opencv2

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>
using namespace cv;

int main()
{
Mat image0 = imread("E://3.jpg", 2 | 4);//载入无损的源图像
Mat image1 = imread("E://3.jpg", 0);//载入灰图像
Mat image2 = imread("E://3.jpg", 199);//载入三通道的彩色图像

imshow("0", image0);
imshow("1", image1);
imshow("2", image2);

waitKey(0);
}

/////////////////////////////////////////////////////opencv生成一幅png图片，并写入当前工程目录下
#include<opencv2/opencv.hpp>
#include<vector>

using namespace cv;
using namespace std;

void createAlphaMat(Mat &mat)
{
for (int i = 0; i < mat.rows; ++i) {
for (int j = 0; j < mat.cols; ++j) {
Vec4b&rgba = mat.at<Vec4b>(i, j);
rgba[0] = UCHAR_MAX;
rgba[1] = saturate_cast<uchar>((float(mat.cols - j)) / ((float)mat.cols) *UCHAR_MAX);
rgba[2] = saturate_cast<uchar>((float(mat.rows - i)) / ((float)mat.rows) *UCHAR_MAX);
rgba[3] = saturate_cast<uchar>(0.5 * (rgba[1] + rgba[2]));
}
}
}
int main()
{
//创建带alpha通道的Mat
Mat mat(480, 640, CV_8UC4);
createAlphaMat(mat);

vector<int>compression_params;
compression_params.push_back(CV_IMWRITE_PNG_COMPRESSION);
compression_params.push_back(9);
//显示图片
try{
imwrite("透明Alpha值图.png", mat, compression_params);
imshow("生成的png图", mat);
fprintf(stdout, "PNG图片文件的alpha数据保存完毕~ 可以在工程目录下查看由imwrite函数生成的图片 ");
waitKey(0);
}
catch (runtime_error& ex) {
fprintf(stderr, "图像转换成PNG格式发生错误：%s ", ex.what());
return 1;
}
return 0;
}