Be care using the WriteableBitmap as you may run out of memory if resizing a lot of images. If you only have a few, then pass the size you want saved to the SaveJpeg method. Also make sure you use a value higher than 0 for the quality (last param of SaveJpeg)
var width = wb.PixelWidth/4;
var height = wb.PixelHeight/4;
using (MemoryStream stream = new MemoryStream())
{
wb.SaveJpeg(stream, width, height, 0, 100);
...
...
}
You can also use the JpegRenderer from the Nokia Imaging SDK to resize an image.
var width = wb.PixelWidth/4;
var height = wb.PixelHeight/4;
using (var imageProvider = new StreamImageSource(e.ChosenPhoto))
{
IFilterEffect effect = new FilterEffect(imageProvider);
// Get the resize dimensions
Windows.Foundation.Size desiredSize = new Windows.Foundation.Size(width, height);
using (var renderer = new JpegRenderer(effect))
{
renderer.OutputOption = OutputOption.PreserveAspectRatio;
// set the new size of the image
renderer.Size = desiredSize;
IBuffer buffer = await renderer.RenderAsync();
return buffer;
}
}