1. A method of reducing noise in a sequence of digital video frames, comprising the steps of: estimating motion between a current noisy frame and a previous noise-reduced frame using a processor, to generate motion vectors indicating relative motion between the pixels in the current noisy frame and the corresponding pixels in the previous noise-reduced frame; and removing noise from the current noisy frame by computing the weighted average of pixels in the current noise frame and said corresponding pixels in the previous noise-reduced frame based on the motion vectors in the processor, to generate a noise-reduced output frame, wherein: the step of estimating motion further includes the steps of estimating motion between a current noisy frame g t at time t and a previous noise-reduced frame ĝ t−1 , to generate a motion vector (dy,dx) for a pixel g t (i,j) in the frame g t , such that the corresponding matching pixel in the previous noise-reduced frame ĝ t−1 is ĝ t−1 (i+dy,j+dx); and removing noise from the current noisy frame further comprises the steps of computing the weighted average further includes the steps of computing the weighted average of the pixel g t (i,j) in the frame g t and the pixel ĝ t−1 (i+dy,j+dx) in the frames ĝ t−1 to generate the noise-reduced output frame ĝ t , wherein the step of generating the noise-reduced output frame ĝ t further comprises the steps of computing: g ^ t ⁡ ( i , j ) = g t ⁡ ( i , j ) + w ^ t - 1 ⁡ ( i + dy , j + dx ) · g ^ t - 1 ⁡ ( i + dy , j + dx ) w ^ t - 1 ⁡ ( i + dy , j + dx ) + 1 , ⁢ and w t ⁡ ( i , j ) = min ⁡ ( w max , w ^ t - 1 ⁡ ( i + dy , j + dx ) + 1 ) , wherein (dy,dx) is the motion vector of the pixel g t (i,j); w t (i,j) is the potential weight of ĝ t (i,j) in filtering the pixels in the next frame g t+1 with an initial value w 0 (i,j)=1; ŵ t−1 (i+dy,j+dx) is the associated weight of the pixel ĝ t−1 (i+dy,j+dx) and also an adjustment of w t−1 (i+dy,j+dx) as a function of reliability of the motion vector (dy,dx); and w max is a threshold that the value w t (i,j) can not exceed.