Block-based detection systems for visual artifact location

The core of many video coding standards is formed by the Discrete Cosine Transform (DCT) for decorrelating spatial video data. When quantizing DCT coefficients, artifacts may appear such as mosquito noise and ringing. Spatial artifact reduction requires artifact-location information, to control the filter process, thereby avoiding unnecessary blurring of non-visual artifact-contaminated regions. This location information can be derived either in the spatial or frequency domain. In this paper, we will present two systems: one for each domain. As coding artifacts are most annoying in flat or low-frequency regions, the objective of the detector is to localize these artifact-sensitive locations. The detection accuracy, coverage and sensitivity differ between the two different detection systems. Experiments have revealed that the spatial-domain system has a better performance on edge tracking and detection of small-sized flat region. However, the system degrades in separating originally present low-amplitude texture from artifact contamination, compared to the same capability of the frequency-domain system.