spatial detail and this is controlled by a two dimensional highpass filter 41 such as a sobel filter followed by an envelope squarer 43 and a first control amplifier 45 a second aspect is sensitivity to noise at different local contrasts and this is controlled by a two dimensional lowpass filter 47 followed by a transfer offset circuit 49 and a second control amplifier 51 the parameters a 1 and a 2 represented by the first and second control amplifiers 45 51 are adjusted for a desired minimum data pattern visibility over a range of picture material a third aspect may be that of temporal masking 55 where noise on screen cuts or motion is temporarily less visible the resulting outputs from these paths describing the complexity of the image rendered by the digital video signal are summed by a summer 53 to produce a gain signal to control a multiplier 50 to which the modulated frequency signal is input prior to the adder 20 thus for portions of the digital video signal where the image is unchanging in motion and or has low spatial detail and contrast or color shading variations the gain is relatively low and where the image is complex due to motion and or high spatial detail the.