前段时间做的一个项目需要上传图片，同时上传的时候生成缩略图，恰好有人写了这么个类，于是修改了一下，现贴出来。
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using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Collections;
/// <summary>
/// 创建缩略图
/// </summary>
public class CreateBreviaryImage
{
private static Hashtable htmimes = new Hashtable();
internal readonly string AllowExt = ".jpe|.jpeg|.jpg|.png|.tif|.tiff|.bmp";
private string sExt = ".jpg";
public CreateBreviaryImage()
{
htmimes[".jpe"] = "image/jpeg";
htmimes[".jpeg"] = "image/jpeg";
htmimes[".jpg"] = "image/jpeg";
htmimes[".png"] = "image/png";
htmimes[".tif"] = "image/tiff";
htmimes[".tiff"] = "image/tiff";
htmimes[".bmp"] = "image/bmp";
}
#region 生产缩略图
/// <summary>
/// 返回缩略图Size对象
/// </summary>
/// <param name="maxWidth">缩略图宽度</param>
/// <param name="maxHeight">缩略图高度</param>
/// <param name="width">原图宽度</param>
/// <param name="height">原图高度</param>
/// <returns>缩略图大小</returns>
private Size NewSize(int maxWidth, int maxHeight, int width, int height)
{
double w = 0.0;
double h = 0.0;
double sw = Convert.ToDouble(width);
double sh = Convert.ToDouble(height);
double mw = Convert.ToDouble(maxWidth);
double mh = Convert.ToDouble(maxHeight);
if (sw < mw && sh < mh)
{
w = sw;
h = sh;
}
else if ((sw / sh) > (mw / mh))
{
w = maxWidth;
h = (w * sh) / sw;
}
else
{
h = maxHeight;
w = (h * sw) / sh;
}
return new Size(Convert.ToInt32(w), Convert.ToInt32(h));
}
/// <summary>
/// 获取图像编码解码器的所有相关信息
/// </summary>
/// <param name="mimeType">包含编码解码器的多用途网际邮件扩充协议 (MIME) 类型的字符串</param>
/// <returns>返回图像编码解码器的所有相关信息</returns>
private static ImageCodecInfo GetCodecInfo(string mimeType)
{
ImageCodecInfo[] CodecInfo = ImageCodecInfo.GetImageEncoders();
foreach (ImageCodecInfo ici in CodecInfo)
{
if (ici.MimeType == mimeType) return ici;
}
return null;
}
/// <summary>
/// 检测扩展名的有效性
/// </summary>
/// <param name="sExt">文件名扩展名</param>
/// <returns>如果扩展名有效,返回true,否则返回false.</returns>
private bool CheckValidExt(string sExt)
{
bool flag = false;
string[] aExt = AllowExt.Split('|');
foreach (string filetype in aExt)
{
if (filetype.ToLower() == sExt)
{
flag = true;
break;
}
}
return flag;
}
/// <summary>
/// 保存缩略图到指定文件
/// </summary>
/// <param name="sourcePath">源图片路径(注意：绝对路径)</param>
/// <param name="savePath">保存路径(注意：绝对路径)</param>
/// <param name="newWith">缩略图宽度</param>
/// <param name="newHeight">缩略图高度</param>
public void SaveBreviaryImageTo(string sourcePath, string savePath, int newWith, int newHeight)
{
System.Drawing.Image image = CreateImage(
sourcePath,
newWith,
newHeight);
//设置 原图片 对象的 EncoderParameters 对象
EncoderParameters parameters = new EncoderParameters(1);
parameters.Param[0] = new EncoderParameter(Encoder.Quality, ((long)100));
image.Save(
savePath,
GetCodecInfo((string)htmimes[sExt]),
parameters);
parameters.Dispose();
}
/// <summary>
/// 生产缩略图，获取缩略图的字节数组
/// </summary>
/// <param name="sourcePath">源图片路径(注意：绝对路径)</param>
/// <param name="savePath">保存路径(注意：绝对路径)</param>
/// <param name="newWith">缩略图宽度</param>
/// <param name="newHeight">缩略图高度</param>
public byte[] ReadNewImageBytes(string sourcePath,int newWith, int newHeight)
{
System.Drawing.Image image = CreateImage(
sourcePath,
newWith,
newHeight);
//设置 原图片 对象的 EncoderParameters 对象
EncoderParameters parameters = new EncoderParameters(1);
parameters.Param[0] = new EncoderParameter(Encoder.Quality, ((long)100));
System.IO.MemoryStream stream = new System.IO.MemoryStream();
image.Save(
stream,
GetCodecInfo((string)htmimes[sExt]),
parameters);
stream.Position = 0;
byte[] bytes= new byte[stream.Length];
stream.Read(bytes, 0, bytes.Length);
parameters.Dispose();
stream.Dispose();
return bytes;
}
/// <summary>
/// 生成缩略图
/// </summary>
/// <param name="sourceImagePath">***原图片路径(注意：绝对路径)***</param>
/// <param name="maxWidth">缩略图的宽度</param>
/// <param name="maxHeight">缩略图的高度</param>
/// <param name="imageContentType">文件类型(MIME)的字符串</param>
private Bitmap CreateImage(string SourceImagePath,int maxWidth, int maxHeight)
{
sExt = SourceImagePath.Substring(SourceImagePath.LastIndexOf(".")).ToLower();
if (SourceImagePath.ToString() == System.String.Empty)
throw new NullReferenceException("SourceImagePath is null!");
if (!CheckValidExt(sExt))
{
throw new ArgumentException(
"原图片文件格式不正确,支持的格式有[ " + AllowExt + "]", "SourceImagePath");
}
//从 原图片 创建 Image 对象
System.Drawing.Image image =
System.Drawing.Image.FromFile(SourceImagePath);
Size newSize = NewSize(maxWidth, maxHeight, image.Width, image.Height);
//用指定的大小和格式初始化 Bitmap 类的新实例
Bitmap bitmap = new Bitmap(newSize.Width, newSize.Height,PixelFormat.Format32bppArgb);
//从指定的 Image 对象创建新 Graphics 对象
Graphics g = Graphics.FromImage(bitmap);
//清除整个绘图面并以透明背景色填充
g.Clear(Color.Transparent);
// 设置画布的描绘质量
g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
//在指定位置并且按指定大小绘制 原图片 对象
g.DrawImage(image, new Rectangle(0, 0, newSize.Width, newSize.Height),
0, 0, image.Width, image.Height, GraphicsUnit.Pixel);
g.Dispose();
image.Dispose();
return bitmap;
}
#endregion
}
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来源：http://www.cnblogs.com/meteorcui/archive/2006/04/24/2021199.html