Automatic dynamic range adjustment in digital imaging

• US 20080247661A1
• Filed: 04/04/2007
• Published: 10/09/2008
• Est. Priority Date: 04/04/2007
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Li, Xing, Cuciurean-Zapan, Mihai
• Granted Patent: US 8,000,554 B2
• Time in Patent Office: Days
• US Class Current: 382/254
• CPC Class Codes: G06T 2207/10008 from scanner, fax or copier
• CPC Class Codes: G06T 2207/30176 Document
• CPC Class Codes: G06T 5/92 based on global image properties

Abstract

A method of performing non-linear transformation of a digital image for contrast modification. The original video input is compared to a linear transformation with gain and offset; and, the differential Δ multiplied by a factor m obtained from a look-up table and the product mΔ added to the original input to obtain the output video.

Claims

1. a method of controlling contrast in digital printing comprising:

(a) scanning the document to be copied and printed and generating a digital image thereof;

(b) rasterizing the digital image and mapping the pixel count and values on a scale between the black point and the white point range of pixel values for the image;

(c) performing a linear transformation of the mapped values over said range; and

,

(d) selecting a portion of said range and modifying the transformation outside said portion and altering the image contrast.

2. The method defined in claim 1, wherein the step of altering includes modifying the linear transformation by addition of an adjustment factor obtained from a look-up table for values of the pixels and a correction factor.

3. The method defined in claim 2, wherein said step of altering includes computing the difference (delta) between the output obtained from the linear transformation and the input value.

4. The value defined in claim 2, wherein the adjustment factor includes the product of delta and the correction factor.

5. A method of controlling contrast in digital document copying and printing comprising:

(a) scanning the document to be copied and printed and generating a digital image thereof;

(b) rasterizing the digital image and mapping the pixel count and values on a scale between the black point and white point range of pixel values for the image;

(c) performing a transformation of the mapped pixel values over the range; and

,

(d) modifying the image contrast based upon the transformation of the mapped pixel values.

6. The method defined in claim 5, wherein the step of performing a transformation includes a linear transformation for a portion of the range of pixel values for the image.

7. The method defined in claim 5, wherein the step of performing a transformation includes an adjustment factor obtained from a look-up table of the factor and pixel values.

8. The method defined in claim 5, wherein the step of performing a transformation includes an adjustment factor obtained from a curvilinear function over at least a portion of the range of pixel values of the image.

9. The method defined in claim 8, wherein the step of performing a transformation includes a continuous curvilinear function.

10. A method of digital reproduction of documents comprising:

(a) scanning the document to be reproduced and generating a digital image thereof;

(b) rasterizing the digital image and mapping the pixel count and values on a scale between the black point and white point range of pixel values for the image;

(c) performing a transformation of the mapped pixel values over the range; and

,

(d) modifying the image contrast based upon the transformation of the mapped pixel values.

11. The method defined in claim 10, further comprising displaying the image with the modified contrast on a screen.

12. The method defined in claim 10, further comprising printing the image with the modified contrast on a print media sheet.

13. The method defined in claim 10, wherein the step of performing a transformation includes obtaining a correction factor from a look-up table of values of the factor and pixel values.

14. The method defined in claim 10, wherein the step of mapping pixel values includes mapping values of pixel luminance.