- Seven-tiered colour coding is used to demonstrate the variability of the average subjective image qualities. Data are mean (SD), n = 3. For the statistical significance of the difference, p < 0.05 (c, e), p < 0.01 (a, i, l), p < 0.001 (h, j), and p < 0.0001 (b, d, f, g, k, m, n, o, p, q, r, s, t, u, v, w, x, y, z).