JP2006203921A - Color printing system and color printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform color printing without effort even if the throughput of a host computer is low. <P>SOLUTION: A host computer 1 transmits to a printer 11 color image data of a resolution lower than a maximum printing resolution. Color image data color-matched by an adjustment unit 13 are converted from an RGB color system to a YUV color system by a first color conversion unit 14. An image processing unit 15 performs interpolation processing or the like based on YUV data. The color system of the processed color image data are returned to the RGB color system by a second color conversion unit 16. Since various kinds of processing such as color matching, color system conversion, interpolation processing are performed in the printer, even if the throughput of the host computer is low like a digital camera, etc., color printing can be performed without effort. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to various color printers and color printing systems such as a color laser printer and a color inkjet printer.

  For example, in color image processing in personal computers, workstations, personal digital assistants, etc., in order to display a color image on a monitor display or the like, R (red), G (green), and B (blue), which are the three primary colors of light, are displayed. An RGB color system raster image having three components as components is generated. In recent years, so-called “full color” images are often used. In the case of a full color image, 8 bits are assigned to each of RGB of each pixel constituting the image. A full-color image can be formed by superimposing three planes: an R plane having only R gradation, a G plane having only G gradation, and a B plane having only B gradation. RGB data is displayed on a monitor display via a video adapter or the like. On the other hand, when printing a color image, the RGB data is converted into CMY color system data composed of the three primary colors C (cyan), M (magenta), Y (yellow), and K (black). Theoretically, K is not essential, but in order to express beautiful black, the above four colors are adopted as process colors. In this specification, the CMY color system including both CMY and CMYK is referred to unless otherwise specified. The color system conversion (also referred to as color space conversion) from the RGB color system to the CMY color system is due to the difference in color development structure between the monitor display and the printer.

  As a problem in color image processing, it is widely known that a color displayed on a monitor display is different from a color output from a printer. This is because the RGB color system adopted by the monitor display and the CMY color system adopted by the printer are for directly controlling the respective coloring mechanisms and are not intended to define colors objectively. In other words, the RGB color system defines how bright each R, G, B phosphor emits light, and the CMY color system also uses C, M, Y (and K). It only defines the amount of each ink. Therefore, even if the values of R, G, and B are the same, if the monitor display is different, the characteristics of the phosphors are also slightly different, so the actual display colors are different. Similarly, even if the same CMY data is sent to two types of printers having slightly different ink colors, the printing results are different. Therefore, standard color systems such as the Lab color system defined by the CIE (International Lighting Commission) are introduced, and color matching such as conversion to neutral color data independent of the color development structure is performed.

  In color matching, the input color system is converted to the standard color system, and the standard color system can be converted to the color system of the output device, or colors that can be reproduced in a range that cannot be reproduced. Each process such as allocating to (gamut mapping) is performed. Further, when the color image displayed on the monitor display is enlarged and printed out, it is necessary to perform an interpolation process for increasing the resolution of the color image data in consideration of the print resolution, the enlargement ratio, and the like. At the time of interpolation processing, not only the position of the newly inserted pixel but also the gradation value (color) of the pixel must be determined together.

  The color image data that has been color-adjusted and interpolated in this way is transmitted to the printer via the transmission path. The printer generates image data for printing based on the received color image data, and performs printing.

  As described above, when performing color printing, it is necessary to perform various processes such as color matching and interpolation. Therefore, CPU (Central Processing Unit), memory, graphics processing LSI, OS (Operating System) and other computer resource Many are used for color image processing, increasing the load on the host computer side. In addition, although it differs depending on the bit depth and resolution of the pixel, the size of the image, the file format, etc., in general, color image data has a large amount of data. The transmission time also becomes longer. Therefore, it takes time until the host computer is released, and the usability is low.

  The lower the processing capacity of the OS, CPU, etc., and the smaller the amount of installed memory, the heavier the burden on the host computer, the longer it takes to process color images, and the ease of use is greatly reduced. In particular, in recent years, for example, it has been proposed to send color image data directly to a printer from a host computer having a relatively low processing capability such as a digital camera or a portable information terminal. However, when color image processing is performed by such a host computer with low processing capability, data processing takes a long time and usability is reduced.

