Shading compensation for scanning apparatus

Claim 3

The method according to claim 1 including the step of reducing interference with said test signals from dust and defects by defocusing said test image.

Claim 4

The method according to claim 1 including the step of modifying said compensating signals by a predetermined constant to offset differences between said first and second operating modes.

Claim 7

The method according to claim 4 including the steps of: (a) converting image signals processed in said first operating mode from analog signals to digital signals; and (b) adjusting the analog-to-digital signal converting level in response to said compensating signals.

Claim 8

In a multi-mode raster scanner having a first image processing mode wherein analog image signals are converted to multi-bit digital signals representative of the image gray level and a second image processing mode wherein analog image signals are converted to single bit binary signals, selector means for selecting one of said first and second image processing modes, a platen for supporting image bearing originals for scanning, and at least one multi-element scanning array movable relative to said platen along a predetermined scan path to scan said platen and any original thereon line by line, the combination of: (a) a calibrating strip disposed in said scan path, said strip having an image of predetermined optical density, scanning of said strip by said array producing calibration signals; (b) said selector means routing said calibration signals to said first image processing mode whereby to produce multi-bit digital calibration signals; (c) means for averaging said calibration signals in blocks, each of said blocks consisting of a predetermined number of said scanning array elements; (d) a memory for storing said calibration signals; (e) address means for addressing said memory to access said calibration signals; and (f) means to combine said calibration signals from said memory with image signals output by said array in each of said first and second image processing modes, said calibration signals being combined with image signals from the blocks of scanning array elements from which said calibration signals are derived.

Claim 9

In a multi-mode raster scanner having a first image processing mode wherein analog image signals are converted to multi-bit digital signals representative of the image gray level and a second image processing mode wherein analog image signals are converted to single bit binary signals, selector means for selecting one of said first and second image processing modes, a platen for supporting image bearing originals for scanning, and at least one multi-element scanning array movable relative to said platen along a predetermined scan path to scan said platen and any original thereon line by line, the combination of: (a) a calibrating strip disposed in said scan path, said strip having an image of predetermined optical density, scanning of said strip by said array producing calibration signals; (b) said selector means routing said calibration signals to said first image processing mode whereby to produce multi-bit digital calibration signals; (c) means for averaging said calibration signals in blocks, each of said blocks consisting of a predetermined number of said scanning array elements; (d) a memory for storing said calibration signals; (e) address means for addressing said memory to access said calibration signals; and (f) means to combine said calibration signals from said memory with image signals output by said array in each of said first and second image processing modes, said calibration signals being combined with image signals from the blocks of scanning array elements from which said calibration signals are derived.

Claim 10

The scanner according to claim 6 in which said combining means includes analog-to-digital converting means for each of said first and second image processing modes.

Claim 11

In a raster scanner having a platen for supporting image bearing originals for scanning, at least one array for line scanning an original on said platen, said array being comprised of a plurality of photosensors producing analog image signals representative of the image area scanned, and analog-to-digital converting means for converting said analog image signals to digital image signals, the combination of: (a) a calibration image, scanning of said calibration image by said array producing analog calibration signals; (b) means for feeding said analog calibration signals to said analog-to-digital converting means; said analog-to-digital converting means converting said analog calibration signals to digital calibration signals; (c) means for averaging groups of said digital calibration signals, each of said groups comprising digital calibration signals from a preset number of said array photosensors; (d) digital-to-analog conversion means for converting the averaged calibration signals to analog signals; (e) compensating means for compensating the image signals produced by said array with said averaged calibration signals; (f) thresholder means for processing said analog image signals produced by said array to provide binary image signals, (g) selector means for routing said analog image signals produced by said array to said analog-to-digital conversion means to provide digital image signals or to said thresholder means to provide binary image signals selectively, and (h) means for inputting said averaged calibration signals to said analog-to-digital conversion means or said thresholder means to modify image signals input to said analog-to-digital conversion means and to said thresholder means.

Claim 12

In a raster scanner having a platen for supporting image bearing originals for scanning, at least one array for line scanning an original on said platen, said array being comprised of a plurality of photosensors producing analog image signals representative of the image area scanned, and analog-to-digital converting means for converting said analog image signals to digital image signals, the combination of: (a) a calibration image, scanning of said calibration image by said array producing analog calibration signals; (b) means for feeding said analog calibration signals to said analog-to-digital converting means; said analog-to-digital converting means converting said analog calibration signals to digital calibration signals; (c) means for averaging groups of said digital calibration signals, each of said groups comprising digital calibration signals from a preset number of said array photosensors; (d) digital-to-analog conversion means for converting the averaged calibration signals to analog signals; (e) compensating means for compensating the image signals produced by said array with said averaged calibration signals; (f) thresholder means for processing said analog image signals produced by said array to provide binary image signals, (g) selector means for routing said analog image signals produced by said array to said analog-to-digital conversion means to provide digital image signals or to said thresholder means to provide binary image signals selectively, and (h) means for inputting said averaged calibration signals to said analog-to-digital conversion means or said thresholder means to modify image signals input to said analog-to-digital conversion means and to said thresholder means.

Claim 13

The raster scanner according to claim 8 in which said calibration image is out of focus relative to said array to enhance the calibration signals obtained.

