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EP0851666A2 Expired / Lapsed EP ⏱️ 0.0 years remaining

Sharpening filter for images with automatic adaption to image type

Assignee: HP Inc
•
Filing: 1997-09-16
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Granted: —
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Expires: 2017-09-16
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Abstract

Abstract A method of filtering images with a filter that is dependent on image type. For binary images, a fixed Laplacian filter is used (202) for all pixels. For non-binary images, an automatic level-sensitive Laplacian filter is used (206, 208). For non-binary images, Laplacian filter coefficients and normalization divisors are made a function of intensity on a pixel by pixel basis. Pixels indicating a high intensity may be greatly changed by neighboring pixels. Pixels indicating a low intensity receive relatively little or no filtering. In a specific example embodiment, the intensity range is divided to bands, with a different filter for each band. The resulting images are visually sharpened (edge enhanced) with very little impact in darker areas of the image.

Inventors

  • 👤 Patricia D. Lopez
  • 👤 Jeffrey P. Lee
  • 👤 Hal Hansen

Bibliographic Details

Application Number —
Jurisdiction EP
Data Source google_patents
Last Synchronized 2026-11-09 12:22
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/40; H04N1/409; H04N1/4092

Claims Analysis

Total Claims: 2
Claim 1
Independent Claim 180 words
A method of spatially filtering an image, the image comprising an array of pixels, each pixel having a numerical value that is a measure of light intensity, the method comprising the following steps: (a) determining (200) an image type; (b) applying (202) a fixed spatial filter to the numerical values of the array of pixels when the image type is binary; and (c) applying (206, 208) a variable spatial filter to the numerical values of the array of pixels, when the image is other than binary, as follows: (c1) defining at least a first threshold range and a second threshold range; (c2) reading the numerical value of a pixel; (c3) applying (206) the variable spatial filter, with a first central coefficient, to the numerical value of the pixel, when the numerical value is within the first threshold range; (c4) applying (208) the variable spatial filter, with a second central coefficient, to the numerical value of the pixel, when the numerical value is within the second threshold range; and (c5) repeating steps (c2) through (c4) for all pixels in the array.
Claim 2
Dependent Claim 19 words
The method of claim 1 where the fixed spatial filter and the variable spatial filter are both Laplacian filters.

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