US 7,064,770 B2Granted

Single-pass image resampling system and method with anisotropic filtering

AssigneeSilicon Optix Inc.

InventorsVladimir Lachine, Gregory Lionel Smith, Louie Lee

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Abstract

A method and system for circularly symmetric anisotropic filtering over an extended elliptical or rectangular footprint in single-pass digital image warping are disclosed. The filtering is performed by first finding and adjusting an ellipse that approximates a non-uniform image scaling function in a mapped position of an output pixel in the input image space. A linear transformation from this ellipse to a unit circle in the output image space is determined to calculate input pixel radii inside the footprint and corresponding filter coefficient as a function of the radius. The shape of the footprint is determined as a trade-off between image quality and processing speed. In one implementation, profiles of smoothing and warping components are combined to produce sharper or detail enhanced output image. The method and system of the invention produce natural output image without jagging artifacts, while maintaining or enhancing the sharpness of the input image.

Claims14

Dependent claims

A digital signal processing method for optimized hardware and software implementation of single-pass digital image resampling with an anisotropic filter to transform a two-dimensional video input image having an input pixel coordinate space and input digital pixel data, into an output image having an output pixel coordinate space and output digital pixel data, said method comprising:

(a) obtaining two-dimensional video input digital image data for an output pixel;
(b) mapping the output pixel coordinates onto the input image coordinate space to determine a mapped coordinate position;
(c) determining the Jacobian matrix of the output pixel coordinates with respect to the input coordinates at the mapped coordinate position determined in (b);
(d) determining major and minor radii and the orientation of the major radius to uniquely determine an ellipse around the mapped coordinate position determined in (b), formed by two row vectors of the determined Jacobian matrix in (c);
(e) extending and adjusting the radii of said ellipse based on a required image quality and a required processing speed;
(f) determining a footprint based on the result of (e) in the input image coordinate space around said mapped coordinate position determined in (b), to include input pixels participating in the filtering;
(g) transforming the ellipse of (d) into a circle having a radius of one unit to facilitate distance calculation of the included input pixels from the center of the circle;
(h) determining coefficients of the anisotropic filter for all input pixels in the footprint from a circularly symmetric profile as a function of the distance in (g);
(i) determining the value of the output pixel by accumulating values of the input pixels inside the footprint with coefficients determined in (h);
and
saving the value of the output pixel.

8 more elements

A digital signal processing system for optimized hardware and software implementation of single-pass digital image resampling with an anisotropic filter to transform a two-dimensional video input image having an input pixel coordinate space and input digital pixel data, into an output image having an output pixel coordinate space and output digital pixel data, said system comprising the following stages:

(a) an input interface for obtaining two-dimensional video input digital image data for an output pixel;
(b) a coordinates generator for mapping the output pixel coordinates onto the input image coordinate space to determine a mapped coordinate position;
(c) a local scale estimator, coupled to said input interface and said coordinate generator, for determining the Jacobian matrix of the output pixel coordinates with respect to the input coordinates at the mapped coordinate position;
(d) said local scale estimator, being further adapted for determining the major and minor radii and the orientation of the major radius to uniquely determine an ellipse around the mapped coordinate position, formed by two row vectors of the determined Jacobian matrix in (c);
(e) said local scale estimator, being further adapted to extend and adjust the radii of said ellipse based on a required image quality and a required processing speed;
(f) a footprint generator, coupled to said local scale estimator and said coordinates generator, for determining a footprint in the input image coordinate space around the mapped coordinate position, to include input pixels participating in the filtering;
(g) a filter coefficients generator, coupled to said footprint generator and said local scale estimator, to transform the ellipse of (d) into a circle having a radius of one unit to facilitate distance calculation of the included input pixels from the center of the circle;
(h) said filter coefficient generator, being further adapted to determine coefficients of the anisotropic filter for input pixels in the footprint from a circularly symmetric profile as a function of the distance in (g);
(i) a filter, coupled to said filter coefficient generator and said footprint generator, to determine the value of the output pixel by accumulating values of the input pixels inside the footprint with coefficients determined in (h);
and
(j) an output interface, coupled to said filter, to save the value of the output pixel.

8 more elements

Dependencies are inferred from the claim text.