JPH1146306A - Image-processing device and method and recording medium for recording image-processing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the processing load when the threshold is read out of a dither matrix and turned into N values by comparing the threshold that is substantially multiplied by M times in the processing direction with the inputted original color image data and turning the threshold into N values. SOLUTION: A pre-scale number modulation part 140 performs the pre-scale number conversion by a dither method, to turn the inputted original color image data ORG into the color data on one of eight lattice points. Based on the obtained lattice point data, a color correction part 142 refers to a color correction table contained in a color correction table memory 134 for obtaining the color correction data Cc, Mc and Yc. When the pre-scale number conversion and color correction processes are finished, a post-scale number conversion part 146 binarizes the color corrected image data to convert them up into the final scale number, corresponding to a scale number that can be expressed by an image output device and then outputs the binarized image data as the final color image data FNL.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, an image processing method, and a recording medium on which a program for realizing the image processing is recorded, and more particularly to a processing for reducing the number of gradations of input color image data. The present invention relates to an image processing apparatus, an image processing method, and a recording medium storing a program for realizing these functions by a computer.

[0002]

2. Description of the Related Art Conventionally, there have been known scanners for reading color originals and the like and digital cameras capable of transferring image data. Original color image data is read from these image input devices, and the read image data is read. For example, an image processing apparatus for reproducing and displaying a display such as a CRT or a color printer is known.

[0003] Among the devices that output such images, in a color printer or the like, the number of gradations that can be directly expressed is often smaller than the number of gradations of the original image. For example, in an ink jet type color printer, it is only possible to control whether or not to form dots of a predetermined color. That is, in this case, the number of gradations is two. In recent years, an ink jet printer capable of directly expressing several gradations by preparing ink having a low ink density has been proposed, but in any case, the number of gradations is far from the number of gradations of the original image data. In such an image output device, it is necessary to perform a process of reducing the number of tones included in the original image and converting it into N values that can be expressed. For example,
In the color printer described above, the dot density per unit area is changed by controlling the on / off of the dots,
Expresses the gradation of the original image.

Further, since image output devices such as a color display and a color printer have unique color reproduction characteristics, a color of a color image input using a scanner or the like is reproduced well regardless of the characteristics of the output device. Therefore, it is necessary to perform color correction processing in accordance with the color reproduction characteristics of the image output device to be used. The present applicant has proposed an image processing method that does not increase the capacity of the color correction table and does not require a long time for the interpolation operation of the color correction as one of the methods of performing the color correction processing. (See, for example, Japanese Patent Application Laid-Open No. 7-30772). This image processing method divides the color space at predetermined intervals, prepares color correction data only for the grid points obtained by the division, and, for image data other than the grid points, That is, color correction is performed without interpolating by assigning to such grid points. In this case, since the original image data is allocated to grid points in the vicinity thereof, an error occurs every time allocation to grid points is performed. Therefore, when sequentially processing the image data of each pixel constituting the image, allocation to grid points is performed so that this error is as small as possible on average. Such allocation of the grid points may be performed by an error diffusion method or the like, but may be performed by adopting a dither method and using a threshold value read out from an appropriately prepared threshold value matrix.

[0005]

According to the above-described image processing method, if attention is paid to each pixel, an error exists in the color, but the error is eliminated within a certain range, and the output is performed. This is an excellent method that greatly reduces the operation time required for image processing without deteriorating the image quality.However, since the threshold is read out with reference to a dither matrix for each pixel, processing may take time. There was a problem. In particular, when a small image of about 320 × 240 captured by an electronic camera is processed by being enlarged to 640 × 480, usually two pixels of the same data are arranged in the horizontal direction. The threshold value must be read out each time by referring to the dither matrix.

SUMMARY OF THE INVENTION It is an object of the present invention to solve such a problem and to reduce the processing load when a threshold value is read from a dither matrix to perform N-value conversion.

[0007]

A first image processing apparatus according to the present invention for achieving the above object is an image processing apparatus for reducing the number of gradations of a multi-gradation color image, Input means for inputting the multi-gradation original color image data for each pixel along the processing direction, threshold storage means for storing a threshold corresponding to a dither matrix of a predetermined size, A threshold expansion unit for substantially multiplying a threshold value by M in the processing direction of the pixel (M is an integer of 2 or more), and a threshold substantially multiplied by M in the processing direction by the threshold expansion unit, The gist of the invention is to provide an N-value conversion means for performing N-value conversion (N is an integer of 2 or more) by comparing with the original color image data.

An image processing method corresponding to this image processing apparatus is an image processing method for reducing the number of gradations of a multi-gradation color image. Each time, a threshold value corresponding to a dither matrix of a predetermined size is stored, and under a predetermined condition, the threshold value is substantially multiplied by M (M) in the processing direction of the pixel.
Is an integer of 2 or more), and compares the threshold value substantially multiplied by M in the processing direction with the input original color image data to perform N-value conversion (N is an integer of 2 or more). The main point is.

A recording medium on which a program for realizing these image processing apparatuses and methods on a computer is recorded stores a program for causing a computer to realize a function of reducing the number of gradations of a multi-gradation color image. A recording medium, a function of inputting the multi-tone original color image data for each pixel along a processing direction, a function of reading a threshold corresponding to a dither matrix of a predetermined size stored in a predetermined area in advance, Under predetermined conditions, the threshold is increased substantially M times (M
Is an integer of 2 or more), substantially M in the processing direction.
Comparing the multiplied threshold value with the input original color image data and recording a program for realizing a function of performing N-value conversion (N is an integer of 2 or more) in a manner readable to the computer. It is a gist.

In the image processing apparatus and method described above, the threshold value stored in the dither matrix is compared with the original color image data to perform N-value conversion. M is substantially multiplied in the pixel processing direction (M is an integer of 2 or more), and comparison is performed using this. Therefore, M continuous in the processing direction
As for the pixels, the comparison is performed using the same threshold value, and there is no need to read a new threshold value from the dither matrix. In such a method, the original color image data sets the original image at least in the horizontal direction.
This is particularly effective when the image is a doubled image.

[0011] The expansion of the threshold value is performed in advance when storing the threshold value.
The same threshold value may be stored continuously in the processing direction M times, or the same position may be used M times consecutively once the threshold value is read out. In the latter case, in particular, when the original color image data is an image obtained by multiplying the original image by M in the horizontal direction (M is an integer of 2 or more), the pixel of interest is M · S + 2 in the horizontal direction. When the pixel is located at a position from M to (S + 1) (S is an integer of 0 or more),
The same threshold as that used for the pixel at the position of S + 1 may be used.

A second image processing apparatus according to the present invention is an image processing apparatus for reducing the number of gradations of a multi-gradation color image,
Input means for inputting the multi-tone original color image data for each pixel along the processing direction, threshold storage means for storing a threshold corresponding to a dither matrix of a predetermined size, and the stored threshold and N-value conversion means for comparing the input original color image data with the input original color image data to perform N-value conversion (N is an integer of 2 or more); If the same as the original color image data of the pixel, the N
The gist of the present invention is to provide an N-value omitting means that does not perform N-value conversion by the value conversion means and uses the result of the N-value conversion as it is.

An image processing method corresponding to this image processing apparatus is an image processing method for reducing the number of gradations of a multi-gradation color image, wherein the multi-gradation original color image data is processed in a processing direction. Along with each pixel, storing a threshold corresponding to a dither matrix of a predetermined size, comparing the stored threshold with the input original color image data,
If N-ary conversion (N is an integer of 2 or more) is performed and the input original color image data is the same as the original color image data of the immediately preceding pixel in the processing direction of the pixel, the previous pixel Without performing the N-value conversion for
The gist is to use the result of the quantification as it is.

A recording medium on which a program for realizing the image processing apparatus and method on a computer is recorded has a function of inputting the multi-tone original color image data for each pixel along a processing direction, a predetermined function. A function of storing a threshold value corresponding to a dither matrix of a size, comparing the stored threshold value with the input original color image data,
A function of performing N-value conversion (N is an integer of 2 or more); if the input original color image data is the same as the original color image data of the immediately preceding pixel in the processing direction of the pixel, The gist is that a program for realizing a function of using the result of the N-value conversion without performing the N-value conversion for a pixel is recorded in the computer in a readable manner.

