c#生成图片缩略图的类(2种实现思路)

/**//// <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（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

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();

}

}

using System.IO;

using System.Drawing;

using System.Drawing.Imaging;

/// <summary>

/// 图片处理类

/// 1、生成缩略图片或按照比例改变图片的大小和画质

/// 2、将生成的缩略图放到指定的目录下

/// </summary>

public class ImageClass

{

public Image ResourceImage;

private int ImageWidth;

private int ImageHeight;

public string ErrMessage;

/// <summary>

/// 类的构造函数

/// </summary>

/// <param name="ImageFileName">图片文件的全路径名称</param>

public ImageClass(string ImageFileName)

{

ResourceImage=Image.FromFile(ImageFileName);

ErrMessage="";

}

public bool ThumbnailCallback()

{

return false;

}

/// <summary>

/// 生成缩略图重载方法1，返回缩略图的Image对象

/// </summary>

/// <param name="Width">缩略图的宽度</param>

/// <param name="Height">缩略图的高度</param>

/// <returns>缩略图的Image对象</returns>

public Image GetReducedImage(int Width,int Height)

{

try

{

Image ReducedImage;

Image.GetThumbnailImageAbort callb=new Image.GetThumbnailImageAbort(ThumbnailCallback);

ReducedImage=ResourceImage.GetThumbnailImage(Width,Height,callb,IntPtr.Zero);

return ReducedImage;

}

catch(Exception e)

{

ErrMessage=e.Message;

return null;

}

}

/// <summary>

/// 生成缩略图重载方法2，将缩略图文件保存到指定的路径

/// </summary>

/// <param name="Width">缩略图的宽度</param>

/// <param name="Height">缩略图的高度</param>

/// <param name="targetFilePath">缩略图保存的全文件名，(带路径)，参数格式：D:Images ilename.jpg</param>

/// <returns>成功返回true，否则返回false</returns>

public bool GetReducedImage(int Width,int Height,string targetFilePath)

{

try

{

Image ReducedImage;

Image.GetThumbnailImageAbort callb=new Image.GetThumbnailImageAbort(ThumbnailCallback);

ReducedImage=ResourceImage.GetThumbnailImage(Width,Height,callb,IntPtr.Zero);

ReducedImage.Save(@targetFilePath,ImageFormat.Jpeg);

ReducedImage.Dispose();

return true;

}

catch(Exception e)

{

ErrMessage=e.Message;

return false;

}

}

/// <summary>

/// 生成缩略图重载方法3，返回缩略图的Image对象

/// </summary>

/// <param name="Percent">缩略图的宽度百分比 如：需要百分之80，就填0.8</param>

/// <returns>缩略图的Image对象</returns>

public Image GetReducedImage(double Percent)

{

try

{

Image ReducedImage;

Image.GetThumbnailImageAbort callb=new Image.GetThumbnailImageAbort(ThumbnailCallback);

ImageWidth=Convert.ToInt32(ResourceImage.Width*Percent);

ImageHeight=Convert.ToInt32(ResourceImage.Width*Percent);

ReducedImage=ResourceImage.GetThumbnailImage(ImageWidth,ImageHeight,callb,IntPtr.Zero);

return ReducedImage;

}

catch(Exception e)

{

ErrMessage=e.Message;

return null;

}

}

/// <summary>

/// 生成缩略图重载方法4，返回缩略图的Image对象

/// </summary>

/// <param name="Percent">缩略图的宽度百分比 如：需要百分之80，就填0.8</param>

/// <param name="targetFilePath">缩略图保存的全文件名，(带路径)，参数格式：D:Images ilename.jpg</param>

/// <returns>成功返回true,否则返回false</returns>

public bool GetReducedImage(double Percent,string targetFilePath)

{

try

{

Image ReducedImage;

Image.GetThumbnailImageAbort callb=new Image.GetThumbnailImageAbort(ThumbnailCallback);

ImageWidth=Convert.ToInt32(ResourceImage.Width*Percent);

ImageHeight=Convert.ToInt32(ResourceImage.Width*Percent);

ReducedImage=ResourceImage.GetThumbnailImage(ImageWidth,ImageHeight,callb,IntPtr.Zero);

ReducedImage.Save(@targetFilePath,ImageFormat.Jpeg);

ReducedImage.Dispose();

return true;

}

catch(Exception e)

{

ErrMessage=e.Message;

return false;

}

}

}