JP2008042842A - Multi-color printing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that when applying CMS to gradation data, an arithmetic quantization error of interpolation or the like may become a problem occasionally and since there is generated a problem in the case that a change amount is reduced in a device color value in particular, processing or the like for determining a color value appropriately through interpolation processing from a device color value of an end point for intermediate image formation is proposed but this is correct when a color space of gradation and a device-side color space are linearly corresponding to each other but it does not become right processing as CMS if the color spaces are non-linear. <P>SOLUTION: By appropriately dividing the gradation, a gradation graphic is constituted to realize right color reproduction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a multicolor printing apparatus that performs development of characters and graphics or drawing of natural images such as photographs.

  In an output device such as a color printer that prints graphics and image data, the color data to be handled is specified by RGB values specified by a color mode or command in the case of graphic data, and RGB dot sequential or RGB in the case of image data Given in frame-sequential form. In addition, the color space to be handled is not limited to RGB, and there are some that handle a YMC color space (depending on ink characteristics or the like) unique to each printing apparatus, an XYZ color space defined by CIE, or the like. In any case, in the color space defined by the printer, the input data is subjected to a color reproduction process corresponding to the printing inside the printer (for example, conversion from RGB to YMCK), and actual print output is performed. .

  In general, when color matching with color data handled by other devices (color scanner devices, color display devices such as CRTs) is considered, one reference color space is defined, and each color processing device emits light. Color correction suitable for (color) characteristics may be performed. In this case, the color processing inside the color printer also corresponds to the reference color space, and for example, an image displayed on the color display can be output by the color printer and faithfully reproduced.

  Many color difference formulas have been proposed in a method for evaluating whether two colors represented on different media are equal. However, there is nothing that has been absolutely established, and in many cases, they are used properly depending on the purpose of use. At the same time, there are several methods for color reproduction, which are also properly used depending on the purpose. When color matching is taken into consideration, the method of evaluation depending on the purpose of color reproduction is inevitably different. Particularly in a color printer, the internal color reproduction method is an important factor affecting the image quality of the output printed matter. In general, as described above, attempts have been made to perform correction so as to minimize the color difference using the CIE 1976 L * a * b * color difference formula or the like. This method is effective when color data read from a color scanner device is reproduced by a color printer. This is because the original is a reflection original (color that has been reproduced on paper) and it is relatively easy to reproduce it with the ink of the printing apparatus. Since the mechanism of physical color development is basically the same, color reproduction is easier compared to other media, even if there are differences in ink characteristics and problems with their density (gradation).

"Color matching by object"
Since colors such as those emitted on the screen of a color display device have physical characteristics that are different from those of a reflective original, there is a limit to the pursuit of color reproducibility by a general color difference formula. When an image output on such a medium is a natural image, color reproduction called preferred matching is often used in many cases. This is intended to achieve a more favorable color reproduction for some of the most important colors in the image (for example, human skin color), apart from the viewpoint of whether the reproduced image is the same color as the original image. . However, even when such color reproduction is effective when handling data such as a natural image, inconvenience occurs in color reproduction processing that does not consider uniform colors when handling data such as a CG image. .

  Therefore, this problem can be solved if the color reproduction process can be changed in accordance with the data to be processed. Conventionally, methods for solving the above-described problems have been proposed, and it is possible to provide a multi-color printing apparatus capable of printing out with more preferable image quality by selecting a color reproduction process corresponding to the data to be handled. It has become.

  In general, input data is first temporarily recorded in an input unit inside a printer, and then sent to a data analysis unit to analyze what kind of data is from the data format. If the input data is image data, the pixel size and the RGB value of each pixel are arranged in a dot-sequential format. If the input data is CG data, the data representing the type of figure and the RGB data of the coordinate values and color designation values are processed. Since they are arranged in a form that matches the body shape, this is analyzed by the data analysis unit, and the processing is branched to a development system that matches the processing of the data. When processing image data, it branches from the data analysis unit to the image development processing system, is converted into YMC data while referring to the color reproduction processing unit, and is drawn in a page buffer inside the printer. When processing CG data, the data analysis unit branches to the CG development system, converts to YMC data while referring to the color reproduction processing unit, and draws it in the page buffer.

  By the way, the drawing object includes a transparent figure and a gradation figure.

  Hereinafter, transparent figures will be described.

