One of the most important characteristics of television is picture quality. It affects the viewer's opinion of the services and it can be used to describe video coding hardware and software both on the service provider and the consumer side of the service chain. In the digital video broadcasting era, quality assessment is growing even more important. New services are introduced into the system: satellite broadcasting, high definition television (HDTV), video conference etc. The requirements are diverse, so must the coding and transcoding apparatus be, so that subjective quality impressions reach the best values possible. While conducting subjective picture quality assessments is both time-consuming and costly, known objective QA methods provide varying correlations with the subjective results to predict the viewer's impressions.
In this thesis, I summarize the characteristics of the human visual system, and recite common subjective (DSIS, DSCQS, SS, SSCQE, SDSCE) and objective (PSNR, VQM, SSIM, JND, VIF) quality assessment methods. Using these can aid the classification of coders and transcoders, the specification of their efficiency and set the direction of the possible developments. I also look at the impact of transcoding steps without encoding on the picture quality.
The aim of this research is to identify the scale in which the necessary video manipulation steps as well as the available encoding tools effect video quality and its subjective evaluation by the viewers and also to look at the characteristic picture faults resulting from these elements. I characterise each procedure quantitatively.