/// <summary> 

/// 生成jpg缩略图字节,本人的小软件中需要用到的功能，所以自己做了一个函数，和大家分享 

/// 为什么要生成字节而不是文件，这是为了方便后续处理啦^_^ 

/// </summary> 

/// <param name="originalImagePath">原始路径</param> 

/// <param name="quality">质量0-100</param> 

/// <param name="width">宽度</param> 

/// <param name="height">高度</param> 

/// <param name="mode">模式：HW,W,H,Cut</param> 

/// <returns></returns> 

public static byte[] MakeJPGThumbnailBytes(string originalImagePath, long quality, int width, int height, string mode) 

{ 

Image originalImage = Image.FromFile(originalImagePath); 

MemoryStream s = new MemoryStream(); 

int towidth = width; 

int toheight = height; 

 

int x = 0; 

int y = 0; 

int ow = originalImage.Width; 

int oh = originalImage.Height; 

 

switch (mode) 

{ 

case "HW"://指定高宽缩放（可能变形） 

break; 

case "W"://指定宽，高按比例 

toheight = originalImage.Height * width / originalImage.Width; 

break; 

case "H"://指定高，宽按比例 

towidth = originalImage.Width * height / originalImage.Height; 

break; 

case "Cut"://指定高宽裁减（不变形） 

if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight) 

{ 

oh = originalImage.Height; 

ow = originalImage.Height * towidth / toheight; 

y = 0; 

x = (originalImage.Width - ow) / 2; 

} 

else 

{ 

ow = originalImage.Width; 

oh = originalImage.Width * height / towidth; 

x = 0; 

y = (originalImage.Height - oh) / 2; 

} 

break; 

default: 

break; 

} 

 

//新建一个bmp图片 

Image bitmap = new System.Drawing.Bitmap(towidth, toheight); 

 

//新建一个画板 

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

 

//设置高质量插值法 

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

 

//设置高质量,低速度呈现平滑程度 

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

 

//清空画布并以透明背景色填充 

g.Clear(Color.Transparent); 

 

//在指定位置并且按指定大小绘制原图片的指定部分 

g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight), 

new Rectangle(x, y, ow, oh), 

GraphicsUnit.Pixel); 

 

try 

{ 

//以jpg格式保存缩略图 

EncoderParameters eps = new EncoderParameters(1); 

EncoderParameter ep = new EncoderParameter(Encoder.Quality,quality); 

eps.Param[0] = ep; 

bitmap.Save(s, GetCodecInfo("image/jpeg"), eps); 

return s.GetBuffer(); 

} 

catch (System.Exception e) 

{ 

throw e; 

} 

finally 

{ 

originalImage.Dispose(); 

bitmap.Dispose(); 

s.Dispose(); 

g.Dispose(); 

} 

} 

 

/**/ 

/// <summary> 

/// 保存JPG时用 

/// </summary> 

/// <param name="mimeType"></param> 

/// <returns>得到指定mimeType的ImageCodecInfo</returns> 

private static ImageCodecInfo GetCodecInfo(string mimeType) 

{ 

ImageCodecInfo[] CodecInfo = ImageCodecInfo.GetImageEncoders(); 

foreach (ImageCodecInfo ici in CodecInfo) 

{ 

if (ici.MimeType == mimeType) return ici; 

} 

return null; 

}