According to the image processing apparatus and the image processing method, the original color image data of the pixel being processed is not expanded but the original color image data of the immediately preceding pixel in the processing direction is expanded. If the data is the same as the data, the result of the N-value conversion performed on the immediately preceding pixel is used as it is, thereby omitting processes such as reading a threshold from the dither matrix and comparing with the threshold, thereby simplifying image processing. can do.

A third image processing apparatus according to the present invention is an image processing apparatus for reducing the number of gradations of a multicolor image represented by coordinate values in a two-dimensional or more color space, wherein each pixel of the image is Input means for sequentially inputting color image data expressing the coordinate values using a predetermined number of gradations, and dividing the color space by a number of gradations smaller than the number of gradations expressing the coordinate values. Grid point information storage means for storing coordinate values of grid points obtained by performing the division for each of the dimensions for the color space; and threshold storage means for storing threshold values corresponding to a dither matrix having a predetermined size. Threshold expansion means for substantially multiplying the threshold of the threshold matrix by a factor M (M is an integer of 2 or more) in a processing direction of the pixel under a predetermined condition; The color The coordinate values within the interval are corrected using the substantially extended threshold value, and among the coordinate values of the grid points stored in the grid point information storage unit, the coordinates that are close to the corrected coordinate values. The gist of the present invention is to provide a grid point conversion unit for converting into a value.

An image processing method corresponding to this is as follows.
An image processing method for reducing the number of gradations of a multicolor image represented by coordinate values in a color space of three or more dimensions, wherein the coordinate value is expressed using a predetermined number of gradations for each pixel of the image. Color image data is sequentially input, the color space is divided by the number of gradations smaller than the number of gradations expressing the coordinate values, and the coordinates of the lattice points obtained by performing the division for each dimension. Values are stored for the color space, threshold values corresponding to a dither matrix of a predetermined size are stored, and under predetermined conditions, the threshold value of the threshold matrix is substantially changed in the processing direction of the pixel. (M is an integer of 2 or more), and the coordinate value of the input color image data in the color space is corrected using the substantially extended threshold value. Grid stored in storage means Of the coordinate values, it is summarized as to convert the coordinate values close to the coordinate value after the correction.

Further, a recording medium on which a program for realizing these image processing apparatuses and methods on a computer is recorded is a multi-color image represented by coordinate values in a two-dimensional or more color space. A recording medium that records a program for causing a computer to implement the function of reducing, and for each pixel of the image, a function of sequentially inputting color image data expressing the coordinate values using a predetermined number of gradations, An area in which the color space is divided by the number of gradations smaller than the number of gradations expressing the coordinate values, and the coordinate values of grid points obtained by performing the division for each dimension are stored in the color space. A function of reading the coordinates of the grid point, a function of reading a threshold value corresponding to a dither matrix of a predetermined size stored in a predetermined area in advance, a predetermined condition A function of substantially multiplying the threshold value of the threshold value matrix in the processing direction of the pixel by M (M is an integer of 2 or more), and calculating coordinate values of the input color image data in the color space. A program for realizing a function of performing correction using the substantially extended threshold value and converting the read coordinate values of the grid points to coordinate values close to the corrected coordinate values. The gist is that the information is recorded so as to be readable on the computer.

According to the above image processing apparatus and method,
For each pixel of the image, color image data expressing coordinate values using a predetermined number of gradations is input, and the coordinate values are corrected using an extended threshold, and a grid close to a grid point prepared in advance is input. Convert to point coordinates. With such a conversion,
Without performing a complicated interpolation operation using a plurality of grid point data, it is possible to suppress deterioration in image quality and reduce the number of gradations.

In such image processing, a color correction table storing correction data relating to the color of the color image data is prepared corresponding to each grid point, and the correction data of the grid point corresponding to the converted coordinate value is stored in the color correction table. It is also preferable to adopt a configuration in which data is read from the correction table and output as corrected color image data. In this case, it is only necessary to prepare color correction data in a number corresponding to the number of grid points, and the total data amount can be reduced. Further, by preparing a color correction table, it is possible to prepare color image data corresponding to various uses. For example, if the color correction table stores, as the correction data, data that is suitable for the color reproduction characteristics of the image output device that finally processes the output color image data, the color image can be appropriately adjusted for each image output device. Data can be output.

Further, it is preferable to perform a process of averaging the correction data of each pixel based on the correction data of the pixels near the pixel. This is because it is possible to reduce the influence of the quantization error that occurs when converting the coordinates to the coordinates of the neighboring grid points. In the averaging process, when the pixel being processed is a pixel other than the pixel corrected using the extended threshold value, the averaging process is performed with the immediately preceding pixel in the processing direction. What should be done. The averaging process can also be performed between pixels in a direction intersecting the direction in which the color image data is input.

It is also useful to finely divide grid points in a low density area. If the grid points are finely divided in the low-density area, the intervals between data in the color correction table in the low-density area will also be fine, and quantization when converting the coordinate values of the input data into the coordinate values of the grid points will be performed. The error is reduced in the low-density region where it is a problem, and the deterioration of the image quality is suppressed. As a result, the color correction calculation adapted to the image output device is performed at high speed, good color reproduction is obtained, and deterioration of image quality is suppressed. Here, the low density area means an area where the density of dots output to the image output device is low. For example, when the final image output is an ink jet printer that expresses a gradation by turning on and off dots, it refers to a region where the density of ink dots such as CMY is low. When the output device is a CRT or the like, focusing on the white dots, it is an area where the white dots are sparsely distributed (high-density area in the entire image).
Paying attention to black dots, it is an area where black dots are sparsely distributed (low density area in the entire image). As will be described later, if a printer is provided with high-density ink and low-density ink for the same color and separates dark dots and light dots, an area where light dots are sparsely distributed (low in the entire image). Not only the density area) but also the area where the dark dots are sparsely distributed corresponds to the low density area for the ink.

When the color space is divided, the target two-dimensional or more color space includes not only the RGB and CMY color spaces but also the color space represented by the XYZ color system, L * a * b *
Various color spaces such as a color system, an L * C * h color system, and a Munsell color system can be considered. When these coordinate values are represented by n-bit digital information, the number of gradations is 2 to the power of n (for example, 2 for 8 bits).
In many cases, the number of gradations is expressed by 56), but the number of gradations other than 100 gradations, 17 gradations, or 2 to the power of n may be used. In the above configuration, the coordinates of the grid points are finely divided in the low-density area, but the intervals between the gradations of the respective color components of the color image data corrected by the color correction means are narrow in the low-density area. As such, it is also preferred to choose. As a result, the quantization error of the pre-gradation number conversion in the low-density region in the data after the color correction is reduced, so that the deterioration of the image quality due to the division of the color space by the small number of gradations is more reliably suppressed. be able to.

[0024]

Next, a preferred embodiment of an image processing apparatus according to the present invention will be described in detail with reference to the drawings. FIG. 1 shows an image processing apparatus 3 according to a first embodiment of the present invention.
An example of a color image processing system centered on 0 is shown. In this image processing system, original color image data OR output from an image input device 10 such as a scanner is provided.
G is input to the image processing device 30. Image processing device 3
The image data processed by 0 is finally output to an image output device 20 such as a printer, where a final image is obtained.

(1) Hardware of Image Processing Apparatus The image processing apparatus 30 receives the input original color image data O
As image processing for matching RG to the color reproduction characteristics of the image output device 20, color correction and gradation number conversion are performed. The color correction is a process for correcting output characteristics of the image output device, such as gamma correction. Further, the gradation number conversion means that when the number of tones that can be output from the image output device 20 is smaller than the number of tones that can be output from the color image data ORG output from the image input device 10, color correction is performed. This is a process of converting the color image data thus obtained into a final number of gradations suitable for the image output device 20. For example, the image data ORG read from a scanner or the like has 256 gradation levels (8 bits) for each of R, G, and B colors, and the image output device 20
An ink jet printer that performs expression by turning on / off C, M, Y or C, M, Y, K inks may have a configuration in which the final number of gradations is 2.
In this case, the image processing device 30 converts the image data of 256 gradations of RGB into CMY (K) data, performs color correction, further converts the data into two gradations, and outputs the image as final color image data FNL. Output to the device 20. In the above description, the conversion is collectively referred to as gradation number conversion.
In practice, the input original color image data ORG is assigned to grid points with a small number of gradations before color correction, thereby reducing the number of gradations by pre-gradation number conversion. Tone conversion by so-called halftone processing for binarizing according to the number of tones that can be expressed is performed. In the following description, the former is referred to as pre-gradation number conversion, and the latter is referred to as post-gradation number conversion. For each gradation number conversion,
This will be described in detail later.

