opencv 遍历图片像素并生成新图片（两种方式对比）

来源：互联网发布：美国动画专业知乎编辑：程序博客网时间：2024/05/17 06:13

由于图片尺寸过大，对图像进行resize处理用到的各种差值方法比较耗费时间，于是手动将图片缩小，每8*8个像素取一个点组成新的图片。主要考虑两种方式，第一种at方法取图像中的点的用法：image.at<uchar>(i,j)：取出灰度图像中i行j列的点；image.at<Vec3b>(i,j)[k]：取出三通道图像中的某一通道对应的值。第二种(明显较为高效):image.ptr<uchar>(i)。

#include <stdio.h>#include <opencv.hpp>#include <cxcore.h>#include <iostream>using namespace cv;using namespace std;int main(){    double t = getTickCount();    Mat src = imread("test.bmp", 0);    t = double(getTickCount() - t) * 1000 / getTickFrequency();    cout << "the load src pic time is " << t << "ms" << endl;    //double t00 = getTickCount();//start    //int nr = src.rows;    //int nc = src.cols;    //Mat img_src(cv::Size(nc / 8, nr / 8), CV_8U);    //for (int i = 1; i < nr / 8; i++){    //  for (int j = 1; j < nc / 8; j++){    //      img_src.at<uchar>(i, j) = src.at<uchar>(8 * i , 8 * j);    //  }    //}    //t00 = double(getTickCount() - t00) * 1000 / getTickFrequency();    //cout << "the test time=" << t00 << "ms" << endl;//end    ///*Mat img_src(cv::Size((nc + 1) / 3,(nr + 1) / 3),CV_8U);    //for (int i=1; i < (nr + 1) / 3; i++){    //  for (int j=1; j < (nc + 1) / 3; j++){    //      img_src.at<uchar>(i, j) = src.at<uchar>(3 * i - 1, 3 * j - 1);    //  }    //}*/    double t00 = getTickCount();//start    int nr = src.rows;    int nc = src.cols;    Mat img_src(cv::Size(nc / 8, nr / 8), CV_8U);    for (int i = 1; i < nr / 8; i++){        //取出原始图像中8*i行的指针，对应新的图像中的out指针        const uchar*inData = src.ptr<uchar>(8*i);        uchar*outData = img_src.ptr<uchar>(i);        for (int j = 1; j < nc / 8; j++){            outData[j] = inData[8*j];        }    }    t00 = double(getTickCount() - t00) * 1000 / getTickFrequency();    cout << "the test time=" << t00 << "ms" << endl;//end    imshow("the resized img", img_src);    //fast detect cornors    //Mat src_copy = src.clone();    double t_fast = getTickCount();    vector<cv::KeyPoint>keypoints;    cv::FastFeatureDetector fast(40, true);    fast.detect(img_src, keypoints);    drawKeypoints(img_src, keypoints, img_src, cv::Scalar::all(255), cv::DrawMatchesFlags::DRAW_OVER_OUTIMG);    t_fast = double(getTickCount() - t_fast) * 1000 / getTickFrequency();    cout << "the fast detect corners time = " << t_fast << "ms" << endl;    cout << "the keypoints size=" << keypoints.size() << endl;    //resize(src, src, cv::Size(0.5*src.cols, 0.5*src.rows));    imshow("corners", img_src);    waitKey();}

第一种image.at(i,j)：用时431ms。
第二种image.ptr(i)：用时9.6ms。

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