故事：用户上传将添加到照片库的图像。作为上传过程的一部分，我们需要 A) 将图像存储在 Web 服务器的硬盘驱动器上，并且 B) 将图像的缩略图存储在 Web 服务器的硬盘驱动器上。
这里的“最佳”定义为
- 相对容易实施、理解和维护
- 生成质量合理的缩略图
性能和高质量的缩略图是次要的。
Brad Tutterow
问问题
26463 次
6 回答
37
GetThumbnailImage 可以，但如果您想要更好的质量，您可以为 BitMap 类指定图像选项并将加载的图像保存到那里。这是一些示例代码：
Image photo; // your uploaded image
Bitmap bmp = new Bitmap(resizeToWidth, resizeToHeight);
graphic = Graphics.FromImage(bmp);
graphic.InterpolationMode = InterpolationMode.HighQualityBicubic;
graphic.SmoothingMode = SmoothingMode.HighQuality;
graphic.PixelOffsetMode = PixelOffsetMode.HighQuality;
graphic.CompositingQuality = CompositingQuality.HighQuality;
graphic.DrawImage(photo, 0, 0, resizeToWidth, resizeToHeight);
imageToSave = bmp;
这提供了比 GetImageThumbnail 开箱即用的更好的质量
于 2008-08-26T12:58:19.733 回答
15
我想您最好的解决方案是使用.NET Image类中的GetThumbnailImage 。
// Example in C#, should be quite alike in ASP.NET
// Assuming filename as the uploaded file
using ( Image bigImage = new Bitmap( filename ) )
{
// Algorithm simplified for purpose of example.
int height = bigImage.Height / 10;
int width = bigImage.Width / 10;
// Now create a thumbnail
using ( Image smallImage = image.GetThumbnailImage( width,
height,
new Image.GetThumbnailImageAbort(Abort), IntPtr.Zero) )
{
smallImage.Save("thumbnail.jpg", ImageFormat.Jpeg);
}
}
于 2008-08-26T12:53:53.800 回答
6
使用上面的示例和其他几个地方的示例，这是一个简单的函数（感谢 Nathanael Jones 和其他人）。
using System.Drawing;
using System.Drawing.Drawing2D;
using System.IO;
public static void ResizeImage(string FileNameInput, string FileNameOutput, double ResizeHeight, double ResizeWidth, ImageFormat OutputFormat)
{
using (System.Drawing.Image photo = new Bitmap(FileNameInput))
{
double aspectRatio = (double)photo.Width / photo.Height;
double boxRatio = ResizeWidth / ResizeHeight;
double scaleFactor = 0;
if (photo.Width < ResizeWidth && photo.Height < ResizeHeight)
{
// keep the image the same size since it is already smaller than our max width/height
scaleFactor = 1.0;
}
else
{
if (boxRatio > aspectRatio)
scaleFactor = ResizeHeight / photo.Height;
else
scaleFactor = ResizeWidth / photo.Width;
}
int newWidth = (int)(photo.Width * scaleFactor);
int newHeight = (int)(photo.Height * scaleFactor);
using (Bitmap bmp = new Bitmap(newWidth, newHeight))
{
using (Graphics g = Graphics.FromImage(bmp))
{
g.InterpolationMode = InterpolationMode.HighQualityBicubic;
g.SmoothingMode = SmoothingMode.HighQuality;
g.CompositingQuality = CompositingQuality.HighQuality;
g.PixelOffsetMode = PixelOffsetMode.HighQuality;
g.DrawImage(photo, 0, 0, newWidth, newHeight);
if (ImageFormat.Png.Equals(OutputFormat))
{
bmp.Save(FileNameOutput, OutputFormat);
}
else if (ImageFormat.Jpeg.Equals(OutputFormat))
{
ImageCodecInfo[] info = ImageCodecInfo.GetImageEncoders();
EncoderParameters encoderParameters;
using (encoderParameters = new System.Drawing.Imaging.EncoderParameters(1))
{
// use jpeg info[1] and set quality to 90
encoderParameters.Param[0] = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 90L);
bmp.Save(FileNameOutput, info[1], encoderParameters);
}
}
}
}
}
}
于 2009-06-03T11:47:09.263 回答
3
这是 VB.NET 中 Image 类的扩展方法
Imports System.Runtime.CompilerServices
Namespace Extensions
''' <summary>
''' Extensions for the Image class.
