（24）像素重映射

所谓的像素重映射就是：我们对原图的每一个像素值进行提取，然后经过一个函数变换，映射到我们空白的目标图片上，就得到一张新的图片，这个就是像素重映射。具体的基础知识，看这个博客：https://blog.csdn.net/qq_41167777/article/details/84947439

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下面这个代码运行，有好几种结果，主要就是，你按下 1，2，3，0，等等，会出现不同的图片展示。

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

Mat src, dst, map_x, map_y;
const char* input_win = "input";
int index = 0;
const char* out_put = "hough-line-detection";
void update_map(void);
int main(int agrc, char** agrv) {
    src = imread("C:\Users\32829\Desktop\111.jpg");
    if (!src.data) {
        printf("no load..
");
        return -1;
    }
    namedWindow(input_win, CV_WINDOW_AUTOSIZE);
    namedWindow(out_put, CV_WINDOW_AUTOSIZE);
    imshow(input_win, src);
    map_x.create(src.size(), CV_32FC1);
    map_y.create(src.size(), CV_32FC1);
    int c = 0;
    while (true) {
        c = waitKey(500);
        if ((char)c == 27) {
            break;
        }
        index = c % 4;
        update_map();
        remap(src, dst, map_x, map_y, CV_INTER_LINEAR, BORDER_CONSTANT, Scalar(0, 255, 255));
        imshow(out_put, dst);
    }
}
void update_map(void) {
    for (int row = 0; row < src.rows; row++) {
        for (int col = 0; col < src.cols; col++) {
            switch (index) {
            case 0:
                if (col > (src.cols*0.25) && col<(src.cols*0.75) && row>(src.rows*0.25) && row < (src.rows*0.75)) {
                    map_x.at<float>(row, col) = 2 * (col - (src.cols*0.25));
                    map_y.at<float>(row, col) = 2 * (row - (src.rows*0.25));
                }
                else {
                    map_x.at<float>(row, col) = 0;
                    map_y.at<float>(row, col) = 0;
                }
                break;
            case 1:
                map_x.at<float>(row, col) = (src.cols - col - 1);
                map_y.at<float>(row, col) = row;
                break;
            case 2:
                map_x.at<float>(row, col) = col;
                map_y.at<float>(row, col) = (src.rows - row - 1);
                break;
            case 3:
                map_x.at<float>(row, col) = (src.cols - col - 1);
                map_y.at<float>(row, col) = (src.rows - row - 1);
                break;
            }
        }
    }
}