.net C# 生成缩略图 用白色填充空白部分

#region 生成缩略图

/// <summary>

/// 生成缩略图

/// </summary>

/// <param name="originalImagePath">原来图片的绝对路径及文件名</param>

/// <param name="thumbnailPath">缩略图保存的绝对路径及文件名</param>

/// <param name="width">缩略图长度</param>

/// <param name="height">缩略图宽度</param>

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

{

//获取原始图片

System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath);

//缩略图画布宽高

int towidth = width;

int toheight = height;

//原始图片写入画布坐标和宽高(用来设置裁减溢出部分)

int x = 0;

int y = 0;

int ow = originalImage.Width;

int oh = originalImage.Height;

//原始图片画布,设置写入缩略图画布坐标和宽高(用来原始图片整体宽高缩放)

int bg_x = 0;

int bg_y = 0;

int bg_w = towidth;

int bg_h = toheight;

//倍数变量

double multiple = 0;

//获取宽长的或是高长与缩略图的倍数

if (originalImage.Width >= originalImage.Height)

multiple = (double)originalImage.Width / (double)width;

else

multiple = (double)originalImage.Height / (double)height;

//上传的图片的宽和高小等于缩略图

if (ow <= width && oh <= height)

{

//缩略图按原始宽高

bg_w = originalImage.Width;

bg_h = originalImage.Height;

//空白部分用背景色填充

bg_x = Convert.ToInt32(((double)towidth - (double)ow) / 2);

bg_y = Convert.ToInt32(((double)toheight - (double)oh) / 2);

}

//上传的图片的宽和高大于缩略图

else

{

//宽高按比例缩放

bg_w = Convert.ToInt32((double)originalImage.Width / multiple);

bg_h = Convert.ToInt32((double)originalImage.Height / multiple);

//空白部分用背景色填充

bg_y = Convert.ToInt32(((double)height - (double)bg_h) / 2);

bg_x = Convert.ToInt32(((double)width - (double)bg_w) / 2);

}

//新建一个bmp图片,并设置缩略图大小.

System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);

//新建一个画板

System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);

//设置高质量插值法

g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBilinear;

//设置高质量,低速度呈现平滑程度

g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

//清空画布并设置背景色

g.Clear(System.Drawing.ColorTranslator.FromHtml("#F2F2F2"));

//在指定位置并且按指定大小绘制原图片的指定部分

//第一个System.Drawing.Rectangle是原图片的画布坐标和宽高,第二个是原图片写在画布上的坐标和宽高,最后一个参数是指定数值单位为像素

g.DrawImage(originalImage, new System.Drawing.Rectangle(bg_x, bg_y, bg_w, bg_h), new System.Drawing.Rectangle(x, y, ow, oh), System.Drawing.GraphicsUnit.Pixel);

try

{

//获取图片类型

string fileExtension = System.IO.Path.GetExtension(originalImagePath).ToLower();

//按原图片类型保存缩略图片,不按原格式图片会出现模糊,锯齿等问题.

switch (fileExtension)

{

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();

}

}

#endregion