改变图片分辨率

/// <summary>
        /// 更改背景图片的分辨率
        /// </summary>
        /// <param name="bmp"></param>
        /// <param name="newW"></param>
        /// <param name="newH"></param>
        /// <returns></returns>
        private Bitmap ResizeImage(Image bmp, int newW, int newH)
        {
            try
            {
                Bitmap b = new Bitmap(newW, newH);
                Graphics g = Graphics.FromImage(b);
                // 插值算法的质量
                g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                g.DrawImage(bmp, new Rectangle(0, 0, newW, newH), new Rectangle(0, 0, bmp.Width, bmp.Height), GraphicsUnit.Pixel);
                g.Dispose();
                return b;
            }
            catch
            {
                return null;
            }

        }