ASP.NET 你肯定会用到的图片裁剪功能，可按长度或宽度裁剪，也能绘制一个更大图

以下包括3个功能，

1.按照长度裁剪

2.按照宽度裁剪

3.不用裁剪，直接生成一张大图，把原图包含进去

以上功能不会影响图片质量，这个也是一个亮点

public class UploadPicCut
    {
        /// <summary>
        /// 计算图片大小
        /// </summary>
        /// <param name="maxWidth"></param>
        /// <param name="maxHeight"></param>
        /// <param name="width"></param>
        /// <param name="height"></param>
        /// <returns></returns>
        public Size NewSize(int maxWidth, int maxHeight, int width, int height)
        {
            double w = 0.0;
            double h = 0.0;
            double sw = Convert.ToDouble(width);
            double sh = Convert.ToDouble(height);
            double mw = Convert.ToDouble(maxWidth);
            double mh = Convert.ToDouble(maxHeight);

            if (sw < mw && sh < mh)
            {
                w = sw;
                h = sh;
            }
            else if ((sw / sh) > (mw / mh))
            {
                w = maxWidth;
                h = (w * sh) / sw;
            }
            else
            {
                h = maxHeight;
                w = (h * sw) / sh;
            }

            return new Size(Convert.ToInt32(w), Convert.ToInt32(h));
        }

        /// <summary>
        /// 按最大长宽裁剪
        /// </summary>
        /// <param name="fileName"></param>
        /// <param name="SavaFile"></param>
        /// <param name="maxWidth"></param>
        /// <param name="maxHeight"></param>
        public void SendSmallImage(string fileName,string SavaFile ,int maxWidth, int maxHeight)
        {
            System.Drawing.Image img = System.Drawing.Image.FromFile(System.Web.HttpContext.Current.Server.MapPath(fileName));
            System.Drawing.Imaging.ImageFormat thisFormat = img.RawFormat;

            Size newSize = NewSize(maxWidth, maxHeight, img.Width, img.Height);
            Bitmap outBmp = new Bitmap(newSize.Width, newSize.Height);
            Graphics g = Graphics.FromImage(outBmp);
            Color BgColor = Color.FromArgb(235, 235, 235);
            g.Clear(BgColor);
            // 设置画布的描绘质量
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;

            g.DrawImage(img, new Rectangle(0, 0, newSize.Width, newSize.Height),0, 0, img.Width, img.Height, GraphicsUnit.Pixel);
            g.Dispose();

            //if (thisFormat.Equals(ImageFormat.Gif))
            //{
            //    System.Web.HttpContext.Current.Response.ContentType = "image/gif";
            //}
            //else
            //{
            //    System.Web.HttpContext.Current.Response.ContentType = "image/jpeg";
            //}

            // 以下代码为保存图片时，设置压缩质量
            EncoderParameters encoderParams = new EncoderParameters();
            long[] quality = new long[1];
            quality[0] = 100;

            EncoderParameter encoderParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
            encoderParams.Param[0] = encoderParam;

            //获得包含有关内置图像编码解码器的信息的ImageCodecInfo 对象。
            ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
            ImageCodecInfo jpegICI = null;
            for (int x = 0; x < arrayICI.Length; x++)
            {
                if (arrayICI[x].FormatDescription.Equals("JPEG"))
                {
                    jpegICI = arrayICI[x];//设置JPEG编码
                    break;
                }
            }

            if (jpegICI != null)
            {
                outBmp.Save(System.Web.HttpContext.Current.Server.MapPath(SavaFile), jpegICI, encoderParams);
            }
            else
            {
                outBmp.Save(System.Web.HttpContext.Current.Server.MapPath(SavaFile), thisFormat);
            }

            img.Dispose();
            outBmp.Dispose();
        }

        /// <summary>
        /// 按最大长宽裁剪
        /// </summary>
        /// <param name="fileName"></param>
        /// <param name="SavaFile"></param>
        /// <param name="maxWidth"></param>
        /// <param name="maxHeight"></param>
        public void SaveToBig(string fileName, string SavaFile, int ToWidth, int ToHeight)
        {
            System.Drawing.Image img = System.Drawing.Image.FromFile(System.Web.HttpContext.Current.Server.MapPath(fileName));
            System.Drawing.Imaging.ImageFormat thisFormat = img.RawFormat;
            Bitmap outBmp = new Bitmap(ToWidth, ToHeight);
            Graphics g = Graphics.FromImage(outBmp);
            Color BgColor = Color.FromArgb(235, 235, 235);
            g.Clear(BgColor);
            // 设置画布的描绘质量
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
           

            g.DrawImage(img, 0, 0, ToWidth, ToHeight);
            g.Dispose();

