image generated by the first image data processing device A memory device for storing data and incidental information, a second image data processing device for generating output image data of a color signal in a format different from the unified image data stored in the memory device, and the second image data Interface function for connecting an image writing device for printing output image data generated by a processing device and an external output device for processing image data And an interface device that outputs the output image data generated by the second image data processing device to the external output device, wherein the first image data processing device is generated by the image reading device. The input image data is unified with characteristics corresponding to the image writing device and the external output device connected to the interface device, and the second image data processing device uses the n-dimensional lookup table to store the memory device. The stored unified image data is color-converted into the format of the output image data, and the range of the image data obtained by the color conversion is virtually reduced to a color gamut larger than the color gamut that can be reproduced by the image writing device and the external output device. After the expansion, the range of the expanded image data is set as an image writing device or output destination of the output image data. The clipped to the range of the external output device can reproduce the color gamut, the image data clipped comprise color conversion means for outputting as the output image data, characterized by.

  According to a third aspect of the present invention, in the image processing apparatus according to the first or second aspect, the color conversion unit performs undercolor removal black processing on the image data obtained by clipping the range of the expanded image data. Image data that has been subjected to black ink processing is output as the output image data.

  According to a fourth aspect of the present invention, in the image processing apparatus according to the third aspect, the color conversion unit is configured to change the color according to the incidental information stored in the memory device and / or the mode designation input from the outside. It is characterized in that the range for extending the range of the image data obtained by the conversion is changed.

  The invention according to claim 5 is the image processing apparatus according to claim 4, wherein the supplementary information is information indicating that the input image data is a pixel in a picture area or a character area. .

  According to a sixth aspect of the present invention, in the image processing apparatus according to any one of the first to fourth aspects, the color conversion unit converts the image data converted using the n-dimensional lookup table, into the image data. It is characterized in that it is expanded for each plane of output image data.

  The invention according to claim 7 is connected to at least one image output device, and input image data of a color signal expressed in an n (n is a natural number) dimensional color space is different from the input image data. In an image processing method applied to an image processing apparatus that converts output image data of a color signal in a format and outputs the converted output image data to an image output apparatus, the input image data is converted to the input image data using an n-dimensional lookup table. A color conversion processing step for color conversion into the format of the output image data, and a value range of the image data color-converted by the color conversion processing step is virtually expanded to a color gamut larger than the color gamut that can be reproduced by the image output device. An expansion processing step and a range of image data expanded by the expansion processing step to a range that can be reproduced by an image output device that outputs the output image data A clip processing step of the lip, characterized in that it comprises an output processing step of outputting the clipped image data as the output image data by the clip processing step.

  The invention according to claim 8 is characterized in that the image processing method according to claim 7 is executed by a computer.

  According to the first aspect of the present invention, using the n-dimensional lookup table, the input image data of the color signal expressed in the n-dimensional color space is output in the format of the color signal different from the input image data. After color conversion to image data, the range of the color-converted image data is virtually expanded to a color gamut larger than the color gamut that can be reproduced by the image output device connected to the device, and then the range of the expanded image data is output. The image output device that outputs image data is clipped to a range that can be reproduced, and the clipped image data is output as the output image data. Therefore, without increasing the scale of the color conversion table, the color reproduction range ( There is an effect that it is possible to obtain an image processing apparatus capable of converting to a color of a color image output apparatus with a limited gamut) with high accuracy.

  According to the second aspect of the present invention, an image is generated by reading a document and generating input image data of color signals expressed in an n-dimensional color space (n is a natural number) and auxiliary information indicating attributes of the input image data. A first image data processing device that generates unified image data in which input image data generated by the image reading device is unified with predetermined characteristics; and unified image data generated by the first image data processing device. And a memory device for storing auxiliary information, a second image data processing device for generating output image data of a color signal in a format different from the unified image data stored in the memory device, and a second image data processing device. An interface function for connecting an image writing device for printing the generated output image data and an external output device for processing the image data; And an interface device that outputs the output image data generated by the image data processing device to the external output device. The first image data processing device outputs the input image data generated by the image reading device to the image writing device and The characteristics corresponding to the external output device connected to the interface device are unified, and the second image data processing device converts the unified image data stored in the memory device into a format of output image data using an n-dimensional lookup table. After color conversion, the range of image data obtained by color conversion is virtually expanded to a color gamut larger than the color gamut that can be reproduced by the image writing device and the external output device, and then the range of the expanded image data is output as an image Clip to the color gamut range that can be reproduced by the image writing device or external output device that is the data output destination, Since the ripped image data is output as the output image data, the input image data read by the image reading device can be reused for the writing device and the external output device, and the color conversion table There is an effect that it is possible to obtain an image processing apparatus capable of converting to a color of a color image output apparatus with a limited color reproduction range (gamut) without increasing the scale.

  According to the third aspect of the present invention, the image data obtained by clipping the range of the expanded image data is subjected to black processing for removing the lower color, and the image data subjected to the black processing is output as output image data. Therefore, according to the characteristics of the input color image, it does not increase the scale of the color conversion table, and it is suitable for characters, designs, etc. while maximizing the color reproduction range (gamut) of the color image output device. In addition, there is an effect that an image processing apparatus that performs color matching processing can be obtained.

  According to the invention of claim 4, the range for expanding the range of the image data obtained by the color conversion is changed in accordance with the auxiliary information stored in the memory device and / or the mode designation input from the outside. Therefore, even when the unified image data stored in the memory device is processed and reused, it does not increase the scale of the color conversion table according to the characteristics of the input color image. Thus, there is an effect that it is possible to obtain an image processing apparatus that can convert the color reproduction range (gamut) into colors of a color image output apparatus with a limited color reproduction range (gamut).

  According to the invention according to claim 5, since the incidental information is information indicating that the input image data is a pixel of the picture area or the character area, the range in which the image data is expanded is the picture area. And the character area, and according to the characteristics of the input color image, without increasing the scale of the color conversion table, while making the best use of the color reproduction range (gamut) of the color image output device, There is an effect that it is possible to obtain an image processing apparatus that performs color matching processing suitable for characters, pictures, and the like.

  According to the invention of claim 6, since the image data converted using the n-dimensional lookup table is expanded for each plane of the output image data, the extended RGB space having a wide color reproduction range and Even when the color reproduction range (gamut) of the color image output device is greatly different, it is possible to obtain an image processing device that converts the color of the color image output device with high accuracy without increasing the scale of the color conversion table. There is an effect.

  According to the invention of claim 7, the color conversion processing step uses an n-dimensional lookup table to convert the input image data of the color signal expressed in the n-dimensional color space into a format different from the input image data. The color conversion is performed on the output image data in the color signal format, and the expansion processing step virtually performs a color gamut larger than the color gamut that the image output device can reproduce the range of the image data color-converted by the color conversion processing step. The image data that has been extended and clipped in the clip processing step is clipped to a value range that can be reproduced by the image output device that outputs the output image data, and the output processing step is clipped by the clip processing step. Is output as output image data, so color reproduction is possible without increasing the scale of the color conversion table. An effect that it is possible to obtain an image processing method that can be converted to high-precision color of the color image output apparatus circumference (gamut) is limited.

  According to the invention of claim 8, the color conversion processing step uses an n-dimensional lookup table to convert the input image data of the color signal expressed in the n-dimensional color space into a format different from the input image data. The color conversion is performed on the output image data in the color signal format, and the expansion processing step virtually performs a color gamut larger than the color gamut that the image output device can reproduce the range of the image data color-converted by the color conversion processing step. The image data that has been extended and clipped in the clip processing step is clipped to a value range that can be reproduced by the image output device that outputs the output image data, and the output processing step is clipped by the clip processing step. Is output as output image data, so color reproduction is possible without increasing the scale of the color conversion table. An effect that it is possible to obtain an image processing program that can be converted to high-precision color of the color image output apparatus circumference (gamut) is limited.

  Exemplary embodiments of an image processing apparatus, an image processing method, and an image processing program according to the present invention are explained in detail below with reference to the accompanying drawings.

