In this note, improvements to the non-local means
image denoising method introduced in [2], [3] are presented.
The original non-local means method replaces a noisy pixel by
the weighted average of pixels with related surrounding neighborhoods.
While producing state-of-the-art denoising results, this
method is computationally impractical. In order to accelerate the
algorithm, we introduce filters that eliminate unrelated neighborhoods
from the weighted average. These filters are based on local
average gray values and gradients, pre-classifying neighborhoods
and thereby reducing the original quadratic complexity to a
linear one and reducing the influence of less-related areas in the
denoising of a given pixel. We present the underlying framework
and experimental results for gray level and color images as well
as for video.