Patent ID: 7485834

Claim:
A method of estimating an in-focus level of a target in an image scanning apparatus, the image scanning apparatus configured to obtain one or more scan lines to produce a scan of the target, the method comprising: scanning a first part of the target at a nominal focus level so as to obtain a plurality of scan lines comprising corresponding image information; scanning one or more further parts of the target at one or more respective further focus levels so as to obtain one or more scan lines at each of the one or more respective further focus levels, the one or more scan lines comprising corresponding image information wherein the number of scan lines obtained at the nominal focus level is greater than the number of scan lines obtained at each of the one or more respective further focus levels; calculating a focus parameter for each of the nominal and the one or more further focus levels using the respective scan lines; and, estimating an in-focus level common to each of the first and further parts of the target using the calculated focus parameters; and adjusting the nominal focus level to coincide with the estimated focus level.