Patent Publication Number: US-2021183018-A1

Title: Filtering Device, Associated System and Method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of French Patent Application No. 1914576, filed on Dec. 17, 2019, which application is hereby incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates generally to an electronic system and method, and, in particular embodiments, to a filtering device, associated system and method. 
     BACKGROUND 
     A time-of-flight sensor is particularly sensitive to noise arising from the sensor itself and from its environment, necessitating effective filtering. 
     However, existing filtering devices take only a limited number of parameters into account, such that the filtering is not optimal, lowering the quality of the representation of the scene. 
     There is a need to improve the filtering of data from time-of-flight sensors. 
     SUMMARY 
     Some embodiments relate to the filtering of data signals transmitted by pixels, and more particularly pixels of time-of-flight sensors that measure three-dimensional scenes. 
     Some embodiments configure a filtering device for filtering data signals generated by a pixel in an array of pixels according to the position of the pixel in the array and according to the signal-to-noise ratio of a plurality of pixels. 
     Some embodiments relate to a method for filtering data signals transmitted by pixels in an array of pixels comprising the operation of determining, for each pixel, a signal-to-noise ratio on the basis of the data signals transmitted by the pixel, and the operation of filtering the data from each pixel by using an adaptive filter configured on the basis of a plurality of the signal-to-noise ratios. 
     Using the signal-to-noise ratios to filter the noise in the data generated by the pixels in an array of pixels of a sensor makes it possible in particular to enhance the quality of the images. 
     In some embodiments, the signal-to-noise ratio is determined on the basis of the amplitude of the signal, of an ambient value and of a predetermined standard deviation. 
     In some embodiments, if the signal-to-noise ratio of the data signal from the pixel is below a first threshold, the filter is configured to average the data from the pixel on the basis of the data from pixels in the vicinity of the pixel (e.g., such as pixels immediately adjacent to the pixel, such as by using a 3×3 kernel). 
     In some embodiments, if the signal-to-noise ratio of the data signal is above the first threshold, the filtering operation comprises the operation of determining the data filtered from the pixel on the basis of a weighted combination of the data contained in the signals from the pixel and of the data contained in the signals from pixels in the vicinity of the pixel, the weighting coefficients being determined on the basis of the signal-to-noise ratio of the data signals from the pixel and of the data signals from the pixels neighboring the pixel and on the basis of data coefficients calculated on the basis of the data from the pixel and of the data from the pixels neighboring the pixel. 
     In some embodiments, if the signal-to-noise ratio is within an interval defined by the value of the first threshold minus a first difference and the value of the first threshold plus the first difference, the filtering operation comprises the operation of determining the data filtered from the pixel on the basis of a weighted combination between the average of the data from the pixel with the data from pixels in the vicinity of the pixel, and the weighted combination of the data from the pixel and from pixels in the vicinity of the pixel. 
     In some embodiments, the extent of the pixels neighboring the pixel is determined on the basis of the signal-to-noise ratio of the data signal from the pixel. 
     In some embodiments, the filtering is advantageously adapted according to the quality of the received data. 
     In some embodiments, the pixels are incorporated within a time-of-flight sensor. 
     Using the signal-to-noise ratios to filter the noise in the data signals generated by the pixels in an array of pixels of a time-of-flight sensor advantageously makes it possible in particular to enhance the quality of the images and the representation of scenes. 
     Some embodiments relate to a device for filtering data signals transmitted by pixels in an array of pixels, which device is configured to filter the data contained in the data signals on the basis of a plurality of signal-to-noise ratios calculated on the basis of the data signals. 
     In some embodiments, the device comprises a calculating module configured to calculate the signal-to-noise ratio of the data signals from each pixel, and an adaptive filter configured to filter data from each pixel on the basis of a plurality of the signal-to-noise ratios. 