Claim 14

In a raster scanner having a platen for supporting image bearing originals for scanning, at least one array for line scanning an original on said platen, said array being comprised of a plurality of photosensors and producing analog image signals representative of the image area scanned, and analog-to-digital converting means for converting said analog image signals to digital image signals, the combination of: (a) a calibration image, scanning of said calibration image by said array producing analog calibration signals; (b) means for feeding said analog calibration signals to said analog-to-digital converting means; said analog-to-digital converting means converting said analog calibration signals to digital calibration signals; (c) means for averaging groups of said digital calibration signals, each of said groups comprising digital calibration signals from a preset number of said array photosensors; (d) digital-to-analog conversion means for converting the averaged calibration signals to analog signals; (e) compensating means for compensating the image signals produced by said array with said averaged calibration signals; (f) thresholder means for processing said analog image signals produced by said array to provide binary image signals, (g) selector means for routing said analog image signals produced by said array to said analog-to-digital conversion means to provide digital image signals or to said thresholder means to provide binary image signals selectively, and (h) means for inputting said averaged calibration signals to said analog-to-digital conversion means or said thresholder means to modify image signals input to said analog-to-digital conversion means and to said thresholder means, said thresholder means including a screen for screening said image signals and a thresholder for thresholding said image signals, and second selector means to route said image signals to one of said screen and thresholder selectively.

Claim 15

In a raster scanner having a platen for supporting image bearing originals for scanning, at least one array for line scanning an original on said platen, said array being comprised of a plurality of photosensors and producing analog image signals representative of the image area scanned, and analog-to-digital converting means for converting said analog image signals to digital image signals, the combination of: (a) a calibration image, scanning of said calibration image by said array producing analog calibration signals; (b) means for feeding said analog calibration signals to said analog-to-digital converting means; said analog-to-digital converting means converting said analog calibration signals to digital calibration signals; (c) means for averaging groups of said digital calibration signals, each of said groups comprising digital calibration signals from a preset number of said array photosensors; (d) digital-to-analog conversion means for converting the averaged calibration signals to analog signals; (e) compensating means for compensating the image signals produced by said array with said averaged calibration signals; (f) thresholder means for processing said analog image signals produced by said array to provide binary image signals, (g) selector means for routing said analog image signals produced by said array to said analog-to-digital conversion means to provide digital image signals or to said thresholder means to provide binary image signals selectively, and (h) means for inputting said averaged calibration signals to said analog-to-digital conversion means or said thresholder means to modify image signals input to said analog-to-digital conversion means and to said thresholder means, said thresholder means including a screen for screening said image signals and a thresholder for thresholding said image signals, and second selector means to route said image signals to one of said screen and thresholder selectively.

Claim 16

In a raster scanner having a platen for supporting image bearing originals for scanning, at least one array for line scanning an original on said platen, said array being comprised of a plurality of photosensors and producing analog image signals representative of the image area scanned, and analog-to-digital converting means for converting said analog image signals to digital image signals, the combination of: (a) a calibration image, scanning of said calibration image by said array producing analog calibration signals; (b) means for feeding said analog calibration signals to said analog-to-digital converting means; said analog-to-digital converting means converting said analog calibration signals to digital calibration signals; (c) means for averaging groups of said digital calibration signals, each of said groups comprising digital calibration signals from a preset number of said array photosensors; (d) digital-to-analog conversion means for converting the averaged calibration signals to analog signals; (e) compensating means for compensating the image signals produced by said array with said averaged calibration signals; (f) thresholder means for processing said analog image signals produced by said array to provide binary image signals, (g) selector means for routing said analog image signals produced by said array to said analog-to-digital conversion means to provide digital image signals or to said thresholder means to provide binary image signals selectively, (h) means for inputting said averaged calibration signals to said analog-to-digital conversion means or said thresholder means to modify image signals input to said analog-to-digital conversion means and to said thresholder means; (i) said thresholder means including digital-to-analog conversion means for converting digital threshold signals to analog threshold signals, said averaged calibration signals being input to said digital-to-analog conversion means to bias said digital-to-analog conversion means and modify the threshold level output by said digital-to-analog conversion means; and (j) proportionality means for correlating the average calibration signals input to said analog-to-digital conversion means and said digital-to-analog conversion means with the operating characteristics of said analog-to-digital conversion means and said digital-to-analog conversion means.

Claim 17

In a raster scanner having a platen for supporting image bearing originals for scanning, at least one array for line scanning an original on said platen, said array being comprised of a plurality of photosensors and producing analog image signals representative of the image area scanned, and analog-to-digital converting means for converting said analog image signals to digital image signals, the combination of: (a) a calibration image, scanning of said calibration image by said array producing analog calibration signals; (b) means for feeding said analog calibration signals to said analog-to-digital converting means; said analog-to-digital converting means converting said analog calibration signals to digital calibration signals; (c) means for averaging groups of said digital calibration signals, each of said groups comprising digital calibration signals from a preset number of said array photosensors; (d) digital-to-analog conversion means for converting the averaged calibration signals to analog signals; (e) compensating means for compensating the image signals produced by said array with said averaged calibration signals; (f) thresholder means for processing said analog image signals produced by said array to provide binary image signals, (g) selector means for routing said analog image signals produced by said array to said analog-to-digital conversion means to provide digital image signals or to said thresholder means to provide binary image signals selectively, (h) means for inputting said averaged calibration signals to said analog-to-digital conversion means or said thresholder means to modify image signals input to said analog-to-digital conversion means and to said thresholder means; (i) said thresholder means including digital-to-analog conversion means for converting digital threshold signals to analog threshold signals, said averaged calibration signals being input to said digital-to-analog conversion means to bias said digital-to-analog conversion means and modify the threshold level output by said digital-to-analog conversion means; and (j) proportionality means for correlating the average calibration signals input to said analog-to-digital conversion means and said digital-to-analog conversion means with the operating characteristics of said analog-to-digital conversion means and said digital-to-analog conversion means.