Figure 3

Pairwise image comparisons: ROC plot and “guess or incorrect” analysis. A. ROC plot showing sensitivity and (1 - specificity) at each of the levels of compression tested in pairwise (compressed vs. original) image comparisons (Q values of 5, 20, 35, 50, 65, 80, and 95 compared to 100). Point estimates for each Q value (see labels) are solid circles; 95% CI for sensitivity are shown as vertical bars and 95% CI for specificity are shown as horizontal bars. The dotted oblique line represents the “line of unity” where sensitivity = (1 - specificity): points on a ROC plot along this line represent a cut point at which no reliable discrimination has been found. B. Plot of guess or incorrect choice as a function of Q value for the compressed image. The percentage of responses representing an incorrect choice or a known guess are shown at each of the Q values for the compressed image in each randomly presented image pair.