Create a pix-it image.

CreateImage.cs

private static Image CreateImage(PixItData data)
{
  int width = data.PixelSize * data.PixelsWide;
  int height = data.PixelSize * data.PixelsHigh;
  var image = new Bitmap(width, height);
  using (Graphics g = Graphics.FromImage(image))
  {
    if (data.Background.HasValue)
    {
      Color bgColor = data.Background.Value;
      using (var brush = new SolidBrush(bgColor))
      {
        g.FillRectangle(brush, 0, 0,
          data.PixelSize * data.PixelsWide,
          data.PixelSize * data.PixelsHigh);
      }
    }
    foreach (Color color in data.Data.Keys)
    {
      using (var brush = new SolidBrush(color))
      {
        foreach (Pixel p in data.Data[color])
        {
          g.FillRectangle(brush,
            p.X*data.PixelSize,
            p.Y*data.PixelSize,
            data.PixelSize,
            data.PixelSize);
        }
      }
    }
  }
  return image;
}