Beginning in mid-1995 cable TV operators must measure the quality of the color signals they are delivering to subscribers. The measurements chosen to judge color quality are differential gain, differential phase, and chrominance-to-luminance delay.
Local insertion of full-field signals allow the operator to test the performance of the system but requires program interruption. Local vertical interval test signal (VITS) insertion allows in-service testing without program interruption or picture impairment.
Another in-service approach utilizes programmer supplied VITS. In addition to lower cost, this is an end-to-end test which more closely links the test result to the actual subscriber picture quality. This approach, however, risks the signal not being present when needed or that the signal, if present, is already impaired enough to call its value into question.