FIG. 2 is a block diagram showing a specific configuration example of the color image processing system shown in FIG. Here, a scanner 12 that optically reads a color image from a document is used as the image input device 10. The scanner 12 converts the read color image data into R, G,
It is output as original color image data ORG composed of three color components of B. In the embodiment, each color of R, G, and B is represented by 8-bit digital data.
The number of gradations is 256. In this case, the scanner 12
Represents the original color image data by three primary colors of R, G, and B, and where the color of each pixel is located in a three-dimensional color space using the respective colors of R, G, and B as coordinate axes. In other words, no matter what color system such as L * a * b * is adopted, where the color of a certain pixel is located in the color space That is, it can be expressed as a coordinate value.

As the image input device 10, in addition to the scanner 12, for example, a video camera, a host computer for creating computer graphics, and other means can be used.

In the image processing system of the embodiment, a color printer 22 that cannot perform gradation control in pixel units is used as the image output device 20. In the color printer 22, a binarization process for reducing the number of gradations of each color component of the original color image data ORG output from the scanner 12 to two gradations corresponding to ON / OFF of each pixel is required. Has been described above.

In addition, as the image output device 20, for example, a color display 21 or the like can also be used. Many color displays 21 for computers and the like have a smaller number of displayable gradations than ordinary home TVs. Even when such a color display 21 is used, it is necessary to convert the number of tones of the original color image data ORG into a number of tones corresponding to the display 21. Various other image output devices can be considered, such as a plate making device for printing, a thermal transfer type printer, a sublimation type printer capable of expressing gradation to some extent, and a color laser printer.

Next, a specific configuration corresponding to the image processing apparatus 30 will be described. FIG. 2 is a block diagram showing an internal configuration of the image processing device 30. The hardware of the image processing device 30 is a normal computer 90. As shown in the figure, the computer 90 includes the following units interconnected by a bus 80 centering on a CPU 81 that executes various arithmetic processes for controlling operations related to image processing according to a program. ROM 82 is a CPU
A program and data necessary for executing various arithmetic processes are stored in advance in the RAM 81, and the RAM 83
A memory for temporarily reading and writing various programs and data necessary for executing various arithmetic processes in U81.
The input interface 84 controls the input of signals from the scanner 12 and the keyboard 14, and the output interface 8.
Reference numeral 5 controls output of data to the printer 22. CRTC
86 controls the signal output to the CRT 21 capable of color display, and the disk controller (DDC) 87 controls the exchange of data with the hard disk 16, the flexible disk drive 15, or a CD-ROM drive (not shown). The hard disk 16 has a RAM 83
In addition, various programs loaded and executed on the PC, various programs provided in the form of a device driver, and the like are stored. In addition, a serial input / output interface (SIO) 88 is connected to the bus 80. This S
The IO 88 is connected to the modem 18 and the modem 48
Through a public telephone line PNT. The image processing apparatus 30 is connected to an external network via the SIO 88 and the modem 18, and can download a program required for image processing to the hard disk 16 by connecting to a specific server SV. is there. In addition, it is also possible to load a necessary program from a flexible disk FD or a CD-ROM, and cause the computer 90 to execute the program.

Next, referring to FIG.
The functional configuration of the image processing performed inside 0 will be described. The image processing device 30 functions as an image processing device only after an image processing program is executed on a computer 90 that is hardware. More specifically, a program for performing image processing is loaded from a hard disk 46 or the like as a medium storing the program into a RAM 83 constituting a main storage, and is executed by the CPU 81. It works. In the computer 90, an application program 95 for executing image processing operates under a predetermined operating system. A video driver 91 and a printer driver 96 are incorporated in the operating system, and the final color image data FNL is output from the application program 95 via these drivers. An application program 95 for retouching an image reads an image from the scanner 12 and displays the image on a CRT display 93 via a video driver 91 while performing predetermined processing on the image.

This application program 95
When a print command is issued, the printer driver 96 of the computer 90 receives the image information from the application program 95 and converts the image information into a signal that can be printed by the printer 22 (in this case, a CMY binary signal). . In the example shown in FIG.
6, a rasterizer 97 that converts color image data handled by the application program 95 into dot-based image data, and an ink color used by an image output device (here, the printer 22) for the dot-based image data. A color correction module 98 that performs color correction according to CMY and color development characteristics, a color correction table CT referred to by the color correction module 98, and an area based on the presence or absence of ink in dot units based on image information after color correction. A halftone module 99 that generates so-called halftone image information expressing density is provided.

The pre-gradation number conversion described above is performed by the color correction module 98, and the post-gradation number conversion is performed by the halftone module 99. Color correction module 98
Is equivalent to the lattice point conversion processing. The functional configuration of each module will be described later. Note that such a module can be provided in a driver other than the printer driver 96. For example, color display 2
These modules may be provided in the video driver 91 that performs display on the LCD 1 to perform multi-level conversion according to the characteristics of the color display 21.

Next, the structure of the printer 22 as an output device will be briefly described. FIG. 4 is a schematic configuration diagram of the printer 22. As shown in FIG.
A mechanism for transporting the paper P by the paper feed motor 23, a mechanism for reciprocating the carriage 31 in the axial direction of the platen 26 by the carriage motor 24, and a mechanism for driving the print head 28 mounted on the carriage 31 to discharge ink and form dots. It comprises a mechanism for controlling the formation and a control circuit 40 for controlling the exchange of signals with the paper feed motor 23, the carriage motor 24, the print head 28 and the operation panel 32.

The mechanism for transporting the paper P is a paper feed motor 2
A gear train (not shown) for transmitting the rotation of No. 3 not only to the platen 26 but also to a paper transport roller (not shown) is provided. The mechanism for reciprocating the carriage 31 includes an endless drive belt 36 extending between the carriage motor 24 and a slide shaft 34 that is erected in parallel with the axis of the platen 26 and slidably holds the carriage 31. Pulley 38,
Position detection sensor 3 for detecting the origin position of carriage 31
9 and so on. The control circuit 40 has a built-in CPU, ROM, RAM, and the like (not shown), and operates according to a program stored in the ROM in advance.
Control each part of

The carriage 31 of the printer 22 includes
Black (K) ink cartridge 71 and cyan (C),
A color ink cartridge 72 containing three color inks of magenta (M) and yellow (Y) can be mounted.
A total of four ink discharge heads 61 to 64 are formed on the print head 28 below the carriage 31, and at the bottom of the carriage 31, an introduction pipe 65 (for introducing ink from the ink tank to each color head). (See FIG. 4). When a black ink cartridge 71 and a color ink cartridge 72 are mounted on the carriage 31 from above, an inlet tube is inserted into a connection hole provided in each cartridge, and ink from the ink cartridge to the ejection heads 61 to 64 is inserted. Supply becomes possible.

The mechanism for ejecting ink will be briefly described. As shown in FIG. 5, the ink cartridges 71, 7
When the cartridge 2 is mounted on the carriage 31, the ink in the ink cartridge is sucked out through the introduction pipe 65 by utilizing the capillary phenomenon, and is sent to the color heads 61 to 64 of the print head 28 provided below the carriage 31. Be guided. When the ink cartridge is installed for the first time,
Ink is supplied to each color head 61 to 64 by a dedicated pump.
In the present embodiment, illustration and description of a pump for suction, a cap for covering the print head 28 at the time of suction, and the like are omitted.

As shown in FIG. 5, a plurality of heads (32 in this embodiment) are provided for each color as shown in FIG.
Are provided, and a piezo element PE which is one of the electrostrictive elements and has excellent responsiveness is arranged for each nozzle. FIG. 6 shows the structure of the piezo element PE and the nozzle n in detail. As shown, the piezo element P
E is installed at a position in contact with an ink passage 68 that guides ink to the nozzle n. As is well known, the piezo element PE is an element that distorts the crystal structure due to the application of a voltage and converts electro-mechanical energy very quickly. In this embodiment, by applying a voltage having a predetermined time width between the electrodes provided at both ends of the piezo element PE, the piezo element PE expands by the voltage application time as shown in the lower part of FIG.
One side wall of the ink passage 68 is deformed. As a result, the volume of the ink passage 68 contracts in accordance with the expansion of the piezo element PE, and the ink corresponding to this contraction becomes particles Ip and is ejected at a high speed from the tip of the nozzle n. When the ink particles Ip soak into the paper P mounted on the platen 26, printing is performed.

