IMAGE INPUT DEVICE PROVIDING BACKGROUND DETECTION ARRANGEMENT

A document background member is provided with a distinctive background patterning including image data of a selected frequency, that the background can be detected by an image frequency detection circuit. Detection or non-detection of the distinctive patterning enables determination of edges of a scanned original. In an electrophotographic-type copier, an edge sensing ararngement may be provided with a distinctive background patterning against which the image is illuminated, to provide an electronically detectable and clear delineation between document and background for the purpose of edge detection. The edge detection arrangement may also control various erasure arrangements that erase the detectable patterning, to prevent it from showing up in the image. A sensor may be fabricated to produced a strong detectable beating pattern when used against selected background patternings.