Subjective evaluation methods of facsimile image quality

Methods for measuring facsimile image quality are needed to evaluate facsimile quality of service. Three subjective evaluation measures, i.e., mean opinion score (MOS), readable rate and retransmission request rate, are examined. These measures assess high-resolution facsimile images degraded by scanning line errors as a function of image characteristics (the language and character size of the text). Subjective assessment test results indicate that the MOS linearly decreases with an increasing number of consecutive errored scanning lines in log-scale, that the MOS for images including three or more consecutive errored scanning lines tends to deteriorate considerably with an increase in error events per sheet, and that the subjective quality of an English test image is less affected by the same scanning line errors than a Japanese image. The relationships among test results are examined, and the application of the evaluation methods is discussed