  The present invention has been made in view of the various problems as described above, and an object thereof is to provide a color printing system and a color printer capable of performing color printing while reducing the processing burden on the host computer side. It is in.

  To achieve the above object, the present invention provides a color printing system comprising a host computer and a color printer capable of color printing based on color image data from the host computer, wherein the printer transmits from the host computer. Receiving means for receiving the color image data, color adjusting means for adjusting the color image data in accordance with a color characteristic of a printer, and generating binary color image data based on the color image data adjusted in color And binarizing means for printing, and printing means for performing printing based on the binary color image data.

  “Color adjustment” is represented by, for example, so-called color matching processing, but is not limited thereto. “Binary color image data” means data generated by a binarization algorithm such as dithering or error diffusion. In the present invention, since the color adjustment is performed by the color adjustment means on the printer side, the processing load on the host computer can be reduced.

  More preferably, the host computer sets the resolution of the color image data lower than the maximum resolution of the printing unit.

  By transmitting color image data having a resolution lower than the print output resolution from the host computer to the printer, the amount of transmission data is reduced, and the transmission time is shortened. As a result, the host computer can be released early and the usability is improved.

  According to a third aspect of the present invention, the printer further includes an interpolation unit that performs an interpolation process so that the resolution of the color image data color-adjusted by the color adjustment unit is equal to the maximum resolution of the printing unit. The binarization unit can generate the binary color image data based on the color image data processed by the interpolation unit.

  By providing an interpolation means in the printer, high-quality enlarged printing can be performed even when the resolution of the color image data transmitted from the host computer is lowered.

  According to a fourth aspect of the invention, the printer converts the color image data color-adjusted by the color adjusting means into color image data of a predetermined color system composed of a luminance component and two types of color components. First color conversion means that inputs to the interpolation means, and reversely converts the color system of the color image data processed by the interpolation means to the color system before being converted by the first color conversion means. A second color conversion unit, and the binarization unit may generate the binary color image data based on the color image data converted by the second color conversion unit.

  “Luminance” in this specification means a degree related to the brightness of an image. Examples of the “color system comprising a luminance component and two color components” include a YUV color system, a YIQ color system, and a YCbCr color system.

  In general, human vision is sensitive to changes in brightness, but insensitive to changes in color. Therefore, the image quality of the color image data depends on the information processing related to the brightness of the image. In particular, the quality of character images tends to be determined by the luminance component. Therefore, the first color conversion means converts the color system of the color image data into a predetermined color system composed of a luminance component and two types of color components. Thereby, the interpolation means can easily perform processing such as performing interpolation processing with emphasis on the luminance component and interpolating the color component with reduced accuracy. The interpolated color image data is returned to the original color system data by the second color conversion means.

  The first color conversion unit and the second color conversion unit may be realized by a dedicated hardware circuit.

  In general, when performing color system conversion, an operation such as adding (or subtracting) each color system component of each pixel by multiplying each color system component by a predetermined weight coefficient is performed. Of course, such calculation can also be performed on software using the main processor of the printer. However, conversion for all pixels is expensive, and other important processing such as command interpretation is left to the main processor. Therefore, each color conversion means is configured by a dedicated hardware circuit, thereby speeding up the conversion process and reducing the burden on the main processor. As the “dedicated hardware circuit”, for example, an ASIC (Application Specific Integrated Circuit) such as a custom LSI, a gate array, a standard cell, or a PLD (Programmable Logic Device) can be typically cited.

  Further, the present invention can be grasped as a color printer and can be grasped as a printing method.

  Furthermore, the present invention can be realized as a computer program such as a print control program. For example, the computer program can be fixed to a tangible recording medium such as a hard disk, a floppy (registered trademark) disk, or a memory, and can be provided to a printer computer from the recording medium. The present invention is not limited to this, and for example, an intangible medium such as a communication line can be used, such as downloading a predetermined program from a server on the network.

