System and method for correcting image vignetting

• US 20060204128A1
• Filed: 03/07/2005
• Published: 09/14/2006
• Est. Priority Date: 03/07/2005
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Silverstein, D. Amnon
• Granted Patent: US 7,634,152 B2
• Time in Patent Office: Days
• US Class Current: 382/275
• CPC Class Codes: G06T 5/94 based on local image properties, e.g. for local contrast enhancement

Abstract

A method of correcting vignetting in an image. The image inlcudes a plurality of pixels, each pixel having an intensity. The image is flattened by adjusting the intensity of each pixel based on a vignette function representative of vignetting characteristics of the image, the vignette function having a plurality of free parameters, each free parameter having a value. A vignette metric is determined based on the flattened image. The values of one or more of the free parameters are adjusted based on the vignette metric, and the flattening is performed based on the adjusted values of the free parameters.

Claims

1. A method of correcting vignetting in an image, the image comprising a plurality of pixels each having an intensity, the method comprising:

flattening the image by adjusting the intensity of each pixel based on a vignette function representative of vignetting characteristics of the image, the vignette function having a plurality of free parameters, each free parameter having a value;

determining a vignette metric based on the flattened image;

adjusting the values of at least one of the free parameters based on the vignette metric; and

performing the flattening based on the adjusted values of the free parameters.

2. The method of claim 1, including

palettizing the flattened image using a selected number of colors to create a rendered image;

determining the vignette metric based on a comparison of the rendered image to the flattened image; and

performing the palettizing based on the adjusted values of the free parameters.

3. The method of claim 2, including performing the flattening, palettizing, and adjusting of the values of the free parameters until the vignette metric is substantially optimized.

4. The method of claim 3, wherein the flattened image resulting in a substantially optimized vignette metric comprises a vignette-corrected image.

5. The method of claim 1, including selecting a vignette function.

6. The method of claim 1, wherein the vignette function is based on a Cosine4 model.

7. The method of claim 2, wherein the vignette metric is based on a mean square error between the intensity of pixels of the rendered image and corresponding pixels in the flattened image.

8. The method of claim 2, wherein palettizing the flattened image is based on K-means clustering techniques.

9. The method of claim 1, including selecting initial values for the free parameters.

10. The method of claim 1, wherein adjusting the value of the free parameters is based on non-linear regression techniques.

11. The method of claim 2, wherein the adjusting the value of the free parameters is based on steepest descent techniques.

12. The method of claim 1, further including adjusting the number of colors employed for palettizing the flattened image.

13. A method for correcting vignetting in a collection of related images, each image comprising a plurality of pixels with each pixel having an intensity, the method comprising:

flattening each image by adjusting the intensity of each pixel with a corresponding vignette function representative of vignetting characteristics of the image, the vignette function having a plurality of free parameters, each free parameter having a value;

palettizing each flattened image using a selected number of colors to create a rendered image;

determining a vignette metric for each image based on a comparison of the corresponding rendered image to the corresponding flattened image; and

adjusting the values of at least one of the free parameters of each vignette function based on the corresponding vignette metric and performing the flattening and palettizing for each image until the corresponding vignette metric is substantially optimized.

14. The method of claim 13, including:

determining an average value for each of the free parameters associated with the substantially optimized vignette metrics of all images of the collection of related images; and

flattening each image of the collection of related images by adjusting the intensity of each pixel based on a same vignette function, each free parameter of the vignette function having a value substantially equal to the corresponding average value.

15. A computer-readable medium including instructions executable by a processing system for performing a process for correcting vignetting in an image, the image comprising a plurality of pixels each having an intensity, the process comprising:

flattening the image by adjusting the intensity of each pixel based on a vignette function representative of vignetting characteristics of the image, the vignette function having a plurality of free parameters, each free parameter having a value;

determining a vignette metric based on the flattened image;

adjusting the values of one or more of the free parameters based on the vignette metric; and

performing the flattening based on the adjusted values of the free parameters.

16. The computer-readable medium of claim 15, including instructions for:

palettizing the flattened image using a selected number of colors to create a rendered image;

determining the vignette metric based on a comparison of the rendered image to the flattened image; and

performing the palettizing based on the adjusted values of the free parameters.

17. The computer-readable medium of claim 16, including instructions for performing the flattening, palettizing, and adjusting of the values of the free parameters until the vignette metric is substantially optimized.

18. The computer-readable medium of claim 16, including instructions for adjusting the number of colors employed for palettizing the flattened image to create the rendered image.

19. A system for processing an image, the image comprising a plurality of pixels each having an intensity, the system comprising:

a flattening module configured to flatten the image by adjusting the intensity of each pixel based on a vignette function representative of vignetting characteristics of the image, the vignette function having a plurality of free parameters, each free parameter having a value;

a vignette metric determination module configured to determine a vignette metric based on the flattened image; and

a parameter adjustment module configured to adjust the values of at least one of the free parameters based on the vignette metric.

20. The system of claim 19, including a palettizing module for palettizing the flattened image using a selected number of colors to create a rendered image, wherein the vignette metric determination module is configured to determine the vignette metric based on a comparison of the rendered image to the flattened image.

21. The system of claim 20, wherein the system is configured to perform the flattening and the palettizing based on the adjusted values of the free parameters.

22. The system of claim 21, wherein the system is configured to perform the flattening, palettizing, and adjusting of the values of the free parameters until the vignette metric is substantially optimized.

23. The system of claim 20, including a color adjustment module configured to adjust the number of colors employed by the palettizing module to create the rendered image.

24. A system for correcting vignetting in an image, the image comprising a plurality of pixels each having an intensity, the system comprising:

means for flattening the image by adjusting the intensity of each pixel based on a vignette function representative of vignetting characteristics of the image, the vignette function having a plurality of free parameters, each free parameter having a value;

means for determining a vignette metric based on the flattened image; and

means for adjusting the values of at least one of the free parameters based on the vignette metric.

25. The system of claim 24, including:

means for palettizing the flattened image using a selected number of colors to create a rendered image, wherein the means for determining the vignette metric includes means for determining the vignette metric based on a comparison of the rendered image to the flattened image.

26. The system of claim 25, including:

means for performing the flattening and palettizing based on the adjusted values of the free parameters.