Fast Impulsive Vector Filter

效果和 Median filter 類似，實用性..還好..

// Fast Impulsive Vector Filter 濾波器
//
// Mi = 相似性累積和
// 像素間差值小於 threshold 者, 此差值才會被加進 Mi 中  
// if (M0 < Mk) F0 = Fk

void FIVF (const IplImage* in, IplImage* out, int threshold)
{
    uchar* p  = (uchar*) in->imageData;
    uchar* o  = (uchar*) out->imageData;
    int    W  = in->widthStep;                  //真實寬度
    int    OW = out->widthStep;                 //真實寬度
    int    h  = in->height - 1;                
    int    w  = in->width  - 1;                  
    int    x, y, k, r;
    int    sum, dist, v, M[9], P[8];

    p+=W; o+=OW;                                //只掃描 [1,1]
    w--;  h--;                                  //~[w-2,h-2]
    
    for (y=1; y<h; ++y, p+=W, o+=OW)
        for (x=1; x<w; ++x)         
        {
            P[0] = p[x-W-1]; P[1] = p[x-W]; P[2] = p[x-W+1];
            P[7] = p[x  -1];                P[3] = p[x  +1];
            P[6] = p[x+W-1]; P[5] = p[x+W]; P[4] = p[x+W+1];
            
            for (r=0; r<9; ++r) {
                v = r==0? p[x]: P[r-1];
                for (sum=k=0; k<8; ++k) {
                    dist = abs (v - P[k]);
                    if (dist > threshold) dist = 0;
                    else dist = threshold - dist;
                    sum += dist;
                }
                M[r] = sum;
            }
            for (k=1; k<9; ++k)                 //若週圍點的相似性
                if (M[0] < M[k]) {              //累積和高於中央點
                    for (v=k, r=k+1; r<9; ++r)  //則將中央點灰度值
                        if (M[v] < M[r]) v = r; //代換成具有最高相似性
                    o[x] = P[v-1];              //累積和的週圍點灰度
                    break;
                }
        }
}