  As described above, according to the color printing system and the color printer according to the present invention, the load on the host computer can be reduced, and even a host computer with low processing capability can perform color printing without difficulty. .

  Further, since the resolution of the color image data transmitted from the host computer is set lower than the maximum print resolution, the amount of transmission data can be reduced, the transmission time can be shortened, and the host computer can be released early.

  Furthermore, since the color image data color system is converted into a predetermined color system consisting of a luminance component and two types of color components for interpolation processing, the processing should be optimized according to the nature of the color image data. Is also possible.

  Hereinafter, a case where the embodiment of the present invention is applied to a color printing system will be described as an example with reference to FIGS.

  FIG. 1 is a block diagram schematically showing the overall configuration of a color printing system. For example, a host computer 1 that can be realized as a personal computer, a workstation, a portable information terminal, a digital camera or the like includes an application program 2, a print data generation unit 3, an interface (hereinafter abbreviated as "I / F") unit 4, and It has. For example, based on data passed from the application program 2 such as image processing software, the print data generation unit 3 generates print data in a form that can be interpreted by the printer 11 described later. For example, the graphic device interface (GDI) cooperates with a bitmap generation engine (DIB engine) or the like to generate RGB color system color image data. Since this RGB color system data is data before being adjusted for a printer, “RGBd” is displayed in the figure. Further, the host computer 1 generates data having a resolution lower than the maximum printing resolution such as 300 dpi, and transmits the data to the printer 11 via the I / F unit 4. Here, the resolution of the color image data transmitted by the host computer 1 can be set to, for example, half or less of the maximum print resolution. When the host computer 1 is a digital camera, RGB color system color image data is generated based on an output signal from the CCD element and transmitted to the printer 11.

  The printer 11 capable of color printing receives print data (RGBd (300 dpi)) from the host computer 1 via the I / F unit 12. The adjustment unit 13 as “color adjustment means” performs color matching of print data based on the color characteristics of the printer 11. The data after color matching is indicated as “RGBp”. The adjustment unit 13 does not change the resolution. That is, the adjustment unit 13 performs color adjustment with the low resolution.

  The first color conversion unit 14 as “first color conversion means” converts the color image data “RGBp (300 dpi)” after color matching into color image data “YUV (300 dpi)” of the YUV color system. To do. Here, the Y component indicates a luminance component, and the U component and the V component indicate color difference components, respectively. The color conversion from the RGB color system to the YUV color system can be performed, for example, based on the following conversion formula, or by referring to a color conversion table prepared in advance. The color conversion unit 14 converts the RGB color system data into YUV color system data without changing the resolution, that is, with a low resolution.

Y = 0.2990 * R + 0.5870 * G + 0.1140 * B (Formula 1)
U = −0.1684 * R−0.3316 * G + 0.5000 * B (Formula 2)
V = 0.5000 * R-0.4187 * G-0.0813 * B (Formula 3)
The image processing unit 15 as “interpolation means” increases the resolution of the input color image data to the resolution of the printing unit 19 (maximum resolution, 600 dpi in the drawing). The image processing unit 15 performs interpolation processing by appropriately selecting, for example, three types of image processing algorithms, that is, curved surface interpolation processing, linear interpolation processing, and nearest neighbor processing. For example, the image processing unit 15 performs curved surface interpolation processing for the Y plane composed of the Y component, performs linear interpolation processing for the U plane composed of the U component, and performs nearest neighbor processing for the V plane composed of the V component. It can also be done. That is, in consideration of human visual characteristics, relatively high-precision interpolation processing is performed for the plane of the luminance component Y, and relatively low-precision interpolation processing is performed for the U and V planes of the color difference components (color components). Thereby, the entire processing time can be shortened while maintaining the image quality. The present invention is not limited to this, and the same algorithm may be applied to each plane.

  The color image data “YUV (600 dpi)” processed by the image processing unit 15 is returned to RGB color system data “RGB (600 dpi)” by the conversion unit 16 as “second color conversion means”. For example, color conversion from the YUV color system to the RGB color system can be performed by the following conversion formula.

