A method includes: separately creating a rectangular area R1 and a rectangular area R2 by using the first line segment as one side; determining a vector V1=(V1r,V1g,V1b) of an RGB color space of the rectangular area R1 and a vector V2=(V2r,V2g,V2b) of the RGB color space of the rectangular area R2; converting the vector V1 to a vector a1=(h1,s1,b1) of an HSB color space, and converting the vector V2 to a vector a2=(h2,s2,b2) of the HSB color space; determining a vector a0=(h0,s0,b0) of the first line segment in the HSB color space based on the vector a1 and the vector a2; and converting the vector a0 to a vector V0=(V0r,V0g,V0b) in the RGB color space; and after each edge line segment in the target quadrilateral is processed, displaying the target quadrilateral based on a vector of each edge line segment in the target quadrilateral in the RGB color space.