diff --git a/libisofs/filter.c b/libisofs/filter.c
index a7f2be6..27c72e1 100644
--- a/libisofs/filter.c
+++ b/libisofs/filter.c
@@ -47,3 +47,20 @@ int iso_file_add_filter(IsoFile *file, FilterContext *filter, int flag)
     file->stream = filtered;
     return ISO_SUCCESS;
 }
+
+
+/* ts A90328 */
+int iso_file_remove_filter(IsoFile *file, int flag)
+{
+    IsoStream *file_stream, *input_stream;
+
+    file_stream = file->stream;
+    input_stream = iso_stream_get_input_stream(file_stream, 0);
+    if (input_stream == NULL)
+        return 0;
+    file->stream = input_stream;
+    iso_stream_ref(input_stream); /* Protect against _unref(file_stream) */
+    iso_stream_unref(file_stream);
+    return 1;
+}
+
diff --git a/libisofs/filters/external.c b/libisofs/filters/external.c
index c1ce501..4462953 100644
--- a/libisofs/filters/external.c
+++ b/libisofs/filters/external.c
@@ -473,6 +473,9 @@ void extf_stream_free(IsoStream *stream)
         return;
     }
     data = stream->data;
+    if (data->running != NULL) {
+        extf_stream_close(stream);
+    }
     iso_stream_unref(data->orig);
     if (data->cmd->refcount > 0)
         data->cmd->refcount--;
@@ -488,8 +491,20 @@ int extf_update_size(IsoStream *stream)
 }
 
 
+IsoStream *extf_get_input_stream(IsoStream *stream, int flag)
+{
+    ExternalFilterStreamData *data;
+
+    if (stream == NULL) {
+        return NULL;
+    }
+    data = stream->data;
+    return data->orig;
+}
+
+
 IsoStreamIface extf_stream_class = {
-    1,
+    2,
     "extf",
     extf_stream_open,
     extf_stream_close,
@@ -498,7 +513,8 @@ IsoStreamIface extf_stream_class = {
     extf_stream_is_repeatable,
     extf_stream_get_id,
     extf_stream_free,
-    extf_update_size
+    extf_update_size,
+    extf_get_input_stream
 };
 
 
diff --git a/libisofs/fs_image.c b/libisofs/fs_image.c
index 4b3f4e2..c0544a1 100644
--- a/libisofs/fs_image.c
+++ b/libisofs/fs_image.c
@@ -3229,18 +3229,28 @@ int iso_file_get_old_image_sections(IsoFile *file, int *section_count,
          * to get the sections. This break encapsultation, but safes memory as
          * we don't need to store the sections in the IsoFile node.
          */
-        IsoStream *stream = file->stream;
+        IsoStream *stream = file->stream, *input_stream;
         FSrcStreamData *data;
         ImageFileSourceData *ifsdata;
 
-        /* <<< ts A90327 : provisory patch on SIGSEGV */
+        /* ts A90328 : Get the most original stream */
+        while (1) {
+            input_stream = iso_stream_get_input_stream(stream, 0);
+            if (input_stream == NULL || input_stream == stream)
+        break;
+            stream = input_stream;
+        }
+
+        /* ts A90327 : From here on it must be a stream with FSrcStreamData. */
+        /* ??? Shall one rather check :
+                stream->class == extern IsoStreamIface fsrc_stream_class
+               (its storage location is global in stream.c)
+         */
         if (stream->class->type[0] != 'f' || stream->class->type[1] != 's' ||
             stream->class->type[2] != 'r' || stream->class->type[3] != 'c')
             return 0;
 
-        /* >>> need a method to get the most original stream */
-
-        data = file->stream->data;
+        data = stream->data;
         ifsdata = data->src->data;
 
         *section_count = ifsdata->nsections;
diff --git a/libisofs/libisofs.h b/libisofs/libisofs.h
index 30fccfe..17c2ec8 100644
--- a/libisofs/libisofs.h
+++ b/libisofs/libisofs.h
@@ -766,10 +766,13 @@ extern ino_t serial_id;
 struct IsoStream_Iface
 {
     /*
-     * Current version of the interface, set to 1.
-     *
-     * -version 1 (since 0.6.8)
+     * Current version of the interface, set to 1 or 2.
+     * Version 0 (since 0.6.4)
+     *    deprecated but still valid.
+     * Version 1 (since 0.6.8) 
      *    update_size() added.
+     * Version 2 (since 0.6.18)
+     *    get_input_stream() added. A filter stream should have version 2.
      */
     int version;
 
