System and method for correcting image vignetting

• US 7,634,152 B2
• Filed: 03/07/2005
• Issued: 12/15/2009
• Est. Priority Date: 03/07/2005
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Silverstein, D. Amnon
• Primary Examiner(s): Bali, Vikkram
• Assistant Examiner(s): ENTEZARI, MICHELLE M
• Application Number:
  US11/074,979
• Publication Number:
  US 20060204128A1
• Time in Patent Office: 1,744 Days
• Field of Search: 382/275
• 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 includes 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 comprising:

receiving, in a processing system, an image comprising a plurality of pixels each having an intensity;

flattening the images using a processor of the processing system by adjusting the intensity of each pixel by applying a vignette function derived independently of the image and being representative of image vignetting characteristics, the vignette function having a plurality of free parameters, each free parameter representative of a vignetting factor and having a value;

palettizing the flattened image with the processor using a selected number of colors to create a rendered image,

determining a vignette metric using the processor by comparing the flattened image to the rendered image;

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

performing the flattening with the processor using the adjusted values of the free parameters.

2. The method of claim 1, including iteratively adjusting the values of at least one of the free parameters and performing the flattening and palettizing until the vignette metric is substantially optimized.

3. The method of claim 2, wherein the flattened image resulting in a substantially optimized vignette metric comprises a vignette-corrected image.

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

5. The method of claim 1, wherein the vignette function is based on a Cosine 4 model.

6. The method of claim 1, 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.

7. The method of claim 1, wherein palettizing the flattened image is based on K-means clustering techniques.

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

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

10. The method of claim 1, wherein the adjusting the value of the free parameters is based on steepest descent techniques.

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

12. A method for correcting vignetting in a collection of related images comprising:

receiving in a processing system, a collection of related images, each image comprising a plurality of pixels with each pixel having an intensity;

flattening each image using a processor of the processing system by adjusting the intensity of each pixel by applying a vignette function derived independently of the image and being representative of image vignetting characteristics, the vignette function having a plurality of free parameters, each free parameter representing a vignetting factor and having a value;

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

determining a vignette metric for each image using the processor by comparing the corresponding rendered image to the corresponding flattened image; and

using the processor, iteratively adjusting the value of at least one of the free parameters of a set of free parameters associated with each image based on the corresponding vignette metric and performing the flattening and palettizing for each image until the corresponding vignette metric is substantially optimized.

13. The method of claim 12, 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.

14. A computer-readable medium including instructions executable by a computer 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 using a vignette function derived independently of the image and being representative of image vignetting characteristics, the vignette function having a plurality of free parameters, each free parameter representative of a vignetting factor and having a value;

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

determining a vignette metric based on comparing the flattened image to the rendered 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.

15. The computer-readable medium of claim 14, including instructions for iteratively adjusting the values of the one or more of the free parameters and performing the flattening and palettizing until the vignette metric is substantially optimized.

16. The computer-readable medium of claim 14, including instructions for adjusting the number of colors employed for palettizing the flattened image to create the rendered image.

17. A system for processing an image comprising:

an input/output unit to receive an image comprising a plurality of pixels each having an intensity;

a flattening module, executed by a processor of the system, configured to flatten the image by adjusting the intensity of each pixel by applying a vignette function derived independently of the image and being representative of image vignetting characteristics, the vignette function having a plurality of free parameters, each free parameter representative of a vignetting factor and having a value;

a palettizing module, executed by the processor, for palettizing the flattened image using a selected number of colors to create a rendered image;

a vignette metric determination module, executed by the processor, configured to determine a vignette metric based on a comparison of the rendered image to the flattened image; and

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

18. The system of claim 17, wherein the system is configured to perform the flattening and the palettizing based on the adjusted values of the free parameters.

19. The system of claim 18, wherein the system is configured to iteratively perform the flattening, palettizing, and adjusting of the values of the free parameters until the vignette metric is substantially optimized.

20. The system of claim 17, including a color adjustment module configured to adjust the number of colors employed by the palettizing module to create the rendered image.