Alignment of ink dots in an inkjet printer

A printing compensation method for a printer incorporating at least one printhead which scans across a medium in a scan direction while printing dots on said medium, said at least one printhead having a column of ink ejection elements arranged generally perpendicular to said scan direction, said method comprising:

• energizing said ink ejection elements to print a first test pattern prior to said printhead being installed in said printer;
• detecting said first test pattern;
• generating first positional data for at least some of said ink ejection elements based on said first test pattern;
• storing said first positional data in a memory for said printhead;
• energizing said ink ejection elements to print a second test pattern after said printhead is installed in said printer;
• detecting said second test pattern;
• generating second positional data for at least some of said ink ejection elements based on said second pattern;
• calculating third positional data for at least some of said ink ejection elements based on said first positional data and said second positional data;
• generating information for energizing signal timing corrections for at least some of said ink ejection elements to correct for any misalignment between printed matter printed by said ink ejection elements while said printhead is installed in said printer;
• storing information to generate said timing corrections for said ink ejection elements;
• and
• time-correcting energization signals to said ink ejection elements, as appropriate, by said timing corrections while said printhead is printing across said medium,
• wherein said ink ejection elements are divided into groups, all ink ejection elements within a group receive a common enabling pulse, and wherein said timing corrections comprise a single timing correction for each group.