@@ -846,6 +849,7 @@ struct IsoStream_Iface
     void (*free)(IsoStream *stream);
 
     /**
+     * Present if .version is 1 or higher:
      * Updates the size of the IsoStream with the current size of the
      * underlying source. After calling this, get_size() will return
      * the new size. This should never be called after
@@ -856,9 +860,26 @@ struct IsoStream_Iface
      *
      * @return
      *     1 if ok, < 0 on error (has to be a valid libisofs error code)
+     *
      * @since 0.6.8
      */
     int (*update_size)(IsoStream *stream);
+
+    /**
+     * Present if .version is 2 or higher:
+     * Obtains the eventual input stream of a filter stream.
+     * @param stream
+     *      The eventual filter stream to be inquired.
+     * @param flag
+     *      Bitfield for control purposes. Submit 0 for now.
+     * @return
+     *      The input stream, if one exists. Elsewise NULL.
+     *      No extra reference to the stream is taken by this call.
+     *
+     * @since 0.6.18
+     */
+    IsoStream *(*get_input_stream)(IsoStream *stream, int flag);
+
 };
 
 /**
@@ -4045,6 +4066,22 @@ int iso_stream_update_size(IsoStream *stream);
 void iso_stream_get_id(IsoStream *stream, unsigned int *fs_id, dev_t *dev_id,
                       ino_t *ino_id);
 
+/* ts A90328 */
+/**
+ * Obtain the eventual input stream of a filter stream.
+ * @param stream
+ *      The eventual filter stream to be inquired.
+ * @param flag
+ *      Bitfield for control purposes. Submit 0 for now.
+ * @return
+ *      The input stream, if one exists. Elsewise NULL.
+ *      No extra reference to the stream is taken by this call.
+ * 
+ * @since 0.6.18
+ */    
+IsoStream *iso_stream_get_input_stream(IsoStream *stream, int flag);
+
+
 /************ Error codes and return values for libisofs ********************/
 
 /** successfully execution */
@@ -4685,6 +4722,8 @@ typedef struct iso_external_filter_command IsoExternalFilterCommand;
  * Install an external filter command on top of the content stream of a data
  * file. The filter process must be repeatable. It will be run once by this
  * call in order to cache the output size.
+ * This call creates a new IsoStream which uses the existing IsoStream of the
+ * data file as input.
  * iso_file_get_stream() will return the filter stream.
  * iso_stream_get_size() will return the cached size of the filtered data,
  * iso_stream_open()     will start again the external filter process,
@@ -4705,6 +4744,27 @@ typedef struct iso_external_filter_command IsoExternalFilterCommand;
 int iso_file_add_external_filter(IsoFile *file, IsoExternalFilterCommand *cmd,
                                  int flag);
 
+/* ts A90328 */
+/**
+ * Delete the top filter stream from a data file. This is the most recent one
+ * which was added by iso_file_add_*_filter().
+ * Caution: One should not do this while the IsoStream of the file is opened.
+ *          For now there is no general way to determine this state.
+ *          Filter stream implementations are urged to eventually call .close()
+ *          inside method .free() . This will close the input stream too.
+ * @param file
+ *      The data file node which shall get rid of one layer of content
+ *      filtering.
+ * @param flag
+ *      Bitfield for control purposes, unused yet, submit 0.
+ * @return
+ *      1 on success, 0 if no filter was present
+ *      <0 on error
+ *
+ * @since 0.6.18
+ */
+int iso_file_remove_filter(IsoFile *file, int flag);
+
 
 /* ------------------------------------------------------------------------- */
 
diff --git a/libisofs/stream.c b/libisofs/stream.c
index 3a996e6..8ecc56b 100644
--- a/libisofs/stream.c
+++ b/libisofs/stream.c
@@ -642,3 +642,14 @@ void iso_stream_get_file_name(IsoStream *stream, char *name)
         strcpy(name, "UNKNOWN SOURCE");
     }
 }
+
+/* ts A90328 API */
+IsoStream *iso_stream_get_input_stream(IsoStream *stream, int flag)
+{
+    IsoStreamIface* class = stream->class;
+
+    if (class->version < 2)
+        return NULL;
+    return class->get_input_stream(stream, 0);
+}
+