图像的创建和储存

#include <opencv.hpp>
#include <vector>
using namespace std;
using namespace cv;
void creatAlphaMat(Mat &mat) // 创建一个图像
{
	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);
	creatAlphaMat(mat);
	vector<int>compression_params;
	compression_params.push_back(IMWRITE_PNG_COMPRESSION);
	compression_params.push_back(9);
	try{
		imwrite("透明值图.png", mat, compression_params);
		imshow("生成的PNG图", mat);
		fprintf(stdout, "PNG图片文件的数据保存完毕");
		waitKey(0);
	}
	catch (runtime_error& ex){
		fprintf(stderr, "图像转换发生错误:%s\n", ex.what());
		return 1;
	}
	return 0;
}