Coefficients for the three example images (threshold = background mean + 3 SD = 16 in both channels):
  image A: Pearson 0.991; Manders M1 0.957, M2 0.980
  image B: Pearson 0.952; Manders M1 0.963, M2 0.977
  image C: Pearson 0.490; Manders M1 0.603, M2 0.615
Per-cell Welch's t-test (150 cells treated as independent): t = -2.72, p = 0.0073
Mean Pearson per experiment (back-transformed): experiment 1: control 0.580, treated 0.426; experiment 2: control 0.469, treated 0.525; experiment 3: control 0.607, treated 0.559
Paired t-test on experiment means (n = 3 experiments): difference in z -0.069 (95% CI -0.420 to 0.282), t = -0.84, p = 0.4873