A Basic Multimedia Quality Model Majid Bagheri

Introduction Multimedia Quality Measurement o Objective o Cost effective o Fast o Automated o Subjective / Perceptual o Matches human perception o Modalities o Audio o Video o Cross-Modal Interaction

Information Integration Theory Developed by Norman Anderson, Social Psychology professor at UCLA in 1970's Explains how human subjects integrate information from different sources into an overall judgment Video quality influences perception of audio quality and vice versa

Basic Multimedia Model

General Method 1/4 Two experiments are designed to identify the fundamental combination rule Test Environment o Sound insulated cabinet containing table, chair, monitor, speaker o Viewing condition according to ITU standard BT.500

General Method 2/4 Test Material o Includes practice and test Sequences o 5-sec sequences (talking head, high motion)  long enough for subjects to arrive at reliable quality rating while removing any extraneous factors Degraded versions of audio produced using MNRU (Modulated Noise Reference Unit) o ITU standard (P.810) for generating controlled degradation For the vidoe, blockiness is manipulated

General Method 3/4 Test Methodology (ITU B.500) o DSCQS (Double Stimulus Continuous Quality Scale)  Both reference and test sequences are presented  Subjects do not know which one is the reference o SSQS (Single Stimulus Quality Scale) Subjects mark their judgment on a small screen by moving a pointer

General Method 4/4 Subjects and Test Procedure o All subjects are non-expert, changed for each experiment o Test trials are proceeded by some test trails o For audio only test, the monitor is black o Subjects mark their judgment on a small screen by moving a pointer Two-way ANOVA is applied with F-test to decide if each component has an impact Multi-regression analysis is then used to identify the combination rule

Experiment 1 Talking head sequences (low motion) 1A: only the audio component (screen is black) 1B: only the video component (no sound) 1C: both components Subjects mark their judgment on a small screen by moving a pointer DSCQS Mean difference score (MDS) is computed over all subjects

Experiment 1A

Experiment 1B

Experiment 1C

Regression Analysis 1

Discussion Previous work by Beerends & Caluwe o concluded that video has more significance o used longer commercial sequences (high motion) o audio quality did not vary much o single stimulus test method More experiment is needed to verify results from Experiment 1

Experiment 2 High motion content is introduced (cycling) Single Stimulus method (SSQS) 2A: only the audio component (screen is black) 2B: only the video component (no sound) 2C: both components Subjects mark their judgment on a small screen by moving a pointer Mean opinion score (MOS) is computed over all subjects

Experiment 2A

Experiment 2B

Experiment 2C

Regression Analysis 2

Conclusion A basic model for Multimedia quality was introduced The model is based on cross-modal interactions Video quality influences perception of audio quality and vice versa The degree of interaction depends on the content In high motion media, video has more impact What if one of modalities is of extremely poor quality? The user perception may become worse due to the sharp contrast