| 摘要 |
PURPOSE:To maintain an appropriate gradation characteristic by reading a prescribed gradation pattern on a photosensitive drum and updating a gradation correction means based on the read result. CONSTITUTION:The gradation pattern is formed on the photosensitive body and the gradation pattern is altered. The secular change of a gamma correction coefficient is corrected and the gradation characteristic which is always accurate is obtained. The luminance signal of an image is obtained in the CCD input element 21 and the luminance signal is converted into a digital luminance signal in an A/D conversion circuit 22, and it passes through a shading circuit 23 correcting the sensitivity variance of the CCD elements. Then, it is logarithm- corrected by a LOG conversion circuit 24 and is converted into a density signal. The density signal is converted so that original image density and output image density agree in the gamma characteristic of a printer at the time of initialization in a loop-up table 25. An LUT correction table 28 corrects LUT 25. Thus, the satisfactory image holding the appropriate gradation characteristic can always be obtained. |
