Fig. 4.

Drift Correction by registration of fluorescent fiducial markers. The localized coordinate of fiducial (e.g., Fig. 2e) allows the measurement of mechanical drift of the sample during the acquisition period. An example of a rather high drift is shown for an acquisition of 20,000 frames (a, position of the fiducial; c, fluctuation of the X coordinate of the fiducial; d, fluctuation of the Y coordinate of the fiducial). The sample exhibits large drift along the Y-direction of more than 5 pixels or almost a micron. Such drift will smear the super-resolution image if not corrected for. Drift correction can be calculated by subtracting the moving averaged X and Y trajectories, resulting in a well-registered fiducial (b, using 200 frame moving average correction), and small residuals (e)