How to save BitmapImage / WriteableBitmap using SaveFileDialog in Silverlight 3.0?

Question

How can a WriteableBitmap from Silverlight be Saved onto the File System, I am unsure what to do with the FileStream to make this work, it can be in Bitmap, PNG, Jpeg format etc, as long as a commercial library is not required.
Is it possible to do this?

Here is my call to SaveDialog, below:

    Dim SaveDialog As New SaveFileDialog
    If SaveDialog.ShowDialog Then
        Try
            Using FileStream As Stream = SaveDialog.OpenFile
               ' Save Image File Code Here
            End Using
        Catch ex As Exception

        End Try
    End If

Edit

Added mention of WritableBitmap as this is what my XAML is writing to, I just need to save it, there is a WriteableBitmap.Pixels property which is a 1-dimensional array of integer pixels, can this be put into a filestream, and if so, how?

---

Here is some example code I have that writes the Pixel Stream to a File, however this works it does not "bitmapify" the data and the resulting output is useless but it is writing my image stream, I just need to know how to mark-it-up so that it is a Bitmap file (or anything else). I have found the JPEG and PNG examples before, but none of them explain well how they work, I may have to use the PNGEncoding method as this is the only one that will integrate into my codebase. But is there a simple BMP file version out there?

        Dim Image As Imaging.WriteableBitmap = _Style.Image
        Dim Area As Integer = Image.PixelWidth * Image.PixelHeight
        For Raster As Integer = 0 To Area - 1
            Dim Pixel As Integer = Image.Pixels(Raster)
            Dim Bytes() = BitConverter.GetBytes(Pixel And &HFF)
            FileStream.Write(Bytes, 0, 4)
        Next

Answer 1

There are a several open-source encoders out there:

FJCore: http://code.google.com/p/fjcore/

Joe Stegman's PNG Encoder: http://blogs.msdn.com/jstegman/archive/2008/04/21/dynamic-image-generation-in-silverlight.aspx

FreeImage: http://freeimage.sourceforge.net/

You can use any of these to encode various formats. Here's a post on saving a WriteableBitmap once it's baked:

http://community.irritatedvowel.com/blogs/pete%5Fbrowns%5Fblog/archive/2009/03/18/Silverlight-3-%5F1320%5F-The-Bitmap-API-%5F2F00%5F-WriteableBitmap.aspx

UPDATE: After doing some more searching it looks like saving a WriteableBitmap to a file is limited in SL3 due to security issues. There is a workaround:

http://geekswithblogs.net/braulio/archive/2009/07/12/export-canvas-to-png-and-save-it-in-your-local.aspx

Looks like you have to save the contents of a Canvas to a file. You should be able to modify the sample to save JPEG or other formats.

Answer 2

I have previously written this post that goes through how to save XAML to a bitmap using a writeable bitmap, the save dialog box and FJCore.

http://blog.blueboxes.co.uk/2009/07/21/rendering-xaml-to-a-jpeg-using-silverlight-3/