椒盐噪声

椒盐噪声就是给图片添加黑白噪点，椒指的是黑色的噪点(0,0,0),盐指的是白色的噪点(255,255,255)，通过num来控制噪声多少，值越大添加的噪声越多，图像损坏的更加严重。

void add_salt_pepper_noise(Mat& src,Mat& dst,int num)
{
    dst = src.clone();

    unsigned seed = std::chrono::system_clock::now().time_since_epoch().count();
    std::default_random_engine generator (seed);

    std::uniform_int_distribution<int> distribute_x(0, src.cols - 1);//包含max
    std::uniform_int_distribution<int> distribute_y(0, src.rows - 1);//包含max

    //black
    for(int i = 0;i < num;i ++){
        int x = distribute_x(generator);
        int y = distribute_y(generator);
        dst.at<Vec3b>(y,x) = Vec3b(0,0,0);
    }

    //white
    for(int i = 0;i < num;i ++){
        int x = distribute_x(generator);
        int y = distribute_y(generator);
        dst.at<Vec3b>(y,x) = Vec3b(255,255,255);
    }
}

下图是设置num=1000时产生的噪声图像：

高斯噪声

高斯噪声就是给图片添加一个服从高斯分布的噪声，可以通过调节高斯分布标准差sigma的大小来控制添加噪声程度，sigma越大添加的噪声越多图片损坏的越厉害.

void add_gassion_noise(Mat& src,Mat& dst,int mean,int sigma)
{
    dst = src.clone();

    Mat _gassion = Mat::zeros(src.rows,src.cols,CV_8UC3);
    cv::RNG rng;
    rng.fill(_gassion, RNG::NORMAL, mean, sigma);

    dst = dst + _gassion;
}

下图是mean=50,sigma=50时产生的噪声图像：

随机形状斑点噪声

随机斑点噪声是通过生成随机的多变形来实现的。

注意以下代码中image是QImage，num表示产生20个斑点。

    Mat _msk = Mat::zeros(image->height(),image->width(),CV_8UC1);
    num = 20;
    Mat kernal = Mat::ones(3,3,CV_8UC1);
    kernal.at<uchar>(0,0) = 0;
    kernal.at<uchar>(0,2) = 0;
    kernal.at<uchar>(2,0) = 0;
    kernal.at<uchar>(2,2) = 0;

    for(int i = 0;i < num;i ++){
        quint32 value = QRandomGenerator::global()->generate();
        int cx = value % (this->width() / 2 - 1);

        value = QRandomGenerator::global()->generate();
        int cy = value % (this->height() - 1);

        std::vector<Point> _polygon;
        int _line_num = 20,_min_radius = 2,_max_radius = 7;
        double _angle_step = 2 * 3.1415926 / _line_num;
        Point center(cx,cy);
        for (int i = 0;i < _line_num;i ++){
            quint32 value = QRandomGenerator::global()->generate();
            double k = value % 100 / 100.0;
            double _angle = _angle_step * i;
            _angle = _angle + (k - 0.5) * _angle_step * 0.25;

            value = QRandomGenerator::global()->generate();
            k = value % 100 / 100.0;
            double radius = _min_radius + k * (_max_radius - _min_radius);

            int x = radius * cos(_angle);
            int y = radius * sin(_angle);

            _polygon.push_back(Point(center.x + x,center.y + y));
        }

        value = QRandomGenerator::global()->generate();
        int c = value % 255;

        cv::fillPoly(_msk,_polygon,Scalar(c));

        //cv::morphologyEx(_msk,_msk,MORPH_DILATE,kernal,Point(-1,-1),1);
    }

    cv::GaussianBlur(_msk,_msk,Size(5,5),0);

    for (int h = 0;h < _msk.rows;h ++)
    {
        uchar *d1 = image->scanLine(h);
        uchar *d2 = _msk.ptr<uchar>(h);
        for (int w = 0;w < _msk.cols;w ++)
        {
            int w4 = 4*w;

            double v = d1[w4 + 0] * (1 - d2[w] / 255.0);
            if (v > 255)v = 255;
            if (v < 0)v = 0;
            d1[w4 + 0] = v;

            v = d1[w4 + 1] * (1 - d2[w] / 255.0);
            if (v > 255)v = 255;
            if (v < 0)v = 0;
            d1[w4 + 1] = v;

            v = d1[w4 + 2] * (1 - d2[w] / 255.0);
            if (v > 255)v = 255;
            if (v < 0)v = 0;
            d1[w4 + 2] = v;
        }
    }

以上代码只产生黑色斑点，白色斑点只要将合并方式改成加即可：double v = d1[w4 + 0] * (1 + d2[w] / 255.0);

图像噪声--添加噪声

椒盐噪声

高斯噪声

随机形状斑点噪声