# X, Y, Z coordinate in opencv

Hello, I am capturing picture using video cam and displaying with opencv. Now in the screen what's the x,y, z coordinate of the image. I tried to muliply the rotation matrix of head pose estimation by the following matrix:

[ 1, 0, 0, 0, -1, 0, 0, 0, -1]

But z coordinate gives negative direction. I don't understand why. Could any one explain a bit?

Thanks in advance.