초록 ▼

This invention is directed to an image processing arrangement used to estimate image displacement relative to a reference frame. It comprises a discrete complex correlator, an associated interpolator, and a displacement estimator. The unique nature of the system is its ability to estimate shifts of

This invention is directed to an image processing arrangement used to estimate image displacement relative to a reference frame. It comprises a discrete complex correlator, an associated interpolator, and a displacement estimator. The unique nature of the system is its ability to estimate shifts of a fraction of a pixel for sparcely sampled data. This is accomplished by extracting the complex gradients from the gray scale data and in turn correlating the gradients via a discrete complex correlator. The resulting cross correlation function is then interpolated to yield an accurate estimate of the shift. The invention is particularly adapted for use in the autofocus portion of a synthetic aperture radar imaging system.

대표청구항 ▼

1. An autofocus device in combination with a synthetic aperture radar system to extract error phase from detected data, said autofocus device comprising: a complex gradient generator receiving said detected data from said synthetic aperture radar system and generating a complex gradient from said

1. An autofocus device in combination with a synthetic aperture radar system to extract error phase from detected data, said autofocus device comprising: a complex gradient generator receiving said detected data from said synthetic aperture radar system and generating a complex gradient from said detected data; a complex correlator receiving said complex gradient from said complex gradient generator and outputting a line per line complex correlation; an interpolator receiving said complex correlation from said complex correlator and performing an interpolation to obtain a shift estimate; and a displacement estimator receiving said shift estimate from said interpolator and converting said shift estimate into said error phase. 2. An autofocus device as defined in claim 1 wherein said complex gradient generator is a data processor which generates said complex gradient by performing a Sobel Window process on said detected data. 3. An autofocus device as defined in claim 2 wherein said complex correlator is a data processor which performs said line per line complex correlation by processing said complex gradient with the following algorithm: ##EQU## where A is the complex gradient for reference frame A; and B is the complex gradient for reference frame B. 4. A process of correlating detected data from radar range processing to extract an error phase estimate comprising the steps of: generating a complex gradient of the detected data; complex correlating said complex gradient overall range cells after said generating step and producing a complex correlation; interpolating said complex correlation and producing a shift estimate after said complex correlating step; and estimating displacement of said shift estimate to produce said error phase estimate. 5. A process of correlating detected data as defined in claim 4 wherein said generating step comprises processing said detected data with a Sobel Window to produce said complex gradient; and said complex correlating step comprises producing a complex correlation by processing said complex gradient with the following algorithm: ##EQU## where A is the complex gradient for reference frame A; and B is the complex gradient for reference frame B. 6. A process of correlating detecting data as defined in claim 5 wherein said interpolating step comprises: performing a Fast Transform on said complex correlation and producing a Fast Fourier Transform output signal; adding zeros to said Fast Fourier Transform output signal at its midpoint and producing a convenient binary number; and performing an Inverse Fast Fourier Transform on said binary number to produce a shift estimate. 7. A process of correlating detected data as defined in claim 6 wherein said estimating displacement step comprises: multiplying said shift estimate by a constant to produce a phase rate; and performing a least square estimate on said phase rate to produce said error phase estimate. 8. A process of correlating detected data as defined in claim 6 wherein said estimating displacement step comprises: multiplying said shift estimate by a constant to produce a phase rate; and integrating said phase rate to produce said error phase estimate.