  An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing a configuration of an image processing apparatus according to an embodiment of the present invention. In FIG. 1, an image processing apparatus includes a reading apparatus 1, image data processing apparatuses 2 and 4, a bus control apparatus 3, an HDD 5, a CPU 6, a memory 7, a plotter I / F apparatus 8, a plotter apparatus 9, an operation display apparatus 10, and a line. An I / F device 11, an external I / F device 12, a south bridge device 13, and a ROM 14 are provided, and are connected to a FAX 15 and a personal computer (hereinafter referred to as a PC) 16.

  The reading device 1 includes a line sensor composed of a CCD photoelectric conversion element, an A / D converter, and a drive circuit thereof, and generates digital input image data from density information of a document obtained by scanning the document. The input image data includes red (R), green (G), and blue (B) image data for each pixel of the document (image) and accompanying information of the image data. The incidental information is information indicating the attribute of the image data. Here, the incidental information is an image area separation signal indicating whether the pixel is a picture area pixel or a character area pixel. It is not limited to. For example, as auxiliary information, a signal indicating the characteristics of an input color image indicating whether it is a graphic document created by a personal computer or a photo original read by a scanner or the like may be used. Hereinafter, R, G, and B image data may be referred to as R image data, G image data, and B image data, and R image data, G image data, and B image data may be collectively referred to as RGB image data.

  The image data processing device 2 unifies the RGB image data of the input image data generated by the reading device 1 with predetermined characteristics, and combines the unified RGB image data with the unified characteristics and the incidental information corresponding to the unified RGB image data. Generate unified image data. FIG. 2 is a block diagram showing a configuration of the image data processing device 2. In FIG. 2, the image data processing apparatus 2 includes a γ conversion unit 20, a filter processing unit 21, a color conversion unit 22, and a scaling processing unit 23.

  The γ conversion unit 20 unifies the brightness of the RGB image data of the input image data generated by the reading device 1 to a predetermined characteristic. The filter processing unit 21 unifies the sharpness of the RGB image data whose brightness characteristics are unified by the γ conversion unit 20 to predetermined characteristics. The color conversion unit 22 unifies the colors of the RGB image data whose sharpness is unified by the filter processing unit 21 to a predetermined characteristic. The scaling processing unit 23 unifies the size (resolution) of the RGB image data whose colors are unified by the color conversion unit 22 to a predetermined characteristic. In addition, the scaling processing unit 23 generates an image area separation signal associated with the pixels of the RGB image data having a uniform size, and includes a unified image including the RGB image data having the uniform size and the image area separation signal of the RGB image data. Generate image data.

  Returning to FIG. 1, the bus control device 3 has a bridge function between a plurality of main bus standards, and stores various data such as image data (including an image separation signal) and control commands necessary in the image processing device. Controls the data bus to be exchanged. In FIG. 1, the image data processing devices 2 and 4 and the CPU 6 are connected by a PCI-Express bus, and are connected to the HDD 5 by an ATA bus and are made into an ASIC.

  The image data processing device 4 converts the unified image data whose characteristics are unified by the image data processing device 2 into output image data suitable for the output destination designated by the user. FIG. 3 is a block diagram showing the configuration of the image data processing device 4. In FIG. 3, the image data processing device 4 includes a filter processing unit 40, a color conversion unit 41, a scaling processing unit 42, and a gradation processing unit 43. The filter processing unit 40 corrects the sharpness of the unified RGB image data and extracts image feature amounts (edge amount information).

  The color conversion unit 41 performs color matching from RGB to CMYK or R′G′B ′ and color conversion on the unified RGB image data whose sharpness has been corrected by the filter processing unit 40. Further, the color conversion unit 41 adaptively generates black according to the feature amount extracted by the filter processing unit 40, and removes under color (UCR: Under) suitable for the pattern / character based on the image area separation signal. Color removal) and under color addition (UCA) are performed to perform effective blackening. Furthermore, the color conversion unit 41 performs undercolor processing as necessary.

  FIG. 4 is a block diagram showing a configuration of the color conversion unit 41 shown in FIG. 4, the color conversion unit 41 includes a linear masking processing unit 411, a three-dimensional LUT conversion unit 412, a GCR processing unit 413, a UCR processing unit 414, and a UCA processing unit 415.

  The linear masking processing unit 411 performs masking RGB image data msk (msk_R, msk_G, msk_B) obtained by performing linear masking processing on the unified RGB image data IN (showing IN_R, IN_G, IN_B) whose sharpness has been corrected by the filter processing unit 40. And masking K image data msk_k.

  The three-dimensional LUT conversion unit 412 performs color conversion by the three-dimensional LUT on the masking RGB image data msk generated by the linear masking processing unit 411, and generates CMYK image data lut (indicating lut_c, lut_m, lut_y, lut_k). Generate.

  FIG. 5 is a block diagram illustrating a configuration of the three-dimensional LUT conversion unit 412. In FIG. 5, the three-dimensional LUT conversion unit 412 includes a three-dimensional LUT color conversion unit (hereinafter referred to as 3DLUT color conversion unit) 4121, a mink calculation unit 4122, and a selector 4123.

  The 3DLUT color conversion unit 4121 has two types of three-dimensional LUTs, a design area LUT 4121a and a text area LUT 4121b, and selects the design area LUT 4121a or the text area LUT 4121b based on the image area separation signal sepi. The 3DLUT color conversion unit 4121 performs conversion from RGB to CMYK by three-dimensional memory map interpolation on the masking RGB image data msk for each pixel using the selected LUT, and performs C image data lut_c, M image data lut_m, and Y Image data lut_y is generated.

  The mink calculation unit 4122 calculates the minimum value mink of the CMY image data lut_cmy (showing lut_c, lut_m, and lut_y) generated by the 3DLUT color conversion unit 4121. The selector 4123 selects the minimum value mink calculated by the mink calculation unit 4122 based on the image area separation signal sepi or the masking K image data msk_k generated by the linear masking processing unit 411 and outputs it as K image data lut_k. .

  Returning to FIG. 4, the GCR processing unit 413 performs black generation on the K image data lut_k generated by the three-dimensional LUT conversion unit 412 based on the GCR mode signal gcr_mode, the image area separation signal sepi, and the feature amount gcr_edgei. K image data gcr_bk is generated. Also, the GCR processing unit 413 generates UCR K image data ucr_bk indicating the amount of UCR black used for UCR processing from the generated K image data gcr_bk based on the GCR mode signal gcr_mode and the image area separation signal sepi. .

  The UCR processing unit 414 performs UCR processing on the CMY image data lut_cmy generated by the three-dimensional LUT conversion unit 412 based on the UCR mode signal ucr_mode and the K image data ucr_bk generated by the GCR processing unit 413. CMY image data ucr_cmy (indicating ucr_c, ucr_m, and ucr_y) obtained by correcting the CMY image data lut_cmy is generated.

  The UCA processing unit 415 performs UCR processing on the CMY image data ucr_cmy generated by the UCR processing unit 414 based on the UCA mode signal uca_mode and the K image data gcr_bk generated by the GCR processing unit 413, thereby obtaining CMY image data. CMY image data uca (indicating uca_c, uca_m, and uca_y) in which ucr_cmy is corrected is generated.

  Returning to FIG. 3, the scaling processing unit 42 converts the size (resolution) of the CMYK image data converted by the color conversion unit 41. The gradation processing unit 43 converts the number of gradations of the CMYK image data whose size has been converted by the scaling processing unit 42.

  Returning to FIG. 1, the HDD 5 is a large-capacity hard disk storage device connected to an ATA (AT Attachment) bus, which is standardized by expanding IDE (Integrated Drive Electronics), and mainly includes image data and incidental information of the image data. (In this case, the image area separation signal) is accumulated.

  The CPU 6 is a microprocessor that controls the image processing apparatus. For example, a CPU in which a connection function with a general-purpose standard I / F or a bus connection function using a crossbar switch is added to a CPU core alone, such as RM11100 manufactured by PMC.

  The memory 7 stores data to be temporarily exchanged in order to absorb a speed difference when bridging a plurality of types of buses and a processing speed difference between the connected components themselves. It is a volatile memory that temporarily stores programs and intermediate processing data when performing control. Since the CPU 6 is required to perform high-speed processing, the system is activated by the boot program stored in the ROM 14 at the normal activation, and after the activation, the processing is performed by the program developed in the memory 7 that can be accessed at high speed. Therefore, the memory 7 uses a device that can be accessed at high speed, for example, a DIMM used in a standardized personal computer.

