Extended Data Figure 4: Quantifying the contrast to determine the number of layers in 2D ice.

a, An example of the original TEM images used in our analysis (same image as in Fig. 2a). b, The filter calculates the local variance that is displayed as a greyscale value. c, The lattice pattern that remains visible in the variance image (b) is suppressed by applying the Gaussian blur. d, The final root-mean-square contrast map (that is, the standard deviation map) is obtained by calculating the square root of each pixel value of the variance image (c).