gistfile1.txt

// Quick-and-dirty (and untested!) port of https://gist.github.com/3169945 to C#
Bitmap DecodeFile (string path)
{
    var opts = new BitmapFactory.Options () {
        InJustDecodeBounds = true,
    };
    using (var b = BitmapFactory.DecodeFile (path, opts)) {
        // Ignore; we're filling `opts`
    }
    const int RequiredSize = 70;
    int w = o.OutWidth;
    int h = o.OutHeight;
    int scale=1;
    while (true) {
        if ((w/2 < RequiredSize) || (h/2 < RequiredSize))
            break;
        h /= 2;
        w /= 2;
        scale *= 2;
    }
    var scaleOpts = new BitmapFactory.Options () {
        InSampleSize = scale,
    };
    return BitmapFactory.DecodeFile (path, scaleOpts);
}