diff --git a/screening/source/java/ch/systemsx/cisd/openbis/dss/screening/server/DssServiceRpcScreening.java b/screening/source/java/ch/systemsx/cisd/openbis/dss/screening/server/DssServiceRpcScreening.java
index c6540ff4516922bfc2e80169d55795fa91a63daf..ead7a1a114cb76881f039a4fb3d2232144e5bb01 100644
--- a/screening/source/java/ch/systemsx/cisd/openbis/dss/screening/server/DssServiceRpcScreening.java
+++ b/screening/source/java/ch/systemsx/cisd/openbis/dss/screening/server/DssServiceRpcScreening.java
@@ -403,7 +403,7 @@ public class DssServiceRpcScreening extends AbstractDssServiceRpc implements
         transformerDAO.commit();
     }
     
-    public IImageTransformerFactory getImageTransformerFactory(String sessionToken,
+    public IImageTransformerFactory getImageTransformerFactoryOrNull(String sessionToken,
             List<IDatasetIdentifier> dataSetIdentifiers, String channel)
     {
         List<String> experimentPermIDs = getExperimentPermIDs(sessionToken, dataSetIdentifiers);
diff --git a/screening/source/java/ch/systemsx/cisd/openbis/dss/screening/shared/api/v1/IDssServiceRpcScreening.java b/screening/source/java/ch/systemsx/cisd/openbis/dss/screening/shared/api/v1/IDssServiceRpcScreening.java
index b9bd891562c70428bfd43823e647265d3d692a32..5c8e86ba0f4bb4ad0206d6495c431b5fba1beffb 100644
--- a/screening/source/java/ch/systemsx/cisd/openbis/dss/screening/shared/api/v1/IDssServiceRpcScreening.java
+++ b/screening/source/java/ch/systemsx/cisd/openbis/dss/screening/shared/api/v1/IDssServiceRpcScreening.java
@@ -168,6 +168,10 @@ public interface IDssServiceRpcScreening extends IRpcService
             @AuthorizationGuard(guardClass = SingleDataSetIdentifierPredicate.class) IDatasetIdentifier dataSetIdentifier,
             List<WellPosition> wellPositions, String channel, ImageSize thumbnailSizeOrNull);
     
+    /**
+     * Saves the specified transformer factory for the specified channel and the experiment to
+     * which the specified data sets belong.
+     */
     @MinimalMinorVersion(4)
     @DataSetAccessGuard
     public void saveImageTransformerFactory(
@@ -175,9 +179,15 @@ public interface IDssServiceRpcScreening extends IRpcService
             @AuthorizationGuard(guardClass = DatasetIdentifierPredicate.class) List<IDatasetIdentifier> dataSetIdentifiers,
             String channel, IImageTransformerFactory transformerFactory);
 
+    /**
+     * Returns the transformer factory for the specified channel and the experiment to which
+     * the specified data sets belong.
+     * 
+     * @return <code>null</code> if such a factory has been defined yet.
+     */
     @MinimalMinorVersion(4)
     @DataSetAccessGuard
-    public IImageTransformerFactory getImageTransformerFactory(
+    public IImageTransformerFactory getImageTransformerFactoryOrNull(
             String sessionToken,
             @AuthorizationGuard(guardClass = DatasetIdentifierPredicate.class) List<IDatasetIdentifier> dataSetIdentifiers,
             String channel);