在网站开发时,生成缩略图是一个非常常见和实用的功能.以前在asp里只能借助com组件实现,现在在.net里可以利用框架的强大的类库轻松实现.下面帖出完整的代码(带详细注释),参考了网上的一些文章及.net sdk相关内容.QQROOM网络家园的图片上传用到了所有的4种生成方式.

        

/**/

/// <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();

            }

        }

关键方法Graphics.DrawImage见ms

-

help:

//

MS.NETFrameworkSDKv1.1.CHS/cpref/html/frlrfsystemdrawinggraphicsclassdrawimagetopic11.htm