上传图片生成略缩图“最佳解决”_[Asp.Net教程]

从用 .Net Web 开发到现在所看到的略缩生成代码都不尽人意，要不太局限，要不失真厉害。

为此写了一个相对完善的函数供大家学习。

其中的 SaveIamge 函数提供了失真解决方法，对于处理过的图片（如加水印……）要求保持高品质可以直接调用。


using System;
using System.IO;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.Drawing.Text;
using System.Text.RegularExpressions;

///

// 图片处理。
// (c) 2008 Dao
///

public class Image
{
///

/// 缩略模式。
///

public enum ThumbMode : byte
{
///

/// 完整模式
///

Full = 1,
///

/// 最大尺寸
///

Max
}

///

/// 缩略图。
///

/// 要缩略的图片
/// 要缩放的尺寸
/// 缩略模式
/// 对齐方式
/// 返回已经缩放的图片。
public static Bitmap Thumbnail(Bitmap image, Size size, ThumbMode mode, ContentAlignment contentAlignment)
{
if (!size.IsEmpty && !image.Size.IsEmpty && !size.Equals(image.Size))
{
//先取一个宽比例。
double scale = (double)image.Width / (double)size.Width;
//缩略模式
switch (mode)
{
case ThumbMode.Full:
if (image.Height > image.Width)
scale = (double)image.Height / (double)size.Height;
break;
case ThumbMode.Max:
if (image.Height / scale < size.Height)
scale = (double)image.Height / (double)size.Height;
break;
}
SizeF newSzie = new SizeF((float)(image.Width / scale), (float)(image.Height / scale));
Bitmap result = new Bitmap(size.Width, size.Height);
using (Graphics g = Graphics.FromImage(result))
{
g.FillRectangle(Brushes.White, new Rectangle(new Point(0, 0), size));
g.InterpolationMode = InterpolationMode.HighQualityBicubic;
g.SmoothingMode = SmoothingMode.HighQuality;
g.PixelOffsetMode = PixelOffsetMode.HighQuality;
g.CompositingMode = CompositingMode.SourceOver;
g.CompositingQuality = CompositingQuality.HighQuality;
g.TextRenderingHint = TextRenderingHint.AntiAliasGridFit;
//对齐方式
RectangleF destRect;
switch (contentAlignment)
{
case ContentAlignment.TopCenter:
destRect = new RectangleF(new PointF(-(float)((newSzie.Width - size.Width) * 0.5), 0), newSzie);
break;
case ContentAlignment.TopRight:
destRect = new RectangleF(new PointF(-(float)(newSzie.Width - size.Width), 0), newSzie);
break;
case ContentAlignment.MiddleLeft:
destRect = new RectangleF(new PointF(0, -(float)((newSzie.Height - size.Height) * 0.5)), newSzie);
break;
case ContentAlignment.MiddleCenter:
destRect = new RectangleF(new PointF(-(float)((newSzie.Width - size.Width) * 0.5), -(float)((newSzie.Height - size.Height) * 0.5)), newSzie);
break;
case ContentAlignment.MiddleRight:
destRect = new RectangleF(new PointF(-(float)(newSzie.Width - size.Width), -(float)((newSzie.Height - size.Height) * 0.5)), newSzie);
break;
case ContentAlignment.BottomLeft:
destRect = new RectangleF(new PointF(0, -(float)(newSzie.Height - size.Height)), newSzie);
break;
case ContentAlignment.BottomCenter:
destRect = new RectangleF(new PointF(-(float)((newSzie.Width - size.Width) * 0.5), -(float)(newSzie.Height - size.Height)), newSzie);
break;
case ContentAlignment.BottomRight:
destRect = new RectangleF(new PointF(-(float)(newSzie.Width - size.Width), -(float)(newSzie.Height - size.Height)), newSzie);
break;
default:
destRect = new RectangleF(new PointF(0, 0), newSzie);
break;
}
g.DrawImage(image, destRect, new RectangleF(new PointF(0F, 0F), image.Size), GraphicsUnit.Pixel);
image.Dispose();
}
return result;
}
else
return image;
}

///

/// 保存图片。
///

/// 要保存的图片
/// 品质（1L~100L之间，数值越大品质越好）
/// 保存路径
public static void SaveIamge(Bitmap image, long quality, string filename)
{
using (EncoderParameters encoderParams = new EncoderParameters(1))
{
using (EncoderParameter parameter = (encoderParams.Param[0] = new EncoderParameter(Encoder.Quality, quality)))
{
ImageCodecInfo encoder = null;
//取得扩展名
string ext = Path.GetExtension(filename);
if (string.IsNullOrEmpty(ext))
ext = ".jpg";
//根据扩展名得到解码、编码器
foreach (ImageCodecInfo codecInfo in ImageCodecInfo.GetImageEncoders())
{
if (Regex.IsMatch(codecInfo.FilenameExtension, string.Format(@"(;|^)\*\{0}(;|)", ext), RegexOptions.IgnoreCase))
{
encoder = codecInfo;
break;
}
}
Directory.CreateDirectory(Path.GetDirectoryName(filename));
image.Save(filename, encoder, encoderParams);
}
}
}

///

/// 保存图片。
///

/// 要保存的流
/// 品质（1L~100L之间，数值越大品质越好）
/// 保存路径
public static void SaveIamge(Stream stream, long quality, string filename)
{
using (Bitmap bmpTemp = new Bitmap(stream))
{
SaveIamge(bmpTemp, quality, filename);
}
}
}

调用方法如下：

using (Bitmap bmpAvatar = Image.Thumbnail(new Bitmap(/*<流，FileUpload 控件的 PostedFile.InputStream 属性>*/), new Size(48, 48), Image.ThumbMode.Full, ContentAlignment.MiddleCenter))
{
Image.SaveIamge(bmpAvatar, 95L, Server.MapPath("~/upfiles/Avatar.jpg"));
}

来源：http://www.cnblogs.com/dao