Image recording apparatus, dither mask, and image recording method

A dither mask used in halftone processing for recording an image on a recording medium by repeating a main scan operation of jetting ink from nozzles, while relatively moving a recording head that includes a nozzle row in which a plurality of the nozzles that jet the ink are arranged in a sub scan direction with respect to the recording medium in a main scan direction that is orthogonal to the sub scan direction, to perform recording and a sub scan operation of relatively moving the recording medium with respect to the recording head in the sub scan direction,

• wherein in a recording process of completing, with respect to each scan band that is a region having a width of a sub scan movement amount of one sub scan operation of the recording medium in the sub scan direction, recording of the scan band by repeating a plurality of the main scan operations,
• in a case where the plurality of scans necessary for the completion of the recording of the scan band are divided into a first half scan and a second half scan on the basis of a scan order, when a nozzle disposed closest to a central side of the nozzle row in a first half scan nozzle group that is a nozzle group used in the recording of the first half scan in the nozzle row is referred to as a first half side central nozzle, a nozzle disposed closest to an end side of the nozzle row in the first half scan nozzle group is referred to as a front end nozzle, a nozzle disposed closest to a central side of the nozzle row in a second half scan nozzle group that is a nozzle group used in the recording of the second half scan in the nozzle row is referred to as a second half side central nozzle, a nozzle disposed closest to an end side of the nozzle row in the second half scan nozzle group is referred to as a rear end nozzle, the number of the main scan operations necessary for recording of one of rasters formed in the main scan direction is referred to as the number of overlaps, a region of a unit area represented by a product of the number of overlaps in the main scan direction and a nozzle pitch of the nozzle row in the sub scan direction is referred to as a unit region, and nozzles that record the same unit region in the nozzle groups for the respective scans used in the recording of the plurality of scans are referred to as corresponding nozzles,
• the dither mask is subjected to threshold setting for generating a dot disposition in which nozzle jetting rates that are relative usage rates of the respective nozzles of the nozzle row become nozzle jetting rates that satisfy a predetermined specific condition, in at least a part of a range of a recording duty, and
• the nozzle jetting rates that satisfy the specific condition are set such that
• the nozzle jetting rates are decreased at two or more kinds of different inclinations, from the first half side central nozzle toward the front end nozzle in the first half scan nozzle group,
• the nozzle jetting rates are decreased at two or more kinds of different inclinations, from the second half side central nozzle toward the rear end nozzle in the second half scan nozzle group,
• with respect to the nozzle groups for each scan used in recording of each scan that belongs to the first half scan, a first half jetting rate sum obtained by summing up the nozzle jetting rates of the corresponding nozzles is increased from the front end nozzle to the first half side central nozzle,
• with respect to the nozzle groups for each scan used in recording of each scan that belongs to the second half scan, a second half jetting rate sum obtained by summing up the nozzle jetting rates of the corresponding nozzles is decreased from the second half side central nozzle toward the rear end nozzle, and
• with respect to the nozzle groups for each scan used in recording of each of the plurality of scans, a sum of the first half jetting rate sum and the second half jetting rate sum of the corresponding nozzles becomes a specific value that is in a defined allowable range.

An image recording method for recording an image on a recording medium using a recording head that includes a nozzle row in which a plurality of nozzles that jet ink are arranged in a sub scan direction, the method comprising:

• a halftone processing step of performing halftone processing with respect to image data by using a dither mask;
• and
• a recording control step of controlling the jetting of the ink from the nozzles on the basis of dot data generated through the halftone processing and performs a control for recording an image on a recording medium by repeating a main scan operation of jetting the ink from the nozzles while relatively moving the recording head with respect to the recording medium in a main scan direction that is orthogonal to the sub scan direction to perform recording and a sub scan operation of relatively moving the recording medium with respect to the recording head in the sub scan direction,
• wherein in a recording process of completing, with respect to each scan band that is a region having a width of a sub scan movement amount of one sub scan operation of the recording medium in the sub scan direction, recording of the scan band by repeating a plurality of the main scan operations,
• in a case where the plurality of scans necessary for the completion of the recording of the scan band are divided into a first half scan and a second half scan on the basis of a scan order, when a nozzle disposed closest to a central side of the nozzle row in a first half scan nozzle group that is a nozzle group used in the recording of the first half scan in the nozzle row is referred to as a first half side central nozzle, a nozzle disposed closest to an end side of the nozzle row in the first half scan nozzle group is referred to as a front end nozzle, a nozzle disposed closest to a central side of the nozzle row in a second half scan nozzle group that is a nozzle group used in the recording of the second half scan in the nozzle row is referred to as a second half side central nozzle, a nozzle disposed closest to an end side of the nozzle row in the second half scan nozzle group is referred to as a rear end nozzle, the number of the main scan operations necessary for recording of one of rasters formed in the main scan direction is referred to as the number of overlaps, a region of a unit area represented by a product of the number of overlaps in the main scan direction and a nozzle pitch of the nozzle row in the sub scan direction is referred to as a unit region, and nozzles that record the same unit region in the nozzle groups for the respective scans used in the recording of the plurality of scans are referred to as corresponding nozzles,
• the dither mask is subjected to threshold setting for generating a dot disposition in which nozzle jetting rates that are relative usage rates of the respective nozzles of the nozzle row become nozzle jetting rates that satisfy a predetermined specific condition, in at least a part of a range of a recording duty, and
• the nozzle jetting rates that satisfy the specific condition are set such that
• the nozzle jetting rates are decreased at two or more kinds of different inclinations, from the first half side central nozzle toward the front end nozzle in the first half scan nozzle group,
• the nozzle jetting rates are decreased at two or more kinds of different inclinations, from the second half side central nozzle toward the rear end nozzle in the second half scan nozzle group,
• with respect to the nozzle groups for each scan used in recording of each scan that belongs to the first half scan, a first half jetting rate sum obtained by summing up the nozzle jetting rates of the corresponding nozzles is increased from the front end nozzle to the first half side central nozzle,
• with respect to the nozzle groups for each scan used in recording of each scan that belongs to the second half scan, a second half jetting rate sum obtained by summing up the nozzle jetting rates of the corresponding nozzles is decreased from the second half side central nozzle toward the rear end nozzle, and
• with respect to the nozzle groups for each scan used in recording of each of the plurality of scans, a sum of the first half jetting rate sum and the second half jetting rate sum of the corresponding nozzles becomes a specific value that is in a defined allowable range.