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  • C#教程之C# jpg缩略图函数代码

 
/// <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; 
} 

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