General purpose image enhancement algorithm which augments the visual perception of detail in digital images

• US 20030021488A1
• Filed: 07/27/2001
• Published: 01/30/2003
• Est. Priority Date: 07/27/2001
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Shaw, Rodney, McGuire, Michael D.
• Granted Patent: US 6,792,160 B2
• Time in Patent Office: Days
• US Class Current: 382/260
• CPC Class Codes: G06T 2200/24 involving graphical user interfaces [GUIs]
• CPC Class Codes: G06T 5/008 Local, e.g. shadow enhancement
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/94 based on local image properties, e.g. for local contrast enhancement

Abstract

A tone correction system, method and interface is described in which a digital image is initially filtered to obtain a corresponding locally averaged value for each pixel value of the image. The image is optimally filtered using a cone-type filter having a small filter radius and which favorably weights the center pixel values of the radius. Shadow and highlight values are obtained from selected shadow and highlight functions, respectively, using the locally averaged values. A tone function is derived from each of the shadow an highlight values for each pixel. Each pixel value of the image is then remapped according to its derived shadow and highlight tone functions. The tone corrected image can be reinteratively corrected by adjusting parameters of the shadow and highlight functions and remapping the image data until a desired image quality is achieved.

Claims

1. A method of processing digital image data comprising a plurality of pixel values, the method comprising:

filtering the image data to obtain a locally averaged value for each pixel value;

for each pixel value in the image data;

a) using its locally averaged value, to obtain a corresponding shadow value and highlight value from a selected shadow function and a selected highlight function, respectively;

b) deriving at least one tone function from one of the corresponding shadow value and highlight value; and

c) remapping each pixel according to its at least one derived tone function to obtain a tone adjusted pixel value.

2. The method as described in claim 1 wherein each of the selected highlight and selected shadow functions are both bounded by a dynamic range of the digital image data, the method further comprising:

d) varying function parameters of the highlight and shadow functions within the dynamic range;

e) performing a)-d) until a desired image quality is obtained.

3. The method as described in claim 1 wherein deriving at least one tone function comprises deriving a first tone function from the shadow value and deriving a second tone function from the highlight value.

4. The method as described in claim 3 wherein remapping each pixel value according to its at least one derived tone function comprises remapping each pixel value according to the first tone function to obtain an intermediate pixel value and remapping the intermediate pixel value according to the second tone function to obtain the tone adjusted pixel value.

5. The method as described in claim 3 wherein the first tone function is derived from a first ratio of:

each pixel value/shadow value.

6. The method as described in claim 3 wherein the second tone function is derived from a second ratio of:

7. The method as described in claim 2 wherein the function parameters are varied through a user interface.

8. The method as described in claim 1 wherein filtering further comprises filtering using a center-weighted circularly symmetric filter.

9. The method as described in claim 8 wherein a filtering radius of 7 pixels is selected when the image data has a corresponding dpi of 300.

10. The method as described in claim 8 wherein a filtering radius of 0 pixels is selected.

11. The method as described in claim 8 wherein a filter radius in the range of one pixel to the plurality of pixel values of the digital image is selected.

12. A system for processing image data including a plurality of pixel values comprising:

image data filter for generating a corresponding locally averaged pixel value for each of the plurality of pixel values;

means for providing a corresponding highlight value and a corresponding shadow value according to selected highlight and shadow functions, respectively, in response to each locally averaged value;

tone function derivator for deriving at least one tone function based on one of the corresponding highlight value and shadow value; and

remapper for remapping each pixel value according to the at least one derived tone function to obtain a tone adjusted pixel value.

13. The system as described in claim 12 further comprising a control input coupled to the means for providing corresponding highlight and shadow values, the control input for receiving control signals to adjust function parameters of the selected highlight and shadow functions.

14. The system as described in claim 12 wherein the image data filter, the means for providing corresponding highlight and shadow values, the derivator, and the remapper are implemented as one of software, hardware, firmware, and any combination of software, hardware, and firmware.

15. The system as described in claim 12 wherein the filter is a center weighted circularly symmetric filter.

16. The system as described in claim 15 wherein the image data has a resolution of 300 dpi and the filter has a pixel radius of 7 pixels.

17. The method as described in claim 15 wherein the filter has a pixel radius of 0 pixels.

18. The method as described in claim 15 wherein the filter has a pixel radius in the range of greater than or equal to one pixel and less than or equal to the plurality of pixel values of the digital image is selected.

19. The system as described in claim 13 further comprising:

A user interface displayed on a display screen including;

a display area for displaying the digital image prior to remapping the plurality of pixel values of the digital image and after remapping the plurality of pixel values;

a means for receiving user adjustments to the parameters of the highlight and shadow functions, wherein the plurality of pixel values are remapped according to the user adjustments and the image is redisplayed in the display area.

20. A system for processing image data including a plurality of pixel values comprising:

means for processing the plurality of pixel values for generating a corresponding locally averaged pixel value for each of the plurality of pixel values;

means for providing a corresponding highlight value and a corresponding shadow value according to selected highlight and shadow functions, respectively, in response to each locally averaged value;

means for deriving at least one tone function based on one of the corresponding highlight value and shadow value; and

means for remapping each pixel value according to the at least one derived tone function to obtain a tone adjusted pixel value.

21. An article of manufacture for a computer, the article comprising:

computer memory; and

a program stored in the computer memory, the program, when executed, causing the computer to;

filter the image data to obtain a locally averaged value for each pixel age data;

for each pixel value in the image data;

a) use its locally averaged value, to obtain a corresponding shadow value and highlight value from a selected shadow function and a selected highlight function, respectively;

b) derive at least one tone function from one of the corresponding shadow value and highlight value; and

c) remap each pixel according to its at least one derived tone function to obtain a tone adjusted pixel value.