| http://www.w3.org/ns/prov#value | - An image forming apparatus according to claim 1, wherein the gradation patch pattern image is made up of a plurality of patch patterns each having a plurality of gradation tones arranged such that corresponding gradation tones of the respective patch patterns are displaced by an interval of 1/n of a cycle length of a photosensitive drum in said image forming section, wherein n is an integer.
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