Image analysis – Image enhancement or restoration
Statutory Invention Registration
1998-05-29
2001-11-06
Pihulic, Daniel T. (Department: 3662)
Image analysis
Image enhancement or restoration
C382S275000, C382S293000, C382S299000, C382S300000
Statutory Invention Registration
active
H0002003
ABSTRACT:
COPYRIGHT NOTICE
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the xerographic reproduction by anyone of the patent document or the patent disclosure in exactly the form it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
BACKGROUND OF THE INVENTION
The present invention relates generally to a technique for retouching, or removing defects or blemishes from, an image, and more specifically to a method and apparatus for recalculating values of pixels selected or identified using a computer generated brush.
When using an image processing system, it is often desirable to alter one or more pixels in an image. For example, it is desirable to correct images containing defective or missing pixels caused by imperfections in the optical equipment used to acquire the image, such as scratches, smudges or other blemishes on camera lenses, photocopier platens or on the surface of the contact glass of a scanner. It is also desirable to manipulate images by replacing selected portions and filling in those portions with a continuation of the surrounding image. For instance, one may wish to alter a picture by removing a portion of the image, such as a person or writing on a wall, while maintaining continuity with the surrounding image.
Some techniques for replacing, or correcting pixels in an image typically employ low pass filtering. However, low pass filtering often tends to blur the image. Other techniques use extrapolation based on the nearest neighbors. That is, the value of bad or missing pixels will be extrapolated based on the value of neighboring pixels having correct or valid values. These techniques can also result in a blurred image, mostly because they do not allow for smoothing of the image when there is a large variation in color in the neighboring pixels. Extrapolation techniques also can result in visual discontinuities or other visual artifacts at the edge of the filled-in region. Thus, it is clear that what is needed in the art is an improved technique for retouching, or removing defects or blemishes from, an image.
SUMMARY OF THE INVENTION
The present invention provides systems and methods for enhancing an image by removing defects or blemishes from the image. The techniques of the present invention use interpolation to determine interpolated values for pixels in a selected region based on the values of pixels surrounding the selected region. Thereafter, a smoothing function determines new values for each pixel in the region based on the values of pixels adjacent the pixels being “smoothed”. The selected region comprises one or more pixels.
A user selects a portion of an image comprising one or more pixels using a computer-generated eraser brush or air brush, for example. Alternatively, a region of one or more pixels is selected by designating pixels having a certain value, or no value (i.e., missing pixels). The selected portion is erased (or the values of the pixels in the region are ignored, for example), and the erased portion is filled in so as to “blend in” with the surrounding image. That is, a new value is determined for each pixel within the selected region. Specifically, the to-be-replaced pixels in the selected region are filled in using interpolation and a smoothing function. Initially, straight interpolation is used to fill in the to-be-replaced pixels based on the average of the pixel values of the surrounding area. For example, in a one-dimensional image, linear interpolation is used; in a two-dimensional image, four-way linear interpolation is used. A smoothing function such as a minimum curvature solution algorithm is then iteratively applied to each of the to-be-replaced pixels (now with interpolated values). The smoothing function calculates new values for the to-be-replaced pixels based on each pixel's nearest neighbors. For each iteration, the smoothing function uses the previously calculated values for each nearest neighbor pixel that lies within the selected region of to-be-replaced pixels.
According to an aspect of the invention, a method is provided for calculating new values of pixels in an image desired to be altered, comprising the steps of: providing an image including a region of first pixels desired to be altered, and a perimeter surrounding the region and comprising second pixels having known values; calculating a pixel value for each of the first pixels using linear interpolation based on at least a portion of the second pixels; applying a smoothing function to the first pixels, wherein the function recalculates the pixel values for each of the first pixels based on the value of at least the first and second pixels adjacent the pixel being recalculated, wherein the recalculation is done using the previously calculated pixel values for the first adjacent pixels; and reapplying the smoothing function if a stop condition is not satisfied.
According to another aspect of the present invention, a method is provided for enhancing a computer generated image, comprising the steps of: acquiring a digital image; selecting a portion of the image including a plurality of first pixels surrounded by second pixels having known values; calculating a pixel value for each of the first pixels using linear interpolation based on the known values of at least a portion of the second pixels; and iteratively applying a minimum curvature algorithm to the first pixels until a stop condition is satisfied, wherein the algorithm recalculates the pixel values for each of the first pixels based on the value of at least the first and second pixels adjacent to the pixel being recalculated, the recalculation using previously calculated pixel values for any of the first adjacent pixels.
According to yet another aspect of the present invention, an image processing system is provided, comprising: means for providing an image; means for selecting a portion of the image including a plurality of first pixels surrounded by second pixels having known values; a processor, wherein the processor calculates an initial pixel value for each of the first pixels using linear interpolation based on the known values of at least a portion of the second pixels, and wherein the processor thereafter iteratively applies a smoothing function to each of the first pixels until a stop condition has been satisfied, the function recalculating each of the first pixel values using the pixel values of at least the pixels adjacent the pixel being recalculated; and means for displaying the image using the recalculated values of the first pixels after the stop condition has been satisfied.
Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.
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Island Graphics Corporation
Pihulic Daniel T.
Townsend and Townsend / and Crew LLP
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