# Intrinsic Matrix vs Perspective projection matrix

I was going through the camera matrix explained in the wikipedia article and understand how the matrix K $$\begin{bmatrix}f_x&s&x_0\\0&f_y&y_0\\0&0&1\end{bmatrix}$$ is built. The projection matrix is then essentially K * [R | T]

However, I am not able to understand what the perspective projection matrix is and how is it same to the intrinsic matrix K

• "The **projection matrix is then essentially...". AFAICS That's not a projection matrix.. it's not really a "2D" rotation + translation matrix either. Are you familiar with homogeneous coordinates? You really need to understand those first. – Simon F Jan 14 at 8:40
• @SimonF this matrix can be easily broken into 2D Scaling "+" 2D translation. Also, this is essentially the simple perspective projection matrix. (multiply by it and then homogenise the co-ordinates.) – midi Jan 14 at 17:28
• @SimonF I now understand that the projection matrix (with the viewing frustum mapped to a cube) is used as it contains depth information which is lost in the simple perspective projection matrix I had written earlier. – midi Jan 14 at 17:30
• Oh good. :-) FWIW my first comment was that you'd written [R|T] which seemed to me to imply Rotation +Scaling, but the matrix requires another term. – Simon F Jan 15 at 9:42