  In general, an overlapping portion of colors of an image to be drawn can be calculated according to an arbitrary color mixture calculation formula. Each graphic data has a composite attribute (α value). Since the composition attribute of each graphic data is set for each pixel forming the image, the composition pixel can be calculated for each pixel at the time of composition. As described above, the composition processing using the value of “composition attribute” is also called α blend.

  By these conversions, the color spaces of the two rectangular objects to be combined can be made uniform. Each object is subjected to synthesis processing in the same color space (that is, rendering color space). On the printer side, the color space value after composition of each object is received. Further, in the printer, conversion from the device RGB color space to the printer color space CMYK is performed, and print output is executed.

  Next, the gradation graphic processing will be described.

  A gradation object is a figure whose color changes, and is defined by several points, for example, a rectangular area, and the end point color is defined by a plurality of points. The intermediate color value is a figure represented by a change from the end point to the end point.

  When color matching is applied to the gradation figure, unnecessary streaks may occur on the gradation image due to the quantization error generated by the computer, resulting in a problem that the image quality deteriorates. appear. In particular, when the color is in the vicinity of the highlight and the change in the drawing color is small with respect to the movement distance (gradient is small), the quantization error increases and the streak tends to be noticeable.

  In order to solve this problem, for example, color matching means for applying color matching processing to an input graphic object to its own device color space, and a geometric object having a color change (so-called gradation object). ), Color change control means for interpolating a color change value in the geometric object on the device color space based on the color matching result at the control point of the geometric object is solved. It can be considered.

  That is, the case where the color matching is first performed only for the end points of the gradation object, and the intermediate pixel drawing is generated in the CMYK rendering process. If an image is formed on the premise of gradation in the CMYK color space, it is possible to form an image while satisfying the monotonous increase condition.

For example, Patent Literature 1 can be cited as a conventional example.
JP 10-1555094 A

  As described above, it is desirable to process the alpha blend object in the RGB color space (rendering color space) and the gradation in the device CMYK color space (device color space). There was a problem that it was difficult to apply a color space. In addition, as described above, if only one method is adopted, not all print requests can be satisfied. For example, load distribution of job processing is performed on the host PC side and the printer controller side. However, there is a problem that the internal structure becomes very complicated and difficult to realize.

  In the present invention, three types of gradation modes are prepared, and the CMS processing is appropriately switched between the host side and the printer controller side.

  Thereby, the RGB color space (rendering color space) can be applied to the α blend object, and the device CMYK color space (device color space) can be applied to the gradation.

  Even when the job processing load is distributed on the host PC side and the printer controller side, the performance of the entire printing system can be improved by selecting the optimum method from the three types of combinations. It becomes like this.

(Example 1)
A preferred embodiment 1 of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic diagram illustrating a printing system that performs processing necessary for printing in a host PC or a printer controller in a distributed manner. In this system, when the color matching processing capability is set to A on the host side and B on the printer controller side, they are compared with each other, and processing is performed with the higher processing capability.

  Normally, in designing a printer controller, a dedicated ASIC for processing a color LUT is prepared for color matching processing, and is configured to perform high-speed arithmetic processing by hardware. The hardware to be implemented is designed, developed and put on the market by collecting the best performance (or the one with high cost performance considering cost balance) at the time of design.

  On the other hand, there is a current situation that the processing capability on the host side has been dramatically improved due to the improvement of the user's PC environment, particularly the operating frequency of the CPU. In such a situation, the printing system shown in FIG. 1 is configured to compare the processing capabilities of the host side and the printer controller side and always perform processing with the higher processing capability. . That is, when A <B in the figure, data is set in the hardware circuit 112 via the CMS-IF 111 and color matching processing is performed inside the printer controller.

  On the contrary, when A> B, the color matching process is performed in the software process F121 on the host PC side.

  Now consider the case of printing a job containing three different types of data: flat fill, gradation, and transparent objects.

  FIG. 2 shows a case where A <B, and as described above, hardware processing is performed via the CMS-IF 111 inside the printer controller. Data input to the host PC is converted into PDL or the like, for example, inside the driver as print processing. At this time, color matching processing is not performed, and the color space and color value (RGB, etc.) of each object are expressed as they are in the description (command or operand parameter, etc.) in the PDL language. The PDL data generated by the driver flows as a print job to the printer controller via the network. Inside the controller, the grid data value corresponding to the input value is read out in a timely manner from a color LUT (not shown), and the value is appropriately set in a register in the hardware circuit. The operation in the hardware circuit is executed by pipeline processing, and is configured to calculate the output value for the input value at high speed.

