Image forming apparatus and method

An image forming apparatus, comprising:

• a first group of large nozzles which eject large droplets of liquid for a color;
• a second group of small nozzles which eject small droplets of the liquid for color, the small droplets having volume smaller that the large droplets;
• a dot data creation device which creates dot data according to input image data;
• a dot data correction device which corrects the dot data if there is an abnormal nozzle in one of the first and second groups, in such a manner that a corrective nozzle is selected from the other of the first and second groups, and droplet ejection performed by the corrective nozzle substitutes for droplet ejection that is originally to be performed by the abnormal nozzle;
• and
• a driving device which drives the large and small nozzles to eject the large and small droplets according to the corrected dot data, wherein:
• the dot data correction device corrects the dot data if the abnormal nozzle belongs to the first group, in such a manner that a total amount of the liquid ejected by the corrective nozzle is less than a total amount of the liquid that was originally to be ejected by the abnormal nozzle;
• the dot data correction device controls ink-droplet ejection such that the large droplets are ejected and deposited onto a porous surface of paper to form large dots on the paper, and the small droplets are ejected and deposited onto the porous surface of the paper to form small dots on the paper;
• wherein the dot data correction device corrects the dot data taking into account that
• the volume of each of the large droplets is x times the volume of each of the small droplets, and
• for a total volume of a first number of the small droplets which is equal to the volume of each of the large droplets, a total surface area of the first number of the small dots formed on the paper is greater than a surface area of each of the large dots formed on the paper,
• so that the dot data correction device corrects the dot data if the abnormal nozzle belongs to the first group, in such a manner that y small dots substitute for one large dot, where 1<y<x.

An image forming method for an image forming apparatus having a first group of large nozzles and a second group of small nozzles, the large nozzles ejecting large droplets of liquid for a color, the small nozzles ejecting small droplets of the liquid for the color, the small droplets having volume smaller that the large droplets, the method comprising the steps of:

• creating dot data according to input image data;
• finding an abnormal nozzle in the large and small nozzles;
• correcting the dot data if the abnormal nozzle is found in one of the first and second groups, in such a manner that a corrective nozzle is selected from the other of the first and second groups, and droplet ejection performed by the corrective nozzle substitutes for droplet ejection that is originally to be performed by the abnormal nozzle;
• and
• driving the large and small nozzles to eject the large and small droplets according to the corrected dot data, wherein:
• in the correcting step, if the abnormal nozzle belongs to the second group, the dot data is corrected in such a manner that a total amount of the liquid ejected by the corrective nozzle is greater than a total amount of the liquid that is originally to be ejected by the abnormal nozzle;
• the correcting step controls ink-droplet ejection such that the large droplets are ejected and deposited onto a porous surface of paper to form large dots on the paper, and the small droplets are ejected and deposited onto the porous surface of the paper to form small dots on the paper;
• wherein the correcting step corrects the dot data taking into account that
• the volume of each of the large droplets is x times the volume of each of the small droplets, and
• for a volume of each of the large droplets which is equal to a total volume of a first number of the small droplets, a surface area of each of the large dots formed on the paper is smaller than a total surface area of the first number of the small dots formed on the paper,
• so that in the correcting step, if the abnormal nozzle belongs to the second group, the dot data is corrected in such a manner that one large dot substitutes for y small dots, where 1<y<x.

An image forming method for an image forming apparatus having a first group of large nozzles and a second group of small nozzles, the large nozzles ejecting large droplets of liquid for a color, the small nozzles ejecting small droplets of the liquid for the color, the small droplets having volume smaller than the large droplets, the method comprising the steps of:

• creating dot data according to input image data;
• finding an abnormal nozzle in the large and small nozzles;
• correcting the dot data if the abnormal nozzle is found in one of the first and second groups, in such a manner that a corrective nozzle is selected from the other of the first and second groups, and droplet ejection performed by the corrective nozzle substitutes for droplet ejection that is originally to be performed by the abnormal nozzle;
• and
• driving the large and small nozzles to eject the large and small droplets according to the corrected dot data, wherein:
• in the correcting step, if the abnormal nozzle belongs to the first group, the dot data is corrected in such a manner that a total amount of the liquid ejected by the corrective nozzle is less than a total amount of the liquid that is originally to be ejected by the abnormal nozzle;
• the correcting step controls ink-droplet ejection such that the large droplets are ejected and deposited onto a porous surface of paper to form large dots on the paper, and the small droplets are ejected and deposited onto the porous surface of the paper to form small dots on the paper;
• and
• wherein the correcting step corrects the dot data taking into account that
• the volume of each of the large droplets is x times the volume of each of the small droplets, and
• if a total volume of a first number of the small droplets is equal to the volume of each of the large droplets, then a total surface area of the first number of the small dots formed on the paper is greater than a surface area of each of the large dots formed on the paper,
• so that in the correcting step, if the abnormal nozzle belongs to the first group, the dot data is corrected in such a manner that y small dots substitute for one large dot, where 1<y<x.