Abstract: Sequential/interlace scan conversion of NTSC or PAL color television signals is effected by an encoder the output of which is connected to the input of scan conversion apparatus. Controllable phase shift means is included in either the color signal input or the subcarrier input of the encoder and is adapted to vary the phase of the modulated subcarrier for each line of the received color signal by an essentially integral number of quarter cycles in dependence upon the line number. The control is such that the conversion apparatus provides an encoded output signal with the color subcarrier in PAL or NTSC format. The invention can also be used in converting between different types of interlace systems.