     In some embodiments, the adaptive filter is configured to average the data contained in the data signal from the pixel with the data contained in the data signals from pixels in the vicinity of the pixel if the signal-to-noise ratio of the data signal from the pixel is below a first threshold, the filtered data from the pixel comprising the averaged data. 
     In some embodiments, the adaptive filter is configured to determine the data filtered from the pixel on the basis of a weighted combination of the data from the pixel and from pixels in the vicinity of the pixel if the signal-to-noise ratio of the data signal from the pixel is above the first threshold, the weighting coefficients being determined on the basis of the signal-to-noise ratio of the data signal from the pixel and of the data signals from the pixels neighboring the pixel and on the basis of data coefficients calculated on the basis of data from the pixel and data from the pixels neighboring the pixel. 
     In some embodiments, the adaptive filter is configured to determine the data filtered from the pixel on the basis of a weighted combination between the average of the data from the pixel with the data from pixels in the vicinity of the pixel, and of the weighted combination of the data from the pixel and of the data from pixels in the vicinity of the pixel, if the signal-to-noise ratio is within an interval defined by the value of the first threshold minus a first difference and the value of the first threshold plus the first difference. 
     In some embodiments, the device further comprises a selection module configured to determine the extent of the pixels neighboring the pixel on the basis of the signal-to-noise ratio of the data signal from the pixel. 
     Some embodiments relate to a system comprising a device such as defined above, and at least one sensor comprising an array of pixels, the device being connected to the sensor. 
     According to one embodiment, the sensor is a time-of-flight sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages and features of the invention will become apparent upon examining the detailed description of completely non-limiting embodiments and the appended drawings, in which: 
         FIG. 1  illustrates a system, according to an embodiment of the present invention; 
         FIG. 2  illustrates the array of the sensor  2  of  FIG. 1 , according to an embodiment; 
         FIG. 3  illustrates the sequencer of  FIG. 1 , according to an embodiment; 
         FIG. 4  illustrates a map generated by the mapping module of  FIG. 3 , according to an embodiment of the present invention; 
         FIG. 5  illustrates the data filtering device of  FIG. 1 , according to an embodiment of the present invention; 
         FIG. 6  illustrates a configuration of the adaptive filter of  FIG. 5 , according to an embodiment of the present invention; and 
         FIG. 7  illustrates a flow chart of an embodiment method for filtering data signals received from the array of  FIG. 2 , according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Reference is made to  FIG. 1 , which represents an exemplary embodiment of a system  1  comprising a sensor  2  comprising an array of pixels  3  and a sequencer  4  that is connected to the sensor  2 . 
     The sequencer  4  is configured to condition and to filter the data contained in a signal S 2  transmitted by the sensor  2 , and comprises a data filtering device  5 . In some embodiments, the sequencer is implemented by custom or general purpose controller or processor (e.g., digital signal processor) comprising combinatorial logic coupled to a memory. 
     In some embodiments, the sensor  2  may be a time-of-flight sensor. 
     The sequencer  4  delivers an output signal S 4  on the basis of the input signal S 2  received from the sensor  2 . 
       FIG. 2  illustrates an exemplary embodiment of the array  3  of the sensor  2 . 
     The array  3  comprises twenty-five pixels numbered  31  to  55 , the pixel  31  being arranged at the center of the array  3 . 
     Of course, the array  3  may comprise more or fewer than twenty-five pixels. 
     Reference is now made to  FIG. 3 , which illustrates an exemplary embodiment of the sequencer  4 . 
     The sequencer  4  comprises the device for filtering data signals  5 , a conditioning module  6  connected to the filtering device  5  and a mapping module  7  connected to the conditioning module  6  and to the filtering device  5 . 
     The sequencer  4  further comprises a processing unit UT that controls the device for filtering data signals  5 , the conditioning module  6  the mapping module  7  as described hereinafter. 
     The conditioning module  6  receives the input signal S 2  comprising the data transmitted by the pixels  31  to  55  and generates, for each pixel  31  to  55 , a data vector DATA 31  to DATA 55  comprising a numerator NUM 31  to NUM 55  and a denominator DEM 31  to DEM 55  from the received data. 
