| 摘要 |
PURPOSE:To calculate the correct white level over the whole area by storing an image signal corresponding to the brightness of the light source which changes following the passing of the time, and correcting the level to slice the image signal based upon the stored image. CONSTITUTION:A fluorescent lamp 1 lights up, brightness is increased gradually and the characteristic, in which this is large, exists at the peripheral part of the tube ball. By the light radiated from such a fluorescent lamp 1, an original 2 is irradiated, the reflected light is image-picked up on the photodetecting surface of a CCD 4 by a lens 3 and the analog image signal can be obtained. An image signal is converted to the digital image signal by an A/D converter 5, supplied to a slice circuit 6, and the prescribed scanning line is stored into a memory 7. The image signal supplied to the slice circuit 6 is converted and sent to a binary image signal, for example, with the half value of said white level signal as a slice level, by using the white level signal calculated by a shading correcting calculating means 11, and therefore, the correct white level can be obtained over the whole area of the fluorescent lamp.
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