Texture2D.LoadRawTextureData can be load ETC1 format Texture with no opposite?

When I use Texture2D.LoadRawTextureData to Load ECT1 format Tetxture but the loaded texture is opposite. it can be slove?

This is the code

     string path = Application.dataPath + "/a.pkm";
     byte[] source = File.ReadAllBytes(path);

     Debug.Log(source.Length);

     int headerSize = 16;
     for(int i = 0 ; i < headerSize ; i++)
     {
         Debug.Log(source[i]);
     }

     byte[] buffer = new byte[source.Length - headerSize];
     System.Buffer.BlockCopy(source, headerSize, buffer, 0, source.Length - headerSize);

     Texture2D tex = new Texture2D(512,512, TextureFormat.ETC_RGB4, false, true);

     tex.LoadRawTextureData(buffer);
     tex.Apply();