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 research and broadcasting. Several methods have been recommended for the subjective evaluation of image quality: the double-stimulus continuous-quality scale method (DSCQS), the double stimulus impairment scale method variant II(DSTS II), and a newly proposed comparison method. In order to evaluate the effect of context on different scales, each scale was used to rate the same video sequences. The ratings from the scales were strongly correlated. The degree to which each method was affected by contextual effects was assessed. The results have revealed no contextual effects for the DSCQS method, moderate contextual effects for the comparison method and large contextual effects for the DSIS II method. It was concluded that the DSCQS method is the best method to use in order to minimize contextual effects for subjective picture quality assessment. (C) 1999 Elsevier Science B.V. All rights reserved.