# A Fast Algorithm for VVC Intra Coding Based on the Most Probable Partition Pattern List
## 3 Proposed Method
### Partition Mode Decision  
After the construction of the MPPPL was completed, the partition mode was decided in advance on this basis or the length of the MPPPL was reduced. We conducted a statistical analysis on the probability of a particular direction being selected as the final partition direction when the first two partition modes in the MPPPL were of the same direction, and the results are shown in Table 1. When both Mode-a and Mode-b in the MPPPL were either horizontal partition modes or vertical partition modes, it indicates that the current CU exhibits strong directional texture and is more inclined towards either horizontal or vertical partition. In such cases, the MPPPL can be modified by removing all partition modes except for Mode-a and Mode-b. In the partition process of VVC, the probability of a TT partition being adopted is very small (no more than 20%) [25]. Therefore, when determining the direction of a CU partition, further consideration is given as to whether to skip TT partition and decide the optimal partition mode. If Mode-a is a TT partition at this time, it indicates that in the previous calculation, the TT partition had a high probability of being the optimal partition mode, and the TT partition is not skipped at this time. If Mode-a is a BT partition, we would consider skipping the TT partition directly at this time. It is not difficult to determine from Figure 5 that when the texture structure in a CU is mainly concentrated on the left and right sides or at the upper and lower sides of a CU boundary, the TT division structure is used. At this time, there was a significant difference in the average pixel values between the sub-CUs, and so we used the pixel mean difference between the sub-CUs to decide whether to skip the TT partition. The pixel mean difference of the horizontal binary partition (P\({}_{HBT}\)) was calculated as follows:  
\[\mathrm{P}_{HBT}=p_{ave}(x,y,x+w,y+\frac{h}{2})-p_{ave}(x,y+\frac{h}{2},x+w,y+ h). \tag{11}\]  
The pixel mean difference of the horizontal ternary partition (P\({}_{HTT}\)) was calculated as follows: \begin{table}
\begin{tabular}{c c c} \hline \hline
**Coding Sequence** & **Both Vertical** & **Both Horizontal** \\ \hline Campfire & 85\% & 79\% \\ Cactus & 94\% & 83\% \\ BasketballPass & 83\% & 85\% \\ BQSquare & 86\% & 87\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mode-a and Mode-b partition mode selection probability in the same direction. Figure 5: Schematic diagram of the TT division structure: (**a**) HTT, and (**b**) VTT. \[\mathrm{P}_{HTT}=p_{ave}(x,y+\frac{h}{4},x+w,y+\frac{3h}{4})-min(p_{ave}(x,y,x+w,y+ \frac{h}{4}),p_{ave}(x,y+\frac{3h}{4},x+w,y+h)). \tag{12}\]  
Similarly, the formulas used for calculating the pixel mean difference of the vertical binary partition (P\({}_{VBT}\)) and the pixel mean difference of the vertical ternary partition (P\({}_{VTT}\)) are as follows:  
\[\mathrm{P}_{VBT}=p_{ave}(x,y,x+\frac{w}{2},y+h)-p_{ave}(x+\frac{w}{2},y,x+w,y+h)\ \mathrm{and} \tag{13}\]  
\[\mathrm{P}_{VTT}=p_{ave}(x+\frac{w}{4},y,x+\frac{3w}{4},y+h)-min(p_{ave}(x,y,x+ \frac{w}{4},y),p_{ave}(x+\frac{3w}{4},y,x+w,y+h)). \tag{14}\]  
We selected different coding sequences and conducted a statistical analysis on the relationship between the selection of partition modes in the MTT partition process and the difference in the pixel mean values. The statistical results are shown in Table 2.  
It can be observed that when the pixel mean difference of the horizontal binary partition is greater than that of the horizontal ternary partition, there is a stronger preference for selecting the horizontal binary partition. Similarly, when the pixel mean difference of the vertical binary partition is greater than that of the vertical ternary partition, there is a stronger preference for selecting the vertical binary partition. Therefore, when both Mode-a and Mode-b in the MPPPL are either horizontal partition modes or vertical partition modes, an early decision on the optimal partition mode is considered.