Sinc filter in linear lumen space for scanner

• US 5,572,608 A
• Filed: 08/24/1994
• Issued: 11/05/1996
• Est. Priority Date: 08/24/1994
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Edgar, Albert D.
• Primary Examiner(s): Couso, Jose L.
• Application Number:
  US08/295,317
• Time in Patent Office: 804 Days
• Field of Search: 382/268, 382/269, 382/260, 382/279, 382/298, 382/299, 382/300, 348/581, 348/597, 348/61, 358/474, 358/488, 367/45, 360/45, 359/189, 364/413.13, 364/724.1, 324/142
• US Class Current: 382/321
• CPC Class Codes: H04N 1/047 Detection, control or error compensation of scanning velocity or position H04N1/0402 and H04N1/17 take precedence
• CPC Class Codes: H04N 1/12 using the sheet-feed movement or the medium-advance or the drum-rotation movement as the slow scanning component, e.g. arrangements for the main-scanningsheet-feed movement by translatory movement of a flat picture-bearing surface H04N1/1008; main-scanning using oscillating or rotating mirrors H04N1/113; using multi-element arrays H04N1/19
• CPC Class Codes: H04N 1/193 using electrically scanned linear arrays , e.g. linear CCD arrays
• CPC Class Codes: H04N 1/40068 Modification of image resolution, i.e. determining the values of picture elements at new relative positions H04N1/3935 takes precedence
• CPC Class Codes: H04N 2201/02425 Self-adjusting arrangements, e.g. compensating for temperature fluctuations
• CPC Class Codes: H04N 2201/02439 Positioning method
• CPC Class Codes: H04N 2201/03162 Original guide plate
• CPC Class Codes: H04N 2201/0408 Scanning film strips or rolls
• CPC Class Codes: H04N 2201/04705 using inactive scanning elements, e.g. elements outside the scanning area
• CPC Class Codes: H04N 2201/04708 which remain outside the scanned image area
• CPC Class Codes: H04N 2201/0472 on or adjacent the sheet support
• CPC Class Codes: H04N 2201/04729 in the main-scan direction
• CPC Class Codes: H04N 2201/04731 in the sub-scan direction
• CPC Class Codes: H04N 2201/04732 Detecting at infrequent intervals, e.g. once or twice per line for main-scan control
• CPC Class Codes: H04N 2201/04734 Detecting at frequent intervals, e.g. once per line for sub-scan control
• CPC Class Codes: H04N 2201/04749 Detecting position relative to a gradient, e.g. using triangular-shaped masks, marks or gratings
• CPC Class Codes: H04N 2201/04787 by changing or controlling the addresses or values of pixels, e.g. in an array, in a memory, by interpolation
• CPC Class Codes: H04N 2201/04789 in the main-scan direction
• CPC Class Codes: H04N 2201/04791 in the sub-scan direction
• CPC Class Codes: H04N 2201/04794 Varying the control or compensation during the scan, e.g. using continuous feedback or from line to line

Abstract

A scanner which converts an oversampled substrate image into a digital pixel array which may be at an arbitrary sampling frequency lower than the first sampling frequency. The scanner sensor converts the substrate image into an array of analog pixel at a first sampling frequency. Preferably the first sampling frequency substantially oversamples the image from the actual frequency desired in the final digital image. The analog pixels are converted into a first array of digital pixels. The first digital pixel array is converted by a sinc filter in the linear lumen domain, i.e. the digital pixels are linearly representative of the brightness of light sensed by the sensor, to a second array of pixels at a second sampling frequency. The second sampling frequency should be much lower than the first sampling frequency to produce high quality images with substantially fewer pixels than required by the prior art.

Claims

1. A scanner for converting an image on a substrate comprising:

a sensor for converting the substrate image into an array of analog pixels at a first sampling frequency;

a digital converter for converting the array of analog pixels into a first array of digital pixels stored in a digital memory;

a sinc digital filter for converting digital pixel values contained in the first array of digital pixels which are linearly representative of the brightness of light as the image is intended to be displayed to digital pixel values stored in a second array of digital pixels at a second sampling frequency lower than the first sampling frequency; and

means for outputting from the scanner apparatus the digital pixel values of the second array of digital pixels.

