opencv图片内存占用过大优化

        // 读取图片文件到内存
        std::ifstream file(img.toStdString(), std::ios::binary);
        std::vector<char> buffer((std::istreambuf_iterator<char>(file)), std::istreambuf_iterator<char>());
        cv::Mat image = cv::imdecode(cv::Mat(buffer), cv::IMREAD_COLOR);

        std::vector<uchar> result;
        cv::imencode(".png", image, result);
        std::ofstream os("test.png", std::ios::binary);
        os.write(reinterpret_cast<char*>(buffer.data()), buffer.size());