JP2005205881A - Method of detecting displacement of dot and method for generating dither matrix in consideration of displacement, and printer, printing method and displacement adjusting method, using dither matrix - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To print high quality image without making adjustment of a dot forming position. <P>SOLUTION: In printing an image by forming rasters with s times main scannings per raster, while a head having n pieces of nozzles arranged at intervals of a nozzle pitch k is being driven, a displacement of a dot is detected by a position of each pixel in a block which extends n×s pixels in a main scanning direction, and m×N×k pixels in a sub scanning direction as one block. The displacement is generated with a cycle of s pixels in the main scanning direction, and with a cycle of N×k pixels in the sub scanning direction. Then, displacements in all the pixel positions of the image are determined only by detecting the displacement in each pixel position in the block. When a dot is displaced and formed like this, a dither matrix is generated so that a proper dot dispersion is obtained. The high quality image with well dispersed dots is printed thereby. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a technique for printing an image by forming dots on a print medium, and more particularly to a technique for generating a dither matrix by detecting a positional deviation of dots formed on a print medium.

  2. Description of the Related Art Printing apparatuses that form dots and print images are widely used as so-called various digital image output apparatuses such as images created with a computer or images taken with a digital camera.

  These printing devices can only express the state of whether or not to form dots for each pixel, but by forming dots with an appropriate density according to the gradation value of each area of the image It is possible to express a multi-tone image. In these printing apparatuses, in order to form dots with an appropriate density according to the gradation value of the image, first, the image data is represented by data expressed in a dot distribution (dot data) by performing predetermined image processing. ). Thus, the process of converting image data into dot data is called halftone processing. Next, dots are formed on the print medium based on the dot data obtained by the halftone process. In this way, dots can be formed with an appropriate density according to the gradation value.

  Various methods for halftone processing have been proposed, and a typical method is called a dither method. In the dither method, the gradation value of the image data and the threshold value set in the dither matrix are compared for each pixel, and it is determined that a dot is formed for a pixel having a larger image data, and a dot is formed for a pixel that is not. This is a method of converting image data into dot data by determining that no dot is formed. In addition, in order to obtain a high-quality image, it is important not only to generate dots with an appropriate density but also to generate dots with appropriate dispersion. In order to generate dots in an appropriately dispersed manner, it is important to set a threshold value with an appropriate distribution in the dither matrix, and various improvements have also been attempted for the method for setting the threshold value (for example, Patent Document 1).

  Of course, even if the halftone process is properly performed so that the dots are well dispersed, if the positions of the dots actually formed on the printing medium are misaligned, good image quality Can't get. Therefore, various adjustment mechanisms for adjusting the dot formation position have also been proposed (for example, Patent Document 2, Patent Document 3).

JP 2000-261669 A Japanese Patent Laid-Open No. 11-77991 JP 2000-280461 A

  However, if the dot formation position is to be adjusted, a special adjustment mechanism or adjustment method must be installed, resulting in a problem that the printing apparatus becomes complicated and large, and the cost is increased. In addition, since it is not easy to completely adjust the dot formation position, a more complicated adjustment mechanism or adjustment method must be installed in order to completely adjust the dot formation position. There is a problem of inviting enlargement.

  The present invention has been made to solve the above-described problems of the prior art, and is a technology capable of printing a high-quality image without performing complicated or special adjustment for adjusting the dot formation position. For the purpose of providing

In order to solve at least a part of the problems described above, the first printing apparatus of the present invention employs the following configuration. That is,
A printing apparatus that applies a dither method to image data, performs halftone processing, and forms dots on a print medium based on the result of the halftone processing to print an image,
A head in which N nozzles forming the dots are provided at intervals of a nozzle pitch k;
By repeating the main scanning, which is an operation of driving the nozzles to form dots, while moving the head in a direction crossing the arrangement of the nozzles from one end to the other end of the print medium, Raster forming means for forming a plurality of rasters that are rows of dots on a medium;
Inspection image printing means for printing a predetermined inspection image for inspecting a positional deviation between an actual formation position where the dot is formed on the print medium and a design formation position;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), A displacement detection means for detecting the displacement at each pixel position in the block from the printed inspection image;
The present invention includes a dither matrix generation unit configured to generate a dither matrix by setting a threshold value of a dither matrix used in the dither method based on the detection result of the displacement.

Further, the first printing method of the present invention corresponding to the printing apparatus described above is
A printing method that applies a dither method to image data, performs halftone processing, and forms dots on a print medium based on the result of the halftone processing to print an image,
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. Forming a plurality of raster lines of dots on the print medium by repeatedly performing main scanning, which is an operation for forming dots by driving;
A predetermined inspection image for inspecting a positional deviation between an actual formation position where the dots are formed on the print medium and a design formation position by forming a plurality of rasters on the print medium. Printing process,
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ) Detecting the position shift at each pixel position in the block from the inspection image;
And a step of generating the dither matrix by setting a threshold value of the dither matrix used in the dither method based on the detection result of the misregistration.

  In the printing apparatus and the printing method of the present invention, a predetermined inspection image is printed on the print medium in order to inspect the positional deviation between the actual position where dots are formed on the print medium and the design position. . Then, a printing inspection is performed with a positional deviation at each pixel position in the block, where n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). Detect from image. Here, s is the number of main scans required to form one raster, and N is the number of nozzles provided in the head. K is the nozzle pitch, that is, the ratio between the distance between adjacent nozzles provided in the head and the distance between adjacent rasters in the image. For example, when the distance between the nozzles and the distance between the rasters are equal, the nozzle pitch k = 1, and when the distance between the nozzles is the distance of two rasters, the nozzle pitch k = 2. As will be described in detail later, according to the knowledge found by the inventor, dot misalignment occurs with a period of s pixels in the main scanning direction and N × k pixels in the sub scanning direction. Therefore, assuming a block whose size is an integral multiple of this cycle and detecting the dot displacement at each pixel position in the block, it is possible to obtain the dot displacement at all pixel positions in the image. It is. If the positional deviation of dots is known at all pixel positions in the image, an appropriate dither matrix can be generated on the assumption that the positions where dots are actually formed deviate from the designed positions. . In the dither matrix generated in this way, the threshold value is set in accordance with the actual positional deviation, so that the dots are properly dispersed without adjustment to bring the dot formation position closer to the design formation position. As a result, it is possible to print a high-quality image.

  In such a printing apparatus and printing method, the size of the dither matrix is set to p × s pixels in the main scanning direction and q × N × k pixels in the sub scanning direction (p and q are positive integers). It is good.

  As described above, dot misregistration occurs at a cycle of s pixels in the main scanning direction and N × k pixels in the sub scanning direction. If q × N × k pixels are used in the direction, the relationship between the dither matrix and the positional deviation of the dots is always the same. That is, no matter where the dither matrix is applied in the image, the dot formation positions are always shifted by the same in the pixels at the same position in the matrix. For this reason, it is preferable because the process of setting an appropriate threshold value for each pixel of the dither matrix can be simplified in consideration of the shift of the dot formation position from the designed formation position.

  In such a printing apparatus, as an inspection image, an image in which dots are not formed in adjacent pixels may be printed at least in the main scanning direction and the sub-scanning direction.

  When dots are formed in adjacent pixels in the main scanning direction or the sub-scanning direction, the distance between the dots is too close, making it difficult to identify the dot formation position, and as a result, it is difficult to detect dot misalignment. There are cases. In particular, when dots are formed in adjacent pixels, the dots may partially overlap and the dot formation position may not be identified. In such a case, at least in the main scanning direction and the sub-scanning direction, if an inspection image that does not form dots on adjacent pixels is printed, the dot formation position can be detected easily and reliably, It is possible to detect the positional deviation.

  If a plurality of types of dots having different sizes can be formed, the inspection image may be formed using dots other than the largest dot.

  If the inspection image is printed using other dots excluding the largest dot, even if dots are formed on adjacent pixels, the distance between the dots is too small, making it difficult to identify the dot formation position. As a result, it is preferable because it is possible to easily and reliably detect the positional deviation of dots.

  Further, when printing an inspection image, the image data of the inspection image is stored in a state in which at least halftone processing is performed, and inspection is performed by forming dots based on the image data stored in advance. An image may be printed.

  If image data for printing an inspection image is stored in a state in which at least halftone processing is performed, dots can be reliably formed at desired pixel positions. Accordingly, by appropriately setting the pixel positions where dots are formed as the inspection image in advance, it is possible to detect the positional deviation of the dots efficiently or accurately.

Further, in the above-described printing apparatus and printing method, based on the knowledge found by the inventors, that is, the knowledge that dot misalignment occurs with a period of s pixels in the main scanning direction and N × k pixels in the sub scanning direction, An appropriate dither matrix is generated in consideration of dot displacement. Therefore, the present invention can also be grasped as a method for generating such a dither matrix. That is, the dither matrix generation method of the present application is
A method of generating a dither matrix to be referred to when halftone processing is performed by applying a dither method,
While moving the head in which N nozzles for forming dots on the print medium are provided at intervals of the nozzle pitch k, moving from one end of the print medium to the other end in a direction intersecting with the arrangement of the nozzles, Performing a main scan as an operation of driving the nozzle to form dots;
By repeating the main scanning and forming a plurality of rasters as dot rows on the print medium, the positions of the actual formation position and the design formation position where the dots are formed on the print medium. A step of printing a predetermined inspection image for inspecting misalignment;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ) Detecting the position shift at each pixel position in the block from the inspection image;
And a step of setting a threshold value for each pixel of the dither matrix based on the detection result of the misregistration.

  When printing an image, a positional shift between the actual position where dots are formed on the print medium and the designed position occurs at a cycle of s pixels in the main scanning direction and N × k pixels in the sub scanning direction. Therefore, assuming a block whose size is an integral multiple of this cycle and detecting the dot displacement at each pixel position in the block, it is possible to obtain the dot displacement at all pixel positions in the image. It is. If the positional deviation of dots is known at all pixel positions in the image, an appropriate dither matrix can be generated on the assumption that the positions where dots are actually formed are different from the designed positions. If halftone processing is performed using the dither matrix generated in this way, high-quality images that are formed in a state where dots are appropriately dispersed can be obtained without making adjustments to bring the dot formation position closer to the design formation position. An image can be printed.

  At this time, the generated dither matrix may be a matrix having a size of p × s pixels in the main scanning direction and q × N × k pixels (p and q are positive integers) in the sub-scanning direction.

  As described above, dot misalignment occurs at a period of s pixels in the main scanning direction and N × k pixels in the sub scanning direction. Therefore, if the dither matrix is set to such a size, the dither matrix is included in the image. In any case, the dot formation positions are always shifted by the same amount in the pixels at the same position in the matrix. For this reason, it is possible to simplify the process of setting an appropriate threshold value for each pixel of the dither matrix in consideration of the shift of the dot formation position from the designed formation position.

In the above printing apparatus, printing method, and dither matrix generation method, s pixels in the main scanning direction and N × k pixels in the sub-scanning direction are used as blocks, and dot misregistration is detected for each pixel position in the block. By doing so, it is possible to determine the positional deviation at all the pixels in the image. If attention is paid to these points, the present invention can be grasped as a method for detecting the positional deviation of dots, and further as a method for adjusting the positional deviation of dots based on the detection result. That is, the method of detecting the positional deviation of the dots of the present application is as follows:
This is a detection method in which a printing apparatus that forms dots on a print medium and prints an image detects a positional shift between the design position of the dots formed on the print medium and the positions where dots are actually formed. And
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. A step of performing main scanning as an operation of driving to form dots;
Repetitively performing the main scanning to form a plurality of raster lines of dots on the print medium, thereby printing a predetermined inspection image for inspecting the misregistration of the dots;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). And a step of detecting the position shift at each pixel position in the block from the inspection image.

  According to such a positional deviation detection method, it is possible to obtain the positional deviation at every pixel position in the image only by detecting the positional deviation of the dots for each pixel position in the block.

Moreover, the adjustment method of the positional deviation of the dot of this application is:
A printing apparatus that forms dots on a print medium and prints an image is an adjustment method that adjusts the positional deviation between the design position of the dots formed on the print medium and the positions where dots are actually formed. And
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. A step of performing main scanning as an operation of driving to form dots;
Repetitively performing the main scanning to form a plurality of raster lines of dots on the print medium, thereby printing a predetermined inspection image for inspecting the misregistration of the dots;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ) Detecting the position shift at each pixel position in the block from the inspection image;
And a step of adjusting the dot formation position based on the detection result of the positional deviation.

  According to this positional deviation adjustment method, the dot formation position is adjusted based on the positional deviation of the dots detected at each pixel position in the block. As described above, if the positional deviation at each pixel position in the block is known, the positional deviation at any pixel position in the image can be determined. Based on the detection result of the positional deviation within the block. If the dot formation position is adjusted, the dot formation position can be adjusted appropriately and simply in the entire image.

In addition, a dither matrix generated in consideration of the above-described dot misregistration may be generated for each printing apparatus during or after manufacturing the printing apparatus, and an image may be printed using the obtained dither matrix. Is possible. Therefore, the present invention can be grasped as a printing apparatus having the following mode. That is, the second printing apparatus of the present invention is
A printing apparatus that applies a dither method to image data, performs halftone processing, and forms dots on a print medium based on the result of the halftone processing to print an image,
A dither matrix storage means which is referred to in the halftone process and stores a dither matrix unique to the printing apparatus;
A head in which N nozzles forming the dots are provided at intervals of a nozzle pitch k;
The print medium is repeatedly subjected to main scanning, which is an operation of driving the nozzles to form dots while moving the head in a direction crossing the arrangement of the nozzles from one end to the other end of the print medium. A raster forming means for printing the image by forming a plurality of rasters as a row of dots on the top;
The dither matrix storage means is a dither matrix specific to the printing apparatus,
A predetermined inspection image for inspecting a positional deviation between an actual formation position where the dots are formed on the print medium and a design formation position is printed using the printing apparatus,
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), Detecting the displacement at each pixel position in the block from the printed inspection image;
The gist of the present invention is a means for storing a matrix in which a threshold value of the dither matrix is set based on the detection result of the displacement.

