Inkjet printer

1. An inkjet printer, comprising:

a first ink head including a plurality of nozzles through which a first ink is ejected towards a recording medium to form ink dots of the first ink on the recording medium;

a second ink head including a plurality of nozzles through which a second ink is ejected towards the recording medium to form ink dots of the second ink on the recording medium;

a moving mechanism to move the first ink head and the second ink head, and the recording medium, with respect to each other; and

a controller connected with the first ink head, the second ink head and the moving mechanism, to control the first ink head, the second ink head and the moving mechanism;

wherein

the controller includes:

a converter to convert image data of the first ink into the ink dots of the first ink, and to convert image data of the second ink into the ink dots of the second ink;

a generator to generate, upon receipt of data on the ink dots of the second ink converted by the converter, a plurality of dot groups, including at least a first dot group and a second dot group, of the ink dots of the second ink, the first dot group including at least a portion of the ink dots of the second ink, and the second dot group including at least a portion of the ink dots of the second ink;

a first printing controller to form, on the recording medium, a first printing layer of the ink dots of the first ink and the ink dots of the first dot group; and

a second printing controller to form a second printing layer of the ink dots of the second dot group, above or below the first printing layer; and

the generator generates the plurality of dot groups such that the plurality of dot groups include all the ink dots of the second ink;

the first ink is a special color ink; and

the second ink is a process color ink.

2. The inkjet printer according to claim 1 , wherein the generator generates the plurality of dot groups such that the plurality of dot groups match the ink dots of the second ink.

3. The inkjet printer according to claim 1 , wherein the generator generates the plurality of dot groups such that a portion of, or an entirety of, the ink dots of the second ink overlap in the plurality of dot groups.

4. The inkjet printer according to claim 3 , wherein the generator generates the plurality of dot groups such that the second dot group matches the ink dots of the second ink.

5. The inkjet printer according to claim 1 , wherein

the controller includes a ratio setter to set a ratio of ink dots belonging to each of the plurality of dot groups with respect to the ink dots of the second ink; and

the generator generates the plurality of dot groups such that the ratio of the ink dots belonging to each of the plurality of dot groups with respect to the ink dots of the second ink is the same as the ratio set by the ratio setter.

6. The inkjet printer according to claim 1 , wherein the controller includes a mode selector to select any one of a plurality of printing modes including a first printing mode of forming the first printing layer below the second printing layer and a second printing mode of forming the first printing layer above the second printing layer.

7. The inkjet printer according to claim 1 , wherein

the second ink head includes actuators causing the second ink to be ejected from the nozzles; and

the controller includes:

a first color size controller to control the actuators such that a dot size of the second ink forming the first dot group is a first size; and

a second size controller to control the actuators such that a dot size of the second ink forming the second dot group is a second size.

8. The inkjet printer according to claim 7 , wherein the controller includes:

a first size setter connected with the first size controller to allow the first size to be set; and

a second size setter connected with the second size controller to allow the second size to be set.

9. The inkjet printer according to claim 7 , wherein the first size is smaller than the second size.

10. The inkjet printer according to claim 1 , wherein the generator randomly extracts the ink dots belonging to the first dot group from the ink dots of the second ink.

11. The inkjet printer according to claim 6 , further comprising a user interface that is connected to the mode selector and that enables a user to select the one of a plurality of printing modes.

12. The inkjet printer according to claim 6 , wherein the plurality of printing modes includes a third printing mode of printing only one layer.

13. An inkjet printer comprising:

a first ink head including a plurality of nozzles through which a first ink is ejected towards a recording medium to form ink dots of the first ink on the recording medium;

a second ink head including a plurality of nozzles through which a second ink is ejected towards the recording medium to form ink dots of the second ink on the recording medium;

a moving mechanism to move the first ink head and the second ink head, and the recording medium, with respect to each other; and

a controller connected with the first ink head, the second ink head and the moving mechanism, to control the first ink head, the second ink head and the moving mechanism;

wherein

the controller includes:

a generator to generate, upon receipt of data on the ink dots of the second ink, a plurality of dot groups, including at least a first dot group and a second dot group, of the ink dots of the second ink;

a first printing controller to form, on the recording medium, a first printing layer of the ink dots of the first ink and the ink dots of the first dot group; and

a second printing controller to form a second printing layer of the ink dots of the second dot group, above or below the first printing layer; and

the generator generates the plurality of dot groups such that the plurality of dot groups include all the ink dots of the second ink;

the moving mechanism includes a feeding mechanism to feed the recording medium;

the first ink head and the second ink head are located side by side in a scanning direction perpendicular or substantially perpendicular to a feeding direction in which the recording medium is fed;

the first ink head includes:

a first upstream nozzle array including a portion of the plurality of nozzles arrayed in the feeding direction; and

a first downstream nozzle array including another portion of the plurality of nozzles arrayed in the feeding direction, the first downstream nozzle array being located downstream with respect to the first upstream nozzle array in the feeding direction;

the second ink head includes:

a second upstream nozzle array including a portion of the plurality of nozzles arrayed in the feeding direction; and

a second downstream nozzle array including another portion of the plurality of nozzles arrayed in the feeding direction, the second downstream nozzle array being located downstream with respect to the second upstream nozzle array in the feeding direction;

the first printing controller:

in a case in which the first printing layer is to be formed below the second printing layer, causes the nozzles of the first upstream nozzle array to eject the first ink, and causes the nozzles of the second upstream nozzle array to eject the second ink to form the ink dots of the first dot group, to form the first printing layer; and

in a case in which the first printing layer is to be formed above the second printing layer, causes the nozzles of the first downstream nozzle array to eject the first ink, and causes the nozzles of the second downstream nozzle array to eject the second ink to form the ink dots of the first dot group, to form the first printing layer; and

the second printing controller:

in the case in which the first printing layer is to be formed below the second printing layer, causes the nozzles of the second downstream nozzle array to eject the second ink to form the ink dots of the second dot group, to form the second printing layer; and

in the case in which the first printing layer is to be formed above the second printing layer, causes the nozzles of the second upstream nozzle array to eject the second ink to form the ink dots of the second dot group, to form the second printing layer.