There is conventionally known an image reading apparatus for illuminating a transparent original and reading its image, as disclosed in U.S. Pat. No. 5,038,227. The conventional image reading apparatus will be described with reference to FIGS. 1A and 1B.
FIG. 1A is a sectional view showing an image reading apparatus, and FIG. 1B is a perspective view. A bar-like fluorescent tube 700 is attached to the end of a light guide plate 701 which is arranged in parallel to a platen glass 702 for setting an original. The light guide plate 701 is a resin light diffusion panel for diffusing light emitted by the fluorescent tube 700 and emitting the light from the surface.
The platen glass 702 is an original table for setting a transparent original such as a photographic film. A transparent original set on the platen glass 702 is sandwiched and fixed between the light guide plate 701 and the platen glass 702. A CCD 703 is a linear imaging element for converting image information into an electric image signal. An imaging optical system 704 optically guides the image information of the transparent original to the CCD 703.
A carriage 705 supports the CCD 703 and imaging optical system 704, and is movable in the subscanning direction along guides 706 and 707. When the entire surface of a transparent original is illuminated by the light guide plate 701, image information of the transparent original is read by the CCD 703 via the imaging optical system 704. The carriage 705 is moved in the subscanning direction to sequentially read the image of the entire transparent original.
If, however, dirt such as dust exists on a transparent original or an original is scratched, the conventional image reading apparatus reads even the dirt or scratch, so the image degrades owing to the dirt or scratch.