In the printer 22 having the hardware configuration described above, the carriage 31 is reciprocated by the carriage motor 24 while the paper P is conveyed by rotating the platen 26 and other rollers by the paper feed motor 23, and at the same time, the print head By driving the piezo elements PE of the 28 color heads 61 to 64, the respective color inks are ejected, and a multicolor image is formed on the paper P.

Although the configuration of the printer 22 is as described above, the color correction and the like according to the output characteristics of the printer 22 are processed inside the computer 90. No processing related to the above is performed. The processing executed inside the printer 22 is performed only by receiving the data output from the computer 90 and driving the respective color piezo elements PE of the print head 28 in synchronization with the above-described paper feeding and the reciprocating operation of the carriage 31. is there. Therefore, the control circuit 40 of the printer 22
The detailed description and its processing are omitted.

(2) First Example Next, a specific first example of the image processing apparatus 30 as the above embodiment will be described. Here, from the scanner 12 shown in FIG.
The 6-gradation original color image data ORG is output to the image processing device 30.
Input to the computer 90 as the
It is assumed that the printer driver 96 of 0 processes the original color image data ORG and outputs the final color image data FNL to the color printer 22. The color printer 22 used here uses a three-color ink of cyan C, magenta M, and yellow Y and prints in two gradations of ON (dot existence) / OFF (no dot) of each color dot. . The specific configuration of printing in the printer 22 has already been described.

FIG. 7 is a specific block diagram of the image processing apparatus 30 used in this case. Focusing on the processing, the image processing apparatus 30 can be regarded as being composed of a pre-gradation number conversion unit 140, a color correction unit 142, a color correction table memory 134, and a post-gradation number conversion unit 146. . The pre-gradation number conversion unit 140 and the color correction unit 142 correct the color of the input original color image data ORG, and further convert the color system from R, G, B to C, M, Y, and Output as CCD. The steps up to here correspond to the color correction module 98 of the computer 90. Then, the color correction data CCD is binarized using the post-gradation number conversion unit 146 according to the number of gradations that can be displayed by the printer 22, and output as final color image data FNL. The post-tone number conversion unit 146 corresponds to the halftone module 99 of the computer 90.

The above-described processing will be further supplemented. In the pre-gradation number conversion processing in the pre-gradation number conversion unit 140 of the present embodiment, the original color image data ORG having 256 gradations for each color is input, and the original color image data is converted into 16 gradations for each color of RG. , B are converted into eight gradations. In the original color image data ORG input from the scanner 12, R = 12, G = 20, B = 24
It is assumed that a color area having such a gradation continues for a certain area. Then, it is assumed that the color data of this color area is input to the image processing device 30.

FIG. 8 shows a rectangular parallelepiped formed of the original color image data ORG and eight grid points surrounding the original color image data ORG in the color space. If the original color image data X is (12,
20, 24) in the vicinity of this coordinate position.
The coordinate positions of the grid points are expressed by the following equation (1).

(Ri, Gj, Bk) = (0, 16, 16) (Ri + 1, Gj, Bk) = (16, 16, 16) (Ri, Gj + 1, Bk) = (0, 32, 16) (Ri + 1, Gj + 1, Bk) = (16, 32, 16) (1) (Ri, Gj, Bk + 1) = (0, 16, 32) (Ri + 1, Gj, Bk) +1) = (16, 16, 32) (Ri, Gj + 1, Bk + 1) = (0, 32, 32) (Ri + 1, Gj + 1, Bk + 1) = (16, 32, 32) )

In this image processing apparatus 30,
As shown in FIG. 9, the color space is finely divided by a low-density area of the used ink CMY of the printer 22, which is the final output device. If the number of gradations after the conversion of the pre-gradation number conversion is sufficiently larger than the final gradation number of the post-gradation number conversion, the quantization noise of the pre-gradation number conversion is sufficiently small, and the effect on practical use is small. small. However, since the quantization noise of the pre-gradation number conversion exists, this appears as disorder in the appearance position of the on-dot in the output image. Therefore, strictly speaking, the effect of the quantization noise does not substantially cause a problem in a high-density or medium-density region where the on-dot density is high, but may cause image quality deterioration in a low-density region where the dot density is low. It can be said that there is a possibility. Therefore, in order to solve this problem, in the present embodiment, as shown in FIG.
A color correction table CT having 0 is used. Correspondingly, in the pre-gradation number conversion, the original image data is converted into the gradation value (grid point color data) of the lattice point 500.

As a specific example, if the original image data is 0 to 2
When the gradation values up to 55 are taken, the gradation values are converted to 0, 16, 3 for the R, G, and B colors by pre-gradation value conversion.
2, 48, 64, 80, 96, 112, 128, 14
4, 160, 176, 192, 208, 224, 24
It is quantized to eighteen gradation values of 0, 248 and 255.
In this example, the quantization step, that is, the interval between adjacent grid points is basically a value 16 for RGB, but in the vicinity of the gradation value 255, that is, in a low density region, the quantization step is a value 8 or a value. It is smaller like 7. The color correction values of each of the R, G, and B color components are prepared in the color correction table memory 134 corresponding to the grid points thus prepared.

In the first embodiment, the pre-gradation number conversion unit 140 performs pre-gradation number conversion by the dither method using the grid points. The pre-gradation number conversion unit 140 performs the pre-gradation number conversion so that the input original color image data ORG becomes any color data on the eight grid points. Based on the grid point data obtained by the pre-gradation number conversion, the color correction unit 142
4 with reference to the color correction table CT in the color correction data C
c, Mc, and Yc are obtained.

Here, correction data is set in the color correction table memory 134 as follows. In order to determine the correction data, first, only the post-gradation number conversion unit 146 (the halftone module 99 shown in FIG. 2) was taken out from the image processing apparatus shown in FIG. 7 and combined with the target color printer 22. Construct the system. Then, various C, M, and Y values are given to the post-gradation number converter 146 to be binarized, and the result output to the target color printer 22 is subjected to color measurement. Then, the correspondence between the C, M, and Y values given to the post-gradation number converter 146 and the R, G, and B values obtained by measuring the output result of the color printer 22 is checked.

Next, the correspondence is reversed, and the C, M, and Y values necessary for obtaining the R, G, and B value colors corresponding to the grid point color data in the color space are obtained. Is set in the color correction table memory 134 as color correction data. Prior to actual image processing, the above processing is performed to prepare a color correction table CT.

After such pre-gradation number conversion processing and color correction processing, the post-gradation number conversion section 146 converts the color-corrected image data into a final image corresponding to the number of gradations that can be expressed by the image output device 20. A post-gradation number conversion process is performed to convert the number of gradations to a maximum. The post-gradation number conversion unit 146 also generates quantization noise due to the gradation number conversion. In the embodiment, the quantization noise generated by the pre-gradation number conversion is sufficiently smaller than the quantization noise generated by the post-gradation number conversion at the final stage. The quantization noise does not cause any problem in practical use, and the deterioration of image quality due to the pre-gradation number conversion processing is prevented.

Next, the details of the processing in the pre-gradation number conversion section 140 will be described. Pre-gradation number conversion unit 140
Is input original color image data O of 256 gradations for each color.
Each color component of R0, G0, B0 of RG is set to 1 for RGB.
The number of gradations is converted into eight levels, and the grid point color image data GCD
Output the respective color components of Pk, Gk and Bk.

The pre-gradation number conversion is performed by the process shown in FIG. FIG. 11 shows an example of the dither matrix in this embodiment. Although the dither matrix itself is 4 × 4 vertically and horizontally, this is shown as 4 × 8 in FIG. This is because each element of the dither matrix is used twice in the horizontal direction, and it is possible to think that the dither matrix is expanded twice in the horizontal direction. That is, in the processing described later using the dither matrix, each element of the matrix is used twice each along the processing direction of the pixel.

In the following description, DiTh indicates a dither matrix number, and as shown in FIG.
Take the value of Also, as described above, the lattice points prepared for the pre-gradation number conversion are narrowly divided in the low-density region. . . 18], RSLT [0] = 0, RSLT [1] = 16, RS
LT [2] = 32, RSLT [3] = 48, RSLT
[4] = 64,... RSLT [17] = 255 is set. In addition, the distance Dist between grid points
[I] is defined as Dist [i] = RSLT [i + 1] −RSLT [i] i = 0, 1,... The original color image data Da has a value of 255.
Is defined as Dist [18] = 1 in order to guarantee the result of the calculation for obtaining the offset offst, which will be described later.

