# Is central projection of the imaging process a projective transformation?

I am reading the book Multiple View Geometry in Computer Vision(Second Edition) and encounter some questions.

On Page 7, it says

In applying projective geometry to the imaging process, it is customary to model the world as a 3D projective space, equal to $$\mathbb{R}^3$$ along with points iat infinity. Similarly the model for the image is the 2D projective plane $$\mathbb{P}^2$$. Central projection is simply a map from $$\mathbb{P}^3$$ to $$\mathbb{P}^2$$.

Does it mean that central projection is a projective transformation? If not, what is the reason? From other pages, it seems that projective transformation can only be the map between two spaces of the same dimension. Any help are appreciated.