c语言数字图像处理（二）：图片放大与缩小-双线性内插法

int is_in_array(short x, short y, short height, short width)
{
    if (x >= 0 && x < width && y >= 0 && y < height)
        return 1;
    else
        return 0;
}

void bilinera_interpolation(short** in_array, short height, short width, 
                            short** out_array, short out_height, short out_width)
{
    double h_times = (double)out_height / (double)height,
           w_times = (double)out_width / (double)width;
    short  x1, y1, x2, y2, f11, f12, f21, f22;
    double x, y;

    for (int i = 0; i < out_height; i++){
        for (int j = 0; j < out_width; j++){
            x = j / w_times;
            y = i / h_times;
            x1 = (short)(x - 1);
            x2 = (short)(x + 1);
            y1 = (short)(y + 1);
            y2 = (short)(y - 1);
            f11 = is_in_array(x1, y1, height, width) ? in_array[y1][x1] : 0;
            f12 = is_in_array(x1, y2, height, width) ? in_array[y2][x1] : 0;
            f21 = is_in_array(x2, y1, height, width) ? in_array[y1][x2] : 0;
            f22 = is_in_array(x2, y2, height, width) ? in_array[y2][x2] : 0;
            out_array[i][j] = (short)(((f11 * (x2 - x) * (y2 - y)) +
                                       (f21 * (x - x1) * (y2 - y)) +
                                       (f12 * (x2 - x) * (y - y1)) +
                                       (f22 * (x - x1) * (y - y1))) / ((x2 - x1) * (y2 - y1)));
        }
    }
}