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Visual grading characteristics (VGC) analysis: a non-parametric rank-invariant statistical method for image quality evaluation

¹ Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, SE-413 01 Göteborg, ² Department of Radiation Physics, Göteborg University, SE-413 01 Göteborg, Sweden

View larger version (13K): [in this window] [in a new window]   Figure 1. (a) Probability distributions (A = noise, B = signal) of a detection task showing 4 levels of decision thresholds X1 – X4. Values of X < X1 correspond to the first rating category ("1"), X1 < X < X2 to the second ("2"), etc., and X > X4 to the last ("5"). (b) The resulting ROC curve, giving the true positive fraction (TPF) as a function of the false positive fraction (FPF). The four operating points corresponding to the four decision thresholds in (a) are given by the boxes in (b).

View larger version (12K): [in this window] [in a new window]   Figure 2. The visual grading characteristic(VGC) curve from the data presented in Tables 1 and 2. The boxes represent the operating points corresponding to the observer's interpretation of the scale steps of the rating scale.

View larger version (12K): [in this window] [in a new window]   Figure 3. (a) Two image quality distributions and (b) the resulting asymmetrical visual grading characteristic (VGC) curve.