Document edge detection by linear image sensor

Claim 1

A method for detecting edges of a document, comprising the steps of: positioning the document against a background having a background width dimension larger than a document width dimension, with a portion of the background exposed along opposed edges of the document whose positions are to be detected; illuminating the document with light from a light source; capturing successive lines of pixel data representing luminance of scanned pixels, wherein a first group of pixels represents luminance of an exposed portion of the background and a second group of pixels represents luminance of the document; processing a line of pixel data, by correlating, for successive current pixels, a group of n adjacent pixels with a successive group of n pixels to provide a correlation value S R , comparing the correlation value with a predetermined threshold value, and selecting a current pixel as a line edge position if the correlation value exceeds the threshold value, and wherein said correlating step employs, for each pixel in a group, a pixel value of (L i -L B ) r , where L i represents a luminance value for the pixel, L B represents a background luminance value, and r is a parameter which affects a sensitivity of the detection.

Claim 2

A method for detecting edges of a document, comprising the steps of: positioning the document against a background having a background width dimension larger than a document width dimension, with a portion of the background exposed along opposed edges of the document whose positions are to be detected; illuminating the document with light from a light source; capturing successive lines of pixel data representing luminance of scanned pixels, wherein a first group of pixels represents luminance of an exposed portion of the background and a second group of pixels represents luminance of the document; processing a line of pixel data, by correlating, for successive current pixels, a group of n adjacent pixels with a successive group of n pixels to provide a correlation value S R , comparing the correlation value with a predetermined threshold value, and selecting a current pixel as a line edge position if the correlation value exceeds the threshold value, and wherein said correlating step employs, for each pixel in a group, a pixel value of (L i -L B ) r , where L i represents a luminance value for the pixel, L B represents a background luminance value, and r is a parameter which affects a sensitivity of the detection.

Claim 12

A method for finding left and right edges of a document, comprising the following steps: placing the document against a background having a background width dimension larger than a document width dimension, with a portion of the background exposed along opposed left and right edges of the document whose positions are to be detected; illuminating the document with light from a light source; capturing successive lines of pixel data representing luminance of scanned pixels using a linear sensor array, wherein a first group of pixels represents luminance of a first exposed portion of the background adjacent the left edge of the document, a second group of pixels represents luminance of the document, and a third group of pixels represents a second exposed portion of the background adjacent the right edge of the document; processing a line of pixel data, by correlating, for successive current pixels commencing at a first end of the line corresponding to a left end of the sensor array, a group of n adjacent pixels with a successive group of n pixels to provide a correlation value S R , comparing the correlation value with a predetermined threshold value, and selecting the current pixel as a line left edge position if the correlation value exceeds the threshold value; and processing said line of pixel data, by correlating, for successive current pixels commencing at a second end of the line corresponding to a right end of the sensor array, a group of n adjacent pixels with a successive group of n pixels to provide a correlation value S R , comparing the correlation value with said predetermined threshold value, and selecting a current pixel as a line right edge position if the correlation value exceeds the threshold value; and wherein said correlating steps employ, for each pixel in a group, a pixel value of (L i -L B ) r , where L i represents a luminance value for the pixel, L B represents a background luminance value, and r is a parameter which affects a sensitivity of the detection.

Claim 13

A method for finding left and right edges of a document, comprising the following steps: placing the document against a background having a background width dimension larger than a document width dimension, with a portion of the background exposed along opposed left and right edges of the document whose positions are to be detected; illuminating the document with light from a light source; capturing successive lines of pixel data representing luminance of scanned pixels using a linear sensor array, wherein a first group of pixels represents luminance of a first exposed portion of the background adjacent the left edge of the document, a second group of pixels represents luminance of the document, and a third group of pixels represents a second exposed portion of the background adjacent the right edge of the document; processing a line of pixel data, by correlating, for successive current pixels commencing at a first end of the line corresponding to a left end of the sensor array, a group of n adjacent pixels with a successive group of n pixels to provide a correlation value S R , comparing the correlation value with a predetermined threshold value, and selecting the current pixel as a line left edge position if the correlation value exceeds the threshold value; and processing said line of pixel data, by correlating, for successive current pixels commencing at a second end of the line corresponding to a right end of the sensor array, a group of n adjacent pixels with a successive group of n pixels to provide a correlation value S R , comparing the correlation value with said predetermined threshold value, and selecting a current pixel as a line right edge position if the correlation value exceeds the threshold value; and wherein said correlating steps employ, for each pixel in a group, a pixel value of (L i -L B ) r , where L i represents a luminance value for the pixel, L B represents a background luminance value, and r is a parameter which affects a sensitivity of the detection.

Claim 16

A system for detecting an edge of a document, comprising: an optical sensor array of sensor pixel elements; a light source for generating illumination light; a background surface having a width dimension wider than a corresponding width dimension of the document such that, when the document is placed on the background surface, a portion of the background surface is exposed along the edge of the document whose position is to be detected; an optical apparatus for directing the illumination light onto the background surface and document and directing a light reflected from the background surface and document onto the sensor array; a controller/processor for controlling the light source and processing successive lines of sensor pixel data generated by the sensor array, the controller/processor including an algorithm function for processing a line of pixel data, by correlating, for successive current pixels, a group of n adjacent pixels with a successive group of n pixels to provide a correlation value S R , comparing the correlation value with a predetermined threshold value, and selecting a current pixel as a line edge position if the correlation value exceeds the threshold value, and wherein said algorithm function employs, for each pixel in a group, a pixel value of (L i -L B ) r , where L i represents a luminance value for the pixel, L B represents a background luminance value, and r is a parameter which affects a sensitivity of the detection.

