HTML Image SRC Android AsyncTask

Good afternoon, I'm developing an Android application that needs to consume Web Service, but the detail is that the content of one of the data comes in a hypertext format, therefore I have to convert it to Android, sometimes it comes with images src and I also have to show, I have the following code with AsyncTask:

 class ConvertirDatos extends AsyncTask<Html.ImageGetter, String, Html.ImageGetter> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        progressDialog.setTitle("Obteniendo detalles");
        progressDialog.setCancelable(false);
        progressDialog.setIcon(R.drawable.logo);
        progressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);

        progressDialog.show();

    }

    @Override
    **protected Html.ImageGetter doInBackground(Html.ImageGetter... imageGetters) {
        Html.ImageGetter imageHTML = new Html.ImageGetter() {
            @Override
            public Drawable getDrawable(String s) {
                try {
                    Drawable d = Drawable.createFromStream(new URL(s).openStream(), "srcName");
                    d.setBounds(0, 0, d.getMinimumWidth(), d.getMinimumHeight());
                    return d;
                } catch (IOException e) {
                    Log.v("IOException", e.getMessage());
                    e.printStackTrace();
                    return null;
                }
            }
        };
        return imageHTML;**

    }
    @Override
    protected void onPostExecute(Html.ImageGetter imageGetter) {
        super.onPostExecute(imageGetter);
        Bundle bundle = getIntent().getExtras();
        String contenido = (String) bundle.get("contenido");


        if (contenido.equals("") && contenido !=null){
            tvContenido.setText("Para más información descarga los archivos asociados");
        }else {
            **Spanned s = Html.fromHtml(contenido, doInBackground(), null);
            tvContenido.setAutoLinkMask(Linkify.WEB_URLS);
            tvContenido.setLinksClickable(true);
            tvContenido.setText(s);**
        }


        progressDialog.dismiss();
    }

The detail is in when I load heavy images, it is loaded in the main thread, it does not show me the progressDialog, and the screen remains in black, I do not know if I am implementing the AsyncTask badly.

Thanks for the help. Happy year