Asp.net中图片生成缩略图

网上找了串代码，个人 觉得写得很详细，考虑也很周全 地址:

/article/4696661.html 稍加修改。

贴出代码，备用：

/// <summary>
/// 上传文件
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
protected void btnUpLoadFile_Click(object sender, EventArgs e)
{
if (fileUpload1.HasFile)
{
string savePath = Server.MapPath("~/images/maxPic");
if (!System.IO.Directory.Exists(savePath))
{
System.IO.Directory.CreateDirectory(savePath);
}
savePath = savePath + "//" + fileUpload1.FileName;
fileUpload1.SaveAs(savePath);

MakeThumbnail(Server.MapPath("~/images/maxPic/ll.jpg"), Server.MapPath("~/images/minPic/ll_1.jpg"), 100,80, "Cut");
}
}

其中 fileUpload1 是FileUpload空控件名。

下面是生成缩略图的代码，可以按高、宽、等比例缩放：

/// <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(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
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
bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
}
catch (System.Exception e)
{
throw e;
}
finally
{
originalImage.Dispose();
bitmap.Dispose();
g.Dispose();
}
}

注意添加命名空间：

using System.Drawing;
using System.Drawing.Imaging;