1. A method for calibrating image registration for two inkjet printheads, each printhead including a plurality of inkjet nozzles, the method comprising the steps of: automatically printing a first plurality of test patterns onto a media sheet, each one test pattern of the plurality of test patterns including a first portion printed with a first inkjet printhead and a second portion printed with a second inkjet printhead, wherein the first portion and second portion are of the same shape, wherein image registration of one of said two inkjet printheads is varied automatically among each one of the plurality of test patterns; sensing reflectance of each one test pattern of the plurality deriving a reflectance value for said each one test pattern of the plurality of test patterns, said derived reflectance value indicative of the sensed reflectance, and selecting the image registration corresponding to a select test pattern of the plurality of test patterns which has a reflectance value indicative of said select test pattern having the most unprinted background area.