这个是未经优化的简单实现

public static System.Drawing.Image GetImageThumb(System.Drawing.Image sourceImg, int width, int height)

{

System.Drawing.Image targetImg = new System.Drawing.Bitmap(width, height);

using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(targetImg))

{

g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

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

g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;

g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;

g.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;

g.DrawImage(sourceImg, new System.Drawing.Rectangle(0, 0, width, height), new System.Drawing

.Rectangle(0, 0, sourceImg.Width, sourceImg.Height), System.Drawing.GraphicsUnit.Pixel);

g.Dispose();

}

return targetImg;

}

这个方法比较简单，用到的是高质量压缩。经过这个方法压缩后，200K的图片只能压缩到160k左右。

经过改写代码实现了如下的方法

public Bitmap GetImageThumb(Bitmap mg, Size newSize)

{

double ratio = 0d;

double myThumbWidth = 0d;

double myThumbHeight = 0d;

int x = 0;

int y = 0;

Bitmap bp;

if ((mg.Width / Convert.ToDouble(newSize.Width)) > (mg.Height /

Convert.ToDouble(newSize.Height)))

ratio = Convert.ToDouble(mg.Width) / Convert.ToDouble(newSize.Width);

else

ratio = Convert.ToDouble(mg.Height) / Convert.ToDouble(newSize.Height);

myThumbHeight = Math.Ceiling(mg.Height / ratio);

myThumbWidth = Math.Ceiling(mg.Width / ratio);

Size thumbSize = new Size((int)newSize.Width, (int)newSize.Height);

bp = new Bitmap(newSize.Width, newSize.Height);

x = (newSize.Width - thumbSize.Width) / 2;

y = (newSize.Height - thumbSize.Height);

System.Drawing.Graphics g = Graphics.FromImage(bp);

g.SmoothingMode = SmoothingMode.HighQuality;

g.InterpolationMode = InterpolationMode.HighQualityBicubic;

g.PixelOffsetMode = PixelOffsetMode.HighQuality;

Rectangle rect = new Rectangle(x, y, thumbSize.Width, thumbSize.Height);

g.DrawImage(mg, rect, 0, 0, mg.Width, mg.Height, GraphicsUnit.Pixel);

return bp;

}

这样实现的压缩使压缩率大幅度上升。其实代码并没有变多少，最主要的是在保存的时候要是用jpg格式，

如果不指定格式，默认使用的是png格式。

下面这个是园友写的根据设置图片质量数值来压缩图片的方法：

public static bool GetPicThumbnail(string sFile, string outPath, int flag)

{

System.Drawing.Image iSource = System.Drawing.Image.FromFile(sFile);

ImageFormat tFormat = iSource.RawFormat;

//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)

{

iSource.Save(outPath, jpegICIinfo, ep);//dFile是压缩后的新路径

}

else

{

iSource.Save(outPath, tFormat);

}

return true;

}

catch

{

return false;

}

finally

{

iSource.Dispose();

iSource.Dispose();

}

}

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