Embedding image into a phase-only hologram

Abstract

Past research has demonstrated that with error diffusion, a complex Fresnel hologram can be converted into a phase-only hologram, and capable of preserving high fidelity on its reconstructed image. Furthermore, the phase-only hologram can be embedded with an image that is of the same size as the hologram. This is achieved by replacing the least M least significant bits (LSB) of each hologram pixel with the M most significant bits (MSB) of the embedded image in the error diffusion process. The phase-only hologram obtained in this manner is known as a Data Embedded Error Diffusion (DEED) hologram. Despite the success, the quality of the embedded image is rather poor for small value of M. However, if M is increased to preserve the quality of the embedded image, the phase-only hologram will be jeopardized. The DEED hologram also has no protection on the access of the embedded image, as it can be retrieved by simply extracting the M least significant bits of the hologram pixels. In this paper, a method for overcoming the above problems is reported. Briefly, the image to be embedded is first converted into an M bit data with the use of error diffusion. Next, a fixed window is reserved in the binary bit-string of each hologram pixel, within which M bits are randomly selected and replaced with the embedded image data. As such, the bit selection configuration in each hologram pixel can be taken as an encryption key for retrieving the embedded image. The image embedded phase-only hologram realized with such means, which is referred to as the Image Encrypted Error Diffusion (IEED) hologram, is capable of preserving high fidelity on the content of the hologram, as well as favorable visual quality on the embedded image if the correct encryption key is presented.