Further, the second printing method of the present invention corresponding to the printing apparatus described above is
A printing method that applies a dither method to image data, performs halftone processing, and forms dots on a print medium based on the result of the halftone processing to print an image,
Storing a dither matrix that is referred to in the halftone process and is unique to the printing apparatus;
The nozzles are driven while moving a head in which the N nozzles forming the dots are provided at an interval of a nozzle pitch k, moving from one end of the print medium to the other end in a direction crossing the nozzle arrangement. And a step of printing the image by repeatedly performing main scanning, which is an operation of forming dots, to form a plurality of rasters as rows of dots on the print medium, and
The step of storing the dither matrix is a dither matrix specific to the printing apparatus,
A predetermined inspection image for inspecting a positional deviation between an actual formation position where the dots are formed on the print medium and a design formation position is printed using the printing apparatus,
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), Detecting the displacement at each pixel position in the block from the printed inspection image;
The gist of the present invention is a step of storing a matrix in which a threshold value of the dither matrix is set based on the detection result of the positional deviation.

  Also in the second printing apparatus and the second printing method of the present invention, each printing apparatus actually detects the position of the dot actually formed in the printing apparatus on the assumption that the position deviates from the design position. An image can be printed using a dither matrix in which a threshold is set based on the positional deviation. The positional deviation of each printing apparatus can be detected in the manufacturing process of the printing apparatus or can be detected in the final process for manufacturing the printing apparatus. By printing an image using a dither matrix that takes account of misregistration in this way, a high-quality image with properly dispersed dots can be obtained without making adjustments to bring the dot formation position closer to the design formation position. It becomes possible to print.

Furthermore, if the misalignment of each printing apparatus is detected, the present invention can also be grasped as a printing apparatus having the following mode, by focusing on the fact that an appropriate dither matrix can be formed from the detection result. is there. First, in the final process during or after manufacturing of the printing apparatus, a positional shift for each printing apparatus is detected and stored. Prior to printing an image, the stored misregistration is read out, and a dither matrix that takes this into account can be generated so as to be understood as a printing apparatus that prints an image. That is, the third printing apparatus of the present invention is
A printing apparatus that applies a dither method to image data, performs halftone processing, and forms dots on a print medium based on the result of the halftone processing to print an image,
A head in which N nozzles forming the dots are provided at intervals of a nozzle pitch k;
The main scanning, which is the operation of forming the dots by driving the nozzles while moving the head in the direction crossing the arrangement of the nozzles from one end to the other end of the printing medium, is repeated on the printing medium. A raster forming means for printing the image by forming a plurality of rasters, each of which is a row of dots,
A misregistration detection result storage means for storing a detection result for the printing apparatus of a misregistration between an actual formation position for forming dots on the print medium and a design formation position;
A dither matrix generating means for generating the dither matrix by setting a threshold value of the dither matrix used in the dither method based on the stored detection result of the misregistration, and
The misregistration detection result storage means is a misregistration detection result for the printing apparatus.
Printing a predetermined inspection image for inspecting the displacement using the printing apparatus;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), Which is means for storing the positional deviation detected from the inspection image at each pixel position in the block.

Further, the third printing method of the present invention corresponding to the printing apparatus described above is
A printing method that applies a dither method to image data, performs halftone processing, and forms dots on a print medium based on the result of the halftone processing to print an image,
The nozzles are driven while moving a head in which the N nozzles forming the dots are provided at an interval of a nozzle pitch k, moving from one end of the print medium to the other end in a direction crossing the nozzle arrangement. A step of printing the image by repeatedly performing main scanning, which is an operation of forming dots, to form a plurality of rasters that are rows of dots on the print medium;
Storing a detection result for the printing apparatus of a positional deviation between an actual formation position for forming dots on the print medium and a design formation position;
Generating a dither matrix by setting a threshold value of a dither matrix used in the dither method based on the stored detection result of misregistration, and
The step of storing the detection result includes a detection result of misregistration for the printing apparatus,
Printing a predetermined inspection image for inspecting the displacement using the printing apparatus;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), Which is a step of storing the positional deviation detected from the inspection image at each pixel position in the block.

  Also in the third printing apparatus and the third printing method of the present invention, the misregistration actually detected for the printing apparatus is stored for each printing apparatus, and the misregistration is taken into consideration prior to image printing. The image can be printed using a properly generated dither matrix. For this reason, it is possible to print a high-quality image in which dots are appropriately dispersed without performing adjustment for bringing the dot formation position closer to the designed formation position.

Furthermore, the present invention allows a computer to read a program for realizing the above-described various printing methods, a method of generating a dither matrix, a method of detecting dot misregistration, and a method of adjusting misregistration. It can also be realized using a computer. Therefore, the present invention includes the following program or a mode as a recording medium on which the program is recorded. That is, the program of the present invention corresponding to the first printing method described above is
A program for implementing a method for performing a halftone process by applying a dither method to image data and printing an image by forming dots on a print medium based on the result of the halftone process using a computer Because
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. A function of forming a plurality of raster lines of dots on the print medium by repeatedly performing main scanning, which is an operation of forming dots by driving;
A predetermined inspection image for inspecting a positional deviation between an actual formation position where the dots are formed on the print medium and a design formation position by forming a plurality of rasters on the print medium. The ability to print
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), A function of detecting the displacement at each pixel position in the block from the inspection image;
The gist is to realize a function of generating the dither matrix by using a computer by setting a threshold value of the dither matrix used in the dither method based on the detection result of the displacement.

The recording medium of the present invention corresponding to the above program is
A recording medium in which a computer program is recorded so that a halftone process is applied to image data, a dot is formed on the print medium and an image is printed based on the result of the halftone process Because
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. A function of forming a plurality of raster lines of dots on the print medium by repeatedly performing main scanning, which is an operation of forming dots by driving;
A predetermined inspection image for inspecting a positional deviation between an actual formation position where the dots are formed on the print medium and a design formation position by forming a plurality of rasters on the print medium. The ability to print
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), A function of detecting the displacement at each pixel position in the block from the inspection image;
The gist is that a program for realizing the function of generating the dither matrix by using a computer is recorded by setting a threshold value of the dither matrix used in the dither method based on the detection result of the displacement. To do.

The program corresponding to the second printing method of the present invention described above is
A program for implementing a method for performing a halftone process by applying a dither method to image data and printing an image by forming dots on a print medium based on the result of the halftone process using a computer Because
A function of storing a dither matrix that is referred to in the halftone process and is unique to the printing apparatus;
The nozzles are driven while moving a head in which the N nozzles forming the dots are provided at an interval of a nozzle pitch k, moving from one end of the print medium to the other end in a direction crossing the nozzle arrangement. In addition, the main scanning, which is the operation of forming dots, is repeatedly performed to form a plurality of rasters that are rows of dots on the print medium, thereby realizing the function of printing the image using a computer,
The function of storing the dither matrix is as a dither matrix specific to the printing apparatus,
A predetermined inspection image for inspecting a positional deviation between an actual formation position where the dots are formed on the print medium and a design formation position is printed using the printing apparatus,
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), Detecting the displacement at each pixel position in the block from the printed inspection image;
The gist of the present invention is a function of storing a matrix in which a threshold value of the dither matrix is set based on the detection result of the displacement.

The recording medium of the present invention corresponding to the above program is
A recording medium in which a computer program is recorded so that a halftone process is applied to image data, a dot is formed on the print medium and an image is printed based on the result of the halftone process Because
A function of storing a dither matrix that is referred to in the halftone process and is unique to the printing apparatus;
The nozzles are driven while moving a head in which the N nozzles forming the dots are provided at an interval of a nozzle pitch k, moving from one end of the print medium to the other end in a direction crossing the nozzle arrangement. A program that realizes the function of printing the image by using a computer by repeatedly performing main scanning, which is an operation of forming dots, and forming a plurality of rasters that are rows of dots on the print medium is recorded. As well as
The function of storing the dither matrix is as a dither matrix specific to the printing apparatus,
A predetermined inspection image for inspecting a positional deviation between an actual formation position where the dots are formed on the print medium and a design formation position is printed using the printing apparatus,
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), Detecting the displacement at each pixel position in the block from the printed inspection image;
The gist of the present invention is a function of storing a matrix in which a threshold value of the dither matrix is set based on the detection result of the displacement.

A program corresponding to the above-described third printing method of the present invention is as follows.
A program for implementing a method for performing a halftone process by applying a dither method to image data and printing an image by forming dots on a print medium based on the result of the halftone process using a computer Because
The nozzles are driven while moving a head in which the N nozzles forming the dots are provided at an interval of a nozzle pitch k, moving from one end of the print medium to the other end in a direction crossing the nozzle arrangement. A function of printing the image by repeatedly performing main scanning, which is an operation of forming dots, to form a plurality of rasters that are rows of dots on the print medium;
A function of storing a detection result for the printing apparatus of a positional deviation between an actual formation position for forming dots on the print medium and a design formation position;
A function for generating the dither matrix is realized by using a computer by setting a threshold value of the dither matrix used in the dither method based on the stored detection result of the misregistration.
The function of storing the detection result is a detection result of misregistration for the printing apparatus.
Printing a predetermined inspection image for inspecting the displacement using the printing apparatus;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), And a function of storing the positional deviation detected from the inspection image at each pixel position in the block.

The recording medium of the present invention corresponding to the above program is
A recording medium in which a computer program is recorded so that a halftone process is applied to image data, a dot is formed on the print medium and an image is printed based on the result of the halftone process Because
The nozzles are driven while moving a head in which the N nozzles forming the dots are provided at an interval of a nozzle pitch k, moving from one end of the print medium to the other end in a direction crossing the nozzle arrangement. A function of printing the image by repeatedly performing main scanning, which is an operation of forming dots, to form a plurality of rasters that are rows of dots on the print medium;
A function of storing a detection result for the printing apparatus of a positional deviation between an actual formation position for forming dots on the print medium and a design formation position;
By setting a threshold value of the dither matrix used in the dither method based on the stored detection result of misregistration, a program for realizing the function of generating the dither matrix using a computer is recorded. And
The function of storing the detection result is a detection result of misregistration for the printing apparatus.
Printing a predetermined inspection image for inspecting the displacement using the printing apparatus;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), And a function of storing the positional deviation detected from the inspection image at each pixel position in the block.

  If these programs are read into a computer and the various functions described above are realized, the dots are properly dispersed without adjusting the positions of the dots formed on the print medium to approach the designed positions. It is possible to obtain a high-quality image.

The program of the present invention corresponding to the above-described dither matrix generation method is as follows.
A program for realizing, using a computer, a method for generating a dither matrix that is referred to when halftone processing is performed by applying a dither method,
While moving the head in which N nozzles for forming dots on the print medium are provided at intervals of the nozzle pitch k, moving from one end of the print medium to the other end in a direction intersecting with the arrangement of the nozzles, A function of performing main scanning as an operation of driving the nozzle to form dots;
By repeating the main scanning and forming a plurality of rasters as dot rows on the print medium, the positions of the actual formation position and the design formation position where the dots are formed on the print medium. A function of printing a predetermined inspection image for inspecting misalignment;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), A function of detecting the displacement at each pixel position in the block from the inspection image;
The gist is to realize, using a computer, a function of setting a threshold value of each pixel of the dither matrix based on the detection result of the displacement.

The recording medium of the present invention corresponding to the above program is
A recording medium that records a computer-readable program for generating a dither matrix to be referred to when halftone processing is performed by applying a dither method,
While moving the head in which N nozzles for forming dots on the print medium are provided at intervals of the nozzle pitch k, moving from one end of the print medium to the other end in a direction intersecting with the arrangement of the nozzles, A function of performing main scanning as an operation of driving the nozzle to form dots;
By repeating the main scanning and forming a plurality of rasters as dot rows on the print medium, the positions of the actual formation position and the design formation position where the dots are formed on the print medium. A function of printing a predetermined inspection image for inspecting misalignment;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), A function of detecting the displacement at each pixel position in the block from the inspection image;
The gist of the invention is that a program for realizing a function of setting a threshold value of each pixel of the dither matrix using a computer is recorded based on the detection result of the displacement.

  When these programs are read into a computer and the various functions described above are realized, a dither matrix is created in which dots are properly dispersed in consideration of the fact that dot formation positions differ from design formation positions. Can be generated.

Further, the program of the present invention corresponding to the above-described method for detecting the positional deviation of dots is as follows:
A printing apparatus for printing an image by forming dots on a print medium, and a method for detecting a misalignment between a design position of the dots formed on the print medium and a position at which dots are actually formed. A program for realizing using
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. A function of performing main scanning, which is an operation of driving to form dots,
A function of printing a predetermined inspection image for inspecting the misregistration of the dots by repeatedly performing the main scanning and forming a plurality of rasters as a row of dots on the print medium;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), And a function of detecting the positional shift at each pixel position in the block from the inspection image using a computer.

The recording medium of the present invention corresponding to the above program is
A printing apparatus that prints an image by forming dots on a print medium is a computer program that detects a positional shift between a design position of dots formed on the print medium and a position where dots are actually formed. A recording medium recorded so as to be readable by
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. A function of performing main scanning, which is an operation of driving to form dots,
A function of printing a predetermined inspection image for inspecting the misregistration of the dots by repeatedly performing the main scanning and forming a plurality of rasters as a row of dots on the print medium;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), And recording a program for realizing, using a computer, the function of detecting the positional deviation at each pixel position in the block from the inspection image.

  If these programs are read into a computer and the various functions described above are realized, it is possible to easily detect the positional deviation of the dots at each pixel on the print medium.

Furthermore, the program of the present invention corresponding to the above-described dot misregistration adjustment method is
A method for adjusting a positional deviation between a design position of a dot formed on the print medium and a position where the dot is actually formed by a printing apparatus that forms an image on a print medium and prints an image. A program for realizing using
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. A function of performing main scanning, which is an operation of driving to form dots,
A function of printing a predetermined inspection image for inspecting the misregistration of the dots by repeatedly performing the main scanning and forming a plurality of rasters as a row of dots on the print medium;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), A function of detecting the displacement at each pixel position in the block from the inspection image;
The gist is to realize, using a computer, a function of adjusting the dot formation position based on the detection result of the displacement.

