Lossless Phase Conversion Method for Object Wave-based Hologram Compression

An object wave is a suitable intermediate representation format for transmitting holographic application data because it is compatible with various playback devices. However, compressing the phase component of the object wave presents challenges due to its unique signal characteristics, i.e., periodicity and randomness. Hence, object waves significantly differ from ordinary 2D images such as camera-captured and screen pictures. To overcome the challenges, we propose a conversion method for lossless phase image coding using differential pulse-code modulation. Specifically, we calculate phase differences using adjacent pixels in two directions, considering periodic cycles of 2π, and then input them into the existing image coding. This method ensures robustness against randomness by smoothing the phase difference using the average of adjacent pixels. Experimental results show that lossless phase coding with the proposed conversion method achieves coding efficiency improvements of 6.50% over lossless phase coding without the proposed method.