[RESOLVED] Caching thumbnails

[olamm2k]

Hi,

I'm using an asp.net page to dynamically create thumbnails, and I was thinking I should try and cache them to load them a bit faster. I've never tried using the Cache object before, but I'm sure it should work like I'm trying to use it. Anyway, here's the code for caching and retrieving the thumbnail:

Dim bmp As Bitmap = Cache.Get(strPath & "_" & sWidth & "_" & sHeight)
 
  If bmp Is Nothing Then 
    bmp = CreateThumbnail(strPath, sWidth, sHeight)
    Cache.Insert(strPath & "_" & sWidth & "_" & sHeight, _
     bmp, Nothing, DateTime.MaxValue, TimeSpan.Zero)
  End If
  If bmp Is String.Empty Then Return

strPath is the location of the photo, sWidth the width and sHeight the height. The thumbnail is then saved to the output stream. Unfortunately, this doesn't seem to work.

Any ideas?

[mendhak]

If the page itself is serving out the images (dynamic images), then add an OutputCache directive to the page:

<%@ OutputCache duration="10000" varybyparam="ImageID" %>

[olamm2k]

Does that mean I'll need to create an ImageID variable? Something along the lines of the 'strPath & "_" & sWidth & "_" & sHeight' I've used for the Cache key? What kind of scope does this need to have?

Oh - and the error I was getting was 'invalid parameter' in the Bitmap.Save() call. It must be something to do with what gets stored in the Cache object.

[mendhak]

What I mean is, when the image is requested, the request will look like this:

myimage.aspx?ImageID=28391

All you should do in the page is retrieve it from the DB. The next time the image is requested, the cache object will serve it automatically.

[olamm2k]

The image is requested by filename - they're not stored in a database. The resize script also accepts different parameters for the width and height. Does whatever I use as my 'varybyparam' need to be in the QueryString?

[mendhak]

But you're still using a myimage.aspx page right?

Yes, whatever you use as your varybyparam must be in the querystring, else it defeats the purpose of caching it.

[olamm2k]

Well, I somehow missed that last post of yours - failed to get the email notification. Anyway, here's what I ended up doing:

<%@ Page Language="VB" Debug="False" Trace="False" %>
<%@Import Namespace="System.Drawing" %>
<%@Import Namespace="System.Drawing.Imaging" %>
<%@Import Namespace="System.Drawing.Drawing2D" %>
 
<script language="VB" runat="server">
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load 
  Dim strImage As String = Replace(Request.QueryString("image"), "%20", " ")
  Dim strAlbum as String = Replace(Request.QueryString("album"), "%20", " ")
 
  If strImage = String.Empty Or strAlbum = String.Empty Then Exit Sub
  If InStr(strImage, "/") <> 0 Or InStr(strImage, "\") <> 0 Or _
   InStr(strAlbum, "/") <> 0 Or InStr(strAlbum, "\") <> 0 Then
    Exit Sub
  End If
 
  Dim sWidth = Request("w")
  Dim sHeight = Request("h")
 
  If Not sHeight = String.Empty And Not sWidth = String.Empty Then 
    sWidth = Integer.Parse(sWidth)
    sHeight = Integer.Parse(sHeight)
  Else
    sWidth = 20
    sHeight = 20
  End If
 
  Dim strPath As String = Server.MapPath("photos/" & strAlbum & "/" & strImage)
  Dim fsMain As System.IO.FileStream = New System.IO.FileStream(strPath, _
   System.IO.FileMode.OpenOrCreate, System.IO.FileAccess.Read)
 
  'Cache.Remove(strPath & "_" & sWidth & "_" & sHeight)
  Dim bytImage As Byte() = Cache.Get(strPath & "_" & sWidth & "_" & sHeight)
 
  Dim msTempStream As System.IO.MemoryStream
  Dim imgMain As System.Drawing.Image
 
  If bytImage Is Nothing Then
    ReDim bytImage(fsMain.Length)
    fsMain.Read(bytImage, 0, fsMain.Length)
    fsMain.Close()
 
    msTempStream = New System.IO.MemoryStream(bytImage)
    imgMain = System.Drawing.Image.FromStream(msTempStream)
 
