Methods and apparatuses providing noise reduction while preserving edges for imagers

Abstract

Methods and apparatuses of reducing noise in an image by obtaining a first value for a target pixel, obtaining a respective second value for neighboring pixels surrounding the target pixel, for each neighboring pixel, comparing a difference between the first value and the second value to a threshold value and selectively replacing the first value with an average value obtained from the first value and at least a subset of the second values from the neighboring pixels which have an associated difference which is less than the threshold value based on a result of the comparing step. In a further modification, less than all neighboring pixels which have an associated difference which is less than the threshold value are used in the averaging.

1 . A method of processing an image, comprising the steps of: 
 selecting a set of pixel signals from pixels surrounding an identified target pixel having a target pixel signal;    for each of the surrounding pixel signals of the set, determining a respective difference value between the target pixel signal and the surrounding pixel signal;    for each of the surrounding pixel signals of the set, determining if the respective difference value is less than a predetermined threshold; and    substituting an average value as a value for the target pixel signal, the average value is based on the target pixel signal and at least a selected subset of the pixel signals having a respective difference value less than a predetermined threshold.    
     
     
         2 . The method of  claim 1 , wherein the average value is an average of 2 n  pixel signals where n is an integer.  
     
     
         3 . The method of  claim 1 , wherein the target pixel is one of a red, greenred, greenblue, or blue pixel and each of the pixels in the selected set are the same color as the target pixel.  
     
     
         4 . The method of  claim 1 , wherein at least one of the surrounding pixels has been previously denoised.  
     
     
         5 . The method of  claim 1 , wherein the predetermined threshold is based on at least one of an analog and digital gain used in image capture.  
     
     
         6 . The method of  claim 1 , wherein the predetermined threshold is based on the color of the target pixel.  
     
     
         7 . A method of processing an image comprising the steps of: 
 selecting a target pixel having a first signal value;    replacing a first register value with a sum of the first register value and the first signal value;    incrementing a first counter;    selecting a correction kernel having a number of pixels surrounding the target pixel, each of the kernel pixels having a respective second signal value;    grouping the selected kernel pixels into at least one pixel group;    comparing a difference between the first signal value and a one of the respective second signal values to a threshold value;    replacing the first register value with a sum of the first register value and one of the respective second signal values based on a result of the comparing the difference step;    incrementing the first counter based on a result of the comparing the difference step;    comparing a value of the first counter to a set of at least one predetermined number;    replacing a second register value with the first register value based on a result of the comparing the value step;    replacing a value of a second counter with the value of the first counter based on a result of the comparing the value step; and    replacing the first signal value with the result of a division of the second register value by the second counter.    
     
     
         8 . The method of  claim 7 , further comprising repeating the comparing the difference step through replacing the value of the second counter step for each of the respective second signal values.  
     
     
         9 . The method of  claim 7 , further comprising repeating the comparing the difference step through replacing the value of the second counter step for each of the respective second signal values in a first pixel group before repeating the comparing the difference step through replacing the value of the second counter step for each of the respective second signal values in a second pixel group.  
     
     
         10 . The method of  claim 7 , wherein each selected kernel pixel has a respective distance from the target pixel and are grouped based on each kernel pixels' distance from the target pixel.  
     
     
         11 . The method of  claim 7 , wherein the set of at least one predetermined number is comprised of integer powers of the number two.  
     
     
         12 . The method of  claim 7 , wherein the target pixel is one of a red, green, or blue pixel and each of the selected kernel pixels are the same color as the target pixel.  
     
     
         13 . A method of processing an image, comprising the steps of: 
 selecting a target pixel having a signal value;    selecting a correction kernel associated with the target pixel containing a set of correction kernel pixels each having a respective pixel signal and a respective distance from the target pixel;    for each of the correction kernel pixel signals, determining a respective difference value between the target pixel signal and the correction kernel pixel signal;    for each of the correction kernel pixel signals, determining if the respective difference value is less than a predetermined threshold; and    substituting an average value as a value for the target pixel signal, the average value being an average of 2 n  pixel signals where n is an integer, wherein the 2 n  signals are comprised of the target pixel signal and at least a subset of the correction kernel pixel signal having a respective difference value less than a predetermined threshold.    
     
     
         14 . The method of  claim 13 , wherein the at least a subset of correction kernel pixel signals is selected based on the correction kernel pixel signals respective distances from the target pixel.  
     
     
         15 . An imager comprising: 
 a pixel array for capturing an image and comprising a plurality of pixels, each pixel outputting a signal representing an amount of light received; and    a circuit for denoising an image captured by the array,    the circuit being configured to: 
 select from the captured image a target pixel having a signal value;  
 select a correction kernel associated with the target pixel containing a set of correction kernel pixels each having a respective pixel signal and a respective distance from the target pixel;  
 for each of the correction kernel pixel signals, determine a respective difference value between the target pixel signal and the correction kernel pixel signal;  
 for each of the correction kernel pixel signals, determine if the respective difference value is less than a predetermined threshold; and  
 substitute an average value as a value for the target pixel signal, the average value being an average of 2 n  pixel signals where n is an integer, wherein the 2 n  signals are comprised of the target pixel signal and at least a subset of the correction kernel pixel signals having a respective difference value less than a predetermined threshold.  
   
     
     
         16 . The imager of  claim 15 , wherein the at least a subset of correction kernel pixel signals is selected based on the correction kernel pixel signals respective distances from the target pixel.  
     
     
         17 . The imager of  claim 15 , wherein the imager is part of a camera system.  
     
     
         18 . An imager comprising: 
 a pixel array for capturing an image and comprising a plurality of pixels, each pixel outputting a signal representing an amount of light received; and    a processing circuit for denoising an image captured by the array, the processing circuit being configured to: 
 select from the captured image a set of pixel signals from pixels surrounding an identified target pixel having a target pixel signal;  
 for each of the surrounding pixel signals of the set, determine a respective difference value between the target pixel signal and the surrounding pixel signal;  
 for each of the surrounding pixel signals of the set, determine if the respective difference value is less than a predetermined threshold; and  
 substitute an average value as a value for the target pixel signal, the average value is based on the target pixel signal and at least a selected subset of the pixel signals having a respective difference value less than a predetermined threshold.  
   
     
     
         19 . The imager of  claim 18 , wherein the average value is an average of 2 n  pixel signals where n is an integer.  
     
     
         20 . The imager of  claim 18 , wherein the target pixel and each pixel in the selected set are the same color.  
     
     
         21 . The imager of  claim 18 , wherein at least one of surrounding pixels has been previously denoised.  
     
     
         22 . The imager of  claim 18 , wherein the imager is part of a camera system.  
     
     
         23 . A storage medium containing a program for execution by a processor, the processor when executing the program, performs the steps of: 
 selecting a set of pixel signals from pixels surrounding an identified target pixel having a target pixel signal;    for each of the surrounding pixel signals of the set, determining a respective difference value between the target pixel signal and the surrounding pixel signal;    for each of the surrounding pixel signals of the set, determining if the respective difference value is less than a predetermined threshold; and    substituting an average value as a value for the target pixel signal, the average value is based on the target pixel signal and at least a selected subset of the pixel signals having a respective difference value less than a predetermined threshold.