Fixed-Length Coding for Escape Samples in Palette Mode

Palette mode is a powerful tool for screen content coding in the upcoming versatile video coding (VVC) standard. In the palette mode, escape samples are employed to handle an outlier case. In this paper, a quantization parameter (QP) dependent fixed-length binarization is proposed for escape samples coding to 1) simplify the design and 2) improve coding efficiency. The length is calculated according to the QP for the current block and correspondingly, the dequantization process can be also implemented by only left shifting. The proposed method is evaluated with VVC reference software VTM-6.0 on typical sequences containing "text and graphics with motion". Experimental results report that the proposed scheme can achieve up to 2.0% BD-rate savings compared to VTM-6.0 with a much simpler design.