    Dim lnRatio As Decimal
    Dim lnNewWidth As Integer = 0
    Dim lnNewHeight As Integer = 0
    If (imgMain.Width > imgMain.Height) Then
      lnRatio = Integer.Parse(sWidth) / imgMain.Width
      lnNewWidth = Integer.Parse(sWidth)
      Dim lnTemp As Decimal = imgMain.Height * lnRatio
      lnNewHeight = lnTemp
    Else 
      lnRatio = Integer.Parse(sHeight) / imgMain.Height
      lnNewHeight = Integer.Parse(sHeight)
      Dim lnTemp As Decimal = imgMain.Width * lnRatio
      lnNewWidth = lnTemp
    End If
 
    Dim imgThumbnail As System.Drawing.Image = New Bitmap(lnNewWidth, lnNewHeight)
    Dim graThumbnail As System.Drawing.Graphics = System.Drawing.Graphics.FromImage(imgThumbnail)
 
    graThumbnail.InterpolationMode = InterpolationMode.HighQualityBicubic
    graThumbnail.SmoothingMode = SmoothingMode.HighQuality
    graThumbnail.PixelOffsetMode = PixelOffsetMode.HighQuality
    graThumbnail.CompositingQuality = CompositingQuality.HighQuality
    graThumbnail.DrawImage(imgMain, 0, 0, lnNewWidth, lnNewHeight)
 
    Dim iciInfo() As ImageCodecInfo = ImageCodecInfo.GetImageEncoders()
    Dim encpMain As EncoderParameters = New EncoderParameters(1)
    encpMain.Param(0) = New EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 100L)
 
    Dim strOutputFilename As String = String.Empty 
    strOutputFilename = Request.QueryString("OutputFilename") 
 
    If Not strOutputFilename = String.Empty Then 
      Try 
        imgThumbnail.Save(Server.MapPath("photos/" & strAlbum & "/") & strOutputFilename, ImageFormat.Jpeg)
      Catch ex As Exception 
        imgThumbnail.Dispose() 
        Return
      End Try 
    End If
 
    Response.ContentType = "image/jpeg" 
    Dim msSaveStream As System.IO.MemoryStream = New System.IO.MemoryStream
    imgThumbnail.Save(msSaveStream, iciInfo(1), encpMain)
    msSaveStream.WriteTo(Response.OutputStream)
    Dim bytSave(msSaveStream.Length) As Byte
    msSaveStream.Position = 0
    msSaveStream.Read(bytSave, 0, msSaveStream.Length)
    Cache.Insert(strPath & "_" & sWidth & "_" & sHeight, _
     bytSave, Nothing, DateTime.MaxValue, TimeSpan.Zero)
    imgThumbnail.Dispose()
  Else
    msTempStream = New System.IO.MemoryStream(bytImage)
    Response.ContentType = "image/jpeg" 
    msTempStream.WriteTo(Response.OutputStream)
 
    Dim strOutputFilename As String = String.Empty 
    strOutputFilename = Request.QueryString("OutputFilename") 
 
    If Not strOutputFilename = String.Empty Then 
      Try 
        imgMain = System.Drawing.Image.FromStream(msTempStream)
        imgMain.Save(Server.MapPath("photos/" & strAlbum & "/") & strOutputFilename, ImageFormat.Jpeg)
      Catch ex As Exception 
        imgMain.Dispose() 
        Return
      End Try 
      imgMain.Dispose() 
    End If
  End If
End Sub 
</script>

There's a distinct lack of comments, but essentially, instead of caching the Image object, I cache a byte array containing the image.

What do you reckon? Is there going to be a big difference in speed?

[mendhak]

Not a big difference, just a tiny one when it comes to the point where it attempts to query the cache to retrieve the image before it then proceeds to read the image from disk.

If you expect the page to be heavily used then you might want to consider what I suggested. Else you can stick to what you have now, it's fine, good work.

[olamm2k]

Thanks