In autonomous driving systems, the resolution, frame rate and the number of in-vehicle cameras have been increasing, and it is necessary to record images efficiently. The H.264/AVC standard has better coding efficiency comparing with former video coding standards, but it cannot reduce bit rate sufficiently while keeping image quality of ROI regions.
In this paper, we propose a method to reduce bit rate by scaling down the input image in non-ROI regions. In detail, 2×2 MBs are set as a block in the input image, and if ROI regions are included in the block, the coding process is performed as usual. On the contrary, if no ROI region is included in the block, the 2×2 MBs image is scaled down in 1 MB size and then coded. As our evaluation result, we confirmed that our proposed method can reduce bit rate by 20.2-46.9 [%] on city street and 49.6-68.0 [%] on highway while suppressing PSNR deterioration of ROI regions within 0.2 [dB].
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