Claim 17

A system for detecting an edge of a document, comprising: an optical sensor array of sensor pixel elements; a light source for generating illumination light; a background surface having a width dimension wider than a corresponding width dimension of the document such that, when the document is placed on the background surface, a portion of the background surface is exposed along the edge of the document whose position is to be detected; an optical apparatus for directing the illumination light onto the background surface and document and directing a light reflected from the background surface and document onto the sensor array; a controller/processor for controlling the light source and processing successive lines of sensor pixel data generated by the sensor array, the controller/processor including an algorithm function for processing a line of pixel data, by correlating, for successive current pixels, a group of n adjacent pixels with a successive group of n pixels to provide a correlation value S R , comparing the correlation value with a predetermined threshold value, and selecting a current pixel as a line edge position if the correlation value exceeds the threshold value, and wherein said algorithm function employs, for each pixel in a group, a pixel value of (L i -L B ) r , where L i represents a luminance value for the pixel, L B represents a background luminance value, and r is a parameter which affects a sensitivity of the detection.

Claim 25

A method for detecting edges of a document, comprising the steps of: performing a calibration scan of a background to determine a background luminance value; placing the document against a background having a background width dimension larger than a document width dimension, with a portion of the background exposed along opposed edges of the document whose positions are to be detected; illuminating the document with light from a light source; capturing successive lines of pixel data representing luminance of scanned pixels, wherein a first group of pixels represents luminance of an exposed portion of the background and a second group of pixels represents luminance of the document; processing a line of pixel data, by correlating, for successive current pixels, a group of n adjacent pixels with a successive group of n pixels to provide a correlation value S R , comparing the correlation value with a predetermined threshold value, and selecting a current pixel as a line edge position if the correlation value exceeds the threshold value, wherein said step of processing said line of pixel data includes calculating, to determine a left edge, the correlation value S R in accordance with the following formula: ##EQU8## where p is the current pixel being tested, L B represents the background luminance value, L i represents the luminance of the ith pixel, and r is a parameter which affects a sensitivity of the detection.

Claim 26

A method for detecting edges of a document, comprising the steps of: performing a calibration scan of a background to determine a background luminance value; placing the document against a background having a background width dimension larger than a document width dimension, with a portion of the background exposed along opposed edges of the document whose positions are to be detected; illuminating the document with light from a light source; capturing successive lines of pixel data representing luminance of scanned pixels, wherein a first group of pixels represents luminance of an exposed portion of the background and a second group of pixels represents luminance of the document; processing a line of pixel data, by correlating, for successive current pixels, a group of n adjacent pixels with a successive group of n pixels to provide a correlation value S R , comparing the correlation value with a predetermined threshold value, and selecting a current pixel as a line edge position if the correlation value exceeds the threshold value, wherein said step of processing said line of pixel data includes calculating, to determine a left edge, the correlation value S R in accordance with the following formula: ##EQU8## where p is the current pixel being tested, L B represents the background luminance value, L i represents the luminance of the ith pixel, and r is a parameter which affects a sensitivity of the detection.

Claim 27

A system for detecting an edge of a document, comprising: an optical sensor array of sensor pixel elements; a light source for generating illumination light; a background surface having a width dimension wider than a corresponding width dimension of the document such that, when the document is placed on the background surface, a portion of the background surface is exposed along an edge of the document whose position is to be detected; an optical apparatus for directing the illumination light onto the background surface and document and directing an light reflected from the background surface and document onto the sensor array; a controller/processor for controlling the light source and processing successive lines of sensor pixel data generated by the sensor array, wherein the processor/controller is adapted to perform a calibration scan of the background and to process resultant sensor signals to determine a background luminance value, the controller/processor including an algorithm function for processing a line of pixel data, by correlating, for successive current pixels, a group of n adjacent pixels with a successive group of n pixels to provide a correlation value S R , comparing the correlation value with a predetermined threshold value, and selecting the current pixel as a line edge position if the correlation value exceeds the threshold value, said algorithm function including calculating the correlation value S R in accordance with the following formula to determine a left edge: ##EQU9## where p is the current pixel being tested, L B represents the background luminance value, L i represents the luminance of the ith pixel, and r is a parameter which affects the sensitivity of the detection.

Claim 28

A system for detecting an edge of a document, comprising: an optical sensor array of sensor pixel elements; a light source for generating illumination light; a background surface having a width dimension wider than a corresponding width dimension of the document such that, when the document is placed on the background surface, a portion of the background surface is exposed along an edge of the document whose position is to be detected; an optical apparatus for directing the illumination light onto the background surface and document and directing an light reflected from the background surface and document onto the sensor array; a controller/processor for controlling the light source and processing successive lines of sensor pixel data generated by the sensor array, wherein the processor/controller is adapted to perform a calibration scan of the background and to process resultant sensor signals to determine a background luminance value, the controller/processor including an algorithm function for processing a line of pixel data, by correlating, for successive current pixels, a group of n adjacent pixels with a successive group of n pixels to provide a correlation value S R , comparing the correlation value with a predetermined threshold value, and selecting the current pixel as a line edge position if the correlation value exceeds the threshold value, said algorithm function including calculating the correlation value S R in accordance with the following formula to determine a left edge: ##EQU9## where p is the current pixel being tested, L B represents the background luminance value, L i represents the luminance of the ith pixel, and r is a parameter which affects the sensitivity of the detection.