索引图-查表-颜色缩减

// https://docs.opencv.org/3.2.0/d2/de8/group__core__array.html#gab55b8d062b7f5587720ede032d34156f

//其实就是颜色缩减，索引图
#include<opencv2/opencv.hpp>

using namespace cv;

int main()
{
    //<1> 构建一个Mat 表
    Mat look_up_table(1, 256, CV_8U);
    for (int i = 0; i < 256; i++)
    {
        look_up_table.ptr<uchar>(0)[i] = 10 * (i / 10);
    }
    //<2> 利用LUT函数查找
    Mat srcImage = imread("lena.jpg", -1);
    Mat dstImage;
    LUT(srcImage, look_up_table, dstImage);
    imshow("look_up_table", look_up_table);
    namedWindow("srcImage", WINDOW_NORMAL);
    imshow("srcImage", srcImage);
    namedWindow("dstImage", WINDOW_NORMAL);
    imshow("dstImage", dstImage);
    waitKey(0);
    return 1;
}

其实就是一句话概括如下：（类似于统计直方图）

dstImage.ptr<uchar>(y)[x] = look_up_table[0][dstImage.ptr<uchar>(y)[x]];