Barkowsky M (2009)
Publication Language: English
Publication Type: Thesis
Publication year: 2009
Publisher: Verlag Dr. Hut
In recent years, many distribution channels for low-bitrate video transmissions were setup. The parameter settings for the encoder, the transmission channel, the decoder and the playback device are manifold. In order to maintain customer satisfaction, it is necessary to carefully select and continuously tune those parameters and to monitor the resulting video quality at the receiver. This thesis considers the quality measurement by a human observer and by an automated algorithm. In the first part of the thesis, several subjective tests are performed in order to draw conclusions about the choice of transmission parameters. The experience gained from those experiments led to three psychophysical experiments that focus on isolated aspects of the video quality in lossless or lossy low-bitrate transmissions. Three distinct algorithms are deduced from the subjective experiments which deal with the temporal aspects. First, the visibility of artifacts is modeled when the viewer only has a short period of time for the examination. Second, the influence of transmission outages is modeled: The video playback may pause and content may be skipped if retransmission is not possible. Third, the visual degradation introduced by a reduction of the frame rate is modeled. The second part of the thesis is dedicated to the objective measurement. It is assumed that the reference video sequence is available for comparison with the degraded sequence. Because the performance of the automated measurement depends strongly on the correct alignment of the degraded signal to the reference signal, various algorithms are reviewed, enhanced, and compared that locate the corresponding reference frame for a given degraded frame. So far, many algorithms have been published that reliably predict the visual quality of still images or temporally undistorted video sequences. In this thesis, a new framework is presented that allows to evaluate the performance of these algorithms for temporally distorted video transmissions. The processing steps and the signal representations follow the reasoning of a human observer in a subjective experiment as observed in the first part of the thesis. The improvements that can be achieved with the newly proposed framework are demonstrated by comparing the objective scores with the subjective results of the comprehensive Multimedia Phase I database of the Video Quality Experts Group.
Barkowsky, M. (2009). Subjective and Objective Video Quality Measurement in Low-Bitrate Multimedia Scenarios (Dissertation).
Barkowsky, Marcus. Subjective and Objective Video Quality Measurement in Low-Bitrate Multimedia Scenarios. Dissertation, München: Verlag Dr. Hut, 2009.