Pre-demosaic light field image compression using graph lifting transform
A plenoptic light field (LF) camera places an array of microlenses in front of an image sensor, in order to separately capture different directional rays arriving at an image pixel. Using a Bayer pattern, data captured at each pixel is a single color component (R, G or B). The sensed data then undergoes demosaicking (interpolation of RGB components per pixel) and conversion to a series of subaperture images. In this paper, we propose a novel LF image coding scheme based on graph lifting transform, where the acquired sensor data are coded in their original form without pre-processing. Specifically, demosaicking is not performed, and instead we first map raw sensed color data directly to subaperture image 2D grids, then encode the color pixels, which are sparse in spatial distribution, via a graph lifting transform. Our method avoids redundancies stemming from demosaicking, and operates in the original RGB domain without color conversion and sub-sampling. The graph lifting transform efficiently encodes irregularly spaced pixels in each subaperture image, resulting in compact representations. Experiments show that at high PSNRs — important for archiving and instant storage scenarios — our method outperforms demosaicking followed by intra-only High Efficiency Video Coding (HEVC) significantly.