Index: trunk/psModules/src/camera/pmFPAfileDefine.c
===================================================================
--- trunk/psModules/src/camera/pmFPAfileDefine.c	(revision 15893)
+++ trunk/psModules/src/camera/pmFPAfileDefine.c	(revision 15931)
@@ -1219,2 +1219,44 @@
 }
 
+// Select or construct the requested readout.  If the named entry does not exist, generate it based
+// on the specified fpa and binning.  We have 4 possibilities: (INTERNAL or I/O file) and (exists or
+// not).  This call is used after all user-requested pmFPAfiles have been generated.  A missing
+// pmFPAfile is being used internally.
+pmReadout *pmFPAGenerateReadout(const pmConfig *config, // configuration information
+				const pmFPAview *view, // select background for this entry
+				const char *name, // name of internal/external file
+				const pmFPA *fpa, // use this fpa to generate
+				const psImageBinning *binning) {
+  pmReadout *readout = NULL;
+
+  bool status = true;
+  pmFPAfile *file = psMetadataLookupPtr(&status, config->files, name);
+
+  // if the file does not exist, it is not being used as an I/O file: define an internal version
+  if (file == NULL) {
+    readout = pmFPAfileDefineInternal (config->files, name, binning->nXruff, binning->nYruff, PS_TYPE_F32);
+    return readout;
+  } 
+
+  // if the mode is INTERNAL, it has been defined in a previous call.  XXX This seems to require
+  // that the readout have the same dimensions for all entries.
+  if (file->mode == PM_FPA_MODE_INTERNAL) {
+    readout = file->readout;
+    return readout;
+  } 
+
+  // we are using this pmFPAfile as an I/O file: select readout or create
+  readout = pmFPAviewThisReadout (view, file->fpa);
+  if (readout == NULL) {
+    // readout does not yet exist: create from input
+    // XXX we have an inconsistency in this calculation here and in pmFPACopy
+    // XXX use the psImageBinning functions to set the output image size
+    pmFPAfileCopyStructureView (file->fpa, fpa, binning->nXbin, binning->nYbin, view);
+    readout = pmFPAviewThisReadout (view, file->fpa);
+    PS_ASSERT (binning->nXruff == readout->image->numCols, false);
+    PS_ASSERT (binning->nYruff == readout->image->numRows, false);
+  }
+
+  return readout;
+}
+