When the pre-gradation number conversion shown in FIG. 10 is started, first, a process of inputting the original color image data Da of the pixel at the position of interest [p, q] is performed (step S).
40). Then, based on the position [p, q] of this pixel,
As a preparation for the work of allocating the coordinate values of the original color image data Da to adjacent grid points, a process of obtaining a fluctuation value DDH is performed. In this process, from the dither matrix number DiTh corresponding to the position [p, q] of the pixel of interest, a process of obtaining a fluctuation value DDH obtained by normalizing this value in the range of values 0 to 1 is performed (steps S41a and S41).
b). In this processing, first, the position [p,
q], from the dither matrix (FIG. 11):
A process of reading the threshold value DiTh is performed (step S41).
a). In this case, the same threshold value DiTh is used twice in the horizontal direction, as described above. Furthermore, this threshold value DiT
Based on h, a process of obtaining the fluctuation value DDH is performed (step S141b). The fluctuation value DDH is obtained by the following equation (2).

[0056] Here, DiMax is the maximum value of the threshold, and is 16 in this embodiment.

The process for obtaining the threshold value DiTh is performed by setting the position of the pixel of interest in the scanning direction as p (1, 2, 3,... Pmax) and the position in the sub-scanning direction as q (1, 2, 3,..., Qmax). , [P% 8, q% 4] from the matrix shown in FIG. here,
% Is the remainder operator. In order to obtain the threshold value DiTh from the matrix of FIG. 11, a function (eg, GetMatrix [x, y]) having elements [0, 0] to [7, 3] may be defined in advance. The dither matrix shown in FIG. 11 is obtained by expanding the normal 4 × 4 matrix shown in the lower column twice in the horizontal direction, that is, along the image processing direction. Therefore, when data is read from this matrix, the same value is read out continuously for two pixels. It should be noted that the threshold value DiTh is determined from [p% 4, q% 4].
Good to use repeatedly.

After performing the process of normalizing the threshold value DiTh to obtain the fluctuation value DDH, a value 0 is set to a variable X indicating a conversion gradation number (step S42). Grid point value RSLT [X] determined by
And the original color image data Da are compared (step S43). Note that, in this description, the color components of the original color image data Da to be compared do not particularly specify, but actually, the comparison is performed for each color component. The original color image data Da is a grid point value RSLT
If not [X] or less, the variable X is incremented by 1 (step S44), and the two are compared again. That is,
Until the original color image data Da becomes equal to or less than the grid point value RSLT [X], the value corresponding to the grid point is sequentially increased.

As a result, the original color image data Da
Is less than or equal to the grid point value RSLT [X] (step S43).
A process of calculating the offset offst from the lattice point compared in step 3 is performed (step S45). The offset offst is
The distance D between the lattice points sandwiching the original color image data Da
It is calculated by the following equation (3) as a value normalized to ist [X-1].

Offst = (RSLT [X] −Da) / Dist [X−1] (3)

Therefore, a value DDH obtained by normalizing the distance offst and the dither matrix number DiTh is obtained.
Is performed (step S46). If the difference offst is smaller than the comparison between the two, the original color image data Da is assigned to the lattice point having a larger value between the lattice points sandwiching the original color image data Da, and the value RSLT [ X] is set to the result value RSL (step S47). If the offset offst is larger, the variable X is assigned to assign the original color image data Da to the grid point of the smaller grid value of the two grid points sandwiching the original color image data Da. A process of setting the value RSLT [X-1] of the grid point corresponding to −1 to the result value RSL is performed (step S48). Thereafter, a process of moving the target pixel to the next pixel is performed (step S4).
9) The above processing is repeated until the end of the original color image data.

According to the above processing, the number of gradations of the original color image data Da can be converted from 256 gradations to 18 gradations, and a distributed dither matrix (FIG. 11).
Can be used to convert the image data into grid point color image data that has been appropriately dispersed. In the present embodiment, when determining which of the two grid points sandwiching the original color image data Da is to be allocated, a variation using a dither matrix is generated. That is, in this embodiment, the dither matrix number Di prepared as the dither matrix is used.
Since the distance from the adjacent grid point is determined using the value DDH normalized using Th, for example, even if the original color image data Da of the adjacent pixel has the same value, a different grid is used. It happens to be assigned to points. When the systematic dither method is used, compared with the average error minimization method and the error diffusion method, the error diffusion calculation is not required, so that the time required for image processing can be shortened and the error storage There is a great merit that a memory or the like becomes unnecessary and hardware resources are saved.

Further, in the present embodiment, as shown in FIG. 11, the original 4 × 4 dither matrix is extended twice to 8 × 4 along the image processing direction. Have the same value stored in them. Therefore, when reading and processing each threshold data using the dither matrix, the same value can be used twice consecutively along the image processing direction. As a result, the process of reading the threshold data can be simplified. The image to be subjected to the pre-gradation number conversion may be an image obtained by enlarging the original image several times vertically and horizontally. In such a case, the color image data itself is the same data every several dots in the vertical and horizontal directions, and since it is the same color image data, processing using the same threshold value is sufficient, and the image quality is not reduced.

Further, in this embodiment, as shown in FIG. 9, since the color space is divided into smaller areas in a lower density area to determine grid points, the quantization error in the low density area is reduced. The image quality is prevented from deteriorating in a low-density region that is easily noticeable visually. Note that the low density area refers to an area where the density of dots output to the image output device is low. For example, if the final image output is
In the case of an ink-jet printer that expresses gradation by turning off, it refers to a region where the density of ink dots such as CMY is low. When the output device is a CRT or the like, a white dot is an area in which white dots are sparsely distributed (high-density area in the entire image) if attention is paid to white dots, and a black dot is sparsely distributed if attention is paid to black dots. (A low density area in the entire image). In addition, as described later, a high density ink and a low density ink are provided for the same color,
In a printer that separates dark dots from light dots, not only areas where light dots are sparsely distributed (low-density areas in the entire image), but also areas where dark dots are sparsely distributed, have a low ink level. This corresponds to the density region.

(3) Second Embodiment In the above-described embodiment, as shown in the upper section of FIG.
Of the color image data ORG
However, if it is known that the data is enlarged twice in the image processing direction, the processing is performed for each two pixels.
For the second pixel, the pre-gradation number conversion unit 140 and the color correction unit 142 leave the determination result for the first pixel
May be the conversion result. In this case, it is sufficient to refer to the color correction table memory 134 once with two pixels, and the processing speed can be greatly increased.

FIG. 12 shows an example of the tone number conversion process in this case.
Shown in The processing shown in FIG. 12 is basically the same as the processing of allocating the original color image data to adjacent grid points using a dither matrix, and the processing from step S41a to step S48 shown in FIG. , Are collectively shown as grid point assignment processing using a dither matrix (step S410). The dither matrix used in this embodiment is not shown in the upper column of FIG. 11, but is a normal dither matrix that is not expanded in the horizontal direction as shown in the lower column of FIG.

When this processing routine is started, first, processing for inputting the original color image data Da is performed (step S400), and then processing for determining whether or not the processing flag Fodd is 1 is performed (step S405). . Flag Fo
The initial value of dd is set to a value of 0, and by alternately setting the value to 1 and 0 by the following processing, whether the pixel of interest is an odd-numbered pixel counted from the start end of the processing ( F
odd = 0) or an even number (Fodd = 1). Immediately after starting, the initial value is 0
Therefore, the determination in step S405 is “NO”. In this case, first, a process of substituting a value of 1 for the flag Fodd is performed (step S408), and the process proceeds to step S410 to allocate grid points using a dither matrix, as in the above-described embodiment. Execute the process.

On the other hand, if the flag Fodd is the value 1, it is determined that the pixel of interest is an even-numbered pixel (second, fourth,...) From the processing end, and the flag Fodd is returned to the value 0 first ( Then, it is determined whether or not the original color image data Da of the pixel at the position of interest is equal to the color image data Dap of the immediately preceding pixel (step S430). If they do not match, as in the case described above, the process shifts to step S410 to execute processing for allocating grid points using the dither matrix. On the other hand, when the original color image data Da of the pixel of interest is equal to the original color image data Dap of the immediately preceding pixel, all the above-described processing is not performed, and the result of the immediately preceding pixel is not obtained. A process of substituting the value RSLp for the result value RSL of the pixel of interest is performed (step S440).

