Method and apparatus for image value correction in optoelectronic transducers

• US 5,748,803 A
• Filed: 01/24/1996
• Issued: 05/05/1998
• Est. Priority Date: 11/22/1995
• Status: Expired due to Fees

• Current Assignee: Heidelberger Druckmaschinen Ag
• Original Assignee: Linotype-Hell AG (Heidelberger Druckmaschinen Ag)
• Inventors: Schielke, Rainer
• Primary Examiner(s): VU, KIM Y
• Application Number:
  US08/590,813
• Time in Patent Office: 832 Days
• Field of Search: 358/463, 358/474, 358/482-483, 382/274, 382/275, 348/246-251
• US Class Current: 382/275
• CPC Class Codes: H04N 1/409 Edge or detail enhancement; Noise or error suppression
• CPC Class Codes: H04N 25/683 by defect estimation performed on the scene signal, e.g. real time or on the fly detection
• CPC Class Codes: H04N 25/701 Line sensors

Abstract

A method and apparatus for the correction of the image values of faulty sensors of an optoelectronic transducer comprising a plurality of sensor elements. In order to avoid errors at light/dark transitions in the scanned original, the erroneous image value of a faulty sensor element is fully corrected in areas of the original having nearly constant brightness values and is only slightly corrected in regions of light/dark transitions (contours) in the original. In order to achieve this, the erroneous image value of a faulty sensor element is replaced by the image value of the sensor element neighboring the faulty sensor element that comprises the least difference from the erroneous image value in terms of amount. Alternatively, the erroneous image value is replaced by the median value calculated from the image value of the faulty sensor element and from the image values of the sensor elements neighboring the faulty sensor element.

Claims

1. A method for correction of image values of faulty sensor elements of an optoelectronic transducer comprising a plurality of sensor elements, comprising the steps of:

acquiring the image values by point-by-point and line-by-line optoelectronic scanning of an original with the sensor elements;

intermediately storing the image values scanned in the original scan line-by-scan line for image value correction in an image line memory that has a number of memory locations at least corresponding to a number of the sensor elements of the optoelectronic transducer;

allocating an identifier to each sensor element of the optoelectronic transducer;

callably storing the identifiers allocated to the faulty sensor elements in a table memory;

replacing an erroneous image value of a faulty sensor element by an image value calculated from image values of sensor elements neighboring the faulty sensor element; and

for avoiding errors at light/dark transitions in the scanned original, the erroneous image value of the faulty sensor element is fully corrected in areas of the original having nearly constant brightness values and is only relatively slightly corrected in regions of light/dark transitions in the original.

2. A method according to claim 1 including the steps of:

intermediately storing the image values of a scan line scanned in the original in the image line memory under addresses corresponding to the allocated identifiers;

successively calling the identifiers of the faulty sensor elements stored in the table memory;

calling a central address corresponding to a corresponding identifier and neighboring addresses of the image line memory for each called identifier of a faulty sensor element;

respectively calculating a corrected image value from the image values deposited under the called addresses of the image line memory; and

respectively replacing the faulty image value deposited under the central address by the corrected image value.

3. A method for correction of image values of faulty sensor elements of an optoelectronic transducer having a plurality of sensor elements, comprising the steps of:

acquiring the image values by scanning the original with the sensor elements; and

avoiding errors at light/dark transitions in the scanned original by replacing an erroneous image value of a faulty sensor element by an image value selected according to the following steps;

identifying the image value of the sensor element lying at one side of the faulty sensor element and identifying the image value lying at the sensor element at the opposite side of the faulty sensor element;

making an ordered list of the two neighboring sensor element image values and the image value of the faulty sensor element according to value; and

identifying a median image value in the ordered list and replacing the image value of the faulty sensor element with the median image value.

4. An apparatus for correction of erroneous image values of faulty sensor elements of an optoelectronic transducer, comprising:

an optoelectronic transducer comprising a plurality of sensor elements for point-by-point and line-by-line optoelectronic scanning of an original;

an A/D converter connected to the optoelectronic transducer;

an image value correction circuit connected to the A/D converter for the correction of the erroneous image values of the faulty sensor elements;

the image value correction circuit having;

an image line memory for line-by-line intermediate storage of image values of sensor elements of the optoelectronic transducer at addresses that correspond to identifiers allocated to the sensor elements;

a table memory for callably storing the identifiers allocated to the faulty sensor elements;

an address controller connected to the image line memory and to the table memory for calling the identifiers of the faulty sensor elements stored in the table memory and for calling central addresses corresponding to the identifiers called in the table memory and respective neighboring addresses of the image line sensor; and

an arithmetic unit connected to the image line memory for calculating corrected image values from the image values respectively deposited under the called addresses of the image line memory.

5. An apparatus according to claim 4 wherein the optoelectronic transducer is a photodiode line.

6. An apparatus according to claim 4 wherein the optoelectronic transducer is a photodiode array.