            // 以下代码为保存图片时，设置压缩质量
            EncoderParameters encoderParams = new EncoderParameters();
            long[] quality = new long[1];
            quality[0] = 100;

            EncoderParameter encoderParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
            encoderParams.Param[0] = encoderParam;

            //获得包含有关内置图像编码解码器的信息的ImageCodecInfo 对象。
            ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
            ImageCodecInfo jpegICI = null;
            for (int x = 0; x < arrayICI.Length; x++)
            {
                if (arrayICI[x].FormatDescription.Equals("JPEG"))
                {
                    jpegICI = arrayICI[x];//设置JPEG编码
                    break;
                }
            }

            if (jpegICI != null)
            {
                outBmp.Save(System.Web.HttpContext.Current.Server.MapPath(SavaFile), jpegICI, encoderParams);
            }
            else
            {
                outBmp.Save(System.Web.HttpContext.Current.Server.MapPath(SavaFile), thisFormat);
            }

            img.Dispose();
            outBmp.Dispose();
        }

        /// <summary>
        /// 绘成更大的图片
        /// </summary>
        /// <param name="fileName"></param>
        /// <param name="SavaFile"></param>
        /// <param name="maxWidth"></param>
        /// <param name="maxHeight"></param>
        public void SendSmallImageB(string fileName, string SavaFile, int maxWidth, int maxHeight, int FromX, int FromY)
        {
            System.Drawing.Image img = System.Drawing.Image.FromFile(System.Web.HttpContext.Current.Server.MapPath(fileName));
            System.Drawing.Imaging.ImageFormat thisFormat = img.RawFormat;

            //Size newSize = NewSize(maxWidth, maxHeight, img.Width, img.Height);
            //Bitmap outBmp = new Bitmap(newSize.Width, newSize.Height);
            Bitmap outBmp = new Bitmap(maxWidth, maxHeight);
            Graphics g = Graphics.FromImage(outBmp);
            Color BgColor = Color.FromArgb(235, 235, 235);
            g.Clear(BgColor);
            // 设置画布的描绘质量
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;

            g.DrawImage(img, new Rectangle(FromX, FromY, img.Width+2*FromX, img.Height+2*FromY), 0, 0, maxWidth, maxHeight, GraphicsUnit.Pixel);
            //g.DrawImage(img, new Rectangle(FromX, FromY, newSize.Width, newSize.Height),0, 0, img.Width, img.Height, GraphicsUnit.Pixel);
            g.Dispose();

            //if (thisFormat.Equals(ImageFormat.Gif))
            //{
            //    System.Web.HttpContext.Current.Response.ContentType = "image/gif";
            //}
            //else
            //{
            //    System.Web.HttpContext.Current.Response.ContentType = "image/jpeg";
            //}

            // 以下代码为保存图片时，设置压缩质量
            EncoderParameters encoderParams = new EncoderParameters();
            long[] quality = new long[1];
            quality[0] = 100;

            EncoderParameter encoderParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
            encoderParams.Param[0] = encoderParam;

            //获得包含有关内置图像编码解码器的信息的ImageCodecInfo 对象。
            ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
            ImageCodecInfo jpegICI = null;
            for (int x = 0; x < arrayICI.Length; x++)
            {
                if (arrayICI[x].FormatDescription.Equals("JPEG"))
                {
                    jpegICI = arrayICI[x];//设置JPEG编码
                    break;
                }
            }

            if (jpegICI != null)
            {
                outBmp.Save(System.Web.HttpContext.Current.Server.MapPath(SavaFile), jpegICI, encoderParams);
            }
            else
            {
                outBmp.Save(System.Web.HttpContext.Current.Server.MapPath(SavaFile), thisFormat);
            }

            img.Dispose();
            outBmp.Dispose();
        }
    }