Method for sharpening a digital image

• US 7,228,004 B2
• Filed: 09/05/2002
• Issued: 06/05/2007
• Est. Priority Date: 09/05/2002
• Status: Expired due to Fees

• Current Assignee: Monument Peak Ventures, LLC (Dominion Harbor Enterprises, LLC)
• Original Assignee: Eastman Kodak Company
• Inventors: Gallagher, Andrew C., Gindele, Edward B.
• Primary Examiner(s): Mehta; Bhavesh M.
• Assistant Examiner(s): Perungavoor; Sath V.
• Application Number:
  US10/235,130
• Publication Number:
  US 20040047514A1
• Time in Patent Office: 1,734 Days
• Field of Search: 382/274
• US Class Current: 382/274
• CPC Class Codes: G06T 5/75 Unsharp masking
• CPC Class Codes: G06V 10/30 Noise filtering

Abstract

A method of sharpening a digital image having image pixels values includes the steps of: determining a D_min value, representing a value corresponding to a minimum possible exposure for a system that produced the digital image; for each pixel value in the digital image providing a gain factor that is dependent on the difference between the pixel value and the D_min value, such that pixel values nearer the D_min value have smaller gain factors; and using the gain factors to sharpen the digital image.

Claims

1. A method of sharpening a digital image having image pixels values, comprising the steps of:

determining a plurality of D_min values, each said D_min value representing a respective pixel value of a reference dark scene image corresponding to a minimum possible exposure for a system that produced the digital image;

averaging said determined D_min values to remove fluctuations due to noise in the pixel values of the reference dark scene image and provide an average D_min value;

for each pixel value in the digital image providing a gain factor that is dependent on the difference between the pixel value and the average D_min value, such that pixel values nearer the average D_min value have smaller gain factors, said gain factors are provided by a lookup table that models a monotonic function of pixel value, said monotonic function increasing from the average D_min value to a predetermined pixel value and being constant for pixel values that exceed the predetermined pixel value;

applying an image processing path including one or more image transforms to the original digital image resulting in a rendered digital image;

applying the image processing path to the gain factors to form rendered gain factors; and

using the rendered gain factors to sharpen the rendered digital image.

2. A computer program product stored on computer readable medium for sharpening a digital image having image pixels values, comprising the steps of:

determining a plurality of D_min values, each said D_min value representing a respective pixel value of a reference dark scene image corresponding to a minimum possible exposure for a system that produced the digital image;

averaging said determined D_min values to remove fluctuations due to noise in the pixel values of the reference dark scene image and provide an average D_min value;

for each pixel value in the digital image providing a gain factor that is dependent on the difference between the pixel value and the average D_min value, such that pixel values nearer the average D_min value have smaller gain factors, said gain factors are provided by a lookup table that models a monotonic function of pixel value, said monotonic function increasing from the average D_min value to a predetermined pixel value and being constant for pixel values that exceed the predetermined pixel value;

applying an image processing path including one or more image transforms to the original digital image resulting in a rendered digital image;

applying the image processing path to the gain factors to form rendered gain factors; and

using the rendered gain factors to sharpen the rendered digital image.

3. A system of sharpening a digital image having image pixels values, comprising:

means for determining a plurality of D_min values, each said D_min value representing a respective pixel value of a reference dark scene image corresponding to a minimum possible exposure for a system that produced the digital image;

means for averaging said determined D_min values to remove fluctuations due to noise in the pixel values of the reference dark scene image and provide an average D_min;

means for providing a gain factor for each pixel value in the digital image, said gain factor each being dependent on the difference between the pixel value and the average D_min, value, such that pixel values nearer the average D_min value have smaller gain factors, said gain factors are provided by a lookup table that models a monotonic function of pixel value, said monotonic function increasing from the average D_min value to a predetermined pixel value and being constant for pixel values that exceed the predetermined pixel value;

means for applying an image processing path including one or more image transforms to the original digital image resulting in a rendered digital image;

means for applying the image processing path to the gain factors to form rendered gain factors; and

means for using the rendered gain factors to sharpen the rendered digital image.