Discrete cosine transform (DCT) is closely related to discrete Fourier transform. This is a separable linear conversion. It can be said that DCT is simpler and faster than DFT as well as FFT. DCT is suitable for extended periodic and symmetric sequences, while DFT is suitable for long periodic sequences. So DCTs are the equivalent of almost double-length DFTs that work on real data with uniform symmetry. Hilbert Phase Microscopy (HPM) is a shot in nature and is a new optical technique for measuring small, high-resolution transverse images associated with clear optical objects. In this paper, we introduce the phase extraction method of a simulated interference scheme with the cosine discrete Fourier transform algorithm in the Hilbert phase microscope.