A Simple Image Handler

<%@ WebHandler Language="VB" Class="ImageHandlerVB" %>

Imports System
Imports System.Drawing
Imports System.Drawing.Imaging
Imports System.IO
Imports System.Web
Imports System.Web.Caching

Public Class ImageHandlerVB : Implements IHttpHandler
    Public _width As Integer
    Public _height As Integer
    Public Shared noImageUrl As String = "images\no_photo.jpg"
    Public imageURL As String
    
    
    Public Sub ProcessRequest(ByVal context As HttpContext) Implements IHttpHandler.ProcessRequest
        Dim bitOutput As Bitmap
        
        If context.Cache(("ImageQueryURL-" + context.Request.QueryString.ToString())) IsNot Nothing Then
            bitOutput = DirectCast(context.Cache(("ImageQueryURL-" + context.Request.QueryString.ToString())), Bitmap)
        Else
            Dim bitInput As Bitmap = GetImage(context)
            
            bitInput = RotateFlipImage(context, bitInput)
            
            If SetHeightWidth(context, bitInput) Then
                bitOutput = ResizeImage(bitInput, _width, _height)
            Else
                bitOutput = bitInput
            End If
            
            context.Response.ContentType = "image/jpeg"
            bitOutput.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg)
            
            context.Cache.Insert(("ImageQueryURL-" + context.Request.QueryString.ToString()), bitOutput, New CacheDependency(imageURL), Cache.NoAbsoluteExpiration, TimeSpan.FromHours(8), System.Web.Caching.CacheItemPriority.BelowNormal, _
             Nothing)
        End If
        
        context.Response.ContentType = "image/jpeg"
        bitOutput.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg)
        Return
    End Sub
    
    
    ''' <summary>
    ''' Get the image requested via the query string. 
    ''' </summary>
    ''' <param name="context"></param>
    ''' <returns>Return the requested image or the "no image" default if it does not exist.</returns>
    Public Function GetImage(ByVal context As HttpContext) As Bitmap
        If context.Cache(("ImagePath-" + context.Request.QueryString("image"))) Is Nothing Then
            Dim appPath As String = context.Server.MapPath(context.Request.ApplicationPath) + Path.DirectorySeparatorChar
            
            If [String].IsNullOrEmpty(context.Request.QueryString("image")) Then
                appPath += noImageUrl
            Else
                If System.IO.File.Exists((appPath + context.Request.QueryString("image"))) Then
                    appPath += context.Request.QueryString("image")
                Else
                    appPath += noImageUrl
                End If
            End If
            
            Dim bitOutput As Bitmap
            imageURL = appPath
            
            
            bitOutput = New Bitmap(appPath)
            context.Cache.Insert(("ImagePath-" + context.Request.QueryString("image")), bitOutput, New CacheDependency(imageURL), Cache.NoAbsoluteExpiration, TimeSpan.FromHours(8), System.Web.Caching.CacheItemPriority.BelowNormal, _
             Nothing)
            Return bitOutput
        Else
            Return DirectCast(context.Cache(("ImagePath-" + context.Request.QueryString("image"))), Bitmap)
        End If
    End Function
    
    
    ''' <summary>
    ''' Set the height and width of the handler class.
    ''' </summary>
    ''' <param name="context">The context to get the query string parameters, typically current context.</param>
    ''' <param name="bitInput">The bitmap that determines the </param>
    ''' <returns>True if image needs to be resized, false if original dimensions can be kept.</returns>
    Public Function SetHeightWidth(ByVal context As HttpContext, ByVal bitInput As Bitmap) As Boolean
        Dim inputRatio As Double = Convert.ToDouble(bitInput.Width) / Convert.ToDouble(bitInput.Height)
        
        If Not ([String].IsNullOrEmpty(context.Request("width"))) AndAlso Not ([String].IsNullOrEmpty(context.Request("height"))) Then
            _width = Int32.Parse(context.Request("width"))
            _height = Int32.Parse(context.Request("height"))
            Return True
        ElseIf Not ([String].IsNullOrEmpty(context.Request("width"))) Then
            _width = Int32.Parse(context.Request("width"))
            _height = Convert.ToInt32((_width / inputRatio))
            Return True
        ElseIf Not ([String].IsNullOrEmpty(context.Request("height"))) Then
            _height = Int32.Parse(context.Request("height"))
            _width = Convert.ToInt32((_height * inputRatio))
            Return True
        Else
            _height = bitInput.Height
            _width = bitInput.Width
            Return False
        End If
    End Function
    
