diff --git a/src/storage/u64idx/mod.rs b/src/storage/u64idx/mod.rs
index 2aeb750..05265c3 100644
--- a/src/storage/u64idx/mod.rs
+++ b/src/storage/u64idx/mod.rs
@@ -46,7 +46,7 @@ use crate::{
   },
   qty::{Frequency, Hpx, MocQty, Time},
   storage::u64idx::op1::{
-    op1_mom_filter, op1_mom_sum, op1_mom_sum_from_data, op1_mom_sum_from_path,
+    op1_mom_filter, op1_mom_filter_mask, op1_mom_sum, op1_mom_sum_from_data, op1_mom_sum_from_path,
   },
 };
 
@@ -1849,6 +1849,25 @@ impl U64MocStore {
     op1_mom_filter(index, mom_it)
   }
 
+  /// Set to 'false' the booleans associated to the UNIQ HEALPix cells
+  /// intersecting (or fully covered) by the MOC of given index.
+  ///
+  /// # Params
+  /// * `index`: index pf the S-MOC in the storage
+  /// * `it`: iterator on `uniq` HEALPix cells.
+  /// * `fully_covered_only`: set the boolean to false only if the cell is fully covered (else if it intersects)
+  pub fn multiordermap_filter_mask_moc<'a, I>(
+    &self,
+    index: usize,
+    it: I,
+    fully_covered_only: bool,
+  ) -> Result<(), String>
+  where
+    I: Sized + Iterator<Item = (u64, &'a mut bool)>,
+  {
+    op1_mom_filter_mask(index, it, fully_covered_only)
+  }
+
   /// Sum the value of the multi-order map in the given path which are in the given MOC.
   /// Remark: we have no information and cannot make any guess on the order if te `UNIQ` cell
   /// in the iterator.
diff --git a/src/storage/u64idx/op1.rs b/src/storage/u64idx/op1.rs
index 674d5fe..86ef4ed 100644
--- a/src/storage/u64idx/op1.rs
+++ b/src/storage/u64idx/op1.rs
@@ -296,7 +296,7 @@ pub(crate) fn op1_mom_sum_from_data(index: usize, mom_data: &[u8]) -> Result<f64
   })
 }
 
-/// Retuns the `(values, weights)` from the `values` of the input MOM which are in the MOC.
+/// Returns the `(values, weights)` from the `values` of the input MOM which are in the MOC.
 pub(crate) fn op1_mom_filter<I>(index: usize, it: I) -> Result<(Vec<f64>, Vec<f64>), String>
 where
   I: Sized + Iterator<Item = (u64, f64)>,
@@ -311,3 +311,38 @@ where
     InternalMoc::TimeSpace(_) => Err(String::from("MOM Filter not implemented for ST-MOCs.")),
   })
 }
+
+/// Set to 'false' the booleans associated to the UNIQ HEALPix cells
+/// intersecting (or fully covered) by the MOC of given index.
+/// # Params
+/// * `fully_covered_only`: set the boolean to false only if the cell is fully covered (else if it intersects)
+pub(crate) fn op1_mom_filter_mask<'a, I>(
+  index: usize,
+  it: I,
+  fully_covered_only: bool,
+) -> Result<(), String>
+where
+  I: Sized + Iterator<Item = (u64, &'a mut bool)>,
+{
+  store::exec_on_one_readonly_moc(index, move |moc| match moc {
+    InternalMoc::Space(moc) => {
+      if fully_covered_only {
+        for (uniq, flag) in it {
+          let (depth, ipix) = Hpx::<u64>::from_uniq_hpx(uniq);
+          let cell_fraction = moc.cell_fraction(depth, ipix);
+          *flag = cell_fraction < 1.0;
+        }
+      } else {
+        for (uniq, flag) in it {
+          let (depth, ipix) = Hpx::<u64>::from_uniq_hpx(uniq);
+          let cell_fraction = moc.cell_fraction(depth, ipix);
+          *flag = cell_fraction == 0.0;
+        }
+      }
+      Ok(())
+    }
+    InternalMoc::Time(_) => Err(String::from("MOM Filter not implemented for T-MOCs.")),
+    InternalMoc::Frequency(_) => Err(String::from("MOM Filter not implemented for F-MOCs.")),
+    InternalMoc::TimeSpace(_) => Err(String::from("MOM Filter not implemented for ST-MOCs.")),
+  })
+}