Method and apparatus for adaptive sharpening of images

• US 5,524,162 A
• Filed: 07/22/1991
• Issued: 06/04/1996
• Est. Priority Date: 07/22/1991
• Status: Expired due to Fees

• Current Assignee: Raphael L. Levien
• Original Assignee: Raphael L. Levien
• Inventors: Levien, Raphael L.
• Primary Examiner(s): Mancuso, Joseph
• Application Number:
  US07/733,479
• Time in Patent Office: 1,779 Days
• Field of Search: 382/54, 382/43, 382/254, 382/263, 382/280, 358/447, 364/724.05, 364/724.06, 364/724.08, 364/724.19
• US Class Current: 382/263
• CPC Class Codes: G06T 5/20 using local operators

Abstract

A method and apparatus for adaptively sharpening an image includes dividing the image area into smaller sub-areas each containing a sub-image, and adaptively sharpening each sub-area image individually. That is, the sharpening factor SF, and the blur area are automatically and adaptively set differently for each individual sub-area image of the original photograph. The sharpening effect is thus improved over the entire image area since each sub-area image of the original image is sharpened in accordance with the amount of sharpening needed. Areas with more detail needing more sharpening, would receive more sharpening, while other areas such as gray sky, receive almost no sharpening.

Claims

1. In a method for sharpening an image, said method comprising dividing the area of said image into a plurality of sub-area images and sharpening each of said sub-area images individually, wherein said step of sharpening each of said sub-area images includes means responsive to at least a portion of said sub-area image for determining at least one parameter for sharpening said sub-area image, an improved method for sharpening said sub-area image, wherein the improvement comprises:

scanning a plurality of input points of an original of said image for reading input image data corresponding to the input pixels of each said sub-area image to be sharpened;

determining the maximum frequency energy content of a portion of said sub-area image by Fourier transform analysis; and

selecting a sharpening factor based on said determined maximum frequency energy content of said portion of said sub-area image.

2. A method in accordance with claim 1, wherein said step of sharpening each of said sub-area images further comprises:

generating a blurry sub-area image from said sub-area

image;

subtracting said blurry sub-area image from said sub-area image to create a difference sub-area image;

multiplying said difference sub-area image by said sharpening factor to provide a scaled difference sub-area image; and

combining said scaled difference sub-area image with said sub-area image.

3. A method in accordance with claim 2, wherein said step of multiplying said difference sub-area image by said sharpening factor includes applying a non-linear function to said difference sub-area image.

4. In a method for sharpening an image, said method comprising dividing the area of said image into a plurality of sub-area images and sharpening each of said sub-area images individually, wherein said step of sharpening each of said sub-area images includes means responsive to at least a portion of said sub-area image for determining at least one parameter for sharpening said sub-area image, an improved method for sharpening said sub-area image, wherein the improvement comprises:

scanning a plurality of input points of an original of

said image for reading input image data corresponding to the input pixels of each said sub-area image to be sharpened;

determining the maximum frequency energy content of a portion of said sub-area image by Fourier transform analysis;

generating a blurry sub-area image from said sub-area image based on said determined maximum frequency energy content of said portion of said sub-area image; and

subtracting said blurry sub-area image from said sub-area image to create a difference sub-area image,

wherein said step of sharpening each of said sub-area images further comprises;

selecting a sharpening factor based on said determined maximum frequency energy content of said portion of said sub-area image;

multiplying said difference sub-area image by said sharpening factor to provide a scaled difference sub-area image; and

combining said scaled difference sub-area image with said sub-area image.

5. A method in accordance with claim 4, wherein said step of multiplying said difference sub-area image by said sharpening factor includes applying a non-linear function to said difference sub-area image.