    ''' <summary>
    ''' Flip or rotate the bitmap according to the query string parameters.
    ''' </summary>
    ''' <param name="context">The context of the query string parameters.</param>
    ''' <param name="bitInput">The bitmap to be flipped or rotated.</param>
    ''' <returns>The bitmap after it has been flipped or rotated.</returns>
    Public Function RotateFlipImage(ByVal context As HttpContext, ByVal bitInput As Bitmap) As Bitmap
        Dim bitOut As Bitmap = bitInput
        
        If [String].IsNullOrEmpty(context.Request("RotateFlip")) Then
            Return bitInput
        ElseIf context.Request("RotateFlip") = "Rotate180flipnone" Then
            bitOut.RotateFlip(RotateFlipType.Rotate180FlipNone)
        ElseIf context.Request("RotateFlip") = "Rotate180flipx" Then
            bitOut.RotateFlip(RotateFlipType.Rotate180FlipX)
        ElseIf context.Request("RotateFlip") = "Rotate180flipxy" Then
            bitOut.RotateFlip(RotateFlipType.Rotate180FlipXY)
        ElseIf context.Request("RotateFlip") = "Rotate180flipy" Then
            bitOut.RotateFlip(RotateFlipType.Rotate180FlipY)
        ElseIf context.Request("RotateFlip") = "Rotate270flipnone" Then
            bitOut.RotateFlip(RotateFlipType.Rotate270FlipNone)
        ElseIf context.Request("RotateFlip") = "Rotate270flipx" Then
            bitOut.RotateFlip(RotateFlipType.Rotate270FlipX)
        ElseIf context.Request("RotateFlip") = "Rotate270FlipXY" Then
            bitOut.RotateFlip(RotateFlipType.Rotate270FlipXY)
        ElseIf context.Request("RotateFlip") = "Rotate270FlipY" Then
            bitOut.RotateFlip(RotateFlipType.Rotate270FlipY)
        ElseIf context.Request("RotateFlip") = "Rotate90FlipNone" Then
            bitOut.RotateFlip(RotateFlipType.Rotate90FlipNone)
        ElseIf context.Request("RotateFlip") = "Rotate90FlipX" Then
            bitOut.RotateFlip(RotateFlipType.Rotate90FlipX)
        ElseIf context.Request("RotateFlip") = "Rotate90FlipXY" Then
            bitOut.RotateFlip(RotateFlipType.Rotate90FlipXY)
        ElseIf context.Request("RotateFlip") = "Rotate90FlipY" Then
            bitOut.RotateFlip(RotateFlipType.Rotate90FlipY)
        ElseIf context.Request("RotateFlip") = "RotateNoneFlipX" Then
            bitOut.RotateFlip(RotateFlipType.RotateNoneFlipX)
        ElseIf context.Request("RotateFlip") = "RotateNoneFlipXY" Then
            bitOut.RotateFlip(RotateFlipType.RotateNoneFlipXY)
        ElseIf context.Request("RotateFlip") = "RotateNoneFlipY" Then
            bitOut.RotateFlip(RotateFlipType.RotateNoneFlipY)
        Else
            Return bitInput
        End If
        
        Return bitOut
    End Function
    
    
    ''' <summary>
    ''' Resizes bitmap using high quality algorithms.
    ''' </summary>
    ''' <param name="originalBitmap"></param>
    ''' <param name="newWidth">The width of the returned bitmap.</param>
    ''' <param name="newHeight">The height of the returned bitmap.</param>
    ''' <returns>Resized bitmap.</returns>
    Public Shared Function ResizeImage(ByVal originalBitmap As Bitmap, ByVal newWidth As Integer, ByVal newHeight As Integer) As Bitmap
        Dim inputBitmap As Bitmap = originalBitmap
        Dim resizedBitmap As New Bitmap(newWidth, newHeight, PixelFormat.Format24bppRgb)
        
        Dim g As Graphics = Graphics.FromImage(resizedBitmap)
        g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality
        g.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceCopy
        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic
        Dim rectangle As New Rectangle(0, 0, newWidth, newHeight)
        g.DrawImage(inputBitmap, rectangle, 0, 0, inputBitmap.Width, inputBitmap.Height, _
         GraphicsUnit.Pixel)
        g.Dispose()
        
        Return resizedBitmap
    End Function
    
    
    Public ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable
        Get
            Return True
        End Get
    End Property
End Class