请问一下，在上传图片时，怎么样才能让大图片上传后成为规定大小而且不失真呢？

[zck98530]

请问一下，在上传图片时，怎么样才能让大图片上传后成为规定大小而且不失真呢？

我想做的是一个图片预览功能，大图片加载的太慢了，所以要把大图片上传的时候就给处理支规定的大小，而且要图片不失真！

请求高手们指点，万分感谢！！

[laomaoli]

生成缩略图
Public Function GenerateThumbnail(ByVal original As Image, ByVal DescSize As Integer) As Image
Dim tn As Bitmap
Dim DescHeight, DescWidth As Integer
'对图像的高和宽都要判断
If original.Height >= DescSize Or original.Width >= DescSize Then
DescHeight = original.Height
DescWidth = original.Width
If DescHeight >= DescSize Then
DescHeight = DescSize
DescWidth = DescHeight * original.Width \ original.Height
End If
If DescWidth >= DescSize Then
DescWidth = DescSize
DescHeight = DescWidth * original.Height \ original.Width
End If

End If

tn = New Bitmap(CInt(DescSize), CInt(DescSize))
Dim g As Graphics = Graphics.FromImage(tn)
Dim whiteBrush As New SolidBrush(Color.White)
Dim Rectangle As Rectangle = New Rectangle((DescSize - DescWidth) / 2, (DescSize - DescHeight) / 2, DescWidth, DescHeight)
Dim RectangleS As Rectangle = New Rectangle(0, 0, DescSize, (DescSize - DescHeight) / 2)
Dim RectangleX As Rectangle = New Rectangle(0, (DescSize + DescHeight) / 2, DescSize, (DescSize - DescHeight) / 2)
Dim RectangleZ As Rectangle = New Rectangle(0, 0, (DescSize - DescWidth) / 2, DescSize)
Dim RectangleY As Rectangle = New Rectangle((DescSize + DescWidth) / 2, 0, (DescSize - DescWidth) / 2, DescSize)
g.FillRectangle(whiteBrush, RectangleS)
g.FillRectangle(whiteBrush, RectangleX)
g.FillRectangle(whiteBrush, RectangleZ)
g.FillRectangle(whiteBrush, RectangleY)
If DescWidth = DescSize Or DescHeight = DescSize Then
If DescWidth = DescSize Then
g.DrawImage(original, Rectangle, 0, 0, original.Width, original.Height, GraphicsUnit.Pixel)
End If
If DescHeight = DescSize Then
g.DrawImage(original, Rectangle, 0, 0, original.Width, original.Height, GraphicsUnit.Pixel)
End If
Else
g.DrawImage(original, New Rectangle((DescSize - original.Width) / 2, (DescSize - original.Height) / 2, _
original.Width, original.Height), 0, 0, original.Width, original.Height, GraphicsUnit.Pixel)

End If
g.Dispose()

Return CType(tn, Image)
End Function 'GenerateThumbnail

[浩方软件HFWMS]

楼上的不错

[haobojunsun]

有没有 C# 写的？

[bwtgod]

（转）

/**//// <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

[pbwf]

多收集一下.