Encode an image as a single line string

ImgString.cs

static double _Scale = 0.03;

static void Main(string[] args)
{
    byte[] r1 = Zip(EncodeBitmap(new Bitmap(@"C:\Users\brad.martin\Desktop\highMag.jpg")));
    Bitmap bmp = DecodeBitmap(Unzip(r1));
    bmp.Save(@"C:\Users\brad.martin\Desktop\test.png");
    Console.WriteLine(Convert.ToBase64String(r1));
    Console.ReadKey();
}

static string EncodeBitmap(Bitmap bmp)
{
    bmp = new Bitmap(bmp, new Size((int)(bmp.Width * _Scale), (int)(bmp.Height * _Scale)));
    StringBuilder sb = new StringBuilder();
    for (int j = 0; j < bmp.Height; j++)
    {
        for (int i = 0; i < bmp.Width; i++)
            sb.Append((char)Map(bmp.GetPixel(i, j).R));
        sb.Append('~');
    }
    return sb.ToString();
}

static Bitmap DecodeBitmap(string data)
{
    string[] lines = data.Split('~');
    Bitmap bmp = new Bitmap(lines[0].Length - 1, lines.Length - 1);
    for (int j = 0; j < bmp.Height; j++)
        for (int i = 0; i < bmp.Width; i++)
        {
            int val = Map(lines[j][i] - '0', inv: true);
            if (val < 0) val = 0;
            bmp.SetPixel(i, j, Color.FromArgb(255, val, val, val));
        }
    return bmp;
}

static int Map(double value, double fromLow = 0, double fromHigh = 255, double toLow = 0, double toHigh = 125, bool inv = false)
{
    if (inv)
    {
        fromHigh = toHigh;
        toHigh = 255;
    }
    return (int)((value - fromLow) * (toHigh - toLow) / (fromHigh - fromLow) + toLow);
}

public static void CopyTo(Stream src, Stream dest)
{
    byte[] bytes = new byte[4096];
    int cnt;
    while ((cnt = src.Read(bytes, 0, bytes.Length)) != 0)
        dest.Write(bytes, 0, cnt);
}

public static byte[] Zip(string str)
{
    var bytes = Encoding.UTF8.GetBytes(str);
    using (var msi = new MemoryStream(bytes))
    using (var mso = new MemoryStream())
    {
        using (var gs = new GZipStream(mso, CompressionMode.Compress))
            CopyTo(msi, gs);
        return mso.ToArray();
    }
}

public static string Unzip(byte[] bytes)
{
    using (var msi = new MemoryStream(bytes))
    using (var mso = new MemoryStream())
    {
        using (var gs = new GZipStream(msi, CompressionMode.Decompress))
            CopyTo(gs, mso);
        return Encoding.UTF8.GetString(mso.ToArray());
    }
}