KEYWORDS: Sensors, Denoising, Image processing, Optical flow, Image sensors, Data modeling, Image filtering, Image resolution, Cameras, Signal to noise ratio
Temporal accumulation of images is a well-known approach to improve signal to noise ratios of still images taken in a low light conditions. However, the complexity of known algorithms often leads to high hardware resource usage, increased memory bandwidth and computational complexity, making their practical use impossible. In our research we attempt to solve this problem with an implementation of a practical spatial-temporal de-noising algorithm, based on image accumulation. Image matching and spatial-temporal filtering was performed in Bayer RAW data space, which allowed us to benefit from predictable sensor noise characteristics, thus allowing using a range of algorithmic optimizations. The proposed algorithm accurately compensates for global and local motion and efficiently removes different kinds of noise in noisy images taken in low light conditions. In our algorithm we were able to perform global and local motion compensation in Bayer RAW data space, while preserving the resolution and effectively improving signal to noise ratios of moving objects as well as non-stationary background. The proposed algorithm is suitable for implementation in commercial grade FPGA’s and capable of processing 16MP images at capturing rate (10 frames per second). The main challenge for matching between still images is the compromise between the quality of the motion prediction and the complexity of the algorithm and required memory bandwidth. Still images taken in a burst sequence must be aligned to compensate for background motion and foreground objects movements in a scene. High resolution still images coupled with significant time between successive frames can produce large displacements between images, which creates additional difficulty for image matching algorithms. In photo applications it is very important that the noise is efficiently removed in both static, and non-static background as well as in a moving objects, maintaining the resolution of the image. In our proposed algorithm we solved the issue of matching current image with accumulated image data in Bayer RAW data space in order to efficiently perform spatio-temporal noise reduction and reduce the computational requirements. In this paper we provide subjective experimental results to demonstrate the ability of the proposed method to match noisy still images in order to perform efficient de-noising and avoid motion artefacts in resulting still images.
Image de-noising in the spatial-temporal domain has been a problem studied in-depth in the field of digital image
processing. However complexity of algorithms often leads to high hardware resource usage, or computational
complexity and memory bandwidth issues, making their practical use impossible. In our research we attempt to solve
these issues with an optimized implementation of a practical spatial-temporal de-noising algorithm. Spatial-temporal
filtering was performed in Bayer RAW data space, which allowed us to benefit from predictable sensor noise
characteristics and reduce memory bandwidth requirements. The proposed algorithm efficiently removes different kinds
of noise in a wide range of signal to noise ratios. In our algorithm the local motion compensation is performed in Bayer
RAW data space, while preserving the resolution and effectively improving the signal to noise ratios of moving objects.
The main challenge for the use of spatial-temporal noise reduction algorithms in video applications is the
compromise between the quality of the motion prediction and the complexity of the algorithm and required memory
bandwidth. In photo and video applications it is very important that moving objects should stay sharp, while the noise is
efficiently removed in both the static background and moving objects. Another important use case is the case when
background is also non-static as well as the foreground where objects are also moving.
Taking into account the achievable improvement in PSNR (on the level of the best known noise reduction
techniques, like VBM3D) and low algorithmic complexity, enabling its practical use in commercial video applications,
the results of our research can be very valuable.
Image de-noising has been a well studied problem in the field of digital image processing. However there are a number
of problems, preventing state-of-the-art algorithms finding their way to practical implementations. In our research we
have solved these issues with an implementation of a practical de-noising algorithm. In order of importance: firstly we
have designed a robust algorithm, tackling different kinds of nose in a very wide range of signal to noise ratios, secondly
in our algorithm we tried to achieve natural looking processed images and to avoid unnatural looking artifacts, thirdly we
have designed the algorithm to be suitable for implementation in commercial grade FPGA's capable of processing full
HD (1920×1080) video data in real time (60 frame per second).
The main challenge for the use of noise reduction algorithms in photo and video applications is the compromise
between the efficiency of the algorithm (amount of PSNR improvement), loss of details, appearance of artifacts and the
complexity of the algorithm (and consequentially the cost of integration). In photo and video applications it is very
important that the residual noise and artifacts produced by the noise reduction algorithm should look natural and do not
distract aesthetically. Our proposed algorithm does not produce artificially looking defects found in existing state-of-theart
algorithms.
In our research, we propose a robust and fast non-local de-noising algorithm. The algorithm is based on a Laplacian
pyramid. The advantage of this approach is the ability to build noise reduction algorithms with a very large effective
kernel. In our experiments effective kernel sizes as big as 127×127 pixels were used in some cases, which only required
4 scales. This size of a kernel was required to perform noise reduction for the images taken with a DSLR camera.
Taking into account the achievable improvement in PSNR (on the level of the best known noise reduction
techniques) and low algorithmic complexity, enabling its practical use in commercial photo, video applications, the
results of our research can be very valuable.
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