function Fangxiangtu = zhiwen_fangxiangtu( Zhiwentuxiang )

%函數功能計算指紋方向圖

%函數參數指紋圖像Zhiwentuxiang

%函數返回值指紋方向圖Fangxiangtu

SizeZhiwentuxiang = size( Zhiwentuxiang ) ;

Zhiwentuxiang = double( Zhiwentuxiang ) ;

W = 4; % 窗口大小(2W+1)*(2W+1)

W = 4;

%Sobel算子

x_fangxiang = [-1 0 1;

-2 0 2;

-1 0 1];

y_fangxiang = [1 2 1;

0 0 0;

-1 -2 -1];

SizeZhiwentuxiang = size( Zhiwentuxiang );

Gx = zeros( SizeZhiwentuxiang );

Gy = zeros( SizeZhiwentuxiang );

Fangxiangtu = zeros( SizeZhiwentuxiang );

for i = 2 : SizeZhiwentuxiang( 1 , 1 ) - 1

for j = 2 : SizeZhiwentuxiang( 1, 2 ) - 1

Sum_x = 0;%j方向

Sum_y = 0;%i方向

for k = -1 : 1

for r = -1 : 1

Sum_x = Sum_x + x_fangxiang( k + 2 , r + 2 ) * Zhiwentuxiang( i + k , j + r );

Sum_y = Sum_y + y_fangxiang( k + 2 , r + 2 ) * Zhiwentuxiang( i + k , j + r );

end

end

Gx( i , j ) = Sum_x ;

Gy( i , j ) = Sum_y ;

end

end

for i = W+1 : SizeZhiwentuxiang( 1 , 1 ) - W

for j = W+1 : SizeZhiwentuxiang( 1, 2 ) - W

Vx = 0;

Vy = 0 ;

for io = -W : W

for jo = -W : W

Vy = Vy + 2 * Gx( i + io , j + jo ) * Gy( i + io , j + jo );

Vx = Vx + Gx( i + io , j + jo ).^2 - Gy( i + io , j + jo ).^2;