  The plotter I / F device 8 performs a bus bridge process between the CPU 6 and the plotter device 9. The bus bridge process is a process for outputting CMYK digital image data sent via a general-purpose standard I / F integrated in the CPU 6 (for example, a PCI-Express bus) to a dedicated I / F of the plotter device 9. is there.

  The plotter device 9 prints CMYK digital image data input from the plotter I / F device 8 on a transfer sheet. For printing, for example, an electrophotographic process using a laser beam is used.

  The operation display device 10 includes an LCD (liquid crystal display device) and a key switch, and is connected to the CPU 6 via a PCI-Express bus, and is a portion that performs an interface between the image processing device and the user. The operation display device 10 displays various states and operation methods of the image processing device on the LCD, and recognizes an input from the user by detecting a key switch input.

  The line I / F device 11 connects a PCI-Express bus and a telephone line. The external I / F device 12 connects a PCI-Express bus and an external device. With the external I / F device 12, the image processing device exchanges various data with the external device. For example, a LAN (Local Area Network) is used as the connection interface. That is, the image processing apparatus is connected to the network via the external I / F apparatus 12.

  The south bridge device 13 is one of chip sets used for a personal computer and is a general-purpose electronic device called South Bridge. The bus bridge function often used when constructing a CPU system mainly including PCI-Express and ISA bridge is formed as a general-purpose circuit, and bridges between the ROM 14. The ROM 14 is a memory that stores a program (including a boot program) used when the CPU 6 controls the image processing apparatus.

  The FAX 15 is a normal facsimile and exchanges image data with an image processing apparatus via a telephone line. The PC 16 is a so-called personal computer. A user performs various controls and input / output of image data with respect to the image processing apparatus via application software and a driver installed in the personal computer.

  Next, the operation of the image processing apparatus according to the embodiment of the present invention will be described. First, the schematic operation of the image processing apparatus will be described with reference to FIG. The reading device 1 scans a set original and generates 8-bit RGB input image data from the density information of the original obtained by scanning. The reading device 1 outputs the generated input image data to the image data processing device 2.

  The image data processing device 2 performs characteristic unification processing for unifying the input image data input from the reading device 1 to predetermined characteristics. The predetermined characteristics are characteristics suitable for changing the output destination when the input image data is stored in the image processing apparatus and then reused. Specifically, brightness, sharpness, color, resolution It is a characteristic. Details of the characteristic unification processing will be described later.

  The image data processing device 2, the image data processing device 4, and the CPU 6 are connected by a PCI-Express bus. The HDD 5 is connected by an ATA bus. Since the CPU 6 is required to perform high-speed processing, the system is activated by a boot program stored in the ROM 14 at normal activation, and thereafter, the processing is performed by a program developed in the memory 7 that can be accessed at high speed.

  The image data processing device 4 corrects the sharpness according to the output destination designated by the user via the operation display device 10 for the digital image data subjected to the characteristic unification processing by the image data processing device 2, Conversion processing such as conversion from RGB to CMYK, resolution conversion, and gradation number conversion is performed. Details of the conversion process will be described later.

  The plotter I / F device 8 receives the dedicated I / F of the plotter device 9 when CMYK image data sent via a general-purpose standard I / F (in this case, a PCI-Express bus) built in the CPU 6 is input. Performs bus bridge processing to output to / F. When the CMYK image data is input, the plotter device 9 outputs the received image data to transfer paper using an electrophotographic process using a laser beam. The operation display device 10 displays various states and operation methods of the image processing device on the LCD, and detects a key switch input from the user. The image processing apparatus uses the line I / F device 11 to exchange various data via a telephone line. The FAX 15 is a normal facsimile and exchanges image data with a digital image processing apparatus via a telephone line.

  Next, the copying operation of the image processing apparatus according to this embodiment will be described with reference to FIG. The user sets a document on the reading device 1, and uses the operation display device 10 to set a desired mode and input a copy start instruction. The operation display device 10 converts information input from the user into control command data inside the device, and issues a control command. The control command is notified to the CPU 6 via the PCI-Express bus. The CPU 6 executes a copy operation process program in accordance with the copy start control command data, and sequentially performs settings and operations necessary for the copy operation.

  The reading device 1 outputs RGB 8-bit input image data (RGB image data and supplementary information) obtained by scanning a document to the image data processing device 2. The image data processing device 2 performs characteristic unification processing on the RGB image data input from the reading device 1 and outputs it to the bus control device 3. The bus control device 3 outputs the unified RGB image data and the accompanying information input from the image data processing device 2 to the CPU 6, and the CPU 6 stores the unified RGB image data and the accompanying information in the memory 7.

  The CPU 6 reads the unified RGB image data and supplementary information stored in the memory 7 and outputs the unified RGB image data and supplementary information to the image data processing device 4 through the readout unified RGB image data and supplementary information bus control device 3. The image data processing device 4 performs a conversion process on the input unified RGB image data to generate CMYK image data, and outputs the generated CMYK image data to the bus control device 3.

  The bus control device 3 stores the CMYK image data input from the image data processing device 4 in the memory 7 via the CPU 6. The CMYK image data stored in the memory 7 is output to the plotter device 9 via the CPU 6 and the plotter I / F device 8. The plotter device 9 outputs the input CMYK image data to a transfer sheet. Thereby, a copy of the original set on the reading device 1 is generated.

  Next, the fax transmission operation of the image processing apparatus according to this embodiment will be described with reference to FIG. Since the process from the original setting to the issue of the control command is the same as the copying operation, the description thereof is omitted here. The CPU 6 executes a fax transmission operation process program in accordance with the fax transmission start control command data, and sequentially performs settings and operations necessary for the fax transmission operation. The fax transmission operation process will be described below. The detailed description of the same operation as the above-described copy operation process is omitted.

  The reading device 1 outputs RGB image data and incidental information obtained by scanning a document to the image data processing device 2, and the image data processing device 2 performs characteristic unification processing on the RGB image data, and the bus control device 3 Then, the unified RGB image data and the accompanying information subjected to the characteristic unification processing via the CPU 6 are stored in the memory 7. The CPU 6 outputs the unified RGB image data and incidental information stored in the memory 7 to the image data processing device 4 via the bus control device 3.

  The image data processing device 4 performs conversion processing on the unified RGB image data to generate monochrome binary image data for fax transmission. The image data processing device 4 outputs the generated monochrome binary image data to the bus control device 3. The bus control device 3 stores monochrome binary image data in the memory 7 via the CPU 6. The monochrome binary image data stored in the memory 7 is output to the line I / F device 11 via the CPU 6. The line I / F device 11 transmits monochrome binary image data to the FAX 15 connected via the telephone line.

  Next, the scanner delivery operation of the image processing apparatus of this embodiment will be described with reference to FIG. Since the process from the original setting to the issue of the control command is the same as the copying operation, the description thereof is omitted here. The CPU 6 executes a scanner distribution operation process program in accordance with the scanner distribution start control command data, and the scanner sequentially performs settings and operations necessary for the distribution operation. The scanner delivery operation process will be described below. The detailed description of the same operation as the above-described copy operation process is omitted.

  The reading device 1 outputs RGB image data and incidental information obtained by scanning a document to the image data processing device 2, and the image data processing device 2 performs characteristic unification processing on the RGB image data, and the bus control device 3 Then, the unified RGB image data and the accompanying information subjected to the characteristic unification processing via the CPU 6 are stored in the memory 7. The CPU 6 outputs the unified RGB image data and incidental information stored in the memory 7 to the image data processing device 4 via the bus control device 3.

  The image data processing device 4 performs conversion processing on the unified RGB image data to generate image data for scanner delivery such as RGB multi-value, gray scale, and monochrome binary. The image data processing device 4 outputs the generated image data for scanner distribution to the bus control device 3. The bus control device 3 stores the image data for scanner distribution in the memory 7 via the CPU 6. The image data for scanner distribution stored in the memory 7 is output to the external I / F device 12 via the CPU 6. The external I / F device 12 transmits the input image data for scanner distribution to the PC 16 connected via the network.

  Next, referring to FIG. 1 to FIG. 3, the stored data reuse operation of the image processing apparatus of this embodiment (image data obtained by performing characteristic unification processing on RGB image data obtained by scanning a document) The operation of storing / saving and then reusing the stored / saved image data will be described. Since the operation from the original setting to the characteristic unification is the same as the copying operation, the description thereof is omitted here.

