Question

Is it advisable to use a handler to display Images ? the issue is i cannot right click and save these images .It shows the Handler name and Asp.net Generic handler as save type so i cant save the image but the GUI image is amazing in quality.I am showing a single image in different sizes using 2 handlers and the code works fine but if then if I don’t use the Handler i have to re size them individually and then store them in different folders.

Answer 1

I’ve successfully used this method on sites before, but it’s only of use if your particular case is suitable. If you can do it using HTML and your images are the correct size on the server, then it’s probably overkill.

If you find yourself saving several copies of the same image then you may benefit from manipulating it on the fly.

In my scenario, using a .ashx handler enabled me to upload just one large hi-res image per subject and then transform it for use in several different ways:

• Thumbnail
• Cropped image
• ‘Reflection’ effects (like it was above a shiny surface)
• Various galleries

Then it was just a case of calling it from a custom Image control and passing the correct parameters in.

EDIT :
Regarding saving the images, I can do it fine in mine as long as I force the .ashx extension that the browser tries to give it to be JPEG (or whatever).

I can’t give you a full working .ashx example, and there are so many sub-topics you’ll need to consider:

• Security – only read from certain locations
• Formats – are you going to output all images in, say, JPEG, regardles of the original format?
• HttpHandlers – how to create and use them (not just for images)
• Graphics manipulation – familiarise yourself with the Graphics object in .NET
• Memory streams

As a small example (in VB.NET), here’s a simple method to resize an image given the new width and height:

Imports System
Imports System.Web
Imports System.Drawing
Imports System.Drawing.Imaging
Imports System.IO
Imports CustomImaging
Imports System.Collections.Generic

Public Class ImgHandler : Implements IHttpHandler


  Public Sub ProcessRequest(ByVal context As HttpContext) Implements IHttpHandler.ProcessRequest

    'Process the image and output it as a stream from memory

  End Sub

  Public Shared Function ResizeImage(ByVal image As System.Drawing.Image, ByVal width As Integer, ByVal height As Integer) As System.Drawing.Bitmap
        'a holder for the result
        Dim result As New Bitmap(width, height)
        'use a graphics object to draw the resized image into the bitmap
        Dim g As Graphics = Graphics.FromImage(result)
        Try
            'set the resize quality modes to high quality
            g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality
            'draw the image into the target bitmap
            g.DrawImage(image, 0, 0, result.Width, result.Height)
        Catch ex As Exception

        Finally 'clean up resources
            If Not g Is Nothing Then g.Dispose()

        End Try
        'return the resulting image
        Return result
   End Function

   Public ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable
        Get
            Return False
        End Get
    End Property

End Class