  With the growing popularity of smartphones, capturing high-quality images is
of vital importance to smartphones. The cameras of smartphones have small
apertures and small sensor cells, which lead to the noisy images in low light
environment. Denoising based on a burst of multiple frames generally
outperforms single frame denoising but with the larger compututional cost. In
this paper, we propose an efficient yet effective burst denoising system. We
adopt a three-stage design: noise prior integration, multi-frame alignment and
multi-frame denoising. First, we integrate noise prior by pre-processing raw
signals into a variance-stabilization space, which allows using a small-scale
network to achieve competitive performance. Second, we observe that it is
essential to adopt an explicit alignment for burst denoising, but it is not
necessary to integrate a learning-based method to perform multi-frame
alignment. Instead, we resort to a conventional and efficient alignment method
and combine it with our multi-frame denoising network. At last, we propose a
denoising strategy that processes multiple frames sequentially. Sequential
denoising avoids filtering a large number of frames by decomposing multiple
frames denoising into several efficient sub-network denoising. As for each
sub-network, we propose an efficient multi-frequency denoising network to
remove noise of different frequencies. Our three-stage design is efficient and
shows strong performance on burst denoising. Experiments on synthetic and real
raw datasets demonstrate that our method outperforms state-of-the-art methods,
with less computational cost. Furthermore, the low complexity and high-quality
performance make deployment on smartphones possible.