''' </summary>
''' <remarks>Several usefull extensions for the image class.</remarks>
Public Module ImageExtensions
''' <summary>
''' Extends the image class so that it is easier to get a thumbnail from an image
''' </summary>
''' <param name="Input">Th image that is inputted, not really a parameter</param>
''' <param name="MaximumSize">The maximumsize the thumbnail must be if keepaspectratio is set to true then the highest number of width or height is used and the other is calculated accordingly. </param>
''' <param name="KeepAspectRatio">If set false width and height will be the same else the highest number of width or height is used and the other is calculated accordingly.</param>
''' <returns>A thumbnail as image.</returns>
''' <remarks>
''' <example>Can be used as such.
''' <code>
''' Dim _NewImage as Image
''' Dim _Graphics As Graphics
''' _Image = New Bitmap(100, 100)
''' _Graphics = Graphics.FromImage(_Image)
''' _Graphics.FillRectangle(Brushes.Blue, New Rectangle(0, 0, 100, 100))
''' _Graphics.DrawLine(Pens.Black, 10, 0, 10, 100)
''' Assert.IsNotNull(_Image)
''' _NewImage = _Image.ToThumbnail(10)
''' </code>
''' </example>
''' </remarks>
<Extension()> _
Public Function ToThumbnail(ByVal Input As Image, ByVal MaximumSize As Integer, Optional ByVal KeepAspectRatio As Boolean = True) As Image
Dim ReturnImage As Image
Dim _Callback As Image.GetThumbnailImageAbort = Nothing
Dim _OriginalHeight As Double
Dim _OriginalWidth As Double
Dim _NewHeight As Double
Dim _NewWidth As Double
Dim _NormalImage As Image
Dim _Graphics As Graphics
_NormalImage = New Bitmap(Input.Width, Input.Height)
_Graphics = Graphics.FromImage(_NormalImage)
_Graphics.DrawImage(Input, 0, 0, Input.Width, Input.Height)
_OriginalHeight = _NormalImage.Height
_OriginalWidth = _NormalImage.Width
If KeepAspectRatio = True Then
If _OriginalHeight > _OriginalWidth Then
If _OriginalHeight > MaximumSize Then
_NewHeight = MaximumSize
_NewWidth = _OriginalWidth / _OriginalHeight * MaximumSize
Else
_NewHeight = _OriginalHeight
_NewWidth = _OriginalWidth
End If
Else
If _OriginalWidth > MaximumSize Then
_NewWidth = MaximumSize
_NewHeight = _OriginalHeight / _OriginalWidth * MaximumSize
Else
_NewHeight = _OriginalHeight
_NewWidth = _OriginalWidth
End If
End If
Else
_NewHeight = MaximumSize
_NewWidth = MaximumSize
End If
ReturnImage = _
_NormalImage.GetThumbnailImage(Convert.ToInt32(_NewWidth), Convert.ToInt32(_NewHeight), _Callback, _
IntPtr.Zero)
_NormalImage.Dispose()
_NormalImage = Nothing
_Graphics.Dispose()
_Graphics = Nothing
_Callback = Nothing
Return ReturnImage
End Function
End Module
End Namespace
抱歉，代码标签不喜欢 vb.net 代码。
于 2008-08-26T12:54:31.707 回答
0
您可以使用 Image.GetThumbnailImage 函数为您完成此操作。
http://msdn.microsoft.com/en-us/library/system.drawing.image.getthumbnailimage.aspx (.NET 3.5)
http://msdn.microsoft.com/en-us/library/system.drawing.image.getthumbnailimage(VS.80).aspx (.NET 2.0)
public bool ThumbnailCallback()
{
return false;
}
public void Example_GetThumb(PaintEventArgs e)
{
Image.GetThumbnailImageAbort myCallback = new Image.GetThumbnailImageAbort(ThumbnailCallback);
Bitmap myBitmap = new Bitmap("Climber.jpg");
Image myThumbnail = myBitmap.GetThumbnailImage(40, 40, myCallback, IntPtr.Zero);
e.Graphics.DrawImage(myThumbnail, 150, 75);
}
于 2008-08-26T12:54:38.447 回答
0
避免 GetThumbnailImage - 它会提供非常不可预测的结果，因为它会尝试使用嵌入的 JPEG 缩略图（如果可用） - 即使嵌入的缩略图的大小完全错误。DrawImage() 是一个更好的解决方案。
将您的位图包装在 using{} 子句中 - 您不希望泄漏的句柄在周围浮动......
此外，您还需要将 Jpeg 编码质量设置为 90，这是 GDI+ 似乎表现最好的地方：
System.Drawing.Imaging.ImageCodecInfo[] info = System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders();
System.Drawing.Imaging.EncoderParameters encoderParameters;
encoderParameters = new System.Drawing.Imaging.EncoderParameters(1);
encoderParameters.Param[0] = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 90L);
thumb.Save(ms, info[1], encoderParameters);
于 2008-11-05T20:57:53.443 回答