c# 生成微缩图

‍///<summary>
/// 图片微缩图处理
///</summary>
///<param name="srcPath">源图片</param>
///<param name="destPath">目标图片</param>
///<param name="width">宽度</param>
///<param name="height">高度</param>
publicstaticvoid CreateThumbnailPicture(string srcPath, string destPath, int width, int height)
{
//根据图片的磁盘绝对路径获取 源图片 的Image对象
System.Drawing.Image img = System.Drawing.Image.FromFile(srcPath);

//bmp： 最终要建立的 微缩图 位图对象。
Bitmap bmp =new Bitmap(width, height);

//g: 绘制 bmp Graphics 对象
Graphics g = Graphics.FromImage(bmp);
g.Clear(Color.Transparent);
//为Graphics g 对象 初始化必要参数，很容易理解。
g.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;

//源图片宽和高
int imgWidth = img.Width;
int imgHeight = img.Height;

//绘制微缩图
g.DrawImage(img, new System.Drawing.Rectangle(0, 0, width, height), new System.Drawing.Rectangle(0, 0, imgWidth, imgHeight)
, GraphicsUnit.Pixel);

ImageFormat format = img.RawFormat;
ImageCodecInfo info = ImageCodecInfo.GetImageEncoders().SingleOrDefault(i => i.FormatID == format.Guid);
EncoderParameter param =new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 100L);
EncoderParameters parameters =new EncoderParameters(1);
parameters.Param[0] = param;
img.Dispose();

//保存已生成微缩图，这里将GIF格式转化成png格式。
if (format == ImageFormat.Gif)
{
destPath = destPath.ToLower().Replace(".gif", ".png");
bmp.Save(destPath, ImageFormat.Png);
}
else
{
if (info !=null)
{
bmp.Save(destPath, info, parameters);
}
else
{

bmp.Save(destPath, format);
}
}

img.Dispose();
g.Dispose();
bmp.Dispose();
}

调用

/上传成功后网站内源图片相对路径
2 string relativePath = System.Web.HttpContext.Current.Request.ApplicationPath
3+string.Format(@"Content/Upload/Images/{0}", fileName);
4
5/*
6比例处理
7微缩图高度（DefaultHeight属性值为 400）
8*/
9System.Drawing.Image img = System.Drawing.Image.FromFile(toFile);
10int width = img.Width;
11int height = img.Height;
12float ratio = (float)width / height;
13
14//微缩图高度和宽度
15 int newHeight = height <= DefaultHeight ? height : DefaultHeight;
16int newWidth = height <= DefaultHeight ? width : Convert.ToInt32(DefaultHeight * ratio);
17
18FileInfo generatedfile =new FileInfo(toFile);
19string newFileName ="Thumb_"+ generatedfile.Name;
20string newFilePath = Path.Combine(generatedfile.DirectoryName, newFileName);
21
22PictureHandler.CreateThumbnailPicture(toFile, newFilePath, newWidth, newHeight);
23
24string thumbRelativePath = System.Web.HttpContext.Current.Request.ApplicationPath
25+string.Format(@"/Content/Upload/Images/{0}", newFileName);
26
27//返回原图和微缩图的网站相对路径
28 relativePath =string.Format("{0},{1}", relativePath, thumbRelativePath);
29
30return relativePath;