Original color image data D of the pixel of interest
If a is not equal to the original color image data Dap of the immediately preceding pixel, grid points are allocated in step S410, and if both are equal, the previous result value RSLp is substituted and the same. After assigning to the grid points of
In order to store the original color image data Da and the result value RSL of the currently focused pixel as the value of the immediately preceding pixel, the original color image data Dap of the previous pixel and the result value R of the previous pixel are stored.
A process of substituting for SLp is performed (step S485).
Thereafter, a process of moving the target pixel to the next pixel is performed (step S490), and the above process is repeated until the end of the original color image data.

According to the above processing, similar to the first embodiment,
The number of tones of the original color image data Da is changed from 256 to 18
The image data can be converted into gradations, and the image data can be converted into appropriately dispersed lattice point color image data using a distributed dither matrix (lower column in FIG. 11). Furthermore,
In this embodiment, for two consecutive pixels, when the original color image data Da of the pixel of interest is equal to the original color image data Dap of the immediately preceding pixel, a process of referring to the threshold value of the dither matrix All the following processing (step S410) is not performed, and the pixel is assigned to the same grid point as the immediately preceding pixel. Therefore, for example, when processing an image obtained by doubling the original image in the horizontal direction in the original color image data, the processing of step S410 and the subsequent steps need only be performed once every two times, and the image can be processed at high speed. it can. The case where the original image is doubled or quadrupled in the horizontal direction often occurs when the resolution of the image to be printed is lower than the resolution of the printer 22. Further, even if the image to be processed is not an image doubled in the horizontal direction, in the case of a natural image, there is a large correlation between adjacent image data. In many cases, they are the same. Even in such a case, the processing can be speeded up. Although not shown in FIG. 12, in the color correction processing performed subsequent to the pre-gradation number conversion, in view of obtaining the same color correction data for the same grid point, two consecutive pixels If the color image data Da is the same, the same color correction data may be used without referring to the color correction table CT again. In this case, the processing can be further speeded up.

(4) Third Embodiment Next, a third embodiment of the present invention will be described. In the image processing device 30A of the third embodiment, the pre-gradation number conversion unit 14
0, the color correction unit 142, and the smoothing processing unit 150 are realized by the processing shown in FIG. The smoothing processing unit 150 is included in the color correction module 98 in the configuration shown in FIG. In this embodiment, the position of the pixel of interest in the main scanning direction is indicated by h, and the position of the pixel of interest in the sub-scanning direction is indicated by v. In the following description, the pre-gradation number conversion unit 140
Original color image data ORG before gradation number conversion by
Are represented by Rs [h, v], Gs [h, v], Bs
[H, v], and each color component of the grid point color image data GCD after the pre-gradation number conversion is represented by Rn [h, v],
Gn [h, v] and Bn [h, v].
By the pre-gradation number conversion, in this embodiment, the gradation number is 1 for each color.
The data is reduced to eight gradations, and this data Rn [h, v] and the like can be regarded as indicating the number of the grid point assigned to the data. In the second embodiment, the color correction table CT is a table including conversion from RGB to four colors of CMYK. Each color component of the color correction data GCD is represented by Cc [h, v] and Mc [h, v]. , Yc [h,
v] and Kc [h, v]. In FIG. 14,
[H, v] may be omitted for convenience of illustration.

When the process shown in FIG. 14 is started, first, the pre-gradation number conversion section 140 performs pre-gradation number conversion (step S500). The pre-gradation number conversion is performed for each color component Rs [h, v], G corresponding to the original color image data ORG.
As in the first embodiment, s [h, v] and Bs [h, v] are assigned to grid points prepared in advance using a dither matrix, and the number of gradations is reduced. The method has been described in detail in the first embodiment. The pre-gradation number conversion shown in FIG. 14 is based on the original color image data (Rs, G
s, Bs) by applying the function PreConv to obtain the grid point color image data (Rn, Gn, Bn). Each color component of the grid point color image data GCD obtained by this pre-gradation number conversion is Rn
[H, v], Gn [h, v], Bn [h, v].

This pre-gradation number conversion processing (step S5)
00) is a process of determining whether or not the image being processed is an image doubled in the horizontal direction (step S502).
If the image is not an image doubled in the horizontal direction, the threshold data is read out using a regular dither matrix, and the above pre-grayscale conversion is performed (step S504).
If the image is a multiplied image, the process includes a process of performing pre-grayscale conversion using a dither matrix doubled in the horizontal direction (step S506). Note that whether or not the image to be processed is an image doubled in the horizontal direction
Prior to the execution of the image processing routine shown in FIG. 14, for example, the data of pixels at arbitrary several places of the image are compared with the data in the vicinity thereof, and it is determined whether the same color image data is regularly repeated twice at any place. By judging this, it can be performed in advance. Any pre-gradation number conversion may be performed by looking at the value of a flag or the like reflecting the result. The pre-gradation number conversion in steps S504 and S506 is the same as that in the first embodiment (step S41a and subsequent steps in FIG. 10), and therefore, the description is omitted.

Next, based on each color component of the grid point color image data obtained by the pre-gradation number conversion, the color correction table CT stored in the color correction table memory 134 in advance.
, Color correction is performed (step S510). This processing corresponds to the processing by the color correction unit 142. In accordance with the color correction, the final color printer 22 is changed from RGB.
Are also converted into the four colors of CMYK, which are the ink colors output by. Color correction data CC obtained by color correction processing
Each color component of D is Cc [h, v], Mc [h, v], Yc
[H, v] and Kc [h, v]. In FIG. 14, since the color correction process refers to (looks up) the color correction table CT, the function RefLUT () is used.
As shown. In this embodiment, even if it is determined that the image is a doubled image in the horizontal direction, color correction (step S5) is performed.
10), but in this case, the same grid point is 2
Therefore, the process of referring to the color correction table CT is performed every other time, and the same color correction result can be used for an image doubled in the horizontal direction. In this case, the processing itself that refers to the color correction table CT can be omitted every other time, and the processing speed can be further increased.

After each color component of the color correction data CCD is obtained in this way, a smoothing process is performed by the smoothing processing unit 150 of the present embodiment. In this smoothing process,
First, it is determined whether or not smoothing processing is performed between the pixel of interest [h, v] and a pixel adjacent thereto (step S520). Regarding when to perform the smoothing process, various methods can be considered as described above, but in this embodiment,
As shown in FIG. 15, data Rn [h, v], Gn [h, v], Bn [h,
If the difference between v] and each data of the immediately preceding pixel [h-1, v] adjacent thereto is less than or equal to 1 for each color component, it is determined that the smoothing process is performed. That is, when each color component of the pixel of interest and each color component of the immediately preceding pixel in the main scanning direction are located at the same or adjacent grid points by the conversion by the pre-gradation number conversion unit 140, , To perform the smoothing process. With this determination, it is determined that the smoothing process is not performed on an edge or the like inherent in the image.

If it is determined that the smoothing process is not to be performed, the color-corrected color components Cc of the target pixel are determined.
[H, v], Mc [h, v], Yc [h, v], Kc
[H, v] is output data Cs, Ms, Ys, K
s (step S530), and the post-gradation number conversion unit 14
6 is output. On the other hand, if it is determined that the smoothing process is to be performed, each color component C
c [h-1, v], Mc [h-1, v], Yc [h-
[1, v], Kc [h−1, v] and the average of each color component of the pixel of interest are calculated (step S540). Move on to number conversion. In the present embodiment, since the output of the color printer 22 is a binary one in which an ink dot is formed or not, the halftoning process such as error diffusion is performed as the post-gradation number conversion process. . A description of this processing will be omitted.

In the image processing apparatus 30A of the third embodiment configured as described above, in addition to the effect of the first embodiment, since the smoothing is performed by the smoothing processing unit 150, the quantization generated by the pre-gradation number conversion is performed. The influence of the error can be reduced, and the deterioration of the image quality due to the quantization error can be prevented. In addition, based on the data after the pre-gradation number conversion, the pixel is compared with the pixel immediately before the pixel of interest, and even if one of the color components is assigned to a grid point separated by a grid point that is more than an adjacent grid point, , No smoothing process is performed. As a result, sharpness such as an edge which originally exists in an image is not lost by the smoothing process. Also, since the determination as to whether or not to perform smoothing is made by comparing with the data of the pixel processed immediately before, there is no waste in the data stored for comparison,
The storage capacity can be small. Furthermore,
Since only comparison with one adjacent pixel is required, the amount of calculation can be reduced, and the overall processing can be speeded up. Pixels to be smoothed are not limited to two pixels adjacent in the image processing direction, but are smoothed between three pixels adjacent in the image processing direction (horizontal direction in the figure) as shown in FIG. Processing may be performed. Further, FIG.
As shown in FIGS. 6 (B), (C), and (D), smoothing processing may be performed between pixels in a direction intersecting the image processing direction (main scanning direction).

