Formulas are developed for calculating the weighted interference noise power in base band and the interference reduction factor of periodic TV signals and periodic random TV signals in FM TV systems interfered by various digital modulating signals thus making it possible to compute approximately the digital-analog interference for both motionless and motional images. A simplified method for exact calculation is also given. The high degree of accuracy of the approximate calculation formulas is confirmed by the fact that their numerical results are in good agreement with the exact calculations.