A printing method and an image processing method of converting digital image data, in which a first direction resolution in a first direction and a second direction resolution in a second direction intersecting the first direction are set, into digital dot data representing a dot formation state by an error diffusion method, the image processing method comprising:
- determining, by a controller, the dot formation state based on a pixel value and a distributed error in a conversion target pixel included in a plurality of pixels constituting the digital image data;
- diffusing, by the controller, an error generated in the conversion target pixel to a plurality of distribution destination pixels that are not converted;
- and
- forming, at a print head, a print image having the first direction resolution in the first direction and the second direction resolution in the second direction on a medium in accordance with the digital dot data,
- the controller holding a plurality of distribution ratio tables in each of which
- a total sum obtained by multiplying a distribution ratio set for each of the distribution destination pixels by a relative position of the distribution destination pixel in the first direction with respect to the conversion target pixel is a first direction total sum, and the first direction total sum is not 0,
- a total sum obtained by multiplying the distribution ratio set for each of the distribution destination pixels by a relative position of the distribution destination pixel in the second direction with respect to the conversion target pixel is a second direction total sum, and the second direction total sum is not 0, and
- a ratio of the second direction total sum to the first direction total sum is a total sum ratio,
- the plurality of distribution ratio tables including at least a first distribution ratio table and a second distribution ratio table,
- a first total sum ratio for the first distribution ratio table being the total sum ratio for a first resolution ratio that is one of resolution ratios which are settable for the digital image data and each of which indicates a ratio of the second direction resolution to the first direction resolution,
- a second total sum ratio for the second distribution ratio table being the total sum ratio for a second resolution ratio that is a different one of the resolution ratios and is greater than the first resolution ratio, and
- the second total sum ratio for the second distribution ratio table being greater than the first total sum ratio for the first distribution ratio table, and
- the diffusing of the error being performed in accordance with one of the distribution ratio tables that is selected from the distribution ratio tables based on a resolution ratio of the digital image data that is a ratio of the second direction resolution to the first direction resolution.