     The vectors DATA 31  to DATA 55  are transmitted to the device  5  and to the mapping module  7 . 
     The conditioning module  6  further generates an ambient value AM 31  to AM 55  on the basis of the received data transmitted to the device  5 . 
     The operation of determining the numerator, the denominator and the value of the ambient is known to a person skilled in the art and depends on the technology of the sensor  2 . 
     In some embodiments, the ambient is obtained in particular on the basis of a combination of amplitudes of signals obtained from image captures of the same scene, the amplitudes being divided by an exposure time. 
     On the basis of the data vectors DATA 31  to DATA 55 , the mapping module  7  generates a map  8 , which can be seen in  FIG. 4  that associates each pixel  31  to  55  with a vector DATA 31  to DATA 55  according to the position of the pixel  31  to  55  in the array  3 . 
     The device for filtering data signals  5  is configured to filter the data vectors DATA 31  to DATA 55  on the basis of a plurality of signal-to-noise ratios SNR 31  to SNR 55  calculated on the basis of the data DATA 31  to DATA 55 . 
     The device  5  transmits the output signal S 4  comprising filtered data vectors DATA 311  to  551 . 
     Each filtered data vector DATA 311  to DATA 511  comprises the numerator NUM 31  to NUM 55  and the denominator DEM 31  to DEM 55  filtered by the filtering device  5 , the vector DATA 311  to DATA 511  comprising a filtered numerator NUM 311  to NUM 551  and a denominator DEM 311  to DEM 551 . 
       FIG. 5  illustrates an exemplary embodiment of the device for filtering data signals  5 . 
     The device  5  comprises a calculating module  9  configured to calculate the signal-to-noise ratio SNR 31  to SN 55  of the data signal from each pixel  31  to  55 , an adaptive filter  10  configured to filter the data DATA 31  to DATA 55  from each pixel  31  to  55  on the basis of a plurality of signal-to-noise ratios SNR 31  to SNR 55 , and a selection module  11  connected to the filter  10  and receiving, as input, the signal-to-noise ratio SNR 31  to SNR 55  of the signal from each pixel  31  to  55 . 
     The data DATA 31  from the center pixel  31  being filtered by the filtering device  5  is considered hereinafter. 
     Of course, all of the data DATA 31  to  55  from the pixels  31  to  55  in the array  3  are filtered by the device  5 . 
       FIGS. 6 and 7  illustrate an exemplary implementation of the filtering device  5 . 
       FIG. 6  schematically illustrates an exemplary configuration of the filter  10 , the processing unit UT configuring the filter  10 . 
     The filter  10  comprises two filtering algorithms ALG 1  and ALG 2  that are implemented according to the value of the signal-to-noise ratio SNR 31 . 
     If the value of the signal-to-noise ratio SNR 31  is below a first threshold Se, a first algorithm ALG 1  averages the data DATA 31  from the pixel  31  with the data from pixels in the vicinity of the pixel  31 , the filtered data DATA 311  comprising the averaged data. 
     If the value SNR 31  is above a first threshold Se, a second algorithm ALG 2  determines the filtered data DATA 311  on the basis of a weighted combination of the data from the pixel  31  and from pixels in the vicinity of the pixel. 
     The weighting coefficients are determined on the basis of the signal-to-noise ratio SNR 31  of the data signal from the pixel  31  and of the data signals from the pixels neighboring the pixel  31  and on the basis of the data coefficients calculated on the basis of the data DATA 31  from pixel  31  and of the data from the pixels neighboring the pixel  31  (for example bilateral filtering). 
     To decrease threshold effects, in some embodiments the filter  10  may comprise a third filtering algorithm ALG 3  when the signal-to-noise ratio SN 31  is within an interval INT defined by the value of the first threshold Se minus a first difference EC 1  and the value of the first threshold Se plus the first difference EC 1 . 
     The third algorithm ALG 3  determines the filtered data DATA 311  on the basis of a weighted combination of the filtered data determined by the first and second algorithms ALG 1  and ALG 2 . 
     The selection module  11  determines the extent Δ of the pixels neighboring the pixel  31  on the basis of the signal-to-noise ratio SN 31  of the pixel  31 . 
     According to the value of the signal-to-noise ratio SN 31 , the selection module  11  determines a pixel window, the pixel  31  being at the center of the window. 
     In a step  20  ( FIG. 7 ), the calculating module  9  determines the signal-to-noise ratios SNR 31  to SNR 55 : 
     