  The reading device 1 outputs RGB image data and incidental information obtained by scanning a document to the image data processing device 2. The γ conversion unit 20 of the image data processing device 2 unifies the brightness of the RGB image data input from the reading device 1 to a predetermined characteristic. Here, the γ conversion unit 20 converts the brightness of the RGB image data into lightness linear characteristics. The γ conversion unit 20 outputs the RGB image data obtained by converting the brightness of the RGB image data to lightness linear characteristics to the filter processing unit 21.

  The filter processing unit 21 unifies the sharpness of the RGB image data input from the γ conversion unit 20 to a predetermined characteristic. Specifically, the filter processing unit 21 converts the sharpness of the RGB image data input from the γ conversion unit 20 so as to have a predetermined MTF characteristic value for each number of lines when the reference chart is scanned. . The filter processing unit 21 outputs the RGB image data obtained by converting the sharpness of the RGB image data so that the MTF characteristic value is predetermined for each number of lines when the reference chart is scanned, to the color conversion unit 22.

  The color conversion unit 22 unifies the colors of the RGB image data input from the filter processing unit 21 with predetermined characteristics. Specifically, the color conversion unit 22 converts the color space of the RGB image data input from the filter processing unit 21 into a color space such as Adobe-RGB. The color conversion unit 22 outputs the RGB image data converted so that the color space of the RGB image data is a color space such as Adobe-RGB to the scaling processing unit 23.

  The scaling processing unit 23 unifies the size (resolution) of the RGB image data input from the color conversion unit 22 to a predetermined characteristic. Here, the scaling processing unit 23 converts the size (resolution) of the RGB image data input from the color conversion unit 22 to 600 dpi. When converting the size (resolution) of RGB image data to 600 dpi, the number of pixels may be different. In this case, the scaling processing unit 42 converts the incidental information of the RGB image data before conversion into incidental information corresponding to the pixels of the converted RGB image data. The scaling processing unit 23 stores the unified RGB image data obtained by converting the size (resolution) of the RGB image data into 600 dpi and the accompanying information in the memory 7 via the bus control device 3. The unified RGB image data and incidental information accumulated in the memory 7 are accumulated and stored in the HDD 5. The unified RGB image data in the memory 7 is output to the plotter device 9 via the image data processing device 4, and a copy of the document is generated.

  The filter processing unit 40 of the image data processing device 4 corrects the sharpness of the unified RGB image data stored in the memory 7 so that the reproducibility when outputting to the plotter device 9 is improved. Specifically, the filter processing unit 40 performs sharpening / smoothing processing on the unified RGB image data stored in the memory 7 according to desired mode information. For example, in the character mode, a sharpening process is performed to make the character clear / clear, and in the photo mode, a smoothing process is performed to smoothly express gradation. The filter processing unit 40 outputs the RGB image data subjected to the sharpening / smoothing process to the color conversion unit 41.

  The color conversion unit 41 converts the RGB image data input from the filter processing unit 40 into color for the plotter device based on the incidental information and mode designation (designation signal from the user or various mode designation signals generated from the designation by the user). It is converted into CMYK image data that is a space. At this time, the color conversion unit 41 also adjusts the saturation according to the user-desired mode information. The color conversion unit 41 outputs the CMYK image data to the scaling processing unit 42.

  The scaling processing unit 42 converts the size (resolution) of the CMYK image data input from the color conversion unit 41 according to the reproduction performance of the plotter device 9. Here, the performance of the plotter device 9 is 600 dpi output, and the size (resolution) of the RGB image data stored in the memory 7 is converted to 600 dpi by the scaling unit 23 of the image data processing device 2 as described above. Yes. Therefore, since the size (resolution) of the CMYK image data input from the color conversion unit 41 is 600 dpi, the scaling processing unit 42 does not perform any conversion. The scaling processing unit 42 outputs CMYK image data having a size (resolution) according to the reproduction performance of the plotter device 9 to the gradation processing unit 43.

  The gradation processing unit 43 subjects the CMYK image data input from the scaling processing unit 42 to gradation number conversion processing according to the gradation processing capability of the plotter device 9. Here, CMYK 8-bit CMYK image data is converted into CMYK 2-bit CMYK image data using an error diffusion method which is one of pseudo halftone processes. The gradation processing unit 43 outputs the CMYK image data obtained by converting the number of gradations according to the gradation processing capability of the plotter device 9 to the plotter device 9 via the bus control device 3, and the plotter device 9 generates a copy of the document. To do.

  Next, an operation in the case of transmitting a fax by reusing unified RGB image data stored and stored in the HDD 5 will be described. The user uses the operation display device 10 to input an instruction for mode setting and fax transmission start for the unified RGB image data stored in the HDD 5 at the time of copying. The operation display device 10 converts information input from the user into control command data inside the device, and issues a control command. The control command is notified to the CPU 6 via the PCI-Express bus. The CPU 6 executes the fax transmission start process program in accordance with the fax transmission start control command data, and sequentially performs settings and operations necessary for the fax transmission operation.

  The CPU 6 stores the unified RGB image data stored in the HDD 5 via the bus control device 3 in the memory 7. The CPU 6 reads the unified RGB image data stored in the memory 7 and outputs the read unified RGB image data to the image data processing device 4 through the bus control device 3.

  The filter processing unit 40 of the image data processing device 4 improves the reproducibility when transmitting the sharpness of the unified RGB image data stored in the memory 7, that is, the unified RGB image data stored in the HDD 5 at the time of copying, by FAX. to correct. Specifically, the filter processing unit 40 performs sharpening / smoothing processing on the RGB image data stored in the memory 7 according to desired mode information. For example, in the character mode, a sharpening process is performed to make the character clear / clear, and in the photo mode, a smoothing process is performed to smoothly express gradation. The filter processing unit 40 outputs the RGB image data subjected to the sharpening / smoothing process to the color conversion unit 41.

  The color conversion unit 41 converts the RGB image data input from the filter processing unit 40 into a general single color (monochrome) by FAX 15 based on the supplementary information and the mode designation. The color conversion unit 41 outputs the monochrome image data to the scaling processing unit 42.

  The scaling processing unit 42 converts the size (resolution) of the monochrome image data input from the color conversion unit 41 into a size (resolution) transmitted and received with the FAX 15. For example, the scaling processing unit 42 converts the size (resolution) of the monochrome image data input from the color conversion unit 41 to 200 dpi (main scanning) × 100 dpi (sub scanning). The scaling processing unit 42 outputs the monochrome image data converted into the size (resolution) transmitted / received to / from the FAX 15 to the gradation processing unit 43.

  The gradation processing unit 43 subjects the monochrome image data (monochrome 8-bit data) input from the scaling processing unit 42 to gradation number conversion processing according to the gradation processing capability transmitted / received by the FAX 15. The gradation processing unit 43 outputs the monochrome image data converted into the number of gradations according to the gradation processing capability transmitted / received by the FAX 15 to the line I / F device 11 via the bus control device 3, and the line I / F. The apparatus 11 transmits monochrome image data to the FAX 15 via a line.

  Next, an operation for reusing scanner data by reusing unified RGB image data stored and stored in the HDD 5 will be described. The user uses the operation display device 10 to input mode setting and scanner distribution start instruction for the unified RGB image data stored in the HDD 5 at the time of copying. The operation display device 10 converts information input from the user into control command data inside the device, and issues a control command. The control command is notified to the CPU 6 via the PCI-Express bus. The CPU 6 executes a scanner distribution start process program according to the scanner distribution start control command data, and sequentially performs settings and operations necessary for the scanner distribution operation.

  The CPU 6 stores the unified RGB image data and incidental information stored in the HDD 5 via the bus control device 3 in the memory 7. The CPU 6 reads the unified RGB image data and supplementary information stored in the memory 7, and outputs the read RGB image data to the image data processing device 4 through the bus control device 3.

  The filter processing unit 40 of the image data processing device 4 corrects the sharpness of the unified RGB image data so that the reproducibility in the case of scanner distribution is improved. Specifically, the filter processing unit 40 performs sharpening / smoothing processing on the RGB image data stored in the memory 7 according to desired mode information. For example, in the character mode, a sharpening process is performed to make the character clear / clear, and in the photo mode, a smoothing process is performed to smoothly express gradation. The filter processing unit 40 outputs the RGB image data subjected to the sharpening / smoothing process to the color conversion unit 41.

