Television – Monitoring – testing – or measuring
Reexamination Certificate
2001-11-21
2004-12-07
Lee, Michael H. (Department: 2614)
Television
Monitoring, testing, or measuring
C348S189000, C348S192000
Reexamination Certificate
active
06829005
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to video processing, and more particularly to a method of predicting subjective quality ratings of video from corresponding human vision model perceptual difference scores.
Although methods exist for producing perceptual difference scores that may correlate well under certain conditions with standard subjective quality ratings, such as Difference Mean Opinion Scores (DMSO), the actual numerical DMOS values depend among other things on “best” (least impaired) and “worst” (most impaired) video training sequences used to calibrate human subjects doing the scoring. Subjects are told to use a scale with one end for the “best” and the other for the “worst” video training sequence. Then video test sequences are rated by the subjects based on the “calibrated” scale. However the scale of subjective ratings for the video test sequences inherently has a compression near the top and bottom as subjects are conservative with quality ratings at the extremes, reserving a little portion of the scale just in case a more extreme video quality is seen in a later video test sequence.
The existing methods of determining video picture quality, such as that described in U.S. Pat. No. 5,818,520 and implemented in the Tektronix Picture Quality Analyzer PQA200, do not attempt to match DMOS scales for a set of video sequences, such as by using “best” and “worst” video training sequences to set the extremes. Instead correlations are made and typical conversion factors are cited. These typical conversion factors imply a one-to-one or linear mapping, not taking into account the compression at the extremes of the scale or other non-linearities inherent in the DMOS values.
What is desired is a picture quality measurement system that predicts subjective quality ratings of processed video.
SUMMARY OF THE INVENTION
Accordingly the present invention provides a method of predicting subjective quality ratings of processed video from corresponding human vision model perceptual difference scores by obtaining perceptual difference scores for a “Worst” quality video training sequence and for a “Best” quality video training sequence. Corresponding subjective quality rating values are assigned to the perceptual difference scores as modified by any single-ended measures of impairments that may exist in the reference video training sequences from which the “Worst” and “Best” quality video training sequences are derived. A conversion function, which may be a piecewise linear function, an “S” curve function or other function that approximates the non-linearities and compression at the extremes of the subjective quality rating scale, is used to produce a conversion curve of calibration values based on the perceptual difference scores for the “Worst” and “Best” quality video training sequences and heuristically derived constants.
The objects, advantages and other novel features of the present invention are apparent from the following detailed description when read in conjunction with the appended claims and attached drawing.
REFERENCES:
patent: 5596364 (1997-01-01), Wolf et al.
patent: 5790717 (1998-08-01), Judd
patent: 5818520 (1998-10-01), Janko et al.
patent: 6496221 (2002-12-01), Wolf et al.
patent: 6577764 (2003-06-01), Myler et al.
Confidential Report “Subjective Assessment of Sequences Using DSCQS and Impaired References” by The Communications Research Centre Canada RAVS/ATEL Oct., 2000.
Gray Francis I.
Lee Michael H.
Tektronix Inc.
Tran Trang U.
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