Resizing images in Silverlight using WriteableBitmap

// create image source
Stream stream = file.OpenRead();
BitmapImage bmpImg = new BitmapImage();
bmpImg.SetSource(stream);
stream.Close();

// create temporary image from it
Image tmpImg = new Image();
tmpImg.Source = bmpImg;

// this is required by WriteableBitmap
tmpImg.Measure(new Size(100, 100));
tmpImg.Arrange(new Rect(0, 0, 100, 100));

// prepare scaling to 100×100
ScaleTransform scaleTrans = new ScaleTransform();
double scale = (double)100 / (double)Math.Max(bmpImg.PixelHeight, bmpImg.PixelWidth);
scaleTrans.CenterX = 0;
scaleTrans.CenterY = 0;
scaleTrans.ScaleX = scale;
scaleTrans.ScaleY = scale;

// render
WriteableBitmap writeableBitmap = new WriteableBitmap(100, 100);
writeableBitmap.Render(tmpImg, scaleTrans);
writeableBitmap.Invalidate();

// final image
Image img = new Image();
img.Source = writeableBitmap;