  The color conversion unit 41 converts RGB image data (RGB 8-bit data) input from the filter processing unit 40 into a designated color space. The color conversion unit 41 outputs monochrome image data (monochrome 8-bit data) to the scaling processing unit 42. Here, the color conversion unit 41 converts the 8-bit RGB data input from the filter processing unit 40 into 8-bit RGB data (sRGB image data) in the general sRGB color space by scanner distribution. The color conversion unit 41 outputs the sRGB image data converted into sRGB color space data to the scaling processing unit 42.

  The scaling processing unit 42 converts the size (resolution) of the sRGB image data input from the color conversion unit 41 into a size (resolution) transmitted / received by the designated scanner distribution. Here, the scaling processing unit 42 converts the size (resolution) of the sRGB image data input from the color conversion unit 41 into 200 dpi (main scanning) × 200 dpi (sub scanning). The scaling processing unit 42 outputs the sRGB image data converted into the size (resolution) transmitted / received by the designated scanner delivery to the gradation processing unit 43.

  The gradation processing unit 43 subjects the sRGB image data input from the scaling processing unit 42 to gradation number conversion processing according to the gradation processing ability transmitted / received by the designated scanner distribution. Here, it is assumed that the gradation processing unit 43 designates 160,000 colors of 8 bits for each of RGB, and gradation processing is not particularly performed. Even when an output different from that at the time of input is specified for the data stored and stored in the image processing apparatus, the image quality does not change at all from the normal operation when the output destination is specified from the beginning. Therefore, it is easy to change the output destination, and reusability is significantly improved.

  Next, the detailed operation of the color conversion unit 41 will be described with reference to FIGS. The linear masking processing unit 411 performs linear masking processing on each 8-bit unified RGB image data IN whose sharpness has been corrected by the filter processing unit 40, and each 8-bit masking RGB image data msk (msk_R, msk_G, msk_B). And masking K image data msk_k. The linear masking processing unit 411 outputs the generated masking RGB image data msk and masking K image data msk_k to the 3DLUT color conversion unit 4121 of the three-dimensional LUT conversion unit 412.

  The 3DLUT color conversion unit 4121 displays the picture area when the 2-bit image area separation signal sepi corresponding to the pixels of the masking RGB image data msk and the masking K image data msk_k input from the linear masking processing unit 411 indicates the picture area. When the image LUT 4121a is selected and the image area separation signal sepi indicates a character area, the character area LUT 4121b is selected. The 3DLUT color conversion unit 4121 performs three-dimensional memory map interpolation on the masking RGB image data msk of the pixel using the selected LUT to generate 9-bit CMY image data lut_cmy.

  The memory map interpolation method divides a three-dimensional input color space into a plurality of unit cubes, further divides each divided unit cube into six tetrahedrons sharing a symmetry axis, and performs linear operation for each unit cube. An output value is obtained, and data of division boundary points (grid points) are used as parameters (hereinafter referred to as lattice point parameters) for linear calculation.

  Specifically, as shown in FIG. 6, a three-dimensional input color space composed of the X direction, Y direction, and Z direction is divided in each direction (here, eight divisions), and a plurality of three-dimensional input color spaces (here Then, it is divided into 512) unit cubes. If the masking R image data msk_R is x, the masking R image data msk_G is y, the masking R image data msk_B is z, and the coordinates of the masking RGB image data msk in the three-dimensional input color space are A, the masking RGB image data msk is the coordinates. It can be represented by A (x, y, z). The 3DLUT color conversion unit 4121 selects a unit cube containing the coordinates A.

  FIG. 7 is a diagram showing the selected unit cube. In FIG. 7, the coordinates of the grid points are coordinates A0 to A7, the grid point parameters of the coordinates A0 to A7 are P0 to P7, and the output value of the coordinates A indicated by the masking RGB image data msk as input data is P. . The unit cube is a tetrahedron T0 composed of coordinates A0, coordinates A4, coordinates A7, and coordinates A6 (see FIG. 8-1), and a tetrahedron T1 composed of coordinates A0, coordinates A4, coordinates A5, and coordinates A7 (see FIG. 8-2). ), Tetrahedron T2 composed of coordinates A0, coordinates A1, coordinates A5 and coordinates A7 (see FIG. 8-3), tetrahedron T3 composed of coordinates A0, coordinates A1, coordinates A7 and coordinates A3 (see FIG. 8-4), A tetrahedron T4 composed of coordinates A0, coordinates A2, coordinates A7, and coordinates A3 (see FIG. 8-5), and a tetrahedron T5 composed of coordinates A0, coordinates A2, coordinates A6, and coordinates A7 (see FIG. 8-6). Divided into tetrahedrons.

  The 3DLUT color conversion unit 4121 obtains the coordinates (lower coordinates) of the coordinates A when the coordinates A0 is the origin. If the coordinate A0 is (x0, y0, z0), the lower coordinates of the coordinate A (x, y, z) can be obtained by (x-x0, y-y0, z-z0). Here, if x−x0 is Δx, y−y0 is Δy, and z−z0 is Δz, the lower coordinates of the coordinate A are (Δx, Δy, Δz).

  The 3DLUT color conversion unit 4121 selects the tetrahedrons T0 to T5 by comparing the obtained lower coordinates, and selects the lattice point parameters P0 to P7 of the selected tetrahedrons T0 to T5 as interpolation coefficients. FIG. 9 is a diagram showing the relationship between the tetrahedron selected by the size comparison result of the lower coordinates of the coordinate A and the interpolation coefficient. In FIG. 9, when “Δx <Δy <Δz” is established as the magnitude relationship of the lower coordinates, the tetrahedron T0 is selected, the value “P7−P6” is selected as the interpolation coefficient K0, and “ “P6-P4” is selected, and “P0” is selected as the interpolation coefficient K3. When “Δy ≦ Δx <Δz” holds as the magnitude relationship of the lower coordinates, the tetrahedron T1 is selected, the value “P5-P4” is selected as the interpolation coefficient K0, and “P7-P5” is selected as the interpolation coefficient K1. Is selected, and “P0” is selected as the interpolation coefficient K3. When “Δy <Δz ≦ Δx” is satisfied as the magnitude relation of the lower coordinates, the tetrahedron T2 is selected, the value of “P1-P0” is selected as the interpolation coefficient K0, and “P7-P5” is selected as the interpolation coefficient K1. Is selected, and “P0” is selected as the interpolation coefficient K3. When “Δz ≦ Δy ≦ Δx” holds as the magnitude relationship of the lower coordinates, the tetrahedron T3 is selected, the value of “P1-P0” is selected as the interpolation coefficient K0, and “P3-P1” is selected as the interpolation coefficient K1. Is selected, and “P0” is selected as the interpolation coefficient K3. When “Δz ≦ Δx <Δy” is established as the magnitude relationship of the lower coordinates, the tetrahedron T4 is selected, the value of “P3-P2” is selected as the interpolation coefficient K0, and “P2-P0” is selected as the interpolation coefficient K1. Is selected, and “P0” is selected as the interpolation coefficient K3. When “Δx <Δz ≦ Δy” is established as the magnitude relation of the lower coordinates, the tetrahedron T5 is selected, the value “P7-P6” is selected as the interpolation coefficient K0, and “P2-P0” is selected as the interpolation coefficient K1. Is selected, and “P0” is selected as the interpolation coefficient K3.

  In the pattern area LUT 4121a, lattice point parameters P0 to P7 of tetrahedrons T0 to T5 in each unit cube used in the pattern area and various parameters described later are registered, and in the character area LUT 4121b, each unit cube used in the character area. The lattice point parameters P0 to P7 of tetrahedrons T0 to T5 and various parameters described later are registered. The grid point parameters P0 to P7 and various parameters are registered for C, M, and Y, respectively.

