Holographic display apparatus and method for providing expanded viewing window

A display method performed by a holographic display apparatus comprising an image processor, a spatial light modulator configured to form a hologram pattern for modulating an incident light and reproducing a holographic image and comprising a plurality of display pixels two-dimensionally arranged at a first resolution, and an illumination optical system configured to provide an illumination light to the spatial light modulator such that the illumination light is incident on the spatial light modulator in irregular directions, the display method comprising:

• generating, by the image processor, a hologram data array comprising information of the holographic image to be reproduced at the first resolution or a resolution less than the first resolution;
• performing, by the image processor, an off-axis phase computation on the hologram data array at a second resolution higher than the first resolution;
• generating, by the image processor, computer generated hologram (CGH) data at the first resolution;
• and
• providing the CGH data from the image processor to the spatial light modulator.