.netC#生成缩略图实现思路分解

///生成缩略图
///</summary>
///<paramname="originalImagePath">源图路径</param>
///<paramname="thumbnailPath">缩略图路径</param>
///<paramname="width">缩略图宽度</param>
///<paramname="height">缩略图高度</param>
///<paramname="mode">生成缩略图的方式:HW指定高宽缩放(可能变形);W指定宽，高按比例H指定高，宽按比例Cut指定高宽裁减(不变形)</param>　　
///<paramname="mode">要缩略图保存的格式(gif,jpg,bmp,png)为空或未知类型都视为jpg</param>　　
publicstaticvoidMakeThumbnail(stringoriginalImagePath,stringthumbnailPath,intwidth,intheight,stringmode,stringimageType)
{
ImageoriginalImage=Image.FromFile(originalImagePath);
inttowidth=width;
inttoheight=height;
intx=0;
inty=0;
intow=originalImage.Width;
intoh=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
Imagebitmap=newSystem.Drawing.Bitmap(towidth,toheight);
//新建一个画板
Graphicsg=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,newRectangle(0,0,towidth,toheight),
newRectangle(x,y,ow,oh),
GraphicsUnit.Pixel);
try
{
//以jpg格式保存缩略图
switch(imageType.ToLower())
{
case"gif":
bitmap.Save(thumbnailPath,System.Drawing.Imaging.ImageFormat.Gif);
break;
case"jpg":
bitmap.Save(thumbnailPath,System.Drawing.Imaging.ImageFormat.Jpeg);
break;
case"bmp":
bitmap.Save(thumbnailPath,System.Drawing.Imaging.ImageFormat.Bmp);
break;
case"png":
bitmap.Save(thumbnailPath,System.Drawing.Imaging.ImageFormat.Png);
break;
default:
bitmap.Save(thumbnailPath,System.Drawing.Imaging.ImageFormat.Jpeg);
break;
}
}
catch(System.Exceptione)
{
throwe;
}
finally
{
originalImage.Dispose();
bitmap.Dispose();
g.Dispose();
}
}