Global and local statistics controlled noise reduction system

Abstract

A global and local statistics controlled noise reduction system in which the video image noise reduction processing is effectively adaptive to both image local structure and global noise level. A noise estimation method provides reliable global noise statistics to the noise reduction system. The noise reduction system dynamically/adaptively configures a local filter for processing each image pixel, and processes the pixel with that local filter. The filtering process of the noise reduction system is controlled by both global and local image statistics that are also computed by the system.

1 . (canceled)  
   
   
       2 . The method of  claim 3 , wherein the step of computing the global statistics comprises the step of estimating the global noise standard deviation σ to generate the global statistics.  
   
   
       3 . A method for reducing noise in a digital image formed from a plurality of pixels including a given pixel, the method comprising the steps of: 
 computing global statistics from the image;    computing local statistics for the given pixel;    configuring a local filter using the local and global statistics; and    filtering the given pixel using the local filter to reduce image noise,    wherein the step of computing the local statistics for the given pixel further includes the steps of: 
 selecting a window containing the given pixel and a plurality of neighboring pixels;  
 computing a 2-D local variance of the given pixel based on information related to the pixels in the window;  
 computing a plurality of 1-D local variances along multiple directions through the given pixel in the window; and  
   detecting a local edge direction by selecting one of the directions with the smallest 1-D local variance.    
   
   
       4 . The method of  claim 3 , wherein the step of computing the local statistics for the given pixel further includes the steps of: 
 selecting a window containing the given pixel and a plurality of neighboring pixels;    computing the 2-D local variance σ 0   2  of the given pixel based on information related to the pixels in the window;    computing the 1-D local variances σ 1   2 , σ 2   2 , σ 3   2 , and σ 4   2  along the horizontal (L 1 ), vertical (L 2 ), diagonal from upper left to lower right (L 3 ), and diagonal from upper right to lower left (L 4 ) directions through the given pixel, respectively, in the window; and    detecting the local edge direction by selecting the direction with the smallest 1-D local variance.    
   
   
       5 .- 13 . (canceled)  
   
   
       14 . The system of  claim 15 , wherein the global statistics module estimates a global noise standard deviation σ to generate the global statistics.  
   
   
       15 . A noise reduction system for reducing noise in a digital image comprising pixels the system comprising: 
 a global statistics module that computes global statistics from the image;    a local statistics module that computes local statistics for each of a plurality of image pixels including a given pixel;    a filter configuration module that uses the local and global statistics for the given pixel to configure a local filter for filtering the given pixel; and    the local filter as configured by the filter configuration module being adapted for filtering the given pixel to reduce image noise, wherein the local statistics module computes the local statistics for the given pixel by: 
 selecting a window containing the given pixel and a plurality of neighboring pixels;  
 computing a 2-D local variance of said pixel based on information related to the pixels in the window;  
 computing a plurality of 1-D local variances along multiple directions each defined by a pair of the pixels in the window; and  
 detecting a local edge direction for the given pixel by selecting one of the directions with the smallest 1-D local variance.  
   
   
   
       16 . The system of  claim 15 , wherein the local statistics module computes the local statistics for each pixel by: 
 selecting a window containing said pixel and a plurality of neighboring pixels;    computing the 2-D local variance σ 0   2  of the given pixel based on information related to the pixels in the window;    computing the 1-D local variances σ 1   2 , σ 2   2 , σ 3   2 , and σ 4   2  along the horizontal (L 1 ), vertical (L 2 ), diagonal from upper left to lower right (L 3 ), and diagonal from upper right to lower left (L 4 ) directions through the given pixel, respectively, in the window; and    detecting the local edge direction by selecting the direction with the smallest 1-D local variance.    
   
   
       17 .- 24 . (canceled)  
   
   
       25 . A method for reducing noise in a digital image at a selected pixel, comprising: 
 computing global statistics from the digital image;    computing local statistics for the selected pixel by: 
 selecting a window containing the selected pixel and a plurality of neighboring pixels;  
 computing a 2-D local variance of the selected pixel based on the plurality of neighboring pixels in the window;  
 computing a plurality of 1-D local variances along multiple directions through the selected pixel in the window; and  
 identifying a local edge direction by selecting one of the multiple directions with the smallest 1-D local variance;  
   configuring a local filter using the computed local and global statistics after identifying the local edge direction; and    filtering the given pixel using the local filter to reduce image noise.    
   
   
       26 . The method of  claim 25 , wherein computing the global statistics comprises estimating a global noise standard deviation σ.  
   
   
       27 . The method of  claim 25 , wherein computing the plurality of 1-D local variances along multiple directions through the selected pixel in the window comprises: 
 computing the 1-D local variances σ 1   2 , σ 2   2 , σ 3   2 , and σ 4   2  along the horizontal (L 1 ), vertical (L 2 ), diagonal from upper left to lower right (L 3 ), and diagonal from upper right to lower left (L 4 ) directions through the selected pixel, respectively, in the window.