Radial distortion is an optical aberration that causes a deviation from rectilinear projection where straight lines in a scene remain straight in an image. Radial distortions can be classified as either:
- Barrel distortion: lines that do not go through the centre of the image are bulging outwards the centre of the image, like a barrel.
- Pincushion distortion: lines that do not go through the centre of the image are bowed inwards, towards the centre of the image, like a pincushion.