C#等比列放大缩小图片

      public Bitmap ChangeImgSize(Image bit, double Multiple)

        {

            Bitmap newBitmap = new Bitmap(Convert.ToInt32(bit.Width * Multiple), Convert.ToInt32(bit.Height * Multiple));

            Graphics g = Graphics.FromImage(newBitmap);

            g.Clear(Color.Transparent);

            //设置画布的描绘质量           

            g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;

            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;

            g.DrawImage(bit, new Rectangle(0, 0, newBitmap.Width, newBitmap.Height), 0, 0, bit.Width, bit.Height, GraphicsUnit.Pixel);

            g.Dispose();

            return newBitmap;

        }