Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Jan-31
This article describes a shading compensation in a document scanner wherein a curved dichroic filter is positioned between a fluorescent lamp and a document being scanned. Referring to Fig. 1, a document 1 is illuminated by a fluorescent lamp 2 through a dichroic filter 3. Reflected light representing an image pattern of the document 1 is sensed by an optical sensor unit (not shown). Relative movement of the document 1 to the optical sensor unit scans the image of the document 1. Fig. 2(a) shows an uneven distribution of light intensity along the fluorescent lamp 2. The light intensity gradually decreases from the center portion towards both the end portions. The uneven distribution is compensated by the dichroic filter 3 which has a glass layer 4 and a thin film 5, as shown in Fig. 3.