Patent ID: 8040556

Claim:
An image data generating method of generating image data used in an inkjet printer, wherein said printer comprises a head for ejecting fine droplets of ink onto a printing medium and a scanning mechanism for moving said printing medium relatively to said head in a predetermined scan direction, said head has one or more outlet rows arranged in said scan direction, each of said one or more outlet rows includes a plurality of outlets arranged in a width direction perpendicular to said scan direction, and said image data generating method comprises the steps of: a) preparing a threshold matrix which is an array compared with a grayscale original image in generating a halftone image which represents ON/OFF of ejection of ink from said plurality of outlets in printing, said threshold matrix including sleep elements representing sleep of ejection of ink in each element row which is a plurality of elements arranged in a row direction corresponding to said width direction; and b) comparing said threshold matrix with said original image to generate data of a halftone image where while printing is performed, the number of outlets included in each outlet group which is brought into a sleep state continuously in said width direction is made to be equal to or larger than 1 and equal to or smaller than a predetermined number in each of said one or more outlet rows, and the number of outlets included in each outlet group which is not brought into said sleep state continuously in said width direction is made to be equal to or larger than 1 and equal to or smaller than a predetermined number in each of said one or more outlet rows.