An autostereoscopic display apparatus, for displaying a three-dimensional image, comprising: a backlight to emit light from switchable apertures (A1-A5), the light being polarized and having an intensity; a plurality of light modulation panels (320a, 320b), each panel with pixels (P1-P5; P'1-P'5) that can be set to change the polarization of the light emitted from the switchable apertures (A1-A5); and a polarizer arranged to receive light emitted from the switchable apertures, the light having passed through the plurality of light modulation panels (320a, 320b), and the polarizer being arranged to transmit light within a limited range of polarizations; wherein the plurality of light modulation panels (320a, 320b) are positioned between the backlight and the polariser, with a first light modulation panel being positioned to receive the light emitted from the switchable apertures (A1-A5) and a second light modulation panel being positioned between the first light modulation panel and the polarizer to receive light emitted from the first light modulation panel; where each light modulation panel (320a, 320b) is controllable to change the polarization of the light received by each light modulation panel such that an intensity of the emitted light after passing through the polarizer, as perceived by a viewer, can be both increased and decreased irrespective of the polarization of the emitted light before passing the plurality of light modulation panels (320a, 320b), and where switching of the apertures (A1-A5) is synchronised with switching of the pixels (P1-P5; P'1-P'5) on the plurality of light modulation panels (320a, 320b); wherein the first light modulation panel has a first polarization rotation in an off state (voltage Voff) and a second polarization rotation in a fully on state (voltage Von) and the second light modulation panel has a first polarization rotation in an off state (voltage Voff) and a second polarization rotation in a fully on state (voltage Von); voltage application means to apply voltage to the first and the second light modulation panels, the voltage application means being configured to apply voltage V between Voff and Von and each light modulation panel (320a, 320b) in response to application of voltage V between Voff and Von providing an intermediary polarization rotation value between the first and second polarization rotations. a backlight to emit light from switchable apertures (A1-A5), the light being polarized and having an intensity; a plurality of light modulation panels (320a, 320b), each panel with pixels (P1-P5; P'1-P'5) that can be set to change the polarization of the light emitted from the switchable apertures (A1-A5); and a polarizer arranged to receive light emitted from the switchable apertures, the light having passed through the plurality of light modulation panels (320a, 320b), and the polarizer being arranged to transmit light within a limited range of polarizations; wherein the plurality of light modulation panels (320a, 320b) are positioned between the backlight and the polariser, with a first light modulation panel being positioned to receive the light emitted from the switchable apertures (A1-A5) and a second light modulation panel being positioned between the first light modulation panel and the polarizer to receive light emitted from the first light modulation panel; where each light modulation panel (320a, 320b) is controllable to change the polarization of the light received by each light modulation panel such that an intensity of the emitted light after passing through the polarizer, as perceived by a viewer, can be both increased and decreased irrespective of the polarization of the emitted light before passing the plurality of light modulation panels (320a, 320b), and where switching of the apertures (A1-A5) is synchronised with switching of the pixels (P1-P5; P'1-P'5) on the plurality of light modulation panels (320a, 320b); wherein the first light modulation panel has a first polarization rotation in an off state (voltage Voff) and a second polarization rotation in a fully on state (voltage Von) and the second light modulation panel has a first polarization rotation in an off state (voltage Voff) and a second polarization rotation in a fully on state (voltage Von); voltage application means to apply voltage to the first and the second light modulation panels, the voltage application means being configured to apply voltage V between Voff and Von and each light modulation panel (320a, 320b) in response to application of voltage V between Voff and Von providing an intermediary polarization rotation value between the first and second polarization rotations.