山东大学数字图像处理实验（一） 计算机学院

本实验为计算机科学与技术学院计算机专业大四上限选课，2023-2024-1年度课程实验，较以往实验内容发生较大变化

代码中乱码系中文编码错误，可自行更换。本实验使用vs2019，c++语言，需要提前安装opencv，具体方法请自行搜索。

实验1：图像基本处理

实验1.1：图像合成

给定一张4通道透明图像a.png,从中提取alpha通道并显示，并用alpha混合，为a.png替换一张新的背景（背景图自选）

#include <opencv2/opencv.hpp>  
#include <opencv2/core/core.hpp>  
#include <opencv2/highgui/highgui.hpp>  
#include <opencv2/imgproc.hpp>  
#include <iostream>  
using namespace std;
using namespace cv;

int main()
{
    // ��ͼ
    Mat picture = imread("C:/Users/13441/Desktop/����ͼ��/a.png", -1); 
    Mat picture_alpha(picture.rows, picture.cols, CV_8UC1); 
    int i = 0, j = 0;
    while (i < picture.rows)
    {//�����ػ�ȡ�Աȶȣ��洢��һ��������
        j = 0;
        while (j < picture.cols)
        {
            picture_alpha.at<uchar>(i, j) = picture.at<Vec4b>(i, j)[3];
            j++;
        }
        i++;
    }
    imshow("1.png", picture_alpha); // ��ʾAlphaֵ
    waitKey();

    //alpha���
    Mat in = imread("C:/Users/13441/Desktop/����ͼ��/a.png", -1); //ԭʼͼƬ
    Mat background = imread("C:/Users/13441/Desktop/����ͼ��/back.png", -1); //����ͼƬ
    Mat output(in.rows, in.cols, CV_8UC4); //���ͼƬ
    //cout << in.rows << "   " << in.cols << endl;
   // cout << background.rows << "   " << background.cols << endl;
    for (int i = 0; i < in.rows; i++)//�����ظ��ݱ����Dz��ǰ�ɫ�����ı���
    {
        for (int j = 0; j < in.cols; j++)
        {
            //cout << "get   " << i << "  " << j << endl;
            double alpha = in.at<Vec4b>(i, j)[3] / 255.0; //����Աȶ����������Dz��ǰ�ɫ
           // cout << "r   " << i << "  " << j <<"   "<<alpha<< endl;
            output.at<Vec4b>(i, j)[0] = (1 - alpha) * background.at<Vec4b>(i, j)[0] + alpha * in.at<Vec4b>(i, j)[0];
           // cout << "g   " << i << "  " << j << endl;
            output.at<Vec4b>(i, j)[1] = (1 - alpha) * background.at<Vec4b>(i, j)[1] + alpha * in.at<Vec4b>(i, j)[1];
            //cout << "b   " << i << "  " << j << endl;
            output.at<Vec4b>(i, j)[2] = (1 - alpha) * background.at<Vec4b>(i, j)[2] + alpha * in.at<Vec4b>(i, j)[2];
           // cout << "alpha   " << i << "  " << j << endl;
            output.at<Vec4b>(i, j)[3] = (1 - alpha) * background.at<Vec4b>(i, j)[3] + alpha * in.at<Vec4b>(i, j)[3];
           // cout << i << "  " << j << endl;
            continue;
        }
    }
    imshow("new_picture", output);
    waitKey();
    return 0;
}

实验1.2：对比度调整

设计一个Sigmoid函数，实现对象对比度调整，并使得调整幅度可通过参数控制。使用opencv窗口系统的slider控件，交互改变Sigmoid函数的参数，实现不同程度的对比度调整

#include <opencv2/opencv.hpp>  
#include <opencv2/core/core.hpp>  
#include <opencv2/highgui/highgui.hpp>  
#include <opencv2/imgproc.hpp>  
#include <iostream>  
#include <time.h>
using namespace std;
using namespace cv;

int alpha = 50; 
//ԭͼ����ͼ
Mat picture; 
Mat new_picture;

void change_alpha(int, void*)
{
    for (int i = 0; i < picture.rows; i++)
    {
        for (int j = 0; j < picture.cols; j++)
        {
            for (int k = 0; k < 3; k++)
            {
                double tmp = 255.0 / (1 + exp(-(alpha * 0.001 * 0.4) * (picture.at<Vec3b>(i, j)[k] - 127.5)));//�Աȶȼ���
                new_picture.at<Vec3b>(i, j)[k] = saturate_cast<uchar>(tmp);
            }
        }
    }
    imshow("New Image", new_picture);
    return;
}

int main()
{
    picture = imread("C:/Users/13441/Desktop/����ͼ��/b.png");
    new_picture = Mat::zeros(picture.size(), picture.type()); 
    namedWindow("Slider", WINDOW_AUTOSIZE);
    namedWindow("New Image", WINDOW_AUTOSIZE);
    createTrackbar("�Աȶȣ�", "Slider", &alpha, 100, change_alpha);
    change_alpha(alpha, 0);
    waitKey(0);
    return 0;
}