Qt Qimage 读取bmp后转JPG

QImage img(buf, width, height, QImage::Format_RGB888);
            char cPath[2048] = {0};
            getcwd(cPath, 2048);
            sprintf(cPath + strlen(cPath), "/%d.jpg", cameraId);
            QMatrix matrix;
            matrix.rotate(180);
            QImage img_1 = img.transformed(matrix);
            img_1.save(cPath, "JPEG");