Touch screen for privacy display

A method of controlling a touch input display device comprising:

• a spatial light modulator (SLM) arranged to output light;
• a display polariser arranged on an output side of the SLM, wherein the display polariser is a linear polariser;
• an additional polariser arranged on an output side of the display polariser, wherein the additional polariser is a linear polariser;
• a switchable liquid crystal retarder comprising a layer of liquid crystal material arranged between the display polariser and the additional polariser;
• switchable retarder control electrodes arranged to apply a voltage for controlling the switchable liquid crystal retarder;
• at least one touch electrode array arranged in a layer on an output side of the switchable retarder control electrodes;
• and
• an output transparent support substrate, wherein the at least one touch electrode array is arranged between the switchable retarder control electrodes and the output transparent support substrate;
• wherein the method comprises:
• applying a drive voltage to the switchable retarder control electrodes for controlling the switchable liquid crystal retarder, wherein the drive voltage has a waveform including periods where the drive voltage is constant;
• and
• addressing the at least one touch electrode array for capacitive touch sensing during at least one of the periods where the drive voltage is constant.