The recording medium of the present invention corresponding to the above program is
A computer that prints an image by forming dots on a print medium, and a computer program that adjusts the positional deviation between the design position of the dots formed on the print medium and the positions where dots are actually formed A recording medium recorded so as to be readable by
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. A function of performing main scanning, which is an operation of driving to form dots,
A function of printing a predetermined inspection image for inspecting the misregistration of the dots by repeatedly performing the main scanning and forming a plurality of rasters as a row of dots on the print medium;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), A function of detecting the displacement at each pixel position in the block from the inspection image;
The gist of the invention is that a program for realizing, using a computer, the function of adjusting the dot formation position is recorded based on the detection result of the displacement.

  If these programs are read into a computer and the various functions described above are realized, the dot formation position can be adjusted appropriately and simply.

Hereinafter, in order to clarify the contents of the present invention described above, various embodiments will be described in the following order.
A. Summary of Examples:
B. Device configuration:
C. Overview of image printing process:
D. Detection method of dot displacement:
D-1. Misalignment detection principle:
D-2. Misalignment detection method:
D-3. Variation of the displacement detection method:
D-4. Other variations:
E. Dither matrix generation process:
E-1. Overview of dither matrix generation:
E-2. Processing content:
F. Variation:
F-1. First modification:
F-2. Second modification:

A. Summary of Examples:
Prior to detailed description of various embodiments, an outline of a representative embodiment will be described with reference to FIG. FIG. 1 is an explanatory diagram showing an outline of a printing apparatus 10 as a typical embodiment. As shown in the figure, a halftone module 12 and a head 16 are mounted on the printing apparatus 10. When the image data of the image to be printed is input, the halftone module 12 performs a halftone process by applying a dither method to the image data while referring to the dither matrix 14, and the obtained halftone process The result is output toward the head 16.

  In FIG. 1, the halftone module 12, the dither matrix 14, the head 16, and the like are displayed as being mounted on the integrated printing apparatus 10, but the halftone module 12, the dither matrix 14, etc. It may be mounted on an image processing apparatus separate from the printing apparatus, and substantially one printing apparatus may be configured as a whole including the image processing apparatus.

  The head 16 is provided with a plurality (N) of nozzles Nz for forming dots on the printing paper at intervals of the nozzle pitch k. An operation of moving the head 16 from one end to the other end of the printing paper while forming dots (main scanning), and an operation of moving the positional relationship between the head 16 and the printing paper in a direction crossing the main scanning direction. (Sub-scanning) can be performed. Upon receiving the halftone processing result from the halftone module 12, the head 16 prints an image by repeatedly performing main scanning and sub-scanning to form dots on the printing paper.

  As described above, the printing apparatus 10 forms dots using the plurality of nozzles Nz while repeating the main scanning and the sub-scanning. Accordingly, if the timing for forming dots with the nozzle Nz is slightly shifted while the head is being scanned, or even if there is a slight variation in the sub-scanning amount, the position of the dots formed on the printing paper is shifted. Furthermore, since dots are formed using a plurality of nozzles Nz, the dot formation positions may differ slightly depending on the individual nozzles Nz. If the dot formation position is shifted, the print image quality is deteriorated.

  In order to avoid deterioration in print image quality due to dot misalignment, the printing apparatus 10 shown in FIG. 1 employs the following method. First, an inspection image for inspecting dot misregistration is printed on printing paper. The inspection image is printed by supplying data (inspection image data) for printing the inspection image from the inspection image data output module 20 to the head 16. Alternatively, the inspection image may be printed by supplying the image data of the inspection image to the halftone module 12 and outputting the data subjected to the halftone process to the head 16.

  Next, the printed inspection image is read by the scanner 22, and the read data is supplied to the misregistration detection module 24. The scanner 22 that reads the inspection image may be provided separately from the printing apparatus 10 or may be incorporated in the printing apparatus 10. The misregistration detection module 24 analyzes the received data and determines misregistration at each pixel position in the block when n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are used as a block. To detect. Here, s is the number of main scans required to form one raster when printing an inspection image. N and m are arbitrary positive integers. As will be described in detail later, when printing an image by performing s main scans per raster using N nozzles at an interval of a nozzle pitch k, s pixels in the main scan direction and sub scan directions are performed. An image is printed in units of N × k pixels while repeating the same operation. Correspondingly, it has been found that dot misalignment also occurs in such a cycle. Therefore, if a pixel misalignment is detected for each pixel position in the block with n × s pixels in the main scanning direction and m × N × k pixels in the sub-scanning direction as a block, all pixels of the image are detected. Misalignment can be determined.

  The dither matrix generation module 26 generates a dither matrix based on the position shift data detected by the position shift detection module 24 for each pixel in the block. In other words, on the assumption that the positions of the dots actually formed on the printing paper are shifted as shown in the detected positional deviation data, the dots are properly formed in the shifted positions. The threshold value of the dither matrix is set so as to be distributed. When the halftone module 12 performs the halftone process on the image data, the process is performed with reference to the dither matrix thus generated. The dither matrix threshold value is appropriately set based on the actual dot position formed by shifting in each pixel, so that high image quality can be achieved without performing complicated adjustments to eliminate the dot position shift. It is possible to print an image.

  In the above, the printing apparatus has been described as a typical embodiment, but the present invention is not limited to the printing apparatus and can be understood in various aspects. Hereinafter, these various examples will be described in detail.

B. Device configuration :
For convenience of explanation, in the following, a computer that performs halftone processing and data analysis, a printer that is equipped with a head and that actually forms dots on printing paper, and a scanner that reads an image printed on printing paper And are configured separately, and the whole will be described as a single printing system. Of course, it is also possible to configure all of them integrally in one casing, or to select any two and integrally configure them in one casing.

  FIG. 2 is an explanatory diagram illustrating a configuration of the computer 100 according to the present exemplary embodiment that performs image processing (to be described later) such as halftone processing, data analysis, and the like. As is well known, the computer 100 is configured by connecting a ROM 104, a RAM 106, and the like with a bus 116 around a CPU 102. The computer 100 is used to drive a disk controller DDC 109 for reading data from the flexible disk 124, the compact disk 126, and the like, and peripheral device interfaces PIF 108 and CRT 114 used to exchange data with peripheral devices. A video interface VIF 112 and the like are connected. The PIF 108 is connected to a hard disk 118, a printer 200 described later, and the like. Further, if the digital camera 120 or the like is connected to the PIF 108, an image photographed by the digital camera 120 or the like can be printed. As will be described later, when inspecting the positional deviation of dots, in this embodiment, the scanner 122 reads the inspection image and analyzes the read data. The scanner 122 for reading the inspection image is also connected to the computer via the PIF 108. 100. If the network interface card NIC 110 is installed, the computer 100 can be connected to the communication line 300 to acquire data stored in the storage device 310 connected to the communication line.

  FIG. 3 is an explanatory diagram illustrating a schematic configuration of the printer 200 according to the present exemplary embodiment. The printer 200 is an ink jet printer capable of forming dots of four color inks of cyan, magenta, yellow, and black. Of course, in addition to these four colors of ink, ink dots of a total of six colors including cyan (light cyan) ink with a low dye concentration or pigment concentration and magenta (light magenta) ink with a low dye concentration or pigment concentration. A formable ink jet printer can also be used. In the following, cyan ink, magenta ink, yellow ink, black ink, light cyan ink, and light magenta ink are respectively referred to as C ink, M ink, Y ink, K ink, LC ink, and LM ink as necessary. It shall be abbreviated.

  As shown, the printer 200 drives a print head 241 mounted on the carriage 240 to eject ink and form dots, and the carriage 240 is reciprocated in the axial direction of the platen 236 by the carriage motor 230. It includes a mechanism, a mechanism for transporting the printing paper P by the paper feed motor 235, a control circuit 260 for controlling dot formation, carriage 240 movement, and printing paper transport.

  An ink cartridge 242 that stores K ink and an ink cartridge 243 that stores various inks of C ink, M ink, and Y ink are mounted on the carriage 240. When the ink cartridges 242 and 243 are mounted on the carriage 240, each ink in the cartridge is supplied to ink discharge heads 244 to 247 for each color provided on the lower surface of the print head 241 through an introduction pipe (not shown). The ink ejection heads 244 to 247 for each color form ink dots on the print medium by ejecting ink droplets using the ink thus supplied.

  The control circuit 260 is mainly composed of a CPU, a ROM, a RAM, a peripheral device interface PIF, etc., and a D / A converter that converts digital data into an analog signal. Of course, the same function may be realized by hardware or firmware without mounting the CPU. The control circuit 260 controls the main scanning operation and the sub scanning operation of the carriage 240 by controlling the operations of the carriage motor 230 and the paper feed motor 235. Further, ink droplets are ejected by driving the print head 241 at an appropriate timing in accordance with the main scanning and the sub scanning of the carriage 240. In this way, under the control of the control circuit 260, ink droplets are ejected from the ink ejection heads 244 to 247 of each color at an appropriate timing. As a result, ink dots are formed on the printing paper P, and a color image is printed. The

  Note that various methods can be applied to the method of ejecting ink droplets from the ink ejection heads of the respective colors. That is, a method of ejecting ink using a piezo element, a method of ejecting ink droplets by generating bubbles in the ink passage with a heater arranged in the ink passage, and the like can be used. Also, instead of ejecting ink, use a printer that uses a method such as thermal transfer to form ink dots on printing paper, or a method that uses static electricity to attach each color toner powder onto the print medium. It is also possible to do.

  FIG. 4 is an explanatory diagram showing a state in which a plurality of nozzles Nz for ejecting ink droplets are formed on the bottom surface of the ink ejection heads 244 to 247 for each color. As shown in the figure, on the bottom surface of each color ink ejection head, four sets of nozzle rows for ejecting ink droplets of each color are formed, and 48 nozzles Nz are nozzles in one set of nozzle rows. They are arranged in a zigzag pattern at intervals of the pitch k. These nozzles are driven under the control of the control circuit 260, and form ink dots on the printing paper by ejecting ink droplets.

  Further, the printer 200 according to the present embodiment can control the size of the ink dots by controlling the size of the ink droplets to be ejected. Hereinafter, a method for forming ink dots of different sizes by the printer 200 will be described. First, the internal structure of the nozzles that eject each color ink will be described as preparation. FIG. 5A is an explanatory diagram showing the internal structure of a nozzle that ejects ink. Each of the ink discharge heads 244 to 247 for each color is provided with a plurality of such nozzles. As shown in the figure, each nozzle is provided with an ink passage 255 and an ink chamber 256, and a piezo element PE is provided on the upper surface of the ink chamber. When the ink cartridges 242 and 243 are mounted on the carriage 240, the ink in the cartridge is supplied to the ink chamber 256 via the ink gallery 257. As is well known, the piezo element PE is an element that performs electro-mechanical energy conversion at an extremely high speed by distorting the crystal structure when a voltage is applied. In this embodiment, the side wall of the ink chamber 256 is deformed by applying a voltage having a predetermined waveform between the electrodes provided at both ends of the piezo element PE. As a result, the volume of the ink chamber 256 is reduced, and ink corresponding to the reduced volume is ejected from the nozzle Nz as ink droplets Ip. The ink droplet Ip soaks into the printing paper P mounted on the platen 236, whereby ink dots are formed on the printing paper.

  FIG. 5B is an explanatory diagram showing the principle of changing the size of the ink droplets ejected by controlling the voltage waveform applied to the piezo element PE. In order to eject the ink droplet Ip from the nozzle, a voltage is applied to the piezo element PE, the ink is once sucked into the ink chamber 256 from the ink gallery 257, and then a positive voltage is applied to the piezo element PE. The ink chamber volume is reduced and the ink droplet Ip is ejected. Here, if the ink suction speed is appropriate, ink corresponding to the amount of change in the ink chamber volume is sucked, but if the suction speed is too fast, there is a passage resistance between the ink gallery 257 and the ink chamber 256. For this reason, the inflow of ink from the ink gallery 257 is not in time. As a result, the ink in the ink passage 255 flows back into the ink chamber, and the ink interface near the nozzle is largely retracted. A voltage waveform a shown by a solid line in FIG. 5B shows a waveform for sucking ink at an appropriate speed, and a voltage waveform b shown by a broken line shows an example of a waveform for sucking at a speed larger than the appropriate speed. .

  When a positive voltage is applied to the piezo element PE in a state where sufficient ink is supplied into the ink chamber 256, an ink droplet Ip having a volume corresponding to the volume reduction of the ink chamber 256 is ejected from the nozzle Nz. On the other hand, when a positive voltage is applied in a state where the ink supply amount is insufficient and the ink interface is largely retracted, the ejected ink droplets become small ink droplets. As described above, in the printer 200 of this embodiment, the size of the ejected ink droplet is controlled by controlling the negative voltage waveform applied before ejecting the ink droplet and changing the ink suction speed. This makes it possible to form three types of ink dots, large dots, medium dots, and small dots.

  Of course, not only three types but also other types of dots can be formed. Further, the size of the ink dots formed on the printing paper may be controlled by using a method in which a plurality of fine ink droplets are ejected at a time and the number of ejected ink droplets is controlled.

  The printer 200 having the above-described hardware configuration drives the carriage motor 230 to move the ink ejection heads 244 to 247 of the respective colors in the main scanning direction with respect to the printing paper P, and the paper feed motor 235. Is driven to move the printing paper P in the sub-scanning direction. The control circuit 260 ejects ink droplets by driving the nozzles at an appropriate timing while repeating main scanning and sub-scanning of the carriage 240. By doing so, ink dots are formed at appropriate positions on the printing paper P, and as a result, an image is printed.

