PQA500 Predicted DMOS Measurement Checklist

This page was created to facilitate verification of best practices in the use of the Tektronix PQA500 for predicting picture quality mean opinion scores relative to reference scores (or difference of mean opinion scores otherwise known as DMOS). Many of the best practices mentioned in this document are also applicable to other picture quality measurements, virtual or real.

Appropriate Use Of DMOS

Why The Checklist?

The Predicted DMOS is the most direct way to determine the relative mean opinion scores of video sequences as a quantification of differences seen between processed and reference video apart from actually conducting an experiment to gather the data from at least two dozen individuals as per the ITU-R BT.500 standard (for SD video or the equivalent for HD, CIF, etc.). The resulting measurement gives numeric values on a 100 point scale corresponding to the text/adjective scale used by individuals to rate the reference and test video clips (a factor of 20 is used to convert the nominal 5 point scale to 20 after the mean of the reference video is subtracted from the respective mean of the test video clip). The PQA500 conducts a virtual BT.500 study with virtual displays, virtual viewing environment, virtual humans (including very detailed macro-behavioral models of perceptual sensitivity and, optionally, the attentional and classification of artifacts aspects along with the requisite summary judgement component of the cognitive systems used for human vision and comprehension). Just as in real BT.500 studies where if displays, viewing conditions and demographic sampling are significantly different between labs performing the studies, DMOS results can be significantly different, so to can the virtual BT.500 study. Therefore, the checklist given below is important for verifying a match between virtual and the desired real DMOS study.

Use of Predicted DMOS vs PQR Measurement

Note If it is desired to determine the somewhat binary result of whether or not a viewing audience can see any difference between the reference video clip and the processed video clip, PQR is more appropriate. The PQR units are 1 in the difference maps where the difference between the reference and test video clips are just noticable (1 JND). The PQR result per field or frame and the overall result for the sequence use a Minkowski metric to give an overall impression of the difference. For very meticulous checking of any, even minute visible differences the maximum PQR over each field/frame and the overall sequence is also given in the results. However, in applications where visible differences are not unexpected, and where the quantification of these (perhaps very subtle, or perhaps not so subtle) differences are needed, predicting DMOS is more appropriate.

The DMOS Prediction Checklist

For details of control parameters mentioned here, see the "PQA500 Picture Quality Analyser Technical Reference" document.