All subjective scales are not created equal: The effects of context on different scales

Subjective evaluation of image quality is an important tool in video resear ch and broadcasting. Several methods have been recommended for the subjecti ve evaluation of image quality: the double-stimulus continuous-quality scal e method (DSCQS), the double stimulus impairment scale method variant II(DS TS II), and a newly proposed comparison method. In order to evaluate the ef fect of context on different scales, each scale was used to rate the same v ideo sequences. The ratings from the scales were strongly correlated. The d egree to which each method was affected by contextual effects was assessed. The results have revealed no contextual effects for the DSCQS method, mode rate contextual effects for the comparison method and large contextual effe cts for the DSIS II method. It was concluded that the DSCQS method is the b est method to use in order to minimize contextual effects for subjective pi cture quality assessment. (C) 1999 Elsevier Science B.V. All rights reserve d.