C. Overview of image printing process:
FIG. 6 is a flowchart showing a flow of processing in which the computer 100 according to the present embodiment performs predetermined image processing on image data to generate print data, supplies the obtained print data to the printer 200, and prints an image. It is. Although the image printing process is described here as being performed by the computer 100, it is of course possible to perform this process on the printer 200 side. In the following, the outline of the image printing process of this embodiment will be described with reference to the flowchart of FIG.

  When the image printing process is started, the computer 100 first starts reading image data to be converted (step S100). Here, the image data will be described as what is called RGB color image data in which gradation values for RGB colors are set for each of a plurality of pixels constituting the image. The three colors R (red), G (green), and B (blue) are called the three primary colors of light, and these three colors are additively mixed to express a wide color gamut from achromatic to chromatic. It is possible. Of course, the image data is not limited to RGB color image data. For example, gradation values are set for a plurality of colors including C (cyan), M (magenta), and Y (yellow), which are called the three primary colors of ink. Image data can also be used. Furthermore, the present invention can be similarly applied to monochrome image data as well as color image data.

  Subsequently, the computer 100 performs a process of converting the resolution of the read image data into a resolution (printing resolution) for the printer 200 to print (step S102). When the resolution of the image data is lower than the printing resolution, interpolation is performed between adjacent pixels, and new image data is set to increase the resolution. Alternatively, simply, the number of pixels may be simply increased, and the same image data as the original pixel may be set for the increased pixels. On the other hand, when the resolution of the read image data is higher than the print resolution, the resolution is lowered by thinning out the image data at a certain rate from between adjacent pixels. In the resolution conversion process, image data is generated at an appropriate ratio with respect to the read image data, or thinned out to convert the resolution of the read image data into a print resolution.

  When the resolution conversion process ends, the computer 100 starts the color conversion process (step S104). Color conversion processing is processing for converting image data expressed by a combination of R, G, and B gradation values into image data expressed by a combination of gradation values of each color used for printing. It is. As described above, the printer 200 prints an image using four color inks of C, M, Y, and K. Therefore, in color conversion processing, processing is performed to convert image data expressed by RGB colors into data expressed by gradation values of C, M, Y, and K colors.

  The color conversion process can be performed quickly by referring to a three-dimensional numerical table called a color conversion table (LUT). FIG. 7 is an explanatory diagram conceptually showing an LUT referred to for color conversion processing. As shown in the figure, when the color space is considered by taking the R axis, the G axis, and the B axis as three orthogonal axes, all RGB image data is always displayed in association with coordinate points in the color space. be able to. From this, if each of the R-axis, G-axis, and B-axis is subdivided and a large number of grid points are set in the color space, each grid point can be considered to represent RGB image data. The gradation values of the C, M, Y, and K colors corresponding to the RGB image data can be associated with each grid point. The LUT is a three-dimensional number table in which gradation values of each color of C, M, Y, and K are stored in association with the grid points thus provided in the color space. If color conversion processing is performed based on the correspondence between the RGB color image data stored in the LUT and the gradation data of each color of C, M, Y, and K, the RGB color image data is converted into C, M , Y, and K can be quickly converted into gradation data. If the gradation values of each color including other colors such as LC and LM are set in addition to CMYK colors at the grid points of the LUT, the RGB image data can be converted into image data of these colors. Is possible.

  The computer 100 performs halftone processing on the image data obtained by color conversion (step S106). Halftone processing is the following processing. The image data of each color of CMYK obtained by the color conversion process can take values from gradation value 0 to gradation value 255 for each pixel if the image data is 1-byte data. On the other hand, since the printer 200 displays an image by forming either large, medium, or small dots, for each pixel, “form a large dot”, “form a medium dot”, “small” Only one state of “form dot” or “do not form dot” can be taken. Therefore, it is necessary to convert image data having 256 gradations for each pixel into data (dot data) expressed by the presence or absence of dot formation for each pixel. Halftone processing is processing for converting image data into dot data in this way. As described above, since the printer 200 of this embodiment can form three types of dots, large dots, medium dots, and small dots, halftone processing can form dots for each of these three types of dots. The presence or absence will be judged.

  In the halftone processing of this embodiment, halftone processing is performed using a method called a dither method. In the dither method, the threshold value preset in the dither matrix and the gradation value of the image data are compared for each pixel. This is a method of obtaining dot data for each pixel by determining that a dot is not formed for a larger pixel.

  In the following, a method of generating dot data for each of large, medium, and small dots by applying the dither method will be described. As a preparation for this, first, the principle of determining the presence or absence of dot formation using the dither method is described. A brief overview is provided.

  FIG. 8 is an explanatory diagram illustrating an enlarged part of the dither matrix. In the illustrated matrix, threshold values that are uniformly selected from the range of gradation values 0 to 255 are randomly stored in a total of 4096 pixels, 64 pixels in the vertical and horizontal directions. Here, the threshold gradation value is selected from the range of 0 to 255. In this embodiment, the image data is 1-byte data, and the gradation value assigned to the pixel takes a value of 0 to 255. It corresponds to getting. The size of the dither matrix is not limited to 64 pixels in the vertical and horizontal directions as illustrated in FIG. 8, and can be set to various sizes including those having different numbers of vertical and horizontal pixels. It is.

  FIG. 9 is an explanatory diagram conceptually showing a state in which the presence / absence of dot formation is determined for each pixel with reference to the dither matrix. When determining the presence or absence of dot formation, first, the gradation value of the pixel of interest (the pixel of interest) as the object of determination is compared with the threshold value stored at the corresponding position in the dither matrix. The thin dashed arrows shown in the figure schematically represent that the gradation value of the pixel of interest is compared with the threshold value stored at the corresponding position in the dither matrix. When the gradation value of the pixel of interest is larger than the threshold value of the dither matrix, it is determined that a dot is formed on that pixel. On the contrary, when the threshold value of the dither matrix is larger, it is determined that no dot is formed in the pixel.

  In the example shown in FIG. 9, the image data of the pixel at the upper left corner of the image data has a gradation value of 180, and the threshold value stored at the position corresponding to this pixel on the dither matrix is 1. Accordingly, for the pixel in the upper left corner, the gradation value 180 of the image data is larger than the threshold value 1 of the dither matrix, and therefore it is determined that a dot is formed on this pixel. An arrow indicated by a solid line in FIG. 9 schematically shows a state in which it is determined that a dot is to be formed in this pixel and the determination result is written in the memory. On the other hand, for the pixel on the right side of this pixel, the gradation value of the image data is 130, and the threshold value of the dither matrix is 177. Since the threshold value is larger, it is determined that no dot is formed for this pixel. In this way, by comparing the gradation value of the image data with the threshold value set in the dither matrix, it is possible to determine whether or not dots are formed for each pixel.

  FIG. 10 is a flowchart showing the flow of the halftone process performed during the image printing process of this embodiment. In the halftone process shown in FIG. 10, the dot data is generated by determining whether or not to form dots on each pixel while applying the dither method for each of the large, medium, and small dots. Hereinafter, it demonstrates according to a flowchart.

  When the halftone process is started, the computer 100 first converts the image data for each color of CMYK into the recording density data for each of the large, medium, and small dots (step S200). The recording density data is data that defines the density at which dots are formed. The larger the recording density data, the higher the dots are formed. The gradation value “255” of the recording density data indicates that the dots are formed in all the pixels. “0” indicates that no dot is formed in any pixel. Such conversion to recording density data is performed by referring to a recording density conversion table as shown in FIG. In the recording density conversion table, recording density data for small dots, medium dots, and large dots is set for the gradation value of the image data obtained by color conversion.

  As shown in the figure, in the area where the image data is near the gradation value “0”, the recording density data for medium dots and large dots are both gradation values “0”, and the recording density data for small dots. Only have gradation values other than “0”. The recording density data of small dots increases as the gradation value of the image data increases, but when the image data reaches a certain gradation value, it starts to decrease conversely, and instead the recording of medium dots Density data begins to increase. As the gradation value of the image data further increases, the recording density data for small dots decreases accordingly, and the recording density data for medium dots increases. When the image data reaches a certain gradation value, the medium dot recording density data starts to decrease, and instead, the large dot recording density data gradually increases. In the RAM 106 of the computer 100, a table in which the recording density data for each of the large, medium, and small dots is set in this manner is stored in advance. In step S200 of FIG. 10, referring to this recording density conversion table, CMYK image data for each color is converted for each color into recording density data for large dots, recording density data for medium dots, and recording density data for small dots. Perform the process.

  When the recording density data for each of the large, medium, and small dots is obtained in this way, first, it is determined whether or not the large dots are formed (step S202). This determination is made by comparing the recording density data of large dots and the threshold value set in the dither matrix. If the recording density data is larger, it is determined that a large dot is formed, and conversely, the threshold value is larger. It is determined that no large dot is formed. Then, for the pixel determined to form a large dot (step S204: yes), a process of writing dot data “11” is performed (step S206). The dot data “11” is data indicating that a large dot is formed on the pixel. For a pixel determined not to form a large dot (step S204: no), a process for determining whether to form a medium dot is started.

  The determination of whether or not the medium dot is formed is performed as follows. First, medium dot recording density data is added to large dot recording density data to calculate intermediate data for determining whether or not medium dots are formed (step S208). The intermediate data calculated in this way is compared with the above-mentioned dither matrix threshold value to determine whether or not a medium dot is formed (step S210). That is, it is determined that a medium dot is formed for a pixel whose intermediate data is larger than the threshold value, and a medium dot is determined not to be formed for a pixel whose threshold value is larger. Then, for a pixel that forms a medium dot (step S212: yes), a process of writing dot data “10” representing the formation of a medium dot is performed (step S214). For a pixel determined not to form a medium dot (step S212: no), a process for determining whether or not to form a small dot is started.

  Whether or not small dots are formed is determined using intermediate data for small dots. The intermediate data for small dots is calculated by adding the recording density data for small dots to the intermediate data for medium dots (step S216). Next, it is determined whether or not a small dot is formed by comparing the calculated intermediate data for small dots with the above-described dither matrix threshold (step S218). Then, it is determined that the small dot intermediate data is larger than the threshold value, and it is determined that the small dot is formed. For the pixel forming the small dot (step S220: yes), the dot data indicating that the small dot is formed. “01” is stored (step S222). On the contrary, it is determined that no small dot is formed on a pixel having a threshold larger than that of the intermediate data for small dots (step S220: no), and a dot indicating that no dot is formed on this pixel. Data “00” is stored (step S224).

  By performing the above operation on the image data of each color of CMYK obtained by the color conversion process, it is possible to obtain dot data representing the presence / absence of formation of large, medium, and small dots for each color. Therefore, the process returns to the image printing process shown in FIG. In step S108 in FIG. 6, as described above, a process for converting the image data after color conversion into dot data is performed.

  When the halftone process ends as described above, the computer 100 starts the interlace process (step S108). Interlace processing is the following processing. The printer 200 prints an image by forming dots in each pixel according to dot data obtained by halftone processing, but does not form dots in order from the pixels at the edge of the image. In other words, the order in which the printer 200 forms dots on the printing paper is different from the order in which pixels are arranged on the image. Therefore, it is necessary to rearrange the dot data obtained by the halftone process in accordance with the order in which the printer 200 forms dots on the printing paper. In the interlace processing, in consideration of the order in which the printer 200 forms dots in this way, the dot data is converted into print data by rearranging in the order to be transferred to the printer 200, and the obtained print data is converted to the printer 200. It is a process to output to. Here, for convenience of explanation, a method in which the printer 200 forms dots on the printing paper while driving the print head 241 will be described using a specific example.

  FIG. 12 is an explanatory diagram conceptually showing how the print head of the printer 200 forms dots on the printing paper while repeating main scanning and sub-scanning. As described above with reference to FIG. 4, the print head 241 of this embodiment is provided with a large number of nozzles for each color (in this embodiment, 48 nozzles for each color), but the description is complicated. In order to avoid this, FIG. 12 will be described assuming that the number of nozzles is four. Nz1, Nz2, Nz3, and Nz4 shown in the figure represent these four nozzles. The nozzle pitch is 3, and one raster is formed by dividing it into two main scans. Although the printer 200 can form large, medium, and small dots, it is assumed here that only one type of dot is formed.

  The left half of FIG. 12 shows how the print head gradually moves relative to the printing paper by performing sub-scanning. A vertically long rectangle shown in the left half of FIG. 12 represents a print head for one color. As shown in the figure, each nozzle head is provided with four nozzles. Further, since the nozzle pitch is set to “3”, a distance corresponding to two nozzles (nozzle if viewed from the center of the nozzles) as shown by a broken line in the figure. A distance equivalent to three) is provided.

  The right half of FIG. 12 shows a state in which dots are formed on the printing paper by ejecting ink droplets while main-scanning the print head. The circles shown in the right half of FIG. 12 schematically represent dots formed on the printing paper. As described above with reference to FIG. 3, the actual sub-scanning is performed by feeding the printing paper, and the print head 241 does not move in the sub-scanning direction. For convenience, the print paper is taken as a reference, and it is expressed as if the print head is moving.

  In printing, first, main scanning is performed while ejecting ink droplets in a state where the print head is at the position indicated by (1) in the drawing. By this main scanning, dots displayed as “1” in the right half of FIG. 12 are formed on the printing paper. Here, the dots displayed as “1” are formed every other pixel so that one dot row is divided into two main scans. . If one dot row is formed by dividing it into three main scans, two pixels skip, and if it is formed by dividing it into four main scans, dots are skipped by three pixels. Will be formed.

  Next, the print head is moved in the sub-scanning direction by two nozzles. As a result, the print head moves to the position indicated by (2) in the left half of FIG. The solid arrow shown in the left half of FIG. 12 schematically represents the operation of sub-scanning the print head. After performing sub-scanning in this way, main scanning is performed again to form dots on the printing paper. By this second main scanning, dots indicated as “2” in the right half of FIG. 12 are formed on the printing paper. As described above, the nozzles are provided in the print head with an interval of three nozzles. However, since the print head is moved by two nozzles in the sub-scan, the second main scan is performed. The formed dot rows (dot rows labeled “2” in the drawing) are formed between the dot rows formed by the first main scanning (dot rows labeled “1” in the drawing). It will be.

