Dynamic thumbnail images from ASP.NET
Dynamic thumbnail images from ASP.NET Author: Brock Allen
From:
http://staff.develop.com/ballen/blog/ i have had this sampe code of dynamic thumbnail generation kicking around for some time, so I've finally gotten the time to post it here. This sample code is an IHttpHandler implementation that reads a JPG from the filesystem and dynamically generates a thumbnail sized version of the image and emits that to the response stream. What I like about this approach is that you don't need to create a file on the filesystem for the thumbnail as it's all done in memory. This really shows how cool (and useful, of course) IHttpHandler is. Here's the gist of the implementation:
public class ImageHandler : IHttpHandler
{
// the max size of the Thumbnail
const int MaxDim = 120;
public void ProcessRequest(HttpContext ctx)
{
// let's cache this for 1 day
ctx.Response.ContentType = "image/jpeg";
ctx.Response.Cache.SetCacheability(HttpCacheability.Public);
ctx.Response.Cache.SetExpires(DateTime.Now.AddDays(1));
// find the directory where we're storing the images
string imageDir = ConfigurationSettings.AppSettings["imageDir"];
imageDir = Path.Combine(
ctx.Request.PhysicalApplicationPath, imageDir);
// find the image that was requested
string file = ctx.Request.QueryString["File"];
file = Path.Combine(imageDir, file);
// load it up
using (Image img = new Bitmap(file))
{
// do some math to resize the image
// note: i know very little about image resizing,
// but this just seemed to work under v1.1. I think
// under v2.0 the images look incorrect.
// *note to self* fix this for v2.0
int h = img.Height;
int w = img.Width;
int b = h > w ? h : w;
double per = (b > MaxDim) ? (MaxDim * 1.0) / b : 1.0;
h = (int)(h * per);
w = (int)(w * per);
// create the thumbnail image
using (Image img2 =
img.GetThumbnailImage(w, h,
new Image.GetThumbnailImageAbort(Abort),
IntPtr.Zero))
{
// emit it to the response strea,
img2.Save(ctx.Response.OutputStream,
System.Drawing.Imaging.ImageFormat.Jpeg);
}
}
}
public bool IsReusable
{
get { return true; }
}
private bool Abort()
{
return false;
}
}
This was originally published on Brock Allen's Blog here:
http://staff.develop.com/ballen/blog/ brock Allen is an instructor for DevelopMentor where he teaches .NET and ASP.NET. He also manages the ASP.NET curriculum at DevelopMentor by doing research and course development. When not teaching, Brock is an independent consultant doing mentoring, architecture and development work.
(2006-4-05:04:02)
vb.net版本
02/08/2006 by
Jeremy Wadsworth
here is the C# code converted to VB.NET. It contains a few minor modifications that are specific to my site. Anyone using either set of code for the Personal Sit Kit will need to modify it to suit their needs.
<%@ WebHandler Language="VB" Class="Handler" %>
imports System.IO
Imports System.Drawing
Imports System.Drawing.Image
Public Class Handler
Implements IHttpHandler
'the max size of the thumbnail
Const MaxDim As Integer = 120
Dim imagedirectory As String = ""
Dim imagename as String = ""
ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable
Get
Return True
End Get
End Property
Public Sub ProcessRequest(ByVal context As System.Web.HttpContext) Implements System.Web.IHttpHandler.ProcessRequest
With context
If Not .Request.QueryString("Dir") Is Nothing And .Request.QueryString("Dir") <> "" Then
imagedirectory = .Request.QueryString("Dir")
Else
Exit Sub
End If
If Not .Request.QueryString("File") Is Nothing And .Request.QueryString("File") <> "" Then
imagename = .Request.QueryString("File")
imagename = imagename.Replace("\", "/")
imagename = imagename.Replace("//", "/")
End If
With .Response
.contenttype = "image/jpeg"
.Cache.SetCacheability(HttpCacheability.Public)
.Cache.SetExpires(DateTime.Now.AddDays(1))
End With
'find the image that was requested
Dim file As String = ""
file = imagedirectory &;amp; imagename
file = .Request.MapPath(file)
'load the image
Using img As Image = New Bitmap(file)
'do some math to resize the image
Dim h As Integer = img.Height
Dim w As Integer = img.Width
Dim b As Integer
If h > w Then
b = h
Else
b = w
End If
Dim per As Double
If b > MaxDim Then
per = ((MaxDim * 1.0) / b)
Else
per = 1.0
End If
h = CType((h * per), Integer)
w = CType((w * per), Integer)
'create the thumbnail image
Using img2 As Image = img.GetThumbnailImage(w, h, New Image.GetThumbnailImageAbort(AddressOf Abort), IntPtr.Zero)
'emit it to the response stream,
img2.Save(.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg)
End Using
End Using
End With
End Sub
Private Function Abort() As Boolean
Return False
End Function (2006-4-05:04:02)
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