Angle detection algorithm based on triangle similarity theorem

The invention discloses an angle detection algorithm based on the triangle similarity theorem. The angle detection algorithm includes a first step of binarizing an image; a second step of performing expansion operation for the binarized image to highlight an edge curve; a third step of projecting the binarized image from top to bottom and from bottom to top to respectively obtain upper and lower edge curves of the image, and to respectively obtain effective point starting and ending addresses of first effective rows of the upper and lower edge curves; a fourth step of combining the upper and lower edge curves into a complete rectangular edge curve for processing, selecting a segment with the same x-coordinate at the left side of the starting address of each of the upper and lower edge curves of the image, and judging whether an included angle of the two curve segments is a right angle and whether the selected two curve segments are effective curves located on the edge curves of the image; and a fifth steps of