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Figure 6b. Resolution-metric matching with (a) JPEG images and (b) WTCQ images. Scatterplots show the relationship between compression ratio (CR) and percentage resolution for observer A. These data were obtained by matching the blur image set with 20 test images at each of five compression ratios (16:1, 21:1, 32:1, 64:1, and 128:1). The area of each dot is proportional to the number of superimposed data points. The straight lines are the regression lines. (a) The x intercept for JPEG images, determined by means of linear regression on the 100 data points, indicates that the estimated visually lossless threshold is 13:1. (b) The x-intercept for WTCQ images, determined by means of linear regression on the 100 data points, indicates that the visually lossless threshold is 11:1.