FileImageSourceHandler from Xamarin.Forms https://github.com/xamarin/Xamarin.Forms/blob/b96f65bdd9e7e931971338b122a8940e2a35ccc7/Xamarin.Forms.Platform.Android/Renderers/FileImageSourceHandler.cs#L18-L33

FileImageSourceHandler.cs

public async Task<Bitmap> LoadImageAsync(ImageSource imagesource, Context context, CancellationToken cancelationToken = default(CancellationToken))
{
  string file = ((FileImageSource)imagesource).File;
  Bitmap bitmap;
  if (File.Exists (file))
    bitmap = !DecodeSynchronously ? (await BitmapFactory.DecodeFileAsync (file).ConfigureAwait (false)) : BitmapFactory.DecodeFile (file);
  else
    bitmap = !DecodeSynchronously ? (await context.Resources.GetBitmapAsync (file).ConfigureAwait (false)) : context.Resources.GetBitmap (file);


  if (bitmap == null)
  {
    Log.Warning(nameof(FileImageSourceHandler), "Could not find image or image file was invalid: {0}", imagesource);
  }


  return bitmap;
}