  Subsequently, the sub-scan is performed again by two nozzles, the print head is moved to the position indicated by (3), and then ink droplets are ejected while performing the third main scan, thereby “3”. Are formed. The dot row formed by the third main scan (dot row displayed as “3” in the figure) is the dot row formed by the first main scan (dot row displayed as “1” in the drawing). ) And a dot row formed by the second main scanning (dot row labeled “2” in the drawing). That is, four dot rows are formed in the first main scan, but there is an interval between these dot rows so that two dot rows are formed. In the second main scan, dots are formed in one of these two dot rows, and in the third main scan, dots are formed in the remaining one dot row. As described above, when the sub-scan is performed and the operation of forming the dots while moving the print head little by little is repeated, the gap formed between the dot rows is changed to the dot at the stage of the third main scan. The raster can be completed by filling with columns.

  Subsequently, in the fourth main scan, dots are formed so as to overlap the dot row formed in the first main scan. However, as described above, since dots are formed at every other pixel in the first main scan, dots are formed between these dots in the fourth main scan. In the right half of FIG. 12, a dot that is displayed as “4” by the fourth main scanning is formed between the dots that are displayed as “1”, and the raster is completed as a result. It is expressed. That is, in the first main scan, half of the dots on one pixel column are formed, and in the fourth main scan, the remaining half of the dots are formed. It is formed separately for scanning.

  When one dot row is completed in this way, the sub-scan is performed again, the print head is moved to the position indicated by (5) in the figure, the fifth main scan is performed, and “5” in the figure. ”Is formed. In the fifth main scan, dots are formed so as to overlap the dot row formed in the second main scan. In other words, a new raster is completed by forming a dot labeled “5” between dots labeled “2” in the figure. Subsequently, sub-scanning is performed again, the print head is moved to the position labeled (6) in the figure, and the sixth main scanning is performed to form dots labeled “6”. The dots labeled “6” are formed between the dots labeled “3” to complete a new raster. Thereafter, similarly, in the seventh main scan, dots are formed between the dots formed in the fourth main scan, and in the eighth main scan, between the dots formed in the fifth main scan. Dots are formed.

  As described above, when the operation of forming the dot row by repeating the main scan while sub-scanning the print head by a predetermined amount is repeated, dots are formed without gaps, and thereafter, the dot is formed by performing the main scan. It is possible to complete the raster one after another and form dots on the printing paper without gaps. In the example shown in FIG. 12, dots are formed without a gap after the fifth main scan. That is, an area where dots are formed after the fifth main scan is an effective image display area.

  In this way, the printer does not form dots in order from the pixels at the edge of the effective display area of the image, but forms an image while forming dots according to a predetermined order as if it constitutes a mosaic. Printing. Therefore, in the image printing process shown in FIG. 6, the interlace process (step S108) is performed, and the print head 241 of the printer 200 actually forms dots from the dot data obtained by the halftone process (step S106). The process of rearranging in order is performed. The dot data whose order has been rearranged in this way is supplied to the printer 200 as print data.

  As described above, the printer 200 forms dots on the printing paper while performing main scanning and sub-scanning of the head according to the print data output from the computer 100 (step S110). As a result, an image is printed on the printing paper.

  As described above, in a printer that prints an image by forming dots on printing paper, if the dots are conspicuous, the image becomes rough and the image quality deteriorates. Therefore, in order to obtain a good image quality, in the halftone process (step S106 in FIG. 6) during the image printing process, dots are generated with an appropriate density according to the gradation value of the image data. It is important to generate dots by dispersing them as much as possible so as not to stand out. In the halftone processing method called the dither method described above, in order to disperse dots as much as possible, the threshold distribution of the dither matrix is appropriately set. In other words, if the distribution of the threshold value of the dither matrix is changed, the generation position of the dot also changes accordingly. Therefore, the dot is appropriately generated by optimizing the distribution of the threshold value.

  Of course, at the stage of setting the threshold value of the dither matrix, the threshold distribution is optimized by assuming that each dot is accurately formed at the designed position (usually the center of each pixel). This is only natural because it is not known at the design stage how the dot formation position shifts when the dots are actually formed by each printer shipped to the market. Then, various adjustment functions are mounted on the printer, and after being shipped to the market, the positions of the dots that are actually formed are brought closer to the designed positions. In this way, it is possible to print an image with good image quality in which dots are formed with an appropriate distribution.

  However, it is not always easy to bring the actual dot formation position closer to the design position, and a dedicated adjustment mechanism or application software is required, making the printer more complex, larger, and more expensive. It will become. Furthermore, if an attempt is made to obtain a higher-quality printed image, it is necessary to match the position of the dots that are actually formed with the designed position as much as possible. This will lead to increased complexity, size and price.

  In view of these points, in the printer 200 according to the present embodiment, the position of the dots that are actually formed is not matched with the designed position, but the “position between the dot position formed on the printing paper and the designed position”. An appropriate dither matrix is generated on the assumption that the dot positions are shifted in this way. That is, the threshold value of the dither matrix is set so that an appropriate dot distribution can be obtained in a state where the dots are formed at positions shifted from the positions on the design. If halftone processing is performed using the dither matrix generated in this way, it is possible to obtain a high-quality printed image generated in a state where dots are appropriately dispersed without adjusting the dot formation position by the printer 200. . In the following, first, a method for detecting dot misregistration will be described, and then a method for generating a dither matrix based on the detected misregistration will be described.

D. Detection method of dot position deviation:
In this embodiment, the following method is adopted in order to rationally detect the positional deviation of dots. First, a principle capable of rationally detecting a positional deviation will be described, and then a positional deviation detection method based on the principle will be described.

D-1. Detection principle of dot displacement:
As described above with reference to FIG. 12, a printer generally prints an image as if it constitutes a mosaic while forming dots by repeating main scanning and sub-scanning of the print head. In order to reasonably detect the positional deviation of the dots formed in a mosaic shape in this way, in this embodiment, the dots are detected based on the following principle.

  FIG. 13 is an explanatory diagram showing the principle of detecting the positional deviation of dots. In FIG. 13, as in FIG. 12, the print head having four nozzles with the nozzle pitch of 3 forms dots on the printing paper while repeating main scanning and sub-scanning. A state of printing is conceptually shown. However, the viewpoint to which attention is paid in the drawing is different between FIG. 12 and FIG. That is, in FIG. 12, paying attention to the number of main scans in which each dot was formed, the number of main scans in which each dot was formed was identified and displayed. On the other hand, in FIG. 13, attention is paid to which of the four nozzles each dot is formed, and it is displayed in an identifiable state with which nozzle each dot is formed. ing. Specifically, dots formed with Nz1 are displayed with black circles, dots formed with Nz2 are displayed with crosses, dots formed with Nz3 are triangles, and dots formed with Nz4 Is displayed using black square marks. Each raster is displayed by two main scans as in FIG.

  As shown in FIG. 13, by observing the arrangement of dots formed on the printing paper while paying attention to the nozzles on which the dots are formed, it can be found that the dots are formed periodically. That is, in the main scanning direction, dots are repeatedly formed in the same pattern with a period of 2 pixels, and in the sub-scanning direction, dots are repeatedly formed in the same pattern with a period of 12 pixels. Eventually, a total of 24 pixels, 2 pixels in the main scanning direction and 12 pixels in the sub-scanning direction, are grouped, and dots are formed repeatedly in exactly the same pattern.

  This is not limited to the combination of 4 nozzles, 3 nozzle pitches, and rasters formed by two main scans as shown in FIG. 13, and any combination can be found. . That is, assuming that the number of nozzles is N, the nozzle pitch is k, and the raster is formed by s main scans, s pixels in the main scan direction and N × k pixels in the sub scan direction are grouped and repeated in the same pattern. Dots are formed. Therefore, if the dot arrangement that looks complicated at first glance as shown in FIG. 12 is observed by paying attention to the nozzles that form each dot, s pixels in the main scanning direction and N in the sub scanning direction as shown in FIG. The same block is simply repeated with a block of xk pixels. From this, it can be considered that the same pattern is repeated with such a block as a cycle with respect to the positional deviation of the dots. Therefore, if the positional deviation at each pixel position in the block is detected, the entire area of the image is detected. Thus, the positional deviation of dots formed in each pixel can be known. In this embodiment, rational detection is possible by detecting the positional deviation of dots based on such a principle.

D-2. Detection method of dot position deviation:
In the following, a method for detecting the positional deviation between the position of the dots actually formed on the printing paper and the position where the dots are formed by design based on the above-described principle will be described. FIG. 14 is a flowchart showing a method for detecting dot misalignment in this embodiment. Hereinafter, it demonstrates according to a flowchart.

  When the dot misregistration detection process is started, first, an inspection image is printed (step S300). That is, a predetermined inspection image is printed by ejecting ink droplets while repeating main scanning and sub-scanning of the print head 241 to form dots on the printing paper. FIG. 15 is an explanatory diagram conceptually showing a state where the inspection image is printed on the printing paper. Small squares indicated by broken lines in the figure represent pixels. The illustrated inspection image is an image in which one dot is formed for each pixel. As described above, the printer 200 can form large, medium, and small dots, but the inspection image of this embodiment is printed using small dots or medium dots, and large dots are not used. . The reason for this will be described later. The data for printing the inspection image as shown in FIG. 15 is stored in advance in the ROM in the control circuit 260 of the printer 200 in a state where the halftone processing or interlace processing shown in FIG. It is remembered. In step S300 of FIG. 14, the stored print data is output to the print head 241 to print the inspection image shown in FIG.

  Next, by reading the printed inspection image using the scanner 122, the dot image formed on each pixel of the inspection image is read (step S302). The scanner 122 may be any scanner as long as it can read dot images. When the printer 200 is a so-called composite type printer and a scanner is incorporated, the dot image may be read using this scanner.

  The inspection image read in this way is printed by repeating blocks in which dots are formed with the same pattern as described with reference to FIG. Therefore, when the inspection image is read, a process of setting a block for the read inspection image is performed (step S304). The size of the block is determined by the number of nozzles N provided in the print head 241, the nozzle pitch k, and the number of main scans s required to form a raster per line (see FIG. 13). . Here, since the number of nozzles N = 4, the nozzle pitch kk = 3, and the number of main scans s = 2, one block has 2 (= s) pixels in the main scan direction and 12 ( = N × k) pixels. Of course, a large block in which a plurality of blocks are arranged in the main scanning direction or the sub-scanning direction can be set as one block.

  FIG. 16 is an explanatory diagram conceptually showing a state in which a block is set for the read inspection image. In the present embodiment, the size of the inspection image is set to a number of pixels that is an integral multiple of 2 in the main scanning direction and to a number of pixels that is an integral multiple of 12 in the sub-scanning direction. If the inspection image is set to such a size, a plurality of blocks can be arranged vertically and horizontally and spread on the inspection image without any gap. In the example shown in FIG. 16, if the blocks are arranged in 7 rows in the main scanning direction and 2 rows in the sub-scanning direction, the blocks can be spread on the inspection image without any gap. Then, by integrating these 14 blocks together and finely adjusting the positions of these blocks with respect to the inspection image in the main scanning direction and the sub-scanning direction, the center of gravity of the entire plurality of blocks captured after printing and the inspection original image Match the center of gravity. In this way, it is possible to set a block at an accurate position with respect to the inspection image. This is because each dot formed in the inspection image is slightly displaced, so it is not possible to know the set position of the block from the individual dot position, but since the dots are randomly displaced, multiple dots In summary, it is considered that the effects of deviation cancel each other. Therefore, if the center of gravity of the inspection image consisting of a plurality of dots is set to match the center of gravity of the block, it will not be affected by the positional deviation of each dot, so the block can be set at an accurate position. It becomes.

  In FIG. 16, the 14 blocks and the inspection image are described as having the same size. However, as long as the block can be accurately positioned with respect to each pixel of the inspection image, the blocks are integrated. The plurality of blocks to be set need not have the same size as the inspection image. For example, as shown in FIG. 17A, an inspection image larger than 14 blocks or an inspection image smaller than 14 blocks as shown in FIG. 17B can be used. That is, as is clear from the fact that the centroids of these inspection images coincide with the centroid of the inspection image shown in FIG. 16, even when such inspection images and 14 blocks are used in combination, By making the centroids coincide with each other, it is possible to accurately position and set the block with respect to the inspection image.

  Alternatively, instead of matching the centers of gravity in this way, dots (reference dots) used for block positioning are formed inside or outside the inspection image, and the reference dots are used positively and integrated. This block may be set. That is, assuming that the reference dot is formed without positional deviation, the position of the block is temporarily set using this dot as a reference. Of course, the reference dots are actually misaligned, but this misalignment appears as the misalignment of all dots constituting the inspection image. However, since the positional deviations of the dots cancel each other, the positional deviation of the entire inspection image should be “0”. Therefore, the positional deviation of each dot may be corrected so that the overall positional deviation becomes “0”. Or, as will be described in detail later, the dither matrix can be set appropriately even if the data with the entire position shifted is used as it is, so that there is a practical inconvenience without correcting the positional shift of each dot. There is nothing.

  Note that the positioning method described above is based on the principle that if a plurality of dots are combined, the effects of displacement cancel each other. Accordingly, the above description has been made assuming that a plurality of blocks are positioned as a unit, but even a single block can be positioned by the same principle. When a plurality of blocks are positioned as a unit, it is possible to improve positioning accuracy and positional deviation detection accuracy. In addition, when a single block is used, it is possible to speed up processing by the amount of data handled.

  In step S304 in FIG. 14, the process of matching the pixels of the inspection image with the pixels constituting the block is performed by determining the block position with respect to the read inspection image as described above.