       
         
           
             
               
                 
                   
                     SNR 
                     i 
                   
                   = 
                   
                     
                       
                         AMP 
                         i 
                         2 
                       
                       
                         
                           AM 
                           i 
                         
                         + 
                         
                           3 
                           . 
                           
                             σ 
                             2 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     with i varying from  31  to  55 , AMPi being the amplitude of the data DATAi and σ being a standard deviation modelling the intrinsic noise of the sensor. 
     In some embodiments, the calculating module  9  sets up a map of the signal-to-noise ratios SNR 31  to SNR 55  which is similar to the map  8  associating each pixel  31  to  55  with a signal-to-noise ratio SNR 31  to SNR 55  according to the position of the pixel  31  to  55  in the array  3 . 
     If the ratio SNR 31  of the pixel  31  is above or equal to the first threshold Se (step  21 ), and if the ratio SNR 31  of the pixel  31  is higher than the value of the first threshold Se plus the first difference EC 1  (step  22 ), in step  23 , the selection module  11  determines the extent Δ of the neighboring pixels (e.g., the selection module  11  determines the kernel size, which may be, e.g., 3×3, 5×5, 7×7, etc.). 
     It is assumed that the extent Δ comprises for example a window of eight pixels centered on the pixel  31 . 
     In some embodiments, the extent Δ comprises the pixels  32  to  39 . 
     The filtered numerator NUM i  of a vector DATA i  of a pixel i is equal to: 
     
       
         
           
             
               
                 
                   NUMi 
                   = 
                   
                     
                       
                         COEFF 
                          
                         
                           
                             1 
                             i 
                           
                           · 
                           
                             NUM 
                             i 
                           
                         
                       
                       + 
                       
                         
                           ∑ 
                           j 
                           Δ 
                         
                          
                         
                           COEFF 
                            
                           
                             
                               1 
                               j 
                             
                             · 
                             
                               NUM 
                               j 
                             
                           
                         
                       
                     
                     
                       
                         COEFF 
                          
                         
                           1 
                           i 
                         
                       
                       + 
                       
                         
                           ∑ 
                           j 
                           Δ 
                         
                          
                         
                           COEFF 
                            
                           
                             1 
                             j 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     where 
     COEFF 1   i  is the weighting coefficient of the pixel i and COEFF 1   j  is the weighting coefficient of the pixel j for the numerator calculation. 
     The coefficient COEFF 1   i  is equal to the signal-to-noise ratio SNR i  of the pixel i. 
     The coefficient COEFF 1   j  of the pixel j included in the extent Δ is equal to: 
       COEFF1 j =SNR j ·α j   (3)
 
     where α j  is the data coefficient of the pixel j calculated according to the following equation: 
     
       
         
           
             
               
                 
                   
                     α 
                     j 
                   
                   = 
                   
                     1 
                     
                       
                         NUM 
                         i 
                       
                       - 
                       
                         NUM 
                         j 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     Analogously, the filtered denominator DEM i  of a vector DATA i  is equal to: 
     
       
         
           
             
               
                 
                   DEMi 
                   = 
                   
                     
                       
                         COEFF 
                          
                         
                             
                         
                          
                         
                           
                             2 
                             i 
                           
                           · 
                           
                             DEM 
                             i 
                           
                         
                       
                       + 
                       
                         
                           ∑ 
                           j 
                           Δ 
                         
                          
                         
                           COEFF 
                            
                           
                               
                           
                            
                           
                             
                               2 
                               j 
                             
                             · 
                             
                               DEM 
                               j 
                             
                           
                         
                       
                     
                     
                       
                         COEFF 
                          
                         
                             
                         
                          
                         
                           2 
                           i 
                         
                       
                       + 
                       
                         
                           ∑ 
                           j 
                           Δ 
                         
                          
                         
                           COEFF 
                            
                           
                               
                           
                            
                           
                             2 
                             j 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     where 
     COEFF 2   i  is the weighting coefficient of the pixel i and COEFF 2   j  is the weighting coefficient of the pixel j for the denominator calculation. 
     The coefficient COEFF 2   i  is equal to the signal-to-noise ratio SNR i  of the pixel i. 
     The coefficient COEFF 2   j  of the pixel j included in the extent Δ is equal to: 
       COEFF 2   j =SNR j ·β 3   (6)
 
     where β j  is the data coefficient of the pixel j calculated according to the following equation: 
     
       
         
           
             
               
                 
                   
                     β 
                     j 
                   
                   = 
                   
                     1 
                     
                       
                         DEM 
                         i 
                       
                       - 
                       
                         DEM 
                         j 
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     In this instance, the filtered numerator NUM 311  of the vector DATA 311  of  31  is equal to: 
     
       
         
           
             
               
                 
                   
                     NUM 
                      
                     
                         
                     
                      
                     311 
                   
                   = 
                   
                     
                       
                         COEFF 
                          
                         
                             
                         
                          
                         
                           131 
                           · 
                           NUM 
                         
                          
                         
                             
                         
