Algorithm 2: Image random rotation enhancement algorithm

Input: image max_angle

Output: enhanced_image

1:  function random_rotation(image, max_angle)

2:  height, width = image.shape

3:  Randomly generate the rotation angle. Randomly generated rotation angle $\theta$ can be represented by the random number function rand: $$\begin{array}{c}\hfill \theta =\mathrm{rand}\times 2\times \underset{¯}{\max }\mathrm{angle}-\underset{¯}{\max }\mathrm{angle}\end{array}$$

4:  Calculate the center of rotation. Assume that the coordinates of the center of rotation are $(x\_center,y\_center)$. $$\begin{array}{c}\hfill center\_x=\frac{width}{2},center\_y=\frac{height}{2}\end{array}$$

5:  Define the rotation matrix. $$\begin{array}{c}\mathrm{rotation\_matrix}=\left[\begin{array}{ccc}cos\left(\theta \right)& -sin\left(\theta \right)& (1-cos(\theta \left)\right)·\mathrm{center\_x}+sin\left(\theta \right)·\mathrm{cente}\\ sin\left(\theta \right)& cos\left(\theta \right)& -sin\left(\theta \right)·\mathrm{center\_x}+(1-cos(\theta \left)\right)·\mathrm{cent}\\ 0& 0& 1\end{array}\right]\end{array}$$

6:  Performs image rotation. The position of each pixel after rotation is ($x^{\prime }$,$y^{\prime }$). $$\begin{array}{c}(x^{\prime },y^{\prime })=\left\{\begin{array}{c}{x}^{\prime }=(x-\mathrm{center\_x})·cos\left(\theta \right)-(y-\mathrm{center\_y})·sin\left(\theta \right)+\mathrm{center\_x}\hfill \\ y^{\prime }=(x-\mathrm{center\_x})·sin\left(\theta \right)+(y-\mathrm{center\_y})·cos\left(\theta \right)+\mathrm{center\_y}\hfill \end{array}\right.\end{array}$$

7:  return rotated_image

8:  end function