我们在后台上传图片的时候经常会生成几张小图，因为我们网站上面都会有几个小图，我们不可以让用户一张图片要多次处理然后上传一张图片吧，这个不合理，所以我们采用生成小图的方法来完成这一个效果，下面就是我们实现这个方法的代码。
/// <summary>
/// 生成缩略图
/// </summary>
/// <param name="originalImagePath">源图路径（相对路径）</param>
/// <param name="thumbnailPath">缩略图路径（相对路径）</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</param>
public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
{
System.Drawing.Image originalImage = System.Drawing.Image.FromFile(HttpContext.Current.Server.MapPath(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
System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
//新建一个画板
System.Drawing.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(System.Drawing.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 System.Drawing.Rectangle(0, 0, towidth, toheight),
new System.Drawing.Rectangle(x, y, ow, oh),
System.Drawing.GraphicsUnit.Pixel);
try
{
originalImage.Dispose();
string toFileFullPath = HttpContext.Current.Server.MapPath(thumbnailPath.Substring(0, thumbnailPath.LastIndexOf("/")));
//检查是否有该路径没有就创建
if (!Directory.Exists(toFileFullPath))
{
Directory.CreateDirectory(toFileFullPath);
}
//保存缩略图
bitmap.Save(HttpContext.Current.Server.MapPath(thumbnailPath));
}
catch (System.Exception e)
{
//异常
throw e;
}
finally
{
//关闭信息
bitmap.Dispose();
g.Dispose();
}
}
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