When the image area separation signal sepi indicates a picture area, the 3DLUT color conversion unit 4121 selects the lattice point parameters P0 to P7 of the tetrahedrons T0 to T5 in the unit cube of the picture area LUT 4121a, and the image area separation signal sepi is When a character area is indicated, the lattice point parameters P0 to P7 of the tetrahedrons T0 to T5 in the unit cube of the character area LUT 4121b are selected, and linear interpolation with respect to the coordinate A is performed using the following equations 1-1 to 1-3. Output pout (indicating pout_c, pout_m, pout_y).
pout_c =
K0_C × Δx + K1_C × Δy + K2_C × Δz + K3_C Formula 1-1
pout_m =
K0_M × Δx + K1_M × Δy + K2_M × Δz + K3_M Equation 1-2
pout_y =
K0_Y × Δx + K1_Y × Δy + K2_Y × Δz + K3_Y Equation 1-3

  K0_C to K3_C are interpolation coefficients K0 to K3 for C, K0_M to K3_M are interpolation coefficients K0 to K3 for M, and K0_Y to K3_Y are interpolation coefficients K0 to K3 for Y.

In the pattern area LUT 4121a and the character area LUT 4121b, using the lattice point parameters of the unit cube tetrahedron selected by the input in (coordinates indicated by the RGB image data), the above expression 1 (expression 1-1 to expression 1- The slope ltslope and the intercept lintc as shown in FIG. 10 obtained from the relationship between the output pout and the input in obtained by (3) are registered. The 3DLUT color conversion unit 4121 normalizes the output pout obtained by the above equation 1 using the gradient lutslope and the intercept lintc by the following equations 2-1 to 2-3 to obtain the CMY image data lut_cmy.
lut_c = (pout_c * lutslope) −limitc (Formula 2-1)
lut_m = (pout_m * lutslope) -limitc ... Formula 2-2
lut_y = (pout_y * lutslope) -limitc ... Formula 2-3
In Formula 2 (showing Formula 2-1 to Formula 2-3), * indicates a power. In addition, when the image area separation signal sepi indicates a picture area, the 3DLUT color conversion unit 4121 uses the inclination lutslope and the intercept lintc registered in the picture area LUT 4121a, and the image area separation signal sepi indicates a character area. In this case, the gradient lutslope and the intercept lintc registered in the character area LUT 4121b are used.

Note that the range to be expanded may be changed for each output plane (for each CMY) of the three-dimensional LUT. In this case, the slope lutslope and the intercept lintc may be set for each output plane and normalized using the following equations 3-1 to 3-3.
lut_c = (pout_c * lutslope_c) −limitc_c Expression 3-1
lut_m = (pout_m * lutslope_m) −limitc_m Equation 3-2
lut_y = (pout_y * lutslope_y) −limitc_y Equation 3-3
In Formula 3 (showing Formula 3-1 to Formula 3-3), * indicates a power.

  When the range to be expanded is changed for each output plane in this way, the scale of the color conversion table increases even when the extended RGB space with a wide color reproduction range and the color reproduction range (gamut) shape of the color image output device differ greatly. Without conversion, it is possible to convert the color of the color image output apparatus with high accuracy.

  The 3DLUT color conversion unit 4121 clips the CMY image data to “0” when the obtained CMY image data lut_cmy is negative. The 3DLUT color conversion unit 4121 outputs 9-bit CMY image data lut_cmy to the UCR processing unit 414 and the mink calculation unit 4122.

  The mink calculation unit 4122 calculates the minimum value mink of the CMY image data lut_cmy generated by the 3DLUT color conversion unit 4121. If the calculated minimum value mink is 256 or more, the mink calculation unit 4122 clips to 255 and sets the minimum value mink to a value of 255 or less. The mink calculation unit 4122 outputs the 8-bit minimum value mink to the selector 4123.

  The selector 4123 selects the minimum value mink input from the mink calculation unit 4122 when the image area separation signal sepi indicates a picture area, and the linear masking processing unit 411 when the image area separation signal sepi indicates a character area. The masking K image data msk_k input from is selected. The selector 4123 outputs the selected minimum value mink or masking K image data msk_k to the GCR processing unit 413 as K image data lut_k.

  The GCR processing unit 413 performs black generation on the K image data lut_k input from the selector 4123 of the three-dimensional LUT conversion unit 412 based on the GCR mode signal gcr_mode, the image area separation signal sepi, and the feature amount gcr_edgei.

  The GCR mode signal gcr_mode is a signal indicating whether or not the image area separation signal sepi is to be validated, and is generated by the CPU from a direct mode designation by the user or a mode input by the user. Here, the GCR mode signal gcr_mode is a 2-bit signal and indicates whether or not the picture area is enabled and whether or not the character area is enabled.

  When the image area separation signal sepi indicates a picture area and the GCR mode signal gcr_mode indicates that the picture area is valid, or the image area separation signal sepi indicates a character area and the GCR mode signal gcr_mode is If the character area is indicated to be invalidated, the GCR processing unit 413 performs GCR processing according to edge information indicated by the feature value gcr_edgei input from the filter processing unit 40.

  Specifically, the parameter gslopep and the parameter gintp used for the GCR process are changed according to the size of the feature amount gcr_edgei, and the smaller the feature amount gcr_edgei, the lower the feature value gcr_edge and the parameter gintp, the lower the black value, and the larger the feature amount gcr_edgei. The parameter gslopep and the parameter gintp are set to high ink values.

The GCR processing unit 413 uses the K image data lut_k input from the selector 4123 of the three-dimensional LUT conversion unit 412, the parameter gslopep and the parameter gintp corresponding to the feature amount gcr_edgei, and uses the following equation 4 to perform GCR processing The K image data adpk for the pattern area is obtained.
adpk = (gslopep * lut_k) −gintp Equation 4
In Equation 4, * indicates a power.

  Further, the GCR processing unit 413 uses the parameter uslopep and the parameter uintp according to the K image data adpk for the pattern area after the GCR processing and the edge information indicated by the feature value gcr_edgei input from the filter processing unit 40, The K image data adducrk used in the UCR processing unit 414 is obtained. Specifically, the parameter uslopep and the parameter uintp are changed according to the size of the feature quantity gcr_edgei, the smaller the feature quantity gcr_edgei, the lower the parameter gslopepe and the parameter gintp, and the lower the feature quantity gcr_edgei, the greater the parameter gslope_ The parameter gintp is set to a high ink value.

The GCR processing unit 413 uses the K image data adpk obtained by the above equation 4 and the parameter uslopep and the parameter uintp corresponding to the feature value gcr_edgei to obtain the K image data aduprk used in the UCR processing unit 414 from the following equation 5. .
adpurk = (uslopep * adpk) −uintp Equation 5
In Equation 5, * indicates a power.

  On the other hand, when the image area separation signal sepi indicates a character area and the GCR mode signal gcr_mode indicates that the character area is valid, or the image area separation signal sepi indicates a picture area and the GCR mode signal When gcr_mode indicates that the design area is invalidated, the GCR processing unit 413 uses the predetermined character area for the character area without depending on the edge information indicated by the feature value gcr_edgei input from the filter processing unit 40. GCR processing is performed using the parameter gslopec and the parameter gintc.

Specifically, the GCR processing unit 413 uses the K image data lut_k input from the selector 4123 of the three-dimensional LUT conversion unit 412, the parameter gslopec, and the parameter gintc, and uses the following equation 6 to perform GCR processing K image data fixk for the character area is obtained.
fixk = (gslopec * lut_k) −gintc Equation 6
In Equation 6, * indicates a power.

Further, the GCR processing unit 413 uses the K image data fixk for the character area obtained by the above equation 6 and the predetermined parameter uslopec and parameter uintc to obtain the K image used in the UCR processing unit 414 from the following equation 7. Data fixucrk is obtained.
fixucrk = (uslopec * fixk) −uintc Equation 7
In Equation 7, * indicates a power.

  The GCR processing unit 413 clips to 0 when the K image data adpk obtained by the above equation 4 or the K image data fixk obtained by the equation 6 is negative, and the K image data adpk or the K image data fixk is 256 or more. In this case, the data is clipped to 255 and output to the scaling unit 42 as K-image data gcr_bk after 8-bit GCR processing.

  In addition, the GCR processing unit 413 clips to 0 when the K image data adducrk obtained by Equation 5 or the K image data fixucrk obtained by Equation 7 is negative, and the K image data adducrk or the K image data fixucrk is If it is 256 or more, it is clipped to 255 and output to the UCR processing unit 414 as 8-bit ucr processing K image data ucr_bk.

