Index: trunk/psModules/src/detrend/Makefile.am
===================================================================
--- trunk/psModules/src/detrend/Makefile.am	(revision 43037)
+++ trunk/psModules/src/detrend/Makefile.am	(revision 43038)
@@ -11,4 +11,5 @@
 	pmNonLinear.c \
 	pmNewNonLinear.c \
+	pmMaskBadOverscan.c \
 	pmBias.c \
 	pmOverscan.c \
@@ -32,4 +33,5 @@
 	pmNonLinear.h \
 	pmNewNonLinear.h \
+	pmMaskBadOverscan.h \
 	pmBias.h \
 	pmOverscan.h \
Index: trunk/psModules/src/detrend/pmDetrendDB.h
===================================================================
--- trunk/psModules/src/detrend/pmDetrendDB.h	(revision 43037)
+++ trunk/psModules/src/detrend/pmDetrendDB.h	(revision 43038)
@@ -44,4 +44,5 @@
     PM_DETREND_TYPE_PATTERN_ROW_AMP,
     PM_DETREND_TYPE_PATTERN_DEAD_CELLS,
+    PM_DETREND_TYPE_VALID_OVERSCAN,
 } pmDetrendType;
 
Index: trunk/psModules/src/detrend/pmMaskBadOverscan.c
===================================================================
--- trunk/psModules/src/detrend/pmMaskBadOverscan.c	(revision 43038)
+++ trunk/psModules/src/detrend/pmMaskBadOverscan.c	(revision 43038)
@@ -0,0 +1,41 @@
+#include <stdio.h>
+#include <pslib.h>
+
+#include "pmFPA.h"
+#include "pmHDU.h"
+#include "pmHDUUtils.h"
+#include "pmMaskBadOverscan.h"
+
+// model is stored as a FITS table, read into an array
+// each row is one cell, with (min, max) valid overscan range
+bool pmMaskBadOverscanApply(pmReadout *inputReadout, float minValid, float maxValid, psImageMaskType maskValue)
+{
+    PS_ASSERT_PTR_NON_NULL(inputReadout, false);
+    PS_ASSERT_PTR_NON_NULL(inputReadout->image, false);
+    PS_ASSERT_PTR_NON_NULL(inputReadout->mask, false);
+    PS_ASSERT_IMAGE_TYPE(inputReadout->image, PS_TYPE_F32, false);
+    PS_ASSERT_IMAGE_TYPE(inputReadout->mask, PS_TYPE_IMAGE_MASK, false);
+
+    pmHDU *hdu = pmHDUFromReadout(inputReadout); // HDU of interest
+
+    bool status;
+    float overscan = psMetadataLookupF32(&status, hdu->header, "OVER_VAL");
+    if (!status) {
+      // no overscan value measured
+      return false;
+    }
+
+    // readout is either all good or all bad
+    if ((overscan >= minValid) && (overscan <= maxValid)) return true;
+
+    psImage *mask = inputReadout->mask;
+
+    // completely mask the readout
+    for (int i = 0; i < mask->numRows; i++) { // Loop over rows : note: problem with discontinuity here
+	for (int j = 0; j < mask->numCols; j++) { // Loop over columns
+	  mask->data.PS_TYPE_IMAGE_MASK_DATA[j][i] |= maskValue;
+	}
+    }
+    return true;
+}
+
Index: trunk/psModules/src/detrend/pmMaskBadOverscan.h
===================================================================
--- trunk/psModules/src/detrend/pmMaskBadOverscan.h	(revision 43038)
+++ trunk/psModules/src/detrend/pmMaskBadOverscan.h	(revision 43038)
@@ -0,0 +1,17 @@
+/* @file pmMaskBadOverscan.h
+ * @brief mask entire cells based on the overscan value
+ * @author Eugene Magnier, IfA
+ * Copyright 2026 Institute for Astronomy, University of Hawaii
+ */
+
+#ifndef PM_MASK_BAD_OVERSCAN_H
+#define PM_MASK_BAD_OVERSCAN_H
+
+/// @addtogroup detrend Detrend Creation and Application
+/// @{
+
+/// mask bad readouts 
+bool pmMaskBadOverscanApply(pmReadout *inputReadout, float minValid, float maxValid, psImageMaskType maskValue);
+
+/// @}
+#endif