# On-Board Flickering Pixel Dynamic Suppression Method Based on Multi-Feature Fusion
## 2 Methodology
### The Strategy of Flicking Pixel Suppression  
The confidence evaluation mechanism based on multi-features fusion was introduced to evaluate the blinking frequency of a pixel. We use \(C(i,j)\) to represent the confidence of flickering pixel of pixel \((i,j)\). The value range is 0 to 1. The greater the confidence of flickering pixel of a pixel is, the higher the blinking frequency would be. In addition, the step size of updating confidence is defined as \(c\). Considering the iteration speed and reliability of the confidence, we set \(c\) ranging from 0.02 to 0.05. The higher the \(c\), the faster the confidence update, but the lower the reliability. All the pixels' confidences are assigned to 0 at the beginning. If a certain pixel is judged as a flickering pixel by the VFBP model and one of the MFBP models at the same time, the confidence of this pixel will be increased a unit \(c\), as shown in Equation (10). \[C(i,j)=\left\{ \begin{array}{ll}1&C(i,j)+c>1\\ C(i,j)+c&C(i,j)+c\leq 1\end{array} \right.\ if(X_{IM}(i,j)=1)\&\&\Big{(}X_{MOst}(i,j)=1 \Big{|}\Big{|}X_{MOdy}(i,j)=1\Big{)}\,, \tag{10}\]  
If a certain pixel is judged as normal pixel by VFBP model or MFBP model, the confidence of this pixel will be decreased a unit \(c\), as shown in Equation (11). \[C(i,j)=\left\{ \begin{array}{ll}0&C(i,j)-c\leq 0\\ C(i,j)-c&C(i,j)-c>0\end{array} \right.\ if(X_{IM}(i,j)=0)\Big{|}\Big{|}\Big{(}X _{MOst}(i,j)=0\&\&X_{MOdy}(i,j)=0\Big{)}\,, \tag{11}\]  
Especially, a threshold was introduced to maintain the scale of flickering pixels' table. Th\({}_{\text{re}}\) is the reserve threshold and is set to 0.5 \(c\). When CFP of a pixel is greater than Th\({}_{\text{re}}\), the pixel will be added to the flickering pixels' table. Otherwise, it will be removed from the table. In addition, due to changes in working conditions, some flickering pixels will return to normal. Therefore, we introduce forgetting factor (F) with values from 0.96 to 0.98. If a certain pixel within the flickering pixels' table is not updated CFP in the current frame, the CFP of this pixel will be decreased by multiplying the forgetting factor. The block diagram of proposed confidence evaluation mechanism of flickering pixel is shown in Figure 3.  
Subsequently, the dynamic compensation strategy based on confidence was proposed to compensate the flickering pixel accurately to frame. The direct compensation threshold ThD and the compensation after validation threshold ThV are introduced. If the CFP of a certain pixel is equal to or greater than ThD, this pixel will be compensated directly. Correspondingly, if the confidence of a certain pixel is equal to or greater than ThV but less than ThD, this pixel will be validated by the VFBP model again. If it is judged as flickering pixel by the VFBP model in current frame, this pixel will be compensated. Otherwise, this pixel will not be compensated. In this paper, for saving computing resources, flickering pixels would be compensated by the mean filter or median filter. Alternatively, the flickering pixels are simply suppressed by skipping the IRPT detection process for these pixels. Finally, the above parameters and thresholds selection are discussed. Indeed, these values are important because they determine the effect of flickering pixel suppression. The CFP fluctuates nonlinearly with the forgetting factor and steps size of updating CFP. Therefore, it is hard to give a clear interpretation of fluctuations of CFP. Moreover, the relation between blinking frequency of flickering pixel and the corresponding evolution of CFP should be determined to select the thresholds ThV and ThD. Firstly, we introduce the 90 th-percentile CFP (Q90%CFP) to determine thresholds. The probability that the CFP of a pixel with a certain blinking frequency is greater than Q90%CFP is 90%. Then, we define that the flickering pixel with blinking frequency equal to or greater than 80% will be suppressed directly, which corresponds to ThD. The blinking frequency corresponding to ThV is 20%.