In the third embodiment described above, the determination as to whether or not to perform smoothing is made based on the distance between the respective color components of the data after the pre-gradation number conversion.
Various variations can be considered. For example,
The data Rn [h, v], Gn [h,
v], Bn [h, v], instead of data Rn0 [h, v], Gn0 [h, v], Bn0 indicating the range to which the original color image data from which it is derived belongs
The determination may be made using [h, v]. At this time, the data R
n0 [h, v], Gn0 [h, v], Bn0 [h, v]
Indicates which of the rectangular parallelepipeds is surrounded by the eight adjacent grid points. Therefore, the condition is that the target pixel and the adjacent pixel (in the main scanning direction) (The immediately preceding pixel) is equivalent to determining whether or not the pixel belongs to the same rectangular parallelepiped surrounded by eight grid points or a rectangular parallelepiped adjacent thereto. Under the conditions shown in FIG. 15, if the grid points assigned by the pre-gradation number conversion for each color component are the same or adjacent, the smoothing process is performed irrespective of the relationship as the original color image data. However, in the latter example, the condition is that the original color image data is in the same space surrounded by adjacent grid points or in a space adjacent thereto.

Further, it can be determined that smoothing is performed only when the target pixel and the original color image data of the pixel adjacent thereto belong to the same rectangular parallelepiped space surrounded by adjacent grid points. .

The distance between adjacent pixels can be set to a value of 1 or less. However, the condition for performing smoothing may be relaxed, and smoothing may be performed even when the distance is 2 or more. Since the number of gradations after the pre-gradation number conversion is different for each color component, it is possible to set the value to 2 or more only for a specific color.

The preferred embodiment of the present invention has been described above. However, the present invention is not limited to this embodiment, and various modifications, improvements or modifications may be made without departing from the scope of the present invention. can do. For example, the dither matrix storing the threshold value may be expanded three times or more in the image processing direction. Also, the nature of the image to be processed is determined, and the original image is multiplied by N times (N
If it is determined that the image has been converted to an image of 2 or more, a dither matrix expanded N times in the image processing direction may be used.

Further, in the above-described embodiment, the ink is ejected by using the piezo element PE for ejecting the ink and applying a voltage having a predetermined time width to the piezo element PE. Is also easy to adopt. Practically used ink ejection methods can be roughly classified into a method of separating and ejecting ink particles from a continuous ink jet and an on-demand method used in the above-described embodiment. You. In the former,
There are known a charge modulation method in which liquid droplets are split from an ink jet by charge modulation, and a microdot method in which minute satellite particles generated when large-diameter particles are split from an ink jet are used for printing. These methods are also applicable to the printing apparatus of the present invention using inks of a plurality of types.

The on-demand system generates ink particles when ink particles are required in dot units. In addition to the system using the piezo element employed in the above-described embodiment, FIG. As shown in (A) to (E), a method is known in which a heating element HT is provided in the vicinity of an ink nozzle NZ, a bubble BU is generated by heating the ink, and the ink particles IQ are ejected by the pressure. I have. These on-demand ink ejection methods are also applicable to the printing apparatus of the present invention that uses inks of a plurality of types of densities or a plurality of dots of different diameters. Further, as described in the above embodiment, the present invention can be applied to a configuration in which ink of the same density is ejected a plurality of times to form dots with different densities.

Further, the present invention can be applied to a printer capable of ejecting two or more types of ink of dark and light, a printer capable of controlling the number of times of ejecting light ink of low density, and the like. In such a printer, three or more gradations can be expressed by controlling the ejection of high-density dark ink and lower-density light ink, or by overprinting light ink several times. Therefore, the final number of gradations can be set to three or more. Of course, when the post-gradation number conversion is involved, the pre-gradation number conversion can be determined irrespective of the gradation number of the finally output image data, and the desired gradation of two or more gradations can be determined. It can be a process of converting to a key number.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an image processing system according to the present invention.

FIG. 2 is a block diagram showing an example of a mode for realizing the image processing system shown in FIG.

FIG. 3 is a block diagram showing functions of an image processing apparatus 30 shown in FIG.

FIG. 4 is a schematic configuration diagram showing a configuration of a color printer 22 as an example of the image output device 20.

FIG. 5 is an explanatory view illustrating the structure of a print head 28;

FIG. 6 is an explanatory diagram illustrating the principle of ink ejection.

FIG. 7 is an explanatory diagram illustrating an example of a color space divided into a grid.

FIG. 8 is an explanatory diagram showing positions of color image data and neighboring grid point color data in a color space.

FIG. 9 is an explanatory diagram showing how a color space is divided.

FIG. 10 is a flowchart showing a pre-gradation number conversion process of image data.

FIG. 11 is an explanatory diagram of a weight matrix in a case where the pre-gradation number conversion processing is performed using an error diffusion method.

FIG. 12 is a flowchart showing a pre-gradation number conversion process as a second embodiment.

FIG. 13 is a block diagram illustrating functions of an image processing apparatus 30A according to a third embodiment.

FIG. 14 is a flowchart illustrating an image processing routine according to the third embodiment.

FIG. 15 is an explanatory diagram showing details of determination on whether to perform smoothing.

FIG. 16 is an explanatory diagram showing a specific example of a smoothing filter.

FIG. 17 is an explanatory diagram illustrating another configuration example of an ink particle ejection mechanism.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Image input device 12 ... Scanner 14 ... Keyboard 15 ... Flexible disk drive 16 ... Hard disk 18 ... Modem 20 ... Image output device 21 ... Color display 22 ... Color printer 23 ... Paper feed motor 24 ... Carriage motor 26 ... Platen 28 ... Printing Head 30 ... Image processing device 30A ... Image processing device 31 ... Carriage 32 ... Operation panel 34 ... Sliding shaft 36 ... Drive belt 38 ... Pulley 39 ... Position detection sensor 40 ... Control circuit 61 ... Ink ejection head 65 ... Introduction tube 68 ... Ink path 71 ... Black ink cartridge 72 ... Color ink cartridge 90 ... Computer 91 ... Video driver 93 ... CRT display 95 ... Application program 96 ... Printer driver 97 ... Rasterizer 9 ... color correction module 99 ... halftone module 134 ... color correction table memory 140 ... Pre-gradation number conversion section 142 ... color correction unit 146 ... posts tone number conversion unit 148 ... interpolation operation unit 150 ... smoothing processing section 300 ... grid point

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04N 9/68 101 H04N 1/46 Z

Claims (19)

