Printing methods and apparatus for reducing banding due to paper transport

An apparatus for dot matrix printing an image on a printing medium, comprising:

• a printing head,
• at least one array of equally spaced marking elements on the printing head, the marking elements available to be fired at firing moments being a set of active marking elements, the length of the active marking elements on the printing head in a slow scan direction (X) being the head length,
• means for generating a first relative linear movement between the printing head and the printing medium in a fast scan direction (Y) perpendicular to the slow scan direction (X), a movement in the fast scan direction (Y) during which the print head prints being a printing pass,
• means for generating a second relative linear movement between the printing head and the printing medium in the slow scan direction (X),
• printing head driving means for driving the printing head so as to print the image as a combination of mutually interstitial printing steps and/or interlacing steps, the means for generating the second relative linear movement being adapted for generating moving the printing medium relative to the printing head in the slow scan direction (X) with a transport distance step between the printing passes of the at least two sub-images, whereby the sum of all transport distance steps after writing one printing pass of each sub-image is exactly one head length, the transport distance steps being performed in at least two different step lengths,
• the apparatus being adapted to print the image as N sub-images, N being the number of colours used for printing multiplied by the number of mutually interstitial printing steps, and multiplied by the number of interlacing steps (N=C*P*I).

Printing head assembly comprising a plurality of identical neighbouring heads, each head having at least one row of a plurality of marking elements, the marking elements of a row which are available for printing being a set of active marking elements, the length in a slow scan direction (X) of the active marking elements on the printing head assembly being the assembly length, the printing head assembly being intended to be used for dot matrix printing on a printing medium of an image divided into sub-images, wherein during printing the printing medium is moved relative to the printing head assembly between printing passes over a transport distance step (TD) in the slow scan direction (X), the sum of all transport distance steps (TD) after writing one pass of each sub-image being exactly one assembly length of the printing head assembly, wherein all the heads are spread over a distance in the slow scan direction (X) which is equal to the number of marking elements in one row, divided by the number of transport distance steps (TD) needed to reach one head length, and wherein, the distance (x2) in the slow scan direction (X) between a first marking element of a first row of one of the heads and a first marking element of a first row of a neighbouring head equals nozzle pitch, with k an integer, i an integer between 0 and the number of heads −1, nozzle pitch being the distance between two marking elements of one row.