  Next, a process for detecting dot misalignment is performed for each pixel in the block (step S306). The contents of this process will be described with reference to FIG. FIG. 18 is an explanatory diagram conceptually showing how to detect the positional deviation of dots formed in each pixel in a block in one block positioned on the inspection image. A large rectangle indicated by a one-dot chain line in the drawing represents one of the blocks positioned on the inspection image, and a small square indicated by a thin broken line represents a pixel constituting the block. Further, a cross displayed by a broken line in the pixel represents the center position of each pixel, and a black circle displayed in each pixel indicates a dot constituting the read inspection image. Here, since the block is positioned by the above-described method in step S304 of FIG. 14, it can be considered that the position of the pixel constituting the block substantially coincides with the position of each pixel of the inspection image. . Therefore, if the deviation between the dot read from the inspection image and the cross position (center of the pixel of the block) is detected, it is detected how much the position of the actually formed dot is deviated from the designed position. be able to.

  For example, the dot in the upper left corner shown in FIG. 18 is shifted in the diagonally lower left direction with respect to the center of the pixel of the block (the cross position in the pixel). Therefore, it can be considered that the dots are formed to be shifted in the diagonally left direction with respect to the designed formation position. Similarly, the dot in the upper right corner of FIG. 18 is shifted in the diagonally upper right direction with respect to the center of the pixel of the block, and thus formed in the diagonally upward right direction with respect to the design formation position. I understand that. In step S306 in FIG. 14, for each pixel constituting the block as described above, a process of detecting a dot positional deviation for each pixel is performed.

  Here, since 14 blocks are set on the inspection image, the above-described processing for detecting the positional deviation of dots at each pixel in the block is performed for each block, and the detection is performed for each block. The shift amount may be averaged for each pixel position in the block. Thus, if the average of the positional deviations of the dots detected for a plurality of blocks is taken, the positional deviation for each pixel in the block can be accurately detected. However, it is considered that the same value is detected for the positional deviation detected in each block according to the pixel position in the block. Therefore, one block may be selected from a plurality of blocks, and the detection result in this block may be represented by the detection result in this block. In this way, it is possible to easily detect the positional deviation of the dots without causing practical inconvenience.

  When dot misregistration is detected for each pixel in the block as described above, the detected misregistration data is output to a recording medium or memory (step S308). The format of the output data can be various formats. Here, the data indicating the pixel position in the block, the component in the main scanning direction of the shift amount from the center of each pixel, and the sub-scanning direction are used. Are output in a form in which the components are combined into a set. Thus, when the data indicating the dot position deviation at each pixel position in the block is output to the recording medium or the memory, the dot position deviation detection process shown in FIG. 14 is terminated.

D-3. Variation of the displacement detection method:
In the above-described misregistration detection method, misregistration is detected by forming small dots (or medium dots if possible), and large dots are not used. This is because, when a large dot is formed and an inspection image is printed, adjacent large dots overlap each other, making it difficult to detect the position of the dot formed in each pixel. FIG. 19 is an explanatory diagram conceptually showing a state in which large dots are formed in each pixel in the block. This corresponds to the case where the dots formed in each pixel in FIG. 18 are replaced with large dots. As shown in FIG. 19, when an inspection image is printed using large dots, adjacent dots overlap each other, making it difficult to identify individual dots. In this case, even if the block is accurately positioned with respect to the inspection image, it is difficult to detect the positional deviation of the dots at each pixel position. For this reason, the inspection image is printed using dots other than large dots, that is, small dots (or medium dots if possible).

  However, there are many printers that cannot form small dots or medium dots, that is, printers that can form only a single size dot. For such a printer, dot misregistration may be detected using the following method. Hereinafter, as a modification of the positional deviation detection method, a method for detecting the positional deviation of dots with a printer capable of forming only a single dot will be described.

  FIG. 20 is an explanatory diagram conceptually showing a state in which an inspection image is printed using a single dot (hereinafter referred to as a large dot) in order to detect a positional deviation of the dot. In the case of detecting dot misregistration using large dots, misregistration is detected using a plurality of inspection images. In FIG. 20, the inspection image 1, the inspection image 2, and the inspection image 3 are printed on the assumption that three inspection images are used to detect the positional deviation of dots.

  FIG. 21 is an explanatory diagram showing a part of the inspection image 1 in an enlarged manner. In the figure, a small rectangle indicated by a broken line represents a pixel, and a black circle displayed in the pixel represents a dot. Here, the case of forming a large dot has been described, but in order to avoid complicated illustration, the size of the dot is displayed smaller than the actual size in FIG. In the inspection image 1 shown in FIG. 21, dots are formed so as to jump two pixels in both the main scanning direction and the sub-scanning direction. Such an inspection image is read by a scanner, and processing for setting a block is performed on the read inspection image.

  FIG. 22 conceptually shows a state in which blocks are set for the inspection image 1 shown in FIG. A rectangle indicated by a broken line in the drawing represents a block positioned on the read inspection image. In FIG. 22, in order to distinguish the dots by the nozzles to be formed, the dots formed by the nozzle Nz1 are represented by black circles, the dots formed by the nozzle Nz2 are x marks, and the dots formed by the nozzle Nz3 Is a triangle mark, and dots formed by the nozzle Nz4 are indicated by a black square mark.

  As shown in FIG. 22, each dot constituting the inspection image 1 is formed on the first row pixel, the fourth row pixel, the seventh row pixel, and the tenth row pixel in the block. Has been. Therefore, if the block is positioned with respect to the inspection image 1 and the positional deviation of the dots is detected in a plurality of blocks, the pixels in the first row, the fourth row, the seventh row, and the tenth row in the block Can be detected.

  FIG. 23 is an explanatory diagram showing an enlarged part of the inspection image 2 shown in FIG. Again, the dashed rectangle represents a pixel and the black circle represents the position where a large dot is formed. As shown in the drawing, each dot constituting the inspection image 2 is formed in the pixels of the second row, the fifth row, the eighth row, and the eleventh row in the block. Therefore, if the dot displacement is detected using the inspection image 2, it is possible to detect the dot displacement for the pixels in the second row, the fifth row, the eighth row, and the eleventh row in the block. .

  FIG. 24 is an explanatory diagram showing an enlarged part of the inspection image 3 shown in FIG. As shown in the drawing, each dot constituting the inspection image 3 is formed in the pixels of the third row, the sixth row, the ninth row, and the twelfth row in the block. If used, it is possible to detect the positional deviation of dots for the pixels in the third, sixth, ninth and twelfth rows in the block. Eventually, if the detected positional deviations of the dots using the three inspection images shown in FIG. 20 are combined, it is possible to detect the positional deviation of the dots at all pixel positions in the block.

D-4. Other variations:
In the above description, three inspection images are used, and in each inspection image, it is assumed that dots are formed in two pixels skipping in both the main scanning direction and the sub-scanning direction. However, it is not always necessary to form dots every two pixels, and it is not always necessary to use three inspection images. For example, as shown in FIG. 25 or FIG. 26, even when two inspection images are formed by forming dots one pixel jump in the main scanning direction and the sub-scanning direction, dot misalignment is performed using the above-described method. Can be detected.

  Furthermore, the interval between dots to be formed may be set to an appropriate number of pixels, or dots may be formed at random positions while avoiding adjacent dots. Even in such a case, if a sufficiently large inspection image is printed, it is possible to detect the positional deviation of the dots for each pixel in the block using one inspection image.

  In the above-described method, the data for printing the inspection image is stored in a state where halftone processing (and interlace processing or the like is performed in some cases), and this data is supplied to the print head 241. As described above, the inspection image is printed. If the inspection image is printed in this manner, dots can be formed at desired pixels. However, it is also possible to store inspection image data in a state before color conversion processing or before halftone processing. When halftone processing is performed on such image data, it is difficult to form dots regularly. However, if image data in which dots are formed sparsely is stored, from a printed inspection image It is possible to detect the positional deviation of dots at each pixel in the block.

E. Dither matrix generation process:
In the printer 200 of the present embodiment, a “deviation” between the position of the dot formed on the printing paper and the design position is detected, and the threshold value of the dither matrix is set on the assumption that the dot position is displaced in this way. To do. Hereinafter, a method for generating an appropriate dither matrix assuming that the positions of dots that are actually formed are shifted by the amount detected by the above-described method will be described.

  As a method for generating a dither matrix, various methods have been proposed including those generated by trial and error. In this embodiment, any method can be used, but as a typical method, a method of generating a dither matrix using a so-called distance function will be described below. First, an outline of a method for generating a dither matrix using a distance function will be described, and then a method for generating an optimal dither matrix on the premise that the dot formation positions are shifted will be described.

E-1. Overview of dither matrix generation:
27 and 28 are explanatory diagrams showing an outline of a method for generating a dither matrix using a distance function. In order to avoid complicated explanation, here, the size of the dither matrix is a matrix of 4 pixels in total of 2 pixels in the vertical and horizontal directions. If threshold values are set for these four pixels, a dither matrix is generated.

  First, one arbitrary pixel is selected from the four pixels. Then, this pixel is determined to be the pixel in which a dot is most easily formed in the dither matrix, in other words, the pixel having the smallest threshold value. Here, it is assumed that the pixel at the upper left among the four pixels is selected as the pixel in which dots are most easily formed. Of the four pixels indicated by a small square in FIG. 27A, “1” is displayed in the upper left pixel, which schematically indicates that this pixel has been selected as the pixel on which dots are most easily formed. It is a representation. Then, the second pixel on which dots are likely to be formed is selected from the remaining three pixels indicated as “a”, “b”, and “c” in the drawing.

  When the dither matrix is generated using the distance function, the second pixel is selected such that the distance from the first selected pixel is the largest. For example, consider a case where the pixel “a” shown in FIG. 27A is temporarily selected and the distance from the first selected pixel is calculated. FIG. 27B conceptually shows how the distance is calculated when the pixel “a” is selected. Four squares indicated by solid lines in FIG. 27B are dither matrices to be generated, and dots are already formed in the upper left pixel in the matrix. In addition, the same matrix is repeatedly displayed in the vertical direction and the horizontal direction around the dither matrix displayed by the solid line using thin broken lines. This corresponds to the fact that the size of the image to be printed is usually larger than the dither matrix, and therefore the dither matrix is repeatedly used in the main scanning direction and the sub-scanning direction in the halftone process. As described above, when the pixel “a” is selected in a situation where the dither matrix is repeatedly used, the distance from the dots formed around the pixel “a” is calculated. Actually, by using a distance function obtained in advance, the distance from the dots formed in the periphery can be calculated relatively easily.

  Note that the “dots formed around” are normally dots formed within a predetermined distance (for example, a distance about half the diagonal line of the dither matrix to be generated). Here, in order to avoid complicated description, it is assumed that the dots are formed in adjacent pixels. Then, as shown in FIG. 27B, a total of two dots are formed around the pixel “a”, one on each side. If the dot is formed at the center of the pixel, the distance between the dots indicated by the arrows in the figure is one pixel. From this, when the pixel “a” is selected as the second pixel on which dots are likely to be formed, the distance from the surrounding dots is calculated as an average distance for one pixel.

  Next, when the pixel “b” is selected, dots are formed one by one in the vertical direction as shown in FIG. If the dot is formed at the center of the pixel, the distance between the dots indicated by the arrows in the figure is one pixel. Therefore, even when the pixel “b” is selected, the distance to the surrounding dots is It is calculated as a distance for one pixel on average. On the other hand, when the pixel “c” is selected, a total of four dots are formed around the pixel “c” one by one in the oblique direction as shown in FIG. If the dot is formed at the center of the pixel, the distance between the dots indicated by the arrows in the figure is about 1.4 pixels. Therefore, when the pixel “c” is selected, This distance is about 1.4 pixels on average.

  That is, when the pixel “c” is selected from the three pixels “a”, “b”, and “c” shown in FIG. Therefore, the pixel “c” having the largest distance is selected as the pixel in which a dot is most likely to be formed in the dither matrix.

  The third pixel on which dots are easily formed can be selected in the same manner. FIG. 28 is an explanatory diagram conceptually showing a state in which a pixel in which a third dot is most likely to be formed is selected in the dither matrix. The pixel in which dots are most likely to be formed is selected from the two pixels “a” and “b” shown in FIG. 28A, and the pixel having the largest distance from the surrounding dots is selected. That's fine. FIG. 28B is an explanatory diagram conceptually showing a state in which the distance from the dots formed around the pixel “a” is calculated. FIG. 28C is an explanatory diagram showing how the distance to surrounding dots is calculated when the pixel “b” is selected. As shown in the figure, regardless of whether the pixel “a” or the pixel “b” is selected, four pixels are formed around the top, bottom, left, and right. If the dot is formed at the center of the pixel, the distance between the dots indicated by the arrows in the figure is one pixel, and even if either pixel “a” or pixel “b” is selected, The average distance from the dot is one pixel. Thus, when the average distance becomes equal, either pixel may be selected. Here, the pixel “a” is selected, and this pixel is the pixel in which a dot is most likely to be formed in the dither matrix, and the remaining pixel “b” is the pixel in which a dot is most likely to be formed.

  Eventually, as shown in FIG. 28 (d), it is possible to determine the order of ease of dot formation for the four pixels of the dither matrix, and to set a threshold value for each pixel according to this order. For example, if the gradation value of the image data can take a range of 0 to 255, four threshold values (for example, 51, 102, 153, and 204) that appropriately divide this range are set in order from a small threshold value. This may be set according to the order shown in FIG.

  As described above, when the pixels in which the dots are likely to be formed are sequentially selected from the pixels included in the dither matrix while calculating the distance from the surrounding dots, if the dot formation position is shifted, The order of the selected pixels is different. As a result, the resulting dither matrix is also a different matrix. Hereinafter, a specific description will be given with reference to FIGS. 29 and 30.

  FIGS. 29 and 30 are explanatory diagrams showing an outline of a method for generating an appropriate dither matrix on the premise that the dot formation positions are shifted. Here, in order to avoid complicated description, the size of the dither matrix is a matrix of 4 pixels in total of 2 pixels vertically and horizontally.

