C# System.Drawing.Graphics 畫圖后，如何保存一個低質量的圖片，一個占用空間較小的圖片

首先要控制圖片保存后硬盤后的大小（即占用硬盤的空間，而非尺寸），真正要處理的是控制 System.Drawing.Bitmap.Save 方法的參數。

 

具體實現如下：

private void ThumbPicture(Image SourceImage, int TargetWidth,string savePath)
        {
            int IntWidth; //新的圖片寬  
            int IntHeight; //新的圖片高  
            try
            {
                int TargetHeight = (int)Math.Round(TargetWidth / (SourceImage.Width * 1.0f / SourceImage.Height));
                if (TargetWidth * TargetHeight >= SourceImage.Width * SourceImage.Height)
                {
                    SourceImage.Save(savePath);
                    SourceImage.Dispose();
                    return;
                }
                //計算縮放圖片的大小  
                if (SourceImage.Width > TargetWidth && SourceImage.Height <= TargetHeight)//寬度比目的圖片寬度大，長度比目的圖片長度小  
                {
                    IntWidth = TargetWidth;
                    IntHeight = (IntWidth * SourceImage.Height) / SourceImage.Width;
                }
                else if (SourceImage.Width <= TargetWidth && SourceImage.Height > TargetHeight)//寬度比目的圖片寬度小，長度比目的圖片長度大  
                {
                    IntHeight = TargetHeight;
                    IntWidth = (IntHeight * SourceImage.Width) / SourceImage.Height;
                }
                else if (SourceImage.Width <= TargetWidth && SourceImage.Height <= TargetHeight) //長寬比目的圖片長寬都小  
                {
                    IntHeight = SourceImage.Width;
                    IntWidth = SourceImage.Height;
                }
                else//長寬比目的圖片的長寬都大  
                {
                    IntWidth = TargetWidth;
                    IntHeight = (IntWidth * SourceImage.Height) / SourceImage.Width;
                    if (IntHeight > TargetHeight)//重新計算  
                    {
                        IntHeight = TargetHeight;
                        IntWidth = (IntHeight * SourceImage.Width) / SourceImage.Height;
                    }
                }

                var x = (TargetWidth - IntWidth) / 2;
                var y = (TargetHeight - IntHeight) / 2;

                using (var newImage = new Bitmap(TargetWidth, TargetHeight))
                {
                    using (var graphic = Graphics.FromImage(newImage))
                    {
　　　　　　　　　　　　　　// 核心參數啊，感覺相當於PS保存時間的質量設置參數
                        Int64 qualityLevel = 80L;

                        // 高質量
                        graphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                        graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
                        graphic.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
                        qualityLevel = 100L;

                        // 低質量
                        //graphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                        //graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.Low;
                        //graphic.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighSpeed;
                        //qualityLevel = 60L;

                        System.Drawing.Imaging.ImageCodecInfo codec = System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders()[1];
                        System.Drawing.Imaging.EncoderParameters eParams = new System.Drawing.Imaging.EncoderParameters(1);
                        eParams.Param[0]=new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qualityLevel);

                        graphic.DrawImage(SourceImage, 0, 0, TargetWidth, TargetHeight);
                        SourceImage.Dispose();

                        // 使用控制圖片質量的保存方式
                        //newImage.Save(savePath);
                        newImage.Save(savePath, codec, eParams);
                    }
                }
            }
            catch (Exception ex)
            {

            }
        }