1.0 Python读取图片

import cv2
import sys,os

os.chdir(sys.path[0])                   #切换到当前路径

if __name__ =='__main__':
    img_path = "./img/test.jpg"         #定义图片的相对路径
    img = cv2.imread(img_path)          #读入图片
    cv2.imshow("img",img)               #显示图片
    cv2.waitKey(-1)                     #等待按键 不然显示不出来

2.0 C++读取图片

#include <iostream>
#include <opencv2\opencv.hpp>

using namespace std;
using namespace cv;

int main()
{
    string img_path = "./img/test.jpg";     //定义图片的相对路径
    Mat img = imread(img_path);             //读取图片
    imshow("img", img);                     //显示图片
    waitKey(-1);                            //等待按键 不然会一闪而过
    return 0;
}

3.0 运行结果

Python结果显示	C++结果显示

4.0 源码展示

Mat imread( const String& filename, int flags )

/**
 * Read an image
 *
 *  This function merely calls the actual implementation above and returns itself.
 *
 * @param[in] filename File to load
 * @param[in] flags Flags you wish to set.
*/
Mat imread( const String& filename, int flags )
{
    CV_TRACE_FUNCTION();

    /// create the basic container
    Mat img;

    /// load the data
    imread_( filename, flags, img );

    /// optionally rotate the data if EXIF' orientation flag says so
    if( !img.empty() && (flags & IMREAD_IGNORE_ORIENTATION) == 0 && flags != IMREAD_UNCHANGED )
    {
        ApplyExifOrientation(filename, img);
    }

    /// return a reference to the data
    return img;
}

static bool imread_( const String& filename, int flags, Mat& mat )

/**
 * Read an image into memory and return the information
 *
 * @param[in] filename File to load
 * @param[in] flags Flags
 * @param[in] hdrtype { LOAD_CVMAT=0,
 *                      LOAD_IMAGE=1,
 *                      LOAD_MAT=2
 *                    }
 * @param[in] mat Reference to C++ Mat object (If LOAD_MAT)
 *
*/
static bool
imread_( const String& filename, int flags, Mat& mat )
{
    /// Search for the relevant decoder to handle the imagery
    ImageDecoder decoder;

#ifdef HAVE_GDAL
    if(flags != IMREAD_UNCHANGED && (flags & IMREAD_LOAD_GDAL) == IMREAD_LOAD_GDAL ){
        decoder = GdalDecoder().newDecoder();
    }else{
#endif
        decoder = findDecoder( filename );
#ifdef HAVE_GDAL
    }
#endif

    /// if no decoder was found, return nothing.
    if( !decoder ){
        return 0;
    }

    int scale_denom = 1;
    if( flags > IMREAD_LOAD_GDAL )
    {
    if( flags & IMREAD_REDUCED_GRAYSCALE_2 )
        scale_denom = 2;
    else if( flags & IMREAD_REDUCED_GRAYSCALE_4 )
        scale_denom = 4;
    else if( flags & IMREAD_REDUCED_GRAYSCALE_8 )
        scale_denom = 8;
    }

    /// set the scale_denom in the driver
    decoder->setScale( scale_denom );

    /// set the filename in the driver
    decoder->setSource( filename );

    try
    {
        // read the header to make sure it succeeds
        if( !decoder->readHeader() )
            return 0;
    }
    catch (const cv::Exception& e)
    {
        std::cerr << "imread_('" << filename << "'): can't read header: " << e.what() << std::endl << std::flush;
        return 0;
    }
    catch (...)
    {
        std::cerr << "imread_('" << filename << "'): can't read header: unknown exception" << std::endl << std::flush;
        return 0;
    }


    // established the required input image size
    Size size = validateInputImageSize(Size(decoder->width(), decoder->height()));

    // grab the decoded type
    int type = decoder->type();
    if( (flags & IMREAD_LOAD_GDAL) != IMREAD_LOAD_GDAL && flags != IMREAD_UNCHANGED )
    {
        if( (flags & IMREAD_ANYDEPTH) == 0 )
            type = CV_MAKETYPE(CV_8U, CV_MAT_CN(type));

        if( (flags & IMREAD_COLOR) != 0 ||
           ((flags & IMREAD_ANYCOLOR) != 0 && CV_MAT_CN(type) > 1) )
            type = CV_MAKETYPE(CV_MAT_DEPTH(type), 3);
        else
            type = CV_MAKETYPE(CV_MAT_DEPTH(type), 1);
    }

    mat.create( size.height, size.width, type );

    // read the image data
    bool success = false;
    try
    {
        if (decoder->readData(mat))
            success = true;
    }
    catch (const cv::Exception& e)
    {
        std::cerr << "imread_('" << filename << "'): can't read data: " << e.what() << std::endl << std::flush;
    }
    catch (...)
    {
        std::cerr << "imread_('" << filename << "'): can't read data: unknown exception" << std::endl << std::flush;
    }
    if (!success)
    {
        mat.release();
        return false;
    }

    if( decoder->setScale( scale_denom ) > 1 ) // if decoder is JpegDecoder then decoder->setScale always returns 1
    {
        resize( mat, mat, Size( size.width / scale_denom, size.height / scale_denom ), 0, 0, INTER_LINEAR_EXACT);
    }

    return true;
}

5.0 往期回顾

• Opencv等比缩放图片 C++ | Python