update output structure interface in the decryptor class

pvapy/hpc/adImageDataDecryptor.py

@@ -27,11 +27,17 @@ def process(self, pvObject):
         '''
         return DataDecryptor.process(self, pva.NtNdArray(pvObject))
 
-    def getOutputPvObjectType(self):
+    def getOutputPvObjectType(self, pvObject):
         '''
-        Method invoked at processing startup. It defines PVA structure of
-        the output (processed) PvObject. 
-        
-        :Returns: NtNdArray object
+        Method invoked at processing startup that defines PVA structure for
+        the output (processed) PvObject. This method is called immediately after
+        receiving the first input channel update.
+
+        There is no need to override this method if the structure of input and
+        output objects are the same, or if the application will not publish
+        processing output.
+
+        :Parameter: *pvObject* (PvObject) - input channel object
+        :Returns: PvObject with the same structure as generated by the process() method
         '''
         return pva.NtNdArray()