                          
                         3 
                          
                         
                             
                         
                          
                         1 
                       
                       + 
                       
                         
                           ∑ 
                           
                             j 
                             = 
                             
                               3 
                                
                               2 
                             
                           
                           
                             3 
                              
                             9 
                           
                         
                          
                         
                           COEFF 
                            
                           
                             
                               1 
                               j 
                             
                             · 
                             
                               NUM 
                               j 
                             
                           
                         
                       
                     
                     
                       
                         COEFF 
                          
                         1 
                          
                         3 
                          
                         1 
                       
                       + 
                       
                         
                           ∑ 
                           
                             j 
                             = 
                             
                               3 
                                
                               2 
                             
                           
                           
                             3 
                              
                             9 
                           
                         
                          
                         
                           COEFF 
                            
                           
                             1 
                             j 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     and the filtered denominator DEM 311  of the vector DATA 311  of  31  is equal to: 
     
       
         
           
             
               
                 
                   
                     DEM 
                      
                     
                         
                     
                      
                     311 
                   
                   = 
                   
                     
                       
                         COEFF 
                          
                         
                             
                         
                          
                         
                           231 
                           · 
                           DEM 
                         
                          
                         
                             
                         
                          
                         31 
                       
                       + 
                       
                         
                           ∑ 
                           
                             j 
                             = 
                             
                               3 
                                
                               2 
                             
                           
                           
                             3 
                              
                             9 
                           
                         
                          
                         
                           COEFF 
                            
                           
                             
                               2 
                               j 
                             
                             · 
                             
                               DEM 
                               j 
                             
                           
                         
                       
                     
                     
                       
                         COEFF 
                          
                         2 
                          
                         3 
                          
                         2 
                       
                       + 
                       
                         
                           ∑ 
                           
                             j 
                             = 
                             
                               3 
                                
                               2 
                             
                           
                           
                             3 
                              
                             9 
                           
                         
                          
                         
                           COEFF 
                            
                           
                             2 
                             j 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     If the ratio SNR 31  of the pixel  31  is below the first threshold Se (step  21 ), and if the ratio SNR 31  of the pixel  31  is lower than the value of the first threshold Se minus the first difference EC 1  (step  24 ), in step  25 , the selection module  11  determines the extent Δ of the neighboring pixels. 
     If the signal-to-noise ratio SNR 31  is within an interval defined by a second threshold Se 2  and the value of the first threshold Se minus the first difference EC 1 , the selection module determines a first extent Δ 1  of neighboring pixels such that the extent Δ is equal to the first extent Δ 1 , the value of the second threshold Se 2  being lower than the value of the first threshold Se minus the first difference EC 1 . 
     The first extent Δ 1  comprises for example a window of eight pixels  32  to  39 . 
     If the signal-to-noise ratio SNR 31  is within an interval defined by a third threshold Se 3  and the second threshold Se 2 , the selection module determines a second extent Δ 2  of neighboring pixels such that the extent Δ is equal to the second extent Δ 2 . 
     In some embodiments, the second extent Δ 2  comprises for example a window of twenty-four pixels  32  to  55 . 
     The filtered numerator NUM i  of a vector DATA i  of a pixel i is equal to: 
     
       
         
           
             
               
                 
                   NUMi 
                   = 
                   
                     
                       
                         NUM 
                         i 
                       
                       + 
                       
                         
                           ∑ 
                           j 
                           
                             Δ 
                              
                             
                                 
                             
                              
                             k 
                           
                         
                          
                         
                           NUM 
                           j 
                         
                       
                     
                     
                       1 
                       + 
                       
                         N 
                          
                         b 
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     and the filtered denominator DEM i  of a vector DATA i  of a pixel i is equal to: 
     
       
         
           
             
               
                 
                   DEMi 
                   = 
                   
                     
                       
                         DEM 
                         i 
                       
                       + 
                       
                         
                           ∑ 
                           j 
                           
                             Δ 
                              
                             k 
                           
                         
                          
                         
                           DEM 
                           j 
                         
                       
                     
                     
                       1 
                       + 
                       
                         N 
                          
                         b 
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
     where Nb is the number of pixels contained in the extent Δk, k being equal to 1 or 2. 
     The selection module  11  allows the filtering to be adapted according to the quality of the received data. 
     In this instance, if the signal-to-noise ratio SNR 31  is between the second threshold Se 2  and the first threshold Se minus the first difference EC 1 , the filtered numerator NUM 311  is equal to: 
     
