.net C#生成缩略图实现思路分解

/// 生成缩略图

/// </summary>

/// <param name="originalImagePath">源图路径</param>

/// <param name="thumbnailPath">缩略图路径</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:HW指定高宽缩放(可能变形);W指定宽，高按比例 H指定高，宽按比例 Cut指定高宽裁减(不变形)</param>　　

/// <param name="mode">要缩略图保存的格式(gif,jpg,bmp,png) 为空或未知类型都视为jpg</param>　　

public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode, string imageType)

{

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

switch (imageType.ToLower())

{

case "gif":

bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Gif);

break;

case "jpg":

bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);

break;

case "bmp":

bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Bmp);

break;

case "png":

bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Png);

break;

default:

bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);

break;

}

}

catch (System.Exception e)

{

throw e;

}

finally

{

originalImage.Dispose();

bitmap.Dispose();

g.Dispose();

}

}