Method for determining and loading an image-dependent look-up table for generating an enhanced image representation

• US 5,802,214 A
• Filed: 12/08/1995
• Issued: 09/01/1998
• Est. Priority Date: 12/08/1995
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Fuss, William A., Eschbach, Reiner, Hains, Charles M.
• Primary Examiner(s): COUSO, YON JUNG
• Application Number:
  US08/569,808
• Time in Patent Office: 998 Days
• Field of Search: 382/319, 382/318, 382/312, 382/255, 382/274, 382/275, 382/254, 358/505, 358/509, 358/510
• US Class Current: 382/254
• CPC Class Codes: H04N 1/4074 using histograms
• CPC Class Codes: H04N 1/6027 Correction or control of colour gradation or colour contrast H04N1/6058 takes precedence

Abstract

A scanner generates a first set of M-bit signals representing an image in a document. A default table translates the M-bit signals into linearized N-bit signals where M>N. A color image processing module processes the N-bit signals to generate an image-dependent look-up table which, thereafter, is loaded into the scanner. The scanner then generates a second set of M-bit signals using a high resolution re-scan of the same image. The second set of M-bit signals are translated into N-bit signals using the image-dependent look-up table to generate an electronic representation with enhancement characteristics.

Claims

1. A method of generating an enhanced representation of an image from a scanner, comprising the steps of:

loading into a memory a first look-up table for translating scan signals into processor signals;

first scanning the image into the scanner for generating a first scan signal representative of an illumination dynamic range of the image;

translating the first scan signal into a first processor signal with the first look-up table;

determining an image enhancement function for the representation from the first processor signal by comparing the dynamic range with predetermined desired intensity levels;

generating an image dependent look-up table for translating the scan signals into the processor signals while incorporating the image enhancement including adjusting data values of the image dependent look-up table by the function;

loading the image-dependent look-up table into the memory;

rescanning the image to generate a second scan signal representative of the image; and

,

translating the second scan signal into a second processor signal with the image-dependent look-up table wherein the second processor signal comprises an enhancement of the first processor signal.

2. The method as described in claim 1 wherein the first scanning comprises a preliminary scanning of the image for identifying a statistical distribution of scanner stimulus signals representative of reflected light intensity comprising the first scan signal.

3. The method as described in claim 2 wherein the rescanning comprises a high resolution of the image in the scanner.

4. The method as described in claim 2 wherein an image-dependent look-up table comprises applying a stretching function to the statistical distribution of scanner stimulus signals for optimally matching the second scan signal to the second processor signal.

5. A method of using a scanner to generate an electronic representation of a natural scene image, the method comprising the steps of:

loading into scanner memory a pre-set default look-up table for translating scanner multi-bit signals into signals having a format suitable for post-scanner processing;

first scanning the natural scene image to generate a first set of scanner multi-bit signals representing the natural scene image;

translating the first set of scanner multi-bit signals into translated signals with post-scanner processing format, using the pre-set default look-up table;

using the translated signals at an image processing module for generating image-dependent filter coefficients derived by applying a stretching function determined from the translated signals for computing the filter coefficients and for reflecting processing of the natural scene image at the image processing module;

loading the image-dependent filter coefficients into a filter stored in scanner memory;

rescanning the natural scene image and generating a second set of scanner multi-bit signals representing the natural scene image; and

filtering the second set of scanner multi-bit signals with the scanner filter operating in accordance with the image-dependent filter coefficients.

6. The method of claim 5 wherein the first and second set of scanner multi-bit signals are generated as a non-linear representation of the natural scene image.

7. The method of claim 6 wherein the translating step comprises translating non-linear representations of the first and second sets of scanner multi-bit signals into linearized bit signals.

8. The method of claim 5 wherein the first scanning comprises a low resolution scan for generating the first set of scanner multi-bit signals representing the natural scene image.

9. The method of claim 5 wherein the rescanning comprises a high resolution rescan for generating the second set of scanner multi-bit signals representing the natural scene image.

10. The method as described in claim 5 wherein the using the translated signals comprises identifying a dynamic range of the first set of scanner multi-bit signals for optimally matching the image-dependent filter coefficients therewith.

11. An apparatus for generating an enhanced electronic representation of a natural scene image, the apparatus comprising:

an image scanner which generates scan signals representing the natural scene image;

a first memory into which is loaded a first look-up table for translating first scan signals generated by the image scanner into first processor signals;

an image processing module which processes the first processor signals to generate an image enhancement signal derived by comparing the first processor signals with predetermined standards of desired representation of an image for processing of the natural scene image;

a look-up table adjustment circuit which generates an image-dependent look-up table by applying the image enhancement signal to data values of the table to compute adjusted data output values for the table; and

a second memory into which is loaded the adjusted data output values of the image-dependent look-up table for translating second scan signals generated by the image scanner into second process signals.

12. The apparatus of claim 11 wherein the first scan signals are generated by a preliminary scanning of the image for identifying a statistical distribution of scanner stimulus signals representative of reflected light intensity comprising the first scan signal.

13. The apparatus of claim 11 wherein the second scan signals are generated by a high resolution scanning of the image in the scanner.

14. The apparatus of claim 11 wherein the scan signals are defined by M-bits, the processor signals are defined by N-bits, and M is greater than N.

15. The apparatus of claim 11 wherein the imagedependent look-up table stretches the statistical distribution of the second scanner signals for optimally matching the second scan signal to the second processor signal.

16. The apparatus of claim 11 wherein the first and second memories are contained within the image scanner.