Patent ID: 7748813

Claim:
A print apparatus comprising: a rotating unit to rotate a printed object; a print head to print visible information by ejecting ink droplets onto the printed object being rotated by the rotating unit; and a control unit to generate ink ejection data based on the visible information and controls the print head based on the ink ejection data, wherein the control unit converts the visible information, which is expressed using biaxial perpendicular coordinate data, to polar coordinate data and carries out dot density correction that applies a correction weighting to a luminance value of each dot to generate the ink ejection data, the correction weighting being calculated in accordance with a number of dots per unit area for each dot in the polar coordinate data, wherein the print head prints the visible information by moving along an axis which is parallel to a radial direction of a circle traced on the printed object being rotated and which passes through a position offset from a center of rotation of the printed object, and wherein the correction weighting is calculated according to an equation r i L i /r N L N where r i represents radius of a dot to be weighted, r N represents radius of an outermost dot in the polar coordinate data, L i represents width of a ring-shaped zone in a print region to be printed with dots at the radius r i , and L N represents width of a ring-shaped zone in a print region to be printed with dots at the radius r N .