  In this configuration, all objects (flat fill, gradation, transparent object) are configured to be subjected to color matching processing by a hardware circuit inside the printer controller.

  FIG. 3 shows a case opposite to the example of FIG. 2 (A> B). As described above, color matching processing is performed by software via the CMS-IF 111 inside the host PC. is there. Data input to the host PC is converted into PDL or the like, for example, inside the driver as print processing. At this time, color matching processing is performed. The color space and color value (RGB and the like) of each object are expressed by descriptions (commands or operand parameters, etc.) in the PDL language after being subjected to color conversion processing.

  The PDL data generated by the driver flows as a print job to the printer controller via the network. Since all the objects (flat fill, gradation, transparent object) have already undergone color conversion within the controller, there is no need to perform color conversion processing within the controller.

  By the way, let us consider the process of forming a gradation image as shown in FIG. A gradation is a figure whose color is continuously converted. Several points, for example, areas such as rectangles are defined, and the color of the end point is specified by a plurality of points. The intermediate color value is a figure (which can be obtained using mathematical formulas) expressed by a change from the end point to the end point.

  When color matching is applied to the gradation figure, the following problem may occur due to a quantization error generated in a computer. For example, consider a gradation object that changes from red to black from the start point to the end point. This color conversion needs to be performed according to the position Vi on the drawing line, as shown in FIG. At this time, if the change in the drawing position (V1-V2) is loose with respect to the movement distance (X2-X1), that is, if the value of (V1-V2) is relatively low, it is caused by the quantization error of the computer. As a result, the color conversion result may not be a desired value.

  Referring to the left diagram in FIG. 5, this corresponds to a case where each RGB pixel is converted into a CMYK value by color matching processing after the gradation object is developed in the RGB color space. The value of each CMYK pixel is affected by the quantization error caused by the color matching process.

  For example, even when the change on the CMYK color space side needs to be monotonically increased, there may be a case where the monotonous increase is not affected by the quantization error.

  In order to solve this problem, for example, color matching means for applying color matching processing to an input graphic object to its own device color space, and a geometric object having a color change (so-called gradation object). ), Color change control means for interpolating a color change value in the geometric object on the device color space based on the color matching result at the control point of the geometric object is solved. It can be considered.

  Referring to the right diagram in FIG. 5, only the end point of the gradation object is color-matched first, and an intermediate pixel drawing is generated in the CMYK rendering process. If an image is formed on the premise of gradation in the CMYK color space, it is possible to form an image while satisfying the monotonous increase condition.

  An RGB value is specified for the gradation color, but it is necessary to recognize in which RGB color space this is defined. As the notation of PDL, the default RGB color space for the entire job or the specified page is appropriately defined (or specified). Therefore, the RGB value designated by each object is interpreted as the RGB value in the default RGB color space being set. Also, a color space can be specified for each object as PDL notation. In that case, the designated color space is configured to have priority over the default color space.

  Since the gradation color conversion is a value in the designated RGB color space, the color change to be reproduced is in a state where a definition exists. The color space of the printer is usually CMYK, which is also called a device color space, but there is no correlation between a change in color in the RGB color space and a change in color in the device color space. For example, consider a case where there is a gradation figure and the end point color is black: RGB value = (0x00,0x00,0x00) and white: RGB value = (0xff, 0xff, 0xff). Speaking of uniform color space for black, LAB value = (0.0, 0.0, 0.0) and white for LAB value = (100, 0.0, 0.0). In drawing this figure, let us consider when the designated RGB color space is HDTV gamma 1.5 and HDTV gamma 2.2.

  The color in the middle of gradation at the position of about 75%: RGB value = (0xC0,0xC0,0xC0) is LAB value = (65.3, 0.0, 0.0) and HDTV gamma 2.2 when HDTV gamma 1.5 In this case, LAB value = (53.6, 0.0, 0.0).

  The color in the middle of the gradation at the position of about 50%: RGB value = (0x80,0x80,0x80), when HDTV gamma 1.5, LAB value = (35.4, 0.0, 0.0) and HDTV gamma 2.2 In this case, LAB value = (21.8, 0.0, 0.0).

