Clipping and Crushing Video?

OK if intentional, not OK if not intentional.

Analog video broadcast standards allow transmission of signal brighter than pure white and darker than pure black. While this is counterintuitive there are technical reasons for the headroom and toeroom of video signal in both analog and digital domains.

Signal excursions outside of maximum and minimum levels can in certain cases affect the integrity of the signal. In order to prevent illegal excursions above the maximum level the signal may be clipped. Likewise, low levels can be crushed so they flatten at the minimum allowed level. Clipping is often performed prior to analog signal transmission by TV stations.

Clipping and crushing is sometimes performed for creative reasons in color correction. The result of clipped signal is uniform white (or solid color) without any detail (note the white shirt detail). The result of crushed blacks is pure black without any visible detail [Fig.1].

Clipping and crushing in post production is a valuable tool but clipping and crushing in camera or telecine can create unwanted results and should be generally avoided. Clipped and crushed video is devoid of detail information in the affected areas. A crushed night exterior can not be color corrected to show more detail because the detail was irretrievably lost.

Some network delivery specs warn against excessive clipping and crushing. Check the spec before reaching for the scissors.

video clip and crush

Fig. 1. Excessive Video Clip and Crush