R = Y + 1.420 * V (Formula 4)
G = Y−0.3441 * U−0.7139 * V (Formula 5)
B = Y + 1.71818 * U−0.0012 * V (Formula 6)
The CMY conversion unit 17 converts the high-resolution RGB color system data “RGB (600 dpi)” into CMY color system data “CMYK (600 dpi)”. Here, the CMY color system includes any of three CMY colors or four CMYK colors. Next, the CMY color system data is binarized by the binarization circuit unit 18 as “binarization means”. That is, the binarization circuit unit 18 converts the image data into binary color image data by a binarization algorithm such as dither processing or an error diffusion method. The converted binary color image data is sent to the printing unit 19 as “printing means” and printed.

  Each of the color conversion units 14 and 16 is preferably realized by a dedicated hardware circuit such as an ASIC.

  FIG. 2 is a block diagram illustrating a main part of the hardware configuration of the first color conversion unit 14. A total of three stages of conversion circuits including three multiplier circuits 21 and an adder circuit 22 for adding inputs from the multiplier circuits 21 are provided. Predetermined coefficients shown in Equations 1 to 3 are set in each stage of the multiplier circuit. Therefore, the values of Y, U, and V can be extracted from each adder circuit 22 by inputting the values of R, G, and B to each multiplier circuit 21. As shown in FIG. 3, the second color conversion unit 16 can be similarly configured by including three stages of conversion circuits including three multiplication circuits 23 and one addition circuit 24. Predetermined coefficients shown in the equations 4 to 6 are set in each multiplier circuit 23.

  According to the present embodiment configured as described above, the following effects can be obtained.

  First, since color adjustment is performed in the printer 11, the load on the host computer 1 can be reduced. Therefore, even when the processing capacity of the host computer is low, such as a digital camera, color printing can be performed without difficulty.

  Secondly, since the resolution of the color image data transmitted from the host computer 1 is set lower than the maximum print resolution, the amount of transmission data can be reduced, the data transmission time can be shortened, and the host computer 1 can be made early. Can be released to.

  Third, since the printer 11 includes an image processing unit 15 that performs interpolation, color image data transmitted from the host computer 1 at a low resolution can be interpolated to the maximum print resolution, and high-quality printing can be performed. It can be performed.

  Fourth, the color system of the color image data is converted from the RGB color system to a predetermined color system consisting of a luminance component such as a YUV color system and two kinds of color components, and the predetermined color system data is converted into the predetermined color system data. Since interpolation processing is performed based on this, high-speed processing can be performed without causing deterioration in image quality. For example, the overall processing time can be shortened without degrading the image quality by focusing on luminance components that have a large visual impact. For example, when the color image data is centered on characters, interpolation processing can be performed only for the Y plane. This is because the gradation data of the character image is normally concentrated on the Y plane.

  Fifth, by configuring each color conversion unit 14, 16 with an ASIC or the like, the conversion speed can be increased, and the load on the main processor and OS of the printer 11 can be reduced.

  A person skilled in the art can make various additions, modifications, combinations, and the like within the scope of the present invention described in the above embodiments.

  For example, the color system composed of the luminance component and the two types of color components is not limited to the YUV color system, and may be a YIQ color system or a YCbCr color system. For example, the YIQ color system can be calculated by each conversion formula.

Y = 0.299 * R + 0.587 * G + 0.114 * B (Expression 7)
I = 0.596 * R−0.274 * G + 0.322 * B (Formula 8)
Q = 0.212 * R−0.523 * G−0.311 * B (Formula 9)
Further, the YCrCb color system can be obtained by the following conversion formula if it conforms to the ITU recommendation.

