【OpenCV：從零到一】16：像素重映射

前言
這是我《OpenCV：從零到一》專欄的第十六篇博客，想看跟多請戳這。
本文概要
remap
at
案例代碼
大概內容：像素重映射 。

#include <opencv2/opencv.hpp>
#include <iostream>
#include <math.h>

using namespace cv;
Mat src, dst, map_x, map_y;
const char* OUTPUT_TITLE = "remap demo";
int index = 0;
void update_map(void);
int main(int argc, char** argv) {
	src = imread("D:/86186/Documents/opencv/lena.jpg");
	if (!src.data) {
		printf("could not load image...\n");
		return -1;
	}
	char input_win[] = "input image";
	namedWindow(input_win, WINDOW_AUTOSIZE);
	namedWindow(OUTPUT_TITLE, 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;//防止輸入出現非0-3的情況
		update_map();
		remap(src, dst, map_x, map_y, INTER_LINEAR, BORDER_CONSTANT, Scalar(255, 255, 255));
		/*
		InputArray src,// 輸入圖像
		OutputArray dst,// 輸出圖像
		InputArray  map1,// x 映射表 CV_32FC1/CV_32FC2
		InputArray map2,// y 映射表
		int interpolation,// 選擇的插值方法，常見線性插值，可選擇立方等
		int borderMode,// BORDER_CONSTANT
		const Scalar borderValue// color
		*/
		imshow(OUTPUT_TITLE, dst);
	}

	return 0;
}

void update_map(void) {
	for (int row = 0; row < src.rows; row++) {
		for (int col = 0; col < src.cols; col++) {
			switch (index) {
			case 0://縮小一半
				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://y方向對調
				map_x.at<float>(row, col) = (src.cols - col - 1);
				map_y.at<float>(row, col) = row;
				break;
			case 2://x方向對調
				map_x.at<float>(row, col) = col;
				map_y.at<float>(row, col) = (src.rows - row - 1);
				break;
			case 3://xy方向對調
				map_x.at<float>(row, col) = (src.cols - col - 1);
				map_y.at<float>(row, col) = (src.rows - row - 1);
				break;
			}

		}
	}
}

運行效果:

解析及注意事項
dst(x,y)=src(mapx(x,y),mapy(x,y))
Due to current implementation limitations the size of an input and output images should be less than 32767x32767.
插值的方式有很多種，常用的有線性插值