Re-ordered Micro Image based High Efficient Residual Coding in Light Field Compression

Light field (LF), a new approach in three-dimensional image processing, has been actively used in various applications in recent years. LF is based on a large amount of data and this always leads to LF compression (LFC) issues. Pseudo-sequence (PS)-based LFC converts a LF into a video sequence and compresses it through a video codec, whereas synthesis-based LFC (SYN-LFC) synthesizes the rest from some of the LF to reduce the number of bits. SYN-LFC is superior to PS-based LFC at low bitrates. However, its competitiveness decreases at high bitrates due to the inefficient compression of residuals. This paper maximizes the advantages of SYN-LFC by increasing the compression efficiency of residuals. To exploit the characteristic of the residual in favor of compression, this paper compresses the residual in the form of a micro image (MI). The conversion of residuals to MI has the effect of gathering similar residuals of each viewpoint, which increases the spatial coherence. However, the conventional MI conversion does not reflect the geometric characteristics of LF at all. To tackle this problem, this paper proposes the re-ordered micro image (RoMI), which is a novel MI conversion that takes advantage of the geometric characteristics of LF, thereby maximizing the spatial coherence and compression efficiency. To compress MI-type residuals, JPEG2000, an image-level codec, is used. It is highly suitable for RoMI with spatial coherence beyond the block level. In the experimental results, the proposed RoMI shows average improvements of 30.29% and 14.05% in the compression efficiency compared to the existing PS-based LFC and SYN-LFC methods, respectively.