1. An image scanning apparatus comprising: a plurality of line sensors having filters having spectral sensitivities different from each other and being arranged at intervals in a sub-scanning direction in a predetermined order to scan an original document in the sub-scanning direction; a copyboard provided between an original document and said plurality of line sensors; an original document conveyance portion to convey an original document to a scanning position of said plurality of line sensors; a moving portion to move said copyboard and said plurality of line sensors relatively to each other at a speed different from a speed at which said original document conveyance portion conveys an original document; an in-line correction portion to synchronize a plurality of data, each including a plurality of pixels, output by said plurality of sensors such that said plurality of data become data that are output by said plurality of line sensors respectively scanning a same portion of an original document; a position detection portion to detect a position on the copyboard of a foreign object stuck on said copyboard before said original document conveyance portion conveys an original document; a determination pixel decision portion to decide a determination pixel to be used for determination from a plurality of pixels included in each of a plurality of scanned data output by said in-line correction portion while an original document is passing through said scanning position, based on a position detected by said position detection portion; and a determination portion to determine whether an original document is color or black-and-white, based on said decided determination pixel of each of said plurality of scanned data.