diff --git a/bds/source/java/ch/systemsx/cisd/bds/hcs/HCSImageFormattedData.java b/bds/source/java/ch/systemsx/cisd/bds/hcs/HCSImageFormattedData.java
index d734dde6b11f847a980e248335873a19c7f49935..55e29a3ae6aed36784559ca895cb6b7d171a8879 100644
--- a/bds/source/java/ch/systemsx/cisd/bds/hcs/HCSImageFormattedData.java
+++ b/bds/source/java/ch/systemsx/cisd/bds/hcs/HCSImageFormattedData.java
@@ -92,12 +92,12 @@ public final class HCSImageFormattedData extends AbstractFormattedData implement
     {
         if (channel < 1)
         {
-            throw new IndexOutOfBoundsException(String.format("Channel index starts at 1.", channel));
+            throw new IndexOutOfBoundsException(String.format("Channel index must start at 1 (given value is %d).", channel));
         }
         final int channelCount = getChannelCount();
         if (channel > channelCount)
         {
-            throw new IndexOutOfBoundsException(String.format("%d > %d", channel, channelCount));
+            throw new IndexOutOfBoundsException(String.format("Channel index %d exceeds the number of channels %d", channel, channelCount));
         }
     }