1. A printing apparatus, comprising: a halftone unit that performs a halftone process for determining dot formation for each pixel based on a grayscale value of the pixel constituting image data; and a print controlling unit that causes the dot formation determined by the halftone unit on a recording medium by causing a print head which ejects ink drops during a main scanning in a first direction and ejects ink drops during the main scanning in a second direction, which is opposite to the first direction to be driven, the halftone unit obtaining an evaluation index based on a target number which is set in advance for a first number of first dot pairs that generate dot overlap between each of the first dot pairs by a position deviation and a second number of second dot pairs that are far from each other between each of the second dot pairs by the position deviation so that the first number and the second number are the same, each of the first and second dot pairs being constituted by a first dot formed by the main scanning in the first direction and a second dot formed by the main scanning in the second direction, and performing the halftone process based on the evaluation index.