C#压缩图片

1、使用System.Drawing库来压缩图片

using System.Drawing;
using System.Drawing.Imaging;
using System.IO;

    /// <summary>
    /// 压缩图片到目标大小，并覆盖原始图片
    /// </summary>
    /// <param name="imagePath">图片路径</param>
    /// <param name="targetSizeKb">目标大小（单位：KB）</param>
    public static void CompressImage(string imagePath, int targetSizeKb)
    {
        using (var originalImage = Image.FromFile(imagePath))
        {
            // 尝试不同的质量因子进行压缩
            for (int quality = 90; quality > 10; quality -= 5)
            {
                using (var ms = new MemoryStream())
                {
                    // 设置压缩参数
                    var encoderParameters = new EncoderParameters(1);
                    encoderParameters.Param[0] = new EncoderParameter(Encoder.Quality, quality);
                    var codec = GetEncoder(ImageFormat.Jpeg);

                    // 保存图片到内存流中
                    originalImage.Save(ms, codec, encoderParameters);

                    // 如果达到目标大小，则保存并覆盖原图
                    if (ms.Length <= targetSizeKb * 1024)
                    {
                        File.WriteAllBytes(imagePath, ms.ToArray());
                        Console.WriteLine($"压缩成功：{imagePath} (新大小: {ms.Length / 1024} KB)");
                        return;
                    }
                }
            }
            Console.WriteLine($"无法将图片压缩到 {targetSizeKb} KB 以下：{imagePath}");
        }
    }

    /// <summary>
    /// 获取指定格式的图片编码器
    /// </summary>
    /// <param name="format">图片格式</param>
    /// <returns>图片编码器</returns>
    static ImageCodecInfo GetEncoder(ImageFormat format)
    {
        return ImageCodecInfo.GetImageDecoders().FirstOrDefault(codec => codec.FormatID == format.Guid);
    }

2、使用SixLabors.ImageSharp压缩图片

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Formats.Jpeg;
using SixLabors.ImageSharp.Processing;
using System.IO;

    public static void CompressImage(string imagePath, int targetSizeKb)
    {
        using (var image = Image.Load(imagePath))
        {
            int quality = 75;

            for (; quality >= 10; quality -= 5)
            {
                using (var ms = new MemoryStream())
                {
                    var encoder = new JpegEncoder { Quality = quality };
                    image.Save(ms, encoder);

                    if (ms.Length <= targetSizeKb * 1024)
                    {
                        File.WriteAllBytes(imagePath, ms.ToArray());
                        Console.WriteLine($"压缩成功：{imagePath} (新大小: {ms.Length / 1024} KB)");
                        return;
                    }
                }
            }

            Console.WriteLine($"无法将图片压缩到 {targetSizeKb} KB 以下：{imagePath}");
        }

3、

 public static bool CompressImage(Stream stream, string dFile, int flag = 90, int size = 300, bool sfsc = true)
 {
     using (Image iSource = Image.FromStream(stream))
     {
         ImageFormat tFormat = iSource.RawFormat;
         int dHeight = iSource.Height / 2;
         int dWidth = iSource.Width / 2;
         int sW = 0, sH = 0;
         //按比例缩放
         Size tem_size = new Size(iSource.Width, iSource.Height);
         if (tem_size.Width > dHeight || tem_size.Width > dWidth)
         {
             if ((tem_size.Width * dHeight) > (tem_size.Width * dWidth))
             {
                 sW = dWidth;
                 sH = (dWidth * tem_size.Height) / tem_size.Width;
             }
             else
             {
                 sH = dHeight;
                 sW = (tem_size.Width * dHeight) / tem_size.Height;
             }
         }
         else
         {
             sW = tem_size.Width;
             sH = tem_size.Height;
         }

         Bitmap ob = new Bitmap(dWidth, dHeight);
         Graphics g = Graphics.FromImage(ob);

         g.Clear(Color.WhiteSmoke);
         g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
         g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
         g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;

         g.DrawImage(iSource, new Rectangle((dWidth - sW) / 2, (dHeight - sH) / 2, sW, sH), 0, 0, iSource.Width, iSource.Height, GraphicsUnit.Pixel);

         g.Dispose();

         //以下代码为保存图片时，设置压缩质量
         EncoderParameters ep = new EncoderParameters();
         long[] qy = new long[1];
         qy[0] = flag;//设置压缩的比例1-100
         EncoderParameter eParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qy);
         ep.Param[0] = eParam;

         try
         {
             ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
             ImageCodecInfo jpegICIinfo = null;
             for (int x = 0; x < arrayICI.Length; x++)
             {
                 if (arrayICI[x].FormatDescription.Equals("JPEG"))
                 {
                     jpegICIinfo = arrayICI[x];
                     break;
                 }
             }
             if (jpegICIinfo != null)
             {
                 ob.Save(dFile, jpegICIinfo, ep);//dFile是压缩后的新路径
                 FileInfo fi = new FileInfo(dFile);
                 if (fi.Length > 1024 * size)
                 {
                     flag = flag - 10;
                     CompressImage(stream, dFile, flag, size, false);
                 }
             }
             else
             {
                 ob.Save(dFile, tFormat);
             }
             return true;
         }
         catch
         {
             return false;
         }
         finally
         {
             iSource.Dispose();
             ob.Dispose();
         }
     }
 }