(1) Image grayscale

Each pixel point of an iced insulator image is essentially composed of components in three directions of RGB (red, green, and blue). The grayscale is to convert the three-component value of RGB into a single gray value, so that the calculation of the subsequent image processing would be simplified. The calculation is shown in Equation (1). The result is shown in Figure 2.

$$M = 0.3R + 0.59G + 0.11B\tag{1}$$

here, *M*, *R*, *G*, and *B* are the values of the pixel, respectively representing gray value, red value, green value, and blue value. The coefficients in the formula are derived from the sensitivity of human eyes to color.

**Figure 2.** Color image and grayscale image.
