asp.net上传图片生成缩略图

生成缩略图方法：

/// <summary>

/// 生成缩略图

/// </summary>

/// <param name="originalImagePath">源图路径（物理路径）</param>

/// <param name="thumbnailPath">缩略图路径（物理路径）</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)

{

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

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;

case "CutA"://指定高宽裁减（不变形）自定义

if (ow <= towidth && oh <= toheight)

{

x = -(towidth - ow) / 2;

y = -(toheight - oh) / 2;

ow = towidth;

oh = toheight;

}

else

{

if (ow > oh)//宽大于高

{

x = 0;

y = -(ow - oh) / 2;

oh = ow;

}

else//高大于宽

{

y = 0;

x = -(oh - ow) / 2;

ow = oh;

}

}

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;

//清空画布并以白色背景色填充

g.Clear(Color.White);

//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();

}

}

在前台html页面添加一个uploadfile控件，在后台添加一下代码：

if (fileimg.PostedFile.FileName != "")

{

string fileext = Regex.Match(fileimg.PostedFile.FileName, "[^.]*", RegexOptions.RightToLeft).Value;

string fm = DateTime.Now.ToString("yyyyMMdd");

string fm2 = "old" + "." + fileext;

string path = "/UploadFile/User/" + fm + "/";

if (!File.Exists(Server.MapPath(path)))

{

Directory.CreateDirectory(Server.MapPath(path));

}

fileimg.PostedFile.SaveAs(Server.MapPath(path + fm2));

mod.Avatar = fm + "/" + fm2;

string newname = DateTime.Now.ToString("yyyyMMddHHmmss") + "_new_" + fileimg.FileName;

string filename = path + newname;

MakeThumbnail(path + fm + "/" + fm2, filename, 42, 47, "HW");

}