Image reading apparatus and image reading method

An image reading apparatus comprising:

• a reader operable to read an image formed on a sheet to acquire RGB values of pixels that constitute the image, by using a sheet-through method;
• an extractor operable to compare an RGB value of each target pixel in the image with an RGB value of a neighboring pixel thereof to judge whether a difference therebetween is no less than a prescribed threshold, and extract the target pixel as a line-shaped noise pixel if the difference is no less than the prescribed threshold and the target pixel constitutes a series of line-shaped noise pixels extending in a feeding direction of the sheet;
• a corrector operable to defines a plurality of blocks throughout a surrounding area of the line-shaped noise pixel by averaging R, G and B components among each prescribed number of pixels included in the surrounding area, extracts one of the blocks whose non-noise color component has a smallest difference from a non-noise color component of the line-shaped noise pixel, and corrects the RGB value of the line-shaped noise pixel by replacing with an RGB value of the extracted one of the blocks, where the non-noise color component is any component of the RGB value of the line-shaped noise pixel other than a noise color component, and the noise color component is a component that has the difference that is no less than the prescribed threshold;
• and
• a correction prohibiter operable to extract, from RGB components of all the surrounding pixels, a minimum and a maximum of the noise color component, calculate a difference therebetween as a displacement of the noise color component among the surrounding pixels, extract a minimum and a maximum of the non-noise color component, and calculate a difference therebetween as a displacement of the non-noise color component among the surrounding pixels, and
• extract, from RGB values of all the blocks, a minimum and a maximum of the noise color component and calculate a difference therebetween as a displacement of the noise color component among the blocks, extract a minimum and a maximum of the non-noise color component, and calculate a difference therebetween as a displacement of the non-noise color component among the blocks, and
• prohibit the correction if the displacement of the noise color component is greater than a first reference value and the displacement of the non-noise color component is not greater than a second reference value with respect to either the surrounding pixels or the blocks.

An image reading method comprising:

• a reading step of reading an image formed on a sheet to acquire RGB values of pixels that constitute the image, by using a sheet-through method;
• an extracting step of comparing an RGB value of each target pixel in the image with an RGB value of a neighboring pixel thereof to judge whether a difference therebetween is no less than a prescribed threshold, and extracting the target pixel as a line-shaped noise candidate pixel if the difference is no less than the prescribed threshold and the target pixel constitutes a series of line-shaped noise candidate pixels extending in a feeding direction of the sheet;
• a determining step of calculating differences between the R, G and B components included in the RGB value of the line-shaped noise candidate pixel and R, G and B components included in an RGB value of each of surrounding pixels included in a surrounding area of the line-shaped noise candidate pixel respectively, and determining the line-shaped noise candidate pixel as a line-shaped noise pixel if (i) only one of the components has a difference that is no less than a prescribed value, or (ii) two of the components have substantially a same difference that is no less than a prescribed value;
• and
• a correcting step of correcting the RGB value of the line-shaped noise pixel based on an RGB value of at least one of surrounding pixels included in a surrounding area of the line-shaped noise pixel.

An image reading method comprising:

• a reading step of reading an image formed on a sheet to acquire RGB values of pixels that constitute the image, by using a sheet-through method;
• an extracting step of comparing an RGB value of each target pixel in the image with an RGB value of a neighboring pixel thereof to judge whether a difference therebetween is no less than a prescribed threshold, and extracting the target pixel as a line-shaped noise pixel if the difference is no less than the prescribed threshold and the target pixel constitutes a series of line-shaped noise pixels extending in a feeding direction of the sheet;
• a correcting step of defining a plurality of blocks throughout a surrounding area of the line-shaped noise pixel by averaging R, G and B components among each prescribed number of pixels included in the surrounding area, extracting one of the blocks whose non-noise color component has a smallest difference from a non-noise color component of the line-shaped noise pixel, and correcting the RGB value of the line-shaped noise pixel by replacing with an RGB value of the extracted one of the blocks, where the non-noise color component is any component of the RGB value of the line-shaped noise pixel other than a noise color component, and the noise color component is a component that has the difference that is no less than the prescribed threshold;
• and
• a correction prohibiting step of extracting, from RGB components of all the surrounding pixels, a minimum and a maximum of the noise color component, calculating a difference therebetween as a displacement of the noise color component among the surrounding pixels, extracting a minimum and a maximum of the non-noise color component, and calculating a difference therebetween as a displacement of the non-noise color component among the surrounding pixels, and
• extracting, from RGB values of all the blocks, a minimum and a maximum of the noise color component and calculating a difference therebetween as a displacement of the noise color component among the blocks, extracting a minimum and a maximum of the non-noise color component, and calculating a difference therebetween as a displacement of the non-noise color component among the blocks, and,
• prohibiting the correction if the displacement of the noise color component is greater than a first reference value and the displacement of the non-noise color component is not greater than a second reference value with respect to either the surrounding pixels or the blocks.