  The UCR processing unit 414 performs UCR processing on the CMY image data lut_cmy generated by the three-dimensional LUT conversion unit 412 based on the UCR mode signal ucr_mode and the K image data ucr_bk generated by the GCR processing unit 413. The CMY image data lut_cmy is corrected.

  The UCR mode signal ucr_mode is a signal indicating whether or not excessive correction processing for preventing high density crush due to change of density notch or the like is performed, and is generated by the CPU from a direct designation by the user or a mode input by the user. . Here, the UCR mode signal ucr_mode is a 2-bit signal, and indicates whether or not an excessive correction process is performed on a picture area and whether or not an excessive correction process is performed on a character area.

When the image area separation signal sepi indicates the picture area and the UCR mode signal ucr_mode indicates that the image area is excessively corrected, or when the image area separation signal sepi indicates the character area, and the UCR When the mode signal ucr_mode indicates that the character region is subjected to the excessive correction process, the UCR processing unit 414 uses the following equation 8-1 when the C image data lut_c is 256 or more, and the C image data lut_c is If smaller than 256, the corrected C image data hutt_c is obtained using the following equation 9-1. If the M image data lut_m is 256 or more, the following equation 8-2 is used to determine that the M image data lut_m is If it is smaller than 256, the corrected M image data hlt_m is obtained using the following equation 9-2, and the Y image data lut is obtained. y is using Equation 8-3 below in the case of more than 256, if Y image data lut_y is less than 256 using Equation 9-3 below seek Y image data hlut_y corrected.
hlt_c = (256+ (lut_c & 0x00ff)) / 2 Formula 8-1
hlut_m = (256+ (lut_m & 0x00ff)) / 2 Formula 8-2
hlt_y = (256+ (lut_y & 0x00ff)) / 2 Equation 8-3
hlut_c = lut_c Expression 9-1
hlut_m = lut_m ... Formula 9-2
hlut_y = lut_y Equation 9-3

On the other hand, when the image area separation signal sepi indicates a picture area and the UCR mode signal ucr_mode indicates that the image area is not subjected to excessive correction processing, or the image area separation signal sepi indicates a character area. When the UCR mode signal ucr_mode indicates that the character region excess correction process is not performed, the UCR processing unit 414 uses the following expression 10-1 when the C image data lut_c is 256 or more, and C When the image data lut_c is smaller than 256, the corrected C image data htt_c is obtained using the following equation 11-1, and when the M image data lut_m is 256 or more, the following equation 10-2 is used to When the image data lut_m is smaller than 256, the corrected M image data htt_m is obtained using the following equation 11-2. When the Y image data lut_y is 256 or more, the following equation 10-3 is used. When the Y image data lut_y is smaller than 256, the corrected Y image data glut_y is obtained using the following equation 11-3. .
hult_c = 255 Formula 10-1
hult_m = 255 Formula 10-2
hult_y = 255 Formula 10-3
hlut_c = lut_c Formula 11-1
hlut_m = lut_m ... Formula 11-2
hlut_y = lut_y Expression 11-3

  That is, when performing the excessive correction process, correction according to the excessive amount is performed, and when the excessive correction process is not performed, the clip is clipped to the maximum value 255 without depending on the excessive amount, and is not performed even when performing the excessive correction process. Even in this case, if the CMY image data lut_cmy is less than or equal to the maximum value 255, the value of the image data is used as it is.

  The UCR processing unit 414 subtracts the K image data ucr_bk input from the GCR processing unit 413 from each of the corrected CMY image data cult_cmy. The UCR processing unit 414 clips to 0 if the value obtained by subtracting the K image data ucr_bk input from the GCR processing unit 413 from each of the CMY image data hult_cmy is negative, and 255 if the subtracted value is 256 or more. And output to the UCA processing unit 415 as 8-bit CMY image data ucr_cmy (indicating ucr_c, ucr_m, ucr_y).

  The UCA processing unit 415 performs UCR processing on the CMY image data ucr_cmy generated by the UCR processing unit 414 based on the UCA mode signal uca_mode and the K image data gcr_bk generated by the GCR processing unit 413 to obtain CMY image data. ucr_cmy is corrected.

  The UCR processing unit 414 generates CMY image data ucr_cmy by subtracting the UCR processing K image data ucr_bk from the corrected CMY image data hult_cmy. However, since the black amount is excessively subtracted in this UCR processing, the value excessively subtracted by the UCR processing unit 414 may be corrected by the K image data gcr_bk that is the black amount generated by the GCR processing unit 413. The UCA mode signal uca_mode is a signal indicating whether or not this correction is performed, and is generated by the CPU from a direct designation from the user or a mode input by the user. Here, the UCA mode signal uca_mode is a 2-bit signal, and indicates whether correction processing is performed on the picture area or whether correction processing is performed on the character area.

When the image area separation signal sepi indicates a picture area and the UCA mode signal uca_mode indicates that the image area is to be corrected, or the image area separation signal sepi indicates a character area and the UCA mode signal uca_mode Indicates that character area correction processing is performed, the UCA processing unit 415 obtains CMY image data uca_cmy obtained by correcting the CMY image data ucr_cmy using the following formulas 12-1 to 12-3.
uca_c = (ucr_c × (256 + ucr_bk)) / 256 Formula 12-1
uca_m = (ucr_m × (256 + ucr_bk)) / 256 Formula 12-2
uca_y = (ucr_y × (256 + ucr_bk)) / 256 Equation 12-3

  The UCA processing unit 415 clips with 0 when the CMY image data uca_cmy corrected by the above equation 12 (shown by the equations 12-1 to 12-3) is negative, and the corrected CMY image data uca_cmy is 256 or more. In this case, the data is clipped to 255 and 8-bit CMY image data uca_cmy is output to the scaling processing unit 42.

  On the other hand, when the image area separation signal sepi indicates a picture area and the UCA mode signal uca_mode indicates that the image area is not corrected, or when the image area separation signal sepi indicates a character area and the UCA When the mode signal uca_mode indicates that the character area correction process is not performed, the UCA processing unit 415 outputs the CMY image data ucr_cmy as it is to the scaling unit 42 as the CMY image data uca_cmy.

  As described above, in this embodiment, the reading apparatus 1 that reads an original and generates input image data of RGB color signals expressed in a three-dimensional color space and accompanying information indicating attributes of the input image data; An image data processing device 2 (first image data processing device in the claims) that generates unified image data obtained by unifying input image data generated by the reading device 1 with predetermined characteristics; A memory 7 for storing unified image data and supplementary information generated by the device 2, and an image data processing device 4 for generating output image data of CMYK color signals different from the unified image data stored in the memory 7 (claim) A second image data processing device in the range of (2) and a program for printing output image data generated by the image data processing device 4. The data processing device 4 has an interface function for connecting the data device 9 (image writing device in the scope of claims) and the FAX 15 (external output device in the scope of claims). It has an interface function to connect the line I / F device 11 (interface device as defined in the claims) that outputs the output image data to the FAX 15 and the PC 16 (external output device as defined in the claims). And an external I / F device 12 (interface device in the scope of claims) that outputs output image data generated by the image data processing device 4 to the PC 16. The input image data generated by the PC 15 corresponds to the plotter device 9, FAX 15, and PC 16. The image data processing device 4 converts the unified image data stored in the memory 7 from RGB to CMYK using a three-dimensional lookup table, and plots the range of the CMYK image data obtained by the color conversion. After virtually expanding to a color gamut larger than the color gamut that can be reproduced by the device 9, the FAX 15, and the PC 16, the range of the expanded image data is reproduced by the plotter device 9, the FAX 15, or the PC 16 that is the output destination of the output image data. Since the clipped image data is output as output image data by clipping to the range of the color gamut that can be generated, the RGB input image data generated from the original by the reading device 1 is sent to the plotter device 9, FAX 15, and PC 16. Do not increase the scale of the color conversion table. In addition, the color reproduction range (gamut) can be converted with high accuracy into the color of the color image output apparatus. Specifically, for example, even when extended RGB having a wider color gamut than the sRGB space assuming a standard monitor is set as a common color space for performing image processing, the scale of the color conversion table for the interpolation combined system is set. Without increasing the color, the color of the color image output apparatus with a limited color reproduction range (gamut) can be corrected with high accuracy.

