1. An image processing method of converting multiple-value image data of an image into a plurality of dot patterns to form the image on a recording medium, the multiple-value image data being constituted of a plurality of pixels each of which has a graduated tone value that is one of graduated tone numbers, the image being formed by means of: a recording head which has a plurality of recording elements arranged in a first direction, the recording elements forming dots on the recording medium to form the image in accordance with the dot patterns, each of the dot patterns representing an arrangement of the dots corresponding to the graduated tone value for each of the pixels; and a relative movement device which causes the recording head and the recording medium to move relative to each other in a second direction that is substantially perpendicular to the first direction, the image processing method comprising the steps of: preparing a plurality of dot pattern tables respectively for the graduated tone numbers, each of the dot pattern tables being demarcated into blocks of the do patterns correlated with positions of the pixels so that a block row constituted of two of the blocks of the dot patterns that are mutually adjacent in the second direction is defined by a boundary in the second direction that does not coincide with a straight line parallel to the second direction, the dot patterns in each of the dot pattern tables being determined so that banding caused by recording characteristics of the recording elements is corrected in accordance with a correlation between each of the recording elements and surrounding recording elements of said each of the recording elements; and then selecting the dot patterns respectively for the pixels from the dot pattern tables in accordance with the positions of the pixels and the graduated tone values of the pixels to convert the multiple-value image data into the dot patterns, wherein: the pixels in the multiple-value image data are disposed in an arrangement in which the positions of the pixels are shifted by half a pixel in the first direction, between two of the pixels that are mutually adjacent in the second direction; the blocks of the dot patterns in each of the dot pattern tables are disposed in an arrangement corresponding to the arrangement of the pixels so that positions of the blocks are shifted by half a block in the first direction between two of the blocks that are mutually adjacent in the second direction; and each of the blocks has a shape of a rectangle defined by two boundary lines that are parallel to the first direction and two boundary lines that are parallel to the second direction.