Overmodulation distortion occurs when source material has been videotaped with the videotape recording gain set too high. This type of distortion is rarely seen these days, as most video equipment now has overmodulation protection built in. Nonetheless, it is still occasionally seen when old videotapes are transferred to DVD. It is the video equivalent of having the recording level set too high when making an audio tape recording. It manifests itself as horizontal lines of distortion emanating from dark-to-bright transitions.

Frank Sinatra-Ol' Blue Eyes Is Back (28:12)

Close up of Gene Kelly's shirt - note the lines of distortion emanating from the left edge of his tuxedo. Contrast this to the right side which is clear of this artefact.