# US 6,724,945 B1 · Correcting defect pixels in a digital image > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,724,945 B1 - Document ID: US6724945B1 - Status: Granted - Kind: B1 - Application number: 09/578,251 - Filed: 2000-05-24 - Granted: 2004-04-20 - Earliest claimed: 2000-05-24 - Assignees: Hewlett-Packard Development Company, L.P. - Inventors: Jonathan Yen; Daniel R. Tretter; Truong-Thao Nguyen - Web page: https://patentgrep.com/patent/US6724945B1 ## CPC - H04N 19/18: the unit being a set of transform coefficients - G06T 5/20: using local operators - G06T 5/77: Retouching; Inpainting; Scratch removal - H04N 5/772: {the recording apparatus and the television camera being placed in the same enclosure} - H04N 19/527: Global motion vector estimation - H04N 19/593: involving spatial prediction techniques - H04N 19/895: in combination with error concealment - H04N 23/843: {Demosaicing, e.g. interpolating colour pixel values} - H04N 25/134: {based on three different wavelength filter elements} - H04N 25/68: applied to defects - H04N 25/683: by defect estimation performed on the scene signal, e.g. real time or on the fly detection - G06T 2207/10024: Color image - G06T 2207/20032: Median filtering - H04N 5/21: Circuitry for suppressing or minimising disturbance, e.g. moiré or halo - H04N 5/907: using static stores, e.g. storage tubes or semiconductor memories (H04N5/91 takes precedence) - H04N 9/646: {for image enhancement, e.g. vertical detail restoration, cross-colour elimination, contour correction, chrominance trapping filters} - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION - G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL ## Abstract Systems and methods of correcting one or more defect pixels in a source image are described. The source image is formed from a plurality of pixels each having a respective value. In one scheme, a defect pixel is corrected based upon curvature information computed from pixel values located near the defect pixel. In another scheme, a median pixel value is determined from values of pixels located near a defect pixel, and the defect pixel is corrected based upon the median pixel value. ## Claims ### Claim 1 A method of correcting one or more defect pixels in a source image formed from a plurality of pixels each having a respective value, comprising: (a) in response to a determination that curvature information is complete, replacing a defect pixel with a value computed from pixel values located near the defect pixel along a direction selected based upon a comparison of curvature values computed along multiple different directions; (b) in response to a determination that curvature information is incomplete and gradient information is complete, replacing the defect pixel with a value computed from values of pixels positioned near the defect pixel along a direction selected based upon a comparison of gradient values computed along multiple different directions; and (c) in response to a determination that curvature information and gradient information are incomplete, replacing the defect pixel with an average of values of non-defect pixels neighboring the defect pixel. ### Claim 2 (depends on 1) The method of claim 1, further comprising computing a horizontal curvature value based upon pixel values from two groups of horizontally aligned pixels located on opposite sides of the defect pixel. ### Claim 3 (depends on 2) The method of claim 2, further comprising computing a vertical curvature value based upon pixel values from two groups of vertically aligned pixels located on opposite sides of the defect pixel. ### Claim 4 (depends on 3) The method of claim 3, wherein in response to a determination that curvature information is complete, step (a) comprises replacing the defect pixel with a value computed based upon a comparison of the computed horizontal and vertical curvature values. ### Claim 5 (depends on 4) The method of claim 4, wherein step (a) comprises replacing the defect pixel with an interpolation of values of pixels aligned vertically with the defect pixel in response to a determination that the horizontal curvature exceeds the vertical curvature. ### Claim 6 (depends on 4) The method of claim 4, wherein step (a) comprises replacing the defect pixel with an interpolation of values of pixels aligned horizontally with the defect pixel in response to a determination that the vertical curvature exceeds the horizontal curvature. ### Claim 7 (depends on 1) The method of claim 1, further comprising computing a curvature value based upon values of pixels surrounding the defect pixel. ### Claim 8 (depends on 1) The method of claim 1, wherein step (a) comprises replacing the defect pixel with an interpolation of values of pixels aligned with the defect pixel along the selected direction determined from the curvature information. ### Claim 9 (depends on 8) The method of claim 8, wherein in step (a) the selected direction is determined by comparing curvature values computed for two orthogonal directions. ### Claim 10 (depends on 8) The method of claim 8, wherein in step (a) the defect pixel is replaced with a value computed from a linear interpolation of values of pixels aligned with the defect pixel along the selected direction. ### Claim 11 (depends on 10) The method of claim 10, wherein in step (a) the defect pixel is replaced with a value computed from a linear interpolation of values of two non-defective pixels located on opposite sides of the defect pixel. ### Claim 12 (depends on 11) The method of claim 11, wherein in step (a) the defect pixel is replaced with a value computed with only operations of adding and shifting. ### Claim 13 (depends on 1) The method of claim 1, further comprising obtaining the source image from an image sensor having a plurality of light detectors each generating a pixel value of a respective color, wherein the colors are arranged in multiple color planes of non-overlapping pixel locations, and the defect pixel is corrected based upon curvature information computed from values of pixels in the same color plane. ### Claim 14 (depends on 1) The method of claim 1, wherein in response to a determination that interpolation information along the selected direction is complete, step (b) further comprises replacing the defect pixel with an interpolation of pixel values along the selected direction. ### Claim 15 (depends on 1) The method of claim 1, wherein in response to a determination that interpolation information along the selected direction is incomplete, step (b) further comprises correcting one or more neighboring defect pixels with respective interpolated values, and replacing the defect pixel with a linear interpolation approximation along the selected direction based at least in part upon the corrected neighboring defect pixels. ### Claim 16 A system, comprising a correction filter configured to: (a) in response to a determination that curvature information is complete, replace a defect pixel with a value computed from pixel values located near the defect pixel along a direction selected based upon a comparison of curvature values computed along multiple different directions; (b) in response to a determination that curvature information is incomplete and gradient information is complete, replace the defect pixel with a value computed from values of pixels positioned near the defect pixel along a direction selected based upon a comparison of gradient values computed along multiple different directions; and (c) in response to a determination that curvature information and gradient information are incomplete, replace the defect pixel with an average of values of non-defect pixels neighboring the defect pixel correct a defect pixel. ### Claim 17 (depends on 16) The system of claim 16, wherein in response to a determination that curvature information is complete, the defect pixel is replaced with an interpolation of values of pixels aligned with the defect pixel along the selected direction determined from the curvature information. ### Claim 18 (depends on 17) The system of claim 17, wherein in response to a determination that curvature information is complete, the selected direction is determined by comparing curvature values computed for two orthogonal directions. ### Claim 19 (depends on 17) The system of claim 17, wherein in response to a determination that curvature information is complete, the defect pixel is replaced with a value computed from a linear interpolation of values of pixels aligned with the defect pixel along the selected direction. ### Claim 20 (depends on 19) The system of claim 19, wherein in response to a determination that curvature information is complete, the defect pixel is replaced with a value computed from a linear interpolation of values of two non-defective pixels located on opposite sides of the defect pixel. ### Claim 21 (depends on 20) The system of claim 20, wherein in response to a determination that curvature information is complete, the defect pixel is replaced with a value computed with only operations of adding and shifting.