Snow removal--A noise-stripping process for picture signals

It is quite often possible to separate "picture" from "noise" in a television image. We do this when we view television under unfavorable conditions. This ability of the human observer suggests that completely automatic operation might at least partially separate noise and picture. A nonstationary, nonlinear operation has been found which selectively removes moderate amounts of additive Gaussian noise from a received picture signal. Running tests are performed upon the signal to detect the presence of perceptually significant picture detail in a number of different categories. Depending upon the test results, a selection is made from a number of available smoothing filter modes to maximize the suppression of noise without picture blurring. No preparatory operation is required at the transmitter, so that the technique is compatible with existing picture transmission systems. The process is applicable to conventional broadcast television, and could in principle be incorporated in home receivers to improve reception in fringe areas.