Save PoE map to png

TerrainToPng.cs

/// <summary>
/// 
/// </summary>
/// <param name="filename"></param>
/// <param name="data">LokiPoe.TerrainData.Layer0</param> 
/// <param name="terrainSize">LokiPoe.TerrainData.Size</param> 
/// <param name="bpr">LokiPoe.TerrainData.BytesPerRow</param>
public static void GeneratePng(string filename, ref byte[] data, Vector2i terrainSize, int bpr)
{
    Color TerrainColor(int v)
    {
        var color = Color.Black;
        switch (v)
        {
            case 0:
                color = Color.Transparent;
                break;
            case 1:
                color = Color.White;
                break;
            case 2:
                color = Color.Blue;
                break;
            case 3:
                color = Color.Turquoise;
                break;
            case 4:
                color = Color.Green;
                break;
            case 5:
                color = Color.Yellow;
                break;
            case 6:
                color = Color.Orange;
                break;
            case 7:
                color = Color.Red;
                break;
            case 255:
                color = Color.Gray;
                break;
            default:
                color = Color.Pink;
                break;
        }
        return Color.FromArgb(30, color);
    }

    var areaSize = terrainSize * 23;
    var width = areaSize.X % 2 == 0 ? areaSize.X : areaSize.X + 1;
    using (var img = new Bitmap(width, areaSize.Y))
    {
        var terrainBytes = data;
        int dataIndex = 0;
        for (int y = 0; y < areaSize.Y; y++)
        {
            for (int x = 0; x < areaSize.X; x += 2)
            {
                var b = terrainBytes[dataIndex + (x >> 1)];

                img.SetPixel(x, y, TerrainColor(b & 0xf));
                img.SetPixel(x+1, y, TerrainColor(b >> 4));
            }
            dataIndex += bpr;
        }
        img.Save(filename);
    }
}