void Filter(const BYTE *inputImage, BYTE *outputImage, const int width, const int height)
{
    int i, j, k, l;
    double sum;

    for (j = 0; j < height; ++j)
        for (i = 0; i < width; ++i)
            outputImage[GetIndex(i, j, width)] = 0;

    for (i = 0; i < width; ++i)
        for (j = 0; j < height; ++j)
        {
        if (i != 0 && j != 0 && i != width - 1 && j != height - 1)
        {
            sum = 0.0;

            for (k = -1; k <= 1; ++k)
                for (l = -1; l <= 1; ++l)
                {
                if ((k == 0 && l != 0) || (l == 0 && k != 0))
                    sum += 4.0 * inputImage[GetIndex(i + l, j + k, width)] / 28.0;
                else if (k == 0 && l == 0)
                    sum += 8.0 * inputImage[GetIndex(i + l, j + k, width)] / 28.0;
                else
                    sum += inputImage[GetIndex(i + l, j + k, width)] / 28.0;
                }

            outputImage[GetIndex(i, j, width)] = (BYTE)sum;
        }
        }
}