Calibration curves for LCT. Black crosses: uncompressed data at 0° latitude; red circles: uncompressed data at 60° latitude; blue squares: quantized data (n = 2) at 0° latitude; green triangles: JPEG compression (q = 2) at 0° latitude. The error bars are smaller than the symbol size. The amplitudes of the velocities generated by LCT are in general lower than the actual velocities on the Sun, especially for compressed data. We correct for this effect by generating calibration data with a constant flow in the x direction. Three days of data are used for each data point. For more details about this method, see the text.