雙線性插值的實現

雙線性插值根據周圍4個點及與4個點的距離，來計算待插值像素的值
http://baike.baidu.com/link?url=4it85nPzCC9J0oZZGU7HEGuXbcDcOmzhtKuwTP9Nar9HLRyZdwKaocnn1yZOFJ7pdZjnXmTUpiKStH5nPs1qTq2V57th0nHQqc1m0_fzQXIklY4hFLnYg3T5kbqTibxqIUa_JFNV0sy8Y3_YX_XopK

下面是根據插值算法作的一個實現

void bilinear_c_int(uchar *pSrc, int srcWidth, int srcHeight, uchar *pDst, int dstWidth, 
                    int dstHeight) {

    const int N = 8;
    const int FACTOR = pow(2, N);

    float fx = (float)srcWidth / dstWidth;
    float fy = (float)srcHeight / dstHeight;

    int *x = new int[dstWidth];
    int *a = new int[dstWidth];

    int *y = new int[dstHeight];
    int *b = new int[dstHeight];

    for (int j = 0; j < dstWidth; j++) {
        x[j] = (int)(fx * j);
        a[j] = (fx*j - x[j]) * FACTOR ;
        if (x[j] > srcWidth - 2) {
            x[j] = srcWidth - 2;
            a[j] = FACTOR;
        }
    }

    for (int i = 0; i < dstHeight; i++) {
        y[i] = (int)(fy * i);
        b[i] = (fy *i - y[i]) * FACTOR;

        if (y[i] > srcHeight - 2) {
            y[i] = srcHeight - 2;
            b[i] = FACTOR;
        }
    }

    int index, p0, p1;
    for (int i = 0; i < dstHeight; i++) {
        for (int j = 0; j < dstWidth; j++) {
            index = y[i] * srcWidth + x[j];

            p0 = pSrc[index] * (FACTOR - a[j]) + pSrc[index + 1] * a[j];
            p1 = pSrc[index + srcWidth + 1] * (FACTOR - a[j]) + pSrc[index + srcWidth + 1] * a[j];
            pDst[i * dstWidth + j] = (p0 * (FACTOR - b[i]) + p1 * b[i]) >> (2 * N);
        }
    }

    delete[] x;
    delete[] a;
    delete[] y;
    delete[] b;
}