  Now, it is assumed that the dot formation positions are shifted by two pixel periods in the vertical direction and the horizontal direction. That is, it is assumed that the dot formation position is shifted at the same cycle as the dither matrix. FIG. 29A shows a state in which the dot formation position is shifted in each pixel of the dither matrix. The condition that the dot misalignment period and the size of the dither matrix coincide with each other is for the sake of convenience of understanding and avoids complication of the illustration. It does not have to match the size. Further, the integer multiple of the dot misalignment period does not necessarily have to be the size of the dither matrix. This point will be supplementarily described later.

  As in FIG. 27 described above, first, an arbitrary pixel is selected from the four pixels, and this pixel is set as a pixel in which a dot is most easily formed in the dither matrix. FIG. 29B schematically shows that the upper left pixel is selected as the first pixel. Then, from the remaining three pixels displayed as “a”, “b”, and “c”, a pixel in which a dot is most likely to be formed is selected.

  FIG. 29C conceptually shows how the distance to surrounding dots is calculated when the pixel “a” is selected. Similarly, FIG. 29D shows how to calculate the distance to surrounding dots when the pixel “b” is selected, and FIG. 29E shows how the surrounding dots are calculated when the pixel “c” is selected. It is a conceptual representation of how the distance is calculated. Comparing FIG. 29 (c) to FIG. 29 (e), when the pixel “c” is selected, the average distance from the surrounding dots is the largest, so the second dot in the dither matrix The pixel “c” is selected as a pixel on which is easily formed.

  FIG. 30A shows a state in which a pixel in which a dot is easily formed and a pixel in which a dot is easily formed are selected from among four pixels in the dither matrix. The third pixel on which dots are likely to be formed may be selected from the remaining pixel “a” or pixel “b”. FIG. 30B illustrates a state in which a distance from surrounding dots is calculated when the pixel “a” is selected, and FIG. 30C illustrates a distance calculated when the pixel “b” is selected. It shows how to do. Comparing the two figures, the average distance from the surrounding dots is slightly larger when the pixel “b” is selected than when the pixel “a” is selected. Therefore, the pixel “b” is selected as the pixel in which the third dot is most likely to be formed, and the last remaining pixel “a” is the pixel in which the fourth dot is most likely to be formed. As a result, the order of the four pixels included in the dither matrix is the order as shown in FIG. This order is different from the order shown in FIG. 28D obtained when there is no dot misalignment, and therefore the appropriate dither matrix obtained from this order is also different.

E-2. Processing content :
FIG. 31 is a flowchart showing a flow of processing for generating an appropriate dither matrix using the above-described method while taking dot positional deviation into consideration. In the following, a process for generating a dither matrix will be briefly described with reference to the flowchart of FIG.

  When the process for generating the dither matrix is started, first, the variable N is initialized (step S400). The variable N is a variable indicating how many pixels in the dither matrix are likely to form dots, and varies from 1 to the number of pixels included in the dither matrix.

  One arbitrary pixel is selected from the dither matrix, and this pixel is determined as the first pixel, that is, the pixel in which a dot is most easily formed (step S402). When the first pixel is determined in this way, the variable N is incremented by one in order to determine the second pixel on which dots are most likely to be formed (step S404).

  Then, one undetermined pixel is selected from the dither matrix, and the average distance from the selected pixel to the dots formed within the predetermined range is calculated (step S406). As described above, in this embodiment, dot misalignment is detected at each pixel position in a block having a predetermined size. Based on this detection result, dot misalignment is detected at all pixel positions of the image. It is possible to ask. Usually, since the dither matrix is smaller than the image, it is repeatedly used. However, if the size of the image is known, the correspondence between each pixel in the image and each pixel position of the dither matrix can be determined automatically. Therefore, if one undetermined pixel is selected on the dither matrix, a plurality of pixels on the image corresponding to the pixel are determined, and how much the dots are shifted in each pixel. The average distance to a plurality of dots formed in the periphery can be obtained for each pixel. In step S406, one undetermined pixel is selected from the dither matrix, and an average distance is calculated for each pixel on the image corresponding to the selected pixel. And the process which calculates the average distance with respect to the pixel selected on the matrix is performed by calculating the average value about these average distances.

  However, if the size of the dither matrix matches the size of the block where the misregistration of the dots is detected, or if the size of the dither matrix matches the size of multiple blocks, the misalignment of the dither matrix and the dots The relationship with is always kept the same. That is, regardless of where the dither matrix is applied in the image, if the pixel position is the same in the dither matrix, the positional deviation of the dots is the same. Similarly, if the dither matrix is at the same pixel position in the dither matrix, the average distance to a plurality of dots formed in the periphery is the same regardless of where the dither matrix is applied in the image. Therefore, if the size of the dither matrix matches the size of the block in which the positional deviation of the dot is detected or the size of the plurality of blocks arranged, the processing in step S406 is greatly simplified. The That is, it is only necessary to calculate the average distance to the dots formed in the periphery for only one pixel in the image corresponding to the pixel selected on the dither matrix, and the average for the other pixels corresponding to the selected pixel. The process for calculating the distance and the process for obtaining the average value of these average distances are not required.

  When one pixel is selected from the dither matrix and the average distance is calculated as described above, it is determined whether or not the average distance has been calculated for all the pixels on the dither matrix (step S408). If an uncalculated pixel remains on the dither matrix (step S408: no), the process returns to step S406 to select one new pixel from the dither matrix and calculate the average distance for the selected pixel. Then, it is determined whether the average distance of all pixels has been calculated (step S408). If it is determined that the average distance has been calculated for all the pixels on the dither matrix (step S408: yes), the pixel having the largest calculated average distance is determined as the Nth pixel (step S410).

  Next, it is determined whether or not an order has been determined for all pixels on the dither matrix (step S412). Since the Nth pixel is determined in the previously processed step S410, if the variable N has reached the number of pixels included in the dither matrix, it can be determined that the order has been determined for all pixels. If there is still a pixel whose order has not yet been determined (step S412: no), the process returns to step S404, increments the variable N by 1, and then repeats the series of operations described above from step S406 to step S412. If it is determined that the order is determined for all the pixels of the dither matrix (step S412: yes), a threshold is set for each pixel of the dither matrix according to the determined order (step S414). When the threshold values are set for all the pixels in this way, the dither matrix generation process ends.

  In the dither matrix generated as described above, an appropriate dot is formed when the dot is shifted at each pixel in the image, assuming that the actual dot formation position deviates from the design formation position. The threshold of the dither matrix is set so as to obtain a variance of. Therefore, if halftone processing is performed using such a dither matrix, it is possible to print an image with high image quality without performing various adjustments to bring the dot formation position closer to the design formation position. It becomes.

F. Modified example:
F-1. First modification:
In the above-described embodiment, dot misregistration is detected for each pixel, and a dither matrix is set based on the detection result. If the dither matrix is changed, the manner of dot generation will change, so in the embodiment described above, the dot displacement detected in each pixel is reflected in the halftone processing stage. On the other hand, the detected positional deviation of the dots may be reflected in the stage where dots are actually formed. Below, the 1st modification of such a present Example is demonstrated.

  FIG. 32 is an explanatory diagram illustrating a method of correcting the dot formation position based on the detection result of the dot position deviation for each pixel in the first modification of the present embodiment. Similar to FIG. 12 described above, the print head 241 is provided with four nozzles at intervals of the nozzle pitch 3, and one raster is formed by two main scans. The right half of FIG. 32 shows dots formed on the printing paper by the print head 241 performing main scanning and sub-scanning. In the left half of FIG. 32, the print head 241 conceptually shows the state where the print head 241 performs the fifth main scan to form dots and then moves to the position where the sub scan is performed and the sixth main scan is performed. Represents.

  When the print head 241 performs the fifth main scan, a dot labeled “5” is formed in the right half of FIG. Here, if the positional deviation of the dots is detected for each pixel in the block, the deviation amount of each dot displayed as “5” can be obtained. It can be determined in what direction and how much a plurality of dots formed by scanning are shifted as a whole. When the dots are displaced in the direction in which the print head 241 moves, the timing for forming the dots is slightly advanced. By so doing, it is possible to reduce the positional deviation of these dots as a whole in the main scanning direction. Conversely, if the dots are displaced in the direction opposite to the direction in which the print head 241 moves, the positional displacement as a whole can be reduced if the dot formation timing is slightly delayed. Of course, if the dot formation timing can be adjusted for each nozzle provided in the print head 241, the dot formation timing may be detected for each nozzle to adjust the dot formation timing. .

  Further, the positional deviation in the sub-scanning direction can be suppressed by adjusting the sub-scanning amount. For example, consider a case where the sub-scan is performed after the fifth main scan and the print head 241 is moved to the sixth main scan position. In the sixth main scan, dots displayed as “6” in the right half of FIG. 32 are formed, and if the positional deviation at each pixel in the block is known, the dots displayed as “6” as a whole. , How much the direction is shifted in any direction. If these dots are displaced in the sub-scanning direction as a whole, the sub-scanning amount is slightly reduced. On the other hand, when the whole is shifted in the direction opposite to the sub-scanning direction, the sub-scanning amount is slightly increased. As described above with reference to FIG. 3, the printer 200 performs sub-scanning by feeding the printing paper P using the paper feed motor 235, and therefore, if the rotation angle of the paper feed motor 235 is controlled, the sub-scan is performed. It is possible to control the scanning amount. Thus, if the sub-scanning amount is controlled, it is possible to suppress the positional deviation of the entire dot in the sub-scanning direction.

F-2. Second modification:
In each of the various embodiments described above, since the inspection image is printed and the dot position deviation is detected, the scanner 122 for reading the inspection image is necessary. However, as described below, a high-quality image can be printed even when the scanner 122 cannot be used. Hereinafter, a second modification example that does not require the scanner 122 will be briefly described.

  In the second modified example, during manufacture of the printer 200, data for printing an inspection image is supplied to the head, and dot positional deviation data for the printer is acquired from the obtained inspection image. . Then, the obtained positional deviation data is written in a ROM built in the printer 200. Here, the misregistration data may be obtained by providing a process of printing an inspection image during the manufacturing process of the printer 200 and a process of detecting misalignment from the inspection image, or a final process of the manufacturing process. It is good also as acquiring by adding these processes.

  When printing an image, the misregistration data stored in the ROM is read out, a dither matrix is generated by the method described above with reference to FIG. 31, and the image is printed with reference to the obtained dither matrix. To do. By so doing, it is possible to generate dots using a dither matrix in which dot misregistration is taken into consideration, so it is possible to print a high-quality image in which dots are well dispersed.

  More simply, a dither matrix may be generated from the detected dot position deviation data and stored in a ROM built in the printer 200. When printing an image, it reads out the dither matrix stored in the ROM and determines whether or not dots are formed, so that a high-quality image with well dispersed dots can be obtained without adjusting the dot formation position. Can be obtained.

  Although various embodiments have been described above, the present invention is not limited to all the embodiments described above, and can be implemented in various modes without departing from the scope of the invention. For example, a software program (application program) that realizes the above functions may be supplied to a main memory or an external storage device of a computer system via a communication line and executed. Of course, a software program stored in a CD-ROM or a flexible disk may be read and executed.

It is explanatory drawing which showed the outline | summary of the printing apparatus as a typical Example. FIG. 3 is an explanatory diagram illustrating a configuration of a computer that performs image processing such as halftone processing and data analysis in the present embodiment. It is explanatory drawing which shows schematic structure of the printer of a present Example. It is explanatory drawing which showed a mode that the several nozzle Nz which discharges an ink drop was formed in the bottom face of the ink discharge head of each color. It is explanatory drawing which shows the principle which forms the dot from which a magnitude | size differs by controlling the magnitude | size of the ink droplet to discharge. It is the flowchart which showed the flow of the process which performs a predetermined image process to image data and prints an image. It is explanatory drawing which showed notionally the LUT referred for a color conversion process. It is explanatory drawing which expanded and illustrated a part of dither matrix. It is explanatory drawing which showed notionally the mode that the presence or absence of dot formation was judged for every pixel, referring a dither matrix. It is the flowchart which showed the flow of the halftone process performed in an image printing process. It is explanatory drawing which showed notionally the recording density conversion table referred in order to convert image data into recording density data. FIG. 4 is an explanatory diagram conceptually showing how a print head forms dots on a print sheet while repeating main scanning and sub-scanning. It is explanatory drawing which shows the principle which detects the position shift of a dot. It is a flowchart which shows the method of detecting the position shift of a dot in a present Example. It is explanatory drawing which showed notionally the test | inspection image printed in order to detect position shift. It is explanatory drawing which showed notionally the mode that the block was set with respect to the read test | inspection image. It is explanatory drawing which illustrated the other aspect of the test | inspection image. It is explanatory drawing which showed notionally the mode that the position shift of the dot formed in each pixel in a block was detected about one block positioned on the test | inspection image. It is explanatory drawing which showed notionally that a large dot was formed in each pixel in a block. It is explanatory drawing which showed notionally the mode that the test | inspection image was printed in order to detect the position shift of a dot using a large dot. It is explanatory drawing which expanded and showed a part of test | inspection image 1 printed in order to detect position shift using a large dot. It is explanatory drawing which showed notionally the mode that the block was set with respect to the test | inspection image 1. FIG. It is explanatory drawing which expanded and showed a part of test | inspection image 2 printed in order to detect position shift using a large dot. It is explanatory drawing which expanded and showed some inspection images 3 printed in order to detect position shift using a large dot. It is explanatory drawing which illustrated the other aspect of the test | inspection image printed in order to detect the position shift of a dot using a large dot. It is explanatory drawing which illustrated the further another aspect of the test | inspection image printed in order to detect the position shift of a dot using a large dot. It is explanatory drawing which shows the outline | summary of the method of producing | generating a dither matrix using a distance function. It is explanatory drawing which shows the outline | summary of the method of producing | generating a dither matrix using a distance function. It is explanatory drawing which shows the outline | summary of the method of producing | generating an appropriate dither matrix on the assumption that the formation position of a dot has shifted | deviated. It is explanatory drawing which shows the outline | summary of the method of producing | generating an appropriate dither matrix on the assumption that the formation position of a dot has shifted | deviated. It is a flowchart which shows the flow of the process which produces | generates a suitable dither matrix using the method mentioned above in consideration of the position shift of a dot. It is explanatory drawing which shows the method of correcting the dot formation position based on the result of having detected the dot position shift about each pixel in the modification of a present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Printing apparatus 12 ... Halftone module 14 ... Dither matrix 16 ... Head 20 ... Inspection image data output module 22 ... Scanner 24 ... Detection module 26 ... Dither matrix generation module 100 ... Computer 108 ... Peripheral device interface PIF
109 ... Disk controller DDC
110: Network interface card NIC
112 ... Video interface VIF
DESCRIPTION OF SYMBOLS 116 ... Bus 118 ... Hard disk 120 ... Digital camera 122 ... Scanner 124 ... Flexible disk 126 ... Compact disk 200 ... Printer 230 ... Carriage motor 235 ... Paper feed motor 236 ... Platen 240 ... Carriage 241 ... Print head 242 ... Ink cartridge 243 ... Ink Cartridge 244 ... Ink ejection head 255 ... Ink passage 256 ... Ink chamber 257 ... Ink gallery 260 ... Control circuit 300 ... Communication line 310 ... Storage device

