How to get Nearest Neighbor image scaling working in Wilverlight or WP7

PixelImageConverer.cs

using System;
using System.Linq;
using System.Windows.Data;
using System.Windows.Media.Imaging;

namespace WPNearestNeighbor
{
    public class PixelImageConverter : IValueConverter
    {
        /// <summary>
        /// This converter creates a BitmapImage from image path as string that is scaled according
        /// to the widht,height that is specified in the parameter
        /// Expected usage:
        /// <example>
        ///             <Image Source="{Binding Path=TheImage, 
        ///                               Converter={StaticResource PixelImageConverter1}, 
        ///                               ConverterParameter=64\,64}"
        ///              Width="64" 
        ///              Height="64"/>
        /// </example>
        /// </summary>
        /// <param name="value"></param>
        /// <param name="targetType"></param>
        /// <param name="parameter"></param>
        /// <param name="culture"></param>
        /// <returns></returns>
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            var val = (string)value;
            var param = ((string)parameter).Split(',').Select(s => int.Parse(s)).ToArray();
            var width = param[0];
            var height = param[1];

            var src_img = new BitmapImage(new Uri(val, UriKind.Relative));
            src_img.CreateOptions = BitmapCreateOptions.None;
            var src_bmp = new WriteableBitmap(src_img);
            var res_bmp = new WriteableBitmap(width, height);

            var xscale = (double)src_bmp.PixelWidth / (double)width;
            var yscale = (double)src_bmp.PixelHeight / (double)height;

            for (int x = 0; x < width; x++)
            {
                for (int y = 0; y < height; y++)
                {
                    var xsrc = (int)(x * xscale);
                    var ysrc = (int)(y * yscale);
                    res_bmp.Pixels[x + y * width] = src_bmp.Pixels[xsrc + ysrc * src_bmp.PixelWidth];
                }
            }

            return res_bmp;
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            return null;
        }

    }
}