1. A method of sensing a characteristic of an aritcle, as a document, by radiation from a specified window area of said article, comprising the steps of: determining a located window area of said article with the objective that said located window area coincides in area and location with said specified window area; sensing radiation from said located window area of said document by pixels to provide representative pixel signals for said located window area, thereby increasing the tolerance of the system to misalignment of the located window area with the specified window area; weighting said representative pixel signals to enhance those specific pixel signal values that are centrally positioned in said located window area; and processing said weighted pixel signal values by additive combination to provide characteristic data signals representative of said document characteristic at said specified window area and wherein said pixel signal values that are centrally positioned in said located window area are accorded greater significance.