效果图：

 

 

核心代码：

/// 
        /// 等比例缩放图片        /// 
        ///         ///         ///         /// 
             private static Bitmap ZoomImage(Bitmap bitmap, int destWidth, int destHeight)        {            try            {                Image sourImage = bitmap;                int width = 0, height = 0;                //按比例缩放                           int sourWidth = sourImage.Width;                int sourHeight = sourImage.Height;                if (sourHeight > destHeight || sourWidth > destWidth)                {                    if ((sourWidth * destHeight) > (sourHeight * destWidth))                    {                        width = destWidth;                        height = (destWidth * sourHeight) / sourWidth;                    }                    else                    {                        height = destHeight;                        width = (sourWidth * destHeight) / sourHeight;                    }                }                else                {                    width = sourWidth;                    height = sourHeight;                }                Bitmap destBitmap = new Bitmap(destWidth, destHeight);                Graphics g = Graphics.FromImage(destBitmap);                g.Clear(Color.Transparent);                //设置画布的描绘质量                         g.CompositingQuality = CompositingQuality.HighQuality;                g.SmoothingMode = SmoothingMode.HighQuality;                g.InterpolationMode = InterpolationMode.HighQualityBicubic;                //g.DrawImage(sourImage, new Rectangle((destWidth - width) / 2, (destHeight - height) / 2, width, height), 0, 0, sourImage.Width, sourImage.Height, GraphicsUnit.Pixel);                g.DrawImage(sourImage, new Rectangle(12, 0, width, height), 0, 0, sourImage.Width, sourImage.Height, GraphicsUnit.Pixel);                g.Dispose();                //设置压缩质量                     System.Drawing.Imaging.EncoderParameters encoderParams = new System.Drawing.Imaging.EncoderParameters();                long[] quality = new long[1];                quality[0] = 100;                System.Drawing.Imaging.EncoderParameter encoderParam = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);                encoderParams.Param[0] = encoderParam;                sourImage.Dispose();                return destBitmap;            }            catch            {                return bitmap;            }        }

　　

 

Demo下载：