Noise reduction techniques, fractional bi-spectrum and fractional cross-correlation, and applications

Abstract

A measurement method and system include illuminating an object to be measured with light at two different wavelengths and an incident angle; capturing an image of the object; detecting a frequency of an interference pattern from the image using Fractional Bi-Spectrum Analysis; and calculating a thickness of the object based on the Fractional Bi-Spectrum Analysis. The thickness is calculated based on a relationship between the thickness and the frequency of the interference pattern. The Fractional Bi-Spectrum Analysis is performed on a linear medium with the two different wavelengths being known.

What is claimed is: 
     
         1 . A measurement method comprising:
 illuminating an object to be measured with light at two different wavelengths and an incident angle;   capturing an image of the object;   detecting a frequency of an interference pattern from the image using Fractional Bi-Spectrum Analysis; and   calculating a thickness of the object based on the Fractional Bi-Spectrum Analysis.   
     
     
         2 . The measurement method of  claim 1 , wherein the thickness is calculated based on a relationship between the thickness and the frequency of the interference pattern. 
     
     
         3 . The measurement method of  claim 1 , wherein the Fractional Bi-Spectrum Analysis is performed on a linear medium with the two different wavelengths being known. 
     
     
         4 . A measurement system comprising:
 light sources illuminating an object to be measured with light at two different wavelengths and an incident angle;   a camera capturing an image of the object; and   a computer detecting a frequency of an interference pattern from the image using Fractional Bi-Spectrum Analysis, and calculating a thickness of the object based on the Fractional Bi-Spectrum Analysis.   
     
     
         5 . The measurement system of  claim 4 , wherein the thickness is calculated based on a relationship between the thickness and the frequency of the interference pattern. 
     
     
         6 . The measurement system of  claim 4 , wherein the Fractional Bi-Spectrum Analysis is performed on a linear medium with the two different wavelengths being known.