  Further, according to this embodiment, the UCR processing unit 414 applies the undercolor based on the image area separation signal sepi and the UCR mode signal ucr_mode specified by the user to the image data obtained by clipping the range of the expanded image data. The UCR processing unit 414 outputs the image data that has been subjected to the black color addition black ink processing based on the image area separation signal sepi and the UCA mode signal uca_mode specified by the user as output image data. Therefore, according to the characteristics of the input color image, an effective ink can be obtained while making the best use of the color reproduction range (gamut) of the color image output device without increasing the scale of the color conversion table. In addition to performing processing, color matching processing suitable for characters, pictures, and the like can be performed.

  Furthermore, according to this embodiment, since the range to be expanded for the image data of the pattern area and the character area is changed based on the image area separation signal sepi, according to the characteristics of the input color image, It is possible to achieve both color reproduction control of saturated colors frequently used in graphic documents created by the PC 16 and high-precision color reproduction at the color reproduction area boundary.

  It should be noted that the above-described functions realized by the γ conversion unit 20, the filter processing unit 21, the color conversion unit 22, and the scaling processing unit 23 of the image data processing device 2 of this embodiment, and the image data processing device 2 The functions described above realized by the filter processing unit 40, the color conversion unit 41, the scaling processing unit 42, and the gradation processing unit 43 may be provided as an image processing program for causing a general-purpose computer to execute the functions. . In this case, the image processing program is recorded in a computer-readable recording medium such as a CD-ROM, a floppy (registered trademark) disk, and a DVD in a format that can be installed in a computer or a computer-executable format. provide. The image processing program recorded on the recording medium is read from the recording medium and realized on the computer.

  A computer that executes an image processing program according to the present invention includes at least a control device and a storage device. The control device includes an arithmetic processing device such as a CPU that controls the entire computer, and a ROM. The storage device includes a general RAM, stores data necessary for processing, and is used as a processing work memory. The control device reads and executes the image processing program from the recording medium on which the image processing program is recorded, so that the γ conversion unit 20, the filter processing unit 21, the color conversion unit 22, and the scaling unit of the image data processing device 2 are executed. Each function described above realized by the processing unit 23 and each function described above realized by the filter processing unit 40, the color conversion unit 41, the scaling processing unit 42, and the gradation processing unit 43 of the image data processing apparatus 2 Operate the computer.

  Alternatively, the image processing program may be stored on a computer connected to a network and provided by being downloaded via the network. Further, the image processing program may be provided or distributed via a network.

It is a block diagram which shows the structure of the image processing apparatus in embodiment of this invention. It is a block diagram which shows the structure of the image data processing apparatus shown in FIG. It is a block diagram which shows the structure of the image data processing apparatus shown in FIG. FIG. 4 is a block diagram illustrating a configuration of a color conversion unit illustrated in FIG. 3. FIG. 5 is a block diagram illustrating a configuration of a three-dimensional LUT conversion unit illustrated in FIG. 4. FIG. 6 is a diagram for explaining an operation of the 3DLUT color conversion unit illustrated in FIG. 5. FIG. 6 is a diagram for explaining an operation of the 3DLUT color conversion unit illustrated in FIG. 5. FIG. 6 is a diagram for explaining an operation of the 3DLUT color conversion unit illustrated in FIG. 5. FIG. 6 is a diagram for explaining an operation of the 3DLUT color conversion unit illustrated in FIG. 5. FIG. 6 is a diagram for explaining an operation of the 3DLUT color conversion unit illustrated in FIG. 5. FIG. 6 is a diagram for explaining an operation of the 3DLUT color conversion unit illustrated in FIG. 5. FIG. 6 is a diagram for explaining an operation of the 3DLUT color conversion unit illustrated in FIG. 5. FIG. 6 is a diagram for explaining an operation of the 3DLUT color conversion unit illustrated in FIG. 5. It is a figure which shows the relationship between the tetrahedron which the 3DLUT color conversion part shown in FIG. 5 selects, and an interpolation coefficient. FIG. 6 is a diagram for explaining a normalization operation of the 3DLUT color conversion unit illustrated in FIG. 5. It is a figure for demonstrating the conventional color conversion. It is a figure for demonstrating the conventional color conversion. It is a figure for demonstrating the conventional color conversion. It is a figure for demonstrating the conventional color conversion.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reading apparatus 2,4 Image data processing apparatus 3 Bus control apparatus 5 HDD
6 CPU
7 Memory 8 Plotter I / F Device 9 Plotter Device 10 Operation Display Device 11 Line I / F Device 12 External I / F Device 13 South Bridge Device 14 ROM
15 FAX
16 PC
20 γ conversion unit 21, 40 Filter processing unit 22, 41 Color conversion unit 23, 42 Scaling processing unit 43 Gradation processing unit 411 Linear masking processing unit 412 Three-dimensional LUT conversion unit 413 GCR processing unit 414 UCR processing unit 415 UCA processing Part 4121 3DLUT color conversion part 4121a LUT for picture area
4121b LUT for character area
4122 mink calculation unit 4123 selector

Claims (8)

Connected to at least one image output device and converts input image data of color signals expressed in a color space of n (n is a natural number) dimension into output image data of color signals in a format different from the input image data In the image processing apparatus that outputs the converted output image data to the image output apparatus,
The input image data is color-converted into the format of the output image data using an n-dimensional lookup table, and the range of the color-converted image data is virtually increased to a color gamut larger than the color gamut that the image output apparatus can reproduce. After the expansion, color conversion means for clipping the range of the expanded image data to a range that can be reproduced by the image output device that outputs the output image data, and outputting the clipped image data as the output image data;
An image processing apparatus comprising: An image reading device that reads an original and generates input image data of color signals expressed in an n-dimensional color space (n is a natural number) and accompanying information indicating attributes of the input image data;
A first image data processing device for generating unified image data in which the input image data generated by the image reading device is unified with predetermined characteristics;
A memory device for storing unified image data and incidental information generated by the first image data processing device;
A second image data processing device for generating output image data of a color signal in a format different from the unified image data stored in the memory device;
An image writing device for printing output image data generated by the second image data processing device;
An interface device that has an interface function for connecting to an external output device that processes image data, and that outputs output image data generated by the second image data processing device to the external output device;
With
The first image data processing device includes:
Unifying input image data generated by the image reading device into characteristics corresponding to the image writing device and an external output device connected to the interface device;
The second image data processing device includes:
The unified image data stored in the memory device is color-converted into the output image data format using an n-dimensional lookup table, and the range of the image data obtained by the color conversion is converted into the image writing device and the external output device. After virtually expanding to a color gamut larger than the color gamut that can be reproduced, the range of the expanded image data is changed to the range of the color gamut that can be reproduced by the image writing device that is the output destination of the output image data or the external output device Clipped and provided with color conversion means for outputting the clipped image data as the output image data;
An image processing apparatus. The color conversion means includes
Performing black processing of under color removal on the image data clipped from the range of the expanded image data, and outputting the image data subjected to the black processing as the output image data;
The image processing apparatus according to claim 1, wherein: The color conversion means includes
Changing the range for extending the range of the image data obtained by the color conversion according to the auxiliary information stored in the memory device and / or the mode designation input from the outside,
The image processing apparatus according to claim 3.   The image processing apparatus according to claim 4, wherein the auxiliary information is information indicating that the input image data is a pixel in a picture area or a character area. The color conversion means includes
Expanding the image data converted using the n-dimensional lookup table for each plane of the output image data;
The image processing apparatus according to claim 1, wherein: Connected to at least one image output device and converts input image data of color signals expressed in a color space of n (n is a natural number) dimension into output image data of color signals in a format different from the input image data In the image processing method applied to the image processing apparatus that outputs the converted output image data to the image output apparatus,
a color conversion processing step for color-converting the input image data into the format of the output image data using an n-dimensional lookup table;
An expansion processing step of virtually extending the range of the image data color-converted by the color conversion processing step to a color gamut larger than the color gamut that can be reproduced by the image output device;
A clip processing step for clipping the range of the image data expanded by the expansion processing step to a range that can be reproduced by the image output device that outputs the output image data;
An output processing step of outputting the image data clipped by the clipping processing step as the output image data;
An image processing method comprising:   An image processing program for causing a computer to execute the image processing method according to claim 7.

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