Abstract
This paper presents a method of objective evaluation of the edge blur and ringing artefacts produced by image codecs. It is difficult to detect and measure individual artefacts in coded images. A synthetic test pattern is developed to separate and measure edge blur and ringing artefacts due to image compression. The influence of contrast on the quality metrics is investigated. The performance of five JPEG and JPEG2000 codec implementations is compared. All five codecs show an increasing level of artefacts with increasing compression ratio. Different implementations of a codec have different artefact characteristics. The objective artefact measures can be used in the image and video codec development process and in parameter optimisation of codec performance. These metrics can also be used to select suitable parameters for video codecs such as MPEG-1, MPEG-2 and MPEG-4 while creating video streams for the Internet applications and in any multimedia application in general.
Highlights
In digital television broadcasting, video streaming and other multimedia communications, image and video are the dominant components
The artefact metrics were evaluated by applying the synthetic test pattern described in the previous section
The variation of edge blur and ringing were investigated under different step heights by evaluating the artefact metrics for a given quality factor of 20 using a JPEG codec
Summary
Video streaming and other multimedia communications, image and video are the dominant components. With limited communication bandwidth and storage capacity in terminal devices, it is necessary to reduce data rates using digital codecs. The techniques and quantisation used in image and video compression codecs introduce distortions known as artefacts. Tlie Digital Fact Book defines artefacts as "particular visible effects, which are a direct result of some technical limitation" [1]. Artefacts are generally not evaluated by traditional methods of signal evaluation. The visual perception of contouring in a picture cannot be related to signal-to-noise ratio [1]
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