(a) The RN histogram measured at 1X, 2X, 4X, and 8X gains for the “test-in, Δt = 0 μs” and “pixel-in, Δt = 0 μs” modes. The distributions are tight Gaussian-like without noticeable long tails; (b) The RN histograms measured at 1X, 2X, 4X, and 8X gains for the “test-in, Δt = 25 μs” and “pixel-in, Δt = 25 μs” modes. Among the 4 operation modes, only the histograms of the “pixel-in, Δt = 25 μs” mode show significant long tails.