In video encoding, the "essential" is the detail that the human visual system (HVS) detects. The "invisible" is the high-frequency noise or subtle color gradations that the eye ignores. x264 employs (settings such as psy-rd or Psychovisual Rate Distortion). These algorithms deliberately distort the raw mathematical data to preserve what looks "real" to the human eye. The encoder "knows," much like the Fox, that the mathematical accuracy of a pixel is less important than the perceptual truth of the scene.