Y = 0.2125 * R + 0.7154 * G + 0.0721 * B (Equation 10)
Cb = (BY) / (2-2 * 0.0721) (Formula 11)
Cr = (R−Y) / (2-2 * 0.2125) (Formula 12)

1 is a block diagram of a color printing system according to a first embodiment of the present invention. It is a block diagram of a 1st color conversion part. It is a block diagram of the 2nd color conversion part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Host computer 3 Print data generation part 11 Printer 13 Adjustment part 14 1st color conversion part 15 Image processing part 16 2nd color conversion part 17 CMY conversion part 18 Binarization circuit part 19 Printing part 21 Multiplication circuit 22 Addition circuit 23 Multiplier circuit 24 Adder circuit

Claims (12)

In a color printing system comprising a host computer and a color printer capable of color printing based on color image data from the host computer,
The printer is
Receiving means for receiving the color image data transmitted from the host computer;
Color adjusting means for adjusting the color image data according to the color characteristics of the printer;
Binarization means for generating binary color image data based on the color-adjusted color image data;
A color printing system comprising: a printing unit that performs printing based on the binary color image data. The color printing system according to claim 1, wherein the host computer sets the resolution of the color image data to be lower than the maximum resolution of the printing unit and transmits the data to the printer. The printer further includes interpolation means for performing an interpolation process so that the resolution of the color image data color-adjusted by the color adjustment means is equal to the maximum resolution of the printing means,
The color printing system according to claim 2, wherein the binarization unit generates the binary color image data based on the color image data processed by the interpolation unit. The printer includes
First color conversion means for converting the color image data color-adjusted by the color adjustment means into color image data of a predetermined color system composed of a luminance component and two types of color components and inputting the color image data to the interpolation means;
A second color conversion unit that reversely converts the color system of the color image data processed by the interpolation unit to a color system before being converted by the first color conversion unit;
4. The color printing system according to claim 3, wherein the binarizing unit generates the binary color image data based on the color image data converted by the second color converting unit. The color printing system according to claim 4, wherein the first color conversion unit and the second color conversion unit are realized by a dedicated hardware circuit. 6. The color printing system according to claim 4, wherein the predetermined color system is one of a YUV color system, a YIQ color system, and a YCbCr color system. In a color printer that performs color printing based on color image data from a host computer,
Receiving means for receiving color image data transmitted from the host computer at a resolution lower than the maximum print resolution;
Color adjusting means for adjusting the color image data according to the color characteristics of the printer;
Interpolation means for performing interpolation processing so that the resolution of the color image data color-adjusted by the color adjustment means is equal to the maximum print resolution;
A binarizing unit that generates binary color image data based on the color image data processed by the interpolation unit; and a printing unit that performs printing based on the binary color image data. Color printer. First color conversion means for converting the color image data color-adjusted by the color adjustment means into color image data of a predetermined color system composed of a luminance component and two types of color components and inputting the color image data to the interpolation means;
A second color conversion unit that reversely converts the color system of the color image data processed by the interpolation unit to a color system before being converted by the first color conversion unit;
The color printer according to claim 7, wherein the binarizing unit generates the binary color image data based on the color image data converted by the second color converting unit. The color printer according to claim 8, wherein the first color conversion unit and the second color conversion unit are realized by a dedicated hardware circuit. 10. The color printer according to claim 8, wherein the predetermined color system is any one of a YUV color system, a YIQ color system, and a YCbCr color system. In a printing method for causing a printer to perform color printing,
Input color image data with a resolution lower than the maximum print resolution to the printer,
Adjust the color of the input color image data according to the color characteristics of the printer,
Converting the color system of the color image data after the color adjustment into a predetermined color system comprising a luminance component and two types of color components;
Performing an interpolation process so that the resolution of the color image data converted into the predetermined color system is equal to the maximum print resolution,
Binarizing the interpolated color image data to generate binary color image data;
A printing method comprising printing based on the binary color image data. In a recording medium recording a program for controlling a color printer,
A function of receiving color image data input from a host computer with a resolution lower than the maximum print resolution;
A function of adjusting the color of the color image data in accordance with the color characteristics of the printer;
A function of performing an interpolation process so that the resolution of the color-adjusted color image data is equal to the maximum print resolution;
A function of generating binary color image data based on the interpolated color image data;
A function of printing based on the binary color image data;
A recording medium on which a program to be realized on a computer is recorded in a form that can be read and understood by the computer.

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