1. A method of optical inspection, the method comprising: positioning at least one wafer for inspection by an optical inspection tool; and performing, according to a dilution plan, a diluted scan of at least one slice of the wafer, said slice lying along a scanning axis and having a total area, so that at least ten percent of the total area of said slice is not imaged; wherein: (a) performing the diluted scan comprises scanning, following an inspection path, a plurality of areas in at least one slice, and imaging some, but not all, of the areas in the slice; (b) the dilution plan is formulated based on a dilution parameter indicating an amount of dilution for the at least one slice; and (c) the inspection path is calculated according to at least one of: (i) a desired size for an inspected region of the wafer, (ii) a number of imaging unit areas per inspected region, (iii) a number of slices per inspected region, and (iv) a position of each imaging area relative to an inspected region.