Claims (21)

A printing apparatus that applies a dither method to image data, performs halftone processing, and forms dots on a print medium based on the result of the halftone processing to print an image,
A head in which N nozzles forming the dots are provided at intervals of a nozzle pitch k;
By repeating the main scanning, which is an operation of driving the nozzles to form dots, while moving the head in a direction crossing the arrangement of the nozzles from one end to the other end of the print medium, Raster forming means for forming a plurality of rasters that are rows of dots on a medium;
Inspection image printing means for printing a predetermined inspection image for inspecting a positional deviation between an actual formation position where the dot is formed on the print medium and a design formation position;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), A displacement detection means for detecting the displacement at each pixel position in the block from the printed inspection image;
A dither matrix generation unit configured to generate a dither matrix by setting a threshold value of a dither matrix used in the dither method based on the detection result of the displacement. The printing apparatus according to claim 1,
The dither matrix generation means is means for generating the dither matrix having a size of p × s pixels in the main scanning direction and q × N × k pixels in the sub scanning direction (p and q are positive integers). A printing device. The printing apparatus according to claim 1,
The inspection image printing means is a printing apparatus that prints an image in which dots are not formed in adjacent pixels at least in the main scanning direction and the sub-scanning direction as the inspection image. The printing apparatus according to claim 1,
The head is a head capable of forming a plurality of types of dots having different sizes,
The inspection image printing unit is a printing device that is a unit that prints the inspection image using dots other than the largest dot. The printing apparatus according to claim 1,
The inspection image printing unit stores the image data of the inspection image in a state where the halftone process is performed, and forms dots on the print medium based on the image data, thereby A printing apparatus which is means for printing. A printing apparatus that applies a dither method to image data, performs halftone processing, and forms dots on a print medium based on the result of the halftone processing to print an image,
A dither matrix storage means which is referred to in the halftone process and stores a dither matrix unique to the printing apparatus;
A head in which N nozzles forming the dots are provided at intervals of a nozzle pitch k;
The print medium is repeatedly subjected to main scanning, which is an operation of driving the nozzles to form dots while moving the head in a direction crossing the arrangement of the nozzles from one end to the other end of the print medium. A raster forming means for printing the image by forming a plurality of rasters as a row of dots on the top;
The dither matrix storage means is a dither matrix specific to the printing apparatus,
A predetermined inspection image for inspecting a positional deviation between an actual formation position where the dots are formed on the print medium and a design formation position is printed using the printing apparatus,
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), Detecting the displacement at each pixel position in the block from the printed inspection image;
A printing apparatus as means for storing a matrix in which a threshold value of the dither matrix is set based on the detection result of the misregistration. A printing apparatus that applies a dither method to image data, performs halftone processing, and forms dots on a print medium based on the result of the halftone processing to print an image,
A head in which N nozzles forming the dots are provided at intervals of a nozzle pitch k;
The main scanning, which is the operation of forming the dots by driving the nozzles while moving the head in the direction crossing the arrangement of the nozzles from one end to the other end of the printing medium, is repeated on the printing medium. A raster forming means for printing the image by forming a plurality of rasters, each of which is a dot row,
A misregistration detection result storage means for storing a detection result for the printing apparatus of a misregistration between an actual formation position for forming dots on the print medium and a design formation position;
A dither matrix generating means for generating the dither matrix by setting a threshold value of the dither matrix used in the dither method based on the stored detection result of the misregistration, and
The misregistration detection result storage means is a misregistration detection result for the printing apparatus.
Printing a predetermined inspection image for inspecting the displacement using the printing apparatus;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), A printing apparatus which is means for storing the positional deviation detected from the inspection image at each pixel position in the block. A printing method that applies a dither method to image data, performs halftone processing, and forms dots on a print medium based on the result of the halftone processing to print an image,
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. Forming a plurality of raster lines of dots on the print medium by repeatedly performing main scanning, which is an operation for forming dots by driving;
A predetermined inspection image for inspecting a positional deviation between an actual formation position where the dots are formed on the print medium and a design formation position by forming a plurality of rasters on the print medium. Printing process,
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ) Detecting the position shift at each pixel position in the block from the inspection image;
Generating a dither matrix by setting a threshold value of the dither matrix used in the dither method based on the detection result of the misregistration. The printing method according to claim 8, comprising:
The step of generating the dither matrix is a step of generating a matrix having a size of p × s pixels in the main scanning direction and q × N × k pixels in the sub scanning direction (p and q are positive integers). Method. A printing method that applies a dither method to image data, performs halftone processing, and forms dots on a print medium based on the result of the halftone processing to print an image,
Storing a dither matrix that is referred to in the halftone process and is unique to the printing apparatus;
The nozzles are driven while moving a head in which the N nozzles forming the dots are provided at an interval of a nozzle pitch k, moving from one end of the print medium to the other end in a direction crossing the nozzle arrangement. And a step of printing the image by repeatedly performing main scanning, which is an operation of forming dots, to form a plurality of rasters as rows of dots on the print medium, and
The step of storing the dither matrix is a dither matrix specific to the printing apparatus,
A predetermined inspection image for inspecting a positional deviation between an actual formation position where the dots are formed on the print medium and a design formation position is printed using the printing apparatus,
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), Detecting the displacement at each pixel position in the block from the printed inspection image;
A printing method, which is a step of storing a matrix in which a threshold value of the dither matrix is set based on a detection result of the misregistration. A printing method that applies a dither method to image data, performs halftone processing, and forms dots on a print medium based on the result of the halftone processing to print an image,
The nozzles are driven while moving a head in which the N nozzles forming the dots are provided at an interval of a nozzle pitch k, moving from one end of the print medium to the other end in a direction crossing the nozzle arrangement. A step of printing the image by repeatedly performing main scanning, which is an operation of forming dots, to form a plurality of rasters that are rows of dots on the print medium;
Storing a detection result for the printing apparatus of a positional deviation between an actual formation position for forming dots on the print medium and a design formation position;
Generating a dither matrix by setting a threshold value of a dither matrix used in the dither method based on the stored detection result of misregistration, and
The step of storing the detection result includes a detection result of misregistration for the printing apparatus,
Printing a predetermined inspection image for inspecting the displacement using the printing apparatus;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), A printing method which is a step of storing the positional deviation detected from the inspection image at each pixel position in the block. A method of generating a dither matrix to be referred to when halftone processing is performed by applying a dither method,
While moving the head in which N nozzles for forming dots on the print medium are provided at intervals of the nozzle pitch k, moving from one end of the print medium to the other end in a direction intersecting with the arrangement of the nozzles, Performing a main scan as an operation of driving the nozzle to form dots;
By repeating the main scanning and forming a plurality of rasters as dot rows on the print medium, the positions of the actual formation position and the design formation position where the dots are formed on the print medium. A step of printing a predetermined inspection image for inspecting misalignment;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ) Detecting the position shift at each pixel position in the block from the inspection image;
And a step of setting a threshold value for each pixel of the dither matrix based on the detection result of the misregistration. A dither matrix generation method according to claim 12, comprising:
The step of setting the threshold value of the dither matrix includes the steps of: p × s pixels in the main scanning direction and q × N × k pixels in the sub scanning direction (p and q are positive integers). A dither matrix generation method which is a step of setting a threshold value for each pixel. This is a detection method in which a printing apparatus that forms dots on a print medium and prints an image detects a positional shift between the design position of the dots formed on the print medium and the positions where dots are actually formed. And
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. A step of performing main scanning as an operation of driving to form dots;
Repetitively performing the main scanning to form a plurality of raster lines of dots on the print medium, thereby printing a predetermined inspection image for inspecting the misregistration of the dots;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). And a step of detecting the position shift at each pixel position in the block from the inspection image. A printing apparatus that forms dots on a print medium and prints an image is an adjustment method that adjusts the positional deviation between the design position of the dots formed on the print medium and the positions where dots are actually formed. And
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. A step of performing main scanning as an operation of driving to form dots;
Repetitively performing the main scanning to form a plurality of raster lines of dots on the print medium, thereby printing a predetermined inspection image for inspecting the misregistration of the dots;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ) Detecting the position shift at each pixel position in the block from the inspection image;
Adjusting the formation position of the dots based on the detection result of the positional deviation. A program for implementing a method for performing a halftone process by applying a dither method to image data and printing an image by forming dots on a print medium based on the result of the halftone process using a computer Because
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. A function of forming a plurality of raster lines of dots on the print medium by repeatedly performing main scanning, which is an operation of forming dots by driving;
A predetermined inspection image for inspecting a positional deviation between an actual formation position where the dots are formed on the print medium and a design formation position by forming a plurality of rasters on the print medium. The ability to print
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), A function of detecting the displacement at each pixel position in the block from the inspection image;
A program for realizing a function of generating a dither matrix by setting a threshold value of a dither matrix used in the dither method based on a detection result of the misregistration. A program for implementing a method for performing a halftone process by applying a dither method to image data and printing an image by forming dots on a print medium based on the result of the halftone process using a computer Because
A function of storing a dither matrix that is referred to in the halftone process and is unique to the printing apparatus;
The nozzles are driven while moving a head in which the N nozzles forming the dots are provided at an interval of a nozzle pitch k, moving from one end of the print medium to the other end in a direction crossing the nozzle arrangement. In this way, the main scanning, which is the operation of forming dots, is repeatedly performed to form a plurality of rasters that are rows of dots on the print medium, thereby realizing the function of printing the image, and
The function of storing the dither matrix is as a dither matrix specific to the printing apparatus,
A predetermined inspection image for inspecting a positional deviation between an actual formation position where the dots are formed on the print medium and a design formation position is printed using the printing apparatus,
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), Detecting the displacement at each pixel position in the block from the printed inspection image;
A program which is a function for storing a matrix in which a threshold value of the dither matrix is set based on a detection result of the positional deviation. A program for implementing a method for performing a halftone process by applying a dither method to image data and printing an image by forming dots on a print medium based on the result of the halftone process using a computer Because
The nozzles are driven while moving a head in which the N nozzles forming the dots are provided at an interval of a nozzle pitch k, moving from one end of the print medium to the other end in a direction crossing the nozzle arrangement. A function of printing the image by repeatedly performing main scanning, which is an operation of forming dots, to form a plurality of rasters that are rows of dots on the print medium;
A function of storing a detection result for the printing apparatus of a positional deviation between an actual formation position for forming dots on the print medium and a design formation position;
A function of generating the dither matrix is realized by setting a threshold value of the dither matrix used in the dither method based on the stored detection result of the positional deviation, and
The function of storing the detection result is a detection result of misregistration for the printing apparatus.
Printing a predetermined inspection image for inspecting the displacement using the printing apparatus;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), A program that is a function of storing the positional deviation detected from the inspection image at each pixel position in the block. A program for realizing, using a computer, a method for generating a dither matrix that is referred to when halftone processing is performed by applying a dither method,
While moving the head in which N nozzles for forming dots on the print medium are provided at intervals of the nozzle pitch k, moving from one end of the print medium to the other end in a direction intersecting with the arrangement of the nozzles, A function of performing main scanning as an operation of driving the nozzle to form dots;
By repeating the main scanning and forming a plurality of rasters as dot rows on the print medium, the positions of the actual formation position and the design formation position where the dots are formed on the print medium. A function of printing a predetermined inspection image for inspecting misalignment;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), A function of detecting the displacement at each pixel position in the block from the inspection image;
And a function of setting a threshold value of each pixel of the dither matrix based on the detection result of the misregistration. A printing apparatus for printing an image by forming dots on a print medium, and a method for detecting a misalignment between a design position of the dots formed on the print medium and a position at which dots are actually formed. A program for realizing using
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. A function of performing main scanning, which is an operation of driving to form dots,
A function of printing a predetermined inspection image for inspecting the misregistration of the dots by repeatedly performing the main scanning and forming a plurality of rasters as a row of dots on the print medium;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), And a function for detecting the position shift at each pixel position in the block from the inspection image. A method for adjusting a positional deviation between a design position of a dot formed on the print medium and a position where the dot is actually formed by a printing apparatus that forms an image on a print medium and prints an image. A program for realizing using
While moving a head in which N nozzles forming the dots are provided at an interval of a nozzle pitch k in a direction crossing the nozzle arrangement, the nozzles are moved from one end to the other end of the print medium. A function of performing main scanning, which is an operation of driving to form dots,
A function of printing a predetermined inspection image for inspecting the misregistration of the dots by repeatedly performing the main scanning and forming a plurality of rasters as a row of dots on the print medium;
When each of the rasters is formed by s times of the main scanning, n × s pixels in the main scanning direction and m × N × k pixels in the sub scanning direction are blocks (n and m are positive integers). ), A function of detecting the displacement at each pixel position in the block from the inspection image;
A program for realizing a function of adjusting the dot formation position based on the detection result of the positional deviation.

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