Optical image defocus correction

• US 5,307,175 A
• Filed: 03/27/1992
• Issued: 04/26/1994
• Est. Priority Date: 03/27/1992
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Seachman, Ned J.
• Primary Examiner(s): Powell, Mark R.
• Assistant Examiner(s): Ning, John
• Application Number:
  US07/858,828
• Time in Patent Office: 760 Days
• Field of Search: 346/160, 358/227, 358/471, 358/447, 358/401, 358/497, 358/55, 358/209, 250/201, 355/228
• US Class Current: 358/401
• CPC Class Codes: H04N 1/00002 Diagnosis, testing or measuring; Detecting, analysing or monitoring not otherwise provided for error detection, error correction or monitoring in digital computers or digital computer components G06F11/00
• CPC Class Codes: H04N 1/00013 Reading apparatus
• CPC Class Codes: H04N 1/00034 Measuring, i.e. determining a quantity by comparison with a standard H04N1/00031 takes precedence
• CPC Class Codes: H04N 1/00045 using a reference pattern designed for the purpose, e.g. a test chart
• CPC Class Codes: H04N 1/00053 out of service, i.e. outside of normal operation
• CPC Class Codes: H04N 1/00063 using at least a part of the apparatus itself, e.g. self-testing
• CPC Class Codes: H04N 1/00082 Adjusting or controlling interrupting an operation H04N1/00915; inhibiting an operation H04N1/00925
• CPC Class Codes: H04N 1/4092 Edge or detail enhancement

Abstract

In an optical/electrical imaging system, optical depth of focus corrections are accomplished electronically. A plurality of defocus states of the optical system are measured and/or determined and image restoration coefficients corresponding to each of these states are stored. The state of defocus of the imaging system is then determined by deriving an image from a target having known characteristics, which are then correlated to determine a state of defocus. A microprocessor is utilized to provide appropriate defocus correction information to an electronic filter, thereby providing an adaptive filtering arrangement.

Claims

1. Image scanning apparatus comprising:

an image support;

a scanner for scanning an image on the image support, said scanner comprising an optical element for receiving optical image data from an image on the image support and a photoreceptor for receiving optical image data from the optical element and converting the optical data to an electrical data signal;

restoring means for providing a plurality of sets of image restoration data, each set of image restoration data representative of a different one of a plurality of defocus states of the optical element throughout an expected range of focal errors;

determining means for determining at least one defocus state of the scanner;

selecting means for selecting at least one of the sets of image restoration data provided by the restoring means based on the at least one defocus state determined by the determining means;

signal processing means for receiving the electrical data signal from the photoreceptor and the image restoration data from the selecting means and modifying the electrical data signal in accordance with the image restoration data received from the selecting means.

2. Apparatus as in claim 1, further comprising display means for displaying image data received from the processing means.

3. Apparatus as in claim 1, wherein the providing means comprises a memory for storing the plurality of sets of image restoration data.

4. Apparatus as in claim 1, wherein the providing means utilizes a Weiner filter to compute the image restoration data.

5. Apparatus as in claim 1, further including means for providing image quality data to the processing means indicative of the quality of an image on the image support.

6. Apparatus as in claim 5, wherein the means for providing image quality data comprises a manually selectable member.

7. Apparatus as in claim 1, further comprising a focus target and wherein the determining means determines one of a plurality of levels of defocus of the optical system formed by the image support and the scanner from image data from the focus target.

8. Apparatus as in claim 1, wherein the optical element is a lens.

9. Apparatus as in claim 1, wherein the optical element is an array of lenses.

10. Apparatus as in claim 1, wherein the optical element is a gradient index lens array.

11. Apparatus as in claim 1, wherein the photoreceptor comprises a linear array of photosensitive elements.

12. Apparatus as in claim 1, wherein the photoreceptor comprises an area array of photosensitive elements.

13. A method for correcting defocus of an image scanner having an optical element for providing optical image information to a photoreceptor comprising the steps of:

determining the focus characteristics of the optical element at a plurality of levels of defocus throughout an expected range of focal errors;

converting the defocus characteristics of the optical element at each defocus level to a set of correction data and electronically providing the correction data;

determining at least one defocus level of the scanner;

selecting at least one set of correction data corresponding to the at least one defocus level determined in the defocus level determination step; and

electronically correcting an electrical image signal from the photoreceptor in accordance with the correction data selected in the selecting step.

14. A method as in claim 13, wherein the defocus level determining step comprises scanning a predetermined image and determining the defocus level from electrical image data representative of the predetermined image.

15. A method as in claim 13, wherein the step of determining the defocus characteristics of the optical element comprises determining the defocus characteristics for light at a plurality of different wavelengths and the step of determining the defocus level of the scanner includes determining the wavelength of light received by the optical element when the defocus level determination is made.

16. A method as in claim 13, wherein the step of electronically correcting the electrical image signal comprises filtering the signal.

17. A method as in claim 16, wherein the step of filtering the electrical image signal comprises determining filtering characteristics on the basis of at least one of the provided sets of correction data and the level of defocus determined in the defocus level determining step.

18. A method as in claim 13, wherein the step of electronically providing the correction data comprises storing the correction data in a memory.