OpenCV图像编解码实战：JPEG与PNG压缩详解

OpenCV图像编解码实战：JPEG与PNG压缩详解

引用

CSDN

1.

https://blog.csdn.net/chengkun183/article/details/37580751

本文是一篇关于使用OpenCV进行JPEG和PNG图像编解码的教程文章，使用的是OpenCV 2.4.8版本。虽然当前OpenCV已经更新到4.x系列，但本文的代码和原理仍然具有参考价值。读者在实际使用时需要注意API的变化。

代码示例

源码来自：https://code.google.com/p/opencvjp-sample/source/browse/trunk/cpp/encode_decode_test.cpp?r=63

描述：描述读取一张图片进行jpg和png压缩，并解压显示。

主要函数：imencode和imdecode。

环境：windows7+vs2010+opencv2.4.8。

工程地址：http://download.csdn.net/detail/chengkun183/7609491

// JPEGDecodeEncode.cpp : 定义控制台应用程序的入口点。

#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <cv.h>
#include <highgui.h>
using namespace std;
using namespace cv;

double getPSNR(Mat& src1, Mat& src2, int bb=0);

int main(int argc, char** argv)
{
    Mat src = imread("lena.png");
    cout<<"origin image size: "<<src.dataend-src.datastart<<endl;
    cout<<"height: "<<src.rows<<endl<<"width: "<<src.cols<<endl<<"depth: "<<src.channels()<<endl;
    cout<<"height*width*depth: "<<src.rows*src.cols*src.channels()<<endl<<endl;
    //(1) jpeg compression
    vector<uchar> buff;//buffer for coding
    vector<int> param = vector<int>(2);
    param[0]=CV_IMWRITE_JPEG_QUALITY;
    param[1]=95;//default(95) 0-100

    imencode(".jpg",src,buff,param);
    cout<<"coded file size(jpg): "<<buff.size()<<endl;//fit buff size automatically.
    Mat jpegimage = imdecode(Mat(buff),CV_LOAD_IMAGE_COLOR);

    //(2) png compression
    param[0]=CV_IMWRITE_PNG_COMPRESSION;
    param[1]=3;//default(3)  0-9.
    imencode(".png",src,buff,param);
    cout<<"coded file size(png): "<<buff.size()<<endl;
    Mat pngimage = imdecode(Mat(buff),CV_LOAD_IMAGE_COLOR);

    //(3) intaractive jpeg compression
    char name[64];
    namedWindow("jpg");
    int q=95;
    createTrackbar("quality","jpg",&q,100);
    int key = 0;
    while(key!='q')
    {
        param[0]=CV_IMWRITE_JPEG_QUALITY;
        param[1]=q;
        imencode(".jpg",src,buff,param);
        Mat show = imdecode(Mat(buff),CV_LOAD_IMAGE_COLOR);

        double psnr = getPSNR(src,show);//get PSNR
        double bpp = 8.0*buff.size()/(show.size().area());//bit/pixe;
        sprintf(name,"quality:%03d, %.1fdB, %.2fbpp",q,psnr,bpp);
        putText(show,name,Point(15,50), FONT_HERSHEY_SIMPLEX,1,CV_RGB(255,255,255),2);
        imshow("jpg",show);
        key = waitKey(33);

        if(key =='s')
        {
            //(4) data writing 
            sprintf(name,"q%03d_%.2fbpp.png",q,bpp);
            imwrite(name,show);

            sprintf(name,"q%03d_%.2fbpp.jpg",q,bpp);
            param[0]=CV_IMWRITE_JPEG_QUALITY;
            param[1]=q;
            imwrite(name,src,param);;
        }
    }
}
double getPSNR(Mat& src1, Mat& src2, int bb)
{
    int i,j;
    double sse,mse,psnr;
    sse = 0.0;

    Mat s1,s2;
    cvtColor(src1,s1,CV_BGR2GRAY);
    cvtColor(src2,s2,CV_BGR2GRAY);

    int count=0;
    for(j=bb;j<s1.rows-bb;j++)
    {
        uchar* d=s1.ptr(j);
        uchar* s=s2.ptr(j);

        for(i=bb;i<s1.cols-bb;i++)
        {
            sse += ((d[i] - s[i])*(d[i] - s[i]));
            count++;
        }
    }
    if(sse == 0.0 || count==0)
    {
        return 0;
    }
    else
    {
        mse =sse /(double)(count);
        psnr = 10.0*log10((255*255)/mse);
        return psnr;
    }
}

使用的图片为lena.png:

输出的信息：