| 摘要 |
A controller is configured to set a reference gradation value when a gray reference member is illuminated. When the number of pixels, of which the gradation values is equal to or greater than the reference gradation value, is a target number of pixels, both are stored in association with each other. A correction target number which is a minimum target number of pixels from among a plurality of target numbers of pixels respectively providing differences, which is less than a predetermined value, between the reference gradation values stored in association with an M-th target number and an (M+1)-th target number. The controller further determines an anomaly pixel number which is the number of anomaly pixels having gradation values which are equal to or greater than a base gradation value. The gradation values of the determined number of anomaly pixels are corrected. |
| 主权项 |
1. An image scanning apparatus, comprising:
a gray reference member arranged in a conveying path in which an original sheet is to be conveyed, the gray reference member having a reflection coefficient smaller than that of a white color; a scanning unit configured to scan an image on the original sheet on a line basis, the scanning unit including a light source configured to illuminate the original sheet when passing the gray reference member and a plurality of photoelectric conversion elements aligned in a scanning direction which is a transverse direction of the conveying path; a signal conversion unit configured to convert analog signals from the plurality of photoelectric conversion elements to digital signals, respectively; a storage; and a controller, the controller being configured to:
set first to N-th target numbers of pixels, each target number representing the number of a plurality of pixels, N being more than two;changeably set a reference gradation value which represents a value of a white signal output by the signal conversion unit for each pixel when the light source illuminates the gray reference member, between a highest gradation value and a smaller gradation value which is smaller than the highest gradation value;store, in the storage, a specific reference gradation value in association with the target number of pixels when the number of pixels having gradation values equal to or greater than the specific reference gradation value is a specific target number of pixels;determine a correction target number which is a minimum target number of pixels from among a plurality of target numbers of pixels respectively providing differences, which is less than a predetermined value, between the reference gradation value stored in association with an M-th target number among the first to N-th target numbers and the reference gradation stored in association with an (M+1)-th target number;determine an anomaly pixel number which is the number of anomaly pixels having gradation values which are equal to or greater than a base gradation value, the base gradation value being determined based on the reference gradation value stored in the storage in association with the correction target number of pixels from among the gradation values of the with signal output by the signal conversion unit for respective pixels when the light source illuminates the gray reference member; andcorrect the gradation values of the anomaly pixels, the number of the anomaly pixels of which gradation values are to be corrected being the anomaly pixel number. |
