Stray light, also known as flare, is any light that reaches the detector (i.e., the image sensor) other than through the designed optical path. It can be caused by reflections, scattering, and diffraction within the camera. Depending on the mechanism causing the stray light, it can produce phantom objects within the scene (i.e., ghosts/ghosting), reduce contrast over portions of the image (e.g., veiling glare), and effectually reduce system dynamic range. Veiling glare and ghosting are specific forms of stray light, or ways that it can be manifested in an image.
There are two main methods to test for stray light in a camera system:
- The chart-based approach (measures veiling glare, which can generally predict the severity of stray light)
- The small, bright light source approach (measures all forms of stray light caused by small, bright light sources, including diffraction spikes, veiling glare, and ghosting)
- ISO 18844
- IEEE P2020 Flare