[Claims] 1. An image processing apparatus for reducing the number of tones of a multi-tone color image, comprising: input means for inputting the multi-tone original color image data for each pixel along a processing direction; Threshold value storing means for storing a threshold value corresponding to a dither matrix having a size of a threshold value; An expanding unit, and comparing the input original color image data with a threshold substantially multiplied by M in the processing direction by the threshold expanding unit, and performing N-value conversion (N is an integer of 2 or more). An image processing apparatus comprising: a value conversion unit. 2. The image processing apparatus according to claim 1, wherein the threshold value expansion means is means for storing, in advance, when storing the threshold value in the threshold value storage means, the same threshold value is continuously and continuously stored in the processing direction. apparatus. 3. The image processing apparatus according to claim 1, wherein the threshold expansion unit uses the same threshold for the processing direction M times successively when referring to the threshold stored in the threshold storage unit. 4. A threshold expansion unit, wherein, when the original color image data is an image obtained by multiplying an original image by M in the horizontal direction (M is an integer of 2 or more), the pixel is determined to be M in the horizontal direction.
In the case of the position of S + 2 to M · (S + 1) (S is an integer of 0 or more), the threshold value stored in the threshold value storage means is used for the pixel located at the position of M · S + 1. 2. The image processing apparatus according to claim 1, wherein the means uses the same threshold as the threshold. 5. An image processing apparatus for reducing the number of gradations of a multi-gradation color image, comprising: input means for inputting the multi-gradation original color image data for each pixel along a processing direction; Threshold value storing means for storing a threshold value corresponding to a dither matrix having a size of .times..times..times..times..times..times..times..times..times. Do N
The value conversion means, if the input original color image data is the same as the original color image data of the immediately preceding pixel in the processing direction of the pixel, An image processing apparatus comprising: an N-value conversion omitting unit that uses a result of the N-value conversion without performing the conversion. 6. An image processing apparatus for reducing the number of gradations of a multi-color image represented by coordinate values in a two-dimensional or higher color space, wherein the coordinate value is determined for each pixel of the image by a predetermined floor. Input means for sequentially inputting color image data expressed by using a tone; dividing the color space by a number of gradations smaller than the number of gradations expressing the coordinate values; and performing the division for each of the dimensions. Grid point information storage means for storing the coordinate values of the grid points thus obtained for the color space; threshold value storage means for storing a threshold value corresponding to a dither matrix of a predetermined size; The threshold value of the threshold value matrix is substantially multiplied by M in the processing direction of the pixel (M is an integer of 2 or more)
Threshold value expanding means for correcting the coordinate value of the input color image data in the color space using the substantially expanded threshold value, and grid points stored in the grid point information storage means. An image processing device comprising: a grid point conversion unit that converts a coordinate value of the coordinate values into a coordinate value close to the corrected coordinate value. 7. An image processing apparatus for reducing the number of gradations of a multi-color image represented by coordinate values in a two-dimensional or more color space, wherein the coordinate value is determined for each pixel of the image by a predetermined floor. Input means for sequentially inputting color image data expressed by using a tone; dividing the color space by a number of gradations smaller than the number of gradations expressing the coordinate values; and performing the division for each of the dimensions. Grid point information storage means for storing the coordinate values of the grid points obtained by the above for the color space; threshold value storage means for storing a threshold value corresponding to a dither matrix of a predetermined size; and the input color image data The coordinate value in the color space is corrected using the stored threshold value, and among the coordinate values of the grid points stored in the grid point information storage means, the coordinates that are close to the corrected coordinate value Convert to value Grid point conversion means, and if the input color image data is the same as the color image data of the immediately preceding pixel in the processing direction of the pixel, the coordinate values of the immediately preceding pixel by the grid point conversion means And a grid point conversion omitting unit that uses the coordinate values converted for the immediately preceding pixel without performing the conversion. 8. The image processing apparatus according to claim 6, wherein a color correction table storing correction data relating to a color of the color image data corresponding to each of the grid points; A color correction unit that reads correction data of grid points corresponding to the coordinate values obtained from the color correction table and outputs the corrected data as corrected color image data. 9. The image processing apparatus according to claim 8, wherein the color correction table includes, as the correction data, a color reproduction of an image output device that finally processes color image data output by the color correction unit. An image processing device that stores images that match the characteristics. 10. The image processing apparatus according to claim 8, wherein the correction data of each pixel read by the color correction data reading unit is averaged based on the correction data of pixels in the vicinity of each pixel. An image processing apparatus comprising: 11. The image processing apparatus according to claim 8, wherein when the pixel being processed is a pixel other than a pixel corrected using the extended threshold, one pixel is processed in the processing direction. An image processing apparatus comprising: averaging processing means for performing averaging processing using the correction data of both pixels read by the color correction data reading means with a preceding pixel. 12. The averaging processing unit performs the averaging process with a pixel in a direction intersecting a direction in which the input unit inputs the color image data.
The image processing apparatus according to any one of the preceding claims. 13. An image processing method for reducing the number of gradations of a multi-gradation color image, comprising: inputting the multi-gradation original color image data for each pixel along a processing direction; A threshold value corresponding to the dither matrix is stored, and under a predetermined condition, the threshold value is substantially multiplied by M in the processing direction of the pixel (M is an integer of 2 or more). An image processing method in which a threshold value multiplied by M is compared with the input original color image data and N-valued (N is an integer of 2 or more). 14. An image processing method for reducing the number of gradations of a multi-gradation color image, comprising: inputting the multi-gradation original color image data for each pixel along a processing direction; The threshold value corresponding to the dither matrix is stored. The stored threshold value is compared with the input original color image data to perform N-value conversion (N is an integer of 2 or more). If the color image data is the same as the original color image data of the immediately preceding pixel in the processing direction of the pixel, an image using the N-value as it is without performing the N-value conversion on the immediately preceding pixel Processing method. 15. An image processing method for reducing the number of gradations of a multicolor image represented by coordinate values in a two-dimensional or higher color space, wherein the coordinate value is determined for each pixel of the image by a predetermined level. Color image data expressed by using a tone is sequentially input, the color space is divided by a number of gradations smaller than the number of gradations expressing the coordinate values, and the division is performed for each of the dimensions. The coordinate values of the obtained grid points are stored for the color space, and a threshold value corresponding to a dither matrix having a predetermined size is stored. Under a predetermined condition, the threshold value of the threshold matrix is set to the pixel value. Substantially M times (M is an integer of 2 or more) in the processing direction of
Then, the coordinate value of the input color image data in the color space is corrected using the substantially extended threshold, and the coordinate value of the grid point stored in the grid point information storage unit is corrected. And an image processing method for converting the coordinate value into a coordinate value close to the corrected coordinate value. 16. An image processing method for reducing the number of gradations of a multi-color image represented by coordinate values in a two-dimensional or more color space, wherein the coordinate value is determined for each pixel of the image by a predetermined floor. Color image data expressed by using a tone is sequentially input, the color space is divided by a number of gradations smaller than the number of gradations expressing the coordinate values, and the division is performed for each of the dimensions. The coordinate values of the obtained grid points are stored for the color space, and a threshold value corresponding to a dither matrix having a predetermined size is stored, and the coordinate values of the input color image data in the color space are stored. Is corrected using the stored threshold value, and among the stored coordinate values of the grid points, is converted to a coordinate value close to the corrected coordinate value, and the input color image data is Pixel processing direction If it is identical to the immediately preceding pixel color image data of the definitive does not perform conversion of the coordinate values for the immediately preceding pixel, it is used as it is an image processing method of the coordinate values are converted for the previous pixel straight. 17. A recording medium storing a program for causing a computer to realize a function of reducing the number of gradations of a multi-gradation color image, wherein the multi-gradation original color image data is processed along a processing direction. A function of reading out a threshold value corresponding to a dither matrix of a predetermined size stored in a predetermined area in advance in a predetermined area; under a predetermined condition, the threshold value is substantially multiplied by M in the processing direction of the pixel (M is an integer of 2 or more), a threshold substantially multiplied by M in the processing direction is compared with the input original color image data, and N-valued (N is an integer of 2 or more) And a computer-readable storage medium storing a program for realizing a function of performing the function. 18. A recording medium storing a program for realizing a function of reducing the number of gradations of a multi-tone color image on a computer, wherein the multi-gradation original color image data is processed in a processing direction. A function of storing a threshold value corresponding to a dither matrix of a predetermined size along with the input original color image data, and converting the stored threshold value into the N-valued data (N is The integer value of 2 or more), if the input original color image data is the same as the original color image data of the immediately preceding pixel in the processing direction of the pixel, the N value for the immediately preceding pixel A recording medium in which a program for realizing a function of directly using a result of the N-value conversion without performing the conversion is recorded in the computer. 19. A recording medium storing a program for causing a computer to realize a function of reducing the number of gradations of a multi-color image represented by coordinate values in a two-dimensional or more color space, For each pixel, a function of sequentially inputting color image data expressing the coordinate values using a predetermined number of gradations, dividing the color space by a smaller number of gradations than the number of gradations expressing the coordinate values. A function of reading the coordinates of the grid points from the area in which the coordinate values of the grid points obtained by performing the division for each of the dimensions are stored in the color space; and of a predetermined size stored in a predetermined area in advance. A function of reading a threshold value corresponding to a dither matrix. Under a predetermined condition, the threshold value of the threshold value matrix is substantially multiplied by M in the processing direction of the pixel (M is an integer of 2 or more).
Correcting the coordinate values in the color space of the input color image data using the substantially extended threshold value, and performing the correction among the coordinate values of the read grid points. A recording medium in which a program for realizing a function of converting the coordinate value into a coordinate value close to a later coordinate value is readablely recorded on the computer.