The Pinhole Camera and Perspective

A box that keeps one ray per point

Similar triangles give the projection

Distant objects shrink

Three coordinate systems

A camera has focal length $f = 10$. A square sign of world width $X = 4$ is photographed first at depth $Z = 4$ and then at depth $Z = 8$. What happens to the sign's image width under perspective projection?

A camera's pixel map is $n = -ax + n_0$ with $a = 100$ pixels per unit and $n_0 = 320$. A feature lands at virtual-plane coordinate $x = -1.5$. Which statement about the feature's pixel column is correct?

A pinhole camera has focal length $f = 50$. A world point sits at $(X, Y, Z) = (30, 10, 150)$. Using the perspective projection $x = fX/Z$, compute the point's camera coordinate $x$ and write it as a decimal.