Correlations between spark parameters. Joint histograms of amplitude and width (A and B), rise time and width (C and D), and rise time and amplitude (E and F) for the set of all sparks detected in x–y images (A, C, and E) and for in-focus sparks (B, D, and F). The total number of sparks included was 6,906 (all sparks) and 767 (in-focus sparks). The first-order correlation coefficient ρ (a, FWHM) was 0.037 for all sparks and 0.14 for sparks in focus. ρ (T, FWHM) was 0.14 (all) and 0.26 (in focus). ρ (T, a) was 0.33 (all) and 0.36 (in focus). The color table starts at 0 (black) for all panels, whereas the maximum (yellow) corresponds to 143, 35, 201, 85, 149, and 70 events, respectively, for A–F.