6. In a method for sharpening an image, said method comprising dividing the area of said image into a plurality of sub-area images and sharpening each of said sub-area images individually, wherein said step of sharpening each of said sub-area images includes means responsive to at least a portion of said sub-area image for determining at least one parameter for sharpening said sub-area image, an improved method for sharpening said sub-area image, wherein the improvement comprises:

scanning a plurality of input points of an original of said image for reading input image data corresponding to the input pixels of each said sub-area image to be sharpened;

determining the maximum frequency energy content of a portion of said sub-area image by Fourier transform analysis; and

increasing the energy content of said sub-area image for frequencies substantially between said determined maximum frequency energy content and one half said determined maximum frequency energy content relative to the energy content of said sub-area image below one half said determined maximum frequency energy content.

7. In an apparatus for sharpening an image, said apparatus comprising means for dividing the area of said image into a plurality of sub-area images and means for sharpening each of said sub-area images individually, wherein said means for sharpening each of said sub-area images includes means responsive to at least a portion of said sub-area image for determining at least one parameter for sharpening said sub-area image, an improved apparatus for sharpening said sub-area image, wherein the improvement comprises:

means for scanning a plurality of input points of an original of said image for reading input image data corresponding to the input pixels of each said sub-area image to be sharpened;

means for determining the maximum frequency energy content of a portion of said sub-area image by Fourier transform analysis; and

means for selecting a sharpening factor based on said determined maximum frequency energy content of said portion of said sub-area image.

8. An apparatus in accordance with claim 7, wherein said means for sharpening each of said sub-area images further comprises:

means for generating a blurry sub-area image from said sub-area image;

means for subtracting said blurry sub-area image from said sub-area image to create a difference sub-area image;

means for multiplying said difference sub-area image by said sharpening factor to provide a scaled difference sub-area image; and

means for combining said scaled difference sub-area image with said sub-area image.

9. An apparatus in accordance with claim 8, wherein said means for multiplying said difference sub-area image by said sharpening factor includes means for applying a non-linear function to said difference sub-area image.

10. In an apparatus for sharpening an image, said apparatus comprising means for dividing the area of said image into a plurality of sub-area images and means for sharpening each of said sub-area images individually, wherein said means for sharpening each of said sub-area images includes means responsive to at least a portion of said sub-area image for determining at least one parameter for sharpening said sub-area image, an improved apparatus for sharpening said sub-area image, wherein the improvement comprises:

means for scanning a plurality of input points of an original of said image for reading input image data corresponding to the input pixels of each said sub-area image to be sharpened;

means for determining the maximum frequency energy content of a portion of said sub-area image by Fourier transform analysis; and

means for generating a blurry sub-area image from said sub-area image based on said determined maximum frequency energy content of said portion of said sub-area image; and

means for subtracting said blurry sub-area image from said sub-area image to create a difference sub-area image,

wherein said means for sharpening each of said sub-area images further comprises;

means for selecting a sharpening factor based on said determined maximum frequency energy content of said portion of said sub-area image;

means for multiplying said difference sub-area image by said sharpening factor to provide a scaled difference sub-area image; and

means for combining said scaled difference sub-area image with said sub-area image.

11. An apparatus in accordance with claim 10, wherein said means for multiplying said difference sub-area image by said sharpening factor includes means for applying a non-linear function to said difference sub-area image.

12. In an apparatus for sharpening an image, said apparatus comprising means for dividing the area of said image into a plurality of sub-area images and means for sharpening each of said sub-area images individually, wherein said means for sharpening each of said sub-area images includes means responsive to at least a portion of said sub-area image for determining at least one parameter for sharpening said sub-area image, an improved apparatus for sharpening said sub-area image, wherein the improvement comprises:

means for scanning a plurality of input points of an original of said image for reading input image data corresponding to the input pixels of each said sub-area image to be sharpened;

means for determining the maximum frequency energy content of a portion of said sub-area image by Fourier transform analysis; and

means for increasing the energy content of said sub-area image for frequencies substantially between said determined maximum frequency energy content and one half said determined maximum frequency energy content relative to the energy content of said sub-area image below one half said determined maximum frequency energy content.