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ITU-T J.149

2004 Edition, March 1, 2004

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Method for specifying accuracy and cross-calibration of Video Quality Metrics (VQM)

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Description / Abstract:

Video quality metrics are intended to provide calculated values that are strongly correlated with viewer subjective assessments. This Recommendation provides:

a) methods for curve fitting VQM objective values to subjective data in order to facilitate the accuracy calculation and to produce a normalized objective value scale that can be used for cross-correlation between different VQMs;

b) an algorithm (based on statistical analysis relative to subjective data) to quantify the accuracy of a given VQM;

c) a simplified root mean square error calculation to quantify the accuracy of a VQM when the subjective data has roughly equal variance across the VQM scale;

d) a method to plot classification errors to determine the relative frequencies of "false tie", "false differentiation", "false ranking", and "correct decision" for a given VQM.

The methods specified in this Recommendation are based on objective and subjective evaluation of component video such as defined by ITU-R Rec. BT.601 using methods such as described in ITU-R Rec. BT.500-11. A data set for a VQM will consist of objective values and mean subjective scores for a variety of motion video sources (SRC) processed by a variety of hypothetical reference circuits (HRC). An example of such a data set is given in the ITU-T Tutorial (see Appendix I).

The methods specified in this Recommendation are directly applicable to a defined data set as described above. For measurements not specifically part of the data set, the methods specified in this Recommendation provide a reasonable estimate of accuracy and cross-calibration for applications that can be considered to be similar to and within the scope of the defined data set.

The methods specified in this Recommendation are appropriate for use in combination with other statistical calculations in order to evaluate the usefulness of a VQM. Informative information regarding the use of the methods is presented in Appendix I. A complete verification process by suitable independent laboratories is required for a VQM to be considered for inclusion as a normative part of an ITU-R Recommendation.

NOTE – The structure and content of this Recommendation have been organized for ease of use by those familiar with the original source material; as such, the usual style of ITU-T recommendations has not been applied.