       
         
           
             
               
                 
                   
                     NUM 
                      
                     
                         
                     
                      
                     311 
                   
                   = 
                   
                     
                       
                         NUM 
                          
                         
                             
                         
                          
                         31 
                       
                       + 
                       
                         
                           ∑ 
                           
                             j 
                             = 
                             
                               3 
                                
                               2 
                             
                           
                           
                             3 
                              
                             9 
                           
                         
                          
                         
                           NUM 
                           j 
                         
                       
                     
                     
                       1 
                       + 
                       8 
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     and the filtered denominator DEM 311  of the vector DATA 311  of  31  is equal to: 
     
       
         
           
             
               
                 
                   
                     DEM 
                      
                     
                         
                     
                      
                     311 
                   
                   = 
                   
                     
                       
                         DEM 
                          
                         
                             
                         
                          
                         31 
                       
                       + 
                       
                         
                           ∑ 
                           
                             j 
                             = 
                             
                               3 
                                
                               2 
                             
                           
                           
                             3 
                              
                             9 
                           
                         
                          
                         
                           DEM 
                           j 
                         
                       
                     
                     
                       1 
                       + 
                       8 
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
     If the signal-to-noise ratio SNR 31  is between the third threshold Se 3  and the second threshold Se 2 , the filtered numerator NUM 311  is equal to: 
     
       
         
           
             
               
                 
                   
                     NUM 
                      
                     
                         
                     
                      
                     311 
                   
                   = 
                   
                     
                       
                         NUM 
                          
                         
                             
                         
                          
                         31 
                       
                       + 
                       
                         
                           ∑ 
                           
                             j 
                             = 
                             
                               3 
                                
                               2 
                             
                           
                           55 
                         
                          
                         
                           NUM 
                           j 
                         
                       
                     
                     
                       1 
                       + 
                       24 
                     
                   
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
           
         
       
     
     and the filtered denominator DEM 311  of the vector DATA 311  of  31  is equal to: 
     
       
         
           
             
               
                 
                   
                     DEM 
                      
                     
                         
                     
                      
                     311 
                   
                   = 
                   
                     
                       
                         DEM 
                          
                         
                             
                         
                          
                         31 
                       
                       + 
                       
                         
                           ∑ 
                           
                             j 
                             = 
                             
                               3 
                                
                               2 
                             
                           
                           55 
                         
                          
                         
                           DEM 
                           j 
                         
                       
                     
                     
                       1 
                       + 
                       24 
                     
                   
                 
               
               
                 
                   ( 
                   15 
                   ) 
                 
               
             
           
         
       
     
     If the value of the signal-to-noise ratio SNR 31  is lower than the third threshold Se 3 , the pixel  31  is considered to be defective. 
     If the pixel  31  is defective, the filtered numerator NUM 311  and the filtered denominator DEM 311  are determined by replacing the numerator NUM 31  and the denominator DEM 31  with zero. 
     Of course, the first algorithm ALG 1  may comprise more than two thresholds Se 1  and Se 2  for averaging the data from the pixels. 
     To avoid threshold effects, the first algorithm ALG 1  may comprise gradual transition zones in proximity to the second and third thresholds Se 2  and Se 3 , for example by linearly or logarithmically interpolating the filtered data in the transition zones. 
     If the ratio SNR 31  of the pixel  31  is above or equal to the first threshold Se (step  21 ), and if the ratio SNR 31  of the pixel  31  is lower than the value of the first threshold Se plus the first difference EC 1  (step  22 ), or if the ratio SNR 31  of the pixel  31  is below the first threshold Se (step  21 ), and if the ratio SNR 31  of the pixel  31  is higher than or equal to the value of the first threshold Se minus the first difference EC 1  (step  24 ), the method moves on to step  26 . 
     In step  26 , the filtered numerator NUM 311  and the filtered denominator DEM 311  are determined on the basis of a weighted combination of the values of the filtered numerator NUM 311  and of the filtered denominator DEM 311  produced by the first and second algorithms ALG 1  and ALG 2  as described above. 
     Using the signal-to-noise ratios SNR 31  to SNR 55  to filter the noise in the data generated by the pixels  31  to  55  of the sensor  2  makes it possible in particular to enhance the quality and the representation of scenes.