What is "perspective correction" in graphics and when is it applied?

Question

So I have been working on my graphics homework and I have finished doing perspective projection, but then today I just read online something about perspective correction. Can someone explain to me what exactly this is and when is it applied? I have seen a couple of scholar articles, but they were so complex and complicated that I couldn't understand what was happening.

I commonly see articles mention 1/z and something about interpolating it but I am confused about that. So far, I have been simply using barycentric coordinates to interpolate my z coordinates.

Answer 1

this therm is used for more things like:

1. fisheye corrections in ray-tracers

   for this usually cos function is used to handle the peripherial view a bit differently so walls are flat and not curved near edge of views. See:

   • Wolfenstein 2D ratracer

2. image reconstruction from perspective view

   to get some rectified reference frame coordinates from images like:

   • OpenCV Birdseye view without loss of data

3. Depth buffer (de)linearzaion

   So either you got z coordinate after perspective division (z/w) and want to retreive the original z for some computation or you got linear z and want to apply perspective division.

   Linear depth buffer have the same z accuracy on whole frustrum and perspective divided non linear depth buffer have same apparent visual accuracy on whole frustrum (the more distant from camera the less accuracy you got but visually it is the same step size) see:

   • How to correctly linearize depth in OpenGL ES in iOS?

   Sometimes you need linear and some times non linear depth buffer. For almost whole frustrum views or with big z coverage is linear depth buffer best but for near camera objects details is non linear better...

   Non linear:

   

   Linear:

   

My bet is you are talking about #3.