How to convert file .DEX (Dexis image file) to jpg image format using c#

I writing a program that it can read .Dex file (Dexis X-ray image file) and convert it to jpg image. but i can't find out how to decode it. i use this code to read and convert but the image is corrupt.

Read Image:

public static byte[] ImageToByte(string IMG_PATH)
    {
        byte[] img = null;
        try
        {
            FileStream IM_STREAM = new FileStream(IMG_PATH, FileMode.Open, FileAccess.Read);
            BinaryReader IM_BNR = new BinaryReader(IM_STREAM);
            img = IM_BNR.ReadBytes((int)IM_STREAM.Length);
            IM_BNR.Close();
            IM_STREAM.Close();                
        }
        catch (Exception ex)
        {
            StreamWriter swr = new StreamWriter("LOG.txt", true, Encoding.UTF8);
            swr.WriteLine(ex.Message);
            swr.Close();
        }
        return img;
    }

Convert Image:

public static void SaveToFile(string path, byte[] b)
    {
        MemoryStream ms = new MemoryStream(b);
        Image img = Image.FromStream(ms);

        img.Save(path + "\\exam.jpg", System.Drawing.Imaging.ImageFormat.Jpeg);
        img.Dispose();
    }

The image before convert (.Dex, size 800x600px) -> after convert (.jpg, size 80x60). plz help me.