How to Convert RenderTargetBitmap to WriteableBitmap

1. var bitmap = new RenderTargetBitmap();  
2. await bitmap.RenderAsync(Cam); //Cam is your Gird    
3. var pixelBuffer = await bitmap.GetPixelsAsync();  
4. byte[] pixels = pixelBuffer.ToArray();  
5. var wb = new WriteableBitmap((int) bitmap.PixelWidth, (int) bitmap.PixelHeight);  
6. using(Stream stream = wb.PixelBuffer.AsStream())  
7. {  
8.     await stream.WriteAsync(pixels, 0, pixels.Length);  
9. }