2. The scanner as recited in claim 1 wherein the second sampling frequency is lower than the first sampling frequency by an arbitrary ratio.

3. The scanner as recited in claim 1 wherein the output means comprises means for outputting numbers the digital pixel values of the second array of digital pixels.

4. The scanner as recited in claim 1 wherein the sensor comprises means for deriving a signal corresponding to a generally square root function of the brightness of light sensed by the sensor means.

5. The scanner as recited in claim 4 wherein the sinc digital filter produces the second array of digital pixels from numbers corresponding to generally the square function of the digital pixel values contained in the first array of digital pixels.

6. The scanner as recited in claim 1 wherein the sinc digital filter further comprises means for adding a portion of a first digital pixel value of the first array of digital pixels and subtracting a portion of a second digital pixel value of the second array of digital pixels for deriving a digital pixel value in the second array of digital pixels.

7. The scanner as recited in claim 6 wherein the sinc digital filter passes a set of frequencies from the first array of digital pixels, lower than half the second sampling frequency, with an attenuation substantially the inverse of an attenuation with which the optical system attenuates the frequency.

8. The scanner as recited in claim 1 wherein the first and second array of digital pixels, and an intermediate array of digital pixels, contain substantially perpendicular rows and columns of pixels, and wherein the sinc digital filter further comprises means for converting the digital pixel values contained in a column of pixels of the first array of digital pixels to digital pixel values that are stored in a column of pixels of the intermediate array of digital pixels.

9. The scanner as recited in claim 8 wherein the sinc digital filter further comprises means for converting the digital pixel values contained in a row of pixels of the intermediate array of digital pixels to digital pixel values that are stored in a row of pixels of the second array of digital pixels.

10. The scanner as recited in claim 9 wherein a prescaled digital array of pixels contains mutually perpendicular rows and columns of pixels, and wherein the sinc digital filter further comprises a prefilter for converting the digital pixel values contained in a set of rows of pixels of the first array of digital pixels to digital pixel values that are stored in a row of pixels of the prescaled digital array of pixels, and wherein the intermediate array of digital pixels is derived from the prescaled array of digital pixels.

11. A method for converting an image on a substrate comprising the steps of:

a sensor for converting the substrate image into an array of analog pixels at a first sampling frequency;

a digital converter for converting the array of analog pixels into a first array of digital pixels stored in a digital memory;

a sinc digital filter for digitally converting digital pixel values contained in the first array of digital pixels which are linearly representative of the brightness of light as the image is intended to be finally displayed to digital pixel values stored in a second array of digital pixels, at a second sampling frequency lower than the first sampling frequency; and

means for outputting from the scanning apparatus the digital pixel values of the second array of digital pixels.

12. The method as recited in claim 11 wherein the second sampling frequency is lower than the first sampling frequency by an arbitrary ratio.

13. The method as recited in claim 11 which further comprises the step of adding a portion of a first digital pixel value of the first array of digital pixels and subtracting a portion of a second digital pixel value of the second array of digital pixels for deriving a digital pixel value in the second array of digital pixels.

14. The method as recited in claim 13 further comprises the step of passing a set;

of frequencies from the first array of digital pixels, lower than half the second sampling frequency, with an attenuation substantially the inverse of an attenuation with which the optical system attenuates the frequency.

15. The method as recited in claim 11 wherein the first and second array of digital pixels, and an intermediate array of digital pixels, contain substantially perpendicular rows and columns of pixels, and wherein the method further comprises the step of converting the digital pixel values contained in a column of pixels of the first array of digital pixels to digital pixel values that are stored in a column of pixels of the intermediate array of digital pixels.

16. The method as recited in claim 15 wherein the sinc digital filter further comprises the step of converting the digital pixel values contained in a row of pixels of the intermediate array of digital pixels to digital pixel values that are stored in a row of pixels of the second array of digital pixels.

17. The method as recited in claim 16 wherein a prescaled digital array of pixels contains mutually perpendicular rows and columns of pixels, and wherein the method further comprises a step of converting the digital pixel values contained in a set of rows of pixels of the first array of digital pixels to digital pixel values that are stored in a row of pixels of the prescaled digital array of pixels, and wherein the intermediate array of digital pixels is derived from the prescaled array of digital pixels.