  Thus, if the input color space is different, the value in the uniform color space for the RGB values changes. As described above, when the color matching process is not performed, there is no correlation between the input color space and the device color space. Therefore, if the gradation (color) change is performed in the device (CMYK) color space, it is not originally reproduced. The color between the color that should not be (RGB value or LAB value converted from RGB value) and the color that is actually reproduced (CMYK value or LAB value reproduced with the CMYK value of the device) is It can be very different. In particular, in the case of gradation, the color difference at a location far from the end point, that is, in the middle portion becomes large. The left diagram in FIG. 6 shows a state where the color difference in the intermediate portion is large. In order to reduce this color difference, this system is configured to divide the gradation. In the right figure of FIG. 6, it is divided into four areas. By changing the value of the device color space linearly in such a divided area, it is accurate for the color (RGB value or LAB value converted from the RGB value) that should be reproduced originally. It is possible to reproduce with colors (CMYK values).

  FIG. 7 shows an example of a printing system according to the present invention configured to process gradation and transparent objects on the host side. As described above, the present invention relates to a printing system that performs processing necessary for printing in a host PC or a printer controller in a distributed manner. It is configured to process. Assuming that the color matching processing capability is A on the host side and B on the printer controller side, here, the following discussion will be made on the assumption that A> B, that is, the color matching processing capability on the host side is high.

  Here, the designation of gradation mode: 0 is transmitted from the host PC side to the printer side.

Job data is
A command (C1) representing a flat fill and its color value (rgb1),
A command (C2) representing gradation and its color value (rgb2),
A command (C3) representing a transparent object and its color value (rgb3),
Is included.

In this system,
Flat fill is configured on the printer side Transparent objects are configured to be rendered on the host PC side. However, “gradation” can be switched between processing on the host side or processing on the printer side according to the UI designation from the user or the designation from a performance profiler (not shown). . In the configuration example of FIG. 7, rendering is performed on the host side.

  Regarding color matching, as described above, since A> B, that is, the color matching processing capability on the host side is high, color matching of all objects (flat fill, gradation, transparent objects) is performed on the host PC side.

  For gradation processing, color matching processing is required for each of the end points and the intermediate portion. However, the color matching processing for the intermediate portion is performed at the same place as the portion where the gradation rendering processing is executed, that is, on the host PC side. Is called. In this configuration, since there is no need to perform CMS processing on the printer side, the CMS color module is not used, so OFF is designated.

  FIG. 8 is based on the premise that A> B, that is, the color matching processing capability on the host side is high, as shown in FIG. However, the gradation object rendering process is configured to perform processing on the printer side (by UI designation from the user or designation from a performance profiler not shown). In this case, only the color matching processing of the end points of the gradation object is performed on the host PC side, and the converted CMYK value and the command (C2) representing the gradation are transferred to the printer side. At the same time, the designation of gradation mode: 1 is transmitted from the host PC side to the printer side.

  In this configuration, it is necessary for the printer side to perform intermediate CMS processing for gradation rendering processing. For this reason, ON is designated for the CMS color module on the printer side.

  FIG. 9 has the same configuration as that of FIG. 8, but the designation of gradation mode: 2 is transmitted from the host PC side to the printer side. In this case, if the color matching processing capability on the host side and the printer side are almost the same, the gradation color matching processing (end point, intermediate part) is all done on the printer side for the purpose of distributing the load on the color matching process. It is configured to do with. As in FIG. 8, in this configuration, it is necessary on the printer side to perform intermediate CMS processing for gradation rendering processing. For this reason, ON is designated for the CMS color module on the printer side.

(Second embodiment)
Next, a second embodiment suitable for the present invention will be described.

  In the first embodiment, the color matching process is performed only for the end points, and the intermediate portion is obtained by calculation (for example, linear calculation) on the device color space side. Due to this, there is a problem that a color gap and a color difference occur between the input color space and the device color space. In order to solve this problem, the gradation area is divided.

  In the second embodiment, a method of suppressing a color gap (color difference) between the input color space and the device color space without dividing the region by the method shown in FIG. 10 will be described.

  FIG. 10 shows a state in which 1D-LUT data for performing gradation correction in the device color space (CMYK) is searched from information in the input color space (for example, HDTV gamma 1.5).

  In the case of a change of gamma 1.5, a device color space, for example, a plurality of prepared CMYK color gradation correction tables can be searched.

  This system assumes a plurality of typical RGB color spaces (for example, 3 types with different color temperatures and 3 types with different gammas, a total of 9 types) and input color spaces on the printer side. Are prepared for each CMYK gradation table that reproduces the most suitable and beautiful gradation.

  At the stage when the information of the RGB color space used in gradation is acquired, first, the chromaticity point of the RGB color space is obtained and compared with the chromaticity points (three types) of the monitor prepared on the printer side. To do. Here, it is configured to search for a monitor whose gamma value is close to that of the chromaticity point.

