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.
Legal claims defining the scope of protection, as filed with the USPTO.
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 value 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 white signal output by the signal conversion unit for respective pixels when the light source illuminates the gray reference member; and correct 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.
2. The image scanning apparatus according to claim 1 , wherein: when the light source illuminates the gray reference member and the scanning unit performs a scanning operation at a first resolution, the controller sets a second resolution which is lower than the first resolution in a main scanning direction which is orthogonal to a conveying direction of the original sheet when there is no target number of pixels providing the difference equal to or smaller than the predetermined value among the first to N-th target numbers of pixels; and when the light source illuminates the gray reference member and the scanning unit performs the scanning operation at the second resolution, the controller detects a plurality of target numbers of pixels providing the difference equal to or smaller than the predetermined value, and determines a smallest one of the detected target number of pixels.
3. The image scanning apparatus according to claim 2 , wherein: the controller is configured to set a scanning resolution in the main scanning direction at which the scanning unit performs the scanning operation; and when the scanning resolution is different from the second resolution, the controller modifies the number of anomaly pixels in accordance with a ratio of the scanning resolution to the second resolution.
4. The image scanning apparatus according to claim 1 , wherein the controller stores the number of the anomaly pixels and the resolution of the white signal which is output, by the signal conversion unit, when the number of the anomaly pixels is determined in association with each other.
5. The image scanning apparatus according to claim 4 , wherein the controller is further configure to set the light quantity of the light source when the gray reference member is illuminated to obtain the gradation value of the white signal for shading correction to the light quantity when the number of pixels providing gradation values equal to or greater than a predetermined gradation value.
6. The image scanning apparatus according to claim 1 , wherein the reference gradation value is determined by adding a predetermined value to the reference gradation value which is stored in the storage in association with the correction target number of pixels.
7. The image scanning apparatus according to claim 1 , wherein the controller is further configured to: determine whether or not the gradation value of the gray signal output by the signal conversion unit for each of pixels of one line when the light source illuminates the gray reference member is equal to or greater than specific gradation value; count the number of pixels, from among all the pixels in one line, of which gradation values of the gray signal are equal to or greater than the specific gradation value; modify the specific gradation value to set a new specific gradation value by reducing the specific gradation value when the counted number of pixels is less than the number of the anomaly pixel reference value; determine whether the gradation values of the gray signal output by the signal conversion unit is equal to or greater than the new specific gradation value; and count the number of pixels, from among all the pixels in one line, of which gradation values of the gray signal are equal to or greater than the new specific gradation value, and wherein the specific gradation value before modified is a greatest one of the gradation values of the gray signal output by the signal conversion unit when the light source illuminates the gray reference member in accordance with the first light quantity, the first light quantity being defined such that the white signal having the first gradation value is output by the signal conversion unit when the light source illuminates the white reference value in accordance with the first light quantity.
8. The image scanning apparatus according to claim 1 , wherein the controller is further configured to: calculate an average value of gradation values of the white signal output by the signal conversion unit for respective pixels of one line when the light source illuminates the gray reference member; and correct the gradation values of the determined number of anomaly pixels by replacing the gradation values of the anomaly pixels with the average value of the gradation values of the white signal.
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March 26, 2015
February 23, 2016
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