Differential phase

Distortion in TV broadcasting that affects the color hue.

When TV broadcasts become distorted, the color will be affected. This phenomenon is called the differential phase, and it's a major source of image distortion at high-frequency stops (e.g. cable distribution TV boxes, satellite antennas, HEVC/H.265 transcoding devices).

The composite color video signal

The composite color video signal (CCVS) consists of three terms:

  1. Monochrome (luminance) signal
  2. Auxiliary signals (sync pulse and blanking signals )
  3. Color signal, which is actually a subcarrier modulated by chroma information

The first two terms are usually called composite video signals (CVS). The modulation technique of the color subcarrier is quadrature amplitude modulation (QAM) both in PAL and NTSC systems. The amplitude of the color signal represents the saturation of the color and the phase lag of the color signal with respect to a certain reference which is called colorburst represents the hue; i.e., each phase lag is assigned for a different color hue. So, in order to reproduce the original color in the receiver, the phase difference between the colorburst and the color signal must be kept constant throughout the broadcasting.

  • DP
Adapted from content published on wikipedia.org
Last modified on May 6, 2021, 5:35 pm
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