  FIG. 11 shows an example of the printing system of the present invention configured to process a gradation object on the printer side. As described above, the present invention relates to a printing system that performs processing necessary for printing in a host PC or a printer controller in a distributed manner. It is configured to process. Assuming that the color matching processing capability is A on the host side and B on the printer controller side, here, the following discussion will be made on the assumption that A> B, that is, the color matching processing capability on the host side is high.

  Here, the designation of gradation mode: 0 is transmitted from the host PC side to the printer side.

Job data is
A command (C1) representing a flat fill and its color value (rgb1),
A command (C2) representing gradation and its color value (rgb2),
A command (C3) representing a transparent object and its color value (rgb3),
Is included.

In this system,
Flat fill is configured on the printer side Transparent objects are configured to be rendered on the host PC side.

  The “gradation” is configured to perform rendering processing on the printer side.

  Regarding color matching, as described above, since A> B, that is, the color matching processing capability on the host side is high, color matching of all objects (flat fill, gradation, transparent objects) is performed on the host PC side.

  For gradation processing, color matching processing is required for each of the end points and the intermediate portion, but the end points are processed on the host PC side in the same manner as other objects. The color matching process in the middle part of the gradation is performed at the same place as that where the gradation rendering process is executed, that is, at the printer side.

  As described above with reference to FIG. 10, this system is configured to receive a gradation color space on the printer side and search a conversion table (adjustment 1D-LUT) based on the received color space. Rendering is performed using the retrieved conversion table (adjustment 1D-LUT) while performing gradation correction of device colors (each CMYK). In this configuration, the CMS color module is not used because it is not necessary to perform CMS processing on the printer side. Therefore, OFF is designated for the CMS processing unit on the printer side.

  As described above, in the printing system of this embodiment, the processing capacity of the host PC and the printer is compared, and a load distribution configuration is adopted so that high-speed processing can be performed throughout.

  In this configuration, the rendering portion of the gradation object is on the host PC side or the printer side. In either case, the portion that performs color matching processing in the middle portion of the color gradation object is always rendered. It is configured to be performed at the place where For this reason, a beautiful gradation object that eliminates the influence of the quantization error of the color matching process in gradation can be output at high speed.

FIG. 2 is a block diagram illustrating a load distribution type printing system configured to distribute and execute processing necessary for printing by either a host PC or a printer controller. 1 is a block diagram of a printing system, and shows a printing system that performs a color matching process using a hardware circuit inside a printer controller. FIG. FIG. 2 is a block diagram of a printing system, showing a printing system that performs color matching processing by software processing on the host PC side. It is the outline figure explaining gradation It is the schematic explaining the quantization error in gradation processing. It is the schematic explaining the division | segmentation process of gradation. FIG. 3 is a schematic diagram illustrating a processing overview (mode 0) according to the first embodiment. It is the schematic explaining the process outline | summary (mode 1) of the present Example 1. FIG. FIG. 3 is a schematic diagram illustrating a processing overview (mode 2) according to the first embodiment. FIG. 10 is a schematic diagram illustrating gradation conversion processing according to the second embodiment. It is the schematic explaining the process outline | summary (mode 1a) of the present Example 2. FIG.

Claims (4)

  A multi-color printing device that expands objects or draws natural images, and has a mechanism for switching the color space to be applied to each object. A multicolor printing apparatus configured to apply a space and configured to perform rendering of an intermediate portion of the gradation and color matching processing in the intermediate portion by either a host PC or a printer controller.   The multicolor printing apparatus according to claim 1, wherein the multipoint printing apparatus is configured to perform processing by either a host PC or a printer controller when executing color matching processing of end points in gradation.   A gradation color space is received by the printer, and a conversion table (adjustment 1D-LUT) is searched based on the received color space. Using the searched conversion table, gradation correction of device colors (each CMYK) is performed. The multicolor printing apparatus according to claim 1, wherein the multicolor printing apparatus is configured to perform rendering while performing.   There are a plurality of RGB color space setting files inside, and CMYK gradation tables optimized for these input color spaces, and the color space used for gradation is the RGB color space. The CMYK floor corresponding to the selected RGBZ color space has selection means for selecting a color space used in gradation from the RGB color space and a closer color space from the RGB color space. A multi-color printing apparatus that selects a tone table and forms a gradation image using the selected CMYK gradation table.

Images