private static ImageCodecInfo GetImageCodecInfo(ImageFormat imageFormat)

{

    ImageCodecInfo[] imageCodecInfoArr = ImageCodecInfo.GetImageDecoders();

    foreach (ImageCodecInfo imageCodecInfo in imageCodecInfoArr)

    {

        if (imageCodecInfo.FormatID == imageFormat.Guid)

        {

            return imageCodecInfo;

        }

    }

    return null;

}

MemoryStream ms = HttpUtil.HttpDownloadFile(url);

Bitmap bmp = new Bitmap(ms);

EncoderParameters encoderParameters = new EncoderParameters();

EncoderParameter encoderParameter = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 75L);

encoderParameters.Param[] = encoderParameter;

MemoryStream msCompress = new MemoryStream();

bmp.Save(msCompress, GetImageCodecInfo(ImageFormat.Jpeg), encoderParameters);

Bitmap bmpCompress = new Bitmap(msCompress);

bmpCompress.Save(path);

bmp.Save(path2);

msCompress.Close();

ms.Close();

using System;

using System.Collections.Generic;

using System.Drawing;

using System.Drawing.Drawing2D;

using System.Drawing.Imaging;

using System.IO;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace SunCreate.Common.ComLib

{

    /// <summary>

    /// 图片缩放

    /// </summary>

    public class ZoomImageUtil

    {

        #region 图片缩放

        /// <summary>

        /// 图片缩放

        /// </summary>

        /// <param name="bArr">图片字节流</param>

        /// <param name="width">目标宽度，若为0，表示宽度按比例缩放</param>

        /// <param name="height">目标长度，若为0，表示长度按比例缩放</param>

        public static byte[] GetThumbnail(byte[] bArr, int width, int height)

        {

            if (bArr == null) return null;

            MemoryStream ms = new MemoryStream(bArr);

            Bitmap bmp = (Bitmap)Image.FromStream(ms);

            ms.Close();

            bmp = GetThumbnail(bmp, width, height);

            ImageCodecInfo imageCodecInfo = GetEncoder(ImageFormat.Jpeg);

            EncoderParameters encoderParameters = new EncoderParameters();

            EncoderParameter encoderParameter = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 75L);

            encoderParameters.Param[] = encoderParameter;

            ms = new MemoryStream();

            bmp.Save(ms, imageCodecInfo, encoderParameters);

            byte[] result = ms.ToArray();

            ms.Close();

            bmp.Dispose();

            return result;

        }

        #endregion

        #region 图片缩放

        /// <summary>

        /// 图片缩放

        /// </summary>

        /// <param name="bmp">图片</param>

        /// <param name="width">目标宽度，若为0，表示宽度按比例缩放</param>

        /// <param name="height">目标长度，若为0，表示长度按比例缩放</param>

        private static Bitmap GetThumbnail(Bitmap bmp, int width, int height)

        {

            if (width ==  && height == )

            {

                width = bmp.Width;

                height = bmp.Height;

            }

            else

            {

                if (width == )

                {

                    width = height * bmp.Width / bmp.Height;

                }

                if (height == )

                {

                    height = width * bmp.Height / bmp.Width;

                }

            }

            Image imgSource = bmp;

            Bitmap outBmp = new Bitmap(width, height);

            Graphics g = Graphics.FromImage(outBmp);

            g.Clear(Color.Transparent);

            // 设置画布的描绘质量

            g.CompositingQuality = CompositingQuality.Default;

            g.SmoothingMode = SmoothingMode.Default;

            g.InterpolationMode = InterpolationMode.Default;

            g.DrawImage(imgSource, new Rectangle(, , width, height + ), , , imgSource.Width, imgSource.Height, GraphicsUnit.Pixel);

            g.Dispose();

            imgSource.Dispose();

            bmp.Dispose();

            return outBmp;

        }

        #endregion

        #region 椭圆形缩放

        /// <summary>

        /// 椭圆形缩放

        /// </summary>

        /// <param name="bArr">图片字节流</param>

        /// <param name="width">目标宽度，若为0，表示宽度按比例缩放</param>

        /// <param name="height">目标长度，若为0，表示长度按比例缩放</param>

        public static byte[] GetEllipseThumbnail(byte[] bArr, int width, int height)

        {

            if (bArr == null) return null;

            MemoryStream ms = new MemoryStream(bArr);

            Bitmap bmp = (Bitmap)Image.FromStream(ms);

            Bitmap newBmp = new Bitmap(width, height);

            using (Graphics g = Graphics.FromImage(newBmp))

            {

                using (TextureBrush br = new TextureBrush(bmp))

                {

                    br.ScaleTransform(width / (float)bmp.Width, height / (float)bmp.Height);

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

                    g.FillEllipse(br, new Rectangle(Point.Empty, new Size(width, height)));

                }

            }

            MemoryStream newMs = new MemoryStream();

            newBmp.Save(newMs, System.Drawing.Imaging.ImageFormat.Png);

            byte[] result = newMs.ToArray();

            bmp.Dispose();

            newBmp.Dispose();

            ms.Close();

            newMs.Dispose();

            return result;

        }

        #endregion

        #region GetEncoder

        private static ImageCodecInfo GetEncoder(ImageFormat format)

        {

            ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();

            foreach (ImageCodecInfo codec in codecs)

            {

                if (codec.FormatID == format.Guid)

                {

                    return codec;

                }

            }

            return null;

        }

        #endregion

    }

}