.net C#生成缩略图实现思路分解

/// 生成缩略图
/// </summary>
/// <param name="originalimagepath">源图路径</param>
/// <param name="thumbnailpath">缩略图路径</param>
/// <param name="width">缩略图宽度</param>
/// <param name="height">缩略图高度</param>
/// <param name="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>　　
/// <param name="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>　　
public static void makethumbnail(string originalimagepath, string thumbnailpath, int width, int height, string mode, string imagetype)
{
image originalimage = image.fromfile(originalimagepath);
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
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.exception e)
{
throw e;
}
finally
{
originalimage.dispose();
bitmap.dispose();
g.dispose();
}
}