ASP.NET生成高质量缩略图通用函数(VB.NET、c#代码)

时间:2007/7/6 14:50:56      阅读:5031          
      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,俺整理了C#和VB.NET两种代码。
先看下面这一段代码:
'将图片缩小后保存
Private Sub SaveSmallPic(ByVal sFileName As String)
Dim image As System.Drawing.Image, newimage As System.Drawing.Image
Dim callb As System.Drawing.Image.GetThumbnailImageAbort
image
= System.Drawing.Image.FromStream(Me.File1.PostedFile.InputStream)
If image.Width < image.Height Then
newimage
= image.GetThumbnailImage(480, 640, callb, New System.IntPtr(0))
Else
newimage
= image.GetThumbnailImage(640, 480, callb, New System.IntPtr(0))
End If

image.Dispose()

'将新图片及图片变小后存到临时路径中
newimage.Save(sFileName, System.Drawing.Imaging.ImageFormat.Jpeg)
newimage.Dispose()
End Sub

再看以下生成高质量缩略图代码(VB和C#)
VB.NE代码:
''' <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>
''' <remarks></remarks>
Public Shared Sub MakeThumbnail(ByVal originalImagePath As String, ByVal thumbnailPath As String, ByVal width As Integer, ByVal height As Integer, ByVal mode As String)

Dim originalImage As System.Drawing.Image = System.Drawing.Image.FromFile(originalImagePath)

Dim towidth As Integer = width
Dim toheight As Integer = height

Dim x As Integer = 0
Dim y As Integer = 0
Dim ow As Integer = originalImage.Width
Dim oh As Integer = originalImage.Height

Select Case mode
Case "HW" '指定高宽缩放(可能变形)
Case "W" '指定宽,高按比例
toheight = originalImage.Height * width / originalImage.Width
Case "H" '指定高,宽按比例
towidth = originalImage.Width * height / originalImage.Height
Case "Cut" '指定高宽裁减(不变形)
If System.Convert.ToDouble(originalImage.Width) / System.Convert.ToDouble(originalImage.Height) > System.Convert.ToDouble(towidth) / System.Convert.ToDouble(toheight) Then
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
End If
Case Else
End Select

'新建一个bmp图片
Dim bitmap = New Drawing.Bitmap(towidth, toheight)

'新建一个画板
Dim g As Drawing.Graphics = 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(Drawing.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 Drawing.Rectangle(0, 0, towidth, toheight), New Drawing.Rectangle(x, y, ow, oh), System.Drawing.GraphicsUnit.Pixel)

Try
'以jpg格式保存缩略图
bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg)
Catch e As Exception
Throw e
Finally
originalImage.Dispose()
bitmap.Dispose()
g.Dispose()
End Try
End Sub


C#代码:   
**//// <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 Bitmap(towidth, toheight);

//新建一个画板
Graphics g = Graphics.FromImage(bitmap);

//设置高质量插值法
g.InterpolationMode = InterpolationMode.High;

//设置高质量,低速度呈现平滑程度
g.SmoothingMode = 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, ImageFormat.Jpeg);
}

catch (Exception e)
{
throw e;
}

finally
{
originalImage.Dispose();
bitmap.Dispose();
g.Dispose();
}

}


很明显示,第一段代码生成出来的缩略图质量非常差,而下面的代码生成出来的缩略图非常清晰,大家试试吧。
评论
  • Re:ASP.NET生成高质量缩略图通用函数(c#代码)  (2007/8/1 10:35:15) by 潘兆勇 
    给站长的建议:
    这里的贴图功能,好像不大行啊,我要上传图的时候,提示已经达到100m。而且每个人的目录互相不隔离,可以操作别人的图。
  • Re:ASP.NET生成高质量缩略图通用函数(c#代码)  (2007/8/1 10:38:51) by 潘兆勇 
    不知道谁试过这种方法?不过,我们这么久一直用这种方法,统一的反响就是,图片会失真。不信大家试试看,经过这个程序处理过的图,就算不缩小,效果也会必原来的差。不信你试试看。
  • Re:ASP.NET生成高质量缩略图通用函数(c#代码)  (2007/8/1 12:31:41) by 踢西 
    你指的是那里的贴图功能?
    图片缩小质量肯定会变差,这是肯定的。
  • Re:ASP.NET生成高质量缩略图通用函数(VB.NET、c#代码)  (2007/12/4 11:45:56) by 张炜 
    为什么有的网站截的图片是空白的?
  • Re:ASP.NET生成高质量缩略图通用函数(VB.NET、c#代码)  (2007/12/29 11:37:02) by lwlfox 
    谢谢了
  • Re:ASP.NET生成高质量缩略图通用函数(VB.NET、c#代码)  (2008/9/23 16:40:26) by 俞俞 
    好像有点问题哦
  • Re:ASP.NET生成高质量缩略图通用函数(VB.NET、c#代码)  (2009/11/26 21:56:27) by y2222 

    我觉得比较简单呀。没有什么的

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