Question

I’m making a Windows Phone 7 application which involves getting large images from the web and putting it in a ScrollViewer for the user to scroll through. I think I’m hitting a limitation of BitmapImage, though, as the image seems to get cut off at 2048 pixels in either height or width.

Is this a known limitation of Silverlight BitmapImage and is there some other class to use in this case to allow scrolling through the large images?

Thanks

Answer 1

Yes, there is a limit of 2k x 2k. This is limitation and a workaround are described in the white paper “Creating High Performing Silverlight Applications for Windows Phone” http://www.microsoft.com/downloads/en/details.aspx?displaylang=en&FamilyID=3a8636bf-185f-449a-a0ce-83502b9ec0ec

Size Limitations: Since the Windows
Phone camera is 5 MP and the screen
resolution is smaller than on other
platforms, the limits for images that
can be processed are 2k x 2k pixels.
Anything larger than that will be
automatically sampled at a lower
resolution and the image will lose
some richness. Processing Images
Larger than 2k x 2k There are
scenarios where you need to process
images larger than 2k x 2k, e.g. Photo
editor, or cropping images. In those
scenarios, you can process the images
that are larger than 2k x 2k into a
file, and then display a portion that
fits into 2K x 2K. You can use the
combination of WriteableBitmap with
LoadJpeg to do it.   Example #5 –
LoadingLargeImages

XAML:

<StackPanel>
    <Image Height="3000" Width="3000" Name="image1" Stretch="Fill" />
    <Button Content="Load" Height="70" Width="152" Click="btnLoad_Click" />
</StackPanel>

Code Behind:

private void btnLoad_Click(object sender, RoutedEventArgs e)
{
    StreamResourceInfo sri = null;
    Uri uri = new                                                                           Uri("LoadJpegSample;component/Test3k3k.JPG", UriKind.Relative);
    sri = Application.GetResourceStream(uri);

    WriteableBitmap wb = new WriteableBitmap((int)this.image1.Width, (int)this.image1.Height);

    Extensions.LoadJpeg(wb, sri.Stream);
    this.image1.Source = wb;
}

Things to Know When Using Larger than
2k x 2k Images:

• It is significantly slower to display
• Do NOT use it for animation or panning scenarios.

The Resize method of the WriteableBitmapEx can also be used for this task if no JPEG stream is available.