What is that purple fringe around high contrast areas in my photos?
Purple fringing (PF) has been a subject of great debate in the digital photography community. A popular, but demonstrably incorrect, theory for some time was that PF was caused by sensor blooming. The following suggest strongly that blooming is not a factor: • PF decreases with smaller apertures and constant EV. • PF does not occur along readout lines in CCDs (as is typical with blooming) and CCDs are no more susceptible to PF than CMOS sensors, which have high blooming resistance. • PF remains the same with higher ISO and constant EV. (At high ISO only a fraction of the sensor’s well capacity is used, so blooming is far less likely.) • PF varies with position in the frame • PF is typically radial. • PF is colored Despite these arguments, some persisted in the belief that PF was caused by blooming, so I took these sample images to debunk the blooming theory. In these shots, we see that the lens is the factor that controls PF, and not the exposure. The identical exposure with two differ
