Image and printhead control

A method of preparing a two-dimensional bit-mapped image having n pixels per row for printing using one or more printheads each having a row of ejection locations, each ejection location having associated ejection electrodes to which a voltage is applied in use sufficient to cause particulate agglomerations to be formed from within a body of printing fluid, and wherein, in order to cause charged particulate agglomerations to be ejected as printed droplets from selected ejection locations, voltage pulses of predetermined amplitude and duration, as determined by the respective bit values Pi, where 1≦i≦n, of the individual pixels of rows of the image, are applied to the electrodes of the selected ejection locations, wherein Pi is determined by the expression:

• FOR i=1 to n:
• FOR j=1 to (4k+1):
• IF Pi≦PL AND Pi+1 . . . Pi+(1+k)≧PH then Pi+j:=αj·Pi+j
• or
• IF Pi≦PL AND Pi−1 . . . P1−(1+k)≧PH then Pi−j:=αj·Pi−j
• where αj<1 for j=1 or j=2k and αj≦1 for j=3k or j=4k
• OR
• FOR i=1 to n:
• FOR j=1 to (4k+1):
• IF Pi≦PL AND Pi+1 . . . Pi+(1+k)≧PH then Pi+j:=αj·Pi+j
• or
• IF Pi≦PL AND Pi−1 . . . Pi−(1+k)≧PH then Pi−j:=αj·Pi−j
• where αj>1 for k≧2 and (j=k or k+1), and αj≧1 for k≧3 and
• (2≦j≦k−1 or k+2≦j≦2k−1 or j=2k+1, 3k+1, or 4k+1),
• where PL is a low threshold and PH is a high threshold defined as 0<PL<PH<1, and where the arrangement of the printheads forms an array of ejector locations on a spacing parallel to the rows of the image of k times the pixel spacing of the image arranged parallel to the width of the image, with A interleaved printheads arranged to print on B interleaved passes, such that k=A·B such that a given printhead on a given pass will print the pixels of every kth column of the image.